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Chapter 2

Cells

Siti Sabrina Kasri

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Learning Objectives

State the cell theory.

Compare and contrast the structures of prokaryotic

and eukaryotic cells.

Describe the structure and function of organelles.

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CHAPTER FOCUS

Subtopics You should be able to understand:

1. Prokaryotic and Eukaryotic (with cell

theory

-Differences between prokaryotic and eukaryotic.

-Differences between plant and animal cells

-Plasma membrane and cytoplasm

*2. Cells Genetic Control Center Structure and function

-Nucleus

-Ribosomes

*3. The Endomembrane System

*2 and 3: Cell Structures Involved in

Manufacturing and Breakdown

Structure and Function for Organelle:-Nuclear envelope

-Endoplasmic reticulum

-Golgi apparatus

-Lysosomes

-Vacoules

-Peroxisome

4. Energy Converting Organelles Structure and Function for Organelle:

-Mitochondria

-Chloroplasts

5. Internal and External Support Structure and Function ofCytoskeleton (microtubules,

microfilaments, intermediate filaments), Extracellular

Structure (Cell Wall, ECM and Intercellular Junctions)

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Cells Theory

All organisms are made of cells.

smallest structural unit, simplest collection of matter that can live.

independent functioning cells.

- consists of a nucleus, cytoplasm and various organelles surrounded by

selectively permeable membrane.

Cells= basic unit of life.

all living organisms are made up of one or more cells (unicellular, multicellular).

new cells are formed by the division of pre-existing cells.

cells contain genetic material of an organism which is passed from parent to

daughter cells.

all metabolic reactions takes place within the cells.

Cell structure is correlated to cellular function.

life at cellular level arises from structural order (still remember macromolecules? )

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1. Prokaryotic and Eukaryotic Cells

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1. Prokaryotic and Eukaryotic Cells

The basic structural and functional unit of every organism is one of two types of cells:

prokaryotic or eukaryotic.

Pro: before ,Eu: true, Karyon: kernel which refer to the nucleus.

Prokaryotic cells- Only organisms of the domains Bacteria and Archaea.

Eukaryotic cells- Protists, Fungi, Animals, and Plants.

All cells have several basic features in common:

1. Bounded by a membrane-plasma membrane.

2. Enclosed in the membrane is cytoplasm.

3. Contain chromosomes which carry genes.

4. Have ribosomes- tiny complexes that make proteins according to instructions from gene.

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Prokaryotic cells

Prokaryotic cells are characterized by having:

No nucleus not enclosed by nuclear membrane.

DNA in an unbound region called the nucleoid (region where the cellss DNA is

located).

as DNA is not enclosed by nuclear membrane - the DNA coils on itself to form highlycompact supercoiled structure.

the nucleoid - usually found in the center of the cell

- represents about 20% of the cells total volume.

DNA in plasmid- exists separately, contain genes to help cell to survive in different

environment.

No membrane-bound organelles- eg. Mitochondria, chloroplast.

Ribosomes- smaller and differ from those of eukaryotes, synthesize protein.

Cytoplasm bound by the plasma membrane.

Range in size: 1.0-10 m (refer to figure 4.2A, pg no 54, Biology)7

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Fimbriae/ Pili

Nucleoid

Ribosomes

Plasma membrane

Cell wall

Capsule

Flagella

BacterialChromosome

(a) A typicalrod-shaped

bacterium

(b) A thin sectionthrough the

bacteriumBaci l luscoagulans(TEM)

0.5 m

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Structure of prokaryote

(Bacteria)

Description

1. Bacterial chromosomes - Carrying genes containing DNA.

2. Fimbriae/ Pili - Help attach prokaryotes to the surface.

3. Nucleoid - Regions where DNA is located.

4. Ribosomes - Synthesize protein.

5. Plasma membrane - Membrane enclosing the cytoplasm that function as a selective

barrier.

6. Cell wall - Rigid and chemically complex cell wall that helps protect the cell

and maintain its shape.

7. Capsule - A sticky outer coat that surround the cell wall and protects the cell

surface.

- Also help glue prokaryotes to surface (eg sticks, rocks or tissues

within the human body)

8. Flagella - Locomotion organelles of some bacteria (propel the prokaryotic

cell through its liquid environment).

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Eukaryotic Cells

Eukaryotic cells are generally much larger than prokaryotic cells- 10 to 100 m.

Eukaryotic are characterized by having basic features of all cells:

Plasma membrane.

function as a selective barrier.

Semifluid substance called cytosol (refer to Raven, pg no 62, part The cytoplasm)

cytoplasmic solution that is semi fluid.

consists of various components (eg water, sugars, amino acids, enzymes, fatty

acids, nucleotides, ATP ,dissolved gas, proteins, microfilaments, microtubule etc).

Chromosomes contain DNA that carry genes.

DNA in a nucleus that is bounded by a membranous nuclear envelope

Membrane bound organelles.

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Comparison of Prokaryotic and Eukaryotic Cells.

Prokaryotes Eukaryotes

Size: 1.0-10 m Size: 10-100 m

No membrane bound organelle Have membrane bound organelles

No nucleus. The DNA region is called the

nucleoid

True nucleus bounded by a double

membrane.

Has one circular chromosomes composed

of DNA not associated to histone proteins

Most DNA are associated with histone

proteins to form chromosomes

Some bacteria contain plasmids No plasmid

Most prokaryotes have flagella and they do

not have cilia

May have flagella or cilia

Small size ribosomes: consists of a 50S

subunit and a 30S subunit forming a 70Sribosome.

Ribosomes are composed of a 60S subunit

and a 40S subunit forming an 80Sribosome

Rigid cell walls containing murein

(peptidoglycan)

Cell walls: cellulose (plants and algae),

fungi (chitin).

Animal cells have no cell walls.

Cell divides by binary fusion Cell divides by mitosis and/or meiosis

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INTRODUCTION OFCELL

Manufacturing andbreakdownorganelles

Endomembranesystem

Nuclearenvelope

Golgiapparatus

Vacuole

Endoplasmicreticulum

Lysosome

Plasmamembrane

Nucleus Ribosome

Energyconvertingorganelles

Mitochondria

Chloroplast

Network offibres

structures(cytoskeleton

)

Microtubules

Microfilaments

Intermediatefilaments

Extracellularstructures

Cell wall

Extracellularmatrix

Intercellularjunctions

Oxidativeorganelle

Peroxisome

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ENDOPLASMIC RETICULUM (ER)

Smooth ERRough ERFlagellum

Centrosome

CYTOSKELETON:

Microfilaments

Intermediatefilaments

Microtubules

Microvilli

Peroxisome

Mitochondrion

Lysosome

Golgiapparatus

Ribosomes

Plasmamembrane

Nuclearenvelope

Nucleolus

Chromatin

NUCLEUS

ANIMAL CELLS

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NUCLEUS

Nuclear envelope

Nucleolus

Chromatin

Rough endoplasmicreticulum

Smooth endoplasmicreticulum

Ribosomes

Central vacuole

MicrofilamentsIntermediatefilaments

Microtubules

CYTO-SKELETON

Chloroplast

Plasmodesmata

Wall of adjacent cell

Cell wall

Plasmamembrane

Peroxisome

Mitochondrion

Golgiapparatus

PLANT CELLS

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Comparison of Animal Cells and Plant Cells.

Animal cells Plant cells

No cell wall, only plasma membrane Has cell wall composed of cellulose

Irregular shape that is not fixed Has fixed, regular shape due to presence

of cell wall.

No chloroplast Has chloroplast

Small vacuoles which may be numerous Has a large central vacuole with various

function

No tonoplast Tonoplast around vacuole

Centrioles/ centrosome are present No centriole

Lysosomes present Lysosomes absent

No plasmodesmata Has plasmodesmata

Some cells have cilia or flagella No cilia and flagella

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*The Structure of Membranes Correlates With Their Functions-

Plasma Membrane

The plasma membrane controls the movement of molecules into and out of the cell,

a trait called selective permeability.

The structure of the plasma membrane with its component molecules is responsible for

this characteristic.

Plasma membranes are made of lipids, proteins, and some carbohydrate, but the most

abundant lipids are phospholipids.

Phospholipids form a two-layer sheet called a phospholipid bilayer.

Hydrophilic heads face outward, and hydrophobic tails point inward.

Thus, hydrophilic heads are exposed to water, while hydrophobic tails are shielded from

water.

Proteins are attached to the surface, and some are embedded into the phospholipid

bilayer.

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Hydrophilic head

Hydrophobic tails

Symbol

Phosphategroup

Phospholipid molecule

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Hydrophilicheads

Hydrophobictails

Proteins

Hydrophobic

region ofprotein

Inside cell Hydrophilic

region ofprotein

Outside cell

Phospholipid Bilayer with Associated Proteins.

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*Cytoplasm Cytoplasm is the entire region between the nucleus and the plasma membrane.

Jelly like subtance consists of two parts: cytosol (cytoplasmic solution) and cell

organelles (organs of the cell).

Cytosol= semi fluid portion.

Organelles = Structures in the cell that carry out specialised functions.

= All organelles (except nucleus) is part of the cytoplasm.nucleus is considered as a discrete cellular component due to itscharacteristics and important role in the cell.

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2. Cells Genetic Control Center

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The Nucleus = Cells Genetic Control Center

The nucleus contains most of the cells genes and is usually the most conspicuous

organelle.

The nuclear envelope (that separates nucleus from the cytoplasm) is a double

membrane (each membrane consists of a lipid bilayer that are separated by space of

20-40 nm ) withpores complex (diameter: 100 nm) that allow material to flow in and

out of the nucleus. It is attached to a network of cellular membranes called the endoplasmic reticulum.

Pores complex regulate the entry and exit of molecules from the nucleus.

At the lip of the each pore, the inner and the outer membrane of nuclear envelope are

continous.

The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein.

Nuclear lamina lines the inner surface of the two nuclear envelope.

The nucleoplasm is the semifluid subtances in the nucleus

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The nucleolus is located within the nucleus and is the site of ribosomal RNA

(rRNA) synthesis.- Synthesis of rRNA is according to instructions in the DNA.

- Proteins imported from the cytoplasm are assembled with rRNA into large and small

ribosomal subunits.

- These subunits exits nucleus via nuclear pores to the cytoplasm, where both subunits

(large and small) assembled into a functional ribosome.

The nucleus controls the cells activities and is responsible for inheritance

Inside is a complex of proteins + DNA = chromatin, which condense to makes up the

cells chromosomes chromatin appears as diffuse mass.

DNA (in chromosomes) is copied within the nucleus prior to cell division.

Act as a control centre that directs all activities of cell by regulating protein and enzymesynthesis

- Directs protein synthesis by making messenger RNA (mRNA).

- Assist production of ribosomes (rRNA)

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Nucleolus

Nucleus

Rough ER

Nuclear lamina (TEM)

Close-up of nuclearenvelope

1 m

1 m

0.25 m

Ribosome

Porecomplex

Nuclear pore

Outer membraneInner membrane

Nuclear envelope:

Chromatin

Surface ofnuclear envelope

Pore complexes (TEM)

The Nucleus and Its Envelope

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Nucleoplasm

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Ribosomes Make Proteins for Use in the Cell and Export

Ribosomes are involved in the cells protein synthesis.

It is particles made of ribosomal RNA and protein.

Ribosomes are synthesized in the nucleolus, which is found in the nucleus.

Cells that must synthesize large amounts of protein have a large number of ribosomes.

eg cells that secrete digestive enzyme in pancreas

Some ribosomes are:

Free ribosomes that are suspended in the cytoplasm.

Bound ribosomes that are attached to the endoplasmic reticulum (ER) associated with the

nuclear envelope.

Both are structurally identical.

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Ribosomes carry out protein synthesis in two locations:

In the cytosol (free ribosomes). On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes).

Free ribosomes

proteins made by these ribosomes function within the cytosol.

eg, enzymes that catalyze the first steps of sugar breakdown.

Bound ribosomes

proteins made by these ribosomes:

1. are destined for insertion into membranes

2. for packaging within certain organelles such as lysosomes or

3. for export from the cell (secretion).

eg, cells of pancreas that secrete digestive enzymes.

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Cytoplasm

Endoplasmic reticulum (ER)

Free ribosomes

Bound ribosomes

Ribosomes

ER

SmallsubunitDiagram ofa ribosome

TEM showing ERand ribosomes

Largesubunit

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Cytosol

Endoplasmic reticulum (ER)

Free ribosomes

Bound ribosomes

Largesubunit

Smallsubunit

Diagram of a ribosomeTEM showing ER and ribosomes

0.5 m

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3. The Endomembrane System

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3. The Endomembrane System

The endomembrane system consists of set of organelles that involved in synthesis of

proteins and their transport into membranes and organelles or out of the cell.

- One of the fundamental distinctions between eukaryotes and prokaryotes.

The membranes within a eukaryotic cell are physically connected and compose the

endomembrane system.

regulates protein traffic and performs metabolic functions in the cell.

1. Synthesis of proteins and their transport into membranes and organelles or outof the cell.

2. Metabolism and movement of lipids.

3. Detoxification of poisons.

Components of the endomembrane system:

Nuclear envelope

Endoplasmic reticulum

Golgi apparatus

Lysosomes

Vacuoles

Plasma membrane (not actually an endomembrane in physical location but nevertheless

related to the endoplasmic reticulum and other internal membrane).

These components are either continuous or connected via transfer by vesicles. 31

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The Endoplasmic Reticulum: Biosynthetic Factory

The endoplasmic reticulum (ER) accounts for more than half of the total membrane in

many eukaryotic cells.

Endoplasmic: within the cytoplasm, reticulum: little net

The ER membrane is continuous with the nuclear envelope.

- It consists of a network of membranous tubules and flattened sacs called cisternae.

- The ER membrane separates the internal compartment of the ER= ER lumen/ cisternal space.

There are two distinct regions of ER:

Smooth ER, which lacks ribosomes, in the form of interconnected tubes and not

flattened sac. Rough ER, with ribosomes studding its surface.

Both smooth ER and rough ER:

They differ in structure and function.

However, they are connected. 32

Smooth ER

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Smooth ER

Rough ER Nuclearenvelope

Transitional ER

Rough ERSmooth ERTransport vesicle

Ribosomes

CisternaeER lumen

200 nm

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Functions of Smooth ER The smooth ER:

Synthesizes lipids

- has enzymes in smooth ER for the synthesize of lipids including oils, phospholipids and steroid.

Metabolizes carbohydrates

- certain enzymes in smooth ER in the liver help regulate the amount of sugar released from livercells into the bloodstream.

Detoxifies drugs and poisons

- enzymes in the smooth ER help detoxify drugs and poisons especially in theliver cells.

- detoxification involves adding hydroxyl groups to drug molecules, making them more soluble and

easier to flush out from the body.

-eg alcohols, sedative phenobarbital and other barbiturates are examples of drugs metabolized in

this manner by smooth ER and its associated detoxification enzymes.

Stores calcium

- due to specialised form of smooth ER known as the sarcoplasmic reticulum, it is the site ofstorage and release of calsium ions in muscle cells important in contraction of the cell & cell

signalling. 34

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Functions of Rough ER

The rough ER:

1. Has bound ribosomes, synthesize protein.

-as polypeptide chain grows from a bound ribosome, it is threaded into the ER

lumen through a pore.

- in the ER lumen, the new protein (now known as secretory protein) folds into

its native shape and is stored there temporarily.

- a short carbohydrate chain (an oligosaccharide) is added to the proteinconverting it to glycoproteins.

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Functions of Rough ER

Rough ER:

3. Is a membrane factory for the cell

- some of the proteins made by the ER ribosomes are inserted into the ER

membrane.

- it grows in place by adding membrane proteins (anchored there by its

hydrophobic portion) and phospholipids to its own membrane.

- as a result, the ER membrane enlarges and some of it can be transferred to

other organelles as well as the plasma membrane through transport vesicles.

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S th i d P k i f S t P t i b th R h ER

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Transport vesiclebuds off

Secretoryproteininside trans-port vesicle

Glycoprotein

Polypeptide

Ribosome

Sugarchain

Rough ER

1

2

3

4

Synthesis and Packaging of a Secretory Protein by the Rough ER.

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Functions of the Golgi apparatus:

Modifies products of the ER.

- Products travel in transport vesicles from the ER to Golgi apparatus.

- Products are modified as they go from cis face of the Golgi apparatus to the trans faceand travel in vesicles to other sites.

Golgi apparatus receives vesicles from ER. Vesicles that has glycoprotein shall be

modify by various enzyme in Golgi by modifying carbohydrate portion of

glycoprotein.

Manufactures certain macromolecules by itself.- Like secretory proteins, non protein Golgi products that will be secreted depart from the

trans face of the Golgi (inside transport vesicles) will fuse with the plasma membrane.

- Eg: Many polysaccharides secreted by cells are Golgi products (such as pectin in plant)

Sorts and packages materials into transport vesicles.- Before a Golgi stack dispatches its products by budding vesicles from the trans face,

molecular identification tags (eg, phosphate groups) are added to the Golgi products.

- Finally, transport vesicles budded from the Golgi have external molecules on their

membranes which recognized docking sites (on the plasma membrane), thus targetting

the vesicles destination (to plasma membrane or to cytosol) appropriately.

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c isface

(receiving side ofGolgi apparatus)Cisternae

transface(shipping side of Golgi apparatus) TEM of Golgi apparatus

0.1 m

Transportvesicle fromthe Golgi

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The Golgi apparatus is abundant in secretory cells and in rapidly dividing cells eg,

pancreatic cells, cells in testes and ovaries.

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Lysosomes: Digestive Compartments

Lysosomes are digestive compartments within a cell.

Under the electron microscope, lysosomes appearas dark spherical bodies in thecytoplasm.

- Diameters are smaller than mitochondria.

A membranous sac of hydrolytic enzymes that can digest macromolecules.

The fluid within the lysosome is highly acidic. It contain enzymes that work best in acidicenvironment. What happen if this enzyme leaks to cytosol? Think!!!!!!

The enzymes and membrane of lysosomes are produced by the ER and transferred to the

Golgi apparatus for further processing.

The Golgi apparatus chemically refines the enzymes and releases mature lysosomes to

cytosol.

The membrane of lysosomes safely isolate these potent enzymes from the rest of the cell.it has a single membrane that can prevent leakage of enzymes and able to resist digestion.

illustrate the main theme of the eukaryotic cell structure:compartmentalisation

this is important as excessive leakage of enzyme from a number of lysosomes can lead to

the autodigestion of the cell. However autodigestion is essential during embryonic

development.

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Main function (IMPORTANT !!!!)

- the lysosomes enzymes involves in

i. hydrolyzing macromolecules (food).

ii.breaking down the pathogens (defense system), eg bacteria.

iii. breaking down worn-out/damaged organelles.

- i and ii - via phagocytosisby forming a food vacuole.- a lysosome fuses with the food vacuole and digests the molecules.

- iii via autophagy : Recycle the cells own organelles, thus helping cell to continually renews itself.

The damaged organelle is first enclosed in a double membrane (vesicle).

Then a lysosome fuses with the vesicle, dismantling its contents and breaking down the damagedorganelle.

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Nucleus 1 m

Lysosome

Digestive

enzymesLysosome

Plasma

membrane

Food vacuole

(a) Phagocytosis

Digestion

(b) Autophagy

Peroxisome

Vesicle

Lysosome

Mitochondrion

Peroxisome

fragment

Mitochondrion

fragment

Vesicle containing

two damaged organelles1 m

Digestion

44

Lysosome contains

active hydrolytic

enzymes.

Food vacuole fuses

with lysosome

Hydrolytic enzymes

digest food particles.

Lysosome fuses with

vesicle containing

damaged organelles.

Hydrolytic enzymes

digest organelle

components.

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Vacuoles: Diverse Maintenance Compartments Vacuoles are membranous sacs that are found in a variety of cells and possess an

assortment of functions. It is bounded by single membrane.- eg vacuoles: central vacuole, contractile vacuole and food vacuole.

Central Vacoule

A plant cell or fungal cell lack lysosomes. Thus, they have central vacuole.

- Single membrane that surrounds the vacuole is called the tonoplast. The fluid within the vacuoleis called cell sap.

- Central vacuole carry out hydrolysis (like lysosome), however they play other roles as well.

- The other roles:

= Hold important organic compounds, eg proteins stockpiled in the vacuoles of storage

cells in seeds.

= Main repository inorganic ions, eg pottasium, sodium.

= Disposal sites for metabolic by product that would endangered in the cell if they

accumulated in cytosol. Eg, Tannin.

= Colour the cell because they hold pigment.

= Protect the plant against predators by containing compound that are poisonous or

unpalatable to animals .

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Tonoplast

- Semipermeable membrane.

- Actively transport of certain ions into the vacuole.-As vacuole contain hydrolytic enzyme too, the tonoplast just like other

membranes will lose its semipermeability after cell death and release enzymes

from the vacoule, causing autolysis of the cell.

Cell sap- is a concentrated solution of mineral salts, sugars, amino acid, wastes (tannin)

and pigments (eg to provide color to flowers).

- generally hypertonic relative to the external medium. This helps plants to absorb

water from its environment by osmosis.

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Central vacuole

Cytosol

Centralvacuole

Nucleus

Cell wall

Chloroplast

5 m 47

Tonoplast

Cell sap

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Food Vacuole

Formed by phagocytosis. (refer to slide 44 for figure phagocytosis)

Animals and many single cell protozoa (protist) have food vacuoles that contain

food that undergoing digestion.

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Peroxisomes: Oxidation

A specialized metabolic compartments bounded by a single membrane.

It is not part of the endomembrane system but involved in various metabolic

functions.

Peroxisomes do not bud from the endomembrane system. It grow larger by:

1. Incorporating proteins made primarily in the cytosol

2. Lipids made in the ER, and

3. Lipids synthesized within the peroxisome itself.

Peroxisomes may increase in number by splitting in two when they reach a certainsize.

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Peroxisomes involvement in Various Metabolic Functions.

To detoxify alcohol and other harmful substances (eg Hydrogen),

peroxisomes produce hydrogen peroxide and convert it to water.

How?

- enzyme in peroxisomes transferhydrogen from various substrates to oxygen,

producing hydrogen peroxide.

- the hydrogen peroxide is toxic but the organelle also has an enzyme that

converts hydrogen peroxide to water.

Some peroxisomes use oxygen to break down different types of molecules.

- eg, fatty acids are break down into smaller molecules that can be transportedto mitochondria to be used as fuel in cellular respiration.

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1 m

Chloroplast

Peroxisome

Mitochondrion

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The Endomembrane System:A Review

The endomembrane system is a complex and dynamic player

in the cells compartmental organization.

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Smooth ER

Nucleus

Rough ER

Plasmamembrane

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Smooth ER

Nucleus

Rough ER

Plasmamembrane

c isGolgi

t ransGolgi

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Smooth ER

Nucleus

Rough ER

Plasmamembrane

c isGolgi

t ransGolgi

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2

1

3

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Review Relationships Among Organelles of the Endomembrane

1. Nuclear envelope is connected to rough ER, which is also continous with smooth ER.

2. Membranes and proteins produced by the ER flow in the form of transport vesicles to the

Golgi.

3. Golgi pinches off transport vesicles and other vesicles that give rise to lysosomes, (other

types of specialized vesicles).

4. Lysosome is available for fusion with another vesicle for digestion.

5. Transport vesicle carries proteins to plasma membrane for secretion.

6. Plasma membrane expands by fusion of vesicles; proteins are secreted from cell.

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CHAPTER FOCUS

Subtopics You should be able to understand:

4. Energy Converting Organelles Structure and Function for Organelle:

-Mitochondria

-Chloroplasts

5. Internal and External Support Structure and Function ofCytoskeleton (microtubules,

microfilaments, intermediate filaments), Extracellular

Structure (Cell Wall, ECM and Intercellular Junctions)

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4. Energy Converting Organelles

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Chloroplasts and Mitochondria Change Energy From One Form to

Another

Mitochondria are the sites of cellular respiration (a metabolic process that

generates ATP).

Chloroplasts, found in plants and algae, are the sites of photosynthesis (aprocess of converting light energy to the chemical energy).

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Mitochondria and Chloroplasts

Are not part of the endomembrane system- both aresemiautonomous organelles that grow and reproduce within

the cell.

- evolved by endosymbiosis.

Have a double membrane.

Contain their own DNA.

Have proteins made by free ribosomes.

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Mitochondria: Chemical Energy Conversion

Mitochondria occur in all eukaryotic cells.

The word mitochondria means thread granule.

Under the light microscope- it appear as a tiny, rod likestructure in the cytoplasm of almost all cell.

Under the electron microscope- cylindrixal organelles.

The mitochondria are abundant in cells which aremetabolically active. Eg skeletal muscle cells, spermatozoa,liver and pancreatic cells.

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Mitochondrion structure includes:

1. Bound by a double membrane.

2. They have a smooth outer membrane and an inner membrane folded

into cristae.

- Cristae present a large surface area for enzymes that synthesize ATP due to stalkedparticles (sites for ATP synthesis) .

3. The inner membrane creates two compartments: intermembrane space

(narrow region between the inner and outer membrane) and mitochondrial

matrix. Both compartments filled with fluid.

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Freeribosomes

in themitochondrialmatrix

Intermembrane space

Outer

membrane

Innermembrane

Cristae

Matrix

0.1 m

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cristae (fold)

Intermembrane

space

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Chloroplasts: Capture of Light Energy

Plastids are a group of large organelles found in the cytoplasm of all plants but

not in animal cells.

Divided to 3 categories; chloroplasts, chromoplasts and leucoplasts.

Type of Plastids Descriptions

Chloroplasts Green coloured plastids, play role in photosynthesis.

Chromoplasts Coloured plastids rich in pigment (eg carotenoid) that

give fruits, flowers and leaves their orange, red and

yellow colours.

Leucoplasts Non coloured plastids such as amyloplasts stored starch

in root and tuber, elaioplast stored oil, aleuroplasts stored

protein.

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Chloroplast: the most studied due to its important role in photosynthesis.

Chloroplasts are found in leaves and other green organs of plants and in

algae.

Chloroplast structure includes:

1.Size: bigger than mitochondrion (measuring about 2 m and 5 m).

2.Shape: bioconvex disc.

3.Chloroplasts contain the green pigment chlorophyll, as well as enzymes and

other molecules that function in photosynthesis.

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Chloroplast structure includes :

4.Consists of an envelope of two membranes (outer membrane and inner

membrane ) separated by a very narrow intermembrane space.

5.Thylakoids

- Membranous system in the form of flattened and interconnected sacs. Thecompartment inside these sacs thylakoid space.

- Thylakoids are stacked (like poker chips) to form a granum (plural:grana).

- Connecting one granum to another granum are intergranal lamellae.

- Granum: solar power pack- chlorophyll embedded in membrane.

6. Stroma

- The internal thick fluid of the chloroplast.

- Contains the chloroplast DNA and ribosomes as well as many enzymes.

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Ribosomes

Thylakoid

Stroma

Granum

Inner and outer

membranes

1 mIntergranallamellae

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Functions of chloroplasts:

The one and only PHOTOSYNTHESIS as it absorb light

energy and convert to chemical energy.

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5. INTERNAL AND EXTERNALSUPPORT

72

Cytoskeleton,

Extracellular Structure

(Cell Wall, ECM and

Intercellular Junctions)

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Cytoskeleton

The cytoskeleton:

- a network of fibers that organizes structures and activities in the cell,

anchoring many organelles.

- (refer to Fig 4.4A, pg 56, Biology. Look at GA, Rough ER and Plasma

membrane, can you identify cytoskeleton?).

- a network of fibers extending throughout the cytoplasm.

The cytoskeleton is composed of three kinds of fibers

1. Microtubulesare the thickest of the three components of the

cytoskeleton

2. Microfilaments, also called actin filaments, are the thinnest components

3. I ntermediate fi lamentsare fibers with diameters in a middle range

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Four Roles of the Cytoskeleton in Support, Motility, and

Regulation

1. The cytoskeleton helps to support the cell and maintain its shape.

-important to animal cells that lack cell walls.

-provides anchorage for many organelles and even cytosolic enzyme

molecules.

-cytoskeleton more dynamic to an animal skeletoncanbe quickly dismantled in one part of the cell and reassembled in a

new location, thus changing the shape of the cell. Eg: actin filaments that

responsible for amoeboid movement.

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2. It interacts with motor proteins to produce motility.

- with motor protein, the whole cells moves along fibers outside the cell.

-eg, motor proteins bring about the bending of cilia and flagella by

gripping microtubules within those organelles and sliding them against each

other.

3. Regulating biochemical activities in the cell in response to mechanicalstimulation.

- eg, if plasma membrane proteins that attached to the cytoskeleton were

pull, there were instantaneous rearrangements of nucleolus and other

structures in the nucleus.

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4. Inside the cell, vesicles can travel along monorails provided by the

cytoskeleton.

- eg, vesicles that bud off from the ER travel to the Golgi along cytoskeletaltrack.

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1 Mi t b l

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1. Microtubules

Microtubules are hollow rods about 25 nm in diameter and about 200 nm to

25 m long.

Two types of microtubules

- Centrosome and centrioles.

- Cilia and flagella.

Constructed from a globular protein called tubulin.

- A tubulin dimer consists of-tubulin and -tubulin.

- It grow in length by adding tubulin dimers.

Functions of microtubules:

Shaping and support the cell. Motility. Eg; Flagella and cilia.

Guiding movement of organelles- serve as tracks (which organelles equipped with

motor proteins can move). Eg vesicles move from GA to plasma membrane with the

help of microtubule.

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Column of tubulin dimers

Tubulin dimer

25 nm

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Centrosomes and Centrioles

The centrosome is a microtubule-organizing center.

In many cells, microtubules grow out from a centrosome near the nucleus.

Function as compression-resisting girders of the cytoskeleton.

In animal cells, the centrosome has a pair ofcentrioles, each with nine triplets

of microtubules arranged in a ring.

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Microtubule

Centrioles

0.25 m

Longitudinal sectionof one centriole

Microtubules Cross sectionof the other centriole

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Cilia and Flagella

Microtubules control the beating ofcilia and flagella, locomotors appendages

of some cells.

The length and quantity of these microtubules are differ.

- Cilia: occur in large number, about 0.25 m in diameter and about 2-20 m long.

- Flagella: limited to just one or a few per cell, same diameter like cilia but longer,about 10-200 m.

Cilia and flagella differ in their beating patterns.

- Cilia: Back and forth motion. The rapid power stroke moves the cell in a direction

perpendicular to the axis of the cilium. Then during the slower recovery stroke, thecilium bends and sweeps sideways, closer to the surface.

- Flagella: Undulating motion that generates force in the same directions as theflagellums axis. Its snakelike motion driving a cell in the same direction as the axis of

the flagellum.

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Direction of swimming

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5 m(a) Motion of flagella

Direction of organisms movement

Power stroke Recovery stroke

(b) Motion of cilia15 m

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Cilia and flagella share a common ultrastructure though both different in

length, number per cell and beating pattern:

A core of microtubules sheathed by the plasma membrane.

An arrangement of 9+2pattern .

- Nine doublets of microtubules, the member of each pair sharing part of their

walls are arranged in ring.

- In the center of the ring are two single microtubules.

A basal body that anchors the cilium or flagellum with the arrangement of 9+0

pattern.

- Composed of nine sets of triplet microtubules arranged in ring (just like

centrioles.

A motor protein called dynein, which drives the bending movements of a cilium

or flagellum.

- The movements caused by changes in the shape of the protein with ATP

providing the energy for these changes.

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Core of microtubules for each cilia and

flagellum sheathed in an extension of the

plasma membrane

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Plasmamembrane

Outer microtubuledoublet

D i t i

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0.1 m

Triplet

(c) Cross section of basal body

(a) Longitudinalsection of cilium

0.5 m

Plasmamembrane

Basal body

Microtubules

(b) Cross section ofcilium

Dynein proteins

Centralmicrotubule

Radialspoke

Protein cross-linking outerdoublets

9+2 pattern

9+0

pattern

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2 Microfilaments (Actin Filaments)

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2. Microfilaments (Actin Filaments)

Microfilaments are solid rods about 7 nm in diameter, built as a twisted

double chain ofactin (globular protein) subunits.

The structural role of microfilaments is to bear tension (resisting pulling forces

within the cell).

They form a 3-D network just inside the plasma membrane to help support thecells shape. This network gives the outer cytoplasmic layer of a cell, called the

cortex (semisolid consistency of gel) .

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10 mStructure and Function of the Cytoskeleton

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Actin subunit

7 nm

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Microfilaments and Motility

1 .Microfilaments are well known in cell

motility, as part of the contractile

apparatus of the muscle cells andcontain the protein myosin (muscle

contraction)

- Thousands of actin filaments are

arranged parallel to one another along the

length of a muscle cell, interdigitated with

thicker filaments made of protein myosin.

- Myosin acts as a microfilament-based

motor protein.

- Contraction of the muscle cell results

from the actin and myosin filaments

sliding past one another in this way,shortening the cell.

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2. Localized contraction brought about by

actin and myosin also drives amoeboid

movement. (changes in cell shapes and cell

motility)

- Pseudopodia (cellular extensions) extend

and contract through the reversible

assembly and contraction of actin subunits

into microfilaments.

3. Cytoplasmic streaming is a circular flow

of cytoplasm within cells.

- This streaming speeds distribution of

materials within the cell

- In plant cells, actin-myosin interactionsand sol-gel transformations drive

cytoplasmic streaming

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3 Intermediate Filaments

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3. Intermediate Filaments

Intermediate filaments range in diameter from 812 nanometers, larger than

microfilaments but smaller than microtubules.

Intermediate filaments are more permanent cytoskeleton fixtures than the

other two classes.

- even after cells die, intermediate filament networks often persist.

They support cell shape and fixing the position of certain organelles in

place.

- eg, the nucleus commonly sits within a cage made of intermediate filaments, fixed in

location by branches of the filaments that extend into the cytoplasm.

- eg, nuclear lamina that lines the interior of the nuclear envelope are made from

intermediate filaments.

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Keratin proteinsFibrous subunit (keratinscoiled together)

812 nm

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Extracellular Components and Connections between

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Extracellular Components and Connections between

Cells Help Coordinate Cellular Activities

Most cells synthesize and secrete materials that are external tothe plasma membrane

These extracellular structures include:

Cell walls of plants

The extracellular matrix (ECM) of animal cells

Intercellular junctions

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Cell Walls of Plants

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Cell Walls of Plants

The cell wall is an extracellular structure that distinguishes plant cells from

animal cells. Prokaryotes, fungi, and some protists also have cell walls.

The cell wall protects the plant cell, maintains its shape, and prevents excessive

uptake of water.

Plant cell walls are made of cellulose fibers embedded in other polysaccharidesand protein.

- cellulose fibers are synthesized by an enzyme called cellulose synthase and secreted to the

extracellular space (embedded in other polysaccharides and protein.)

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Plant cell walls have multiple layers:

Primary cell wall: relatively thin and flexible.

- This is the wall that been secreted first in young tree.

Middle lamella: thin layer between primary walls of adjacent cells.

- A thin layer rich in sticky polysaccharides called pectins.

- With pectin, middle lamella glues adjacent cells together.

Secondary cell wall (in some cells): added between the plasma membrane

and the primary cell wall.

- When cell matures and stop growing, its strengthens its walls by secreting

hardening substances into the primary wall.

- Other cell added a secondary cell wall. It is deposited in several laminated layers.

- The wall is strong and durable matrix that affords the cell protection and support.

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EXTRACELLULAR FLUID

Collagen fibers areembedded in a webof proteoglycancomplexes.

Fibronectinattaches theECM to integrinsembbeded in theplasmamembrane

Plasmamembrane

Micro-filaments

CYTOPLASM

IntegrinsMembraneproteins bind tothe ECM on oneside and toassociatedproteins attachedto microfilamentson the other. Thislinkage cantransmit signalbetween the

cells externalenvironment andits interior.

Proteoglycan Complexconsists of hundreds ofproteoglycan molecules.

Polysaccharide

molecule

Carbo-hydrates

Coreprotein

Proteoglycanmolecule

Proteoglycan complex

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Intercellular Junctions

Neighboring cells in tissues, organs, or organ systems often adhere,

interact, and communicate through direct physical contact.

How? Intercellular junctions facilitate these contacts.

There are several types of intercellular junctions.

Plasmodesmata

Tight junctions

Desmosomes

Gap junctions

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Plasmodesmata are channels that perforate plant cell walls.

Through plasmodesmata, water and small solutes (and sometimesproteins and RNA) can pass from cell to cell.

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Secondary

cell wall

Primary

cell wall

Middle

lamella

Central vacuoleCytosol

Plasma membrane

Plant cell walls

Plasmodesmata

1 m

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g , , p

Cells At tight junctions, membranes of neighboring cells are pressed together,

preventing leakage of extracellular fluid.- eg, Tight junctions between skin cells make us watertight by preventing leakage

between cells in our sweat gland.

Desmosomes (anchoring junctions) fasten cells together into strong sheets. At

desmosomes, the intermediate filaments anchor desmosomes in the cytoplasm.- eg, Desmosomes attach muscle cells to each other in a muscle.

Gap junctions (communicating junctions) provide cytoplasmic channels

between adjacent cells and neccesary for communication between cells in

many types of tissues.

- The function is similar to the plasmodesmata.

- The junctions consist of membrane proteins that surround a pore where ions, sugars,

amino acids and small molecules may pass.

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Tight junction

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Tight junction

0.5 m

1 mDesmosome

Gap junction

Extracellularmatrix

0.1 m

Plasma membranesof adjacent cells

Spacebetweencells

Gap

junctions

Desmosome

Intermediatefilaments

Tight junction

Tight junctions preventfluid from movingacross a layer of cells

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Cell Component Structure Function

Concept 6.3

The eukaryotic cells genetic

instructions are housed in

the nucleus and carried out

by the ribosomes

Nucleus Surrounded by nuclear

envelope (double membrane)

perforated by nuclear pores.

The nuclear envelope iscontinuous with the

endoplasmic reticulum (ER).

(ER)

Houses chromosomes, made of

chromatin (DNA, the genetic

material, and proteins); contains

nucleoli, where ribosomal

subunits are made. Poresregulate entry and exit os

materials.

Ribosome Two subunits made of ribo-

somal RNA and proteins; can be

free in cytosol or bound to ER

Protein synthesis

SUMMARY- CELLS

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Cell Component Structure Function

Concept 6.4

The endomembrane system

regulates protein traffic andperforms metabolic functionsin the cell

Endoplasmic reticulum

(Nuclear

envelope)

Golgi apparatus

Lysosome

Vacuole Large membrane-boundedvesicle in plants

Membranous sac of hydrolyticenzymes (in animal cells)

Stacks of flattenedmembranous

sacs; has polarity(c isand trans

faces)

Extensive network ofmembrane-bound tubules and

sacs; membrane separateslumen from cytosol;continuous withthe nuclear envelope.

Smooth ER: synthesis oflipids, metabolism of carbohy-

drates, Ca2+

storage, detoxifica-tion of drugs and poisons

Rough ER: Aids in sythesis ofsecretory and other proteinsfrom bound ribosomes; addscarbohydrates to glycoproteins;produces new membrane

Modification of proteins, carbo-hydrates on proteins, and phos-

pholipids; synthesis of manypolysaccharides; sorting ofGolgi products, which are thenreleased in vesicles.

Breakdown of ingested sub-stances cell macromolecules,and damaged organelles forrecycling

Digestion, storage, wastedisposal, water balance, cellgrowth, and protection

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