Chapter 6A Tour of the Cell

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Basic Structure of every Organism

• Based on 1 of 2 types of cells– Prokaryotic– Eukaryotic

Basic Structure of every Organism

• Based on 1 of 2 types of cells– Prokaryotic• ‘pro’ =before• ‘karyon’ = kernel

– Eukaryotic• ‘eu’ = true• ‘karyon’ = kernel

Basic Structure of every Organism

• Based on 1 of 2 types of cells– Prokaryotic• Only exist in domains of Bacteria or Archaea

Basic Structure of every Organism

• Based on 1 of 2 types of cells– Prokaryotic• Only exist in domains of Bacteria or Archaea

– Eukaryotic• Protists, fungi, animals, and plants

Eukaryotic Cell (plant)

Eukaryotic Cell (animal)

Prokaryotic Cell (Bacteria)

Basic Common Feature of Both

• Bound by selective barrier (plasma membrane)

• Have cytosol (jellylike substance)– Where organelles and other components are

found• Contain chromosomes– Carry genes in the form of DNA

• Have ribosomes

Different Features of Both

• Location of DNA– Eukaryotes• Most DNA is in nucleus• Nucleus is bound by double membrane

– “true kernel”

– Prokaryotes• DNA is concentrated in region not membrane-enclosed

– Nucleoid

• Cytoplasm

Different Features of Both

• Cytoplasm– Eukaryotes• Region between the nucleus and plasma membrane• Contains a variety of organelles of specialized form and

function– Prokaryotes• Interior of prokaryotic cell

Different Features of Both

• Organelles– Eukaryotes• Membrane- bound organelles are Present• Specialized form and function

– Prokaryotes• Absence of organelles

Different Features of Both• Size– Eukaryotes• Generally Larger than prokaryotes• Size relates to function• Logistics of carrying out cellular metabolism limits cell

size• 10 – 100um in diameter• Metabolic requirements limit size practicality of cells

– Prokaryotes• Smallest cells known• 1 – 5 um in diameter

Plasma Membrane

• Acts as a selective barrier• Allows sufficient passage of oxygen, nutrients,

and wastes to service entire cell• Example:– For 1 um2 of membrane, only a limited amount of

particular substance can cross per second• SA to V ratio is critical

Plasma Membrane

• As a cell increases in size, its volume grows proportionately more than surface area– Area is proportional to linear dimension square– Volume is proportional to linear dimension cubed– THEREFORE, smaller object has greater ratio of SA

to V

How does this relate to the size of cells?

How does this relate to the size of cells?

• Specialized cells– Some longer, shorter, thinner depending on

function– Sometimes there are more of one type instead of

an increase in size

Surface Area vs. Volume

When would you need a higher SA:V?

When would you need a higher SA:V?

• Cells that exchange a lot of material with surroundings

• May have projections from surface (microvilli)– This increases SA without increasing volume

Surface Area of the lungs (alveoli)

Digestive Tract Small Intestine averages 23 feet.

Villi and Microvilli on the interior of the small

intestine Key

Nutrientabsorption

Microvilli(brush border)

Epithelial cellsLacteal

Lymphvessel

Villi

Largecircularfolds

Epithelialcells

Bloodcapillaries

Vein carrying bloodto hepatic portalvessel

Muscle layers

Villi

Intestinal wall

Excretory Structures

Nitrogenous Waste filtering

Eukaryotic Cells

• Focus of this chapter

Parts of the Cell

Nucleus

• Contains: Nuclear envelope, nucleolus, and chromatin.

• Nuclear envelope: double membrane enclosing the nucleus; perforated by pores; continuous with ER

• Nucleolus: structure involved in production of ribosomes; a nucleus has one or more nucleoli.

• Chromatin: material consisting of DNA and proteins; visible as individual chromosomes in a dividing cell.

.

Close-up of nuclearenvelope

Nucleus

NucleolusChromatin

Nuclear envelope:Inner membraneOuter membrane

Nuclear pore

Porecomplex

Ribosome

Pore complexes (TEM) Nuclear lamina (TEM)

1 µm

Rough ER

Nucleus1 µm

0.25 µm

Surface of nuclear envelope

Nucleus

• contains most of the genes in the eukaryotic cell• Chromatin: material consisting of DNA and

proteins; visible as individual chromosomes in a dividing cell.

• DNA is organized into discrete units called chromosomes

• Each chromosome is made up of chromatin• typical human cell has 46 chromosomes in its

nucleus

Chromatin vs. Chromosomes appearance within the cell.

Nucleolus

• rRNA is synthesized from instructions in the DNA is here

• proteins imported from cytoplasm are assembled with rRNA into ribosomal subunits here

Ribosomes and RNA

• Ribosomes translate messenger RNA (mRNA) into a protein.– A ribosome binds to the 5’ end of the mRNA.– Transfer RNA attached to an amino acid carries a codon (3

nucleotide sequences) to bind to the mRNA.– This process continues with more tRNA and amino acids

forming peptide bonds.– The process stops when a codon reaches a stop codon.– By then a protein is formed, releases itself from the

ribosome and curls up into a secondary or tertiary structure.

Free and Bound Ribosomes

• Both free and bound ribosomes are structurally the same (both make proteins)

• Bound Ribosomes (attached to the ER)– Make proteins that are to be inserted into

membranes, secreted or packaged• Free Ribosomes (free in the cytosol)– Make proteins and release them into the cytosol

Ribosomes

Endomembrane System

Endomembrane System

• Encompasses the variety of different membranes

What is it responsible for?

• Synthesis of proteins• Transport of proteins into membranes and

organelles or out of cell• Metabolism and movement of lipids• Detoxification of poisons

Endomembrane System

• Related through direct contact or through transfer of vesicles

What is a vesicle?

• Sac made up of membrane

Endomembrane System

• Pieces are not identical– Vary in structure and function

• Vary in chemical reactions carried out in the given membrane

Endomembrane System

• Includes:– the Nuclear envelope– Golgi Apparatus– Lysosomes– Vacuoles– Plasma Membrane

Endoplasmic Reticulum

Function

• The endoplasmic reticulum (ER) is a network of flattened sacs and branching tubules that extends throughout the cytoplasm in plant and animal cells.

• The endoplasmic reticulum manufactures, processes, and transports a wide variety of biochemical compounds for use inside and outside of the cell.

• Accounts for more than half the total membranes in many eukaryotic cells

Smooth ER

• The smooth ER functions in diverse metabolic processes, which vary with cell type

• Lacks ribosomes• (Barbiturates, alcohol, and many other drugs

induce the proliferation of smooth ER and its associated detoxification enzymes thus increasing the rate of detoxification)-increase tolerance to other helpful drugs

Function of Smooth ER

• Process includes synthesis of Lipids, metabolism or carbohydrates, and detoxification of drugs and poisons (in Liver cells)

• In animal cells the steroids produced are the sex hormones of vertebrates and the various steroid hormones secreted by the adrenal glands

• Detoxification usually involves adding Hydroxyl groups to drug molecules making them more soluble and easier to flush from the body

Function of Smooth ER

• Stores Calcium– Important to muscle cells– When stimulated, calcium ions rush back across

the ER membrane into the cytosol and trigger contraction of the muscle cell

Rough ER

• • A complex membrane bound organelle that is composed of a greatly convoluted but flattish sealed sac that is continuous with the nuclear membrane.

• • Called a ROUGH Endoplasmic Reticulum because it is studded on the outside with ribosomes.

• • Found in eukaryotic cells - the cells of plants, animals, and humans.

Function of Rough ER• • The RER is involved in transport of proteins made by

ribosomes on its surface.

• • The Rough ER changes with the needs of the cells. When the cell is actively making proteins, the rough ER can enlarge and become more complex.

• • Ribosomes on the rough endoplasmic reticulum are called 'membrane bound' and are responsible for the assembly of many proteins. This process is called translation.

Golgi Apparatus

• After leaving the ER, transport vesicles go to the golgi apparatus

• FedEx– Manufacturing– Warehousing– Sorting – Shipping

• Here, products of the ER (such as proteins) are modified and stored and then sent to other destinations

• In a lot of cells used for secretion

Structure• Flattened membranous sacs called cisternae• Looks like a stack of pita bread• Distinct structural polarity– Membranes of cisternae on opposite sides of the

stack differ in thickness and molecular composition• Cis face and trans face

– Cis: receiving; trans: shipping• Cis face—located near the ER

Movement • Transport vesicles move material from the ER to

the Golgi apparatus• A vesicle that buds from the ER can add its

membrane and the contents of its lumen to the cis face by fusing with a Golgi membrane

• The trans face gives rise to vesicles, which pinch off of the golgi body and travel to other sites.

• Products of the ER are usually modified during their transit from the cis region to the trans region of the Golgi

Non-protein Golgi Products

• In addition, the Golgi apparatus manufactures certain macromolecules by itself.

• Many polysaccharides secreted by cells are Golgi products– Including pectins and certain other noncellulose

polysaccharides• Non-protein Golgi products that will be

secreted depart from the trans face inside transport vesicles

Cis to Trans

• The Golgi manufactures and refines its products in stages, with different cisternae containing unique teams of enzymes

• The cisternae of the Golgi actually progress forward from the cis to the trans face of the Golgi, carrying and modifying their cargo as they move– Good example in book on page 106, Figure 6.13

Before exiting…• Before a Golgi stack dispatches its products by budding

vesicles from the trans face, it sorts these products and targets them for various parts of the cell

• Molecular identification tags, such as phosphate groups added to the Golgi products, aid in sorting– act like ZIP codes on mailing labels

• Transport vesicles budded from the Golgi may have external molecules on their membranes that recognize “docking sites” on the surface of specific organelles or on the plasma membrane, thus targeting the vesicles appropriately

Lysosomes: the cell’s garbage disposal

• Break down old organelles• Destroy invaders– Viruses– bacteria

• Break down macromolecules– Proteins– Carbohydrates– Nucleic acids– lipids

Lysosomal Acid Hydrolysis

• Contain about 50 degradative enzymes– Hydrolyze proteins, DNA, RNA, lipids

• Lysosomes maintain an acidic pH (5)– Controlled by a hydrogen ion pump– Uses ATP hydrolysis

• Double protection– Enzymes only active in acidic pH

• Enzymatic genetic diseases– “lysosomal storage diseases”– Gaucher’s affects breakdown of glycolipids

Lysosome formation• Cell membrane buds• Becomes an early endosome• Introduction of hydrolases and

enzymes– Created by the ER then transferred to

the Golgi bodies• Becomes a late endosome– Lowering of pH

• New lysosomes are formed with acquisition of adequate hydrolases

Phagocytosis and Autophagy• Phagocytes fuse with

lysosomes– Becomes phagolysosome– Digests extracellular

substances – Ex: bacteria, viruses, food

substances• Autophagosomes fuse with

lysosomes– Endoplasmic reticulum

encloses old organelles– Vesicle fuses with lysosome

.

Phagocytosis: lysosome digesting food

1 µm

Plasmamembrane

Food vacuole

Lysosome

Nucleus

Digestiveenzymes

Digestion

Lysosome

Lysosome containsactive hydrolyticenzymes

Food vacuolefuses withlysosome

Hydrolyticenzymes digestfood particles

Vacuoles

• Two types:– Food• Formed by phagocytosis

– Contractile• Pumps excess water out of the cell• Helps maintain a suitable concentration of ions

Vacuoles

• Different in Plants and Animals• Animal– General description

• Plant– Versatile– Take the job of lysosomes

• Carry out hydrolysis– Disposal site for metabolic by-products– Contain pigments– Contain unpalatable compounds– Aid in growth

Central Vacuole of a plant

Phagocytosis & Pinocytosis

Contractile Vacuole

Removes excess water in aquatic single celled organisms

Mitochondria

.

Mitochondrion

Intermembrane space

Outer membrane

Inner membrane

Cristae

Matrix

100 nmMitochondrialDNA

Freeribosomes in themitochondrialmatrix

Mitochondria

Mitochondria: An Organelle

● Mitochondria are important to the cell because they are the “powerhouse” of the cell.

● Mitochondria are the sites of cellular respiration; cellular respiration is the metabolic process by which ATP is produced.

● Mitochondria are enclosed by membranes, however, they are not considered part of the endomembrane system.

Mitochondria: An Organelle

● Mitochondria are unique in the sense that they have two membranes in order to function correctly.

● Found only in Eukaryotic cells.● Mitochondria are typically 0.5 to 1.0

micrometer in length.● Amount of mitochondria in the cell varies

depending on the type of tissue the cell is found in and on the organism that the cell is found in.

Diagram

OUTER MEMBRANE

MITOCHONDRIAL DNA

INNER MEMBRANEMATRIX

CRISTAERIBOSOME

GRANULE

ATP SYNTHASE

INTERMEMBRANE SPACE

PORINS

Energy Processing❖ “Powerhouse of the cell”❖ site of cellular respiration❖ converts energy from sugar to forms that cell can use❖ involved in other cell processes

❖ semiautonomous

❖Cellular Respiration❖ Glycolysis❖ Citric acid cycle

Prokaryotic Cell (Bacteria)

Chloroplast

What are Chloroplasts?

• Specialized member of a family of closely related plant organelles called plastids

• Lens shaped organelles, 2-5 micrometers • Found in leaves, green organs of plants, and algae• Contain:– The green pigment chlorophyll– Enzymes– Molecules that function in the photosynthetic

production of sugar

The Structure

• Enclosed by two membranes separated by a intermembrane space– Outer compartment

• Second, inner compartment holding the fluid or stroma– surrounds the thylakoid space

• Membranous system in the form of connected, flattened disks called thylakoids– Stacked like poker chips which is called granum

Origin• Chloroplasts are one of the many different types of

organelles in the plant cell. • Considered to have originated from cyanobacteria through

endosymbiosis—when a eukaryotic cell engulfed a photosynthesizing cyanobacterium which remained and became a permanent resident in the cell.

• Mitochondria are thought to have come from a similar event, where a aerobic prokaryote was engulfed.

• This origin of chloroplasts was first suggested by Konstantin Mereschkowski in 1905 after Andreas Schimper observed that chloroplasts closely resemble cyanobacteria in 1883.

• Chloroplasts are similar to mitochondria in that they both originate from an endosymbiotic event, but chloroplasts are found only in plants and some protists.

Chloroplasts

Prokaryotic Cell (Bacteria)

Lynn Margulis

Endosymbiotic Hypothesis

Modern Day Eukaryotic Cells

Animal Plants

Cytoskeleton

Cytoskeleton

• A network of fibers• Gives mechanical support• Stabilized by a system of opposing forces• Aids in cell motility• Interact with motor proteins

Cytoskeleton

• Three main types of fibers– Microtubules– Microfilaments– Intermediate filaments

Cytoskeleton

• Three main types of fibers– Microtubules• Hollow rods• Globular protein called tubulin• Grow out from centrosome

– Within there are a pair of centrioles• Examples:

– Cilia– flagella

Centrioles

Cellular Movement

Cytoskeleton

• Three main types of fibers– Microtubules– Microfilaments• Built from Molecules of actin• Double chain of actin subunits

Microfilaments in muscle tissue

Muscle Tissue under the Microscope

Cytoskeleton

• Three main types of fibers– Microtubules– Microfilaments– Intermediate Filaments• Larger than microfilaments• Smaller than microtubules

A cell is the sum of it’s parts.

Protective Cell Wall in Plants

Cell walls composed of Chitin sugar.

Extra Cellular Matrix(ECM)

EXTRACELLULAR FLUID ProteoglycancomplexCollagen

fiber

Fibronectin

Integrin Micro-filaments

CYTOPLASM

Plasmamembrane