CHAPTER 7A TOUR OF THE CELL

Fluorescent stain of cell

Cell Biology1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism’s cells. As a basis for understanding this concept, Students know:

a. cells are enclosed within semipermeable membranes that regulate their interaction with their surroundings.

b. enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings.

c. how prokaryotic cells, eukaryotic cells (including those from plants and animals), and viruses differ in complexity and general structure.

d. the central dogma of molecular biology outlines the flow of information from transcription of ribonucleic acid (RNA) in the nucleus to translation of proteins on ribosomes in the cytoplasm.

e. the role of the endoplasmic reticulum and Golgi apparatus in the secretion of proteins.

f. usable energy is captured from sunlight by chloroplasts and is stored through the synthesis of sugar from carbon dioxide.

g. the role of the mitochondria in making stored chemical-bond energy available to cells by completing the breakdown of glucose to carbon dioxide.

h. Students know most macromolecules (polysaccharides, nucleic acids, proteins, lipids) in cells and organisms are synthesized from a small collection of simple precursors.

i.* how chemiosmotic gradients in the mitochondria and chloroplast store energy for ATP production.

j* Students know how eukaryotic cells are given shape and internal organization by a cytoskeleton or cell wall or both.

Organisms must exchange matter with the environment to grow, reproduce and maintain organization.

Growth, reproduction and maintenance of the organization of living systems require free energy and matter.

Molecules and atoms from the environment are necessary to build new molecules.

• 1. Carbon moves from the environment to organisms where it is used to build carbohydrates, proteins, lipids or nucleic acids. Carbon is used in storage compounds and cell formation in all organisms.

• 2. Nitrogen moves from the environment to organisms where it is used in building proteins and nucleic acids.

• 3. Phosphorus moves from the environment to organisms where it is used in nucleic acids and certain lipids.

why are cells microscopic in size?

• http://www.youtube.com/watch?v=xuG4ZZ1GbzI

Geometric relationships explain why most cells are microscopic

The smaller the object, the greater Its ratio of surface area to volume.

Metabolic requirements depend on passage of oxygen, nutrients and Carbon dioxide & other metabolicWaste through the plasma membrane.

why are cells microscopic in size?

• Cell size is limited by the surface to volume ratio.

• As cells get larger the volume increases at a greater rate compared to surface area.

• Large cells can not get enough materials inside to stay alive.

b. Surface area-to-volume ratios affect a biological system’s ability to obtain necessary

resources or eliminate waste products.

• 1. As cells increase in volume, the relative surface area decreases and demand for material resources increases; more cellular structures are necessary to adequately exchange materials and energy with the environment. These limitations restrict cell size.– Ex. root hairs, cells of the alveoli, cells of the villi

2. The surface area of the plasma membrane must be large enough to adequately exchange materials; smaller cells have a more favorable surface area-to-volume ratio for exchange of materials with the environment.

• villi cells within the small intestine• root hair cells of plants• cells of the alveoli within lungs• All shaped and arranged in ways that

increase surface area to volume ratio and maximize diffusion.

what types of microscopes are used to view cells?

• Light (2,000x)• Transmission

Electron TEM (2,000,000x)

• Scanning Electron

SEM (3-D)

Scanning electron microscopecreates 3-D image of the surfaceof the same cell.

Rabbit trachea (windpipe) cell

Transmission electron microscope

(TEM)

(SEM)

1665 1st MicroscopeRobert Hooke discovered cells-cork

1950’s Electron MicroscopeRevealed the geography of the cell

ORGANELLES• Subcellular structures specialized for various specific functions.• “tiny organ”• compartments or “rooms” • each contains specific enzymes

The plasma membrane

What is the difference between prokaryotic and

eukaryotic cells?THINGS IN COMMON DIFFERENCES

Overview of a prokaryotic cell

Overview of an eukaryotic animal cell Overview of a plant cell

Prokaryotic Vs. Eukaryotic

Both have:1) Plasma membrane2) Cytosol- semifluid

substance in which organelles are found.

3) Chromosomes/genes4) Ribosomes (tiny

organelles that make proteins according to instructions from the genes)

Only eukaryotic cells:

1) Have chromosomes inside a membrane bound organelle- the nucleus.

“eu” = true

“karyon” = kernel

2) Are “large” -10x bigger than bacteria.

3) Have other membrane-bound organelles.

FYI: CELL FRACTIONATIONTechnique used to determine the function of organelles.

ORGANELLES are sub cellular structures that perform specific sets of chemical reactions for the cell within Eukaryotic Cells.

Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.

• a. Internal membranes facilitate cellular processes by minimizing competing interactions and by increasing surface area where reactions can occur.

• b. Membranes and membrane-bound organelles in eukaryotic cells localize (compartmentalize) intracellular metabolic processes and specific enzymatic reactions.

For example: • Endoplasmic Reticulum• Chloroplasts / Mitochondrion • Golgi• Nuclear envelope

CHARACTERISTICS OF THE NUCLEUS:1) Contains most of the genes*2) Most conspicuous (big)

part of the cell

STRUCTURES ofTHE NUCLEUS (out to in):1) Nuclear envelope (double

membrane system- 2plbls)2) Pores (protein tunnels)3) Lamina (protein fiber

scaffolding- network)4) Chromatin (DNA & protein)5) Nucleolus (makes ribosomes)

*Chloroplasts and Mitochondria have their own DNA

Chromosomes are thick coiled chromatin fibers that condense when the cell is

ready to divide.

• Nucleosome = subunit of a chromosome…

• DNA wrapped around 8 histone proteins.

Nuclei and F-actin in BPAEC cells

Big Idea 4: Biological systems interact, and these systems and their interactions

possess complex properties.

The structure and function of subcellular components, and their interactions, provide essential cellular processes.

Figure 7.10 Ribosomes

RIBOSOMES are small universal structures (proks & euks)- made of ribosomal RNA (rRNA) and protein - carry out protein synthesis in 2 areas

1) free- suspended in the cytosol2) bound- attached to the outside of the endoplasmic

reticulum or nuclear envelope.Ex. PANCREAS CELLS have a few million ribosomes(synthesize: pancreatic juices, insulin, glucagon)

The Endoplasmic Reticulum• “within the cytoplasm” “little net”• Labyrinth of membrane tubes and sacs• > 1/2 the total membrane of the cell• Connected to the nucleus • FUNCTIONS: • Occurs in 2 forms: rough & smooth• rough ER provides site-specific protein

synthesis with membrane-bound ribosomes

• plays a role in intracellular transport = endomembrane system.

• smooth ER synthesizes lipids.

Smooth ER vs. Rough ERSmooth ER• Lacks ribosomes• Functions:1) Synthesis of lipids

sex hormones, oils, phospholipids

2) Metabolism of carbohydrates3) Detoxification of drugs/poisons• LIVER CELLS • MUSCLE CELLS (store Ca+)

Rough ER• Ribosomes attached to

the cytoplasmic surface• Functions:1) Protein synthesis on

ribosomes, protein enters cisternal space to fold into native conformation.

2) Secretory Glycoproteins 3) Phospholipid membrane

production (factory)

✘ Specific functions of smooth ER in specialized cells are beyond the scope of the course and the AP Exam.

Golgi Complex AKA: golgi apparatus, golgi bodies

• STRUCTURE membrane-bound, consists of a series of flattened membrane sacs (cisternae).

• Looks like a smaller version of the ER but totally separate from nucleus)

• FUNCTIONS include synthesis and packaging of materials (small molecules) for transport & production of lysosomes.

• Receives & ships via transport vesicles- bags of membrane.

Golgi sorts, modifies, and exports

trans“shipping”

cis“receiving”

The formation and functions of lysosomes

Lysosomes are membrane-enclosed sacs that contain hydrolytic enzymes, which are important in 1.intracellular digestion2.The recycling of a cell’s organic materials and3.programmed cell death (apoptosis)

lysosomes• Made by rough ER, finished in the Golgi• Contain hydrolytic enzymes that function at low pH• Pumps hydrogen ions from cytosol into lysosome to maintain acidic pH• Targets of primary lysosomes are:

1) food vacuoles (formed via phagocytosis) ex. Amoeba (protist) & Macrophages (white blood cells)

2) organelles or cytosol (autophagy- recycle materials)3) Apoptosis = programmed destruction of cells

ex. tadpole tail, human hand development- webbing• EX. Tay-Sachs genetic disorder is caused by missing/inactive lipid

digesting enzyme which results in lipid accumulation in brain cells.

Review: relationships among organelles of the endomembrane system 

Endomembrane System

Organelles that share membrane

Components with each other.

Nuclear Envelope, ER, Golgi,

Lysosome, Vacuoles, and

Plasma Membrane

How?

Transport Vesicles- little bag of

Membrane.

Endomembrane System

Rough ER

vesicle

Golgi Apparatus

vesicle

Plasma Membrane

The Golgi apparatus… stack of pita bread… insides = cisternae

lysosome formation

VACUOLES

• Larger than vesicles• Food vacuoles (formed by phagocytosis)• Contractile vacuoles- pump excess water out of

the cell (freshwater protists)• Central vacuole- large vacuole in mature plant

cells (membrane = tonoplast)- contains reserves of important compoundsie. pigments (petals), metabolic by-products (waste), poisons (repel predators), water, proteins and lipids (seeds)

The plant cell vacuole 

plant cells

Which cells have the larger vacuoles- animal or plant?

Mitochondrion / mitochondria (pl)• Energy conversion organelle• Site of cellular respiration

(x,y,z-->ATP)• Mitochondrial membrane proteins made

by free ribosomes in the cytosol• Contain ribosomes and own DNA• Double membrane system

- outer membrane smooth- inner membrane convoluted (cristae=folds) w/ proteins… increases surface area for rxns.

• Two spaces:1) mitochondrial matrix

(inner most area)2) inter membrane space- between the two membranes.

PLASTIDS• Family of closely related plant organelles.• Four kinds:1. Chromoplasts- contain pigments that give fruits

and vegetables their orange and yellow hues.2. Leukoplasts- store starch, protein, oil 3. Amyloplasts- store starch (amylose) in roots and

tubers.4. Chloroplasts- contain green pigment chlorophyll

& enzymes related to photosynthesis.

CHLOROPLAST STRUCTURE

• Double membrane system• Pancakes in a “to-go” box• Thylakoids= flattened sacs

(inside called “thylakoid space”

• Grana= stacks of thylakoids• Stroma= area outside

thylakoids and outer membrane… contains ribosomes, enzymes, and chloroplast DNA.

The chloroplast, site of photosynthesis

* note: chloroplasts are larger than mitochondria.

PEROXISOMES• Specialized, one membrane, metabolic

compartment that detoxifies substances.

• Transfers hydrogen from substrates to oxygen- makes H2O2

• ie. detoxify alcohol or • use oxygen to break fatty acids into

small molecules to be used as fuel for the mitochondria.

• Contains catalase to convert H2O2 to water and Oxygen.

• Liver cells have many.

The process of evolution drives the diversity and unity of life.

Organisms are linked by lines of descent from common ancestry. Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.

Structural evidence supports the relatedness of all eukaryotes.

• Cytoskeleton (a network of structural proteins that facilitate cell movement, morphological integrity and organelle transport)

• Membrane-bound organelles (mitochondria and/or chloroplasts)

• Linear chromosomes

• Endomembrane systems, including the nuclear envelope

THE CYTOSKELETON

made of:1.microtubules2.microfilaments3.intermediate filaments

plays a majorrole in organizing the structures andactivities of the cell

Table 7.2 The structure and function of the cytoskeleton

microtubules• structrure:• hollow fibers of tubulin =

protein that makes microtubules- 2 types: alpha & beta (tubulin)

• functions: 1) shape & support cell- compression resisting2) tracks to move organelles

equipped w/motor molecules.3) assist in cell division (moving chromosomes)

ex. Spindle fibers 4) motion for the cell- cilia/flagella

Figure 7.21 Motor molecules and the cytoskeleton

MICROTUBUELESgrow out of : a centrosome (plant cells)2 centrioles w/in the centrosome in (animal cells)

centriole structure = 9 microtubule triplets in a ring

cilia & flagella:specialized microtubular structures

• basal bodies (same structure as centrioles) anchor cilia and flagella to the cell membrane

• flagella = long tails (few) 10-200 micrometers

• cilia = short hairs (many) 2-20 micrometers (10-6)

• structure of both… nine pairs of tubules arranged around 2 central tubules (“9 + 2” pattern in Euks)

• Dynein = motor molecule (protein) attached to tubules, uses energy from ATP to move cilia.

• Dynein “walking” = like a cat climbing a tree.

Figure 7.23 A comparison of the beating of flagella and cilia

cilia in action (paramecium)

microfilaments• = threads of protein• actin = helix shape• twisted double chain of actin

subunits• present in all Eukaryotic cells• bear tension… used for

structure & movement.• myosin = involved in

movement when interacting with actin.

• “MA!” myosin pulls actin

muscles use actin and myosin for contraction

myosin “pulls” actin…

myosin acts as the motor molecule by extending “arms”that walk along actin.

Cell division uses microfilaments to pull the cell membrane apart

contracting band of microfilaments =cleavage furrow

amoeboid movement via pseudopodia

• pseudopod = “false foot”• cytoplasmic extensions • localized contraction of actin &

myosin move the cell membrane• reversible actin subunit

assembly• “squeezing toothpaste tube”• ex. Amoeba & white blood cells

cytoplasmic streaming

in plant cells occurs similarly to the movement of pseudopods.

microfilament recap

intermediate filaments(named for intermediate diameter)

Built from a family of proteins called keratins

Form: permanent cellular lattice(framework)

& cell to cell junctions

Figure 7.x4 Actin and keratin

THE CELL WALL1) of PLANT CELLS = made of: cellulose

a) Primary wall = 1st wall to formb) Middle lamella = space between two plant cells

pectin is a polysaccharide that fills the middle lamella. As fruit ripens, pectin dissolves, cells loosen and fruit ripens

c) Secondary wall = develops in woody plants

lignin is a molecule that strengthens the secondary wall.2) of FUNGI = made of: chitin3) of BACTERIA = made of organic molecules (polysaccharides &

protein)

THE CELL WALL1) of PLANT CELLS = made of: cellulose

a) Primary wall = 1st wall to formb) Middle lamella = space between two plant cells

pectin is a polysaccharide that fills the middle lamella. As fruit ripens, pectin dissolves, cells loosen and fruit ripens

c) Secondary wall = develops in woody plantslignin is a molecule that strengthens the secondary wall.

2) of FUNGI = made of: chitin

3) of BACTERIA = made of organic molecules (polysaccharides & protein)

Figure 7.28 Plant cell walls

CELL COATING

• Animal cell membranes have short chains of carbohydrates bound to:

• proteins (glycoproteins/proteoglycans) • ie. collagen, fibronectins, integrins • or lipids (glycolipids)• Called glycocalyx or extracellular matrix (ECM)

FUNCTIONS OF THE glycocalyx / ECM:1. recognition sites (cell to cell for tissue formation)2. identification markers (ie. A or B on blood cell)3. communication (hormone messenger receptors)

cell coating/ extracellular matrix

CollagenProteoglycanPolysaccharidemicrofilaments

how are cells connected?

1. Intercellular matrix

2. Cell junctions

CELL TO CELL ADHESION1) Intercellular matrix (ECMs of adjacent cells)

a) Collagen- the most abundant glycoprotein, protein fibers that bind cells togetherb) Elastin- also protein fiber that binds cells together

2) Cell junctions (permanent connections)a) desmosomes = anchoring junctions (plaques & fibers) “rivets”, fasten cells together in strong sheets (keratin- intermediate filament)b) tight junctions = proteins that tie cells together, leaving no space between the cells- cells fused (ie. intestines)c) communication junctions (2 kinds) allow flow of salt ions, sugars, amino acids- cytoplasmic channels between adjacent cells. (ie. heart muscle cells, cells of embryo)

– gap junction (animal cells) membrane channels that allow passage of material between cells.

– Plasmodesmata (plant cells) openings in the cell wall where adjacent membranes contact each other.

desmosome (anchoring junction)

(plaques & fibers) “rivets”

fasten cells together in strong sheets.

keratin- intermediate filament.

tight junction

tight junctions = proteins that tie cells together, leaving no space between the cells- cells fused (ie. intestines)

Gap (communicating junction)communication junctions (2 kinds) allow flow of salt ions, sugars, amino

acids- cytoplasmic channels between adjacent cells.

ie. heart muscle cells, cells of embryo1) gap junction (animal cells)

membrane channels that allow passage of material between cells.

2) Plasmodesmata (plant cells) openings in the cell wall where adjacent membranes contact each other.

Figure 7.30 Intercellular junctions in animal tissues

The End