Unit 3

Cell Structure and Function

As Organisms Get Larger, Why do They

Become Multi-cellular?

It’s all about

the surface area to volume ratio!

I. Prokaryotic vs. Eukaryotic Cells

Prokaryotic cells: Archaebacteria Eubacteria genetic material

not in a nucleus no membrane

bound organelles

Eukaryotic cells: Protists, Plants,

Fungi and Animals true nucleus with

genetic material has membrane

bound organelles

Prokaryotic vs. Eukaryotic Cells

II. Eukaryotic CellsA. Membranous organelles

1. Nucleus2. Endoplasmic reticulum3. Golgi apparatus4. Mitochondrion5. Chloroplast6. Lysosomes7. Peroxisomes

B. Nonmembranous organelles1. Ribosomes2. Microtubules3. Centrioles4. Flagella5. Cytoskeleton

Anatomy of the Nucleus

III. Endomembrane system (eukaryotic) Also called cytomembrane system part of the compartmentalization of the cell

A. Endoplasmic reticulum a system of tubules and sacs continuous with the outer membrane of the

nuclear envelope membranes are folded into sacs, cisternae, and

divide the cell into cytosol and cisternal space (lumen)

1. Smooth ER (no ribosomes)a. Location of synthesis of lipids (steroids, fats,

phospholipids)b. Forms detoxification compartments (full of enzymes)

for drugs and poisonsc. Metabolism of carbohydrates

Can you find the 11 human faces?

2. Rough ER (ribosomes attached) location of the signal mechanism, i.e. how

secreted proteins get into the cisternal space Membrane factory1) Proteins to be secreted from the cell have a

signal sequence at the lead end (20-24 a.a.). 2) When the signal sequence is produced in protein

synthesis, a signal recognition particle (SRP) attaches to it and to the ribosome producing it.

3) The SRP attaches the ribosome to a receptor protein on surface of ER. (hence “rough ER”)

4) The signal sequence and subsequently the rest of the protein are transported (pushed) through the membrane into the cisternal space (lumen).

5-6) Signal sequence is removed, leaving the finished product (protein).

You have to read this!!!!Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is that the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, butthe wrod as a wlohe.

amzanig huh?

3. Golgi apparatus (golgi body) stacks of sacs (cisternae), each stack is called a

“dictyosome” How does Golgi apparatus work?

a. ER containing protein pinches off to form a transport vesicle.

b. Transport vesicle carries protein to internal surface of Golgi apparatus.

c. A series of transport vesicles carries protein to outer cisternae from one cisterna to the next.

d. In transit the proteins are processed, sorted, and modified.

e. In cells that secrete proteins, the outer cisterna pinches off a secretory vesicle, which travels to the plasma membrane.

Click picture or this link for an animation

4. Lysosomesa. Formed as vesicles that bud off of the Golgi

apparatusb. Filled with hydrolytic enzymes, most of which

are effective at pH 5 (Why?)c. Some vesicles join food vacuoles =

phagocytosisd. Some engulf and digest cell organelles =

autophagy

Tay Sachs is considered a storage disease because of a problem in the lysosome.

5. Peroxisomesa. Membrane-bound chambers where H+ is

removed from various molecules and transferred to O2 to form H2O2 (hydrogen peroxide).

b. Helps w/ breakdown of fatty acids and detoxifying poisons.

c. Also contain enzyme catalase, which breaks down

H2O2 into water because it is toxic

itself

Hallmark Cards that should have been:

•How could two people as beautiful as you…

•…Have such an ugly baby? Congratulations Anyway!

•I’ve always wanted to have someone to hold, someone to love. After having met you…

•…I’ve changed my mind.

IV. CytoskeletonA. Microtubules

1. Structurea. Hollow, rod-shaped, 25 nm. in diameterb. Composed of and tubulin dimers (globular

proteins)

2. Functionsa. Structural

i. Radiate from the microtubule organizing center (MTOC), which is the centrosome

ii. Act as girders or as bundles near cell membrane, cell shape

iii. Very dynamic (form and reform)

[Centrioles found in centrosome of animal cells are composed of 9 sets of 3 microtubules.]

b. Movementi. Organelles and vesicles move along

microtubules (little train tracks), being pulled by a protein called kinesin.

ii. Cilia and flagella, composed of “9 + 2” arrangement, use proteins called dynein as contractile side arms

iii. Basal bodies are found at the base of both cilia and flagella

B. Microfilaments helix of actin molecules (globular proteins),

7nm.1. Structural - in microvilli, cell shape, dynamic

2. Functional - involved in cytokinesis, pseudopodia, and muscle contraction

C. Intermediate filamentsheterogeneous, fibrous proteins, 8-12 nm.

1. Structural - Cell shape and stability, dynamic

Do you ever feel like doing this to someone?

V. Plasma Membrane- all cells have them- complex, dynamic structures, not passive- differentially permeable

A. Functions1. Regulates the movement of molecules into and

out of the cell2. Site of cell recognition and communication

B. Structure (Fluid mosaic model) (10nm.)1. Phospholipids

a. 5 - 10 different typesb. Most common = phosphotidylcholinec. Membrane fusion easily accomplishedd. Movement - 2 m./sec.

2. Cholesterol - decreases fluidity of membrane

Membrane Fluidity

Why is it that membrane phospholipids drift laterally, and rarely flip?

How is this fluidity maintained? Kinks in unsaturated fatty acid tails of

phospholipids.

Cholesterol

3. Proteins a. Integral proteins

-part or all the way through membrane (some move like icebergs)b. Peripheral proteins - usually bound to integral proteins (inside surface)

4. Glycoproteins and glycolipids - cell recognition- external surface oligosaccharides (<15 units)

C. Transport across the membrane1. Diffusion

movement of molecules down the concentration gradient

passive process - energy from kinetic energy of molecules

a. Channel proteins - aqueous channel for ions, gated

b. Facilitated diffusion - molecule binds to protein and is transported across membrane

i. Protein changes its shapeii. Specificity

c. Osmosis - diffusion of water through a selectively permeable membrane

Know and understand these terms = isotonic, hypertonic, hypotonic, water potential, turgor, plasmolysis

Lab 1E - Plasmolysis

Plasmolysis video clipAnimation

#1 Onion Cells - Sketch

Homework: Complete Analysis ?’s 1-3 on pg. 18

(Due Tom.)

Osmotic Pressure

2. Active transporta. Movement of molecules

up the concentration gradientb. Requires energy (ATP)c. E.g. sodium-potassium pump

3. Cotransport - transport of one solute coupled to transport of another

4. Endocytosis - movement of large molecules (proteins, polysaccharides) through membrane by forming vesiclesa. Phagocytosis - chunks

b. Pinocytosis - droplets

c. Receptor-mediated endocytosis - receptor-covered depressions (coated pits) form coated vesicles (“ligand”=molecule grabbed on to)

5. Exocytosis - waste removal or secretion

Receptor-mediated Endocytosis

Chapter 9 - Cell Cycle (Movie)

Cetromere / Kinetochore

Spindle Movement

Cytokinesis

Cell plate formation

Control of mitosis1. Density-dependent inhibition and the

role of growth factors

2. Restriction point in G1 (some cells to GO)

3. Cell-cycle clocka. Cyclin-dependent kinases (Cdk’s) -

molecules that activate other proteins through phosphorylation

b. Cyclins - proteins that control Cdk’s, concentrations fluctuate through cell cycle

c. M-cyclin + M-kinase = MPF complex (M-phase promoting factor) – MPF triggers cells passage from G2 to M

p53 turns on repair enzymes and if repair is impossible, p53 causes apoptosis