Cell Membranes

Separating Dead from Alive

Identify the radical below.

19%

0%

57%

24%

1. Amine

2. Hydroxyl

3. Carboxyl

4. Monosaccharide

Identify the molecule shown.

62%

33%

0%0%5%

1. Butene

2. Propene

3. Propane

4. Butane

5. None of the above are a good response.

What is the function of the molecule shown below?

40%

5%5%

50%

1. Energy storage

2. Component of cell membrane

3. Fuel source

4. Regulatory

I. Functions

Living part of the cell-legitimate cell organelle

Separates living from the nonliving world

Semipermeable-regulates what enters and exits the cell

Partitions the cell into different regions where different functions take place

Participates in chemical reactions

Transmits signals between outside of cell and the cytoplasm[

II. Cell membrane characteristics

• A. Semipermeable

• B. Elastic

• C. Wettable

• D. Very thin-around 10 um

II. Early model

• A. Davison Danielli Model

1. mainly lipid

2. aqueous channels

3. surface protein

4. weaknesses

Phospholipids interacting in water-amphipathic

RBC cell membrane-clearly resembles Davson-Danielli model

III. Fluid mosaic model

• A. Main ingredients

• Phospholipids• Proteins both

intrinsic and extrinsic

• Cholesterol• Glycocalyx

Your textbook’s Diagram

B. Protein functions

What do you think the function of this membrane protein might be?

1. Transport

2. Cell to cell adhesion

3. Cell to cell recognition

4. Energy production

Electron micrograph of cell membrane

• http://www.med.uiuc.edu/histo/large/atlas/image/temgi3/75000a1.htm

C. Chemical properties of membrane

• 1. Lateral fluidity• 2. Two dimensional

fluidity-rapid movement of lipids and proteins

• 3. Flexible• 4. Self sealing• 5. Can fuse

C. Chemical properties of membrane

6. Effect of saturated vs. unsaturated

7. Role of cholesterol

IV. Function of Cell Membrane-Passive Transport

A. Diffusion

1. definition

2. example

3. across cell membrane

Your textbook’s figure of diffusion

IV. Function of Cell Membrane-Passive Transport• B. Facilitated

Diffusion1. mediated by intrinsic protein2. diffusion gradient-no ATP3. glucose entrance into cell4. boy scout analogy

C. Osmosis

• 1. Definition• 2. U-tube• 3. Explanation• 4. Common examples• 5. Terms of tonicity• 6. Turgor pressure

In which direction will water move?

1. A => B and B rises

2. B => A and A rises

3. A B and the sides stay at the same level

4. No idea

Your textbook’s figure of osmosis

Figure 5-13

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Plasmamembrane

Vacuole

Vacuolarmembrane(tonoplast)

CytoplasmPlasmamembrane

Vacuole

Nucleus(a) (b) (c)

V. Function of cell membrane-active transport

• A. Definition• B. Endocytosis

– 1. Phagocytosis

Phagocytic vesicles

2. Pinocytosis

Figure 5-19

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Microvilli Pinocytotic vesicle

Cytosol

3. Receptor mediated pinocytosis

Figure 5-20b

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0.25µm(b)

C. Exocytosis

D. Membrane Pumps

1. Materials are moved against concentration gradient

2. An integral protein molecule is involved

3. ATP is necessary

4. Sometimes membrane potentials are produced

5. Na ion-K ion pump is an example

Figure 5-15b

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ATP

ADP

1. Three sodium ions bindto the transport protein

2. A phosphate group istransferred from ATP tothe transport protein

3. The transport protein under-goes a conformationalchange, releasing threesodium ions outside the cell.

6. The transport proteinreturns to its original shape:Two potassium ions arereleased inside the cell

5. The phosphate is released

4. Two potassium ions bindto the transport protein

(b)