Cell membranes-depth

Question 1

What is the main function of?

Answer 1

Contains many metabolic pathways protein synthesis.

Question 2

What is the main function of the nucleus(double membrane)?

Answer 2

contains main genome
DNA and RNA synthesis

Question 3

What is the main function of the endoplasmic reticulum(ER)?

Answer 3

• synthesis of most lipids
• synthesis of proteins for distribution to many organelles.

Question 4

What is the main function of the Golgi apparatus?

Answer 4

Modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelle.

Question 5

What is the main function of the lysosome?

Answer 5

Intracellular degradation

Question 6

What is the main function of the endosome?

Answer 6

Sorting of endocytosed material

Question 7

What is the main function of the mitochondria(double membrane)?

Answer 7

ATP synthesis by oxidative phosphorylation.

Question 8

What is the main function of the chloroplast(plant cells)?

Answer 8

ATP synthesis and carbon fixation by photosynthesis.

Question 9

What is the main function of the peroxisome?

Answer 9

Oxidation of toxic molecules.

Question 10

What 3 things are not in a plant cell?

Answer 10

Lysosomes
Centrioles
Flagella

Question 11

What are the first 4 functions of cell membranes?

Answer 11

1. Define boundaries of the cell and organelles (compartmentalisation)
2. Aid organelle function, e.g. production of energy intermediates

3.import and export of small molecules and ions

4. Signal detection

Question 12

What are the last 4 functions of cell membranes?

Answer 12

5. Adhesion of cells to each other and to extracellular matrix (ECM)
6. Anchoring to the cytoskeleton
7. Cell movement and expansion
8. Cell division

Question 13

What are the two main constituents of cell membranes?

Answer 13

Lipids and proteins.

Question 14

What is a phospholipid composed of?

Answer 14

A hydrophilic head and two hydrophobic hydrocarbon tails.

^Ampiphatic

They spontaneously form bilayers

EXT. Most common phospholipid is phosphatidylcholine.

Question 15

Describe the structure of phosphatifylcholine?

Answer 15

Hydrophillic head
Glycerol(linker) attaches the 2 hydrocarbon chain via their COOH groups.
Hydrophobic tails
Hydrocarbon chains originate as fatty acids.

Question 16

What does an unsaturated lipid do to membrane fluidity?

Answer 16

The more unsaturated the more fluid the membrane is.

Question 17

Where is cholesterol found?

Answer 17

Only in animal cell membranes

Question 18

What is the role of cholesterol?

Answer 18

Controls membrane fluidity in animal cells, especially in the plasma membrane.

Fits into gaps between phospholipid molecules left by kinks formed by the unsaturated hydrocarbon tails in the lipid bilayer.

SHORT and RIGID.

Question 19

Why is membrane fluidity important?

Answer 19

Membrane protein diffusion in signalling .

Distribution of lipids and proteins in daughter cells.

Membrane fusion(molecular trafficking).

Allows membrane lipid and proteins to become distributed after delivery to the membrane.

Question 20

What do B cells do at the plasma membrane?

Answer 20

B cells activate by allowing B cell receptors (BCRs) to cluster at the plasma membrane.

Question 21

What is the relevance of phospholipids being mostly on outer or inner facing regions at the plasma membrane?

Answer 21

This asymmetry is for the function of the phospholipids, with parts like cholesterol being evenly distributed and phosphatidylserine being mostly inner layer.

Question 22

How is asymetry achieved within the lipid bilayer?

Answer 22

Action of scramblases and flippases.

Question 23

What do scramblases do?

Answer 23

Scramblase catalyzes random transfer of phospholipids from one monolayer to the other.

Question 24

What do flipases do?

Answer 24

Catalyse transfer of PE and PS to the cytosolic monolayer.

Question 25

What are the two kinds of membrane

Answer 25

Intrinsic and extrinsic.

Question 26

What is the structure and role of intrinsic proteins?

Answer 26

Penetrate the hydrophobic core of the lipid bilayer. Have predominantly hydrophobic interactions with the bilayer. Directly attach to the lipid bilayer, e.g. transmembrane, associated with lipid monolayer or lipid-linked

Question 27

How are intrinsic proteins removed?

Answer 27

Removed using membrane-disrupting agents such as detergents: SDS – strong ionic detergent (denatures proteins)

Question 28

What is the structure and role of extrinsic proteins?

Answer 28

Not embedded in the lipid bilayer. Have predominantly non-hydrophobic interactions with the bilayer. No membrane spanning region, associated with one side of the bilayer only. pH/ionic changes separate protein-protein interactions and leave the lipid bilayer intact

Question 29

What are the functions of plasma membrane proteins?

Answer 29

Transporters, anchors, receptors, enzymes, markers.

Question 30

What is the function of transporter proteins?

Answer 30

Actively pumps sodium out of cells and potassium in.

Question 31

What is the function of anchor proteins?

Answer 31

Link intracellular actin filaments to extracellular matrix proteins.

Question 32

What is the function of receptor proteins?

Answer 32

Binds extracellular PDGF to signal cell growth and division.

Question 33

What is the function of enzyme proteins?

Answer 33

Production of cAMP in response to extracellular signals.

Question 34

What is the function of marker proteins?

Answer 34

Present peptide antigens on the surface of white blood cells for recognition by T cells.

Question 35

How is speed affecting in the diffusion of a solute?

Answer 35

By size and solubility.

Question 36

What is the lipid bilayer permeable to?

Answer 36

Small uncharged molecules, e.g. (e.g. CO2, O2, water) and to hydrophobic molecules (e.g. ethanol, urea, anaesthetics).

Question 37

What is the lipid bilayer impermeable to?

Answer 37

Charged or large molecules e.g. Na+, K+, Cl-, glucose, amino acids.

Question 38

What do transport proteins required to do?

Answer 38

Transport ions, sugars, amino acids, nucleosides and many cell metabolites.

Question 39

What is the difference between active and passive transport?

Answer 39

Passive follows the concentration gradient whereas active goes against it.

Question 40

Is the membrane potential more positive inside or outside te cell?

Answer 40

More positive outside the cell and therefore more negative inside the cell. Stronger electrochemical gradient when there or more positively charged particles outside of the cell membrane.