M&R - Lipid Bilayer and Lipids/Proteins Flashcards Preview

Semester 2 > M&R - Lipid Bilayer and Lipids/Proteins > Flashcards

Flashcards in M&R - Lipid Bilayer and Lipids/Proteins Deck (26):
1

Do all regions of plasma membrane have the same function?

No
Dynamic environment, constantly changing
Functions include - secretion, transport, interaction with adjacent cells, interaction with basement membrane

2

What is the composition of a membrane?

40% lipid
60% protein
1-10% carbohydrate

20% of total weight = water

3

Membranes are described as amphipathic molecules, what does this mean?

Contain both hydrophobic and hydrophillic moiety

4

What are the three predominant lipids found in a cell membrane?

Phospholipid (Small head groups - choline, amine, )
Sphingomyelin - doesn't have glycerol backbone
Glycolipid - two types = cerebrosides and ganglioside

5

What is the length of a fatty acid chain?

Which is more prevalent?

C14-C24

C16-C18

6

Name some of the roles of membrane proteins

Functional = Enzymes
Transporters
Pumps
Ion channels
Receptors
Energy transducers
Facilitated diffusion

Biochemical = membrane fractionation, freeze fracture

7

What are the four ways lipids can mobilise in a cell membrane?

Flexion
Rotation
Lateral diffusion
Flip Flop - flip head group through hydrophobic domain to the other side

8

What effect does the presence of a double bond in a fatty acid side chain have?

Introduces a kink into the chain that reduces the ability of the phospholipid to pack in crystalline array and so contributes to increased membrane fluidity

9

What is the role of cholesterol in the lipid bilayer?

What effect does cholesterol have on the fluidity of the membrane bilayer?

Stabilises the structure

Cholesterol reduces phospholipid packing and maintains membrane in fluid phase = increasing fluidity

Rigid cholesterol ring structure held closely to fatty acid chains reduces intrachain vibrations = reducing fluidity

10

What ways can a protein mobilise in a cell membrane?

Conformational change
Rotational
Lateral


NO FLIP FLOP - energetically unfavourable

11

How are membrane proteins restricted in movement?

Lipid mediated effects - proteins tend to seperate into fluid phase or cholesterol poor region

Membrane protein associations

Association with extra membranous proteins e.g. Cytoskeleton

12

What are the two types of membrane proteins and describe?

Peripheral proteins - bound to surface.
Electrostatic or hydrogen bond interactions.
Removed by changes in pH or ionic strength

Integral proteins
Interact with hydrophobic domains of bilayer
Removed by detergents/organic solvents which dissolves bilayer to release protein

13

What is the length of amino acids that tend to span bilayer?

18-22 amino acids

14

What arrangement are the transmembraneous domains?

Alpha helical

15

What is the name of the plots used to determine if a membrane is membrane spanning?

Hydropathy plots

High hydrophobic score = membrane spanning

16

What are the functions of a biological membrane? (5)

Highly selective permeability barrier
Control of enclosed chemical environment
Communication
Recognition - signalling molecule, adhesion proteins, immune surveillance
Signal generation in response to stimuli - electrical/chemical

17

How many hydrophobic domains are there in bacteriorhodopsin?

Why is this molecule important?

7 domains

Bacteria that traps light. Can be grown in a dish to make lots of protein. Has the same structure as a lot of the receptors.

18

What terminal of the protein faces in and which faces out?

Why is orientation important?

C terminal out
N terminal in cytosol

Important for function

19

What are the integral proteins of the erythrocyte skeleton?

Glycophorin A
Band 3

20

What are the peripheral membranes of the erythrocyte skeleton?

Actin
Ankyrin
Adducin
Band 4.1

21

What are the two haemolytic anaemias?

Hereditary spherocytosis - Spectrin depleted by 40-50%, erythrocytes round up, less resistant to lysis, cleared by spleen = anaemia

Heridtary elliptocytosis - defect in spectrin molecule, unable to form stable heterotetramers, fragile elliptoid cells

22

Describe the secreted protein biosynthesis

Signal sequence recognised by SRP
Binding of SRP prevents further protein synthesis
SRP recognised by receptor - directs SRP ribosome complex to protein translocator complex
SRP released
Protein synthesis continue
Translocates through until stop sequence reached
Protein released
Ribosome detaches from ER
Signal sequence cleaved by signal peptidase

23

What anchors proteins in the bilayer?

Stop sequence in the middle of the protein
Ribosome continues to make protein, cannot force through bilayer so rest of protein made in cytoplasm

24

What direction would the protein enter bilayer if there are more positive residues at N terminus?

C terminal section will pass into lumen

25

What happens in the presence of N terminal signal sequence in absence of signal peptidase cleavage?

C terminal to ER lumen - C terminus flops in

26

What happens when there are more positive residues at the C terminal end of the start transfer sequence?

N terminal translocated and in ER lumen

Protein orientation reversed
No signal peptidase