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ESA 2 > Membranes and Receptors > Flashcards

Membranes and Receptors Flashcards

1
Q

List 5 main functions of biological membranes.

A
  1. Continues, highly selective permeability barrier
  2. Control of an enclosed environment
  3. Communication - information between cells and the environment
  4. Recognition
  5. Signal generation in response to electrical and chemical stimuli
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2
Q

In what ways can a membrane recognise a signal?

A
  • Receptors detecting signalling molecules
  • Adhesion proteins within cells of a tissue
  • Immune surveillance
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3
Q

List the specialised functions of 3 membranes

A

Mitochondria: Energy conservation by oxidative phosphorylation
Nerves: Signal transduction by myelination
Apical cell membranes: Absorption of bodily fluids

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4
Q

What 4 things are biological membranes made from?

A
  • 40% (DW) Lipid
  • 60% (DW) Protein
  • 1-10% (DW) Carbohydrate
  • 20% Water
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5
Q

What is the main property of phospholipid?

A

It is amphipathic

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6
Q

What does amphipathic mean?

A

It has both hydrophobic and hydrophilic moieties

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7
Q

What is the structure of a phospholipid?

A

A glycerol molecules connected to two fatty acid chains and a phosphate that is lined to a head group

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8
Q

What is the average length of fatty acid chains and why is this the case?

A

C16 and C18

Constant thickness to the bilayer to make it more stable

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9
Q

What is the benefit of an unsaturated fatty acid?

A

Cis conformation introduces a kink which reduces phospholipid packing

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10
Q

List the four possible head groups on a phospholipid

A
  • Choline
  • Amines
  • Amino acids
  • Sugars eg. Inositol (rare and a substrate for messengers)
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11
Q

What is Sphingomyelin?

A

A plasmalogen which is a phospholipid not based on glycerol

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12
Q

Describe 2 types of glycolipid

A

Sugar containing lipids

  • Cerebrosides - head group=sugar monomer
  • Ganglioside - head group=oligosaccharide
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13
Q

What is the average cholesterol content in cell membranes?

A

45% total membrane lipid

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14
Q

What is the purpose of cholesterol in cell membranes?

A

1:1 ration
Decrease fluidity at high temperatures
-Hydrogen bonds to ester on FA part of phospholipid
-Fatty acid chains align making Van de Waal’s forces stronger decreasing mobility
-More stable -> endothermic phase transition stops
- less likely to fracture
Increases fluidity at low temperatures
- Decreases packing of phospholipids making it less saturated

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15
Q

List and describe the 4 modes of mobility for lipids in a lipid bilayer

A
  1. Flexation (kink formation)
  2. Fast axial rotation
  3. Lateral diffusion (within plane of bilayer)
  4. Flip-flop (lipids move between different halves of bilayer, one for one exchange, rare as needs to move hydrophilic sections across membrane)
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16
Q

List 6 functions of membrane proteins

A
  • Enzymes
  • Transporters
  • Pumps
  • Ion channels
  • Receptors
  • Energy transducers
17
Q

Why can proteins undergo every type of motion besides flip-flop?

A
  • Very hydrophilic -> damage bilayer? + not energetically favourable
18
Q

How is protein mobility restrained?

A

Lipid mediated effects:

  • Proteins separate out into fluid phase/cholesterol poor regions
  • Receptors and effectors group together in cholesterol rich ares (signal coupling and transduction)

Associations between membrane proteins to form aggregates

Associations with extra-membranous proteins eg. cytoskelaton

19
Q

List 3 functional types of evidence for membrane proteins and 2 biochemical

A 
Functional:
- Facilitated diffusion
- Ion gradients
- Response to signals
Biochemical:
- Freeze fracture
Membrane fractionation -> gel electrophoresis
20
Q

How do peripheral proteins interact with the lipid bilayer?

A

On surface
Electrostatic and hydrogen bond interactions
Removal: change pH or ionic strength (salt solution)
Possible disulphide bonds

21
Q

How do integral proteins interact with the lipid bilayer?

A

Interact extensively with hydrophobic regions (18-22 aachain)
Removal: detergents/organic solvents
Non-polar interactions

22
Q

Why are proteins asymmetrically orientated?

A

Function:
Receptor to detect signal from extracellular messenger
Effector within cell for response

23
Q

Why are many proteins not proteolysed when treated with pH/ionic strength changes?

A

They are on the cytoplasmic face

24
Q

What is the cytoskeleton of a RBC composed of?

A

Actin and spectrin

25
Q

How does spectrin contribute to the cytoskelaton structure of a RBC?

A

Alpha and beta strands

  • > wind to form antiparallel heterodimer
  • > head to head association to form heterotetramer
  • > Cross linked by actin (junctional complexes) and attached to membrane via peripheral proteins
26
Q

What is the purpose of a cytoskelaton in erythrocytes?

A

Maintain deformability - can travel through capillary beds without lysis

27
Q

What are the causes and effects of Hereditary Spherocytosis?

A

Spectrin levels depleted by 40-50%

RBC round up -> less resistant to lysis -> cleared by spleen

28
Q

Describe haemolytic anaemia and how it is treated

A

Shortened RBC lifespan -> bone marrow unable to compensate -> few RBC

Need repeated transfusions and lifestyle advice

29
Q

What is Hereditary Elliptocytosis?

A

Spectrin can’t form heterotetramers -> fragile elliptoid RBC

Treated with cytochalisin drugs

30
Q

How does membrane protein translation work?

A
  1. mRNA within ribosome begins translation
  2. Signal sequence produced
  3. SRP (signal recognition particle) binds, stopping translation
  4. Movement to the ER and recognition by SRP receptor
  5. Protein docks, SRP released, signal sequence interacts with SSR (signal sequence receptor) on protein translocator complex
  6. Translation continues (amino acid chain released into ER lumen)
  7. Stop transfer sequence (hydrophobic) -> alpha helical transmembrane section
  8. Signal peptidases cleave signal sequence
  9. ER -> golgi -> membrane (cytoplasm side remains in cytoplasm, ER lumen -> outside of cell)
31
Q

How is the N and C terminus location in lume/cytoplasm of ER determined (brief)?

A

Signal peptidase -> N in lumen
No signal peptidase -> C in lumen
Location of of +ve charge in signal sequence (C or N)

32
Q

What are features of right-side out vesicles?

A
  • Vesicles to be exocytosed

- Functional groups on outside only accessible (internal only accessible if leaky)

33
Q

What are features of inside-out vesicles

A
  • Vesicles that have been endocytosed (proteins have reversed membrane orientation)
34
Q

Which molecules are able to diffuse across phospholipid membranes

A
  • Uncharged Non-polar/lipophilic:
  • > O2, CO2, N2 Benzene
  • Small polar uncharged molecules:
  • > H2O (osmosis), Urea, Glycerol
  • Large uncharged polar molecules:
  • > Glucose, Sucrose
  • Ions:
  • > H +, Na +, K +, Ca 2+, Mg 2+, Cl -, HCO3 -
35
Q

What causes the rate of passive transport to increase linearly?

A

Concentration gradient

ESA 2 (2 decks)

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