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Cellular and Molecular Biology > Lecture 36: Membrane proteins and membrane fluidity > Flashcards

Lecture 36: Membrane proteins and membrane fluidity Flashcards

1
Q

Can glycans recognise non-cell cells?

A

Yes

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2
Q

Do both lipids and proteins diffuse through a membrane?

A

Yes, and lipids diffuse laterally

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3
Q

How is the rate of lateral diffusion in a membrane measured?

A

Using FRAP

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4
Q

What does FRAP stand for?

A

Fluorescence Recovery After Photobleaching

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5
Q

What is FRAP?

A
  • Where fluorophores on membrane lipids are bleached with intense light.
  • Rate of fluorescence recovery indicates lateral diffusion.
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6
Q

Which ways can substances in the membrane move?

A
  • Rotation
  • flexion
  • Lateral diffusion
  • Transverse diffusion
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7
Q

Describe the mobement of lipids within a membrane

A

Rotation and Flexion occur at a high rate, much quicker than lateral diffusion, and signficantly quicker than transverse diffusion (which is so slow that it has to be catalysed by enzymes)

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8
Q

Descibe the movement of proteins within a mebrane

A

Proteins move more slowly, primarily through lateral diffusion, and their movement is often constrained by their size, interactions, and specific roles (e.g., signaling or anchoring).

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9
Q

Do proeins flip-flop/transversely diffuse at all?

A

No

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10
Q

What happesn if an increased temperature casuses a membrane to be too fluid?

A

Fluidity is increased as the temperature increases
Lipid molecules move faster
The membrane becomes more permeable

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11
Q

WHat happens if a decrease in temperature causes a membrane to be too solid?

A

Fluidity is decreased as the temperature decreases
Lipid molecules move more slowly: gel-like
The membrane becomes less permeable

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12
Q

Is it true that there’s faster movement in membranes at higher temperatures?

A

Yes

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13
Q

What type of lipids increase membrane fluidity?

A
  • Unsaturated lipids gives kinks and they don’t pack well together
  • Short chains allow fewer interactions between lipids
  • Lower melting points
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14
Q

What types of lipids decrease membrane fluidity?

A

Saturated chains

Long chains

Higher melting points

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15
Q

Is it true that changing lipid composition can help regulate the temperature in organisms that can’t regulate their temperature intrinsically?

A

Yes

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16
Q

How may plants regulate their temperature?

A

Plants have sensors in the plasma membrane that detect changes in fluidity

Fluidity increases indicates temperature is increasing

Allows the plant to prepare for heat stress

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17
Q

Descibe the structure of cholesterol

A
  • Steroid 4 hydrocarbon ring structure, that is stiff
  • Non-polar hydrocarbon tail, that is floppy
  • Polar head group
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18
Q

Is it true that cholesterol can increase fluidity in the middle of the membrane (flexible tail) and decrease fluidity at the edge of the membrane (steroid tail)?

A

Yes

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19
Q

What does ethanol do to the membrane fluidity?

A

It increases it

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20
Q

Alcoholics and membrane fluidity

A
  • One of the toxic effects of alcohol is due to an
    increase in membrane fluidity
  • Chronic alcoholics compensate by increasing cholesterol
    content of membrane
  • So when they finally sober up….
  • Stabilisizing effect of cholesterol remains, and This creates a state of reduced membrane fluidity, as the elevated cholesterol levels are not immediately reversed.
  • Membranes will become too rigid, leading to withdrawal symptoms
21
Q

How often does transverse diffusion of lipids happen?

A

Transverse diffusion (flip-flop) once every 3 days (rare)

22
Q

What catalyses the ‘flip-flop’ of lipids?

A

Proteins known as phospholipid translocators (flippases) catalyze the flip-flop event to maintain phospholipids in the correct monolayer.

23
Q

Proteins destined for membranes are synthesized on one membrane of the endoplasmic reticulum (not in the ER)

A

Proteins destined for membranes are synthesized on one membrane of the endoplasmic reticulum (not in the ER)

24
Q

What are the many functions of membrane proteins?

A
  • Transporters
  • Receptors
  • Enzymes
  • Anchors
25
Q

What do integal membrane proteins do?

A

(a & b) Integral membrane proteins traverse (cross) the membrane

26
Q

What do peripheral membrane proteins do ?

A

(c) Peripheral membrane proteins associate with a membrane face

27
Q

Is it true that some proteins bind to the surface of integral proteins?

A

Yes

28
Q

Are some membrane proteins covalently anchored to the membrane?

A

Yes

29
Q

describe the types of integral membrane proteins

A
  • Single span hydrophobic α-helix
    Either C- or N-terminal can be intra-cellular
  • Multi-spanning containing α-helices
    7 transmembrane helix protein a big family
    But can have more or fewer helices
  • β-barrel protein forming a pore
30
Q

Do integram membrane proteins flip flop?

A

No

31
Q

What is the membrane topolgy maintained by?

A

Topology is maintained by hydrophobic and electrostatic interactions

32
Q

Can the loops of integral proteins form binding sites?

A

Yes

33
Q

What is ICAM?

A

ICAM is a crucial adhesion molecule in cell-cell communication, especially during immune responses. Its ability to mediate interactions between cells makes it essential for inflammation, immune surveillance, and maintaining tissue integrity.

34
Q

On which cells is ICAM expressed?

A

Expressed on cells of the immune system and endothelial cells

35
Q

Describe the structure of ICAM

A
  • It has 5 extracellular immunoglobulin domains
  • Single transmembrane spanning helix
  • Short cytoplasmic tail
36
Q

What is Bacteriorhodopsin?

A

Bacteriorhodopsin is a light-driven proton pump found in the cell membranes of certain archaea, particularly Halobacterium salinarum, which thrives in saline environments. It is a type of protein that captures light energy and uses it to move protons (H⁺ ions) across the membrane, creating a proton gradient that can then be used to generate ATP through chemiosmosis.

37
Q

Are porins a type of outer membrane protein?

A

Yes

38
Q

Describe porins

A
  • Forms a barrel shaped structure with a pore in the centre.
  • Outside of structure is hydrophobic, whilst the inside is hydrophilic
39
Q

Describe peripheral membrane proteins

A
  • Do not interact with the hydrophobic core of the membrane
  • Can be cytoplasmic OR exoplasmic (and does not change)
  • Interact with lipid head groups and integral membrane proteins
  • Interactions are non-covalent
  • Electrostatic interactions, H-bonds, van der Waals bonds
40
Q

Describe anchored proteins

A

Proteins anchored to the membrane through hydrocarbon groups

The protein is covalently attached to a hydrocarbon group

The hydrophobic hydrocarbon group inserts into the lipid bilayer

41
Q

Describe Ankyrin and Spectrin

A
  • Spectrin cytoskeleton protein creating a scaffold on the intra-cellular side of membrane
  • Ankyrin binds to several integral membrane proteins AND to spectrin (attaches spectrin).
  • Maintain plasma membrane integrity via the spectrin-actin based cytoskeletal structure
42
Q

Cells are covered in cybohyrdates….

A
  • Cells are covered in carbohydrates on the exoplasmic side of membranes
  • The carbohydrates can be attached to both lipids (glycolipids) and proteins (glycoproteins)
  • the glycocalyx is a network of glycoproteins with mucus like consistency
  • The function is: Physical barrier (protects against viruses and bacteria), Mechanosensing, Possible roles in cell shape
43
Q

Is it true that most membrane proteins have at least one carbohydrate unit?

A

Yes

( Exist as either oligosaccharide chains or single sugar residues
; Glycoproteins usually have oligosaccharide chains
; Glycolipids usually have single sugar residues
)

44
Q

IS it true that few membrane lipids have carbohydrate units?

A

Yes

45
Q

What is the function of membrane carbohydrates?

A
  • Cell-cell recognition, communication and adhesion
  • This is especially important in immune responses, when cells need to distinguish between self and non-self cells
46
Q

Blood groups and carbohydrates

A

Different carbohydrates are present on different blood group antigens

Our genes determine which enzymes we have and hence which blood group

47
Q

Key messages

A

Membrane fluidity is crucial for correct functioning of cells

Membrane proteins have a variety of different structures and can be integral or peripheral

Glycans are on the outside of membranes and attached to either proteins or lipids

48
Q
A

Cellular and Molecular Biology (36 decks)

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