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Y2 Biostructures > Membranes > Flashcards

Membranes Flashcards

1
Q

What functions do plasma membranes serve?

A

Barrier between environments
Regulating transport of nutrients
Energy transducers
Compartmentalisation
Cellular recognition
Signalling

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2
Q

Why do eukaryotes use compartments?

A

Larger volumes to contain molecules

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3
Q

How are proteins carried from the golgi through the cell?

A

Post bags are carried on microtubule tracks. When microtubules are disrupted, the golgi collapses

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4
Q

What does the golgi do to proteins?

A

Packages proteins into membrane vesicles for transport
Recycling and tagging proteins so they end up where they are meant to be

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5
Q

Outline the fluid mosaic model

A

Lateral movement of fatty acids, but not rotation
Spontaneous rotation of lipids is very slow and called flip-flop
Membranes are two-dimensional solutions of oriented lipids and globular proteins

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6
Q

How do reindeer lipid compositions differ from foot to leg?

A

Lipids have more double bonds to make them more fluid at the foot. Further up, lipids become more rigid and have higher melting points

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7
Q

Outline FRAP

A
  1. A cell has its membrane proteins fluorescently tagged
  2. A laser bleaches the fluorescence
  3. Fluorescence recovery shows how the proteins move around
  4. Fluorescence intensity graphs are made
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8
Q

What do fluorescence intensity graphs show about the fluid mosaic model?

A

It is wrong as membrane proteins move around and freely associate with the membranes

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9
Q

What is the difference between sphingolipids and phosphoglycerides?

A

Phosphoglycerides contain cis double bonds and sphingolipids contain trans double bonds and NH (much more ordered)

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10
Q

How does cholesterol increase membrane fluidity?

A

Cholesterol is flat so packs against trans lipids, squashing them down.

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11
Q

What type of fatty acids are used in curved membranes?

A

Phosphatidylethanolamine. Smaller phosphate head than tail
(alcohol makes me bicurious)

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12
Q

What sorts of fatty acids are cylindrical

A

phosphtiylcholine
(C in choline and cylindrical)

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13
Q

How can a conical shape be made in cell membrane?

A

Chromatophores

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14
Q

What pushes the membrane out or reels it in?

A

Actin cytoskeleton and microtubule motors

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15
Q

What are sphingolipids made up of?

A

Sphingosine backbone
Phosphate head
One fatty acid with trans double bonds

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16
Q

What are phospholipids made up of?

A

Glycerol backbone
At least one fatty acid
Phosphate head
Alcohol attached to the phosphate head

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17
Q

Where are GPI anchored proteins anchored to?

A

Outer membrane

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18
Q

What are membrane rafts made up of?

A

Cholesterol
Sphingosine backbone

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19
Q

What purpose do lipid rafts serve?

A

Concentrate proteins in signal transduction
Make the membrane less fluid
Bridging gaps between differently sized membranes
Organising the start of endocytosis
T cell activation

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20
Q

What is atomic force microscopy?

A

A laser detecting variation of height of a sensitive arm over a sample
The sample is scanned backwards and forwards to give a visualisation of protein structure
Used to detect lipid rafts

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21
Q

What sorts of anchors go into lipid rafts

A

GPI anchors
Palmitoyl anchors
Not prenyl anchors

22
Q

What is altered to allow proteins to move in and out of lipid rafts?

A

GPI anchors (affinity for rafts) and prenylation

23
Q

Outline ligand-mediated endocytosis

A
  1. Ligand actives a receptor
  2. This leads to a lipid raft being formed by phase separation, beginning endocytosis
  3. Calveolin binds to the membrane raft, halfway into the membrane, making it curved
  4. Calveolin recruits cavin and clathrin which coat the caveolae
  5. Caveolae are pinched off the top and move into the cell
24
Q

Describe archaeal membranes

A

Fatty acids are joined to a glycerol backbone by ether linkages (resistance to hydrolysis)
Branched alkyl chains are more resistant to oxidation
This helps archaea resist extreme conditions

25
Q

What is patch clamping used to measure

A

Current across the cell membrane for ion channel openings

26
Q

Outline patch clamping

A
  1. An electrode is gently pushed onto the cell surface
  2. The electronic pipette pulls the outside of the membrane
  3. The inner leaflet can be measured by pushing the pipette in
27
Q

How is channel permeability determined?

A

Time channel is open/ total time

28
Q

Outline voltage-gated Na+ channel opening

A
  1. Voltage-sensing α-helices move up or down depending on the membrane potential
  2. They open at -40mV and the sodium channel plug is moved
29
Q

When does the voltage gated K+ channel open

A

When membrane potential is positive, tey open
Slower opening and closing than Na channels

30
Q

What is the Debye distance?

A

Imbalance in ions which means when ions move out of a membrane, they don’t move far. Cell charge dampens out
Reasons why K+ ions do not diffuse completely out of channels

31
Q

Nerve impulses are transient. What does this mean

A

All or nothing

32
Q

How are signals transmitted through nerve cells?

A

Transmitted by neurotransmitters in vesicles. The vesicles are exocytosed, triggering action potentials which open Ca+ channels

33
Q

Outline an action potential depolarising the cell membrane

A

When the membrane potential is raised above -40mV, Na+ channels open
Na+ moves in and there is positive feedback opening all the Na+ channels, making membrane potential +35mV.
The Na channels are the plugged
K+ channels open and K+ floods out the cell, making the membrane potential more negative.
The refractory period is where the potential is briefly hyperpolarised and K+ channel is plugged

34
Q

How do myelin sheaths make signal conduction 100x quicker?

A

The nerve acts as a capacitor. It has 1μm gaps every 100μm where the membrane contacts extracellular fluid. Na+ channels are here and allow potential to jump from one node to another.

35
Q

What is multiple sclerosis caused by?

A

Loss of myelin in the brain and spinal cord

36
Q

How can ion gradient be calculated?

A

ΔG = zFE

z = charge on ion
F = Faraday constant
E = membrane potential

37
Q

How can membrane potential be related to concentrations inside and outside?

A

E = (RT/zF) x ln([out]/[in])

38
Q

What do receptor kinases and GPCRs have in common?

A

G-proteins

39
Q

How are G protein switches 1 and 2 turned off?

A

GDP binds to a phosphate group which hydrogen bonds to Thr35 and Gly60

40
Q

Why does the G protein switch readily turn off?

A

The GTP:GDP ratio in the cell is around 10:1, so GDP readily dissociates from the active site

41
Q

What turns on and off the G protein?

A

Guanine exchange factor (GEF) turns it on
GTPase activating protein (GAP) turns it off

42
Q

What type of receptors are insulin and cytokine receptors?

A

Receptor-linked kinases

43
Q

Outline the mechanism of a receptor-linked kinase

A
  1. Hormone binds and the receptor dimerises
  2. A kinase domain is phosphorylated, fixing the position of the activating loop so it can bind to the substrate
  3. Activated kinase creates an intracellular signal by phosphorylating tyrosines
  4. The receptor is switched on and acts as a binding site for modular adaptor proteins
44
Q

When a kinase linked receptor is activated, outline the mechanism of Grb2

A
  1. Grb has an SH2 subunit which recognises phosphotyrosines and two SH3 subunits which recognise polyproline helices.
  2. Grb plugs together with SOS and brings GEF to the cell surface, activating G protein Ras
  3. Ras activates Raf which phosphorylates other kinases such as ERK which phosphorylate transcription factors and switch on genes
45
Q

When ligand binds to a GPCR, what causes the conformational change?

A

A bent helix rotates and causes tryptophan flipping.
In rhodopsin, this opens up a groove for the Gα helix. This binding site on Gα opens up, allowing GDP to leave

46
Q

What does Gαq stimulate?

A

Phospholipase Cβ which catalyses
PIP2 -> DAG + IP3

47
Q

Outline a Gs protein response

A
  1. A ligand activates the GPCR which activates the G protein which activates adenylyl cyclase
  2. Adenylyl cyclase synthesises cAMP which activates protein kinase A
  3. PKA enters the nucleus and phophorylates CREB
  4. CREB recruits CREB binding protein (CBP)
  5. CREB-CBP activates genes
48
Q

What does arrestin do?

A

Blocks GPCR action by phosphorylation
Binds to clathrin and endocytoses GCRP to be recycled or degraded

49
Q

Describe ligand-gated channels

A

Multiple subunits as sharp transitions can take place

50
Q

What are calcium channels used for?

A

Muscle contraction
Releasing neurotransmitter at the presynaptic membrane
Egg fertilisation
Inositol phosphate carries signals from second messengers

51
Q

How does cholera lead to diarrhea?

A
  1. Produces a toxin which moves into cells and adds ADP ribose to Gαs subunits
  2. The Gαs subunit is constitutively activated
  3. The cell continues making cAMP, so water and ions continue being released into the gut, leading to diarrhea
52
Q

What mechanism leads to whooping cough?

A

B. pertussis produces a toxin which adds ADP ribose to Gαi subunit. This prevents adenyl cyclase being inhibited, leading to cAMP being produced

Y2 Biostructures (5 decks)

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