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Cell biology and physiology > Hotchins lectures > Flashcards

Hotchins lectures Flashcards

1
Q

Membrane function

A

Define the boundary of a cell and act as a barrier
Organisation and localisation within the cell
Transport in and out of cell
detect and transmit chemical and electrical signals
Cell adhesion

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2
Q

Fluid mosaic model of membrane structure

A
  • Membranes contain lipids and proteins
  • Phospholipids form bilayer due to their amphipathic nature
  • Phospholipids move freely in the membrane (membrane fluidity)
  • Some proteins can move and others cant in membrane
  • Proteins not uniformly distributed ( mosaic)
  • membranes are asymmetrical
  • membrane are selectively permeable
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3
Q

Membrane topology

A

2 sides to membrane
Exoplasmic side (outer membrane - Phosphatidylcholine and sphingomyelin
Cytoplasmic side (inner side) - Phosphatidylserine and Phosphatidylethanolamine

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4
Q

2 types of phospholipids and their sub groups

A

Phosphoglycerides
1. phosphatidylcholine
2. phosphatidylserine
3. phosphatidylethanolamine

Sphingolipids
Sphingomyelin

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5
Q

membrane phospholipid structure

A

HYDROPHILIC head
- choline
- phosphate
- glycerol

HYDROPHOBIC tail
2 fatty acid chains

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6
Q

Amphipathic

A

molecule that has both hydrophilic and hydrophobic regions

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7
Q

Hydrophobic effects

A

Water forces hydrophobic groups together in order to minimise their disruptive effects on the hydrogen bonded network

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8
Q

How do hydrophobic forced form a sealed spherical shape

A

A planar phosphlipid bilayer is energetically unfavourable so the phospholipids fold up to form a sealed spherical compartment that is energetically favourable

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9
Q

Van der waal forces between atoms in bilayer

A

When the phospholipids are too far apart there is no interaction. As they start to get closer attraction increases so more VOW forces and membrane is less fluid however when they get too close they begin to repel each other.

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10
Q

How is asymmetry established and maintained in the membrane

A

Scramblasses and flippasses

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11
Q

role of scramblasses

A

they are phospholipid translocaters

new phospholipids are formed on the cytoplasmic side of the membrane. Scrambalase moves phospholipids from one side of the bilayer to another to ensure equal growth of the membrane. They are non specific.

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12
Q

role of flippases

A

head group specific responsible for the transfer of phosphotidylserine and phosphatidylethanolamine from the exoplasmic to the cytosolic side of the bilayer. It operates to counteract the effects of the scrambalasses.

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13
Q

floppases

A

move the sphingomyelin and phosphatidylcholine from cytoplasmic side to exoplasmic side

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14
Q

cholesterol structure and role

A

polar head group
rigid planar steroid ring structure
non polar hydrocarbon tail
stabilises phospholipid bilayer and regulates membrane fluidity. It does this by restricting the movement of the phospholipids so they dont pack too tightly to prevent membrane from becoming too rigid.

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15
Q

Types of membrane proteins

A

Integral
peripheral
lipid anchored

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16
Q

Integral membrane protein structure and roles

A

Embedded within the phospholipid bilayer of the cell membrane.
Amphipathic
ROLES
1. transport:
Channel proteins - creates pores through membrane for specific molecules
Carrier proteins - changes shape to move substances across the membrane
Pumps - uses ATP to move molecules against their concentration gradient

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17
Q

Peripheral membrane proteins structure and roles

A

Not embedded in the lipid bilayer but losely attached to the surface of the membrane or integral membrane proteins
interact via electrostatic attraction or hydrogen bonds

ROLES:
1. cell signalling
2. Structural support and cell shape
Link membrane to cytoskeleton
3. Enzymatic activity
some act as enzymes
4. involved in endocytosis, exocytosis and vesicle transport

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18
Q

Why is it important for membranes to be fluid

A

Allows membranes to fuse with other membranes
ensures membranes are equally shared between daughter cells following cell divison
cell migration

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19
Q

How can membrane fluidity be demonstrated experimentally

A

FRAP - fluorescent recovery after photobleaching
Label lipids with fluorescent dye then hit small patch of cell with a laser which destroys the fluorescent signal but doesn’t damage the lipids. You’re left with bleached area of lipid, overtime unbleached molecules diffuse into bleached area and fluorescence in the bleached area recovers.

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20
Q

Lateral diffusion

A

Diffusion in bilayer
- Fast and frequent
- spontaneous

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21
Q

flip flop

A

Diffusion in bilayer
- movement of phospholipids from one side of membrane to the other
- rare without help
- slow

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22
Q

Melting point of phosphlipid bilayers

A

Pure phospholipid bilayers exhibit rapid phase transition over a narrow temperature range
Longer carbon chains = more VOW interactions = higher melting points
More double bonds = lower melting point bc double bond cause kinks so lipids cant pack tightly therefore few VOW interactions

23
Q

What happens in the bilayer as temperature decreases in prokaryotes

A

As temp decreases FA chain length decreases resulting in decreases VOW between neighbouring phospholipids and degree of saturation increases resulting in increases spacing between FA chain and therefore a decrease in VOW (vice versa for temp rising)

24
Q

How does temperature affect cholesterol?

A
  • At 37 degrees cholesterol made the membrane less fluid - stabilises interactions between neighbouring phospholipids
  • At lower temperatures phase transition is prevented by cholesterol which prevents the FA chains of interacting with each other
25
Passive transport
Simple diffusion No membrane proteins involved goes down conc gradient Eg. hydrophobic/lipid soluble molecules, small uncharged polar molecules Facilitated diffusion Membrane proteins involved down conc gradient Eg large uncharged polar molecules, ions NO ATP
26
channel proteins
Form hydrophilic pores in membrane. Most are non directional ion channels driven by concentration gradients. Fast diffusion.
27
Types of gated channels
Voltage gated Ligand gated extracellular/intracellular mechanically gated
28
carrier proteins
Transport small organic molecules highly selective slow can be passive or active (down/against conc gradient)
29
Example of a carrier protein carrying out faccilitated diffusion
Glut 1 (glucose transporter) Glucose bind to binding site Protein changes shape glucose is released to inside and protein changes back to original shape
30
How is the concentration gradient of glucose maintained
Once glucose enters the cell it is converted to glucose-6-phosphate. This means that it can no longer bind to the Glut 1 so gradient is maintained and transport is one directional
31
Electrochemical gradient
the net force (desire for an ion to enter/leave a cell) driving a charged solute across a membrane. It is effected by two thing - one due to concentration gradient and the other due to voltage across the membrane. If there is a lower conc of the ion inside the cell the ion will diffuse into the cell. If the charge on the inside of the cell is opposite to the charge on the ion it will move into the cell.
32
Active transport
Moves ions/molecules against the electrochemical gradient ATP required
33
3 main ways Active transport is carried out
1) Coupled transporters 2 molecules go across membrane together. One goes down its gradient which releases energy so the other molecule can go against its gradient - secondary active transport 2) ATP driven pumps Energy derived from the hydrolysis of ATP used to drive the transport of a solute against its gradient - primary active transport 3) light driven pumps couples the transport of a solute against its gradient to the input of energy from light
34
why do we need to maintain electrochemical gradients?
1) electrical forces inside and outside the cell must be balanced - without AT to maintain electrochemical gradients ions would flow down their gradients through channels and disturb osmotic balance 2) In eukaryotic cells the movement of Na+ down its gradient drives the movement of many other substances against their gradient. If this gradient isnt maintained many transport systems would fail. The Na+ gradient is maintained by an ATP driven pump called the sodium potassium pump
35
sodium potassium pump
1. 3 Na+ are taken from inside 2. ATP phosphorylates - ADP 3. pump changes shape to expel 3 Na+ outside 4. two K+ accepted from outside 5. dephosphorylation triggers pump to change shape 6. K+ expelled to inside of cell and pump returns to initial state
36
example of symport
sodium glucose symporter 1. Na+ binds to pump 2. this stimulates glucose to bind and a conformational change 3. pump opens to inside 4. Na+ released inside but continually released back out by the sodium potassium pump 5. Loss of Na+ causes glucose release inside the cell 6. pump back to initial state
37
symport vs antiport
symport - both molecules move in same direction antiport - molecules move in different directions (one out the cell one in the cell)
38
example of antiport
Na+ Ca+ antiporter Na in and Ca out - too much Ca in cell is toxic Important in cardiac muscle Cardiac muscle contraction is triggered by a rise in intracellular Ca2+ operation of the Ca2+/Na+ antiporter reduces intracellular Ca2+ and thereby reduces strength of cardiac muscle contraction - importance of maintaining Na+ gradient
39
Digoxin
A drug used to treat heart failure. Inhibits the Sodium potassium pump which results in an increase in intracellular Na+. This means more Ca2+ builds up in the cell so more is stored in the SER and in the next contraction more Ca2+ is released = stronger contraction
40
What type of pump do prokaryotes use
proton pump
41
movement of glucose from gut across epithelial cells
1. sodium and glucose symporter as glucose conc is higher in the epithelial cells than in the gut. So glucose and sodium move into cell. 2. sodium potassium antiporter bring potassium into cell and sodium out of cell because Na+ concentration in cell increases which disturbs the electrochemical gradient. - ATP required 3. glucose moves out of cell by diffusion into blood supply
42
Why does a vertebrate need a skeleton
Structure localisation protection movement
43
actin filaments structure and role
Formed from gobular actin monomers - G-actin which are asymmetrical proteins that contain ATP - most ATP found on minus end of f actin and new monomers added to plus end. ATP is hydrolysed over time causing the filament to fall apart. The polar and dynamic nature of actin filaments enables cells to move and form specific structures and shape. Behaviour is controlled by interaction with other proteins - cell movement and provides force
44
microtubules
Long tubes made of Alpha - beta - tubulin dimers Both contain GTP but the GTP in the beta tubulin is hydrolysed (GDP) and the one in the alpha tubulin isn't. Has a lumen Made up of protofilaments (+/- end) Hydrolysis of GTP regulates the stability of microtubules cell organisation cell movement transport network
45
intermediate filaments
thick rope like fibre made of hetergenous fibrous proteins strength and protection (structure within a cell and tissue) can form specialist structures like the nuclear envelope or keratins made as a monomer (alpha helical structure) which join to form a coiled coil dimer. THe dimers associate with other dimers in an antiparallel fashion. (N terminus of one dimer is close to the C terminus of another dimer) 2 dimers together = a tetramers the tetramers are packed together in a rope liked filament. not found in plants and fungi
46
Example of how actin allows cells to move
1. signal is received by the cell (eg nutrient source) 2. Disassembly of filament and rapid diffusion of subunits 3. Reassemble of filaments at a new site
47
G actin
Gobular actin - monomers
48
F actin
fibrous actin - polymer
49
Other name for minus and plus end - actin filaments
minus - pointed plus - barbed
50
Hydrolysis of GTP in beta tubulin
When you have GTP - straight protofilament When GTP is hydrolysed to GDP - curved protofilament
51
How do motor proteins use the microtubule network
they use it to move vesicles and organelles. They bind vesicles to proteins which will cause the vesicles to move in different directions based on polarity of microtubules.
52
How is cell division coordinated by the cyto-skeleton use example of animal mitosis
Nuclear lamins (intermediate filaments) break down Microtubules seperate chromatids Cytokenisis: Actin drives cell division (movement of membrane)
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Cell biology and physiology (3 decks)

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