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FunMed Cell Biology > Plasma memrbane > Flashcards

Plasma memrbane Flashcards

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1
Q

what does the plasma membrane do

A
  • Separates the cellular contents from the outside
  • Internal membranes separate the contents of different organelles from the rest of the cell
  • Without membranes, gradients would not exist and no energy would be generated
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2
Q

describe the fatty acids

A
  • Carboxylic acids with long hydrocarbon tails

- COOH group (delta end) on one end and a CH3 methyl (omega end) on the other

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3
Q

what synthesises fatty acid

A
  • Synthesised by fatty acid synthase
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4
Q

what is saturated

A

no double bonds

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5
Q

what is unsaturated

A

one or more double bonds in hydrogen tail (made using desaturase)

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6
Q

what are the differences between saturated and unsaturated fatty acids

A
  • Saturated fatty acids are straight while unsaturated fatty acids have kinks introduced by the cis double bond (both hydrogens are removed from the same size)
  • Saturated – pack more tightly
  • Unsaturated – fatty acids wont pack as tightly and be more fluid
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7
Q

why don’t the trans bonds cause the fatty acid tails to bend

A
  • Can also have trans double bonds these don’t cause the fatty acid tail to bend but this only occur theoretically for example in margarine
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8
Q

what are the essential fatty acids

A

essential means it must be obtained by diet because the body does not have the right desaturate enzyme to introduce the necessary double bond

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9
Q

what are non essential fatty acids

A

these are fatty acids synthesised by the body

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10
Q

give some examples of non essential fatty acids

A
  • Oleic acid – omega 9
  • Palmitic acid
  • Stearic acid
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11
Q

name some essential fatty acids

A
  • omega 6 linoleic acid

- omega 3 - lineolenic acids

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12
Q

where are the bonds in omega 6 - linoleic acid

A

– 2 double bonds with the first double bond is 6C from the omega end

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13
Q

where are the bonds in omega 3 linolenic acid

A

– 3 double bonds with the first double bond is 3C from the omega end

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14
Q

where can you find omega 6

A

sunflower olí and olive oil

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15
Q

where can you find omega 3

A

seeds and nuts

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16
Q

what does the word Lino mean

A

essential

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17
Q

why are the omega 3 and 6 essential fatty acids

A

We do not have the desaturase to remove the hydrogens from omega-3 or omega-6 carbons therefore it is an essential fatty acid e.g. so you must get the from your diet

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18
Q

what are essential fatty acids

A

they are precursors for other molecules

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19
Q

describe how omega 6 and omega 3 can be converted into phospholipids

A
  1. Omega 6 (linoleic acid) and Omega 3 (alpha linolenic acid) can be converted into membrane phospholipids this happens by phospholipase
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20
Q

how are omega 6 and omega 3 converted into paracrines

A
  1. Omega 6 (Linoleic acid) can also be converted into arachidonic acid by the enzyme elongases desaturases
  2. Omega 3 (alpha linolenic acid) can be converted into EPA (eisopentaenoic acid) this happens by elongase desaturase
  3. EPA and Arachidonic acid are both converted to paracrines which are near acting hormones
  4. Arachidonic acid converted to prostaglandins happens by COX-2 enzyme, this makes them a target for NSAIDS
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21
Q

what do NSAIDS do

A

NSAIDS = non-steroidal anti-inflammatory drugs (ibuprofen and paracetamol) can inhibit arachidonic acid being converted to paracrines

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22
Q

what are examples of paracrines

A
  • Leukotrienes are made by leukocytes
  • Prostaglandins are made in all tissues
  • Thromboaxanes are made by platelets
23
Q

what do paracrines do

A

These are mediators of inflammation, pain, fever, immunosuppression, clotting, blood vessel constriction, airway constriction and anti-inflammatory

24
Q

How are fatty acids stored

A

they can be stored in triglycerides

- can be stored in fat droplets but only organelle with lipid monolayers

25
Q

what does triglycerides consist of

A
  • Consist of one molecule of glycerol linked with 3 molecules of fatty acids (via ester bonds)
26
Q

why are triglyerides efficient

A
  • Efficient store of energy = 1g of triglyceride = 6g of glycogen and it takes up less volume
27
Q

What happens when energy is needed to the triglyceride

A
  • Triglyceride splits into glycerol and fatty acids via hydrolysis by lipase this is in response to glucagon being released from the pancreas
  • Fatty acids bind to albumin which transports the fatty acids to the muscle cells through the blood stream
  • Muscle cells takes up the fatty acids and uses it for energy
  • Used to supply ATP by oxidation in the absence of glucose
28
Q

what is the problem with breaking down triglycerides for a source of ATP

A
  • The process is slower than the break down (catabolism) of glycogen so you cannot make energy quickly enough to keep up the same speed so you hit the wall
29
Q

what are the 3 main membrane lipids

A
  • Glycerophospholipids
  • Sphingolipids (these include glycolipids)
  • Cholesterol
30
Q

what is the linker of glcyerophospholipids

A
  • glycerol is the linker
31
Q

describe the structure of glycerophospholipids

A
  • Glycerol is linker
  • Attaches the 2 fatty acids tails which are non-polar
  • 3rd group is attached to a phosphate group
32
Q

Name some examples of glycerophopholipids

A

PICSECS -

  • Phosphatidylinositol
  • Phosphatidylethanolamine
  • Phosphatidylserine
  • Phosphatidylcholine
33
Q

what is the linker of sphingolipids

A
  • serine
34
Q

describe the structure of sphingolipids

A
  • Serine –is th e linker,
  • A sphingosine is 1 fatty acyl chain conjugated to serine) on conjugation with a second acyl chain forms ceramide (so serine plus two fatty acyl chains = ceramide
  • Attaches to the 2 fatty acid tails which are non polar
  • 3rd attachment can be to any functional group
35
Q

name examples of sphingolipids

A
  • Sphingomyelin
  • Cerebroside
  • GM1 – ganglioside
36
Q

describe the structure of glycolipids

A
  • Based on ceramide
  • Ceramide is seriene with two acyl chains
  • NANA carries a negative charge
  • Confined to the outer leaflet
  • Hydrophobic tails; two long hydrocarbon chains
  • Hydrophilic head; one or more sugars but no phosphate e.g. galactose
  • Found on surface of all plasma membranes
37
Q

whats the role of glycolipids

A
  • Important in cell to cell contact
  • Protects the cell from hostile environment
  • Localise to and may be important in lipid raft generation and function
38
Q

what is the structure of cholesterol

A
  • Polar head
  • Central steroid ring structure
  • Non polar acyl chain
39
Q

what is cholesterol stored in

A

fat droplets

40
Q

what is the function of cholesterol

A
  • modulates fluidity of the membrane
  • difference in glycerophospholipids and sphingolipids
  • Bile salts – solubilisation of dietary fat and lipophilic vitamins, 25% is made in the liver
  • Vitamin D – skin, bone formation
  • Steroids (cortisol and aldosterone) in the adrenal gland
  • Sex hormones (progesterone, oestrogen and testosterone) – in the testes and ovaries
41
Q

whats the difference between glycerophospholipids and sphingolipids

A
  • Glycerophospholipids- have more cis double bonds which makes chains shorter and more kinked
  • Sphingolipids are more saturated so have longer straighter fatty acid tails
  • This means that sphingolipids on their own will make a tightly packed and thicker membrane
42
Q

How do cholesterol work on glycerophospholipids and sphingolipids

A
  • In glycerophospholipids adding cholesterol makes membrane less fluid as they become more densely packed and less permeable
  • Sphingolipids adding cholesterol makes the membrane more fluid as it reduces the packing density
  • Therefore the role of cholesterol is modulating the behaviour of the membrane dependent on other lipids it interacts with
  • Cholesterol is enriched along with sphingolipids in membrane invaginations that are important for endocytosis
43
Q

what do lipids rafts do

A
  • Lipid rafts bring together different proteins for a collective function
44
Q

what makes up lipids raft

A
  • Sphingolipid and cholesterol self-associate to create fluid lipid rafts into which different function membrane proteins can dock
45
Q

describe the structure of cell membrane

A
  1. Amphiphillicty – membrane lipids self associate in water, polar head associate with water while non polar hydrocarbon tails associate with each other, they forma. Permeability barrier that most solutes cannot freely diffuse across
  2. Cylindrical shape with 2 fatty acid tails favours the bilayer rather than the micelle, micelle is favoured when only one hydrocarbon chain is in use
  3. Membranes turns itself into a ball to reduce exposure of nonpolar hydrocarbon centre of the bilayer to water (energetically favourable)
    - Membrane lipid ball with no other molecule’s liposome – used to study behaviour of lipid membranes
    - Also can be used by cells as exosomes which can carry signals between cells
    - Used to deliver drugs and DNA to patients
  4. Membrane lipids are also arranged asymmetrically. Glycerophospholipids tend to be on the inside while Sphingolipids are on the outside.
46
Q

what does fluid refer to in the fluid mosaic model

A
  • Fluidity refers to how membrane lipids can
    1. Flex – acyl chains can flex within the bilayer
    2. Rotate – membrane lipids can rotate within the bilayer
    3. Diffuse laterally – memrbane lipids can diffuse laterally within the bilayer
    4. Flip flop (rare) – this is the movement of memrbane lipid from one leaflet to the other
47
Q

what does mosaic refer to in the fluid mosaic model

A
  • Refers to how many membrane proteins are embedded in the bilayer e.g. lipid rafts
48
Q

describe the proportions of lipids and proteins in the cell membrane

A
  • Myelin, contains only 18% protein and 76% lipid (mostly glycolipids)  to insulate nerve impulse
  • Hepatocytes enriched with Phosphatidyl choline (glycerophospholipid,) for bile production
  • ER has many glycerophospholipids which creates a fluid membrane that proteins can easily “dock” into
  • Mitochondrial inner membrane contain 76% protein and only 24% lipid  for active transport of protons
49
Q

describe cholesterol metabolism

A
  • Cholesterol turned into bile in the liver and is then secreted into the gut
  • Cholesterol is carried around the blood by lipoproteins (manly HDL and LDL)
  • Increased LDL from diet and can make it in intracellular synthesis using acetyl COA
  • Statins reduce cholesterol levels by inhibiting HMG Co-A reductase
  • Eating a diet low in phytosteroids reduces cholesterol levels uptake as they are similar in shape
50
Q

what do high levels of LDL lead to

A
  • High levels of LDL can lead to atherosclerosis this is cholesterol being deposited on arterial walls
51
Q

where do fat droplets originate form

A
  • droplets originate from the ER and is bound usually by a membrane lipid monolayer because its contents are hydrophobic therefore there is no water inside the fatty acid droplet
52
Q

what are the limitations to the fluid mosaic model

A
  • While some proteins can diffuse laterally within the membrane others are anchored in protein complexes or tied to the extracellular matrix
  • The lipid content of rafts is important for raft integrity (the lipids influence the protein protein contact)
  • Lipids can also be signalling molecules and PIP3 a source of secondary messengers IP3 and GAD
  • Lipids can also modulate membrane protein activity directly
53
Q

the inner leaflet

A

faces cytosol

54
Q

the other leaflet

A

faces extracellular space

FunMed Cell Biology (5 decks)

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