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Week 3 > Structure of Proteins 1 > Flashcards

Structure of Proteins 1 Flashcards

1
Q

what do proteins do? (5)

A

provide structure, transport molecules, defence, biological catalysts, regulation of genes

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2
Q

what is the most abundant protein in mammals and what percentage of the total protein is it?

A

collagen fibres - 25-35%

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3
Q

collagen fibres is…

A

the main component of connective tissue

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4
Q

where is collagen found? (4)

A

skin, tendon, organs, bone

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5
Q

what are erythrocytes?

A

red blood cells

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6
Q

what does haemoglobin do?

A

selective delivery of O2 to metabolic tissues

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7
Q

how many protein subunits per molecule is there in haemoglobin?

A

4

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8
Q

give an example of a prosthetic group…

A

haem

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9
Q

what is low-density lipoprotein composed of?

A

a monolayer phospholipid shell and a single molecule of apolipoprotein B

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10
Q

what is low-density lipoprotein used for?

A

transportation of cholesterol between cells via the circulatory system

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11
Q

what is the uptake of LDL particles mediated by?

A

the LDL receptor that binds LDL and facilitates internalisation (their uptake into cells)

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12
Q

what do patients with familial hypercholesterolemia have a mutation in?

A

the LDL receptor gene

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13
Q

what is atherosclerosis?

A

disease of which the arteries have fatty material on their inner walls

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14
Q

what can atherosclerosis lead to? (3)

A

restricted blood flow, hypertension, blockages

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15
Q

antibody structure…

A

two identical light chains covalently linked to two identical heavy chains by disulphide bonds

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16
Q

where is the antigen recognition site?

A

on the tips between the heavy and light chains

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17
Q

what does the antigen recognition site do?

A

highly specific and tightly binds the complementary antigen allowing recognition of foreign proteins by the immune system

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18
Q

what does lysozyme do?

A

catalyses the cutting of polysaccharide chains

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19
Q

how does lysozyme work?

A

it binds to the polysaccharide chain, catalyses the cleavage of a specific covalent bond and releases the cleaved product

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20
Q

what does the Lac repressor do?

A

controls production (expression) of proteins metabolising lactose in bacteria

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21
Q

how does the Lac repressor work?

A

the repressor binds to DNA and prevents expression of the gene in the absence of lactose

22
Q

what does binding depend on?

A

conformation

23
Q

what makes an amino acid hydrophilic?

A

if it is polar

24
Q

what makes an amino acid hydrophobic?

A

if it is non-polar - usually contains hydrocarbon or aromatic R groups

25
Q

cysteine can form…

A

disulphide bonds with other cysteine residues

26
Q

glycine is…

A

the smallest amino acid residue and can fit in tight spaces

27
Q

the side chain of proline…

A

bends around to form a covalent bond with the nitrogen atom of the amino group which creates a kink in the protein chain

28
Q

what does an acid do?

A

release a hydrogen ion

29
Q

what does a base do?

A

readily combines with a hydrogen ion

30
Q

what is the equilibrium constant?

A

Ka = [H+][A-] / [HA] (products/reactants)

31
Q

the pH can be calculated using the Henderson Hasselbach equation…

A

pH = pKa + log([A-]/[HA])

32
Q

the overall charge of an amino acid and therefore protein varies with…

A

pH

33
Q

pKa is…

A

the pH at which dissociation is 50% complete

34
Q

give an example of receptor mediated endocytosis…

A

uptake of low-density lipoprotein

35
Q

what does a reduction in the pH in the endosome cause (LDL) ?

A

a change in conformation of the LDL-receptor due to the presence of histidine residues within the protein

36
Q

what does the change in conformation of the LDL-receptor mean in receptor mediated endocytosis?

A

LDL can no longer bind and is released to the lysosome

37
Q

(receptor mediated endocytosis) patients with familial hypercholesterolemia frequently have mutations in the…

A

histidine residues of the LDL-receptor

38
Q

how do the side chains of a polypeptide arrange themselves?

A

usually the hydrophobic side chains are on one side and hydrophilic on the other and they usually alternate as the side chains can be bulky

39
Q

how is a peptide bond formed?

A

a covalent bond is formed when the carbon from the carboxylate group shares electrons with the nitrogen atom from the amino group of a second amino acid

40
Q

what is lost during the formation of a peptide bond?

A

water

41
Q

what does the peptide bond not permit?

A

rotation

42
Q

where are the only places a peptide bond can rotate?

A

on the alpha carbon

43
Q

where are bulky side group positioned and what does this limit?

A

on either side of the back bone limiting the conformations possible for a polypeptide

44
Q

what is secondary structure?

A

the initial folding pattern (periodic repeats) of the linear polypeptide

45
Q

what are the 3 main types of secondary structure?

A

alpha helix, beta sheets and bends/loops

46
Q

what bonds stabilise secondary structures?

A

hydrogen

47
Q

what is an alpha helix?

A

right handed with each turn having 3.6 amino acid residues stabilised by H bonds between the amino and carboxyl groups of every 4th amino acid

48
Q

what are beta sheets?

A

extended stretches of 5 or more amino acids organised next to each other to make beta sheets

49
Q

what is a parallel beta sheet?

A

when adjacent strands are oriented in the same direction (N-end to C-end)

50
Q

what is an anti-parallel beta sheet?

A

when adjacent strands run opposite to each other

51
Q

what is a bend/loop?

A

polypeptides can fold themselves into bends or loops with usually 4 amino acids being required to form the turn

52
Q

what residues are usually found in bends/loops?

A

proline

Week 3 (9 decks)

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