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Proteins Flashcards

1
Q

What are proteins polymers of?

A

amino acids joined by peptide bonds, N terminal with C terminal of next aa

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2
Q

how many essential aa?

A

8 in adults, 9 in infants

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3
Q

what is an essential aa?

A

was that must be supplied by diet

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4
Q

give structure of glycine

A

COOHC(H)(H)NH2

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5
Q

does glycine form stereoisomers?

A

No as no chiral centre

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6
Q

What type of aa classifies glycine?

A

non-polar aliphatic

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7
Q

What type of aa classifies asparagine?

A

polar neutral

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8
Q

draw the r group of asparagine

A

-CH2-CONH2

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9
Q

name a sulphur containing aa and give its r group

A

cysteine, -CH2-SH

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10
Q

name a polar positively charged aa and give the r group

A

histidine

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11
Q

why is proline not a true aa?

A

has a NH rather than a NH2

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12
Q

describe phenylketonuria (PKU)

A

Deficiency in phenylalanine hydroxylase, genetic, leads to accumulation of intermediates which cause brain damage if left untreated

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13
Q

What is quaternary structure?

A

arrangement of protein subunits in multimeric proteins. Proteins held together by non-covalent bonds

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14
Q

give an example of a protein which exhibits quaternary structure

A

immunoglobin (antibody) consists of 2 light chains and 2 heavy chains joined by disulfied bridges and h bonds. Haemoglobin- 2 alpha globin chains and 2 beta globin chains each with a haem group (Fe atom and porphyrin ring),etc

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15
Q

Proteins provide structure, give an example

A

Collagen in bones, tendons and skin

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16
Q

what is the most abundant protein in mammals?

A

collagen

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17
Q

Name the 5 functions of proteins in the body

A

Structure, transport molecules, defence, biological catalysts, regulation of genes(lac repressor)

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18
Q

Name a protein involved in transport

A

haemoglobin, LDL

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19
Q

Name the protein in the LDL molecule

A

apolipoprotein B

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20
Q

What does the LDL receptor do?

A

It takes up LDL particles and facilitates internalisation

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21
Q

what causes familial hypocholesterolemia?

A

A mutation in the LDL receptor gene so less LDL absorbed so LDL levels in blood are high leading to atherosclerosis/ coronary heart disease

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22
Q

Name a defence protein

A

antibody/ immunoglobin

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23
Q

Give an example of a biological catalyst

A

Lysozyme

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24
Q

Describe action of lysozyme

A

Specific receptor site binds to polysaccharide chain, Enzyme-substrate complex forms, enzyme-product complex forms, product is release and enzyme remains unchanged, ready for next specific substrate

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25
Describe lac Repressor
The lac repressor binds to DNA and prevents expression of the gene in the absence of lactose. This controls the production of lactase enzymes metabolising lactose in bacteria
26
What role do some proteins have regarding genes?
they can regulate genes/ control their expression
27
how many aas in a protein?
50 plus
28
no. of aa in body
20
29
What makes cysteine special (think 3rd structure)?
it can form disulphide bonds
30
Give the equilibrium constant (Ka) equation
KA= [H+][A-]/{HA]
31
Give Henderson Hasselbach equation for pH
pH= PKa + log([A-}/{HA])
32
How many acid molecules must be dissociated for the pKa of any acid to equal the pH?
half (pKa is the pH at which dissociation is 50% complete)
33
What does the charge of an aa vary with?
pH
34
Over how many pH units id pH centred on the pKa?
2 (sigmoidal graph)
35
Give an example of how the fact a protein's shape can be altered by pH is useful in the body
pH is lower in endosome than on cell surface/ cytoplasm. This causes a change in the shape of the LDL receptor carrying the LDL molecule which releases the LDL into a nearby lysosome.
36
What type of reaction forms a peptide bond?
Condensation
37
Name the 3 types of 2nd structure
Alpha helix, Beta sheet, bend/loop
38
bonds that hold 2nd together
H bonds between the c=o: and the H-N:
39
How can beta sheets be arranged? (2 ways)
Parallel and anti-parallel (anti parallel= stronger H bonds as closer)
40
What aa frequently is found in bends/loops?
Proline
41
What is a prosthetic group?
Non-protein part of some proteins eg haem group
42
Synonym for protein conformation
folded shape of the protein
43
Name of property that an aa that is attracted to water has
Hydrophilic
44
Bonds in 3rd structure
Ionic interactions, VDWs, Hydrophobic/hydrophilic interactions, disulphide bonds, h bonds
45
What type of bond is a disulphide bridge?
covalent
46
what are each of the peptide chains in a ogliomeric protein called ?
subunits
47
what do u call the complex comprising of many subunits?
ogliomeric protein
48
what bonds are often found in 4th structure?
disulfide
49
What type of bond joins haem to histidine in each globin molecule?
H bond
50
describe the cooperative effect of o2 binding in haemoglobin
The affinity of the first oxygen molecule is low but the affinity for subsequent o2 molecules is increased due to a change in the protein structure (the His that H-bonds to the Haem in F8 changes position) as each consecutive o2 binds making it easier for each subsequent o2 molecule to bind to the other subunits.
51
What causes sickling of erythrocytes?
Aggregation of mutated haemoglobin that forms stiff fibres
52
Does haemoglobin have a higher affinity for 02 at high or low pH?
high
53
Is the pH at the lungs high or low?
high
54
What causes the low pH in working muscle?
CO2
55
What term describes how the pH influences o2 binding to haemoglobin?
Bohr effect
56
How does the Bohr effect facilitate o2 delivery to where its needed in the body?
Muscles cells which are contracting produce co2 and have a lower oH, this allows easier unloading O2 so aerobic respiration can continue for longer
57
How is foetal haemoglobin different to adult haemoglobin?
2 gamma subunits instead of beta subunits
58
what effect do the gamma subunits have on foetal haemoglobin?
increase the haemoglobin's affinity for o2 so it can load sufficient o2 at the placenta where the 02 conc is relatively low (compared to the lungs where adult haemoglobin loads its o2)
59
What genetic blood disease do foetuses not get due to having no beta globin in their haemoglobin?
Sickle cell disease
60
25% of protein in the body is what protein?
Collagen
61
What makes up the collagen fibre?
Tropocollagen- which consists of 3 polypeptide chains with a left handed twist would together in a right handed supercoil
62
Why is glycine important in the structure of the polypeptide chains in tropocollagen?
It has a short side chain which means the turns are tight
63
Why is proline important in the structure of the polypeptide chains in tropocollagen?
It creates the left hand twist in the helix due to the unique shape of this aa.
64
Proline May be oxidised to hydroxyproline how does this help stabilise the polypeptide chains in tropocollagen?
They for strong hydrogen bonds
65
Explain the ‘quarter-stagger’ model with respect to the formation of the collagen fibre
Tropocollagen molecules are bonded together by covalent crosslinks
66
What do the gaps between tropocollagen molecules provide?
They are access sites for lysyl oxidase.
67
Describe the formation of collagen fibres from tropocollagen
Multiple tropocollagen molecules form collagen fibrils, via covalent cross-linking (aldol reaction) by lysyl oxidase which links lysine residues on adjacent tropocollagen molecules. The lysine residues are deanimated my lysyl oxidase forming aldehyde derivatives. Multiple collagen fibrils form into collagen fibers via more covalent cross linking. The lysine derived aldehydes stabilise the collagen fibrils and fibres.
68
Name a form of brittle bone disease
Osteogenesis imperfecta
69
What causes osteogenesis imperfecta?
A mutation in the gene coming for one of the collagen subunits leading to glycine being replaced by cysteine at one point in the chain. This means the tropocollagen subunits can’t pack together properly and therefore collagen doesn’t form properly. Gly-Cis mutation
70
What causes scurvy?
Lack of vit c which results in a lack of proline hydroxylation and therefore defective collagen formation
71
Symptoms of osteogenesis imperfecta
Brittle bones
72
Symptoms of scurvy
Dry skin, gum disorders
73
What causes ehlers-danloss syndrome?
Lack of lysyl oxidase or procollagen peptidase
74
Symptoms of ehlers- danloss syndrome
Loose skin, hyper mobile joints
75
Every how many as is there a glycine in tropocollagen molecules?
3
76
What does procollagen peptidase do?
it cuts the uneven ends off the tropocollagen molecules before they are joined together so that they pack closer together

Proteins (2 decks)

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