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MD2001 Week 3 > Structure of Proteins 2 > Flashcards

Structure of Proteins 2 Flashcards

1
Q

What is tertiary structure?

A

The 3D folding of secondary structure

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2
Q

In an aqueous environment, how is the tertiary structure organised?

A

Hydrophobic residues buried and hydrophilic residues are exposed outwards

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3
Q

What is a protein domain?

A

Specific part of protein that gives a function

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4
Q

What are the three possible tertiary structures?/

A

Alpha-helical

Beta sheets

A mixture of both

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5
Q

What connects regions of alpha helix and beta sheets?

A

Loops and bends

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6
Q

What bonds stabilize the tertiary structure?

A

Disulfide bonds

H-bonds

Ionic interactions

Van der Waals interactions

Hydrophobic interactions

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7
Q

Where does a disulphide bridge occur?

A

Between cystine residues

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8
Q

What is quaternary structure?

A

The association of more than one polypeptide

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9
Q

What is a protein called that has more than one subunit?

A

Oligomeric

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10
Q

What is the structure of mechanosensitive conductance channel?

A

7 identical subunits

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11
Q

What is the structure of stored insulin?

A

6 identical subunits bound to zinc

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12
Q

What is the structure of heterotrimeric G protein?

A

3 different subunits

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13
Q

What is the structure of 70S ribosome?

A

30 different subunits

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14
Q

What is the function of 70S ribosome?

A

Conversion of mRNA into proteins in bacteria

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15
Q

What is the function of haemoglobin?

A

Carries oxygen in red blood cells

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16
Q

What is the structure of haemoglobin?

A

2 alpha and 2 beta globin chains

Each chain contains a haem molecule

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17
Q

What is haem?

A

Porphyrin ring with coordinated Fe atom

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18
Q

What is haem held in place by?

A

Held in place by hydrogen bonds from histidine F8 and the bound oxygen molecule is stabilised by histidine E7

19
Q

What happens when oxygen binds to haem?

A

Changes the structure of haem

Provides an equalizing force on the bonds changing the ring from nonplanar to planar

20
Q

Describe cooperative oxygen binding

A

The affinity of the first oxygen molecule is low but binding of subsequent oxygen molecules is then increased

21
Q

What shape of a graph does cooperative oxygen binding create?

A

Sigmoidal

22
Q

Describe the effect of cooperative oxygen binding on the structure of haem?

A

The histidine that H-bonds to the haem molecule in helix F changes position

This conformation causes an increase in affinity of oxygen

23
Q

What is the biological significance of the cooperative oxygen binding?

A

This equated to tight oxygen binding in the lungs and subsequent release in tissues where oxygen concentration is lower

24
Q

What causes sickle cell anaemia?

A

Single amino acid change at position of 6 in the beta chain of haemoglobin

Hydrophilic glutamic acid to hydrophobic valine

25
Q

What effect does sickle cell anaemia have on erythrocytes?

A

Sickling of erythrocytes due to aggregation of mutated haemoglobin that forms stiff fibres

26
Q

What effect does pH have on oxygen binding?

A

Higher affinity caused by higher pH

Lower affinity caused by lower pH

27
Q

Why is the build up of lactic acid in muscles good?

A

The acidic environment will decrease the affinity of oxygen so will have faster oxygen delivery

28
Q

What is the foetal structure of haemoglobin?

A

2 alpha and 2 gamma

29
Q

Why does foetal haemoglobin have a higher affinity for oxygen?

A

When maternal blood reaches the placenta it already has a low oxygen content so will require high affinity to bind as much as possible

30
Q

Where is collagen found?

A

Bone

Tendons skin

31
Q

What is the building block of collagen?

A

Tropocollagen

32
Q

What does the triple left handed helix shape of tropocollagen form?

A

Microfibril

33
Q

What do many microfibril form?

A

Fibril

34
Q

What is the most common amino acid of tropocollagen?

A

Glycine

35
Q

How does glycine effect the tropocollagen?

A

Glycine occurs every 3 amino acid to allows tight turns as it is very small

36
Q

Why is proline vital for the structure of tropocollagen?

A

It imposes left hand twist in the helix that provides the main stabilising force

37
Q

What other form of proline can stabilise tropocollagen?

A

Proline is hydrolysed to hydroxyproline which can form strong hydrogen bonds

38
Q

Describe the formation of tropocollagen?

A

Individual strands come together called procollagen

Procollagen peptidase cuts off ends leaving tropocollagen

39
Q

What is the quarter-stagger model in collagen?

A

Molecules are stitched together by covalent-crosslinks, each a quarter length further along than the one above

40
Q

What causes the crosslinks in collagen?

A

Lysine is deaminated to from allysine by lysyl oxidase

These then from an aldol condensation product creating the crosslinks

41
Q

What is the mutation causing osteogenesis imperfecta?

A

Glycine being replaced by cysteine

42
Q

What is the consequence of the mutation causing osteogenesis imperfecta?

A

The tropocollagen subunits cannot pack together properly and there is a knock-on effect on collagen fibre formation

43
Q

What causes scurvy?

A

Lack of proline hydroxylation

44
Q

What causes Ehlers-Danloss syndrome?

A

Lack of procollagen peptidase or lysyl oxidase

MD2001 Week 3 (8 decks)

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