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Medicine Year 1 Semester 1 > Proteins > Flashcards

Proteins Flashcards

1
Q

What are the 5 functions of proteins ?

A
  1. Provide Structure
  2. Transport molecules
  3. Defence
  4. Biological Catalysts
  5. Regulation of genes
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2
Q

What is the main component of connective tissues ?

A

Collagen fibres, which is the most abundant protein in the body.

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3
Q

In proteins what component provides structure ?

A

Collagen Fibres

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4
Q

Where is collagen fibre found ?

A

Skin, tendons, organs and bone

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5
Q

What is collagen known as ?

A

The protein of bone, skin and tendon

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6
Q

What protein is a transport molecule which carries oxygen?

A

Haemoglobin

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7
Q

What is the function of haemoglobin ?

A

Oxygen carrier

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8
Q

How many protein molecules are in haemoglobin ?

A

4 protein subunits per molecule

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9
Q

What does each protein subunit in haemoglobin contain ?

A

A haem group which can bind to 1 molecule of o2

The haem group (adult) consists of :
2 alpha subunits
2 beta subunits

In fetus :

2 alpha
2 gamma

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10
Q

What is an example of a prosthetic group ?

A

Haem

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11
Q

Which protein is a transport molecule that transports cholesterol ?

A

LDL and LDL receptors

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12
Q

What is the function of LDL and LDL receptors ?

A

LDL - Transport cholesterol molecules

LDLR - Co-ordinate cholesterol uptake into cells

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13
Q

What is LDL composed of ?

A

Phospholipid shell
Single molecule of apolipoprotein B

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14
Q

What is wrong with patients with familial hypercholesterolemia ?

A

They have a mutation in the LDL receptor gene.

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15
Q

Which proteins are involved in defence ?

A

Antibodies

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16
Q

What is the function of antibodies ?

A

Defence against infection

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17
Q

Structure of antibodies

A

2 identical heavy chains
2 identical light chains
They are covalently linked by disulphide bonds.

They have highly specific antigen recognition sites.

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18
Q

What proteins are biological catalysts ?

A

Enzymes

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19
Q

What is the function of enzymes ?

A

Regulation of all biological systems.

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20
Q

Lysozyme function

A

Catalyses the cutting of polysaccharide chains.

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21
Q

What proteins are involved in regulation of genes ?

A

Lac repressor

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22
Q

Function of the Lac repressor

A

Helps control gene expression of proteins metabolising lactose in bacteria.

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23
Q

How does the Lac repressor help control gene expression ?

A

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

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24
Q

What changes the activity of proteins ?

A

Change in conformation

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25
Q

What are proteins ?

A

Large molecules, which are complex and are linear polymers.

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26
Q

Polymer

A

Amino acids joined together via peptide bonds

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27
Q

Protein structure hierarchy

A

Primary
Secondary
Tertiary
Quaternary Structures

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28
Q

What is the general structure of an amino acid ?

A

Central carbon atom
Amino group
Carboxyl group
H atom
Variable R group

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29
Q

What defines the structure and function of proteins ?

A

The chemical properties of each R group

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30
Q

Basic amino acid examples (3)

A

Lysine
Arginine
Histidine

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31
Q

Acidic amino acid examples (2)

A

Aspartate
Glutamate

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32
Q

Polar amino acid examples (4)

A

Serine
Threonine
Asparagine
Glutamine

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33
Q

Hydrophobic amino acid examples (4)

A

Alanine
Valine
Leucine
Tyrosine

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34
Q

What are the 3 special amino acids ?

A

Cysteine
Glycine
Proline

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35
Q

What is special about cysteine ?

A

Can form covalent disulphide bonds with other cysteine residues.

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36
Q

What is special about glycine ?

A

It is the smallest amino residue and can fit into tight spaces.

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37
Q

What is special about proline ?

A

The side chain of proline bends around to form a covalent bond with the nitrogen atom of the amino group.
By doing this, proline creates a kink in the protein chain.

38
Q

Polypeptide

A

A polymer of amino acids joined by peptide bonds.

39
Q

Amino acid residue

A

When two or more amino acids combine to form a peptide, the elements of water are removed, and what remains of each amino acid is called an amino-acid residue.

40
Q

Prosthetic group

A

A non-protein unit, tightly bound to a protein and is essential for the protein’s function.

41
Q

Conformation

A

The arrangement in space of the constituent atoms which determine the overall shape of the molecule.

42
Q

Acid

A

Any molecule that tends to release a hydrogen ion.

43
Q

Base

A

Any molecule that readily combines with a hydrogen ion.

44
Q

pKa

A

The pKa of any acid is = to the pH at which half of the molecules are disassociated.

45
Q

What can influence pKa ?

A

Local environment

46
Q

When does disassociation occur ?

A

Over 2 pH units centred on the pKa.

47
Q

What is the result of a change in pH on proteins conformation ?

A

A change in pH causes a change in conformation, so the substrate molecule cannot bind and is released into the lysosome.

48
Q

What is a peptide bond ?

A

A covalent bond

49
Q

Why is formation of a protein a condensation reaction ?

A

A molecule of water is lost.

50
Q

What are some constraints of the peptide bond ?

A

It does not permit rotation.
Rotation can occur on the alpha carbon.

51
Q

What is a disadvantage of the bulky R groups ?

A

They are positioned on either side of the backbone.
This limits the number of 3D conformations possible for a polypeptide.

52
Q

Primary Structure function

A

The sequence where the amino acids are synthesised into the polypeptide, which determines the proteins function.

53
Q

Secondary structure function

A

The initial folding pattern of the linear polypeptide.
3 main types of 2ndary structure : alpha helix, beta pleated sheets, turns

54
Q

How is the secondary structure stabilised ?

A

By Hydrogen bonding along the backbone of the polypeptide strand.

55
Q

Features of alpha helix

A

The R group sticks out
The H bonds are between the carboxyl groups of every 4th amino acid.

56
Q

What are beta strands ?

A

Extended stretches of >5 amino acids

57
Q

Features of Beta sheets

A

Beta strands organised next to each other.
The R group sits above and below.

58
Q

How are turns formed ?

A

Polypeptide chains can fold upon themselves forming a bend or a loop.
Usually 4 amino acids are require d to form a turn.

59
Q

What residues are frequently found in turns ?

A

Proline

60
Q

What happens in tertiary structure ?

A

The 3D folding of secondary structure.
Hydrophobic residues are buried and hydrophilic residues are buried outwards to the aqueous environment.

61
Q

What is tertiary structure ?

A

It can be the final folded 3D shape caused by interactions between R groups.
Arrangement of an entire polypeptide to form a globular structure.

62
Q

What are the different interactions between R groups ?

A

Disulphide bonds
H-Bonds
Ionic interactions
Van der Waals interactions
Hydrophobic interactions

63
Q

What is the function of turns in tertiary structure ?

A

They connect regions of alpha helix and beta pleated sheets so that the polypeptide can fold into a globular domain.

64
Q

In cysteine how are disulphide bonds formed ?

A

The SH groups of 2 neighbouring cysteine residues form a covalent S-S bond.

65
Q

Where does quaternary structure exist ?

A

It exists in proteins with 2 or more connected polypeptide sub-units.

66
Q

What stabilises the quaternary structure ?

A

Disulphide bonds

67
Q

What is quaternary structure ?

A

Arrangement of more than one polypeptide to form an oligomeric, functional protein.

68
Q

What is tertiary structure affected by ?

A

High temperature
Changes in pH

69
Q

What does high temperature do to tertiary structure ?

A

It destabilises the structure and weak bonds break.

70
Q

What do changes in pH do to tertiary structure ?

A

Affects the ionisation of acidic and basic R groups.

The conformation of the protein changes until the protein is denatured.

71
Q

What happens when a molecule of oxygen binds to a haem group ?

A

1 molecule of oxygen binds to a haemoglobin subunit.
Change in conformation.
Other subunits have an increased affinity for the remaining oxygen.

72
Q

What is the binding of oxygen affected by ?

A

High temperatures
Low pH

73
Q

What does a high temperature do to oxygen binding ?

A

Lowers the affinity of haemoglobin for oxygen.
This means that binding of oxygen is reduced, so increased oxygen delivery to the tissues.

74
Q

What does a low pH do to oxygen binding ? (Bohr effect)

A

Lowers the affinity of haemoglobin for oxygen.

75
Q

What happens during exercise ?

A

Tissues generate heat and CO2 + H2O —> carbonic acid. This promotes increased oxygen delivery to tissues.

76
Q

What causes sickle cell anaemia ?

A

Mutation at primary structure

A single amino acid change at position 6 in the beta chain of haemoglobin.

Hydrophilic glutamic acids to hydrophobic valine.

77
Q

What is a result of sickle cell anaemia ?

A

Sickling of erythrocytes

78
Q

What is adult haemoglobin composed of ?

A

2 alpha and 2 beta subunits

79
Q

What is foetal haemoglobin composed of ?

A

2 alpha and 2 gamma subunits

80
Q

Why are foetal red blood cells unaffected by sickle cell disease ?

A

Due to the absence of beta chains.

81
Q

What is the function of the protein collagen ?

A

It helps bind cells together to form tissues.
It assembles in long, extremely strong fibres.

82
Q

What is the building block of collagen fibre ?

A

Tropocollagen

83
Q

What is vital for formation of tropocollagen ?

A

Glycine, as it is has a small side chain that allows tight turns.

Proline, as it imposes left hand twist in the helix which provides main stabilising force.

84
Q

What is the structure of tropocollagen ?

A

Triple helix structure

85
Q

How is hydroxyproline formed ?

A

When prolines become hydroxylated.

86
Q

What is the function of hydroxyproline ?

A

Hydroxyproline forms strong hydrogen bonds that help to stabilise the triple helix

87
Q

Formation of collagen fibre

A

Molecules are stitched together by covalent crosslinks

Gaps provide access sites for lysyl oxidase

88
Q

Osteogenesis imperfecta cause

A

Gly-Cys mutation

89
Q

Scurvy cause

A

Lack of proline hydroxylation (Vitamin C)

90
Q

Elhers-Danloss syndrome causes

A

lack of Lysyl oxidase

91
Q

What builds strength in collagen fibres ?

A

Close packing of subunits
(Glycine every 3rd residue)

Opposing twists of subunits and superhelix
(high proline content)

Hydrogen bonding
(Hydroxyproline)

Cross-linking
(Lysine derived aldehydes)

Medicine Year 1 Semester 1 (37 decks)

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