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Flashcards in Biochemistry Deck (556)
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61

Describe the tertiary structure of AAs

Folding of secondary requiring series of non-covalent interactions
Held by electrostatic, VDWs, disulphide, hydrophobic interactions

62

What are electrostatic bonds?

Strong interactions between ions/charged groups of opposite charge
In protein called a salt bridge

63

What are Van der Waals forces?

Weak, close range temporary dipole-dipole interactions

64

What are disulphide bonds?

Strong covalent S-S bonds between specific cysteine residues
Tend to lock molecule into configuration allowing it to withstand v high temperatures

65

What are hydrophobic interactions?

Interactions between polar and non-polar molecules causing the spontaneous folding of hydrophobic residues away from water

66

Describe the quaternary structure of proteins

Association of multiple tertiary polypeptides
Haemoglobin is association of 4 globin groups and 4 heme groups

67

What is a protein domain?

Part of a polypeptide that can fold independently of polypeptide into compact, stable tertiary structure
Usually identified by presence of prolIne
Can be cut, isolated and studied separately from main chain

68

What is protein folding?

Process by which higher structures are formed from primary (AA) sequence

69

What are transitions in shape of tertiary or quaternary structures called?

Conformational changes - proteins may shift between several similar structures in performing their function
(Tertiary and quaternary structures referred to as conformations)

70

What is the reversible nature of protein folding dependent on?

Primary structure being maintained

71

What are the three classes of proteins?

Fibrous
Globular
Membrane-associated

72

Describe globular proteins

Are soluble, nearly all enzymes are globular
Carbonic anhydrase and haemoglobin are examples

73

Describe carbonic anhydrase

Catalyses interconversion of CO2 + H2O to carbonic acid
Different classes have little sequential or structural similarities but share identical AS thus all perform same function and require a Zn atom
Contains large B sheet in centre

74

Describe haemoglobin

Assembly of 4 globular protein subunits each composed of protein chain (2 a chains, 2 B chains) tightly associated with prosthetic heme group

75

What is a prosthetic group?

Non-protein group tightly bound to protein that confers function
Heme has an Fe atom held in heterocyclic ring equally to all 4 N atoms
Fe is site of O2 binding

76

Describe fibrous proteins

Form rod/wire like shapes, usually structural or storage proteins
AA sequence often lacks repeating units
From unusual 2ndary structures (collagen triple helix) due to cross-links between chains e.g. S-S bonds between keratin
Usually used to construct CT, tendons, bone matrix, muscle fibre

77

What are keratins and what do they form?

Family of fibrous structural proteins, they are tough and insoluble
Form non-mineralised structures found in reptiles, birds, amphibians, mammals (hair)

78

Describe the structure of keratin

High proportion of glycine (smallest) and alanine (2nd smallest) AAs
High amounts of cysteine (sulphur containing) required for S-S bridges confer strength, rigidity by permanent, thermally stable cross-links

79

Describe the structure of keratin monomer and the assembly into intermediate filaments

3 domains: head, rod, tail
Monomers associate to dimers, associate to tetramers, finally to intermediate filaments forming part of cytoskeleton

80

What is collagen?

Family of fibrous proteins secreted by CTs with triple helix AA structure
28 different types
Unique sequence of glycine-proline/hydroxyproline-alternative AA

81

What are the 3 type of membrane-associated proteins?

Transmembrane (intrinsic) - cross membrane, usually a-helix
Lipid associated (extrinsic) - bound to outer surface
Proteins attached to transmembrane protein - increase ionic strength to detach i.e. add NaCl

82

What are the 2 domains of membrane proteins?

Interdomain - intracellular
Outer domain - extracellular

83

What are some of the functions of membrane proteins?

Transporters, linkers, receptors, enzymes

84

Define enzyme

Proteins that catalyse biochemical reactions (biological catalysts)

85

Define active site

Parts of enzyme that react with substrate (+ cofactors) in reaction

86

Define co-enzyme

Small, diffusible organic residue that participates in enzyme catalysed reaction, is stable to heat

87

Define prosthetic group

Coenzyme covalently bound to enzyme so that not removed by dialysis

88

Define zymogen

Inactive precursor of enzyme

89

Define holoenzyme

Protein (apoenzyme) with coenzyme/ions required for activity

90

Define apoenzyme

Protein with coenzyme required for activity, liable to heat