AMINO ACIDS, PROTEIN STRUCTURE AND FUNCTION

Question 1

What is the chemical structure of amino acids?

Answer 1

NH3 - CHR - COOH

Question 2

peptide bonds

Answer 2

• amino acids joined by peptide bonds

Question 3

what is an oligopeptide?

Answer 3

small proteins with about 10-40 amino acids

Question 4

one chain polypeptide?

Answer 4

myoglobin for oxygen transport

Question 5

2 chain polypeptide?

Answer 5

A and B chains in insulin

Question 6

3 chain polypeptides?

Answer 6

collagen triple helix

Question 7

2 chain polypeptide?

Answer 7

2 alpha 2 beta subunits of Hb

Question 8

how many R groups are there?

Answer 8

20

Question 9

how many hydrophobic R groups?

Answer 9

9

Question 10

neutral R groups

Answer 10

6. all have OH/=O/NH groups that form H bonds with water.

Question 11

acidic R groups

Answer 11

2. have a carboxyl group

Question 12

basic R groups

Answer 12

3. N-H groups of which lysine and arginine are protonated at physiological pH whilst histadine is physiological buffer

Question 13

give 4 examples of fibrous proteins

Answer 13

collagen - bones - tensile strength

elastin - ligaments - elastic strength

proteoglycans - bone - elastic strength

keratin - hair/skin - external protection

Question 14

give 2 examples of globular proteins; enzymes

Answer 14

trypsin - stomach - cleaves proteins

lysozyme - tears - antimicrobial

Question 15

2 examples of globular protein; transporters?

Answer 15

haemoglobin

transferrin (iron transport)

Question 16

globular protein; hormone example?

Answer 16

insulin

Question 17

globular protein immune system example?

Answer 17

immunoglobulins

Question 18

give 3 examples of hybrid fibrous-globular proteins?

Answer 18

actin, myosin, fibrinogen

Question 19

how is diversity created?

Answer 19

20 different amino acids.
different protein sizes.
chemical modification

Question 20

primary structure

Answer 20

order of covalent polypeptide sequence, sequence of amino acids

Question 21

secondary structure

Answer 21

3D arrangement of amino acids, side chain with each other and main chain. stabilised only by H bonds

Question 22

tertiary structure

Answer 22

3D arrangement of individual protein subunits to form multimeric protein

Question 23

quaternary structure

Answer 23

3d assembly of individual protein subunits to form multimeric protein

Question 24

alpha helix

Answer 24

• rod like with R groups outside
• all H bonds are between separate main chains and perpendicular to the direction of the main chain
• parallel sheets: N-termini are the same end
• antiparallel sheets: the N-termini are at opposite ends

Question 25

b-turns and loops

Answer 25

two conformational extremes that exist at the surface of globular proteins to link together the individual a-helices and b-strands in the protein core. they are hydrophilic.

Question 26

what is super secondary structure?

Answer 26

all the secondary structures inside the structure

Question 27

what are the common folds of a-helices/b-strands?

Answer 27

all a-helix protein = globin fold of myoglobin and Hb

all b-sheet protein = immunoglobin fold of antibodies

mixed a-helix/b-sheet proteins; TIM fold with a closed b-sheet barrel buried in core and a-helices flanking this on surface; the other fold variant based on an open twisted b-sheet buried in the core with a-helices above and below it

Question 28

describe the structure of globular proteins?

Answer 28

• compact protein structure
• soluble in water / lipid bilayers
• secondary structure is complex with mixture of a-helix, b-sheet and loop structures
• quaternary structure held together by non-covalent forces
• functions in all aspects of metabolism

Question 29

fibrous proteins

Answer 29

• extended protein structure
• insoluble in water / lipid bilayers
• secondary structure is simple based on one type only
• quaternary structure usually held by covalent bridge
• functions in structure of body or cell

Question 30

haemoglobin vs myoglobin (globular)

Answer 30

Hb is oxygen carrying protein of blood, myoglobin carries oxygen of muscle.

Hb is formed from 4 polypeptide chains (2 a chains and 2 b-chains); 4 hame groups

myoglobin has one polypeptide with one haem.

hame groups in hb and myoglobin bind to oxygen.

Question 31

immunoglobulins

Answer 31

• part of immune system
• recognition of antigens is based on B - sheet structure called Ig fold.
• antibodies are y shaped molecules; 2 light chains and 2 heavy chains; arranged as 2 Fab and 1 Fc fragments.

Fab recognises antigens, and fc effects the immune response.

Question 32

A-keratin

Answer 32

external protection, toughness, in hair/skin, forms most dry mass of this material, submit contains 2 long a-helices, cross linked by disulphide bridges

Question 33

elastin

Answer 33

connective tissue, relates to elasticity and stretchability, can stretch several times than return to original size, subunits cross linked by covalent bonds, found in arteries (aorta) and lung wall

Question 34

collagen

Answer 34

connective tissue, tensile strength results from use of triple helix secondary structure/assembly of tropocollagen subunits into a fibre/chemical cross linking to strengthen fibre

Question 35

fibrinogen

Answer 35

mixed fibrous - globular proteins; fibrinogen is protective protein that stops bleeding by sealing wounds

Question 36

myosin

Answer 36

responsible for contractile properties of muscle