Amino Acids and Proteins

Question 1

Smallest functional protein

Answer 1

tripeptide called thyrotropin-releasing hormone

Question 2

Protein Basics

Answer 2

can consist of a single polypeptide chain e.g prolactin, or several interacting chains e.g pyruvate dehydrogenase (48 chains)

Question 3

Unbranched

Answer 3

Unbranched polypeptide chain is polymer of amino acids linked by a peptide bond

Question 4

Amino Acid Structure

Answer 4

H2N (potentially basic), COOH (potentially acidic), Alpha carbon, R side chain

Question 5

Amino Acid Functions

Answer 5

Proton donors COOH to COO- + H+
Proton Acceptors NH2 + H+ to NH3+

Question 6

Isomers

Answer 6

Because amino acid a carbon has 4 different groups attached (except for glycine R double H_ it is asymmetric. D and L

Question 7

D and L

Answer 7

Proteins contain only L amino acids. D-isomers occur in bacterial cell walls.
L-amino acid NH2 on left and on right in D-amino acid

Question 8

Ionisation character of amino acid groups

Answer 8

Neutral (R does not ionise), basic and acidic (r does ionise)

Question 9

Examples of types

Answer 9

Neutral - Gly, Ser, Pro
Basic - Lys (strong), Arg (strong), His (weak)
Acidic - Glu (strong) and Cys (weak)

Question 10

Electronegativity

Answer 10

Power of an atom to attract electrons towards itself

Question 11

Protein Structure

Answer 11

Primary structure - amino acid sequence
Secondary structure - arrangement in space of amino acids close to one another in a polypeptide chain e.g a-helix and b-sheet

Question 12

Protein Structure (contd.)

Answer 12

Tertiary structure:
3D structure of all the atoms in a single polypeptide chain
Interactions between R groups fold protein into a compact 3D shape
Quaternary structure: 3D interaction of protein subunits in proteins with more than one polypeptide chain

Question 13

Post-synthetic modifications of amino acid side chains 1

Answer 13

Hydroxyproline - OH group stabilises collagen fibre (insufficient hydroxylation leads to scury)

Question 14

2

Answer 14

Y-carboxyglutamate - carboxylation of Glu in prothrombin (lack of carboxylation leads to haemorrhage)

Question 15

3

Answer 15

O-phosphoserine - phosphorylation of serine is most common form of regulation of protein activity

Question 16

Polar R group

Answer 16

Hydrophilic due to presence at pH 7 of full +ve or -ve charge in R group (polar, charged) or partial charges in permanent-dipole bonds in non-ionisable R groups (polar, uncharged)

Question 17

Nonpolar R group

Answer 17

Hydrophobic, many non polar C-C and C-H groups

Question 18

Ionisation of amino acids

Answer 18

pH 1 cationic (+1) fully protonated NH3+ at top and COOH on right

ph 7.4 dipolar (0) zwitterion NH3+ at top and COO- right

pH 11 anionic (-) all protons lost
NH2 at top and COO- right

Question 19

Transport

Answer 19

O2 on haemoglobin, Na+/K+ pump cellular uptake of glucose

Question 20

Storage

Answer 20

Fe2+ in complex with ferritin in liver

Question 21

Motion

Answer 21

Muscles, intestinal flagellae

Question 22

Skeleton support

Answer 22

Collagen in bone and skin

Question 23

Extra

Answer 23

Control of metabolism, growth and differentiation eg insulin, gene repressors, EGF