amino acids and proteins

Question 1

how many amino acids are there

Answer 1

20

Question 2

all amino acids have similar structures but..

Answer 2

varying side chains

Question 3

proteins are useful to cells because: 6

Answer 3

1) enzymes
2) structural (muscle, bone)
3) transcription factors- transcription and translation
4) lipid bound proteins act as transport systems
5) interact with sugars - glycosidic single on CSM
6) providing recognition of other molecules (e.g. receptors, growth factors, antibodies)

Question 4

chriality

Answer 4

central alpha carbon ha 4 different substituents

–> all amino acids accept glycine have mirror images- all are in the L form

Question 5

nomenclature

Answer 5

• end in -ine
• 3 letters (Gly)
• abbreviated to one latter- however more than one amino acid has a common starting letter e.g. phenylalanine= F

Question 6

amino acids exist as

Answer 6

zwitterions (has positive and negative parts) at a neutral pH of 7

Question 7

as pH increases

Answer 7

COOh grop is deprontonated and gives up proton

Question 8

peptide bond formation

Answer 8

amino acids join together and lose a molecule of water- condensation reaction

Question 9

two types of peptide bonds

Answer 9

cis and trans

Question 10

which peptide bond is more common

Answer 10

trans is favourable to cis- however proline has cis peptide bonds

Question 11

example of how flexible proteins are

Answer 11

on binding with iron, Lactroferrins undergoes a substantial change in conformation which allows other molecule to distinguish between iron friend iron bound forms

Question 12

4 main groups of amino acids

Answer 12

1) hydrophobic T groups with non polar R groups
2) polar amino acids with neutral R groups, but charge not equally distributed
3) positive charge on amino acid and R group (at a certain pH)
4) negative charge on the amino acid and R groups (pH)

Question 13

histidine

Answer 13

• found in Active sites of many enzymes
• only amino acid of pKA of near neutral
• charge can be modulated by other amino acids, surrounding it in the 3d structure of the protein

Question 14

cysteine

Answer 14

• contains a free thiol (SH) group
• covalent bond with another cysteine on the protein chain where they approach each other in a 3d structures

-this disulphide bond is the only covalent bond found to maintain structure

Question 15

cystine

Answer 15

two cysteine joined by a covalent bond

Question 16

glycne

Answer 16

• no chirality
• adds flexibility to proteins. where other side chains would be two bulky
• side chain =H

Question 17

alanine

Answer 17

• used in bio-synthesis of proteins

- non-polar

Question 18

proline

Answer 18

• side chain bonds to the amine group
• imposes tight restraints on the conformation of the protein
• cis and trans peptide bonds
• found in rigid proteins like collagen