B1.2 Proteins

Question 1

what is the word equation for the formation of a dipeptide?

Answer 1

amino acid + amino acid = dipeptide + water

Question 2

what is an essential amino acid?

Answer 2

9 amino acids that are not able to be synthesized by body and have to be consumed in diet

Question 3

why are animal products known as complete proteins?

Answer 3

they contain all 9 essential amino acids

Question 4

what is a non-essential amino acid?

Answer 4

11 amino acids that are able to be synthesized by body

Question 5

how is there so much variety in polypeptide chains?

Answer 5

they can have any number of amino acids (eg 51 in insulin vs 34,000 in titin) in any order, and some amino acids are modified after synthesis

Question 6

define denaturation

Answer 6

when a protein temporarily loses structure due to changes in temperature putting stress on or changes in pH preventing hydrogen bonds; if too extreme, peptide bonds are broken and becomes unreversible

Question 7

what properties of R-groups determine their interactions?

Answer 7

they can be either non-polar, polar because of polar-bonding atoms, polar because of a positive charge (basic), or polar because of a negative charge (acidic)

Question 8

what is the order of structure in proteins?

Answer 8

1. primary
2. secondary
3. tertiary
4. quaternary

Question 9

what is the primary structure of a protein?

Answer 9

number and order of amino acids; held together by peptide bonds

Question 10

what is the secondary structure of a protein?

Answer 10

folding of polypeptide chains into beta-pleated sheets or alpha helices held together by hydrogen bonds between residues; polypeptides with only secondary structure have only non-polar R-groups and are fibrous

Question 11

what are residues?

Answer 11

carboxyl and amine groups that form peptide bonds

Question 12

are amino acids charged, even if their R-groups are not?

Answer 12

yes; COOH acts as acid and donates hydrogen ion, becoming negative; NH2 acts as base and accepts, becoming positive

Question 13

what is the tertiary structure of a protein?

Answer 13

3D folding of polypeptide chain due to R-group interactions

Question 14

what bonds/interactions are responsible for tertiary structure?

Answer 14

ionic, hydrogen, and covalent bonds and hydrophobic/philic interactions

Question 15

what covalent bonds are used to hold together a protein’s tertiary structure?

Answer 15

disulfide bonds between sulphur atoms of cysteine amino acids; strongest bonding force

Question 16

how do hydrophobic/philic interactions influence the structure of a protein?

Answer 16

hydrophobic amino acids cluster into inner globular protein, while hydrophilic amino acids make up outer surface

Question 17

what are examples of hydrophobic/philic interactions in proteins?

Answer 17

integral proteins (embedded in membrane) and lipase (hydrolysing enzyme)

Question 18

what is the quaternary structure of a protein?

Answer 18

folding of multiple polypeptide chains by ionic, hydrogen, and covalent bonds and hydrophobic/philic interactions

Question 19

what is a conjugated protein?

Answer 19

protein with polypeptide chains attached to 1 or more prosthetic group

Question 20

what is a non-conjugated protein?

Answer 20

protein with only polypeptide chains

Question 21

what is a prosthetic group?

Answer 21

non-polypeptide group in protein

Question 22

how many non-polar R-groups are there, and what makes an R-group non-polar?

Answer 22

9; has only hydrocarbons

Question 23

how many polar R-groups are there, and what makes an R-group polar?

Answer 23

11; 6 have elements making polar covalent bonds (O, N, S), 3 act as bases (positive charge), 2 act as acids (negative charge)

Question 24

where does insulin come from and what is its purpose?

Answer 24

hormone secreted from pancreas that controls glucose levels; bonds to receptors, setting off chain of reactions (signal pathway) that opens channels allowing glucose through membrane

Question 25

what is the structure of insulin?

Answer 25

globular, irregular amino acid sequence, stored as dimers or hexamers; starts as 1 chain of 110 amino acids that splits into 2 chains of 21 and 30 amino acids connected by 3 disulfide bonds

Question 26

what are properties of insulin?

Answer 26

soluble, functional

Question 27

what is the purpose of collagen?

Answer 27

supports bodily tissues

Question 28

what is the structure of collagen?

Answer 28

fibrous, repetitive amino acid sequence (glycine, proline, X); 3 polypeptide chains in helix shape connected by hydrogen bonds

Question 29

what are properties of collagen?

Answer 29

insoluble, structural, flexible, tensile, elastic

Question 30

what are similarities of insulin and collagen?

Answer 30

non-conjugated with quaternary structure

Question 31

what is an example of a conjugated protein?

Answer 31

haemoglobin: 4 polypeptide chains with haem group at centre

Question 32

what is the purpose of haemoglobin, and how many are in each blood cell?

Answer 32

270 million/blood cell; Fe+2 in haem group binds to O and CO2 and carries to tissues