2.4 proteins

Question 1

draw the basic structure of a generalized amino acid

Answer 1

see paper

Question 2

outline the structural organisation of a polypeptide chain (monomer —> polymer)

Answer 2

amino acids are joined via condensation reactions to form dipeptides (a water molecule is produced)

the covalent bond that connects amino acids together in a polypeptide chain is called a peptide bond

polypeptide synthesis occurs at the ribosome via the process of translation

Question 3

draw the basic structure of a generalized dipeptide

Answer 3

see paper

Question 4

identify the number of different amino acids present in nature and how they are distinctive

Answer 4

there are 20 different amino acids present in nature

they differ according to the chemical composition of their variable side chain (R group)

Question 5

explain with the aid of the diagram the levels of protein structure and indicate their significance

Answer 5

primary structure:
-the order/sequence of amino acids within a polypeptide chain
-formed via peptide bonds between the amine and carboxyl groups of adjacent amino acids
-primary structure determines all subsequent levels of protein structure

secondary structure:
-the folding of a polypeptide chain into repeating arrangements (alpha helices or beta-pleated sheets)
-formed via hydrogen bonds between the amine and carboxyl groups of non-adjacent amino acids

tertiary structure:
-the overall three dimensional shape of the polypeptide chain
-formed via a variety of bonds/ interactions between the variable side chains (R groups)
-these interactions may include hydrogen bonds, ionic bonds, disulphide bridges or hydrophobic interactions

quaternary structure:
-the presence of multiple polypeptides or prosthetic groups to form a biologically active protein
-not all proteins will have a quaternary structure

Question 6

list seven functions of protein, providing an example for each

Answer 6

structure (spider silk, collagen)
hormones (insulin, glucagon)
immunity (antibodies)
transport (hemoglobin)
sensitivity (rhodopsin)
movement (actin, myosin)
enzymes (catalase, rubisco)

SHITSME

Question 7

define denaturation

Answer 7

a loss of protein structure resulting in a loss of biological activity

Question 8

identify two factors that can cause protein denaturation and explain how this occurs

Answer 8

1. temperature (heat)
   -thermal energy breaks hydrogen bonds responsible for tertiary structure
   -a loss of tertiary structure results in a loss of function

2.pH
-amino acids are zwitterions - possessing both positive and negative regions (amine and carboxyl groups)
-altering the pH will change the charge and solubility of the protein (changing the structure)

Question 9

outline the relationship between genes and polypeptides

Answer 9

genes are sequences of DNA that encode polypeptides

typically one gene equals one polypeptide - however exceptions exist (tRNA genes)

Question 10

define proteome

Answer 10

the totality of proteins expressed within a cell, tissue or organism at a given time