Outline the structure of proteins.

Cells produce a large variety of proteins with different sequences of amino acids. Explain how this is done.

Outline the range of functions of proteins in cells.

a. protein formed from amino acids
OR
20 different amino acids ✔

b. linked together by peptide bonds ✔

c. may consist of one or more polypeptides linked together ✔

d. have a specific shape/conformation/folding ✔

e. shape determines function ✔

a. protein is produced when a gene is expressed / switched on ✔

b. genetic code/codons consists of three nucleotides/bases/base triplet ✔

c. genetic code in DNA is transcribed/transcription (to mRNA) ✔

d. mRNA exits the nucleus ✔

e. mRNA (code) is translated/translation into a polypeptide/protein ✔

f. amino acid sequence/polypeptide formation occurs at a ribosome ✔

g. one codon translates to one amino acid ✔

h. tRNA carries code for specific amino acids ✔

i. tRNA anticodon matches with specific codon in mRNA ✔

j. amino acids joined (by peptide bonds) to form polypeptide ✔

k. sequence of amino acids determined by order of bases/nucleotides/codons in DNA/mRNA ✔

l. proteins vary based on which amino acids are used and their order
OR
protein variety increases by mutations to DNA ✔

a. enzymes that catalyse/speed up/control (the rate and direction of) metabolic reactions ✔

b. proteins can be hormones which are chemical messengers to cells ✔

c. proteins that transport through the membrane such as channel/carrier/pumps / that regulate what enters/leaves the cell ✔

d. hemoglobin in red blood cells that transports/ binds oxygen ✔

e. membrane proteins for cell/tissue recognition/cell adhesion/communication ✔

f. structural elements of muscle fibre/actin/myosin for movement
OR
spindle fibres move chromosomes ✔

g. histones condense DNA into chromosomes ✔

The question requires answer that the function is in cells.

This question was attempted by about 42 % of candidates.

Many candidates used the terms primary, secondary, tertiary and quaternary as their basic outline. These terms occur in AHL but not in the core. Therefore, without an outline of the meaning of these terms few marks could be earned.

This question was attempted by about 42 % of candidates.

Some brilliant, clear answers were given earning the maximum marks. However, coherent essays explaining protein synthesis were rare. Some students dwelled on transcription without ever mentioning translation. Codons, anticodons and their locations were not clearly understood. Valid information did appear but it was frequently mixed up or incomplete.

This question was attempted by about 42 % of candidates.

Generally good answers were received for those who read the question correctly, i.e. protein function within cells.