Practise protein-synthesis questions by tracing transcription and translation, using codons or anticodons and predicting mutation effects on polypeptides.
Starch molecules are the main storage molecules in many types of cereal grain, such as the grain of the barley plant.
When the seed inside a barley grain germinates, genes coding for digestive enzymes are switched on. The enzymes that are synthesised catalyse the hydrolysis of storage molecules such as proteins and starch.
Explain what is meant by a gene.
sequence of nucleotides or length / section / AW, of DNA ;
A bases for nucleotides (a gene can) code for a polypeptide ;
A protein for polypeptide
Cathelicidin LL-37 is a cell signalling compound that stimulates many different cells in humans. One role of cathelicidin LL-37 is stimulating the production of endothelial cells in the formation of capillaries during wound healing.
Mutations of DNA base sequences in a gene can affect the primary structure of proteins.
Use the information in Table 5.1 and Table 5.2 to suggest the effect on the primary structure of cathelicidin LL-37 of:
the substitution of the base T with the base A in the middle of the triplet at position 5
(TTC to TAC) change from phe to tyr (at position 5) ;
I 'tyr' unqualified
the deletion of base T in the triplet at position 2
Marking guidance:
allow two marks for new sequence is leu arg val ile ser ser gly asp leu ;;
or allow any two from:
I refs to frameshift
1 sequence after, first amino acid / first leu, is different ;
R 'after position 2'
A 'from position 2 onwards'
2 any example ;
e.g. amino acid (at position 2) is arg
3 shortened polypeptide / early chain termination ;
the insertion of base G between bases G and T in the triplet at position 3 .
any two from:
peptide is 3 amino acids in length / shortened polypeptide ;
stop codon in position 4 ;
(third) amino acid is still, gly(cine) / the same ;
The genetic code is described as universal.
Explain why the genetic code is described as universal.
(genetic code) is the, same / similar, in all organisms AW
or
idea that each triplet codes for the same amino acid in all living organisms ;
Use Table 5.2 to explain why some mutations have no effect on the primary structure of a protein.
any two from:
1 (most) amino acids have more than one, triplet / codon ;
2 any correct example(s) from Table 5.2 ;
if award this then award mp1 as well
3 genetic code is, degenerate / redundant ;
R degenerative / degenerated
4 idea that 64 / 61, possible codons for 20 different amino acids ;
PUBLISHED
Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis.
The antibiotic rifampicin was introduced as an alternative to streptomycin.
Rifampicin acts by inhibiting the enzyme RNA polymerase.
RNA polymerase is the enzyme used in transcription.
Explain what is meant by transcription.
making/synthesis of, (m)RNA ;
from a DNA, template/sequence of bases/sequence of nucleotides ;
A from a gene
M. tuberculosis and humans both use RNA polymerase for transcription.
Suggest why rifampicin does not affect transcription in human cells.
idea that pathogen and human RNA polymerase are (slightly) different ;
e.g. (slightly) different shaped active sites
A rifampicin unable to, cross cell surface membrane/enter nucleus/ cross nuclear envelope