Pauline lowrie 2015 philip allan for hodder education

© Pauline Lowrie 2015
Philip Allan for Hodder Education
12

Section 4
Genetic information, variation and
relationships between organisms
DNA, genes and chromosomes
1
Word Definition
Triplet Three bases in DNA that code for one amino acid
Locus The fixed position on a chromosome where a gene is found
Gene A sequence of DNA that codes for functional RNA and/or the
amino acid sequence of a polypeptide
Introns Non-coding DNA found within the genes of eukaryotes
Exon The sequence of DNA within a gene that codes for a protein
Histones The protein molecules that associate with the DNA in a eukaryotic
chromosome
2 Circular (short) and not complexed with proteins/histones.
DNA and protein synthesis
1
a Both single-stranded.
b One from:
 tRNA contains hydrogen bonds, mRNA does not
 tRNA has an anticodon, mRNA has codons
2 E, B, G, D, I, C, F, J, H, A.
1 mark for one statement in the wrong order.
3
a The proteome is all the proteins that a cell can produce; the genome is the DNA that
codes for these proteins.
© Pauline Lowrie 2015
Philip Allan for Hodder Education
13

b A codon is a sequence of three bases on mRNA that codes for an amino acid; an
anticodon is a sequence of three bases on tRNA that joins by complementary base
pairing to the codon on mRNA.
c Introns are sections of RNA that are spliced out of pre-mRNA before mRNA is
made; exons are the functional sequences that code for proteins.
4
DNA base sequence A T T G C C A G C T G A
mRNA base sequence U A A C G G U C G A C U
tRNA anticodons A U U G C C A G C U G A
5
a Universal = the code is the same in every living organism.
b Non-overlapping = each base is part of only one codon/triplet.
6 Formation of peptide bonds/attachment of amino acid to tRNA/attachment of mRNA to
ribosome.
Genetic diversity can arise as a result of
mutation or during meiosis
1
a Outcome A = substitution; outcome B = deletion.
b It changes one DNA triplet; a different amino acid is coded for; it changes the
primary/tertiary structure of the protein; altered protein/non-functional protein; it
changes the triplet to another triplet for the same amino acid; there is no change in
protein produced.
c Frame-shift mutation; all the triplets are altered from the point of mutation; is likely to
give a highly altered/non-functional protein.
2 There are more triplets/codons than amino acids; some amino acids have more than one
triplet/codon.
3 Something that increases the rate of mutation; any two examples, such as
ionising/gamma/X/UV radiation/tar in cigarette smoke/benzene/mustard
gas/caffeine/colchicine.
© Pauline Lowrie 2015
Philip Allan for Hodder Education
14

4
Stage Number of chromosomes
per cell
Mass of DNA per
cell/arbitrary units
Immediately before meiosis 28 40
End of the first division of
meiosis
14 20
End of the second division
of meiosis
14 10
1 mark for each correct column.