© 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.
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- DNA, Philip Allan, Pauline Lowrie