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10 Cards in this Set
- Front
- Back
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Define the term 'Allele' [1 mark]
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One of the different forms of a gene
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What is a gene? [1 mark]
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A section of DNA on a chromosome, which codes for specific polypeptide.
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State the characteristics of the genetic code [3-5 marks]
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Triploid
Degenerate 'Start' 'stop' codons Universal code No overlapping |
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What does 'triplet code' mean, and why is it needed? [3-4 marks]
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Codons made up of three bases
As there are only 4 bases, but 21 amino acids, if codons were made up of only 2 bases, there would be 16 possibilities (too few) A triplet code gives 64 possibilities, (more than enough) |
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What does the term 'degenerate code' mean?
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Most amino acids have more then one triplet code.
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Explain what it means when the genetic code is described as 'universal' and 'non-overlapping'. [2 marks]
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Universal meaning that code is exactly the same for all living organisms
Non-overlapping meaning codons read separately |
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What is 'semi-conservative replication' [1 mark]
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Each new DNA molecule made up of: one 'original' template strand and one new strand
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How does DNA undergo replication? [3 mark]
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-Hydrogen bonds break (DNA helicase), strands separate, DNA molecule 'unzips'
-DNA polymerase catalyses addition of free nucleotides to exposed bases. -Each chain acts as 'template', for newly synthesised strand [semi-conservative replication hypothesis] |
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Out line the basic process of protein synthesis. [ 2-4 marks]
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1-DNA does not leave nucleus, but acts as template for production of mRNA (transcription), forming sequences of instructions.
2-mRNA acts as template to which complementary tRNA molecules attach; the amino acids they carry form peptide bonds, so polypeptide chain formed |
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Describe how 'Transcription' occurs, in 3 main points?
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DNA helicase, acts on specific region of DNA (cistron), breaking H bonds, causes 2 stands to separate exposing nucleotide bases in that region
RNA polymerase links to template strand, free nucleotides align opposite template strand, (complementary) RNA polymerase moves along DNA, synthesising a strand of mRNA, which can carry instructions out of nucleus |
