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Genetic Control
AQA Unit 5 Biology

Frihah Parvaiz

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The genetic code
The genetic code as base triplets in mRNA which code for specific amino acids.
The genetic code is universal, non-overlapping and degenerate.

Universal, non-overlapping, degenerate, base triplet code.


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The structure of molecules of and transfer (tRNA).

Structure of tRNA

Structure of mRNA


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Candidates should be able to compare the structure and composition of DNA, mRNA and tRNA.

Features DNA mRNA tRNA
Shape Double stranded- held Single stranded Single stranded
together by hydrogen

Sugar Deoxyribose sugar Ribose sugar Ribose sugar

Bases A,T,C,G A,U,C,G A,U,C,G

Where its found Mostly in the nucleus Manufactured…

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Polypeptide synthesis
Transcription as the production of mRNA from DNA. The role of RNA polymerase.

DNA is too large to move out
of the nucleus so a section is
copied onto RNA

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Steps in transcription
1. RNA helicase unwinds the DNA
2. The promoter region in the DNA
molecule is recognised and RNA
polymerase binds to this section of DNA
3. RNA polymerase lines up RNA
nucleotides along the strand. It moves
along the strand using it as a template

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The splicing of pre-mRNA to form mRNA in eukaryotic cells.


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Translation as the production of from the
of carried by mRNA. The role of and tRNA.

1. The RNA binds to the ribosome
2. The Trna with an anticodon
complementary to the first codon on
Mrna attaches itself to the Mrna by
specific base pairing

3. The peptide bond forms…

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Gene mutation
Gene mutations might arise during DNA replication. The deletion and substitution of bases.



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Gene mutations occur spontaneously. The mutation rate is increased by mutagenic
agents. Some mutations result in a different amino acid sequence in the encoded
polypeptide. Due to the degenerate nature of the genetic code, not all mutations
result in a change to the amino acid sequence of the encoded polypeptide.…


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