4.2.1

Protein Synthesis

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Protein Synthesis

Protein synthesis is the process of making proteins in the cells.

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The genome

  • The genome is the complete set of genes in an individual's DNA.
  • The genes in the genome encode the different proteins a cell needs.
  • The proteome is the full range of proteins an individual can produce.
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Base sequence

  • DNA is made from a combination of four different bases (A, T, C, G).
  • A specific sequence of three bases (called a codon) encodes a specific amino acid.
  • The order of the bases on the DNA tells us the order for combining amino acids to create particular proteins.
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Processes

  • There are two processes involved in synthesising protein from a base sequence. These are:
    • Transcription.
    • Translation.

Types of RNA

RNA is a single-stranded nucleic acid molecule that is made from the same bases as DNA except for uracil (U) which is used instead of thymine (T). There are different types of RNA:

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mRNA

  • Messenger RNA (mRNA) is transcribed from DNA in the nucleus to produce a single-stranded RNA.
  • The mRNA strand is complementary to the DNA base sequence.
  • mRNA travels from the nucleus to the ribosomes in the cytoplasm.
  • Ribosomes are proteins that translate mRNA into amino acids and synthesise the polypeptide.
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tRNA

  • Transfer RNA (tRNA) forms a clover-like shape and is vital for translation.
  • tRNA reads the mRNA codons and brings the corresponding amino acid into the ribosomes.
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Accuracy of tRNA

  • It is important that the correct amino acid is brought to the ribosomes by tRNA so that the protein is assembled correctly.
  • Each tRNA molecule has an anticodon which is complementary to a specific codon on mRNA.
  • The amino acid that corresponds to a specific anticodon binds to a specific attachment site on the tRNA molecule.
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DNA → amino acid

  • There are many processes in producing an amino acid from the original DNA sequence.
  • If the original DNA sequence has the codon GCC, the codon in each step is:
    • DNA codon: GCC.
    • mRNA complementary codon: CGG.
    • tRNA anticodon: GCC.
    • Amino acid: Arginine.

Jump to other topics

1Biological Molecules

2Cells

3Substance Exchange

4Genetic Information & Variation

5Energy Transfers (A2 only)

6Responding to Change (A2 only)

7Genetics & Ecosystems (A2 only)

8The Control of Gene Expression (A2 only)

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