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DNA, RNA and Protein Synthesis

DNA, RNA and Protein Synthesis. DNA is a code for proteins, controlling which proteins are made Proteins are made of amino acids The shape and behaviour of a protein molecule depends on the sequence of these amino acids (their primary structure)

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DNA, RNA and Protein Synthesis

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  1. DNA, RNA and Protein Synthesis

  2. DNA is a code for proteins, controlling which proteins are made Proteins are made of amino acids The shape and behaviour of a protein molecule depends on the sequence of these amino acids (their primary structure) DNA controls protein structure by determining the exact order in which the amino acids join together

  3. Triplet Code The sequence of bases (nucleotides) in a DNA molecule is a code for the sequence of amino acids in a polypeptide CAA-TTT-GAA-CCC Each sequence of 3 bases (CAA) stands for one amino acid (In this case, valine) CAA- Valine (amino acid) TTT- Lysine (amino acid) GAA- leucine (amino acid) CCC- Glycine (Amino Acid)

  4. Transcription • The DNA double helix unwinds and unzips- the hydrogen bonds between the bases break • Free, activated (extra phosphates) RNA nucleotides pair up with the exposed bases of one strand of the DNA • The sugar phosphate groups are bonded together to form a backbone for the new molecule we call mRNA (messenger RNA) • DNA mRNA • A U • T A • C G • G C • 4. mRNA leaves the nucleus via a pore in the nuclear envelope

  5. Lysine U U U In the cytoplasm, there are free amino acids and tRNA (transfer RNA) molecules. amino acids Methionine Valine tRNA anticodon C A A U A C At one end of a tRNA molecule is a site to which the amino acid can bind- The base triplet it binds to is called an anticodon

  6. A U G Translation • During the formation of the tRNA molecule (joining of amino acid and anticodon), the mRNA molecule copied from the original strand of DNA attaches itself to a ribosome • The mRNA binds to a small subunit of the ribosome- 6 bases at a time are exposed to the larger subunit- the ribosome itself is made of rRNA (ribosomal RNA) • The first 3 exposed bases or codons are always AUG on the mRNA Methionine tRNA anticodon 4. The matching (complimentary) tRNA anticodon with attached amino acid binds with hydrogen bonds U A C Hydrogen Bonds mRNA codon

  7. Peptide Bond Large subunit attached amino acid Ribiosome Methionine Lysine tRNA Hydrogen bonds U A C U U U Small subunit A A A mRNA A U G A second tRNA molecule bonds with the next three exposed bases on the mRNA molecule The enzyme peptidyl transferase catalyses the formation of a peptide bond between the two amino acid molecules This enzyme is found in the small subunit of the ribosome

  8. Methionine Lysine U A C U U U A U G Peptide Bond Large subunit attached amino acid Ribiosome tRNA Hydrogen bonds Small subunit A A A mRNA • The ribosome moves along the mRNA ‘reading’ the next 3 bases on the ribosome • A third tRNA molecule bonds to the third mRNA molecule- the first tRNA molecule leaves • The chain (a polypeptide- lots of peptide bonds) continues to grow until a ‘stop’ codon is exposed (mRNA) on the ribosome- ‘UAA’, ‘UAC’ or ‘UGA’

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