A2 Level Biology: Transcription & Translation

RNA Polymerase
1. Enzyme
2. Binds to gene at Start codon
3. Breaks hydrogen bonds between DNA strands
4. Lines up free-floating DNA nucleotide bases to DNA template strand
  1. Bases bind to DNA template strand by complementary base pairing
5. Once RNA Polymerase has passed, the DNA heilx begins to reform
  1. Hydrogen bonds between bases
mRNA
1. Single polynucleotide strand
  1. Ribose sugar, phosphate group, nucleotide base
2. Formed in the nucleus
3. Combines with tRNA in cytoplasm
4. Nucleotide base triplets on mRNA are called CODONS
tRNA
1. Single polynucleotide strand
  1. Clover shape
    1. Held in shape by hydrogen bonds between bases
  2. Anticodon at one end
    1. Sequence of 3 DNA Nucleotide bases
      1. Complementary to a specific triplet on mRNA
  3. Amino Acid binding site at other end
    1. Each tRNA molecule has a specific amino acid attatched
2. Found in cytoplasm
3. Combines with mRNA in a ribosome, in cytoplasm
Translation
1. 1. mRNA enters ribosome
2. 2. tRNA binds to the first codon by complementary base pairing
3. 3. A second tRNA binds to the second codon on mRNA
4. 4. The two amino acids (one on each tRNA) form a peptide bond between them
5. 5. A third tRNA binds to the next codon on mRNA
  1. 6. The first tRNA detatches and leaves the ribosome (leaving its amino acid behind)
  2. 6. This tRNA's amino acid forms a peptide bond to the second amino acid
6. 7. This continues, forming a chain of amino acids, held together by peptide bonds
Ribosome
1. Formed of rRNA and complex proteins
  1. rRNA = Ribosomal RNA
2. Located in cytoplasm of cells
3. Acts as site of protein synthesis
  1. mRNA & tRNA combine here

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A2 Level Biology: Transcription & Translation

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