Transcription and translation

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  • Created by: Steff06
  • Created on: 24-04-16 16:11

Example of process

DNA:     ACT    GAA   CTG

Where? Nucleus

mRNA:  UGA   CUU   GAC

Where? Nucleus

Splicing:  Removes introns

tRNA:   ACU   GAA   CUG

Where?  Ribosome

Polypeptide:  Thr - Glu - Leu

  • Transcription from DNA to mRNA.
  • Translation from splicing to formation of polypeptide
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Transcription

1. DNA HELICASE UNWINDS and UNZIPS DNA, HYDROGEN BONDS between the base pairs BREAK.

2. RNA POLYMERASE CATALYSES binding of nucleotides and hydrogen bases.

3. RNA polymerase travels along the gene to the STOP CODON.

4. Produces mRNA which is COMPLEMENTARY to nucleotide base sequence on the TEMPLATE strand.

5. mRNA RELEASED from DNA. Passes out of nucleus through nuclear PORE to a RIBOSOME in the CYTOPLASM.

DNA ----------> mRNA = Transcription 

RNA polymerase travels from 5' to 3' end.

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Translation

Happens at RIBOSOMES in CYTOPLASM. 

Translation = Amino acids translated into polypeptide. 

mRNA fits into GROOVE between 40s and 60s subunits.

Sequence of amino acids is important, because:

  • Forms primary structure of protein. This determines tertiary structure which allows the protein to function

tRNA: Made in NUCLEUS, passes into cytoplasm.

  • Lengths of DNA at 1 end with 3 EXPOSED BASES where a certain amino acid can BIND.
  • 3 UNPAIRED NUECLEOTIDE BASES at other end (ANTICODONS). 
  • Anticodons can temporarily BIND with COMPLEMENTARY CODON. 
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Steps of translation

1. mRNA BINDS to RIBOSOME - 2 codons attached to small unit of ribosome and exposed to large subunit. 1st codon is always AUG. Using ATP + an enzyme, tRNA with methionine and antiocodon UAC form hydrogen bonds with codon. 

2. 2nd tRNA with different amino acids binds to 2nd exposed codon with its complementary anticodon.

3. PEPTIDE BOND forms between 2 adjacent AMINO ACIDS - Enzyme catalyses reaction.

4. Ribsome moves along mRNA, reading the next codon - 3rd tRNA brings amino acid and peptide bond forms between it - 1st tRNA leaves, collects and brings another one of its amino acids. 

5. POLYPEPTIDE CHAIN grows until STOP CODON is reached - No corresponding codons for UAA, UAC, UGA, so chain is complete. 

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