protein synthesis Flashcards
what is a gene?
A sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, that makes up a specific polypeptide (protein).
What are the two stages of protein synthesis?
Transcription - DNA is transcribed and an mRNA molecule is produced.
Translation - mRNA is transcribed and an amino acid sequence is produced.
First stage of transcription.
DNA helicase unzips gene by breaking hydrogen bonds between bases. DNA molecule unwinds.
Second stage of transcription.
-Free RNA nucleotides are exposed to their bases.
-Thymine is replaced with uracil.
- Free RNA nucleotides pair up with their exposed bases by complementary base pairing.
Third stage of transcripction.
- RNA polymerase will join RNA nucleotides together to form RNA strand.
- Joins nucleotides together by forming phosphodiester bonds, to form sugar phosphate backbone this forms mRNA.
fourth stage of transcription
- mRNA contains the correct sequence of bases/ codon for the correct amino acid sequence.
- mRNA leaves the nucleus through nuclear pore to travel to ribosomes (on RER) for translation.
What is the sense strand?
Runs from 5’ end to 3’ end.
What is the antisense strand?
Runs from 3’ end to 5’ end.
Process of translation.
1- mRNA binds to ribosome, and is sectioned into codons.
2- tRNA with complementary anticodon and specific amino acid binds to mRNA’S codon.
3- Another tRNA with specific amino acid binds to the next complementary codon. A tRNA molecule forms a complementary codon anti-codon complex with hydrogen bonds.
4- 1st amino acid binds to 2nd amino acid through peptide bond catalysed by peptidyl transference.
5- Ribosome moves along mRNA, releasing the first tRNA. The second tRNA becomes the first. This process continues until the ribosome reads a stop codon.
