Protein Synthesis Flashcards
What is a base triplet?
A sequence of 3 nucleotide bases
What are codons?
Base triplets in mRNA
What are 5 features of the genetic code?
- The code is a degenerate code, most AA have more than one codon
- The start of the DNA sequence is always the same triplet
- 3 codons don’t code for any amino acid, these are called stop codons and mark the end of the polypeptide chain
- Code is non-overlapping, each base is only read once
- Universal code, same codon codes for same AA in all organisms
What is transcription?
Occurs in the nucleus, involves transcribing parts of the DNA code into a strand of messenger RNA
Outline transcription
- DNA molecule uncoils and 2 strands are separated as hydrogen bonds are broken by DNA helicase
- One strand acts as the template
- Individual RNA nucleotides line up alongside DNA nucleotide bases on the template strand due to complimentary base pairing
- Sequence of bases in mRNA is the same as non-template strand, except uracil replaces thymine.
- Individual RNA nucleotides are joined together by RNA polymerase, forms a strand of mRNA
- The mRNA strand leaves the nucleus through the nuclear pore and is spliced, and then attaches to the ribosome where translation occurs
- DNA strands will recoil when enough mRNA has been produced
What is the spicing of pre-mRNA?
When the introns are removed from pre-mRNA and the extrons are joined together to form mRNA. This is post transcriptional processing. The exons can form a variety of different combinations which means a gene can code for different proteins.
What is translation?
The process of translating the sequence of an mRNA molecule to a sequence of amino acids during protein synthesis. This is carried out by the ribosomes in the cytoplasm.
Outline translation
Each tRNA molecule has an anticodon. A tRNA molecule with a complimentary anticodon to the first codon on the mRNA strand moves the ribosome, bringing the specific amino acid. The amino acids are connected by peptide bonds. The first tRNA molecule moves away from the ribosome and leaves the amino acid behind, collecting another molecule of the same amino acid from the ‘amino acid’ pool. This process continues until all mRNA codons have been read and the specific polypeptide has been produced. It folds itself into secondary and tertiary structure.
What determines the order of the polypeptide?
The sequence of amino acids is determined by the codons on the mRNA strand, which has been transcribed from the DNA template strand so therefore the sequence of DNA nucleotides determine which specific polypeptide is produced.
