1.5 Protein synthesis Flashcards
(24 cards)
Why is the genetic code a triplet code?
Three bases coded for one amino acid.
More than one triplet can encode each amino acid so the code is described as what?
Degenerate or redundant.
What are the 3 triplet codes that do not code for amino acids?
‘stop codons’.
The triplet code is non-overlapping. What does this mean?
Each base occurs in only one triplet.
The sequences that are removed are called what?
Introns.
Introns are cut out of what using what?
Pre-mRNA using endonucleases.
Exons are what?
The sequences left after introns are removed.
What is transcription?
One strand of DNA acts as a template for the production of the mRNA, a complementary section of part of the DNA sequence.
What is translation?
The mRNA acts as a template to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide.
Where does transcription happen?
In the nucleus.
Where does translation happen?
Ribosomes in the cytoplasm.
What happens in transcription?
The relevant gene in the DNA in the nucleus is ‘copied’ into a molecule of RNA
called mRNA or messenger RNA.
Why does transcription need to happen?
DNA cannot escape the nucleus – the molecules are too large, and proteins are manufactured in ribosomes outside the nuclear envelope.
What is step 1 in transcription?
DNA double helix unzips as hydrogen bonds between complementary bases break and the two polynucleotide strands separate-DNA helicase.
What is step 2 in transcription?
One strand called the sense strand acts as a template, free RNA nucleotides come along and join to the complementary bases. RNA polymerase forms sugar-phosphate bonds between nucleotides.
What is step 3 in transcription?
The mRNA detaches from the sense strand. The two DNA strands join together by complementary base pairing. The DNA molecules winds back up into a helix-hydrogen bonds reform.
What are the 3 bases on the mRNA coding for amino acids called?
Codons.
What is step 4 in transcription?
These introns are removed by enzymes before the mRNA leaves the nucleus. This leaves just EXONS or coding regions of mRNA.
What is step 5 in transcription to translation?
Following the removal of introns the mRNA moves out through a nuclear pore and attaches to a ribosome.
What is step 6, initiation?
The first tRNA with an anticodon
complimentary to the first codon on the
mRNA, attaches to the ribosome. The 3 bases of codon on mRNA bond to the 3
complementary bases of the anticodon on the tRNA-with hydrogen bonds.
What is step 7, elongation?
The two amino acids are sufficiently close for a ribosomal enzyme to catalyse
the formation of the peptide bond between them. The first tRNA leaves the ribosome, it returns to cytoplasm to pick up another amino acid. The ribosome moves along one codon along mRNA. Ribosome moves along mRNA by one codon. ‘empty’ tRNA leaves to pick up another specific amino acid.
What is step 8, termination?
This process is repeated until the ribosome reads a stop codon.
What is a polysome?
several ribosomes binding to a single mRNA strand.
How is an amino acid activated?
When the tRNA is released from the ribosome it goes into the cytoplasm to an
amino acid pool, energy from ATP is needed.
