6.1. - 7.1. Transcription and Translation Flashcards
The central dogma…
The copying of information from DNA –> RNA –> proteins.
DNA…
Two antiparallel strands of nucleotides, one running from the 5’ to 3’ direction, the other running from the 3’ to 5’ direction.
Is defined by the 5’-PO4 and 3’-OH groups at each end of the strand.
RNA…
A single strand running from the 5’ to 3’ direction.
The sugar is a ribose, rather than a deoxyribose.
The fourth base is uracil, rather than thymine.
Transcription initiation…
Requires a promoter (complementary sequence that tells RNA polymerase where to start, which DNA to transcribe and the direction to take from the start).
There is an initiation site on the promoter that specifies where transcription should actually begin.
Transcription elongation…
RNA polymerase breaks the hydrogen bonds between complementary bases and unwinds the DNA.
It then reads in the 3’ to 5’ direction, with complementary bases aligning to the template strand in the 5’ to 3’ direction (antiparallel).
Ribonucleoside triphosphate substrates are hydrolysed as they are added, which provides the energy for RNA synthesis.
Transcription termination…
Particular bases specify termination.
In some processes, the new pre-mRNA just falls away from the DNA and RNA polymerase.
In other processes, a helper protein pulls the new pre-mRNA away.
pre-mRNA must be processed / spliced to produce mature mRNA.
There are 64 possible codons…
1 start codon (methionine).
3 stop codons.
60 codons for 20 amino acids.
Charging tRNA…
Aminoacyl-tRNA synthetases bind with ATP.
A specific amino acid (i.e. alanine) joins the enzyme by binding to the ATP. Alanine is then activated when two phosphate groups are removed (producing AMP).
Alanine-specific tRNA is linked with the alanine by the enzyme, removing the AMP.
There is now a tRNA bonded to alanine, in an enzyme. The tRNA and the amino acid are removed.
Translation initiation…
tRNA becomes charged with a particular amino acid (describe how).
The complex begins at AUG (methionine).
The small ribosomal subunit, bound to mRNA, triggers the beginning of translation.
Translation elongation…
The ribosome moves along the mRNA, one codon at a time, in the 5’ to 3’ direction.
A polypeptide grows from the N terminus towards the C terminus.
Charged tRNA bring amino acids to the ribosomes sequentially.
Specificity is ensured through anticodon-codon interactions and aminoacyl-tRNA synthetases.
Ribosomes…
The ribosome has two subunits (a large and small).
A: aminoacyl-tRNA synthetases (where the enzyme goes).
P: peptidyl-tRNA (where the process of the amino acids being bound onto a chain occurs).
E: exit site.
Polysomes…
Several ribosomes can work together to translate the same mRNA, producing multiple copies of the polypeptide.
A strand of mRNA with associated ribosomes is called a polyribosome, or polysome.
