Transcription and translation Flashcards
What are genes made of?
DNA and are expressed in the phenotype as polypeptides
What is the central dogma (principle) of molecular biology?
DNA—>RNA—>protein (transcription and translation)
What do RNA viruses do to DNA?
They exclude DNA and directly transform RNA into protein.
What do retroviruses do in transcription?
They reverse it
What are the steps to express a gene?
1st DNA is _transcribed_ to RNA;
Then RNA is _translated_ into protein
How is RNA transcribed?
- It is transcribed from a DNA template after the bases of DNA are exposed by unwinding the double helix
- RNA polymerase catalyzes (causes) transcription from the template strand of DNA
- The initiation of transcription requires that RNA polymerase recognize and bind tightly to a promoter sequence on DNA
- RNA elongates in a 5’ -to-3’ direction, antiparallel to the template DNA
- Special sequences and proteins helpers terminate transcription
What happens during elongation?
While the DNA unwinds and rewinds in the 5’ to 3’ direction RNA is doing transcription up until it reaches the termination site
What composes the genetic code?
triplets of nucleotides (codons)
64 possible condons since there are 4 bases
What are the codons’ roles?
- One mRNA codon indicates the starting point of translation and codes for methionine (amino acids)
- 3 stop codons indicate the end of translation
- the other 60 condons code only for particular amino acids
Why is the genetic code called redundant?
Since there are only 20 different amino acids, there is more than one codon for certain amino acids
But a codon can only be found in a specific amino acid, meaning it is unambiguous (always codes for the same amino acid)
What is the start codon?
AUG (Methionine)
What are the 3 stop codons?
UAA, UAG, UGA
When does translation start for prokaryotes?
Before mRNA is completed
Where do transcription and translation happen in eukaryotes?
Transcription happens in the nucleus and translation happens in the cytoplasm
What components does translation need?
tRNA’s, activating enzymes and ribosomes
What does tRNA?
It carries amino avcids to the protein synthesizing machinery of a cell called ribosome
Who do the aminoacyl-tRNA synthetases do?
Attach specific amino acids to their appropriate tRNAs, forming charged tRNAs
What are the large subunits of the ribosome?
E, P,A and T
What triggers translation?
An amino acid-charged tRNA and a small ribosomal subunit bound to mRNA
How do polypeptides grow ?
From 5’ to 3’ of mRNA
On what and how does a ribosome move?
It moves along the mRNA one codon at a time
How does translation stop?
The presence of a stop codon in the A site of the ribosomes causes the termination
What is an anticodon?
They are the complementary nucleotides of the start codon (on mRNA), which are isolated on tRNA
Explain the process
- The ribosome moves along the mRNa one codon (three nucleotides) at a time. until it comes upon the start codon (AUG)
- Then the tRNA with the anticodon of the start codon comes in the P subunit with an amino group (amino terminus) at its C end terminus (3’)
- Another tRNA comes in the A site with another amino group. The ribosome continues moving and the first tRNA leaves leaving its amino group on the amino group of the new tRNA
- This process continues until the ribosome comes over the stop codon
- Then a release factor comes in the A unit over the stop codon and then the tRNA goes away and leaves the polypeptide floating.
- The C-terminus and N-terminus come at each end of the chain of amino groups to form a polypeptide
