The genetic code Flashcards
Define replication
DNA is copied to make more DNA
Define transcription
DNA is copied to make RNA
Define translation
RNA is read and proteins are made
Where does transcription occur?
In the nucleus
Where does translation occur?
In the cytoplasm
What is the basic structure of an amino acid?
NH3 (amino group) Central carbon R group Hydrogen COOH (carboxyl group)
What joins two amino acids?
A peptide bond
Where does the peptide bond form?
Between the carboxylic group of one amino acid and the amino group of the next
What kind of code is the genetic code?
Triplet code
What does triplet code mean?
Three nucleotides specify one amino acid
What is another name for a triplet?
A codon
What is the start codon in all polypeptides?
Methionine
AUG
What are the three stop codons?
UAA
UAG
UGA
What does degenerate mean?
Usually there is more than one codon for an amino acid
What is an open reading frame?
A string of sense codons that start with the codon ATG and end with a stop codon at the 3’ end
What determines which reading frame is read?
The start codon
Also the largest possible protein is always made
How many possible reading frames are there?
6
3 in each direction
What does mRNA consist of?
Leader
Reading frame
Trailer
How many subunits make up a ribosome?
Two
What are the two subunits of a ribosome?
The small and large subunit
What kind of ribosome is involved in protein synthesis and mRNA?
An 80s ribosome
Describe the small subunit
40s
18s rRNA
30 ribosomal proteins
Describe the large subunit
60s
28s + 5.8s + 5s rRNA
50 ribosomal proteins
2 binding sites
What are the two binding sites present in the large subunit?
The P site
The A site
What is the A site?
The aminoacetyl-tRNA binding site
What is the P site?
The peptidyl-tRNA binding site
What is the role of tRNA?
tRNA molecules carry the amino acids to the ribosomes to be assembled into polypeptide chains
What features do all tRNA molecules share?
Similar in size and shape
CCA at the 3’ end which amino acids bind to
What is the anticodon?
The section of the tRNA molecule which during translation reads the matching codon on mRNA
How is an amino acid added to a tRNA molecule?
The enzyme aminoacyl-tRNA synthetase
What is the name of the process given to adding amino acids to tRNA
Aminoacylation
How many aminoacyl-tRNA synthases are there?
As there are 20 amino acids, there are 20 aminoacyl-tRNA synthases
Are aminoacyl-tRNA synthases dependent on the codon?
No
So when an amino acid has multiple codons it will still only have one aminoacyl-tRNA synthase
Describe the role of ATP in aminoacylation
ATP binds to the amino acid once it has bound to the enzyme
Loses to phosphate groups to become AMP
AMP released
tRNA binds
What is the first step of translation?
A small ribosomal subunit binds to mRNA at start codon region
What attracts the large subunit?
Initiation factors
This completes the ribosome
The start codon occupies the P site
What is elongation dependent on?
The appropriate aminoacyl-tRNA binding to the codon in the A site of the ribosome
What happens when a stop codon is reached?
Polypeptide synthesis ends
Polypeptide released from tRNA
tRNA released from the ribosome
Ribosomal subunits separate
Describe the stages of termination
No anticodon on tRNA matches a stop codon
Nothing occupies the A site
Release factor binds to the stop codon
Peptidyl transferase is triggered releasing the polypeptide
Ribosomal subunits separate
How many ribosomes can be on a piece of mRNA at one time?
Many
Name three things that cause DNA mutation?
Substitution
Insertion
Deletion
Name the three kinds of mutation
Silent
Missense
Nonsense
