Genetic Control Of Protein Structure And Function Flashcards
(24 cards)
What is a codon?
The sequence of three bases on mRNA that codes for a single amino acid
Why is RNA required?
In order to transfer the DNA code from the nucleus into the cytoplasm where protein synthesis occurs.
mRNA is small enough to leave the nucleus and enter the cytoplasm
What are some of the main features of the genetic code?
It’s degenerate- most amino acids have more than one codon
Three codons don’t code for an amino acid - stop codons
There’s no overlap of codes
It’s a universal code - the same codon codes for the same amino acid in all organisms
What is a stop codon and why is it needed?
A codon that doesn’t code for an amino acid.
They mark the end of a polypeptide chain and so stop translation
tRNA
Clover shaped Single stranded One end extended which attaches the amino acids At the other end is the anticodon RNA pairs adenine to uracil
What is an anticodon?
A sequence of three organic bases on tRNA that is complimentary to a codon on an mRNA
mRNA
A long strand
Single helix
It is manufactured when DNA forms a mirror copy of part of one of its strands
Formed in the nucleus and leaves through nuclear pores
Acts as a template upon which proteins are built
What is transcription?
The process of making pre-mRNA using part of the DNA as a template
DNA helicase in the process of transcription
DNA helicase breaks the hydrogen bonds between bases of the DNA cussing the two strands to separate.
RNA polymerase in the process of transcription
The enzyme RNA polymerase moves along one of the DNA strands (the template strand) causing the nucleotides to join free, individual nucleotides
Stop codons in the process of transcription
When the RNA polymerase reaches a particular sequence of bases in the DNA that it recognises as a stop triplet code, it detaches and pre-mRNA is complete
The process of splicing
When the introns are removed so only the functional exons are left and they join together
Ribosomes in the process of translation
The ribosome becomes attached to the start codon at one end of the mRNA molecule
Move along the mRNA bringing two tRNA molecules at any one time
Where does translation occur?
In the cytoplasm
tRNA in the process of translation
tRNA has the complementary anticodon sequence and moves to the ribosome, pairing up with the sequence on the mRNA.
The tRNA carries an amino acid
Peptide bonds in the process of translation
An enzyme and ATP join the two amino acids on the tRNA by a peptide bond
What happens after the peptide bond is formed in translation?
The ribosome moves on to the next codon and so releases the first tRNA which is now free to collect another amino acid
When does translation stop?
Synthesis of a polypeptide continues until a ribosome reaches a stop codon
Nonsense mutation
Change in bases results in the formation of a stop codon
So the production of a polypeptide would stop prematurely
Mis sense mutation
Base change results in a different amino acid being coded for
The protein may be a different shape or not function properly
Silent mutation
The substitute base is different but still codes for the same amino acid as before
What causes mutations?
Spontaneous gene mutation during DNA replication
Basic mutation rate is increase by mutagenic agents:
High energy radiation that the disrupts DNA
Chemicals that alter the DNA structure
The role of Proto-oncogenes
Stimulate cell division
Growth factors attach to a receptor on the cell surface
Switch on the genes for DNA replication
Gene mutation can cause Proto-oncogenes to mutate into oncogenes:
- receptors can even permanently activated
- oncogenes may code for a growth factor that is produced in excessive amounts
Cells divide too rapidly developing a tumour
Role of tumour suppressor genes
Inhibit cell division
Maintain normal rates of division
If it mutates, it becomes inactive
Cell division therefore increases
