Gene Expression & Control (Transcription & Translation) Flashcards
What is the genetic code?
The sequence of bases on the mRNA which is transcribed from sections of DNA
What are the main features of the genetic code?
1) Each aa is coded for by a sequence of 3 bases known as a codon
2) Code is degenerate- some aa are coded for by more than one codon
3) 3 stop codons
4) Universal code that works for all organisms
What are the structural features of RNA?
1) Single stranded
2) Uracil
3) Ribose sugar
What is the structure of tRNA?
1) Single stranded chain folded into a clover leaf shape
2) Has an anticodon region which pairs to complementary codons on the mRNA
What are the stages of transcription?
1) DNA Helicase breaks the H bonds in a specific region of the DNA molecule
2) Free RNA nucleotides line up in a complementary fashion
3) RNA polymerase moves along the template strand causing the nucleotides to bind together
4) RNA polymerase reaches a stop codon and detaches itself leaving the pre-mRNA
5) pre-mRNA is spliced to remove introns and combine exon sections
6) mRNA formed leaves the nuclear pores into the cytoplasm to the ribosome.
What are the stages of translation?
1) mRNA arrives at ribosome, attaching at starting codon
2) A tRNA molecule with a complementary anti-codon binds with the mRNA whilst having an aa attached to it
3) Another tRNA molecule with a complementary anti-codon will bind to the next codon on mRNA whilst carrying another aa
4) Enzymes and ATP join the first 2 aa together
5) The ribosome moves along to codon 3 and links the aa’s on the 2nd and 3rd tRNA together
6) At the same time the 1st tRNA is released and free to collect another aa
7) Synthesis continues until the ribosome reaches a stop codon
What are the types of genetic mutations?
1) Addition
2) Deletion
3) Substitution
What are the 3 types of substitution mutations?
1) Non-sense- the substitution results in a stop codon being transcribed onto mRNA
2) Mis-sense- substitution results in a different aa being coded for
3) Silenced- there is no aa change (degenerate)
What happens in deletion mutations?
Frame shift, occurs when a nucleotide is lost.
What happens in addition mutations?
Frame shift, occurs when a nucleotide is added.
How do mutations arise?
1) Radiation
2) Chemicals
3) Genetic inheritance
4) Spontaneous
Which genes control the rate of cell division?
1) Tumour suppressor genes
2) Proto-oncogenes
How do tumour suppressor genes function?
Inhibit cell division
How do proto-oncogenes function?
1) Stimulate cell division
2) Mutations can turn proto-oncogenes into oncogenes
What are totipotent cells?
Cells that can differentiate into any cell in the body.
How are genes prevented from expressing themselves?
1) Prevent transcription thus the production of mRNA
2) Breaking down mRNA before translation
Where can totipotent be found in the mature adult?
1) Inner lining of the intestine
2) Bone marrow
3) Skin
What is required for transcription to start?
A transcriptional factor moves from the cytoplasm into the nucleus and binds to a specific region of DNA
How is transcription prevented?
An inhibitor molecule can bind to a transcription factor and block the site at which it would usually bind to of DNA
How is mRNA broken down before translation?
By siRNA
How does siRNA work?
1) An enzyme cuts the siRNA into 2 smaller sections
2) One of the smaller stands combines with an enzyme
3) siRNA enzyme complex binds to a complementary section of mRNA and cuts it into smaller sections which cannot be translated
