Lecture 15 Flashcards
What must happen to the tRNA before it goes to translation?
before translation iccurs need to charge up the tRNA-add an amino acid to tRNA then calle aminoacyl-tRNA
What are the bases on the tRNA called?
anticodon (3 bases)
How is the tRNA charged up?
- A specific amino acid and ATP bind to the aminoacyl-tRNA synthetase 2. AMP is covalently bound to the amino acid thereby activating it and pyrophosphate is released 3.The correct tRNA binds to the synthetase. The amino acid is covalently attached to the tRNA, AMP is released 4.The charged tRNA is released

How is initiation in translation started?
-need to find the start of the gene to start translation, some transcribed bits don’t go into translation so have to find the start, recognition sequence on the RNA telling the ribosome where to bind

Describe initiation in translation.
first binding is the small subunit of the ribosome (made up of rRNA and protein), the binding site is upstream of the start of the RNA that’s going to be translated into the polypeptide,
-when recognition sequenc eon RNA then small subunit moves,know that AUG is close by, first tRNA has anticodon UAC, in prokaryotes special Methionine
then large subunit binds, create grooves with the small important for translation
initiation: recognition of binding site, translocation of small subunit to AUG, then finished

Describe elongation in translation?
fMet- the first tRNA in prokaryotes
the bases are read 5’- 3’
peptidyl site (orange) - P site, the other A site (amino acyl)
-trial and error with codon anticodon match, tRNA tries to get a match, wobbles and if not leaves

How is translation terminated?
UGA- one of the stop codons, no anticodon for this one, attracts a protein called the release factor= stop codon intiates the positioning of the relase factor on the ribosome then everything dissociates
-polypeptide leaves, mRNA leaves- can be translated again
ribosomal subunits dissociate and the release factor is recycled so can be used again
Which site does the tRNA go to first?
it’s only the fMet that goes in to the P site first all the other
go into the A site first
What is proteome?
part of the genome that will produce protein
What are Genome,Proteome,Transcriptome,Metabalome,Epigenome?
Genome – DNA sequence Proteome – proteins Transcriptome – expressed DNA sequences Metabalome –pathways in cell meatbolism Epigenome – epigenetic state of a cell,part of DNA that can be methylated, involved in epigenetics
What is a mutation?
Mutations are any alteration in DNA sequence from a single base pair substitution, deletion, insertion or several base pairs or a major alteration in the structure of a chromosome
many genes more than two alleles, arisen by mutations
mutations can be gross, but can also be on one base
What is somatic and germ line mutation?
also can be classified as- somatic- occuring in somatic tissue (cells), this will die with the individual, not passed on to the next generation
germ line- consequences for next generation
What is a spontaneous and induced mutation?
spontaneous= just happens,lot of mutations like that (Duschenne etc. can just appear in a family with no history)
induced= caused by the environment
What are mutagens?
- factors causing induced mutations
- can even predict what type of mutation
What is a chromosomal mutation?
gross mutations – deletions translocations involve many genes if visible
under a light microscope - 4Mb approx 200 -300 genes
-can have chromosomal mutations- if you can see that it lost a piece, swapped a piece, dealing with at least 200 genes= gross mutation
Describe an example of chromosomal mutation in chromosomes 22 and 9:
gross mutation, swapping of bit of chromosome 9 to chromosome 22
2 genes c abl-oncogene and bcr = if activated= cancer
when swapped this c abl next to bcr so not kept in check anymore-made hybrid gene from the proto oncogene that produced compound interfered with cell replication leading to CML, translocation caused the leukamia-example of translocation gross mutation

What are the 4 classes of mutations at the DNA level?
Single base substitution
Deletion of bases
Insertion of bases
Triplet Repeat mutations
Where in the genome can mutations occur?
-in coding and non- coding regions of the genome Coding mutations can affect the gene product Non-coding mutations can affect the expression of the gene
-mutations are changes in DNA sequence whereas epigenetic event affetcs only teh expression of the genes
non coding regions can be very important= regulatory function
so even if mutation there= has an effect!
What are the three types of base substitution mutations and what do they mean?
Silent:No change in the gene product,no change in the amino acid(eventough there is a change in the base)
Missense: Amino acid substitution in the gene product
nonsense: Premature termination of translation (chain termination) change the codon to the stop codon= premature stop at translation
What is a silent base substitution mutation?
A change in the third base of a codon may not alter the expression or the functioning of a gene or a gene product – because of the of the code
mutations happen all the time
wobble- first two letter most important plus more codons for one amino acid
-can switch the third base= silent!
What is a missense base substitution mutation?
A change in the nucleotide sequence that converts a codon for one amino acid into a codon for a different amino acid
-get different amino acid due to difference in one base
- the effect of that will depend on how important that amino acid was for the protein, if vital in protein folding and function= can have profound effect
- if not that important or similar in structure to the original= not that bif difference
e.g. : sickle cell anaemia
What is a nonsense base substitution mutation?
A change in the nucleotide sequence that converts a codon for an amino acid into a termination codon
-the base change- what would have been an amino acid is a stop codon, depending how far from the end how serious it is
What is frameshift?
- a base is added or deleted from the DNA sequence
- the code is out of phase after the mutation
- therefore almost all the amino acids are altered downstream
- this is where you add or subtract base
- often serious, unless in multiples of three losing the bases
- shift the reading frame, has to be in threes!
What is a deletion or insertion mutation?
- Loss or addition of one or more nucleotides
- frameshift- can add or subtract multiple bases
