lectures 15-17 Flashcards
(41 cards)
what does transcriptional control do
Transcriptional control
determines when and in what
cells a gene is transcribed to
produce mRNA.
how many genes are in a cell
~21,000 protein coding genes.
whats the break down of gene numbers expressed in a cell
In any cell type about 11,000 to 17,000 genes are
expressed;
* 10,000 of these genes are expressed in all
cells (needed for basic cellular functions)
* About 1,000 to 2,000 are unique to a specific
cell type – these genes make, say, a brain
cell different from a heart cell
* The rest are expressed in some but not all
cell types
what are transcription factor
Transcription factors nare protein that binding to a specific DNA sequence and control the rate of transcription (DNA to RNA).
whats a promoter, whats it do, hows it work
Promoter: The DNA sequence at which transcription factors bind and recruit RNA Polymerase.
Determines if and how much a gene is transcribed.
Contains short sequences that Transcription factors bind to
how do transcription factors control gene transcription?
This gene is only expressed when both activator transcription factors are present and the repressor is absent.
whats the central dogma
two step process of transcription and translation where genes go into rna then protein
whats the law of segregation
Law of segregation: When gametes form, alleles are separated so that each gamete carries only one allele for each gene.
whats the law of independant assortment
Law of independent assortment: the segregation of alleles for one gene occurs independently to that of any other gene.
whats the law of dominance
Law of dominance: some alleles are dominant while others are recessive. An organism with at least one dominant allele will display the effect of the dominant allele.
whats an exception to the law of independent assortment
The exception to this law is when two genes are close together on a chromosome -Genetic linkage.
Depending on the point where the mutation occurs in the path the effects of the misfunctional products gives different effects.
why
This is because different products of the enzyme pathways are precursors for different products. So a build-up of one product will cause a lack of other products or a build-up of other things, leading to the different effects seen by different build-ups.
PKU is an example of a disease that is affected by
envirnoment and genotype
how is PKU affected by genotype
Phenylalanine is
transported across the
blood-brain barrier.
Genetic variation means
the efficiency of this
transporter differs
between individuals.
Individuals with less
efficient transporters have
lower levels of Phe in the
brain and less damage
how is PKU affected by environement
A low phenylalanine diet
prevents intellectual
disability and associated
problems in PKU
individuals
why is PKU a problem
because the PHE is normally made into tyrosine. as the tyrosine is used in other metabolic pathways but the build up in PHE causes a stop to these pathways, so we see the severity of all those symptoms
describe translation stage 1, initation
1: small ribosomal subunit binds to mRNA, the subunit then moves along till AUG start codon is found, this is where Met carrying tRNA comes and binds.
2: once AUG is reched the large ribosome subunit then binds completing the initiation complex.
describe translation stage 2, elongation
Elongation:
In this time the tRNA are randomly diffusing into the initiation complex, so incorrect tRNA then diffuse away. The elongation only starts when the correct tRNA randomly diffuses into the A site.
Once in A site the peptide bond forms between the P site chain and the A site Amino acid, as the Ribosome moves along placing the A site tRNA into the P site. The E site tRNA is then ejected. And process repeats
describe termination of translation
Ribosome reaches stop codon and a release factor, which is a PROTEIN, binds to A site. The release factor protein then hydrolyses the peptide bond to the tRNA which releases the amino acid chain. The subunits of the ribosome then detach.
in general terms, what does the mutation do to the protein
A mutation can result in incorrectly folded proteins. These incorrectly folded proteins then form aggregates which are broken down within the cell, this then means theres no protein in the cell and thus a pathway cannot occur.
some mutations have no effect, why?
this is due to wobble. This refers to how the genetic code is redundant, so a change in the codon, depending on the location of the change, may not affect the amino acid coded for.
describe the 3 mutation types
Subsititution: a change in a single base
Deletion: deletion of a base
insertion: insertion of a base
why are substitution mutations alright most of the time
substitution mutations are not always problematic because of this wobble.
why are the insertion and deletion mutations problematic.
because they result in a reading frame shift depending on nature and location. These frameshifts likely generate a premature stop codon within 5-6 codons of the mutation. making completely dysfunctional proteins
