lectures 15-17

Question 1

what does transcriptional control do

Answer 1

Transcriptional control
determines when and in what
cells a gene is transcribed to
produce mRNA.

Question 2

how many genes are in a cell

Answer 2

~21,000 protein coding genes.

Question 3

whats the break down of gene numbers expressed in a cell

Answer 3

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

Question 4

what are transcription factor

Answer 4

Transcription factors nare protein that binding to a specific DNA sequence and control the rate of transcription (DNA to RNA).

Question 5

whats a promoter, whats it do, hows it work

Answer 5

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

Question 6

how do transcription factors control gene transcription?

Answer 6

This gene is only expressed when both activator transcription factors are present and the repressor is absent.

Question 7

whats the central dogma

Answer 7

two step process of transcription and translation where genes go into rna then protein

Question 8

whats the law of segregation

Answer 8

Law of segregation: When gametes form, alleles are separated so that each gamete carries only one allele for each gene.

Question 9

whats the law of independant assortment

Answer 9

Law of independent assortment: the segregation of alleles for one gene occurs independently to that of any other gene.

Question 10

whats the law of dominance

Answer 10

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.

Question 11

whats an exception to the law of independent assortment

Answer 11

The exception to this law is when two genes are close together on a chromosome -Genetic linkage.

Question 12

Depending on the point where the mutation occurs in the path the effects of the misfunctional products gives different effects.
why

Answer 12

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.

Question 13

PKU is an example of a disease that is affected by

Answer 13

envirnoment and genotype

Question 14

how is PKU affected by genotype

Answer 14

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

Question 15

how is PKU affected by environement

Answer 15

A low phenylalanine diet
prevents intellectual
disability and associated
problems in PKU
individuals

Question 16

why is PKU a problem

Answer 16

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

Question 17

describe translation stage 1, initation

Answer 17

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.

Question 18

describe translation stage 2, elongation

Answer 18

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

Question 19

describe termination of translation

Answer 19

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.

Question 20

in general terms, what does the mutation do to the protein

Answer 20

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.

Question 21

some mutations have no effect, why?

Answer 21

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.

Question 22

describe the 3 mutation types

Answer 22

Subsititution: a change in a single base
Deletion: deletion of a base
insertion: insertion of a base

Question 23

why are substitution mutations alright most of the time

Answer 23

substitution mutations are not always problematic because of this wobble.

Question 24

why are the insertion and deletion mutations problematic.

Answer 24

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

Question 25

whats the specific mutation causing PKU

Answer 25

R408W. codon 408 for argenine is mutated into a codon for tryptophan.

Question 26

what does the R408W mutation cause

Answer 26

R408W mutation in PAH protein results in incorrect folding, This incorrectly folded protein forms an aggregate that the cell degrades. Hence no active PAH protein is made. thus no phenylalanine is broken down.

Question 27

in terms of the biochem, what do the pancreatic beta cells do

Answer 27

Pancreatic b cells ‘sense’ how much glucose is in
the blood and release insulin when glucose is high (feed state).

Question 28

why is glucokinase important

Answer 28

Once we have had glucose it enters the cell. Glucokinase senses the amouint of glucose in the cell and therefore gluocse in the blood. Glucokinase then Phosphorylates glucose, then through a series the Glucose-6-phosphate goes to pyruvate. The pyruvate then alters the production and release of insulin.

Question 29

describe MODY2

Answer 29

MODY2, maturity onset diabetes of the young, type 2. this is a mutation in one of the glucokinase genes. it is a heterozygous disorder. So minor hyperglycemia occurs. This occurs as a dysfunctional gene means less glucokinase enzyme so less glucose-6-phosphate. This means less pyruvate so less insulin released, thus less glucose taken in by other cells, so more blood in glucose.

Question 30

what happens for people who are homozygous recessive for the dysfunctional glucokinase gene

Answer 30

Homozygous individuals – severe diabetes and very high blood glucose levels, as they have no activity of the enzyme, so no way of detecting blood glucose, thus no insulin response and thus severe diabeties.

Question 31

what is needed for PCR amplification

Answer 31

PCR needs nucleotides, primers and Taq DNA polymerase.

Question 32

describe first step of PCR

Answer 32

95 degrees is denaturation. the DNA is heated to separate the strands, giving 2 separate strands which we can use

Question 33

second step of PCR

Answer 33

Cool to ~60oC to anneal (base pair) a DNA primer

Question 34

what does the length of primer in PCR mean

Answer 34

These primers are short segements of DNA, about 20 nucleotides. 20 is sufficient as 2 different sequences of 20 nucleotides being the same in DNA is almost 0. if the primer doesn’t bind to the correct 20 nucleotides, then it doesn’t anneal properly and thus that segment isnt replicated. So the 20 long primer only anneals properly to its correct region.

Question 35

third step of PCR

Answer 35

Heat DNA to 72oC to allow Taq DNA polymerase to copy the DNA, using the free nucleotides in solution

Question 36

what enzyme can we use for the electrophoresis testing for MODY2

Answer 36

HindIII

Question 37

how does HindIII work

Answer 37

– a restriction enzyme that specifically cuts
the sequence AAGCTT, this specific sequence being in the mutated varient

Question 38

HindIII is what type of enzyme and where do these enzymes originate

Answer 38

Or we can use restriction enzymes. These restriction enzymes come from bacteria. Bacteria evolved these to cut Viral DNA in batceria to prevent replication of virus. So a specific mutated sequence is recognised by restriction enzymes. The restriction enzyme then cuts at that place making the dna segment unusable.

Question 39

how can we test for MODY2 genes

Answer 39

We then put these cut segments into gel electrophosis. the gel has current through it. the strands will start to move. This separates the strands by size, as the smaller strands move more easily in the gel.

Question 40

what does MODY2 look like in electrophoresis

Answer 40

it will have the one normal strand behind two further lines, one being further than other as their sizes are again different.

Question 41

what direction does DNA go in the electrophoresis

Answer 41

goes from negative to positive.