Lecture 15

Question 1

What must happen to the tRNA before it goes to translation?

Answer 1

before translation iccurs need to charge up the tRNA-add an amino acid to tRNA then calle aminoacyl-tRNA

Question 2

What are the bases on the tRNA called?

Answer 2

anticodon (3 bases)

Question 3

How is the tRNA charged up?

Answer 3

1. 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

Question 4

How is initiation in translation started?

Answer 4

-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

Question 5

Describe initiation in translation.

Answer 5

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

Question 6

Describe elongation in translation?

Answer 6

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

Question 7

How is translation terminated?

Answer 7

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

Question 8

Which site does the tRNA go to first?

Answer 8

it’s only the fMet that goes in to the P site first all the other
go into the A site first

Question 9

What is proteome?

Answer 9

part of the genome that will produce protein

Question 10

What are Genome,Proteome,Transcriptome,Metabalome,Epigenome?

Answer 10

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

Question 11

What is a mutation?

Answer 11

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

Question 12

What is somatic and germ line mutation?

Answer 12

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

Question 13

What is a spontaneous and induced mutation?

Answer 13

spontaneous= just happens,lot of mutations like that (Duschenne etc. can just appear in a family with no history)

induced= caused by the environment

Question 14

What are mutagens?

Answer 14

• factors causing induced mutations
• can even predict what type of mutation

Question 15

What is a chromosomal mutation?

Answer 15

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

Question 16

Describe an example of chromosomal mutation in chromosomes 22 and 9:

Answer 16

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

Question 17

What are the 4 classes of mutations at the DNA level?

Answer 17

Single base substitution

Deletion of bases

Insertion of bases

Triplet Repeat mutations

Question 18

Where in the genome can mutations occur?

Answer 18

-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!

Question 19

What are the three types of base substitution mutations and what do they mean?

Answer 19

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

Question 20

What is a silent base substitution mutation?

Answer 20

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!

Question 21

What is a missense base substitution mutation?

Answer 21

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

Question 22

What is a nonsense base substitution mutation?

Answer 22

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

Question 23

What is frameshift?

Answer 23

• 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!

Question 24

What is a deletion or insertion mutation?

Answer 24

• Loss or addition of one or more nucleotides
• frameshift- can add or subtract multiple bases

Question 25

What is an in-frame deletion mutation?

Answer 25

-less serious if in multiples of threes

-dystrophin- the biggest gene
if deletion in multiples of threes, just miss out bit but in Duchenne muscular dystrophy- the if some are deleted= get only mild form of the dystrophy

less serious dystrophy if multiples of threes deleted= becker
deletion not in multiples of threes= duchenne

Question 26

What is cystic fibrosis?

Answer 26

-Defect in Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein - chloride ion transport

Accumulation of Cl- ions leads to the accumulation of sticky mucus lining ducts of exocrine glands and lung tissue

-mutation in a gene coding for protein channel- conductance regulator= Cl ion transporter

part of it embedded in membrane, cytoplasm, outside
-with mutation depends on what changed 1900 ways of changing, some more important,

clinical symptoms:

Prenatal blockage of pancreatic ducts and reproductive ducts (vas deferens may be absent)
Postnatal accumulation of mucus in lungs
Poor digestion

Question 27

How is cystic fibrosis inherited?

Answer 27

-Incidence 1 in 2500 caucasians 1 in 25 carriers

-Autosomal recessive (chromosome 7-usually unaffected parent have affected child (1/4 prob if both carriers))

• CFTR gene was cloned in 1989 • >1900 mutations identified in this gene

delta F508 mutation accounts for 70% of mutations in caucasian
populations • [delta]F508 exon 11, deletion of 3 bp between 1652 and 1655 –>
deletion of Phe at 508

• delta F508-most common in Australia, delta= deletion,F-Phenylanine,508-position of the amino acid in the CFTR gene
• F508 is in an exon, get deletion of three bases of DNA, delete Phe

Question 28

How do you discovere cystic fibrosis neonatally?

Answer 28

Genetic diagnosis PCR region of exon 10 with delta F508 mutation Detect deletion on gel (95 bp versus 98 bp)

-polyacramide PCR can separate single base sequences

95-homozygous for the mutation
98-homozygous for normal

Question 29

What does haemoglobin consist of?

Answer 29

98% of haemoglobin consist of 2 alpha and 2 beta chains, 2% 2 alpha chains and 2 delta chains
in utero- have 2 alpha 2 gamma-that’s what they try to do, keep that one not transfer into the beta gene

-mostly have HBA- alpha globin

some HBA2- delta globin

Question 30

What is the difference between sickle cell anaemia and Beta Thalassemia?

Answer 30

beta thalassemia versus sickle cell haemophilia-
sickle=misshapen structure of red blood cell= structure
thalassemia- influence on amount of red blood cells produced= quantity

(same gene as sickle cell anaemia – difference is Thalassaemia is related to quantity of beta globin whereas sickle cell anaemia related to structurally abnormal beta globin

Question 31

What is Beta Thalassemia?

Answer 31

missing or reduced beta chains in haemoglobin, ranges in symptomes from severe anaemia to asymptomatic

homozygote for mutation = Thalassaemia major
• heterozygote = Thalassaemia minor
• mutation results in reduced or absent “ globin (“+ or “o)
• severe transfusion dependent anaemia • untreated child dies by about age 5yrs

-heterozygous- can pick up in blood smear- usually no effect, carriers

homozygous= dependant on blood transfusions or die by the age 5
bones in skull-expanding-making more RBC so bone marrow enlarged!
enlarged spleen- responsible for processing of defective RBCs so overload= bigger

Question 32

How is Beta Thalassemia treated?

Answer 32

treatment- blood transfusion- every 4-6 weeks
-get lot of iron has to get rid of it!
now oral drug for removing iron but some people side effects, otherwise pump
-Cyprus- 1 in 7 people have the carrier gene

Question 33

What chromosome is Beta Thalassemia on? How is it inherited?

Answer 33

• Beta Globin gene chromosome 11
• Autosomal recessive Chromosome 11 beta globin gene Multiple alleles

Question 34

What are the possible mutants for Beta Thalassemia?

Answer 34

Missense mutants – changes amino acid

Nonsense mutants introduces stop codon (beta 0)

Frameshift mutants(beta 0)

splicing mutants-instad of cutting at exactly the junction, cuts a bit further down

=there are lot of types of betta thalassemia- above= examples of how it happens in some

Question 35

What are the clinical sympotms and the mode of inheritance of Huntigton’s?

Answer 35

Autosomal dominant 4p16.3 Age of onset usually between 35 - 45yrs (4 - 70yrs)

-dominant! gain of function

death from onset- 15 years

Clinical symptoms:

movement disorders

dementia

psychiatric disturbances

weight loss

difficulty with speech and swallowing

Question 36

What causes Huntington’s?

Answer 36

Gene cloned in 1993 • Protein huntingtin
• Mutation is a triplet repeat (trinucleotide repeat) CAG in the translated region of the gene” polyglutamine tract in protein
• Progressive neurological disease with late onset (takes time to accumulate toxic substance)
• gain of function mutation

-within coding sequence have CAG

-normal no of repeat up to 20 then have GGGG to have 20 glutamines normal
-in huntigton’s too many GGGGGG next to each other, it is toxic, build it up and late onset than
here you’re gaining function of protein not losing

Question 37

What determines when you get Huntington’s?

Answer 37

-the number of repeats

Defect in gene is a triplet (3 base) repeat (CAG) <35 repeats normal (most 17-20)
• 27-35 rare but unstable when transmitted via a male • 36 - 41 indeterminate (reduced penetrance) • 40-50 most adult cases • >50 generally juvenile onset
• Earlier onset and more severe if inherited from father

-up to 40- depends if you get it, above you get it

above 50 earlier onset and faster progress