Lecture 17: HOW DO GENETIC DIFFERENCES LEAD TO DISEASE?

Question 1

What do the codons within the coding region of the mRNA do?

Answer 1

Specify the amino acid sequence of the polypeptide chain

Question 2

What does each tRNA have?

Answer 2

A different base sequence but about the same overall shape

Question 3

What does each tRNA carry?

Answer 3

An amino acid to be added to the polypeptide chain

Question 4

What is the first step of initiation?

Answer 4

Small ribosomal subunit binds to mRNA

Question 5

What happens after the small ribosomal subunit binds to mRNA?

Answer 5

Large ribosomal subunit completes the initiation complex

Question 6

What is the first step of elongation?

Answer 6

Codon recognition

Question 7

What happens after codon recognition?

Answer 7

Peptide bond formation

Question 8

What happens after peptide bond formation?

Answer 8

Translocation

Question 9

What is the first step of termination?

Answer 9

Ribosome reaches a stop codon on mRNA

Question 10

What are the stop codons?

Answer 10

UAG, UAA and UGA

Question 11

What happens after the ribosome reaches a stop codon on mRNA?

Answer 11

Release factor promotes hydrolysis and release of the polypeptide

Question 12

What happens after the release factor promotes hydrolysis and release of the polypeptide?

Answer 12

Ribosomal subunits and the components dissociate

Question 13

What is the mutated enzyme which causes PKU?

Answer 13

Phenylalanine Hydroxylase

Question 14

What is the mutation causing PKU?

Answer 14

In the coding strand, an A changes to a T meaning an A changes to a U in the mRNA and amino acids change from arginine to tryptophan

Question 15

What is the PKU mutation (short form)?

Answer 15

R408W mutation in PAH gene

Question 16

What does R408W mean?

Answer 16

Codon 408 for arginine (R) is mutated into a codon for tryptophan (W)

Question 17

What does the R408W mutation in PAH protein result in?

Answer 17

Incorrect folding

Question 18

What does the incorrectly folded PAH protein do?

Answer 18

Forms an aggregate that enzymes in the cell degrade

Question 19

What does normal PAH do?

Answer 19

Folds correctly and functions to break down phenylalanine

Question 20

Why will some mutations have no effect?

Answer 20

Because some base changes will result in the same amino acid being produced

Question 21

What is a substitution mutation?

Answer 21

A point mutation where there is a change in one letter

Question 22

What will a substitution mutation do?

Answer 22

May affect the protein slightly if the substitution results in a change of the amino acid

Question 23

What is a deletion mutation?

Answer 23

Frameshift mutation where there is a loss of one letter

Question 24

What will a deletion mutation do?

Answer 24

The amino acids following the deletion will be different and so will be consequences

Question 25

What is an insertion mutation?

Answer 25

Frameshift mutation where there is gain of one letter

Question 26

What will an insertion mutation do?

Answer 26

The amino acids following the insertion will be different and so will be consequences

Question 27

What codon being introduced will have a large effect?

Answer 27

Stop codon

Question 28

What do pancreatic beta cells do?

Answer 28

Sense how much glucose is in the blood and release insulin when glucose is high (fed state)

Question 29

What is a key enzyme in glucose sensing?

Answer 29

Glucokinase

Question 30

What does glucokinase do?

Answer 30

It determines how much glucose is broken down and therefore how much insulin is produced

Question 31

What does a mutation in one glucokinase gene (heterozygous) result in?

Answer 31

Persistent mild hyperglycaemia, a type of diabetes called MODY2 (maturity onset diabetes of the young, type 2)

Question 32

What is the MODY2 mutation?

Answer 32

Dominant so presence of the wild type can't mask the effect of the mutant

Question 33

What do homozygous MODY2 individuals have?

Answer 33

Sever diabetes and very high blood glucose levels

Question 34

What is the mutation that causes MODY2?

Answer 34

Base changes from G to A so amino acid changes from glutamate to lysine

Question 35

What is the first part needed for genetic testing?

Answer 35

Obtain some cells (such as form the mouth)

Question 36

What happens after some cells are obtained?

Answer 36

Isolate DNA

Question 37

What happens after isolate DNA?

Answer 37

PCR amplify a specific gene sequence

Question 38

What happens after PCR amplify a specific gene sequence?

Answer 38

Detect genetic difference of interest

Question 39

What goes in the test tube for PCR?

Answer 39

DNA from cells, DNA nucleotides, primers with sequences that can base pair with the region of DNA that you want to amplify and Taq DNA polymerase

Question 40

What is the first step of PCR?

Answer 40

Heat DNA to 95 degrees to break the hydrogen bonds and separate DNA

Question 41

What is the second step of PCR?

Answer 41

Cool to approximately 60 degrees to anneal (base pair) a DNA primer (a short sequence approximately 20 nucleotides that is chemically synthesised)

Question 42

What is the third step of PCR?

Answer 42

Heat DNA to 72 degrees to allow Taq DNA polymerase to copy the DNA (add complementary nucleotides)

Question 43

What happens when the PCR cycle is repeated?

Answer 43

It doubles the amount of DNA present each time

Question 44

What is used to detect sequence differences?

Answer 44

Enzymes

Question 45

What is HIndlll?

Answer 45

A restriction enzyme that specifically cuts the sequence AAGCTT to recognise the mutation

Question 46

What does Hindlll cut?

Answer 46

The mutated version to give two fragments

Question 47

What does Hindlll not cut?

Answer 47

The wild type

Question 48

What does the wild type show up as on gel electrophoresis?

Answer 48

One band

Question 49

What does the MODY2 show up as on gel electrophoresis?

Answer 49

Fragments