Lecture 17 - How do genetic differences lead to disease?

Question 1

Translation overview

Answer 1

Each tRNA carries an amino acid (Met, Glu, Ala, Leu) to be added to the polypeptide chain and has a different base sequence with same overall shape.

The codons within the coding
region of the mRNA specifies amino acid sequence of polypeptide chain.

Question 2

Mutation causing PKU

Answer 2

R408W mutation in PAH gene

Question 3

R408W mutation in PAH gene

Answer 3

Mutation causing PKU

Codon 408 for Arginine (R) mutated into a codon for Tryptophan (W) in Phenylalanine Hydroxylase

Question 4

Normal PAH
(incl function)

Answer 4

folds correctly

Functions to break down phenylalanine

Question 5

R408W mutation in PAH

protein results in

Answer 5

incorrect folding of protein

forms an aggregate that the cell degrades.
Hence no active PAH protein is made.

Question 6

Types of mutations and their consequences on proteins

Answer 6

Point mutation (change 1 letter)

Frameshift mutation (loss 1 letter)

Frameshift mutation (gain 1 letter)

Question 7

Pancreatic b cells

Answer 7

‘sense’ how much glucose is in blood

release insulin when glucose is high (feed state).

Question 8

Glucokinase

Answer 8

enzyme in glucose

determines how much glucose is broken down – therefore how much insulin is
produced.

Question 9

Hows insulin released?

Answer 9

Glucose from meal
In pancreatic b cells
Glucose
Glucokinase
Glucose 6 phosphate
Pyruvate
Insulin release
Insulin

Question 10

MODY2

Answer 10

Type of diabetes

Mutation in one glucokinase
gene (heterozygous)

persistent mild hyperglycaemia,

(maturity onset diabetes of
the young, type 2).

Decrease insulim
Increase Blood glucose

Question 11

Homozygous mutations of glucokinase

Answer 11

severe diabetes

very high blood glucose levels

Question 12

Genetic testing

Answer 12

Obtain some cells (e.g. mouth cells)

Isolate DNA

PCR amplify a specific gene sequence

Detect genetic difference of interest

Question 13

Mutation that causes MODY2

Answer 13

G changes to A
A*AGCUU

Lys (instead Glu), Leu

Question 14

What you need for PCR?

Answer 14

DNA from cells

DNA nucleotides

Primers (with sequences that can base pair with region of DNA that you want to amplify)

Taq DNA polymerase

Question 15

PCR 3 steps with chosen DNA from cells

Answer 15

1. Heat DNA to 95oC to separate DNA strands
2. Cool to ~60oC to anneal (base pair) a DNA primer
3. Heat DNA to 72oC to allow Taq DNA polymerase to copy the DNA

Question 16

Primer

Answer 16

short sequence (~20 nucleotides) that is chemically synthesized

Question 17

How many times do you repeat PCR cycle?

Answer 17

PCR cycle 3

Copying complete – repeat cycle (three steps 95oC, 60oC and 72oC)

Question 18

HindIII in MODY 2

Answer 18

restriction enzyme that specifically cuts the sequence AAGCTT

cuts to give 2 DNA fragments

Question 19

In Wild-type Sequence does HindIII cut sequence?

Answer 19

no cut

Question 20

Translation 3 steps

Answer 20

Initiation
Elongation
Termination