6.1 Gene Mutations

Question 1

What are the two types of DNA mutation

Answer 1

• Point mutation is where one base pair replaces another

- Indel mutation is where one or more nucleotides are inserted/ deleted from DNA possibly causing Frameshift

Question 2

What are the three types of point mutation

Answer 2

Missense

Nonsense

Silent

Question 3

What is a silent mutation?

Answer 3

Silent mutation is when a change is base pair causes does not result in change of amino acid coded.

This therefore causes no changes to the protein structure, (primary, secondary, tertiary)

This is an example of the “redundancy” and “degenerate “ nature of DNA as more than one base triplet code can code for the same amino acid.

Question 4

What is missense mutation and what genetic disorder does it cause?

Answer 4

Missense mutation is when the base pair change causes a change in amino acid sequence.

This causes changes in primary structure and therefore registry structure. Changes at tertiary structure alter shape preventing protein from carrying out function.

Sickle cell anaemia is caused by mutation of beta-polypeptide chains in haemoglobin. A valine amino acid is added instead of glutamic acid. This causes the deoxygenated haemoglobin to crystallise in erythrocytes blocking capillaries and depriving tissues of oxygen.

Question 5

What is nonsense mutation and what does it cause?

Answer 5

Mutation which causes base triplet to change to a termination triplet.

Creates truncated protein therefore is has an abnormal tertiary structure causes it to be degenerated within cell.

This causes Duchenne muscular dystrophy.

Question 6

What is insertion deletion mutations and what do they cause?

Answer 6

Indel mutation is when there is insertion or deletion of base pairs not in pairs of three.

As DNA is non overlapping and read in groups of three it affects all subsequent base pairs. This may result in a frameshift.

Causing changes to tertiary structure.

Thalassamia is a haemoglobin disorder caused by this.

Question 7

What is an expanding triple nucleotide repeat and what disease does it cause?

Answer 7

Some genes have a base triplet which repeats causing a triple nucleotide repeat.

The number of triple nucleotide repeats increase at meosis and every generation.

When the expanding triple nucleotide repeat goes above a critical number this causes Huntington disease.

Question 8

What is the exon?

Answer 8

Coding or expressed region of DNA.

Question 9

What is an intron?

Answer 9

Non coding regions of DNA.

Question 10

What’s the operon?

Answer 10

A group of genes that act as a single transcription factor first identified in prokaryotic cells.

Question 11

What is the transcription factor?

Answer 11

Protein or non coding RNA which attaches to DNA activating or inhibiting transcription of gene .

Question 12

What is the effect of lactose permease?

Answer 12

Allows more lactose to enter the bacterial cell.

Question 13

What’s the effect of beta galactosidase?

Answer 13

Hydrolyses lactose into glucose and galactose

Question 14

What part of the lac operon codes for lactose permease?

Answer 14

lacY

Question 15

What part of the lac operon codes for beta galactosidase?

Answer 15

LacZ

Question 16

How is gene expression of lactose permease and beta galactosidase switched off?

Answer 16

Production of protein repressor molecules produced by the regulatory gene (I).

These bind to promoter region preventing binding of RNA polymerase therefore transcription of genes do not occur.

Question 17

What causes gene expression in lac operon?

Answer 17

When there is no glucose lactose binds to repressor protein molecules altering their shape.

They can no longer bind to the promoter region.

This allows RNA polymerase to bind to promoter region and carry out transcription of genes.

Question 18

Explain post transcriptional gene regulation.

Answer 18

Gene of DNA transcribed including introns and exons.

This is called primary mRNA. Primary mRNA has RNA introns removed.

Remaining RNA exons joined together.

Endonuclease enzyme used in process of splicing and editing.

Question 19

What happens to the introns that have been removed ?

Answer 19

Introns removed can encode for proteins

Or become short non coding RNA regulating gene expression.

Depending on how spliced DNA can encode for more then one protein

Question 20

Explain post translational gene expression.

Answer 20

1) signalling molecule such as glucagon binds to surface membrane protein.
2) this activates the transmembrane protein activating the G protein.
3) the G protein activates adenyl Cyclase.
4) adenyl cyclase produces cAMP by from ATP molecules.
5) cAMP actives PKA (protein kinase A)
6) this phosphorylation of proteins causes activation enzymes in cytoplasm.
7) PKA may phosphorylase another protein (CERB, cAMP response element binding)
8) this then enters the nucleus acting as a transcription factor.

Question 21

Define apoptosis.

Answer 21

Programmed cell death.

Question 22

Define conserved.

Answer 22

Remains in descendent species throughout evolutionary history.

Question 23

Define homeobox sequence.

Answer 23

It is a sequence of 180 base pairs (excluding introns) found within the genes responsible for anatomical development in animals, plants and fungi.

Question 24

Define hox genes.

Answer 24

They are a subset of the homeobox sequence which are only found in animals. They are responsible for development of anatomical features in the correct locations of the body plan.

Question 25

What is a homeodomain sequence?

Answer 25

It is a 60-amino acid sequence within a protein.

It can take a particular shape and bind to DNA regulating expression of adjacent genes.

It has H-T-H shape which is two alpha helices connected by one T turn.

It is able to recognise the TAAT sequence of an enhancer region of a gene to be transcribed.

Question 26

What is the process of apoptosis?

Answer 26

1) Enzymes break down cytoskeleton.
2) Cytoplasm becomes dense with tightly packed organelles.
3) Changes in surface membrane occur causing protrusions called blebs to form.
4) Chromatin condenses causing nuclear envelope to break and DNA breaks into fragments.
5) Cell breaks into vesicles which are digested by phagocytic cells to avoid any damage to other cells.

Question 27

What molecules can control apoptosis?

Answer 27

Cytokines, growth factors, hormones and nitric oxide.

Question 28

How does nitric oxide control apoptosis?

Answer 28

Nitric oxide makes the inner membrane of the mitochondria more permeable to hydrogen ions dissipating the proton gradient.

This causes proteins to enter the cytoplasm and attach to apoptosis inhibitor proteins, so that apoptosis can occur.

Question 29

Examples of apoptosis?

Answer 29

Causes digits to separate.

Removes ineffective and harmful t lymphocytes from the immune system

Question 30

What happens if too much or not enough apoptosis occurs?

Answer 30

Not enough -> Tumours

Too much -> Cell lose and degeneration