6.1 - B - Gene Mutations

Question 1

What is a mutation?

Answer 1

A random change to the genetic material

Question 2

What is a gene mutation?

Answer 2

A change in the base sequence of DNA

Question 3

What is a mutagen?

List some examples

Answer 3

A physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level.
Tar in tobacco smoke,
Ionising radiation eg: UV light, X-rays and gamma rays.

Question 4

Which types of mutation are/aren’t associated passed onto offspring?

Answer 4

Mutations associated with mitotic division - not passed into offspring.
Mutations associated with meiosis and gamete formation - may be inherited by offspring.

Question 5

List and define the 3 types of mutation

Answer 5

Substitution (point mutation) - when one base pair replaces another.
Insertion - when one or more nucleotides are inserted into a length of DNA.
Deletion - when one or more nucleotides are deleted from a length of DNA.

Question 6

What do insertion and deletion mutations cause?

Define this term

Answer 6

Frameshifts - when the base pairs move left (deletion) or right (insertion).

Question 7

List and explain the 3 types of substitution mutations

Answer 7

Silent - when a substitution occurs but the triplet code still codes for the same amino acid - it doesn’t change amino acid.
Missense - when a substitution occurs that leads to a change in the amino acid sequence.
Nonsense - when a substitution occurs that turns the amino acid sequence into a termination (stop) sequence.

Question 8

What is the name for both insertions and deletions?

Answer 8

Indel mutations

Question 9

In what way can indel mutations not cause a frameshift?

Answer 9

When base pairs are inserted/deleted in multiples of 3, causing there to only be an addition/loss of an amino acid(s).

Question 10

What does E. coli normally do?

What type of microorganism is it?

Answer 10

It normally metabolises glucose as respiratory substrate.

Bacterium.

Question 11

What 2 enzymes does lactose produce?

Under what conditions does this occur?

Answer 11

If glucose is absent but lactose is present, lactose induces the production of 2 enzymes:
Lactose permeate - which allows lactose to enter the bacterial cell (coded for by lac Y).
Beta-galactosidase - which hydrolysed lactose to glucose and galactose (coded for by lac Z).

Question 12

What is an operon?

Answer 12

A length of DNA made out of structural and control (P and Lac O) genes that function together. It’s approx 6,000 base pairs long, containing an operator region lacO next to the structural genes lacZ and lacY that code for the enzymes beta-galactosidase and lactose permease respectively.

Question 13

Where does RNA polymerase bind on an operon?
What type of biological molecule is it?
What does it do there?

Answer 13

The promoter region, P.
Enzyme.
Begins transcription of the structural genes lacZ and lacY.

Question 14

What are the control sites of the lac operon?

Answer 14

The operator region and the promoter region

Question 15

What do structural genes do?

Answer 15

Code for proteins

Question 16

What do regulatory genes do?

Answer 16

Control the expression of structural genes by switching them on/off - this makes the repressor protein/transcription factors (I) (not part of operon)

Question 17

What is the operator region?

Answer 17

The region next to structural genes that the repressor binds to lacO

Question 18

What is the promoter region?

Answer 18

The binding site for RNA polymerase (P).

Question 19

What do repressor proteins do?

Answer 19

Bind to the operator region, preventing RNA polymerase from binding to the promoter region, therefore preventing transcription.

Question 20

Where is the regulatory gene found?

What does it do?

Answer 20

It’s found a small distance away from the operon.
Aka: I, it codes for a repressor protein (LacI). When this happens,the repressor protein produced binds to the operator, preventing RNA polymerase from binding to the promoter region.

Question 21

What happens when lactose isn’t present at the operon?

What happens when lactose is present at the operon?

Answer 21

The lactose binds to the repressor gene made at the regulatory gene, creating an induce-repressor complex that cannot bind to the promoter region, allowing RNA polymerase to bind, which causes enzymes to be synthesised.
With no lactose to stop the repressor gene binding to the regulatory gene, the RNA polymerase can’t bind to it, meaning the enzymes aren’t synthesised.

Question 22

What is a transcription factor?

Answer 22

Protein or short non-coding RNA that can combine with a specific site on a length of DNA and inhibit or activate transcription of the gene. They slide along a part of the DNA molecule, seeking and binding to their specific promoter regions. They may then aid or inhibit the attachment of RNA polymerase to the DNA, and activate or suppress transcription of the gene.

Question 23

What is an exon?

Answer 23

The coding, or expressed region of DNA

Question 24

What is an intron?

Answer 24

The non-coding region of DNA

Question 25

Why are transcription factors important?

Answer 25

They are essential for the regulation of gene expression in eukaryotes

Question 26

What do introns do?

Answer 26

Separate exons

Question 27

Define morphogenesis

Answer 27

Anatomic development

Question 28

What do homeotic genes do?

Answer 28

They control morphogenesis of organisms

Question 29

What is a homeobox gene?

Answer 29

A homeobox gene is a homeotic gene that contains a 180 base pair homeobox sequence that codes for a 60 amino‐acid sequence called homeodomain sequence within a protein. These proteins are transcription factors.
Homeobox genes are master genes and regulatory genes ‐ they switch on/off many other genes.

Question 30

Describe and explain the homeodomain’s shape

Answer 30

The homeodomain sequence’s shape is specific to part of the enhancer region on DNA so it binds to the DNA to initiate/stop transcription to switch genes on or off. This controls the development of the body plan.

Question 31

What is important about homeobox genes?

Answer 31

They are highly conserved and very similar. They are found in all plant, animal and fungal species from a common ancestor throughout evolutionary history. This is to prevent mutations which would most likely cause death.

Question 32

What are hox genes?

What do they do?

Answer 32

A type of homeotic genes only found in animals.

They control the formation of anatomical features in the correct locations of the body plan.

Question 33

What do hox genes do during embryonic development?

Answer 33

In embryonic development Hox genes are expressed one by one along the anterior‐posterior axis which causes the development of particular body parts in this particular order.

Question 34

How many hox gene clusters do tetrapods have?

Answer 34

4

Question 35

Suggest 5 characteristics scientists look for in the animals they use in their experiments

Answer 35

Cheap to buy and keep,
Reproduce quickly,
Small,
Large cells,
Readily available.

Question 36

Suggest why information learnt from these model organisms can be applied to humans

Answer 36

All in the same kingdom,
Have shared ancestors,
Similar cells,
Have shared genes and similar embryonic development/similar homeobox/Hox genes.

Question 37

Explain the link between: homeotic genes, homeobox genes, homeobox sequence, homeodomain sequence and hox genes

Answer 37

Homeotic genes control anatomical development of organisms.
Homeobox genes are a type of homeotic gene that contain a homeobox sequence (180 bp long) that code for a homeodomain sequence (a section of a transcription factor that binds to DNA to control the development of the body plan).
Hox genes are a type of homeobox gene that controls the development of the correct body parts in the right place in animals.

Question 38

Define apoptosis

Answer 38

Programmed cell death

Question 39

How are hox genes regulated?

Answer 39

They’re regulated by other genes called gap genes and pair-rule genes. In turn, these genes are regulated by maternally supplied mRNA from the egg cytoplasm.

Question 40

How is apoptosis different from cell death due to trauma?

Answer 40

Cell death due to trauma involves hydrolytic enzymes

Question 41

List the sequence of events during apoptosis

Answer 41

Enzymes break down the cell cytoskeleton.
The cytoplasm becomes dense with tightly packed organelles.
The cell surface membrane changes and small protrusions called blebs form.
Chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments.
The cell breaks into vesicles that are ingested by phagocytic cells, so that cell debris does not damage any other cells or tissues. The whole process happens quickly.

Question 42

How is apoptosis controlled?

Answer 42

Cell signals such as cytokines from cells of the immune system, hormones, growth factors and nitric oxide. Nitric oxide can induce apoptosis by making the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient. Proteins are released into the cytoplasm where they bind to apoptosis inhibitor proteins, allowing apoptosis to occur.

Question 43

Explain the steps in the post-translational level of gene regulation

Answer 43

A signalling molecule binds to receptor on the plasma membrane of the target cell.
This activates a transmembrane protein which then activates a G protein.
The G-protein then activates adenyl cyclase enzymes.
These enzymes catalyse the formation of many molecules of cyclic AMP from ATP.
cAMP activates PKA (protein kinase A).
PKA catalysts phosphorylation of various proteins, hydrolysing ATP in the process. The phosphorylation activates many enzymes in the cytoplasm.
PKA may phosphorylate another protein.
This then enters the nucleus and acts as a transcription factor.