Cellular Control

Question 1

What is a gene mutation?

Answer 1

Change in base sequence of dna during dna replication (s phase of interphase)

Question 2

When are gene mutations more likely to occur?

Answer 2

When exposed to mutagenic agents.
Eg, high energy radiation (UV light) , ionising radiation (gamma and x rays) and deaminating chemicals (carcinogens like mustard gas and cigarette smoke)

Question 3

What is deletion mutation?

Answer 3

One base is removed, not coded for resulting in frameshift. This changes all subsequent codons and so the polypeptide chain and overall 3d structure of the protein. Harmful or beneficial

Question 4

What is substitution mutation?

Answer 4

One base is swapped for another. So one codon would be different. Can be neutral or harmful. May code for different AA or the same one due to degenerate nature of genetic code.

Question 5

What is a silent mutation?

Answer 5

Type of substitution mutation where new codon still codes for same AA. So no overall effect on AA sequence and polypeptide chain

Question 6

What is an insertion mutation?

Answer 6

A new base is randomly inserted into the DNA sequence. Changes subsequent AA codons = frameshift. Affects ability of polypeptide to function.

Question 7

What is a missense mutation?

Answer 7

A type of substitution mutation that alters a single AA in polypeptide chain.
E.g Sickle cell anaemia

Question 8

What is a nonsense mutation?

Answer 8

Mutation creates a premature stop codon so polypeptide chain is incomplete and final protein structure and function is affected.
E.g cystic fibrosis

Question 9

What mechanisms control gene expression?

Answer 9

Transcription factors. They are proteins that enter the nucleus from the cytoplasm and bind to promoter region of gene in DNA to initiate or inhibit transcription. So, they control protein synthesis. Turning on/off particular genes in a cell is what enables them to become specialised.

Question 10

What are the 3 stages of regulatory mechanisms

Answer 10

Regulation at the transcriptional level (during transcription)
Regulation at the post-transcriptional level (after transcription)
Regulation at the post-translational level (after translation)
These are controlled by many different regulatory genes.

Question 11

What is an operon?

Answer 11

A group of simultaneously controlled genes that are either all expressed or not. More common in prokaryotes than eukaryoes.

Question 12

What does the lac. operon in E.Coli control?

Answer 12

It is a regulatory gene at the transcriptional level. It controls lactase synthesis production to aid in lactose digestion.

Question 13

What is a structural gene?

Answer 13

A gene that codes for a protein whose function is within a cell.
E.g membrane carriers, hormones and enzymes.

Question 14

What is a regulatory gene?

Answer 14

A gene that codes for proteins that control the expression of structural genes.

Question 15

Describe the structure of the lac operon.

Answer 15

Promoter for structural genes
Operator
Structural gene lacZ that codes for lactase
Structural gene lacY that codes for permease (allows lactose into the cell)
Structural gene lacA that codes for transacetylase
Left to the lac operon is:
Promoter for regulatory gene
Regulatory gene lacL that codes for the lac repressor protein which inhibits transcription when lactose isn’t present.

Question 16

What happens on the lac operon when lactose isn’t present?

Answer 16

Regulatory gene is transcribed (lacL) producing repressor protein. Repressor protein binds to operating region, preventing RNA polymerase binding to promoter region, preventing transcription of structural protein so no lactase enzyme is synthesised.

Question 17

What is epigenetics?

Answer 17

A way to control gene expression in eukaryotes.
“The heritable change in gene function without changing the DNA base sequence” - passed from cell to cell when it replicates.
These changes are cause by environmental changes and can inhibit transcription.

Question 18

What happens on the lac operon when lactose is present?

Answer 18

Bacterium takes in lactose. Lactose binds to the second binding site on repressor protein, distorting its shape o it can’t bind to the operator region. RNA polymerase binds to promoter region and transcription occurs. The mRNA of all 3 structural genes (lac Z lac Y and lac A) is translated. Enzyme lactase is synthesised and lactose is broken down.

Question 18

Describe post-transcriptional modification.

Answer 18

Pre-mRNA = a newly synthesised mRNA with both introns and exons.
Introns of pre-mRNA are removed and exons fused together to form mature mRNA that is ready for translation. This is called “splicing”.

Question 19

Describe post translational modification.

Answer 19

Polypeptides go to the Golgi apparatus for modifications and folding into unique 3d shape. Some need activation my cAMP, changing the shape of the enzyme to expose its active site.
Eg glycogen phosphorylase hydrolyses glucagon to produce glucose. it is activated by cAMP.

Question 20

What are homeobox genes?

Answer 20

Sequences of genes that create proteins (transcription factors) which regulate expression of other genes involved in body formation in early embryonic development. Plant, animals and fungi all have these.
-Highly conserved (similar in plants animals and fungi) so maintained by natural selection. A mutation in homeobox genes = non viable organisms, not favoured by natural selection.

Question 21

What are hox genes?

Answer 21

A subset of homeobox genes in animals that control correct body development and positioning of body parts. The order of them is the order in which their effects are expressed.
Many animal bodies are segmented due to the order of these hox genes.

Question 22

What is the role of mitosis in the developmemt of the body?

Answer 22

Mitosis increases cell number, resulting in growth.
Proto-oncogenes are genes that stimulate cell division
Tumour-suppressor genes are genes that reduce cell division
In response to internal (RNA decay, irrepairable genetic damage) and external stimuli (e.g growth factors, cytokines and hormones)

Question 23

What is the role of apoptosis in body development?

Answer 23

Programmed cell death = removed unwanted cells, separating limns like fingers and toes. Also removing unneeded cells that were useful in early embryonic state but not as a fully developed foetus.
In response to internal (RNA decay, irrepairable genetic damage) and external stimuli (e.g stress)

Question 24

Explain the process of apoptosis.

Answer 24

The DNA of the cell becoming denser and more tightly packed
The nuclear envelope of the cell’s nucleus breaking down and chromatin condensing
Vesicles forming that contain hydrolytic enzymes
Phagocytes engulfing and digesting the cell via phagocytosis