Module 6

Question 1

How can gene expression be controlled?

Answer 1

At the transcriptional level by altering the rate of transcription of genes 
transcription factors (proteins) bind to DNA and switch genes on or off

Question 2

What is an operon?

Answer 2

A section of DNA that contains a cluster of structural genes, that are transcribed together, as well as control elements and sometimes a regulatory gene

Question 3

What do structural genes code for?

Answer 3

Useful proteins such as enzymes

Question 4

What do the control elements of an operon contain?

Answer 4

The promoter (a DNA sequence located before the structural genes that RNA polymerase binds to)and on operator (a DNA sequence that transcription factors bind to

Question 5

What does the regulatory gene code for?

Answer 5

An activator or repressor

Question 6

What does the lac operon do in E. coli?

Answer 6

E.coli is a bacterium that respires glucose, but it can use lactose if glucose isn’t available
Genes that produce enzymes needed to respire lactose are found on an operon called the lac operon
Three structural genes: lacZ, lacY and lacA, produce proteins that help the bacteria digest lactose

Question 7

What happens at the lac operon when lactose is NOT present?

Answer 7

The regulatory gene (lacI) produces the lac repressor, binds to the operator site when there’s no lactose present
Blocks transcription because RNA polymerase cant bind to promotor

Question 8

What happens at the lac operon when lactose is present?

Answer 8

It binds to the repressor, changing the repressors shape so that it can no longer bind to the operator site
RNA polymerase can now begin transcription of the structural genes

Question 9

How is mRNA edited?

Answer 9

Genes in eukaryotic DNA contain sections that don’t code for amino acids
These sections are called introns
The bits that do code are called exons
During transcription both are copied to mRNA
mRNA containing both introns and exons are called primary mRNA transcripts
Introns are removed from primary mRNA strands by a process called splicing
introns removed, exons joined forming mature mRNA strands

Question 10

Where does mRNA editing take place and where does it go?

Answer 10

in the nucleus

mature mRNA leaves the nucleus for the next stage of protein synthesis

Question 11

What does cAMP do?

Answer 11

activates proteins inside a cell by altering their three dimensional structure

Question 12

What is apoptosis?

Answer 12

Programmed cell death

Question 13

How is the cell broken down once apoptosis has been triggered?

Answer 13

Enzymes inside the cell break down important cell components such as proteins in the cytoplasm and DNA in the nucleus
As the cell’s contents are broken down it begins to shrink and breaks up into fragments
Cell fragments are engulfed by phagocytes and digested

Question 14

What internal stimulus could happen to cause apoptosis?

Answer 14

DNA damage
If DNA damage is detected during the cell cycle, this can result in the expression of genes which cause the cycle to be paused and cause apoptosis

Question 15

What external stimulus could happen to cause apoptosis?

Answer 15

Stress caused by lack of nutrient availability

result in gene expression that prevents cells from undergoing mitosis

Question 16

What three types of mutation are there?

Answer 16

Substitution
Deletion
Insertion

Question 17

What is substitution mutation?

Answer 17

One or more bases are swapped for another

Question 18

What is deletion mutation?

Answer 18

One or more bases are removed

Question 19

What is insertion mutation?

Answer 19

One or more bases are added

Question 20

Why could a mutation have a neutral effect on an amino acid?

Answer 20

Some amino acids are coded for by one or more triplet
e.g. tyrosine coded for by TAT and TAC so if one of the bases changes the same amino acid will still be produced
Mutation could cause a different amino acid to b made but it could be chemically similar so produce the same function
The mutated triplet code could not be involved in the proteins function at all, e.g. located far away from the active site

Question 21

What benefit could a mutation have on an organism?

Answer 21

Increase chance of survival
e.g. for bacteria, change in active site that breaks down antibiotics, it could work for a wider range of antibiotics which could mean more antibiotic resistance and greater chance of survival

Question 22

What harmful effect could a mutation have on an organism?

Answer 22

Decrease chance of survival
e.g. Cystic fibrosis, caused by deletion of three bases in the gene that codes for CFTR protein
Mutated CFTR folds incorrectly so it’s broken down, leads to excess mucus production, which affects the lungs of CF sufferers