Regulating gene expression

Question 1

What are the 3 different levels gene expression can be controlled at?

Answer 1

1) transcriptional level
2) post-transcriptional level
3) Post- translational level.

Question 2

How can gene expression be controlled at a transcriptional level ?

Answer 2

BY altering the rate of transcription of genes.

using “transcription factors”

Question 3

What are transcription factors?

What are factors that increase the rate and decrease rate called?

Answer 3

Proteins that bind to DNA, and switches genes on and off by increasing or decreasing rate of transcription

Factors that increase the rate: Activators

Factors that decrease the rate: repressors.

Question 4

What is an “operon” ?

Answer 4

A section of DNA that contains a cluster of genes that are transcribed together.

operon also contains “control elements” and sometimes a regulatory gene.

Question 5

What do the structural genes in an operon code for

Answer 5

The useful protein E.g. an enzyme

Question 6

What do the “control elements” in an operon consist of?

Answer 6

Promoter ( where RNA polymerase binds to )

operator ( where transcription factors bind to )

Question 7

What does the regulatory gene in the operon code for?

Answer 7

Either an Activator ( factors that increase the rate)

OR repressor ( factors that decrease the rate)

Question 8

What are the 3 structural genes?

Answer 8

LacZ

LacY

LacA

• these produce proteins which help bacteria to digest lactose

e.g. beta-galactosidase
lactose permease

Question 9

When lactose isn’t present…

Answer 9

• Regulatory gene(lacl) produces the lac repressor

- lacl binds to the operator site , which blocks transcription because RNA polymerase cant bind to the promoter region.

Question 10

When lactose is present….

Answer 10

When lactose is present, it binds to the repressor , changing its shape sp that it can NO LONGER bind to the operator site.

• RNA polymerase can now bind to the promoter region and begin transcription of structural genes.

Question 11

Post-transcriptional level is what ?

Answer 11

Where the mRNA strands are edited.

Question 12

Are exons coding or non coding

Answer 12

exons are CODING

so introns non- coding

Question 13

What is the mRNA strands containing introns and extrons called?

Answer 13

Primary mRNA transcripts ( pre-mRNA)

Question 14

What is splicing?

Answer 14

When introns are removed from primary mRNA strand, and exons join, forming “mature mRNA strand”.

Question 15

Where does the formation of the mature mRNA strand take place?

Answer 15

In the nucleus

The mature mRNA strand then leaves the nucleus to go to translation

Question 16

What happens at the post translational level?

Answer 16

molecule or hormone can bind to he cell membrane causing Cyclic AMP to be produced.

• cAMP is used to activate proteins
• Cyclic AMP alters the 3D structure, which could cause the shape of the active site to change.

Question 17

Example: how cAMP activates protein kinase (PKA):

Answer 17

1) PKA is an enzyme made up of 4 sub units, and when cAMP aren’t bound the 4 units are inactive
2) cAMP binds causing the enzymes 3D structure to change, causing the active sub units to be released.
- PKA is now active.

Question 18

What are hox genes?

Answer 18

Genes that code for proteins that can control body plan development of an organism.

Question 19

What is special about homeobox sequences?

Answer 19

They are highly conserved,

which means over the course of evolution these sequences have changed very little.

Question 20

How do hox genes control development?

Answer 20

1) Homeobox sequences code for a part of the protein called homeodomain
2) Homeodomain binds to a specific site on the DNA, allowing the protein to work as a transcription factor.
3) The protein binds to DNA at the start of developmental genes , which causes the activation or repressing of transcription.
- Which alters with the production of proteins controlling the body plan.

Question 21

What is apoptosis?

Answer 21

Programmed cell death.

Question 22

How apoptosis helps the break down of cells : ( 3 steps).

Answer 22

1) Enzymes inside the cell break down important cell components
2) cell shrinks and breaks up into fragments
3) Cell fragments are ENGULFED AND DIGESTED BY PHAGOCYTES

Question 23

What’s an example of an internal stimuli that could affect apoptosis or cell cycle?

Answer 23

• DNA damage

This could lead to a gene expression that causes the cell cycle to be paused, and can even trigger apoptosis

Question 24

What’s an example of an external stimulus?

Answer 24

• Lack of nutrient availability.

This could lead to the expression of a gene which prevents mitosis from occurring

Question 25

What’s an example of an external stimuli, that causes a gene expression that triggers apoptosis?

Answer 25

• Attack by a pathogen.

Question 26

What are the 3 different types of ways change to DNA base sequence can occur?

Answer 26

1) Substitution: bases being swapped
2) Insertion: Bases being added
3) Deletion: bases being removed
- mutation could cause a change in the final 3D structure of the protein.

Question 27

What are the 3 different ways proteins can have a “neutral effect” on the proteins function?

Answer 27

1) Some amino acids can be coded for by more than one base triplet
2) Mutation can produce a different amino acid, but that amino acid can still be chemically similar.
3) mutated triplet could code for an amino acid not involved with the protein’s function. E.G ones that are located far away from an enzymes active site.

Question 28

What are some beneficial effects of protein function being affected by mutation?

Answer 28

• e.g: increase chances of survival
• Bacterial enzymes can break down antibiotics, mutations in the gene which codes for these enzymes , could cause the enzymes to work on a “wider range” of antibiotics.
• Which is beneficial to bacteria as they could become antibiotic- resistant

Question 29

What are some harmful affects of protein function being affected by mutation?

Answer 29

• E.G: Decrease chance of survival
• Cystic fibrosis.
• The deletion of 3 bases in the gene which code for CFTR protein can cause cystic fibrosis ( CF).
• The mutated CFTR protein folds incorrectly so its broken down -> leading to excess mucus production