Cellular control

Question 1

How can gene expression be controlled?

Answer 1

It can be controlled at the transcriptional level by altering the rate of transcription of genes which is controlled by transcription factors which are proteins that bind to DNA and switch genes on or off by increasing or decreasing rate of transcription.

Question 2

Activators and repressors

Answer 2

Activators increase the rate of transcription and repressors decrease the rate of transcription

Question 3

How does the shape of transcription factor affect the binding?

Answer 3

This is because the shape determines whether it can bind to DNA or not and sometimes can be altered by the binding of some molecules eg hormones. This means the amount of certain molecules in an environment or a cell can control the synthesis of some proteins by affecting transcription factor binding.

Question 4

Operon

Answer 4

How prokaryotes control gene expression. The transcription factor binds to these- An operon is a section of DNA that contains a cluster of structural genes, that are transcribed together as well as control genes and sometimes a regulatory gene.

Question 5

Structural genes

Answer 5

These code for useful proteins such as enzymes

Question 6

Control elements

Answer 6

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

Question 7

Lac operon in E.coli

Answer 7

E.coli is bacterium that respires glucose but can respire lactose if glucose isn’t available - The genes that produce the enzymes needed to respire lactose are found on the operon called lac operon- has 3 structural genes- lacZ, LacY and LacA which produce proteins that help the bacteria digest lactose.

Question 8

How does the Lac operon work when lactose is not present?

Answer 8

When lactose is not present the regulatory gene called lacl produces a lac repressor - transcription factor that binds to the operator site when lactose not present- blocks transcription as RNA polymerase cannot bind to the promotor

Question 9

How does lac operon work when lactose is present?

Answer 9

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

Question 10

Primary mRNA transcripts & splicing

Answer 10

This is when during transcription both introns and exons are both copied into mRNA and are called mRNA transcripts- Introns removed from the mRNA strands by splicing - introns are removed and exons joined, forming mature mRNA strands takes place in nucleus- mature mRNA then leaves nucleus for next stage of protein synthesis.

Question 11

cAMP and activating proteins

Answer 11

Some proteins need to be activated to work and is controlled by molecules such as hormones- some of them work by binding to cell membranes and triggering production of cyclic AMP inside of the cell which then activates proteins by altering their 3d structure like the active site making them more or less active

Question 12

How does cAMP activate PKA?

Answer 12

• PKA enzyme made of 4 sub units
• When cAMP isn’t bound four units bound together and inactive
• When cAMP binds enzymes 3D structure is changed releasing the active sub units and PKA is now active

Question 13

What us a body plan?

Answer 13

The general structure of an organism that are arranged in a particular way and proteins control the development of the body plan and are coded by genes called Hox genes.

Question 14

Hox genes

Answer 14

These are the genes that code for the proteins that control body plan development and similar ones are found in most living organisms which shows how body plans are controlled in a similar way.

Question 15

Homeobox sequences

Answer 15

These are regions of the Hox genes which are highly conserved meaning the sequences have changed very little during the evolution of different organisms that possess the homeobox sequences.

Question 16

How do hox genes control development?

Answer 16

• Homeobox sequences code for part of the protein called the homeodomain
• Homeodomain binds to specific sites on DNA enabling the protein to work as a transcription factor
• Proteins bind to DNA at the start of the developmental genes, activating or repressing transcription and so altering the production of proteins involved in development of body plan.

Question 17

Apoptosis

Answer 17

• Programmed cell death - Enzymes break down important cell components such as proteins in cytoplasm and DNA in the nucleus
• As cell contents break down it shrinks and breaks up into fragments which are then engulfed by phagocytes and digested.

Question 18

What role does mitosis play in the development of the body plan?

Answer 18

Mitosis and differentiation create the bulk of the body parts and apoptosis refines the parts by removing unwanted structures.

Question 19

How are genes that control apoptosis controlled?

Answer 19

The genes are turned off and on in appropriate cells - means some cells die whilst some new cells are produced and the correct body plan develops

Question 20

What stimuli do the genes that regulate apoptosis respond to?

Answer 20

Internal stimuli- could be DNA damage and if DNA damage is detected during the cell cycle this can result in the expression of genes which cause the cell cycle to be paused and can even trigger apoptosis
External stimuli- Stress caused by lack of nutrient available could result in gene expression that prevents cells from undergoing mitosis.

Question 21

What is a mutation

Answer 21

Any change to the base sequence of a DNA strand and include: Substitution, Deletion and Insertion - order of DNA bases in a gene determines the order of amino acids in a particular protein if a mutation occurs the primary structure could be altered.