Cellular Control (Paper 2)

Question 1

Regulatory mechanisms role

Answer 1

To control gene expression (including protein synthesis) at three levels

• transcription level
• post transcription level
• post translation level

Question 2

Transcription level control

Answer 2

By altering the rate of transcription of genes. By TRANSCRIPTION FACTORS
E.g. increased transcription produces more mRNA which can be used to produce more proteins.

Shape of a transcription factor determines if it can bind to DNA or not and can sometimes be altered by the binding of some molecules. E.g. some hormones or sugars
Listening to them out of some molecules in an environment or cell can control the synthesis of some proteins by affecting transcription factor binding.

Question 3

Transcription factor

Answer 3

Proteins that bind to DNA and switch genes in or off by increasing or decreasing the rate of transcription

Question 4

Use of activators

Answer 4

To start transcription

Question 5

Use of repressors

Answer 5

To stop transcription

Question 6

Transcribed binding in Eukaryotes

Answer 6

Transcription factors bind to specific DNA sites near the start of their target genes these are genes that control the expression of. RNA polymerase binds which allows for transcription to take place.

Question 7

Prokaryotic transcription level control including example

Answer 7

Control of gene expression often involves transcription factor binding to operons

The structural gene codes for useful proteins such as enzymes. The control element includes a promoter and an operator. The regulatory gene codes for an activator or repressor.

Example
E. Coli
Bacterium that respires glucose but can use lactose if not available. The genes that produce the enzymes needed to respire lactose are found on an operon called the lac operon.
The lac operon had 3 structural genes lacZ, lacY and lacA which produce proteins that help break down lactose such as B-galactosidase and lactose permease.

If lactose is not present
- the regulatory gene (lacL) produces the lac repressor whish is a transcription factor that binds to the operator site when there is no lactose. This blocks transcription as RNA polymerase can’t bind to the promoter.

Lactose present
- it binds to the repressor, changing the repressor’s shape so that it can no longer bind to operator site. RNA polymerase can now bind and transcription of the structural genes.

Question 8

What is post translational control

Answer 8

Gene expression is controlled by the editing of primary mRNA. Introns are removed from primary mRNA (by splicing) to produce mature mRNA

Question 9

How does post transcriptional control work

Answer 9

During transcription introns and exons are both copied into mRNA.

mRNA strands contain introns and exons are called primary mRNA transcripts or pre mRNA.

Introns are removed from primary mRNA strands by the process called splicing introns are removed and exons are joined together to form mature mRNA strands.

This takes place in the nucleus and mature RNA strands then leaves the nucleus for the next stage of protein synthesis (translation)

Question 10

Extrons

Answer 10

All the bits that do code for amino acids

Question 11

Introns

Answer 11

DNA sections that didn’t code for the amino acid

Question 12

Post translational level control with example

Answer 12

Some proteins on functional straight away after they have been synthesised they need to be activated to work like protein synthesis protein activation is also controlled by molecules e.g. hormones and sugars.

cAMP

• some other for that control protein activation work by binding to the cell membranes in triggering the production of cyclic AMP (cAMP) inside the cell.
• cAMP activates proteins inside the cell by altering the three-dimensional 3D structure
• for example altering the 3D structure to change the active site of an enzyme making it become more or less active.

Example: protein kinase A (PKA) by cAMP,
PKA is an enzyme made up of 4 subunits. When cAMP isn’t bound the 4 units are bound together and inactive. When cAMP is bound it causes the enzymes 3D structure to change releasing the active subunits.

Question 13

What is a body plan with example

Answer 13

General structure of an organism.

Proteins control the development of a body plan so that everything grows in the right place. These proteins are coded for by HOX genes.

E.g. the Drosophila fruit fly had a head, abdomen ect. That is arranged in a specific way by two hox gene clusters. One controls the development of the head and anterior thorax and the other controls the development of the posterior thorax and abdomen.

Question 14

Where are Hox genes found

Answer 14

Animals, plants and fungi.

Hox genes have regions called homeobox sequences which are highly conserved.

Question 15

How do Hox genes control development

Answer 15

Homeobox sequences codes for part of protein called homeodomain.

The homeodomain binds to the specific sites of DNA enabling the protein to work as a transcription factor.

Protein binds to the DNA at the start of the developmental genes, activating or repressing transcription by altering the production of proteins involved in the development of the body plan.

Question 16

Apoptosis

Answer 16

Program cell death is a highly controlled process that least the cells being broken down in stages

Question 17

The role of mitosis and apoptosis in development

Answer 17

Mitosis and differentiation create the bulk of a body plan and then apoptosis defines the parts by removing the unwanted structures.

During development genes that control mitosis and genes that control apoptosis are switched on and off inappropriate cells.
this means that some new cells are produced whilst some cells die in the correct body plan develops.

E.g as tadpoles develop into frogs, tail cells are removed by apoptosis.

Question 18

Responsive genes that regulate the cell cycle and apoptosis

Answer 18

Proteins that regulate progression through the cell cycle and apoptosis respond to both internal and external stimuli.

E.g
Internal stimulus could be DNA damage and DNA damage is detected during the cell cycle to be paused or even trigger apoptosis.
External stimulus such as stress caused by lack of nutrients availability could result in gene expression that prevent cells from maintaining and a undergoing mitosis. Gene expression which leads to apoptosis being triggered can also be caused by external stimuli such as attack by a pathogen.

Question 19

What are gene mutations

Answer 19

Changes to the base (nucleotide) sequence of DNA. These can affect protein function by altering the amino acid sequence (primary structure) and whether proteins are produced at all.

Question 20

Types of mutations

Answer 20

Substitution
- one or more bases are swaped for another base

Deletion
- one or more bases are removed

Inserting
- one or more bases are added

A change to the primary structure may change the final 3D shape so the protein doesn’t work or could lead to the protein not being produced at all.

Question 21

Frame shift mutations

Answer 21

Mutations can have a huge effect on the base sequence of a gene for example deletion or insertion can cause a number of bases present to change causing a shift in the base triplet code.

Question 22

Neutral mutations

Answer 22

The mutations changes a base in a triplet but the amino acid that triplet codes for doesn’t change

The mutation produces a triplet code for a different amino acid but that amino acid is chemically similar to the original functions like the original amino acid

Mutated triplet code for a minute amino acid is not involved with the protein function.

Neutral effect on a protein affects an organism overall

Question 23

Mutations affect on an organism

Answer 23

Beneficial
- this have an advantageous effect on the organism e.g. some bacterial enzymes break down certain antibiotics mutations in these genes that code for these enzymes could make and work a wider range of antibiotics. Allowing for more antibiotic resistance to help them survive. These mutations can be passed down to future generations by natural selection.

Harmful effects
These disadvantage effects on organisms decrease its chance of survival. E.g. cystic fibrosis can be caused by the deletion of three bases in a gene that codes for cystic fibrosis transmembrane conductance regulator (CTFR). The mutated cftr protein folds incorrectly so is broken down. This leads to mucus production which affects the lungs of CF sufferers.

Mutations can also affect whether or not a protein is produced. E.g mutation occurs at the start of a gene so that the RNA polymerase can’t bind to it and so won’t be made. The loss of production of a protein can have a harmful effect in some genetic disorders caused by this such as the genetic disorder beta thalassemia, which leads to little to no production of beta globin , which leads to low levels of haemoglobin.