CELLULAR CONTROL

Question 1

Three ways that gene expressions are controlled

Answer 1

Transcriptional level
Post-transcriptional level
Post translational level

Question 2

Transcriptional level

Answer 2

Gene expression can be controlled by the rate of transcription of genes
Controlled by transcription factors
Shape of transcription factor determines whether it can bind to DNA or not and can sometimes be altered by the binding of molecules (hormones and sugars)
The amount of certain molecules in an environment of a cell can control the synthesis of some proteins by affecting transcription factor binding

Question 3

Transcription factor

Answer 3

Proteins that bind to DNA which switch genes on or off by increasing or decreasing the rate of transcription.
Factors increasing this rate- activators
Factors decreasing this rate- repressors

Question 4

Transcription factors in eukaryotes

Answer 4

Transcription factors bind to specific DNA sites near the start of their target genes- the genes they control the expression of

Question 5

Transcription factors in prokaryotes

Answer 5

Transcription factors bind to operons

Question 6

Operon

Answer 6

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 7

Structural genes, control elements and regulatory genes

Answer 7

Structural genes- code for useful proteins
Control elements- promoter (DNA sequence located before the structural genes that RNA polymerase binds to) and an operator (a DNA sequence that transcription factors bind to)
Regulatory gene- codes for an activator or repressor

Question 8

Example of transcriptional level gene expression in prokaryotic cell

Answer 8

The lac operon in E.Coli
E.coli bacterium respires glucose but can use lactose when glucose isn’t available
The genes that produce the enzymes needed to respire lactose are found on the lac operon
The lac operon has 3 structural genes- lacZ, lacY and lacA

Question 9

Process of prokaryotic transcription gene expression without presence of lactose

Answer 9

The regulatory gene (lacI) produces the lac repressor which is a transcription factor that binds to the oppressor site when there is no lactose present which blocks transcription because RNA polymerase can’t bind to the promoter
The structural genes are not transcribed

Question 10

Process of prokaryotic transcription gene expression with presence of lactose

Answer 10

Lactose binds to the repressor changing it’s shape so that the transcription factor can no longer bind to the operator site
RNA polymerase begins transcribing the structural genes

Question 11

Post-transcriptional level

Answer 11

Genes in eukaryotic DNA contain sections that don’t code for amino acids which are called introns, parts coding for amino acids are called exons
During transcription, the introns and exons are copied into mRNA, these mRNA strands are called primary mRNA transcripts
Introns are removed from primary mRNA strands by a process called splicing
Exons are joined forming a mature mRNA strand (takes place in the nucleus)
The mature mRNA then leaves the nucleus for translation

Question 12

Post-translational level

Answer 12

Protein activation is controlled by molecules (hormones and sugars)
Some of these molecules work by binding to cell membranes and triggering the production of cAMP inside the cell
cAMP activates the proteins inside the cell by altering their 3D shape
Altering their 3D structure can change the active site of an enzyme, making it more or less active

Question 13

Example of post-translational level

Answer 13

PKA is an enzyme made of 4 subunits
When cAMP isn’t bound, the four units are bound together and are inactive
When cAMP binds, it causes a change in the enzymes 3D structure, releasing the subunits
PKA is now active

Question 14

Body plan

Answer 14

General structure of an organism

Proteins control the development of a body plan

Question 15

Hox genes

Answer 15

Code the proteins that control body plan development
Similar hox genes are found in animals, plants and fungi which means that body plan development is controlled in a similar way

Question 16

Hox genes in organism example

Answer 16

2 hox genes control the development of the Drosophila fruit fly- one controls the development of the head and anterior thorax and the other controls the development of the posterior thorax and the abdomen

Question 17

Homeobox sequences

Answer 17

Regions in hox genes which are highly conserved
This means that these sequences have changed very little during the evolution of different organisms that possess the homeobox sequences

Question 18

How hox genes control development

Answer 18

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

Question 19

Apoptosis

Answer 19

The death of cells which occurs as a normal and controlled part of an organism’s growth or development
Programmed cell death

Question 20

What happens when apoptosis is triggered:

Answer 20

Enzymes break down important cell components such as proteins in the cytoplasm and DNA in the nucleus
Cell begins to shrink and break up into fragments
Cell fragments are engulfed by phagocytes and are digested

Question 21

Mitosis role in apoptosis

Answer 21

One cell divides to form 2 daughter cells
Mitosis and differentiation creates the bulk of the body parts and then apoptosis refined the parts by removing unwanted structures
During development, genes controlling apoptosis and mitosis are switched on or off in appropriate cells which means that some cells die and some new ones are produced- creating the correct body plan

Question 22

Examples of apoptosis and mitosis

Answer 22

Tadpoles develop into frogs, their tail cells are removed by apoptosis
When hands and feet are first developed in humans, the digits are connected, apoptosis removes the skin cells between digits

Question 23

Genes regulating apoptosis and the cell cycle

Answer 23

Internal stimulus- if DNA damage is detected during the cell cycle, this can have a result in the expression of genes which cause the cycle to be paused and can trigger apoptosis
External stimulus- stress caused by lack of nutrient availability could result in gene expression that prevents cells from undergoing mitosis, it can also result in gene expression that leads to apoptosis attack by a pathogen

Question 24

Mutation

Answer 24

A change in the base nucleotide sequence of DNA

Question 25

Point mutations

Answer 25

Substitution- one or more bases swapped
Silent mutation- change in a base triplet but the amino acid that the triplet codes for doesn’t change
Missense mutation
Nonsense mutation- creates a stop codon

Question 26

Types of indel mutations

Answer 26

Insertion- one or more bases are added (increasing nucleotide repeats)
Deletion- one or more bases are removed
Causes frameshifts

Question 27

Degenerate code

Answer 27

More than one triplet code (codon) coding for a protein

Question 28

Example of disease caused by indel mutations

Answer 28

Huntington’s disease caused by CAG expansion

Question 29

What changes when a mutation occurs

Answer 29

The primary structure of a protein which my change the final 3D shape of the protein so that it doesn’t work properly

Question 30

Benefits of mutations

Answer 30

Increases chance of survival
Some bacterial enzymes break down certain antibiotics
Mutations in the genes that code for these enzymes could make them work in a wide range of antibiotic beneficial to bacteria because antibiotic resistance helps them survive

Question 31

Harmful effects of mutations

Answer 31

Decreases chances of survival
Cystic fibrosis can be caused by a deletion of 3 bases in a gene that codes for the CFTR protein
The mutated CFTR protein folds incorrectly, so it is broken down
This leads to excess mucus production which affects the lungs of CF sufferers
Affects whether a protein is produced which could cause a genetic disorder