cellular control

Question 1

at what 3 stages is gene expression controlled

Answer 1

transcriptional, post-transcriptional and post-translational

Question 2

outline transcriptional level control
in eukaryotes

Answer 2

the rate of transcription is controlled by transcriptional factors.

shape of transcriptional factor determines whether it binds to DNA

transcription factor binds to specific DNA site at start of their target gene. RNA polymerase binds to the transcription factor and the gene is translated.

Question 3

outline the process of transcriptional level control in prokaryotes (lac operon in E.coli) when lactose is present and is not present

Answer 3

Lactose NOT present:
regulatory gene produces the lac repressor (transcription factor). The repressor protein binds to the operator site and blocks transcription as RNA polymerase cannot bind to the promotor

Lactose IS present:
lactose binds to the repressor protein, changing it’s shape. This means the repressor protein no longer binds to the operator. The promotor region is free to bind to RNA polymerase. structural genes are transcribed. produces lactose permease and B galactosidase (enzymes)

Question 4

what is an operon

Answer 4

section of DNA that contains a cluster of structural genes. These are all transribed together. contains control elements (promotor and operator) and a regulatory gene. Only found in PROKARYOTES

Question 5

what are transcription factors

Answer 5

proteins that bind to DNA and switch genes on and off by altering the rate of transcription

Question 6

outline what happens in post transcriptional control

Answer 6

after transcription mRNA is produced. however this is ‘primary mRNA’ as contains non coding regions (introns)

mRNA is edited so that introns are removed from the mRNA strand by splicing, exons are joined together by splicosomes to make mature mRNA.

a protective cap is added to the 5’ and 3’ end of mRNA - this protects the strand against enzymes

this takes place in the nucleus, mature mRNA leaves the nucleus

Question 7

outline what occurs during post translational control

Answer 7

proteins aren’t functional straight after synthesis, they need to be activated.

molecules that control protein activation bind to cell membranes and trigger the production of cyclic AMP inside the cell. CAMP alters the tertiary structure of the protein eg. the active site making it more or less active.

Question 8

what are some differences between eukaryotes and prokaryotes when it comes to cellular control

Answer 8

prokaryotes do not contain introns

eukaryotes dont have an operator region or an operon.

Question 9

give an example of how hormones can affect transcription factors

Answer 9

Oestrogen is a steroid hormone that can initiate transcription. It does this by binding to a receptor site of a transcriptional factor. When it binds to the transcriptional factor, it causes it to change shape slightly, and this change in shape makes it complementary and able to bind to the DNA to initiate transcription.

Question 10

what is the role of the enzyme lactose permease

Answer 10

increases solubility of membrane to lactose

Question 11

what is the role of the enzyme B galactosidase

Answer 11

breaks the disaccharide bond forming glucose and galactose

Question 12

what is meant by body plan

Answer 12

the general structure of an organism

Question 13

outline the link between hox genes, homeobox sequence and homeodomain

Answer 13

proteins control development of body plan, these proteins are coded for by a homeobox gene

hox genes are a type of homeobox gene which contain regions called homeobox sequences.

Homeobox sequence codes for a homeodomain protein.

The homeodomain is a transcription factor that activates other developmental genes related to body plan development.

Question 14

similar hox genes are found in what

Answer 14

plants animals and fungi

Question 15

why are hox genes highly conserved

Answer 15

they are involved in the start of development of the organism, if a mutation in hox genes occured then cell would die and development would not occur. As there is no evolutionary advantage to this mutation it is selected against.

Question 16

how long is a homeobox sequence

Answer 16

180 bp

Question 17

what does conserved mean

Answer 17

genes have changed very little over a long period of time

Question 18

what is apoptosis

Answer 18

controlled cell death

Question 19

outline the process of apoptosis

Answer 19

triggered by release of Ca 2+ ions, causes lysosomes to pop, these break down the cell components and cytoskeleton forming a bleb. The blebs fragment and are phagocytosed.

Question 20

what is the role of apoptosis in body plan development

Answer 20

refines the parts by removing unwanted structures. for example hands and feet in humans used to be connected, only separated when cells in connecting tissue undergo apoptosis.

Question 21

what 2 cell proccesses are involved in body plan development

Answer 21

mitosis
apoptosis

Question 22

genes that regulate progression through cell cycle respond to both internal and external stimuli, what might this involve

Answer 22

internal: DNA damage is detected during the cycle and can result in the expression of genes which causes the cycle to be paused, apoptosis may occur.

external: stress caused by lack of nutrients could result in gene expression that prevents cells from undergoing mitosis.

Question 23

what is a mutation

Answer 23

a random change to the base sequence of DNA

Question 24

what are the 3 types of mutations that can occur

Answer 24

insertion, deletion, substitution

Question 25

what is a frameshift mutation

Answer 25

The impact of adding or deleting one base is that all subsequent codons are altered.

This type of mutation can be very harmful because all the altered codons could potentially code for different amino acids and result in a very different sequence of amino acids resulting in a non-functioning protein.

the earlier the frameshift mutation appears, the more amino acids affected.

Question 26

why do some mutations have a neutral effect on a proteins function

Answer 26

the genetic code is degenerate - the mutation changes a base in the triplet but the amino acid the triplet codes for is the same, as some amino acids are coded for by more than one triplet.

the mutation produces a triplet that codes for a different amino acid, but the amino acid is chemically similar so functions the same

the mutated triplet codes for an amino acid not involved with the proteins function.

Question 27

discuss mutations with a beneficial effect and mutations with a harmful effect

Answer 27

beneficial: some bacterial enzymes break down antibiotics, this increases the chance of survival, therefore the bacteria are more likely to survive, reproduce and pass the mutation onto future generations

harmful: cystic fibrosis is caused by a deletion of 3 bases in the gene that codes for a CFTR protein. means this protein folds incorrectly and so is broken down.
results in excess mucus production which affects the lungs.

Question 28

how might a mutation prevent a gene being produced at all

Answer 28

if mutation occurs at start of gene, RNA polymerase can’t bind and transcribe the gene. therefore the protein is not made

Question 29

what is a nonesense mutation

Answer 29

codon has changed to a stop codon, results in a shorter than normal protein.

Question 30

what is a missense protein

Answer 30

a DNA change that results in different amino acids being encoded at a particular position in the resulting protein

Question 31

what is an inversion mutation

Answer 31

section of chromasome is turned upside down

Question 32

what is a translocation mutation

Answer 32

A genetic change in which a piece of one chromosome breaks off and attaches to another chromosome