Gene Expression

Question 1

In what two stages can gene expression be controlled?

Answer 1

Transcription and translation

Question 2

What is the process of the stimulatipn of transcription?

Answer 2

Transcriptional factors found in the cytoplasm move to the nucleus.
They bind to the promotor region of DNA (a specific base sequence)
This allows the attachment of RNA polymerase to the DNA, which stimulates transcription.

Question 3

What is Oestrogen?

Answer 3

A lipid soluble, steroid hormone than is released onto the bloodstream

Question 4

How can oestrogen initiate transcription?

Answer 4

Enters the cell by simple diffusion
Bonds to a specific transcriptional factor, which causes the transcriptional factor to change shape.
This causes an inhibitor molecule to be released from the transcriptional factpr, and expose the DNA binding site on the transcriptional factor.
The transcriptional factor can now bind to the promotor region and stimulate transcription

Question 5

What is the function of an inhibitor molecule?

Answer 5

It prevents the transcriptional factor from binding to the promotor region when the synthesis of a protein is not required

Question 6

How can gene expression during translatipn be inhibited?

Answer 6

By double stranded sections of RNA called RNAi
This is called RNA interference

Question 7

How does RNAi inhibit gene expression during translation?

Answer 7

Double stranded RNAi is coded for by special regulatory genes
The RNAi moves into the cytoplasm and becomes single stranded, and associates with a nuclease enzyme
It binds to s specifoc mRNA molecule by complimentary base pairing
The nuclease enzyme cuts the mRNA into tow
The mRNA can no longer be translated

Question 8

When might RNA interference be important?

Answer 8

To stop the translation of viral RNA when infected by a virus

Question 9

How can RNAi be applied in scientific research and medicine?

Answer 9

Can identify the roles of genes in a biological pathway
Can prevent a genetic condition by stopping a faulty protein from being translated

Question 10

What are features of stem cells?

Answer 10

The are undifferentiated, yet can differentiate into specialised cells
They can replace themselves

Question 11

What are the four main types of stem cells?

Answer 11

Totipotent cells
Pluripotent cells
Multipotent cells
Unipotent cells

Question 12

What are totipotent stem cells?

Answer 12

Stem cells that occur for a limited time in early mammalian embryos
They can differentiate into any body cell

Question 13

What are pluripotent stem cells?

Answer 13

Stem cells found in embryos, and can differentiate into any type of tissue except placental cells

Question 14

What are multipotent stem cells?

Answer 14

Stem cells found in many tissues of mature mammals and can differentaite into a limited type of cells

Question 15

What are unipotent stem cells?

Answer 15

Found in mature mammals. Yet can only differentiate into one type of cell or tissue

Question 16

What are induced pluripotent stem cells?

Answer 16

Pluripotent stem cells that are produced from sifferentiated adult body cells

Question 17

How are stem cells used in treating human disorders?

Answer 17

Stem cells are grown in culture in labs
Certain chemical stimuli are added, which trigger the cells to differentiate into specialised bpdy cells of a particular type.
These can then be used to replace damaged cells in patients

Question 18

What are advantages and disadvantages of pluripotent stem cells?

Answer 18

Advantages- can differentiate onto any type of blood cell
Disadvantages- risk lf rejection as they are not the patients own cells. Ethical issues as they must be spurced from embryos

Question 19

What are advantages and disadvantages of multipotent stem cells?

Answer 19

Advantages- no transplant is required as stem cells are the patients own cells- no rejection
Disadvantages- they can only differentiate into a limited number of cell types

Question 20

State three ethical arguments FOR the use of embryonic stem cells

Answer 20

Embryo at such an early stage are undifferentiated, so show no resemblance to a human being
It is wrong to allow human suffering to continue if you can stop it
Spare embryos from IVF treatment can be used rather than being detsroyed

Question 21

Stat three arguments against the use of embryonic stem cells

Answer 21

Embryos have a potential for life so it is unethical to use them
It is wrong to use them as a means to an end
Embryos themselves are unable to give consent

Question 22

What stem cells are in mature plant cells?

Answer 22

Totipotent

Question 23

What is epigenetics?

Answer 23

The heritable changes in gene function, without changes to the base sequence of DNA

Question 24

What is the epigenome?

Answer 24

DNA and histones in chromatin have chemical tags attached to them. The epigenome is all the chemical tags whoch have been added to a persons genome

Question 25

What are chemical tags?

Answer 25

Either acetyl groups or methyl groups that have been added to DNA and histones, and make up an organisms epigenome

Question 26

Describe the process of acetylation of histones

Answer 26

An acetyl group binds to histone proteins DNA is less tightlywrapped around the histone, so comdensation of the chromatin reduces This makes promotor regipns accessible Transcriptional factors can bond to promotor regipns and start transcription Genes are switched on

Question 27

Describe the process lf methylation of DNA

Answer 27

Methyl groups are added to cytosine bases in DNA this decreases the acetylation of histones DNA wraps more tightly round histones, chromatin is more condensed Promotlr regions are inaccessible to transcriptional factors Transcription is inhibited Genes switched off

Question 28

How can evidence of inheritance of environmental epigenetic changes be showed?

Answer 28

Through starvation experiments in mice

Question 29

What are benign tumours?

Answer 29

Non cancerous tumours. It is a mass of cells that has not spread into neighbouring tissues. Its locatipn is restricted to one area

Question 30

What are malignant tumours?

Answer 30

Cencerous tumours. They divide uncontrollably (metastasise) and spread to other parts of the body

Question 31

What are two treatments of malignant tumours?

Answer 31

Chemotherapy- drugs that kill fast growing cencer cells Radiation therapy- ionising radiatipn is used to damage the DNA of cencer tissue to kill the abnormal cells

Question 32

What two types of genes controll the rate of mitosis?

Answer 32

Proto-ongogenes Tumour suppressor genes

Question 33

What is the normal role of a proto-oncogene?

Answer 33

Stimulates cell division

Question 34

What is the role lf a proto-oncogene when it is mutated?

Answer 34

Becomes an oncogene The gene is permanently active so causes continuous cell division

Question 35

What is the normal role of tumour suppressor genes?

Answer 35

They inhibit cell division, repair faulty DNA and cause apoptosis (cell death)

Question 36

What is the role of tumour suppressor genes once mutated?

Answer 36

Gene is inactivated, cells divide uncontrollably by mitosis

Question 37

Give an example of a gene mutation in a tumour suppressor gene?

Answer 37

P53 protein, which is coded for by the p53 gene. It stops the cell cycle moving from the G1 phase to the S phase in mitosis. If the gene mutates the p53 protein is unable to stop the cell cycle, leading to uncontrollable cell division

Question 38

How can hypermethylation of tumour suppressor genes cause cancer?

Answer 38

The gene is inactivated, so the gene is not transcribed No translation so the protein is not produced The protein can no longer inhibit cell division Cell divides uncontrollably

Question 39

How can hypomethylation of a proto-oncogene lead to cancer?

Answer 39

The gene is permanently activated and becomes an oncogene This leads to continuous transcription and translation of the protein The protein stimulates the cell to divide too quickly by mitosis, causing uncontrolled cell division

Question 40

Explain how increased methylation of DNA lead to a tumour suppressor gene being inactivated?

Answer 40

The promoter region becomes inaccessible, so transcriptional factors cannot bind Therefore RNA polymerase cannot bind and transcription is stopped

Question 41

Explain how decreased methylation of a proton-oncogen can lead to the formation of cancer?

Answer 41

The promoter region is now accessible, so the transcriptional factor can bind and RNA polymerase can bind. This leads to increased transcription of the proto-oncogene. The protein stimulates the cell to divide quickly by mitosis

Question 42

What is the genome?

Answer 42

The complete set of genes in a cell/organism

Question 43

What is the proteome?

Answer 43

The full range of proteins produced by a given cell

Question 44

Why is determining the genome of bacteria easy?

Answer 44

The DNA does not contain non-coding regions Most prokaryotes have a single piece of circular DNA that is not associated with histones

Question 45

What are applications of determining the genome of simpler organisms?

Answer 45

Identifying potential antigens for use in vaccines against bacteria Understanding the proteins involved in the metallic pathways of an organism

Question 46

What are prevention, diagnosis and treatments of acquired mutations?

Answer 46

Prevention- avoid the mutagen Diagnosis- regular screening of high risk individuals Treatment- radiotherapy, chemotherapy

Question 47

What are prevention, diagnosis and treatments of hereditary mutations?

Answer 47

Prevention- pre-emptive surgery Diagnosis- more frequent screening for particular genes Treatment- early diagnosis due to screening leads a to a lower dose of chemo and radiotherapy

Question 48

What is the difference between acquired mutations and hereditary mutations?

Answer 48

Acquired mutations are caused by mutagenic agents Hereditary mutations are passed on from generation to generation, and there is a history of the mutation in previous generations