Topic 7.2 Factors affecting gene expression

Question 1

Define cell differentiation

Answer 1

the process by which a cell becomes specialised for a particular function

Question 2

What are transcription factors?

Answer 2

proteins that bind to the DNA in the nucleus and affect the process of transcribing the genetic material

Question 3

What do gene probes do?

Answer 3

allow a particular section if DNA or mRNA to be identified

Question 4

What is the most common way of controlling gene expression?

Answer 4

switching on and off the transcription of certain genes

Question 5

What is transcription?

Answer 5

the process by which the genetic code of DNA is copied to a complementary strand of RNA (mRNA) before protein synthesis can take place

Question 6

What are promoter sequences?

Answer 6

specific regions on the DNA to which transcription factors bind to stimulate transcription

Question 7

Where are promotor sequences usually found?

Answer 7

just above the starting point for transcription upstream of the gene (5’ end)

Question 8

What are enhancer sequences?

Answer 8

specific regions on the DNA to which transcription factors bind and regulate the activity of the DNA by changing the structure of the chromatin, making it more or less available to RNA polymerase so either stimulating or preventing transcription

Question 9

What is an open chromatin structure linked to?

Answer 9

active gene expression

Question 10

What is a closed chromatin structure linked to?

Answer 10

gene inactivity

Question 11

What is pre-mRNA?

Answer 11

the mRNA that is transcribed directly from the DNA before it has been modified

Question 12

What are spliceosomes?

Answer 12

enzyme complexes that act on pre-mRNA, joining exons together after the removal of introns

Question 13

Define DNA methylation

Answer 13

the addition of a methyl (-CH3) group to a cytosine in the DNA molecule next to a guanine (CpG site) in the DNA chain and prevents transcription

Question 14

What is DNA demethlyation?

Answer 14

the removal of a methyl group from methylated DNA allowing genes to become active so they can be transcribed

Question 15

What is chromatin?

Answer 15

the DNA/protein complex that makes up chromosomes, included the protein histones

Question 16

How does DNA methylation silence genes?

Answer 16

the methyl group changes the arrangement of the DNA molecule so prevents transcription from taking place

Question 17

Define heterochromatin

Answer 17

densely supercoiled and condensed chromatin where the genes are not available to be copied to make proteins

Question 18

Define histone acetylation

Answer 18

the addition of a acetyl group (-COCH3) to one of the lysines in the histone structure, which opens up the structure and allows genes in that area to be transcribed

Question 19

Define histone methylation

Answer 19

the addition of a methyl group (-CH3) to a lysine in the histone structure and depending on the position of the lysine, methylation may cause activation or inactivation of the DNA region

Question 20

What is meant by totipotent?

Answer 20

describes an undifferentiated cell that can form any on of the different types of cell needed for an entire new organism

Question 21

Define pluripotent

Answer 21

describes an undifferentiated cell that can form most of the cell types needed for an organism except the placenta

Question 22

What are embryonic stem cells?

Answer 22

the undifferentiated cells of the human embryo which have the potential to develop into many different types of specialised cell

Question 23

What are somatic/adult stem cells?

Answer 23

undifferentiated cells that are found among differentiated cells in a tissue or organ that can differentiate when needed to produce any one of the major cell types found in that particular tissue or organ

Question 24

Define multipotent

Answer 24

a cell that can form a very limited range of differentiated cells within a mature organism

Question 25

Define therapeutic cloning

Answer 25

an experimental technique used to produce embryonic stem cells from an adult cell donor

Question 26

Describe the process of therapeutic cloning

Answer 26

1. remove nucleus from adult cell from the patient and transfer to a human ovum which has had its nucleus removed 2. mild electric shock fuses the nucleus with the new cell and triggers development 3. the new pre-embryo cell develops and divides which produces embryonic cells with the same genetic material as the patient 4. embryonic stem cells cultured in a suitable environment to differentiate into required tissue 5. differentiated cells transferred to patient without rejection problems

Question 27

In therapeutic cloning, what additional factor must be considered in the treatment of genetic diseases?

Answer 27

the adult stem cell nucleus would need to be genetically modified before being added to the ovum, otherwise the cultured stem cells would carry the gene mutation

Question 28

Identify the negatives of stem cell therapy

Answer 28

- use of embryo - risks in the development of cancers - e.g. evidence bone marrow transplants used to overcome leukaemia puts patients at a higher risk for developing other cancers

Question 29

Identify the positives/benefits of stem cell therapy

Answer 29

- no cures for many conditions that stem cell therapy could solve - gives the ability to produce tailor-made cells to take over the function of damaged ones - avoids risk of rejection

Question 30

What are induced pluripotent stem cells?

Answer 30

iPS cells are adult cells that have been reprogrammed by the introduction of new genes to become pluripotent again

Question 31

Give the benefits of iPS

Answer 31

- overcomes ethical objections of using embryonic tissue | - treats a wide range of diseases caused by faulty cells

Question 32

What are the negatives of using iPS?

Answer 32

- tendency to becomes cancerous very quickly - persuading cells to become pluripotent is very difficult - differentiating the cells is also very difficult

Question 33

Give examples where induced pluripotent cells could be used to cure diseases

Answer 33

- parkinson's disease - type 1 diabetes - damaged nerves - organs for transplant

Question 34

How would iPS cure Parkinson's disease?

Answer 34

- replace lost brain cells | - restore dopamine production

Question 35

How would iPS cure Type 1 diabetes?

Answer 35

-give patients a working pancreas so blood glucose control

Question 36

Is iPS used in the medical world?

Answer 36

no they have only done studies on animals

Question 37

Name the 4 ethical principles

Answer 37

1. respect for autonomy, respect for individuals (not performing procedures without consent) 2. beneficence, the aim of doing good (e.g. giving medicine to relieve suffering) 3. non-maleficence, to do no harm 4. justice, treat everyone equally and fairly share resources

Question 38

State the similarities between embryonic stem cells and induced pluripotent stem cells (iPS)

Answer 38

- both have the potential to divide indefinitely | - both have the potential to divide into a number of cell types

Question 39

State the differences between embryonic stem cells and induced pluripotent stem cells (iPS)

Answer 39

- no/less ethical objections using iPS - iPS were adult cells, embryonic taken from morula/inner cell mass - iPS have a gene added - iPS can form adults cells whereas embryonic form younger cells - rejection issues with embryonic cells, patient-matched cells produced from iPS

Question 40

Describe epigenetic modification

Answer 40

- changes that affect gene expression/activation - e.g. DNA methylation, histone acetylation - involved in differentiation/ change in function