Control of Gene Expression

Question 1

What is a zygote?

Answer 1

A newly fertilised ovum by sperm cells

Question 2

What does totipotent mean?

Answer 2

Any cell can become any other cell

Question 3

What is a blastocyst?

Answer 3

The first cell of differentiation from a zygote. Outer cells become cells that aid pregnancy (eg placenta, amniotic sac). These cells are pluripotent

Question 4

What does pluripotent mean?

Answer 4

Stem cells that can develop into any cell type excluding the placenta and embryo

Question 5

What does multipotent mean?

Answer 5

Stem cells that can only differentiate within their category (eg blood, bone, skin, etc.)

Question 6

What are stem cells?

Answer 6

Unspecialised cells that continue to divide

Question 7

What does differentiate mean?

Answer 7

Where the stem cells start to become a different cell type.

Question 8

What does unipotent mean?

Answer 8

Cells that can divide but can only become their own cell type

Question 9

Describe the stages from fertilisation to the formation of a foetus

Answer 9

1) sperm cell meets the ovum
2) fertilisation occurs, forming a zygote
3) The zygote undergoes mitosis, dividing rapidly. These cells are totipotent
4) The zygote forms a blastocyst, outer cells can become cells that aid pregnancy. These cells are pluripotent
5) This forms a human embryo, and at this point these cells are multi potent.
6) A foetus is formed, at this point the cells are unipotent.

Question 10

What arguments are there in favour of embryonic stem cell use?

Answer 10

-An early (not yet implanted) embryo does not have the psychological, emotional or physical properties that we associate with being a person. It doesn’t have any interests to be protected and we can use it for the benefits of patients.
-The embryo cannot develop into a child without being transferred to a woman’s uterus. Something that could become a person should not be treated as if it were a person.
-Blastocysts are just body cells with no status different to other body cells, they have no aim or
desire to be harmed or not harmed.

Question 11

What are the arguments against the use of embryonic stem cells?

Answer 11

• Respecting human life.

- The embryo has full moral status from fertilisation onwards.

Question 12

What are iPS cells?

Answer 12

Induced pluripotent stem cells

Question 13

Give some uses of iPS cells?

Answer 13

• iPS cells can be used to create specialised cells to help treat diseases such as Alzheimer’s, Parkinson’s
• Helps heal nerve injuries (eg paralysis)
• Can be used to clone cells(and potentially people)
• Can be used for fertility treatments

Question 14

What are some advantages of iPS cells?

Answer 14

• Uses
• avoids the complicated debate of using embryonic stem cells
• Has been replicated across the world easily, requiring certain conditions
• Can be created from the cells of the patient, meaning little/no risk of rejection
• Non invasive (only requires skin cells, hair, etc)
• Accessible to a large number of patients compared to embryonic stem cells (eg catholics)

Question 15

What are some disadvantages of iPS cells?

Answer 15

• As these iPS cells have potential to divide and become an embryo, it fails to completely avoid the embryonic stem cell debate
• Allows for easy, non-invasive cloning of people
• Not filly refined (can result in gene translocation).

Question 16

What is a transcription factor?

Answer 16

A protein molecule that moves from the cytoplasm to the nucleus, binds to a promoter region (upstream of a gene) and switches on gene expression. It does this by making it easier for RNA polymerase to bind to the gene.

Question 17

What is a promoter?

Answer 17

A short region of DNA upstream from a gene, which the transcription factor binds to.

Question 18

What is an inhibitor? (COGE)

Answer 18

This blocks the site on the transcription factor, which binds to the promoter

Question 19

Describe how oestrogen “switches on” gene expression

Answer 19

1) Oestrogen diffuses into the cell as it is lipid-soluble
2) Oestrogen binds to the transcription factor receptor
3) The TF undergoes a conformational shape
4) The TF enters the nucleus
5) the TF binds to the promoter and stimulates gene expression

Question 20

Describe RNA interference

Answer 20

RNAi are small pieces of double stranded RNA, usually about 21 nucleotides long, with 3’ overhangs (2 nucleotides) at each end.

Question 21

How can (double strand) RNAi molecules be used to control gene expression?

Answer 21

Can be used to “interfere” with the translation of proteins by binding to and promoting the degradation of messenger RNA at specific sequences.

Question 22

Describe siRNA

Answer 22

Each siRNA strand has a 5’ phosphate group and a 3’ hydroxyl group. They are produced from dsRNA or hairpin looped RNA

Question 23

Describe how siRNA controls gene expression

Answer 23

After entering a cell this is cleaved by an enzyme called Dicer. The siRNA are then incorporated into a multi-subunit protein complex called RISC. RISC seeks out an appropriate target mRNA, where the siRNA then unwinds. The antisense strand directs degradation of the complementary mRNA strand. The siRNA-enzyme complex will bind via complementary base pairing and cugd the mRNA.

Question 24

What is epigenetics?

Answer 24

The interface between environmental effects and the proteome which could be passed to future genetics.

Question 25

What is the epigenome?

Answer 25

DNA and histones are covered in chemical tags, the chemical tags form a second layer of influence known as the epigenome.

Question 26

What is an epigenetic mechanism?

Answer 26

Something that affects the expression of a gene without changing the base sequence of DNA

Question 27

What is genetic imprinting?

Answer 27

A change in inherited gene function without a change in the genotype/base sequence caused by an environmental factor.

Question 28

Describe methylation?

Answer 28

The nutrients we extract from food enter metabolic pathways where they are manipulated, modified and moulded into molecules the body can use. One such pathway is responsible for making methyl groups, which are important for silencing genes.

Question 29

Describe the features of a benign tumour.

Answer 29

• Grow very slowly
• Often specialised cells
• Nucleus appears normal
• Rarely reoccur
• Much less lifethreatening
• they do not metastasise

Question 30

Describe the features of a malignant tumour.

Answer 30

• Grow rapidly
• Cell nucleus is larger and appears to darker due to abundance of DNA
• Unspecialised cells
• More likely to be lifethreatening
• Tumours can metastasise

Question 31

What do proto-oncogenes do?

Answer 31

They stimulate cell division when growth factors attach to a membrane receptor

Question 32

What do oncogenes code for?

Answer 32

Proteins that -

• Stimulate cell division
• Inhibit cell differentiation
• Halt cell death

Question 33

What do increased production of oncogenes lead to?

Answer 33

• Increased cell division
• Decreased cell differentiation
• Inhibition of cell death

Question 34

What do tumour suppressor genes do?

Answer 34

• Slow down cell division
• Repair mistakes in DNA
• Cause cell apoptosis

Question 35

Give some sources of stem cells in mammals.

Answer 35

• Embryonic stem cells
• Umbilical cord blood stem cells
• Placental stem cells
• Adult stem cells

Question 36

What are embryonic stem cells?

Answer 36

Stem cells that come from embryos in the early stages of development, and can differentiate into any type of cell (pluripotent)

Question 37

What are adult stem cells?

Answer 37

Despite their name, are found in the body tissues of the foetus through to the adult. They are specific to a particular tissue or organ within which they produce the cells to maintain and repair tissues throughout an organism’s life.

Question 38

How does deacetylation affect the epigenome?

Answer 38

Decreased acetylation increases the positive charges on histones and increases the attraction to the negative phosphate groups of DNA, making DNA-histone attraction stronger, making the DNA less accessible to transcription factors

Question 39

How does methylation of DNA affect the epigenome?

Answer 39

Methyl groups are added to cytosine bases in the DNA helix, preventing the binding of transcription factors

Question 40

Describe how totipotent plant cells can be formed?

Answer 40

• Scrape leaves off a plant
• Place these in a Petri dish containing nutrients, auxins, IAA, etc
• This stimulates cells to undifferentiate and forms roots and shoots

Question 41

How is double stranded RNA (dsRNA) formed?

Answer 41

RNA dependent RNA polymerase catalyse the production of dsRNA from mRNA found in the cytoplasm.

Question 42

What happens to totipotent cells during embryonic development?

Answer 42

Certain parts of the DNA are selectively translated so that only some genes are “switched on” in order to differentiate the cell into a specific type and form the tissues that make up the foetus.

Question 43

Give a unique feature of pluripotent cells and the use of this feature

Answer 43

They can divide in unlimited numbers, and can therefore be used to repair or replace damaged tissues

Question 44

What is a unipotent cell and give an example.

Answer 44

A cell that can only develop into one type of cell. This happens at the end of specialisation when the cell can only propagate its own type. An example is cardiomyocetes (heart cells)