3.11 - 3.14 : Stem Cells & Epigenetics

Question 1

What are stem cells ?

Answer 1

Stem cells are cellas that are unspecialised which have the ability to become specialised or can divide to produce more stem cells, such as heart cells or neurons.

Question 2

What is cell differentiation/specialisation ?

Answer 2

The process by which a stem cell is converted from an unspecialised cell to a specialised cell

Question 3

What are totipotent cells.

Answer 3

totipotent cells have the ability to divide into any type of cell (including the extraembryonic cells and placenta cells).

Question 4

What is meant by the term Totipotency

Answer 4

A cells that has the ability to differentiate into all cell types.

Question 5

What is mean by the term Pluripotency.

Answer 5

A cell that has the ability to differentiate into any cell type excluding extra embryonic tissues.

Question 6

Give one difference between a tissue and an organ.

Answer 6

• A tissue is made of one type of cell and an organ is made of different tissue.

Question 7

What is an organ ?

Answer 7

A specialised structure that is composed of multiple tissues that work together to perform a specific function within an organism.

Question 8

What is a tissue ?

Answer 8

A tissue is an group of cells that have a similar structure and function, and work together to perform a specific task within an organism.

Question 9

Describe how cells become specialized ?

Answer 9

• Chemical signals cause some genes to be activated. (1)
• Only activated genes are transcribed.(1)
• mRNA leads to the synthesis of specific proteins which cause cell modification. (1)

Question 10

Give some uses of stem cells.

Answer 10

• Used to treat disease, such as parkinson’s and multiple sclerosis
• Replace damaged tissues, such as spinal cords.

Question 11

Explain the advantages of using stem cells from the patient instead of using stem cells from
a donor.
(2)

Answer 11

Question 12

Why is the use of stem cells controversial ?

Answer 12

• Stem cells involves destroying embryos. Which some people believe that the destruction of human embryos, even at the earliest stages of development, is morally wrong and constitutes the taking of human life.
• There is a risk of infection after transplant.

Question 13

What are transcription factors ?

Answer 13

Proteins that carry out the activation and deactivation of genes.

Question 14

What are activators ?

Answer 14

Tfs which activate genes.
Activators can work by binding to the beginning of the gene (the promoter region) and helping RNA polymerase to bind and transcribe the gene.

Question 15

What are repressors ?

Answer 15

Tfs that deactivate genes. Repressors can work by binding to the gene and blocking RNA polymerase from binding.

Question 16

What is meant by epigenetics ?

Answer 16

A heritable change in gene function without change to base sequence of DNA.

Question 17

Epigenetic changes can cause monozygotic twins to have different body masses. Explain how epigenetic changes can cause differences in a characteristic. (3)

Answer 17

Question 18

As pluripotent stem cells divide, epigenetic changes are passed on.
Explain how epigenetic changes affect the activation of genes in daughter cells. (3)

Answer 18

Question 19

What is *epigenetic modification**.

Answer 19

Epigenetic modification involves the addition or removal of chemical ‘tags’ onto DNA or histone proteins.

These modifications are caused by environmental factors (such as diet, stress and smoking) and can occur from as early as when we are in the womb.

Question 20

What does the removal of epigenetic tags do ?

Answer 20

It makes the chromosome more or less accessible to RNA Polymerase, transcription factors and other proteins which are involved in transcription.

Question 21

What are the two main types of epigenetic tags.

Answer 21

methyl groups and acetyl groups.

Question 22

DNA methylation

Answer 22

Methyl groups (-CH3) added directly onto the DNA. methylation typically occurs at cytosine bases that are followed by guanine bases, forming what is known as a CpG site. The addition of a methyl group can either activate or inactivate genes depending on the position.

Question 23

What is acetylation ?

Answer 23

Acetyl groups (COCH3) can be added to lysine amino acids on histone proteins. Acetylation of histones alters accessibility of chromatin and allows DNA binding proteins to interact with exposed sites to activate gene transcription.

Question 24

Describe the role of DNA methylation in regulating gene expression.

Answer 24

DNA methylation is the addition of methyl groups (CH3) to cytosine bases in the DNA sequence, typically occurring at CpG sites. Methylation can lead to gene silencing by inhibiting transcription factor binding or by recruiting proteins that promote chromatin condensation.

Question 25

What is a transcription factor ?

Answer 25

Something (protein) that affects the rate of transcription.

Question 26

What is an mRNA enzyme.

Answer 26

Enzymes that destroy mRNA strands. We can then recycle the RNA nucleotide.

Question 27

Continuous vs Discontinuous data ?

Answer 27

Question 28

What does it mean by monogenetic ?

Answer 28

Characteristics which are controlled by the expression of a single gene. These kinds of characteristics typically give rise to discontinuous variation in the phenotype that is expressed e.g blood type.

Question 29

What does it mean by polygenetic ?

Answer 29

Characteristics which are controlled by many genes at different loci. Polygenic characteristics show continuous variation which is when the individuals in a population vary within a range. e.g weight, skin colour and height.

Question 30

What is meant by a multifactorial condition ?

Answer 30

Conditions where several genetic and environmental factors are said to be involved.

Question 31

What is beta-galactosidase ?

Answer 31

An enzyme that hydrolyses the glycosidic bond in lactose into glucose and galactose
B.

Question 32

What is lactose permease ?

Answer 32

A transport protein (carrier protein) that when embedded in the e.coli membrane it allows the lactose to enter into the cell.
Y

Question 33

Things to clear up.

Answer 33

Although the whole point of the lac operon is to allow lactose into the cell, there is still some lactose inside of the cell already this lactose binds to the repressor gene, changing its shape inhibiting it from binding to the operator so that the promoter region is freed up.

Also the Whole thing is calle the lac operon.

Question 34

What is the repressor protein in terms of lac operon.

Answer 34

The repressor protein is transcribed from the regulatory gene. It then binds to the operator region, this blocks RNA polymerase from binding to the promoter region so the structural genes(Y and Z) not transcribed.

Question 35

How would the operon look if lactose was absent outside the cell ?

Answer 35

When lactose is absent, a regulatory gene (lacI) produces a protein called the lac repressor. The lac repressor is a transcription factor which binds to the operator region. This blocks RNA polymerase from binding to the promoter region so the structural genes are not transcribed.

Question 36

How would the operon look if lactose was present outside the cell ?

Answer 36

Lactose (that is already inside the cell) binds to the repressor and changes its shape. This shape change means that the repressor can no longer bind to the operator, allowing RNA polymerase to bind to the promoter region. RNA polymerase transcribes the structural genes - lacZ and lacY. LacZ codes for an enzyme called beta-galactosidase which breaks the glycosidic bond in lactose, breaking it down into glucose and galactose. LacY codes for a protein called lactose permease, a carrier protein which transports lactose into the cell.

Question 37

What is the operon.

Answer 37

A section of DNA containing a structural genes and regulatory genes. Operons DO NOT exist in eukaryotic cells.

Question 38

What elements make up operons:

Answer 38

• Structural genes: these code for useful proteins such as enzymes e..g lacZ (beta-galactosidase) and lacY (lactose permease).
• Control elements: these contain a promoter region where RNA polymerase can bind and an operator region where transcription factors can bind.
• Regulatory gene: these codes for transcription factors (activators or repressors). e.g lac repressor.