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). They are found during the early stages of embryonic development. E.g in the zygote

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 placenta cells. The are found in embryos.

Question 6

What is a multipotent stem cell

Answer 6

stem cells that are found in the bone marrow whereas pluripotent are found in embryonic stem cells

Question 7

Give one difference between a tissue and an organ.

Answer 7

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

Question 8

What is an organ ?

Answer 8

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

Question 9

What is a tissue ?

Answer 9

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 10

Describe how cells become specialized ?

Answer 10

• 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 11

Give some uses of stem cells.

Answer 11

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

Question 12

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

Answer 12

Question 13

Why is the use of stem cells controversial ?

Answer 13

• 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 14

What are transcription factors ?

Answer 14

Proteins that carry out the activation and deactivation of genes.

Question 15

What are activators ?

Answer 15

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 16

What are repressors ?

Answer 16

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

Question 17

What is meant by epigenetics ?

Answer 17

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

Question 18

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

Answer 18

Question 19

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

Answer 19

Question 20

What is epigenetic modification.

Answer 20

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 21

What does the removal of epigenetic tags do ?

Answer 21

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

Question 22

What are the two main types of epigenetic tags.

Answer 22

methyl groups and acetyl groups.

Question 23

DNA methylation

Answer 23

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 24

What is acetylation ?

Answer 24

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 25

Describe the role of DNA methylation in regulating gene expression.

Answer 25

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 26

What is a transcription factor ?

Answer 26

Something (protein) that affects the rate of transcription.

Question 27

What is an mRNA enzyme.

Answer 27

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

Question 28

Continuous vs Discontinuous data ?

Answer 28

Question 29

What does it mean by monogenetic ?

Answer 29

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 30

What does it mean by polygenetic ?

Answer 30

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 31

What is meant by a multifactorial condition ?

Answer 31

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

Question 32

What is **beta-galactosidase** ?

Answer 32

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

Question 33

What is **lactose permease** ?

Answer 33

A **transport protein** (carrier protein) that when embedded in the **e.coli membrane** it allows the lactose to enter into the cell cytoplasm **Y** • Lactose permease is encoded by the lacY gene. • It works via facilitated diffusion or active transport (using the proton gradient) to move lactose across the cell membrane.

Question 34

Things to clear up.

Answer 34

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 35

What is the repressor protein in terms of lac operon.

Answer 35

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 36

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

Answer 36

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 37

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

Answer 37

**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 38

What is the operon.

Answer 38

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

Question 39

What elements make up operons:

Answer 39

- **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**.

Question 40

Answer 40