Module 8 - Gene expression is controlled by a number of features

Question 1

What are stem cells?

Answer 1

They are unspecialised cells that can develop into many different types of cells

Question 2

Where are stem cells found?

Answer 2

Bone marrow

Question 3

What is a totipotent stem cell?

Answer 3

They can develop into any type of cell in an organism but they only remain in the first few cell divisions of an embryo where they eventually because pluripotent

Question 4

What is a pluripotent stem cell?

Answer 4

These are also found in embryos and can divide into any time of specialised body cell besides cells that make the placenta

Question 5

What are the two adult stem cells?

Answer 5

• Multipotent stem cells
• Unipotent stem cells

Question 6

What are multipotent stem cells?

Answer 6

They can divide into only a few types of stem cells
They can only differentiate into one type of cell

Question 7

How are specialised cells produced?

Answer 7

During development, not all genes are transcribed and translated. Therefore under the right conditions, some genes are expressed and others aren’t

Question 8

What are cardiomyocytes?

Answer 8

These are heart muscle cells that make up lots of tissue in the heart. In mature mammals, it is thought that they can’t divide to replicate themselves

Question 9

What does new research show about cardiomyocytes?

Answer 9

Heart muscle has some reproductive capability. New heart muscle cells are derived from a smaller number of unipotent cells in the heart

Question 10

What is Stem cell therapy?

Answer 10

Sometimes, bone marrow produce abnormal blood cells and so transplants can be done to replace bone marrow in patients where it is faulty

Question 11

The benefits of using stem cells in medicine?

Answer 11

• Save lives as they can be used to grow organs whilst waiting for a transplant
• Improve the quality of life for some people

Question 12

What are the 3 ways stem cells are derived to be used to treat human disorders?

Answer 12

• Adult stem cells
• Embryonic stem cells
• iPS cells

Question 13

How are stem cells derived from an embryo?

Answer 13

Embryos are created in a lab. When they are 4-5 days old, stem cells are removed and the remaining embryo is destroyed. These can divide an unlimited number of times into any body cell

Question 14

What are induced pluripotent cells?

Answer 14

They are made in a lab by reprogramming specialised adult body cells so they become pluripotent. Transcription factors determine the genes associated with pluripotency will be expressed

Question 15

How do iPS cells work?

Answer 15

Transcription factors determine the genes associated with pluripotency will be expressed
- A virus that contains the genes coding for the transcription factors is introduced to an adult cell. It then infects the adult cell causing the genes to be pass into the adult’s cells DNA

Question 16

What are the ethical concerns around embryonic stem cells?

Answer 16

• Destroys an embryo which could have been grown in the womb
• Some people think only adult stem cells should be used but these don’t divide into specialised stem cells

Question 17

What are transcription factors?

Answer 17

This is when transcription of genes is controlled by protein molecules

Question 18

How do transcription factors work?

Answer 18

1. They move from the cytoplasm to the nucleus
2. They bind to specific DNA sites near the target genes in the nucleus
3. Some transcription factors known as activators, stimulate or increase the rate of transcription. Others known as repressors inhibit or decrease the rate of transcription

Question 19

What is oestrogen ?

Answer 19

It is a hormone that affects transcription

Question 20

How does oestrogen work?

Answer 20

It binds to a transcription factor, forming an oestrogen-oestrogen receptor complex. The complex moves from the cytoplasm to the nucleus where it binds to specific DNA sites near the target gene.
The complex can act as a repressor or activator, depending on the gene

Question 21

What is RNAi?

Answer 21

This is RNA interference when RNA molecules stop mRNA from target genes being translated into proteins

Question 22

What molecules are involved in RNAi? Where does it take place?

Answer 22

SiRNA, miRNA - Plants

Question 23

How does RNAi take place in plants?

Answer 23

The mRNA that has been transcribed will leave the nucleus and enter the cytoplasm. In the cytoplasm, the double-stranded RNA will associate with proteins and unwinds where a single stranded RNA binds with the complementary target mRNA. The proteins associated with the siRNA cut the mRNA into fragments and the processing body is where the fragments are moved to be degraded

Question 24

What molecules are involved in RNAi in mammals?

Answer 24

miRNA

Question 25

How does RNAi in mammals work?

Answer 25

miRNA isn't fully complementary to the target mRNA. This makes it less specific than siRNA and so it may target more than one RNA. The miRNA associates with proteins and binds to target mRNA in the cytoplasm. The miRNA-protein complex physically blocks the translation of the target mRNA. The mRNA is then moved into the processing body where is is either stored or degraded. When it is stored it can be revived and translated another time.

Question 26

What is epigenetics?

Answer 26

The heritable changes to gene function without changes to the base sequence DNA

Question 26

What is transcriptional machinery?

Answer 26

This is anything that stimulates transcription

Question 27

What do epigenetic markers affect?

Answer 27

They alter how easy it is for transcriptional machinery to bind instead of altering the base sequence

Question 28

Are epigenetic genes hereditary?

Answer 28

Yes, they can be passed on through inheritance

Question 29

How does increases methylation of the DNA inhibit transcription?

Answer 29

The methyl group will bind to a cpg binding site where cytosine and guanine are next to each other, on a DNA coding for a gene. Increased methylation changes the DNA structure so that the transcriptional machinery cannot interact with the gene - so that the gene is not expressed

Question 30

How does decreased acetylation of associated histone proteins, inhibit transcription?

Answer 30

When the histones are acetylated - acetyl group binds to the protein - the chromatin becomes less condensed. This means transcriptional machinery can access the DNA, allowing the genes to be transcribed. When the acetyl groups are removed, the protein can't be transcribed as the transcriptional machinery can't bind

Question 31

What is responsible for the removal of acetyl groups

Answer 31

The enzyme Histone deacetylase (HDAC)

Question 32

How can drugs be used to treat diseases caused by epigenetic changes?

Answer 32

HDAC can be inhibited which are responsible for removing acetyl groups from histones. Therefore they remain acetylated and transcription can continue to occur

Question 33

What is one problem with epigenetic genes?

Answer 33

They are present in many cells and so it is important to make them as specific as possible.

Question 34

What is a medical benefit to using iPS cells instead of embryonic stem cells in stem cells therapies?

Answer 34

The iPS cells are made from a patient's own cells. This means that the iPS cells are genetically identical to the body cells so the chances of them being rejected is small

Question 35

The insertion of the DNA copy in one of the host cell's genes may cause the cell to make a non-functional protein?

Answer 35

It alters the base sequence which leads to a different sequence of amino acids

Question 36

Explain how activated oestrogen receptor affects the target cell?

Answer 36

Receptor binds to the promoter which stimulates RNA polymerase. Transcribes genes

Question 37

Explain why oestrogen does not affect other cells in the body?

Answer 37

Other cells in the body don't have oestrogen

Question 38

How could treatments that reverse epigenetic changes prevent cancer?

Answer 38

1. Drugs could increase methylation of oncogenes 2. Drugs could increase the methylation of tumour suppressor genes 3. Increased methylation of DNA inhibits the transcription of genes