Chapter 20 - Gene expression

Question 1

What are totipotent stem cells?

Answer 1

Stem cells which can differentiate into any type of cell they have total potential

Question 2

What are two key features of stem cells?

Answer 2

1. Ability to differentiate into other cells and become specialised
2. Self renewal

Question 3

Can you explain how cells lose their totipotency and become specialised?

Answer 3

Certain genes are turned on or off which causes the totipotent cells to differentiate and become specialised then cannot un differentiate the process is reversible

Question 4

Can you describe cell differentiation and cell specialisation?

Answer 4

Cell differentiation is the process in which cells become specialised for a particular function by particular genes being expressed or not

Question 5

Can you describe the origins of stem cells?

Answer 5

Stem cells originate in the fetus as embryonic stem cells then become fetal and adult stem cells

Question 6

Can you describe the different types of stem cells?

Answer 6

Totipotent - found in the embryo and can differentiate into any type of cell
Pluripotent - can differentiate into almost all types of cell but not the placenta
Multipotent - Can differentiate into a limited number of cells
Unipotent - can only differentiate into one type of cell

Question 7

What are some sources of stem cells in mammals?

Answer 7

Embryonic stem cells, fetal stem cells in umbilical cord, cortex, retina and cortex and adult stem cells om bone marrow, skin, blood, eyes and brain

Question 8

What are the two ways to control gene expression?

Answer 8

1. Regulating transcription

2. Regulating translation

Question 9

What controls transcription?

Answer 9

Transcription factors

Question 10

How does oestrogen affect transcription?

Answer 10

1. Oestrogen is a steroid hormone lipid soluble which enters the cells membrane through simple diffusion across the phospholipid bilayer
2. Oestrogen binds to the oestrogen receptor on the transcription factor and causes a change in shape of the DNA binding site on the transcription factor
3. The DNA binding site can then bind to the promotor region of DNA and allows RNA polymerase to bind and transcription occurs so gene is switched on

Question 11

What is epigenetics?

Answer 11

The study of an organisms genetics caused by modification of gene expression rather than alteration of the genetic code itself

Question 12

What is a nucleosome made up of?

Answer 12

A 8 histone protein core with DNA wrapped round it

Question 13

What is the type of DNA called that is more condensed, less accessible to transcription factors so inactive?

Answer 13

Heterochromatin

Question 14

What is the type of DNA called that is less condensed, more accessible to transcription factors and so active?

Answer 14

Euchromatin

Question 15

What are two processes that affect the shape of the DNA - histone complex?

Answer 15

1. Acetylation of histone proteins

2. Methylation of DNA

Question 16

What is the epigenome?

Answer 16

The epigenome is the chemical changes to the DNA and histone proteins of an organism which can be passed down to an organisms offspring with the DNA. It is flexible unlike the DNA sequence and alters due to the environment

Question 17

What is acetylation and what effect does it have on the epigenome?

Answer 17

Acetylation is where an acetyl group is added to the histone protein this causes the DNA to pack more loosely so transcription factor can more easily bind to the promoter region so gene is switched on
Decreased acetylation causes he negatively charged phosphate groups to attract more strongly to DNA causing tighter more condensed DNA histone complex

Question 18

What is methylation and what effect does it have on the epigenome?

Answer 18

Methylation is the addition of a methyl group onto the cytosine base in DNA
Methylation attracts proteins that cause deacetylation of histone and block promotor transcription factors from binding
Switches off the genes

Question 19

What causes methylation and acetylation?

Answer 19

Aging, environmental influences, lifestyle e.g. smoking or diet

Question 20

How can gene expression be controlled by translation?

Answer 20

1. Double strand of RNA is broken up by an enzyme into small interfering RNA (siRNA)
2. One of the two strands of siRNA combines with an enzyme
3. siRNA strand pairs with complementary bases on a mRNA strand
4. The enzyme cuts the mRNA into smaller sections so it can longer be translated

Question 21

What is cancer?

Answer 21

Cancer is a group of diseases caused by mutations to genes that regulate and control the cell cycle and mitosis resulting in uncontrolled growth of cells

Question 22

What are the two types of tumour?

Answer 22

1. Benign - non cancerous

2. Malignant - cancerous

Question 23

What are some features of a benign tumours?

Answer 23

1. Can grow to a large size but grow slowly
2. Cells produce adhesion molecules on their cell surface membranes causing them to stick to each other so they don’t spread
3. Surrounded by a dense capsule so remain in a compact structure
4. Usually only have a localised effect
5. Can usually be removed by surgery and rarely recur

Question 24

What are some features of malignant tumours?

Answer 24

1. Can grow to a large size and grow rapidly
2. Cells usually have a large nucleus that appears dark due to large amount of DNA caused by uncontrolled cell division
3. Cells often unspecialised unlike in benign where they are usually specialised
4. Cells do not produce adhesion molecules on their surface so tend to spread to other areas called metastasis
5. Tumours are not surrounded by a capsule so grow finger like projections into surrounding tissues
6. More likely to be life threatening and effects whole body
7. Removal usually involves surgery as well as chemotherapy and radiotherapy and usually recurs

Question 25

What is metastasis?

Answer 25

The process by which primary tumours spread and result in secondary tumours in other parts of the body

Question 26

What are the two main genes involved in control of cell division?

Answer 26

1. Proto-oncogenes (accelerator for cell division)

2. Tumour suppressor genes ( breaks for cell division)

Question 27

What two things can lead to cancer?

Answer 27

1. Activation of oncogenes

2. Inactivation of tumour suppressor genes

Question 28

What may cause activation of oncogenes?

Answer 28

Hypomethylation (reduced methylation)

Question 29

What many cause inactivation of tumour suppressor genes?

Answer 29

Hypermethylation (increased methylation)

Question 30

What is the link between oestrogen and breast cancer?

Answer 30

After menopause oestrogen not needed so it is more likely to to regulate menstrual cycle instead it is found in breast tissues and promotes transcription so will be activated to continually divide and positive feedback occurs as the tumour increases in size more oestrogen is produced and increases size even further

Question 31

Can you explain how pluripotent stem cells can be used to treat human disorders?

Answer 31

Induced pluripotent cells are produced from unipotent stem cells which are genetically modified by inducing genes and transcriptional factors to turn on genes and acquire characteristics of embryonic stem cells a type of pluripotent stem cell.
Can be used to regrow tissues as they can self replicate so can be used to regrow tissue that has been damaged in an accident or due to disease