3.8.2 Gene Expression

Question 1

Whats cell differentiation

Answer 1

Process how a cell develops a specialised structure to carry out a suited role

Question 2

What are totipotent cells

Answer 2

Divide and produce any type of body cell

Question 3

How are totipotent cells specialised

Answer 3

During development, only part of their DNA is translated into proteins, only produces proteins needed for its specialised function

Question 4

When are totipotent cells present

Answer 4

Occur for a limited time in an early mammalian embryo

Question 5

What are pluripotent stem cells

Answer 5

Differentiate into almost any type of cell
(All body cells except placenta cells)

Question 6

Where are pluripotent stem cells found

Answer 6

Found in embryos

Question 7

What’s a characteristic of pluripotent stem cells

Answer 7

Divide in unlimited numbers and can be used to treat human disorders

Question 8

What are multipotent stem cells

Answer 8

Divide to form a limited number of different cell types

Question 9

Where are multipotent stem cells found

Answer 9

Mature mammals

Question 10

What are unipotant stem cells

Answer 10

Differentiate into a single type of cell

Question 11

Where are unipotent stem cells found

Answer 11

Mature mammals

Question 12

Give an example of unipotent stem cells

Answer 12

Cardiomyocites, heart muscle cells which divide to produce new heart tissue repairing damage to heart muscle

Question 13

What are induced pluripotent stem cells, iPS cells

how are they produced

And their features

Answer 13

A pluripotent cell produced from a unipotent stem cell

Genetically altered to acquire characteristics of embryonic stem cells by inducing genes and protein transcriptional factors

Self renewal, divide indefinitely

Replaces embryos on research overcoming ethical issues

Question 14

How can pluripotent stem cells treat human disorders

Answer 14

Regrow damaged tissue

Question 15

What are transcriptional factors

Answer 15

A specific molecule causing genes to be switched on for transcription to start
These molecules move from the cytoplasm into the nucleus

Question 16

What’s a steroid hormone and name one

Answer 16

Oestrogen
Lipid soluble molecule

Question 17

What’s the role of oestrogen in initiating transcription

Answer 17

Lipid soluble, easily diffused through phospholipid bilayer
Oestrogen binds with a complimentary receptor of the transcriptional factor
Oestrogen changes shape of DNA binding site on transcriptional factor casing it to bind to DNA
Transcritpional factor enters the nucleus through a nuclear pore, binds to a specific base sequence on DNA
Transcriptional factor with DNA stimulates transcription of the gene

Question 18

How do transcriptional factors work

Answer 18

Transcriptional factors move from cytoplasm to nucleus, transcriptional factor binds to a specific base sequence of DNA, after binding it causes the region of DNA to begin transcription, mRNA is produced and the information it carries is translated into a polypeptide, when a gene isn’t expressed the site on the transcriptional factor binding to DNA is inactive, no transcription nor polypeptide synthesis

Question 19

What’s epigenetics

Answer 19

Heritable change in the gene function without changing the base sequence of DNA
Changes are caused by environmental factors like stress diet and toxins, this can inhibit transcription

Question 20

What’s the epigenome

Answer 20

DNA is wrapped around proteins called histones forming a DNA histone complex

The DNA histone complex is covered in chemicals, these chemicals form a layer called the epigenome

Epigenome determine the shape of the DNA histone complex

Question 21

How do environmental factors inhibit transcription

Answer 21

Chemicals forming the epigenome respond to environmental changes

Two examples of these chemical processes are increased methylation of DNA and decreased acetylation of associated histones forming

Question 22

How does increased methylation of DNA inhibit transcription

Answer 22

A methyl group is added to cytosine bases of DNA, methylation inhibits transcription

It prevents transcriptional factors from binding to the DNA
Attracts proteins that condense the DNA histone complex, DNA is inaccessible to transcription factors

Methylation, works on me and I’m made of DNA, mutes the gene

Question 23

How does decreased acetylation of associated histones inhibit transcription

Answer 23

Acetylation, an acetyl group from acetyl co A is transferred to a molecule

Decreased acetylation increases the +ve charges on histones, increasing their attraction to phosphate groups on DNA, stronger association between DNA and histones, not accessible by transcription factors, mRNA production isn’t initiated, gene is switched off

Question 24

How can epigenetics detect and treat disease such as cancer

Answer 24

Altering epigenetic processes causes abnormal activation/silencing of genes, this increases the risk of mutations, which is associated with cancer

Treatments use drugs to inhibit enzymes involved with histone acetylation/DNA methylation to counteract the initial epigenetic changes
These treatments can only be used in cancerous cells or would cause cancer in healthy cells

Diagnostic tests for cancer, brain disorders and arthritis, test detects levels of DNA methylation and histone acetylation at an early stage, allows treatment to be sought earlier

Question 25

Whats transcritpion and translation in basic terms

Answer 25

Transcritpion results in mRNA production Translation, mRNA attaches to a ribosome and produces a protein

Question 26

What does RNAi RNA interference do and explain how

Answer 26

Inhibits translation of mRNA from target genes in eukaryotes and some prokaryotes 1. An enzyme cuts large double stranded molecules of RNA into smaller sections called small interfering RNA (siRNA) 2. 1 of the 2 strands of siRNA combines with an enzyme 3. siRNA guides the enzyme to an mRNA molecule, pairing up its own bases with complimentary ones on the section of mRNA 4. The enzyme cuts mRNA into smaller sections 5. mRNA can no longer be translated into a polypeptide as the gene is not expressed

Question 27

What’s a tumor Give some similarities and differences between benign and malignant ones

Answer 27

Tumour, a group of abnormal cells dividing uncontrollably Benign S grow large in size D grow slowly D form primary tumours as adhesion molecules make cells stay within tissues D rarely reoccur after treatment Malignant S grow to a large size D grow rapidly D form secondary tumours, no adhesion molecules so spread through body called metastasis D frequently reoccur after treatment

Question 28

How do tumour suppressor genes and oncogenes result in tumours

Answer 28

(Normal) car driving at limit Protoncogenes stimulate a cell to divide when growth factors attach to a protein receptor in its cell surface membrane, activates the gene for DNA replication (Cancer) car speeding it can mutate into an oncogene being permanently activated if the receptor protein is permanently activated even without growth factors or the oncogene codes for a growth factor produced in excessive amounts both of these stimulate excess cell division (Normal) slowly brake tumour suppressor genes slow down cell division, repair mistakes in DNA and promote programmed cell death (adoptosis) (Cancer) no brake If a tumor suppressor gene becomes mutated it is inactivated, stops inhibiting cell division cells grow out of control, these are structurally and functionally different some survive and make clones forming tumours Oncogenes cause cancer when activated Tumour suppressor genes cause cancer when inactivated

Question 29

How does abnormal methylation of tumour suppressor genes and oncogenes lead to tumours

Answer 29

Increased methylation at the promoter region of tumour suppressor genes, tumour suppressor gene is inactivated, transcription at the promoter region is inhibited, tumour suppressor gene is silenced, increased cell division leading to the formation of a tumour Reduced methylation at the promoter region of oncogenes, oncogenes are activated, transcription at the promoter region occurs, oncogenes are expressed, increased cell division forming tumours

Question 30

How do increased oestrogen levels lead to the development of breast cancer

Answer 30

Oestrogen can activate a gene that controls cell division (protooncogenes) by binding to a receptor, promoting transcription, activates the gene (oncogene) development of breast cancer A tumour further increases oestrogen conc, white blood cells drawn to the tumour also increase oestrogen conc both leading to greater development of the tumour