Control of Gene Expression- BP

Question 1

What is a stem cell?

Answer 1

 a unspecialised/undifferentiated cell
 potential to form different types of cells

Question 2

How does a stem cell become specialised?

Answer 2

 differentiation
 3 changes: cell shape, number of organelles, new content
 occurs by controlling gene expression (some gene are activated, other genes are inhibited)

Question 3

Stem Cell in Animals/Mammals/Humans?

Answer 3

• embryonic
• umbilical cord blood stem cells
• placental stem cells
• adult stem cells

Question 4

What are Induced Pluripotent Stem Cells (iPS Cells)?

Answer 4

• turning unipotent body cells into pluripotent cells (like embryonic stem cells)
• involves activating certain deactivated genes using transcription factors

Question 5

Stem Cell Therapy in Humans? (2 uses)

Answer 5

 use stem cells to produce tissues/organs for transplant
 use stem cells to treat irreversible diseases e.g. heart disease, type 1 diabetes, paralysis (inject stem cells at site of disorder – will differentiate to become local specialised cells e.g. heart muscle cells, beta cells of pancreas, neurones)

Question 6

what is a totipotent stem cell?

Answer 6

• found in the early embryo
• can differentiate into any type of cell

Question 7

what is a pluripotent stem cell?

Answer 7

• found in embryos
• can differentiate into almost any type of cell

Question 8

what is a multipotent stem cell?

Answer 8

• found in adults
• can differentiate into a limited number of specialised cells
• eg. adult stem cells and umbilical cord blood stem cells

Question 9

what are unipotent stem cells?

Answer 9

• can only differentiate into a single type of cell
• derived from multipotent stem cells
• made in adult tissue
• eg. cardiomyocytes

Question 10

Stem Cell in Plants?

Answer 10

 In embryo = Zygote/Embryonic Stem Cells
 In adult = Meristem Cells in Stem/Shoot/Root

Question 11

Uses of Stem Cells from Plants?

Answer 11

 traditionally cuttings were taken from plants (stem/shoot/root) and used to grow genetically identical plants – possible due to presence of meristem cells
 tissue culture (micro propagation) = large scale application of cuttings

Question 12

process of growing genetically identical plants?

Answer 12

 take cutting from shoot/stem/root (called explant)
 place explant in nutrient rich medium so meristem cells divide by mitosis
 produces a mass of meristem cells (called callus)
 take each meristem cell and grow in plant growth factor medium to promote differentiation and formation of shoot/root
 transfer plant to soil and greenhouse
 then transfer to field

Question 13

what is controlling gene expression?

Answer 13

 either Activating or Inhibiting a Gene
 activating gene = protein made
 inhibiting gene = protein not made

Question 14

Example of activating genes? (using oestrogen)

Answer 14

 oestrogen can enter a cell by simple diffusion and bind to receptors on the transcriptional factor
 causes transcriptional factor to change shape
 so transcriptional factor can now enter nucleus and bind to promoters on the DNA to activate transcription
= activated genes (protein to be made)

Question 15

Example of inhibiting genes?

Answer 15

• using siRNA (small interfering RNA)
• double stranded RNA cut down into small sections
• made single stranded
• then attaches to an enzyme
• siRNA will bind to complementary sections on mRNA
• the enzyme will cut the mRNA so translation cannot occur
• gene inhibited (protein not made)

Question 16

What is Epigenetics?

Answer 16

 Heritable changes in gene function without changes to base sequence of DNA
 Changes may due to lifestyle, stress, diet

Question 17

How does Methylation affect the Genome?

Answer 17

Increased Methylation :
- adding methyl groups
- this attracts proteins which condense the DNA-Histone Complex
- transcription factors cannot gain access (gene inhibited)

Question 18

What is a Gene Mutation?

Answer 18

 a change in the base sequence of DNA
 2 types = substitution and insertion/deletion

Question 19

what is subsitution?

Answer 19

• substitution = replace one base for another, changes one triplet code
• can be silent (new triplet code codes for same AA), mis-sense (codes for a different AA, so protein shape changes slightly), non-sense (codes for a stop codon, so polypeptide chain not produced)

Question 20

where are stem cells found in plants?

Answer 20

meristems

Question 21

what is the epigenome and what does it determine?How?

Answer 21

 Chromatin (DNA-Histone Complex) is surrounded by an Epigenome (chemical layer)
 Epigenome can either cause the Chromatin to become more condensed or more loose
 Chromatin becoming more condensed means transcription factors cannot reach the DNA and the gene will be inactivated
 Chromatin becoming more loose means transcription factors can reach the DNA and the gene will be activated
 These changes may be brought about by Acetylation or Methylation

Question 22

Cancer?

Answer 22

 caused by mutation of genes that control cell division
 causes of mutation = random or mutagens (chemicals/radiation)
 mutation of proto-oncogene leads to formation of a oncogene = over production of growth factor or receptor proteins permanently active = over stimulation of cell division (uncontrolled cell division)
 mutation of tumour-suppressor gene = loss of protein to inhibit cell division (uncontrolled cell division)

Question 23

Oestrogen and Cancer?

Answer 23

Oestrogen leads to activation of genes – high levels of oestrogen can lead to over activation of Proto-Oncogene forming an Oncogene = Cancer (uncontrolled cell division)

Question 24

Oestrogen and Cancer?

Answer 24

Oestrogen leads to activation of genes – high levels of oestrogen can lead to over activation of Proto-Oncogene forming an Oncogene = Cancer (uncontrolled cell division)

Question 25

Epigenetics and Cancer?

Answer 25

Main Example = increased methylation of tumour suppressor genes leads to inhibition of tumour suppressor genes leading to cancer (uncontrolled cell division)

Question 26

How does Acetylation affect the Genome?

Answer 26

Decreased Acetylation:
- removing acetyl groups
- increases positive charges on the Histone
- increases the attraction to the phosphate groups on DNA
- condense the DNA-Histone Complex
- transcription factors cannot gain access (gene inhibited)