Gene expression is controlled by a no. of features

Question 1

define stem cells

Answer 1

unspecialised cells that can develop into other types of cell and keep dividing/replacing themselves

Question 2

Explain how Totipotent stem cells work

Answer 2

• present for limited time (in the first few divisions of mammalian embryo)
• can divide and produce any body cell type
• not all stem cells expressed in development=some not transcribed/translated into proteins
• mRNA transcribed from specific genes and translated into proteins which determines cell structure/function by modifying the cell (now specialised cell which is irreversible)

Question 3

Explain how Pluripotent stem cells work

Answer 3

• embryonic stem cells which can divide in unlimited numbers and can develop into most body cell types except placenta
• used to treat human disorders so obtained from 4-5 day old embryos spare from usage in IVF (rest of embryo destroyed)

Question 4

Explain how Multipotent stem cells work

Answer 4

Adult cells which can develop into a limited no. of cell types e.g. obtains bone marrow cells to develop into red/white blood cells

Question 5

Explain how Unipotent stem cells work

Answer 5

only differentiates into one type of cell e.g. cardiomyocytes(heart muscle cells) can’t regenerate BUT formed from one type of unipotent cell

Question 6

How are induced pluripotent stem cells used in research/medicine?

Answer 6

somatic adult specialised cells infected with modified virus with genes coding for transcription factors so cells become pluripotent

Question 7

how do cells become specialised?

Answer 7

stem cells contain same genes but to become specialised is due to different genes being expressed.

Question 8

How do transcription factors control the rate of transcription of target genes?

Answer 8

• moves from cytoplasm to nucleus

- binds to specific promoter regions near start of target gene and controls expression of that gene

Question 9

define promoter region

Answer 9

a region of DNA where transcription of a gene is initiated.

Question 10

What are activators?

Answer 10

they stimulate and increase the rate of transcription e.g. by helping RNA polymerase bind.

Question 11

What are repressors?

Answer 11

inhibit and decrease the rate of transcription e.g. by binding to the start of a gene and preventing RNA polymerase from binding.

Question 12

How does oestrogen initiate the transcription of a target gene?

Answer 12

• it’s small and hydrophobic so diffuses through the membrane into cells
• binds to ERa oestrogen receptor in the cytoplasm which is held in a protein complex but changes shape and releases it
• ERa oestrogen receptor now enters nucleus and binds to promoter region of one of its target genes and stimulates RNA polymerase to transcribe that target gene

Question 13

How does small interfering RNA (siRNA) inhibit the translation of mRNA?

Answer 13

• found in cytoplasm and associates with proteins and unwinds to form single strands
• single strand binds to target mRNA by complementary base pairing
• proteins associated with siRNA cut mRNA into pieces so it can’t be translated anymore
• fragments move to the processing body where they’re degraded
• similar process with miRNA in plants

Question 14

How does microRNA (miRNA) inhibit translation of mRNA?

Answer 14

• miRNA in mammals not fully complementary to target mRNA so targets more than one mRNA molecule usually
• associates with proteins and binds to target mRNA in cytoplasm
• miRNA-protein complex blocks translation of target mRNA
• mRNA moved to processing body to be stored/degraded

Question 15

Define epigenetic

Answer 15

heritable changes in gene function.

Question 16

Explain epigenetic control of gene expression in eukaryotes

Answer 16

• DNA wrapped around histones where if wound around tightly, genes are ‘switched off’
• chemicals can attach to histones/DNA to affect winding
• no changes to DNA base sequence so epigenetic changes may be inherited

Question 17

How does increased methylation of DNA inhibit transcription? (change in environment)

Answer 17

• could be result of diet/stress/smoking/food availability
• methyl group attached to gene/CG sequence of bases
• growth of tumours can be due to abnormal methylation of tumour suppressor genes (changes DNA structure so proteins/enzymes can’t interact)

Question 18

How does decreased acetylation of associated histones inhibit transcription?

Answer 18

acetyl groups (COCH3) removed which condenses chromatin (DNA + histones) so can’t be transcribed

The looser arrangement of nucleosomes increases transcription

Question 19

How can drugs reverse epigenetic changes?

Answer 19

can switch DNA methylation off so can treat cancers caused by increased methylation of tumour suppressor genes.

Question 20

Define a tumour

Answer 20

mass of abnormal cells if a cell divides by mitosis uncontrollably

Question 21

Explain what tumour suppressor genes are

Answer 21

• slows cell division by producing proteins that can also cause cell death.
• can be inactivated by mutations or increased methylation

Question 22

What are proto-oncogenes?

Answer 22

stimulates cell division effect can be increased by mutations/decreased methylation becoming oncogenes by hypomethylation (too little)

Question 23

Define benign tumours

Answer 23

not cancerous tumours which grow slow and tend to be harmless non-spreading tumours BUT can cause blockages which puts pressure on organs.

Question 24

Define malignant tumours

Answer 24

cancerous tumours which grow rapidly and invade/destroy surrounding tissue.Cells can break off and spread to other parts of the body in blood or lymph.

Question 25

What does hyper-methylated lead to?

Answer 25

genes not being transcribed.

Question 26

Increased oestrogen can contribute to some breast cancers, what increases oestrogen?

Answer 26

• starting menstruation earlier/later than usual

- taking it in hormone replacement therapy

Question 27

What does the equation f=ix^2n indicate?

Answer 27

f=final no. of bacteria/cells
i=initial no. of bacteria
n=no. of generation