gene expression

Question 1

gene mutation =

Answer 1

change in the DNA base seq. of a gene

Question 2

when do gene mutations occur?

Answer 2

randomly during replication (interphase)

Question 3

what increases the freq of gene mutations?

Answer 3

mutagenic agents

Question 4

how can a gene mutation result in a non-functioning protein?

Answer 4

• change in a.a seq so change in primary struc
• H-bonds & ionic bonds will form in diff places
• change in tertiary struc
  (diff shape so diff/non function)

Question 5

how many types of mutation are there?

Answer 5

6

Question 6

mutation

addition

Answer 6

• causes frame-shift to right
• all subsequent codons altered
• codes for diff a.a seq

Question 7

mutation

deletion

Answer 7

• causes frame shift to left
• codes for diff a.a seq

Question 8

mutation

substitution

Answer 8

1. genetic code = degenerate –> new codon may still code for same a.a
2. mutation may occur in intron –> a.a seq not affected

Question 9

mutation

inversion

Answer 9

• section of bases –> inverted
• codes for diff a.a seq

Question 10

mutation

duplication

Answer 10

• one particular base duplicated at least once
• causes frame shift to right
• codes for diff a.a seq

Question 11

mutation

translocation

Answer 11

• a section of bases on one chromosome detaches and attaches onto another chromosome
• results in substantial alteration
• can cause signif impacts on gene exp.

Question 12

stem cells =

Answer 12

undifferentiated cells that can continually divide and become specialised

Question 13

types of stem cells

(all have diff differentiation abilities)

Answer 13

• totipotent
• pluripotent
• multipotent
• unipotent

Question 14

2 uses of stem cell therapy

Answer 14

1. produce tissues/organs for transplants
2. treat irreversible diseases eg. heart disease

Question 15

totipotent

Answer 15

• can divide to prod any type of body cell
• occurs only for limited time in early mammalian embryos

Question 16

pluripotent

Answer 16

• can divide into unlimited numbers
• used to treat human disorders
• found in embryos

Question 17

multipotent & unipotent

Answer 17

• can divide to form a limited no. of diff cell types
• found in mature mammals

Question 18

what are unipotent stem cells used to make?

Answer 18

cardiomyocytes

Question 19

induced pluripotent cells

Answer 19

• prod from adult somatic cells –> overcomes ethical issues of using embryo stem cells
  (to do this, the genes that were switched off to make the cell specialised must be switched back on –> done via use of transcription factors)

Question 20

what is ‘controlling gene expression’?

Answer 20

either activating or inhibiting a gene

Question 21

example of activating genes

(initiating transcription)

Answer 21

using oestrogen

Question 22

example of inhibiting genes

(inhibiting transcription)

Answer 22

using siRNA to inhibit the translation of mRNA

Question 23

transcription factors

Answer 23

• transcription only occurs when a protein from the cytoplasm enters the nucleus and binds to the DNA in the nucleus –> protein = transcription factor
• initiates transcription of genes –> creates mRNA for that gene which can be translated in the cytoplasm

without binding of transcription factor, gene is inactive/not expressed

Question 24

oestrogen

Answer 24

initiates transcription
1. steroid hormone so it diffuses through cell membrane –> lipid soluble
2. binds to receptor site on transcription factor –> causes shape to change slightly
3. change in shape makes it comple. to DNA –> thus, binds to DNA

Question 25

epigenetics =

Answer 25

the **heritable** **change** in gene function, without changing the DNA base seq (changes caused by change in environment)

Question 26

name the methods of **inhibiting** transcription via epigenetics

Answer 26

1. increased methylation of DNA 2. decreased acetylation of histone proteins | (doing the opposite would initiate transcription)

Question 27

increased methylation of DNA

Answer 27

1. methyl groups attach to **cytosine** bases in DNA 2. prevents transcription factors from binding to DNA 3. causes nucleosomes to pack **tightly** together 4. gene will **not** be expressed | (inhibits transcription)

Question 28

decreased acetylation of histone proteins

Answer 28

1. histone acetylation results in **loose** packing of nucleosomes 2. if acetyl groups removed, histones become **more** positive --> more attr to **phosphate** on the DNA --> DNA & histones more strongly associated 3. prevents transcription factors from binding to DNA 4. gene will **not** be expressed | (inhibits transcription)

Question 29

what is RNA interference? (RNAi) | (only for eukaryotes and SOME prokaryotes)

Answer 29

* inhibits **translation** of mRNA prod from target genes * an mRNA that has alr been transcribed is destroyed before translation

Question 30

process of RNA interference (RNAi)

Answer 30

1. an enzyme cuts the mRNA into **siRNA** 2. one strand of the siRNA combines with another enzyme 3. the siRNA-enzyme complex binds to **another** mRNA via comple base pairing 4. once bound, the enzyme **cuts** up the mRNA --> cannot be translated --> gene inhibited

Question 31

cancer =

Answer 31

results from mutations in genes that regulate mitosis --> uncontrolled cell division --> formation of **malignant** tumour

Question 32

benign tumours

Answer 32

grow very large but at slow rate 1. **non-cancerous** --> prod **adhesive** molecules, sticking them together & to a particular tissue 2. often surrounded by **capsule** --> remain compact --> easily removed by surgery 3. impact = **localised** 4. not life-threatening

Question 33

malignant tumours

Answer 33

cancerous & grow rapidly 1. cell nucleus grows large --> becomes **unspecialised** again 2. don't prod the adhesive --> instead **metastasise** --> tumour breaks off & spreads to other tissues in the body 3. tumour **not** encapsulated --> instead grow projections into surrounding tissues --> grows its own blood supply 4. **life-threatening** --> **recurrence** also likely

Question 34

3 causes of tumour development

Answer 34

1. gene mutations in tumour suppressor genes & oncogenes 2. abnormal methylation of TSGs & oncogenes 3. increased oestrogen concs in the development of breast cancer

Question 35

how do tumour supressor genes work?

Answer 35

prod proteins to **slow down** cell division & cause cell death if DNA copying errors detected

Question 36

# 1 TSG mutations

Answer 36

* protein no longer prod./**apoptosis** occurs * cell division continues * mutated cells **not** identified & destroyed

Question 37

# 1 oncogene mutations

Answer 37

* oncogene = mutated version of proto-oncogene which creates a protein involved in the **initiation** of DNA replication & cell division * oncogene mutation --> causes process to be **permanently activated** --> makes cells divide **continually**

Question 38

# 2 abnormal methylation of TSGs

Answer 38

* ***hypermethylation*** of TSGs * transcription of TSGs inhibited/gene becomes inactivated * protein no longer prod./apoptosis * uncontrolled cell division

Question 39

# 2 abnormal methylation of oncogenes

Answer 39

* ***hypomethylation*** of oncogenes * gene becomes permanently activated * continually produces protein which **initiates** DNA replication & cell division

Question 40

# 3 increased oestrogen conc

Answer 40

* oestrogen can bind to a gene that **initiates** transcription, **activating** it * if its a proto-oncogene, permanently activating it causes cells to **continually** divide * increased oestrogen conc, increased chance of binding

Question 41

when & where is oestrogen prod?

Answer 41

* prod by **ovaries** to regulate mentrual cycle --> stops after menopause * **fat tissues** in breasts can prod oestrogen --> causes breast cancer post-menopause