gene expression

Question 1

universal

Answer 1

same 3 bases on triplet/codon code for the same amino acids in all organisms

Question 2

non overlapping

Answer 2

each base is read as part of only one triplet/codon

Question 3

degenerate

Answer 3

more than one triplet codes for an amino acid

Question 4

mutations

Answer 4

• substitution (silent)
• addition (frame shift
• chromosomal nondisjunction (chromosomes fail to split during metaphase 1. down syndrome caused by chromosome 21, 3 instead of 2 chromosomes)
• inversion
• duplication
• translocation (bw non homologous chromosomes)

Question 5

mutagenic agents

Answer 5

high energy ionising radiation (gamma rays, beta particles) interferes with dna replication
- dna reactive chemicals: benzene, hydrogen peroxide
- biological agents: viruses/ bacteria

Question 6

totipotent stem cells

Answer 6

can give rise to complete human/all cell types
- translate only part of their DNA, producing specific proteins leading to cell specialisation
- divide by mitosis
- occurs during zygote, up to 8 cell stage

Question 7

pluripotent

Answer 7

• divide by mitosis
• only translate part of their DNA
• can only give rise to some cell types (ie: cells that make up tissue in the mammalian feotus)
• embryonic and fetal stem cells

Question 8

multipotent

Answer 8

• exist in tissues
• retain the ability to differentiate into a limited number of cell types (eg: bone marrow only RBCs and WBCs)
• used for vital growth and repair of damaged tissues
• adult stem cells

Question 9

unipotent

Answer 9

give rise to only one type of cell
(eg: heart stem cells differentiate into cardiomyocytes)
- used for vital growth and repair of damaged tissues

Question 10

key points

Answer 10

• only stem cells can divide by mitosis
• differentiation of stem cells determined by gene expression (only some parts of dna expressed, others inactive)

Question 11

explain how cells produced from stem cells ahve the same genes yet be of different types?

Answer 11

not all genes are switched on/active
- gene expression involves transcription factors (proteins that bind a genes promoter region and either promote or inhibit the transcription of a gene)

Question 12

describe the mechanism by which a signal protein causes the synthesis of mRNA

Answer 12

• signal protein binds to the receptor on surface membrane
• messenger molecule moves from cytoplasm and enters nucleas
• activate transcription factor
• binds to promoter region
• RNA polymerase transcribes target gene

Question 13

applications for stem cells

Answer 13

• produces tissues for skin grafts
• organ transplant research
• research into how cells become specialised
• cancer research

Question 14

stem cell concerns

Answer 14

• may divide rapidly out of control, forming tumours
• embryos have human status from mone tof conception
• not true human being, ebnefits outweigh risks
• no moral rights

Question 15

iPSC

Answer 15

induced pluripotent stem cells
- lab grown pluripotent cells prpduced from somatic cells using transcription factors
-capable of self renewal and limitless supply

Question 16

promoter region

Answer 16

one or more base sequences found upstream of a gene
control the expression of that gene

Question 17

transcription factors

Answer 17

proteins, when activated, bind to the promoter region of the gene
stimulates RNA polymerase to begin transcription of the target gene

Question 18

describe how oestrogen enables RNA polymerase to begin transcription of its target gene

Answer 18

• oestrogen diffuses via phospolipid cell membrane and diffuses through the nuclear envelope (is lipid soluble)
• binds to the oestrogen receptor
• changes the 3 structure of the receptor
• releases transcription factor which binds to the dna
• at the promoter region
• stimulates RNA polymerase to transcribe the gene

Question 19

rna interference

Answer 19

miRNA = microRNA
small interfering RNA = siRNA
- single strand of miRNA and siRNA binds to a protein in cytoplasm to form a RISC (RNA-induced silencing) complex
- complementary base sequence to specific mRNA molecule

Question 20

RISC

Answer 20

RISC inhibits gene expression by binding to complementary mRNA; mRNA hydrolysed by enzyme into fragments OR initiation of ribosomal translation inhibited.
- translation doesnt take place, polype[tide not produced
- expression of gene silenced

Question 21

why might a protein still be present even after the introduction of RNAi?

Answer 21

not all mRNA has been destroyed
so some translation still occurs

Question 22

epigenetics

Answer 22

inheritable changes in gene expression
without changes in DNA base sequence
inhibits translation via methylation of DNA / acylation of histones

Question 23

compare the structure of dsRNA and DNA

Answer 23

dsRNA = double stranded RNA
- polymer of nuclepotides
- A,C and G
pentose sugar
double stranded
- dsRNA contains U, DNA contains T
- dsRNA ribose DNA deoxyribose
dsRNA shorter than DNA

Question 24

explain how methylation of tumour suppressor genes can lead to cancer

Answer 24

-methylation prevents transcription of a gene
-protein that prevents cell division not produced
-no control of mitosis

Question 25

process of methylation

Answer 25

CH3 added to c5 of cytosine base
methyltransferase enzyme catalyses this reaction
cpg islands silence genes by preventing TF binding to promoter

Question 26

process of acetylation of histones

Answer 26

DNA in chromosomes wrapped around histones creating nuclosomes
- become loosely packed so dna less condensed
- promoter regions are exposed TF bind
- RNA polynerase to bind an dtranscribe target gene

Question 27

describe how alterations of tumour suppressor gene can lead to development of tumours

Answer 27

• increased methylation of TSG
• mutation in TSG
• TSG not transcribed
• uncontrolled cell division

Question 28

DESCRIBE what is meant by a MALIGNANT tumour

Answer 28

mass of undifferentiated cells
- uncontroled cell division
- metastasis forms new tumours
- spread to other parts of body
- fast growing
- non capsulated

Question 29

describe benign tumours

Answer 29

surrounded by a capsuke
dont metastasise
slow growing

Question 30

describe how altered DNA can lead to cancer

Answer 30

• dna altered by mutation
• mutation changes base sequence
• of gene controlling cell growth (oncogene)
  -of TSG
  changes protein structure
  TSG produces proteins that inhibit cell division
• mitosis: uncontrolled cell division forming malignant tumours

Question 31

define epigenetics

Answer 31

heritable changes not involving changes in DNA base sequence

Question 32

proto-oncogenes

Answer 32

stimulate cell division
codes for proteins that increase rate of CD

Question 33

Tumour suppresor genes

Answer 33

slow cell division
code for proteins decreasing rate of CD
- code for proteins repair mistakes in DNA
- code for proteins instructing cells to die
eg: BRCA2, TP53

Question 34

mutations in genes

Answer 34

proto oncogene mutation causes oncogene
- overstimulation of cd so persmanently switched on

tsg mutation = inactivated
- stops inhibiting cd, rate of cd increases

Question 35

epigenetic changes to TSG

Answer 35

increased methylation of tsg increases rate of cd
increased acetylation of tsg decreases rate of cd

Question 36

epigenetic changes to oncogene

Answer 36

decreased methylation increases rate of cd
decreased acetylation of histones decreases rate of cd