7.2

Question 1

what is cell differentiation

Answer 1

the process by which a cell becomes specialized for a particular function

Question 2

why are gene probes important

Answer 2

they identify particular sections of DNA and mRNA

Question 3

how does a gene probe work

Answer 3

the gene probe finds the unique sequence of nucleotides in the DNA using RNA with a complementary sequence
then it is isolated and heated to break hydrogen bonds and a florescent label mRNA is added so that the gene can be identified

Question 4

how can gene probing be used to show that all genes are present in cells but not all are expressed

Answer 4

by comparing the DNA and RNA gene probing for proteins expressed in some cells and not all

Question 5

define transcription

Answer 5

the process by which the genetic code of the DNA is copied to a complementary strand of (m)RNA

Question 6

what is a transcription factor

Answer 6

proteins that bind to the DNA in the nucleus and affect the process of transcribing genetic material

Question 7

what is a promoter sequence

Answer 7

specific regions of DNA found just above the starting point for transcription, upstream from the gene that transcription factors bind to in order to stimulate transcription

Question 8

what are enhancer sequences

Answer 8

specific regions of DNA found anywhere in the base sequence which transcription factors bind to in order to either stimulate or prevent transcription of a gene

Question 9

how does a enhancer sequence stimulate or prevent transcription of a gene

Answer 9

they change the structure of chromatin so it becomes more or less open to RNApolymerase

Question 10

what is pre-mRNA

Answer 10

the mRNA that is transcribed directly from the DNA before it has been modified

Question 11

what are spliceosomes

Answer 11

enzyme complexes that act on pre-mRNA, joining exons together after the removal of introns

Question 12

what is the point of RNA splicing

Answer 12

a single gene may produce several versions of functional mRNA transcribed from the same section of DNA, these different mRNA sequences code for different arrangements of amino acids, different polypeptides and different proteins

Question 13

how does RNA splicing occur

Answer 13

spliceosome removes an intron from in between two exons on a pre-mRNA molecule, the removed intron forms a loop and the 2 exons join together to create mature mRNA

Question 14

define DNA methylation

Answer 14

the addition of a methyl group to a cytosine in the DNA molecule next to a guanine in the DNA chain

Question 15

what does DNA methylation do

Answer 15

stops the transcription of a gene and modifies the structure of the histones

Question 16

what enzyme is involved in DNA methylation

Answer 16

methyltransferase enzyme

Question 17

define DNA demethylation

Answer 17

the removal of the methyl group from the methylated DNA enabling the DNA to become active so that it can be transcribed

Question 18

what are histones

Answer 18

positively charged proteins which DNA helices winds around

Question 19

what is chromatin

Answer 19

the DNA/protein complex that makes up chromosomes

Question 20

what is heterochromatin

Answer 20

densely supercoiled and condensed chromatin where the genes are not available to be copied to make proteins

Question 21

why does chromatin allow transcription to take place whereas heterochromatin does not

Answer 21

active chromatin is more loosely held together with uncoiled regions of DNA opening up more genes for transcription whereas heterochromatin is densely supercoiled so no genes are available for transcription

Question 22

what is histone acetylation

Answer 22

an acetyl group (COCH3) is added to one of the lysines in the histone structure which opens up the structure and activates the chromatin allowing genes in that area to be transcribed

Question 23

what is histone methylation

Answer 23

the addition of a methyl group (CH3) to lysine in the histone, can cause activation or deactivation of the DNA

Question 24

what is the non-coding RNA (ncRNA) often used for

Answer 24

affects the transcription of the DNA code and modifies the products of transcription

Question 25

how does ncRNA affect the X chromosome in females

Answer 25

X chromosomes in females are inactivated at random, active Xist gene produces Xist it causes the X chromosome to supercoil and condense to form a stable inactive Barr body

Question 26

why are X chromosomes inactivated in some female cells

Answer 26

to maintain the balance of gene products in males

Question 27

why does cell differentiation occur

Answer 27

unspecialized cells switch different genes on and off so that they can become more specialized

Question 28

what can cause epigenetic changes

Answer 28

response to internal stimuli or changes outside the cell which effects the inside of the cell

Question 29

define totipotent and give an example

Answer 29

undifferentiated cell which can form any one of the different cell types needed for a new organism (embryo)

Question 30

define embryonic stem cell

Answer 30

undifferentiated cells of early human embryo with potential to develop into any specialized cell

Question 31

define pluripotent and give an example

Answer 31

undifferentiated cell that can form most cell types needed for a new organism (stem cells)

Question 32

what are somatic stem cells/adult stem cells

Answer 32

undifferentiated cells found in organs and tissues that can differentiate when needed to produce any one of the major cells found in that tissue/organ

Question 33

define multipotent

Answer 33

a cell that can form a very limited range of differentiated cells within a mature organism

Question 34

how is the formation of a cleavage different to regular cell division

Answer 34

cells divide repeatedly without interphase growth between divisions

Question 35

what does the cleavage result in the formation of

Answer 35

a mass of small, identical and undifferentiated cells forming a hollow sphere known as a blastocyte

Question 36

explain how potency changes as an embryo develops

Answer 36

earliest embryonic stem cells are totipotent but by the blastocyst when the embryo implants on the uterus the inner cells are pluripotent

Question 37

where can pluripotent stem cells be taken from at birth

Answer 37

blood that drains from the placenta and umbilical cord

Question 38

why would taking a babys pluripotent stem cells be beneficial

Answer 38

the stem cells will be available for the childs lifetime for stem cell therapy

Question 39

what are the limitations of taking a baby pluripotent stem cells

Answer 39

it would take a lot of storage space it would be expensive precursor cells of conditions such as leukemia are already present in the blood at birth

Question 40

how is cell determination related to its position and age of the cell (experiment)

Answer 40

early 'skin' cell from embryo transferred to early 'brain' cell and became brain tissue older 'skin' cell from embryo transferred to early 'brain' embryo and formed skin tissue in the brain

Question 41

why do fetuses have higher affinity for oxygen than adult human

Answer 41

adult human hemoglobin contains 2 alpha and 2 beta globin chains whereas embryos contain 2 alpha and 2 gamma globin chains

Question 42

what are the issues of stem cell therapy

Answer 42

difficult to control the differentiation of cells successful transplants have developed cancer ethical objections of the use of embryonic stem cells

Question 43

how are adult stem cells used to make organs

Answer 43

stem cells from the patient are seeded onto a framework which may be collogen based or completely synthetic and the stem cells grow to form the required cells then can be returned to the patient with no chance of rejection

Question 44

why are adult stem cells better than embryonic stem cells

Answer 44

adult stem cells won't be rejected and there are no ethical concerns

Question 45

what is somatic cell/therapeutic cloning

Answer 45

an experimental technique used to produce embryonic stem cells from an adult cell donor

Question 46

how is somatic cell/therapeutic cloning done (theoretically)

Answer 46

- produce healthy clones of cells from patient - remove nucleus from cloned patient cells and put the nucleus in a human ovum which has had its nucleus removed - mild electric shock to fuse nucleus and trigger development - pre-embryo starts to develop and divide - stem cells harvested from the embryo - cells cultured in suitable environment differentiate into the required tissue - transfer tissue/organ to patient

Question 47

what is the main reasons for why somatic cell/therapeutic cloning is not used in everyday medical procedures

Answer 47

it is still unknown the exact triggers of that control cell differentiation ethical issues - the patient nucleus must be genetically modified to be fused with ovum to stop genetic mutation

Question 48

what are the reasons for stem cell therapy

Answer 48

gives cures to many conditions which currently have no cure tailor-made cells would revolutionise medicine

Question 49

what are induced pluripotent stem cells (IPSC)

Answer 49

adult cells that have been reprogrammed by the introduction of new genes to become pluripotent again

Question 50

what are the advantages and disadvantages of induced pluripotent stem cells (IPSC)

Answer 50

+/ overcomes ethical objections no risk of rejection regenerate on their own -/ not easy to differentiate into the tissue you want it is hard to make cells become pluripotent and not always successful it is unknown how long they will remain pluripotent have shown potential to become cancerous

Question 51

what are the 4 main ethical concerns with stem cell therapy

Answer 51

respect for autonomy - consent beneficence - research for good purposes non maleficence - do not harm justice - share resources equally