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Biology > 7.2 > Flashcards

7.2 Flashcards

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1
Q

what is cell differentiation

A

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

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2
Q

why are gene probes important

A

they identify particular sections of DNA and mRNA

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3
Q

how does a gene probe work

A

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

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4
Q

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

A

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

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5
Q

define transcription

A

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

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6
Q

what is a transcription factor

A

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

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7
Q

what is a promoter sequence

A

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

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8
Q

what are enhancer sequences

A

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

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9
Q

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

A

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

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10
Q

what is pre-mRNA

A

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

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11
Q

what are spliceosomes

A

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

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12
Q

what is the point of RNA splicing

A

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

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13
Q

how does RNA splicing occur

A

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

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14
Q

define DNA methylation

A

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

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15
Q

what does DNA methylation do

A

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

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16
Q

what enzyme is involved in DNA methylation

A

methyltransferase enzyme

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17
Q

define DNA demethylation

A

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

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18
Q

what are histones

A

positively charged proteins which DNA helices winds around

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19
Q

what is chromatin

A

the DNA/protein complex that makes up chromosomes

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20
Q

what is heterochromatin

A

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

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21
Q

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

A

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

22
Q

what is histone acetylation

A

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

23
Q

what is histone methylation

A

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

24
Q

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

A

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

25
Q

how does ncRNA affect the X chromosome in females

A

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

26
Q

why are X chromosomes inactivated in some female cells

A

to maintain the balance of gene products in males

27
Q

why does cell differentiation occur

A

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

28
Q

what can cause epigenetic changes

A

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

29
Q

define totipotent and give an example

A

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

30
Q

define embryonic stem cell

A

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

31
Q

define pluripotent and give an example

A

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

32
Q

what are somatic stem cells/adult stem cells

A

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

33
Q

define multipotent

A

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

34
Q

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

A

cells divide repeatedly without interphase growth between divisions

35
Q

what does the cleavage result in the formation of

A

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

36
Q

explain how potency changes as an embryo develops

A

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

37
Q

where can pluripotent stem cells be taken from at birth

A

blood that drains from the placenta and umbilical cord

38
Q

why would taking a babys pluripotent stem cells be beneficial

A

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

39
Q

what are the limitations of taking a baby pluripotent stem cells

A

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

40
Q

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

A

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

41
Q

why do fetuses have higher affinity for oxygen than adult human

A

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

42
Q

what are the issues of stem cell therapy

A

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

43
Q

how are adult stem cells used to make organs

A

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

44
Q

why are adult stem cells better than embryonic stem cells

A

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

45
Q

what is somatic cell/therapeutic cloning

A

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

46
Q

how is somatic cell/therapeutic cloning done (theoretically)

A
  • 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
47
Q

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

A

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

48
Q

what are the reasons for stem cell therapy

A

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

49
Q

what are induced pluripotent stem cells (IPSC)

A

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

50
Q

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

A

+/ 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

51
Q

what are the 4 main ethical concerns with stem cell therapy

A

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

Biology (33 decks)

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