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Biology Mock AS 2 > Differentiation and Variation > Flashcards

Differentiation and Variation Flashcards

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1
Q

what is a stem cell

A

an undifferentiated cell that can divide (by mitosis) an unlimited number of times, each new cell has the potential to remain a stem cell or to develop into a specialised cell such as a blood cell or a muscle cell by a process known as differentiation

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2
Q

what is the ability to differentiate into more specialised cells

A

potency

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3
Q

what is totipotent

A

totipotent stem cells are stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (the cells that make up the placenta and umbilical cord)

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4
Q

what is pluripotent

A

pluripotent stem cells are embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into cells forming the placenta and umbilical cord

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5
Q

are stem cells found in adult tissues

A

Stem cells are also found in some adult tissues but they are much less potent than embryonic stem cells

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6
Q

what is multi potency

A

gives rise to many different cells. They are adult stem cells that are less potent than embryonic stem cells and are no longer pluripotent

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7
Q

examples of how stem cells are beneficial in medicine

A

treatment of leukaemia where stem cells in bone marrow are killed and replaced using bone marrow stem cell transplant

replace damage nerve tissue to treat spinal cord injuries

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8
Q

what ability does embryonic stem cells have

A

differentiate into any cell type

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9
Q

What are the two potencies of embryonic stem cells

A

totipotent - taken in the first 3-4 days after fertilisation

pluripotent- taken on day 5

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10
Q

where are the embryos from that are used in research

A

waste embryos from in vitro fertilisation
so they have the ability to develop into humans and there is ethical considerations

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11
Q

what can adult stem cells do

A

divide by mitosis unlimited times but only produce limited type of cells

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12
Q

give examples of adult stem cells

A

Bone marrow - produce different types of blood cells

Brain - different types of neural and glial cells

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13
Q

why should stem cells produce new cells

A

for essential processes such as growth , cell replacement, tissue repair

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14
Q

why is adult stem cells less controversial

A

donor is able to give permission

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15
Q

what is something to look out for when donating adult stem cell

A

must be close match in terms of blood type otherwise rejected by immune system as foreign and attacked so own adult stem cells have a lower chance of rejection

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16
Q

why is stem cell use questionable

A

viable embryo destroyed

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17
Q

what is a disadvantage of adult stem cells

A

unable to differentiate into specialised cell types

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18
Q

what are tasks regulatory authorities carry out

A

reviewing proposals
licensing and monitoring
provide guidelines
monitoring developments
up to date information and advice to governments

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19
Q

risks of stem cells

A

risk of infection and mutations which lead to cancer cells

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20
Q

how do stem cells get specialised

A

differential gene expression

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21
Q

what is the same in all stem cells of an multicellular organism

A

same genes and identical genome

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22
Q

similarity between stem cells

A

same genes and identical genome
despite having same genome they can specialise into diverse range if cell types because during differentiation certain genes are expressed

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23
Q

why is controlling gene expression important

A

as stem cells can differentiate due to different genes

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24
Q

steps of differentiation

A

some genes in a stem cell are activated, whilst others are inactivated
mRNA is transcribed from active genes only
This mRNA is then translated to form proteins
These proteins are responsible for modifying the cell
As these proteins continue to modify the cell, the cell becomes increasingly specialised
The process of specialisation is irreversible

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25
Q

what do eukaryotes use to control gene expression

A

transcription factors

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26
Q

what is a transcription factor

A

protein that controls the transcription of genes by binding to a specific region of DNA they ensure that genes are being expressed in the correct cells

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27
Q

what are transcription factors that increase rate known as

A

Activators work by helping RNA polymerase to bind to the DNA at the start of a gene and to begin transcription of that gene

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27
Q

what are transcription factors that increase rate known as

A

Activators work by helping RNA polymerase to bind to the DNA at the start of a gene and to begin transcription of that gene

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28
Q

what are transcription factors that decrease rate known as

A

Repressors work by stopping RNA polymerase from binding to the DNA at the start of a gene, inhibiting transcription of that gene

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29
Q

what does binding of transciption factor to the promotor do

A

either allow or prevent the transcription of the gene from taking place
Transcription factors interact with RNA polymerase, either by assisting RNA polymerase binding to the gene (to stimulate expression of the gene) or by preventing it from binding (to inhibit gene expression)
Therefore, the presence of a transcription factor will either increase or decrease the rate of transcription of a gene

30
Q

what does an operon do

A

In prokaryotes, control of gene expression often requires the binding of transcription factors to operons

31
Q

what does operon consist of

A

A cluster of structural genes that are transcribed together
Control elements, including a promoter region and an operator region. Some operons may include regulatory genes that code for activators or repressors

32
Q

what is a lac operon

A

The lac operon controls the production of the enzyme lactase (also called β-galactosidase) and two other structural proteins

33
Q

what is lactase used for

A

Lactase breaks down the substrate lactose so that it can be used as an energy source in the bacterial cell and is known as an inducible enzyme

34
Q

structure of lac operon

A

Promoter for structural genes
Operator
Structural gene lacZ that codes for lactase
Structural gene lacY that codes for permease (allows lactose into the cell)
Structural gene lacA that codes for transacetylase

35
Q

what does the lac repressor have

A

two binding sites that allow it to bind to the operator in the lac operon and also to lactose

36
Q

what happens when lac repressor binds to operator and lactose

A

When it binds to the operator it prevents the transcription of the structural genes as RNA polymerase cannot attach to the promoter
When it binds to lactose the shape of the repressor protein distorts and the repressor protein can no longer bind to the operator

37
Q

what happens when lactose is absent

A

The regulatory gene is transcribed and translated to produce lac repressor protein
The lac repressor protein binds to the operator region upstream of lacZ
Due to the presence of the repressor protein RNA polymerase is unable to bind to the promoter region
Transcription of the structural genes does not take place
No lactase enzyme is synthesized

38
Q

what happens when lactose is present

A

There is an uptake of lactose by the bacterium
The lactose binds to the second binding site on the repressor protein, distorting its shape so that the repressor protein cannot bind to the operator region
RNA polymerase is then able to bind to the promoter region and transcription takes place
The mRNA from all three structural genes is translated
The enzyme lactase is produced and lactose can be broken down and used for energy by the bacterium

39
Q

what is the levels of regulatory proteins or transcription factors affected by

A

environmental stimuli such as light, and chemicals

40
Q

what is epigenetics

A

control of gene expression by factors other than an individual’s DNA sequence

41
Q

what does epigenetics involve

A

Epigenetics involves the switching-on and switching-off of genes, but without changing the actual genetic code

42
Q

In eukaryotic cells how is nuclear dna sorted

A

nuclear DNA is wrapped around proteins called histones to form chromatin

43
Q

can chromatin be modified

A

Methylation of DNA (chemical addition of -CH3 groups)
Histone modification via acetylation of amino acid tails

44
Q

what are epigenetic tags

A

Such modifications are called epigenetic tags and collectively, all the epigenetic tags in an organism is called the epigenome

45
Q

what does chemical modification of histones and DNA control

A

how tightly the DNA is wound around the histones as the intermolecular bonding between the histones and DNA changes
If the DNA is wound more tightly in a certain area, the genes on this section of DNA are ‘switched off’ as the gene and promoter regions are more hidden from transcription factors and RNA polymerase

46
Q

What is DNA methylation do

A

methyl groups attached to DNA (1)
prevent transcription (of the gene) (1)
{transcription factors / RNA nucleotides} cannot bind to { DNA / promoter region of gene) (1)
{deactivating / switching off) a gene

47
Q

explain Acetylation of histones

A

Acetyl groups (-COCH3) can be added to lysine amino acids on histone proteins

causes the DNA to be less tightly wrapped
When the DNA is less tightly wrapped, RNA polymerase and transcription factors can bind more easily and therefore gene expression can occur

The gene is said to be activated

48
Q

how can mutations and epigenetics be differentiated

A

whilst mutations affect the genetic code itself, by altering nucleotide sequences, epigenetic changes only affect the way the code is read

49
Q

what is a phenotype

A

Phenotype - the characteristics of an organism, due to genes of the organism with the environment in which it lives.

50
Q

what is phenotypic variation

A

difference in phenotypes between organisms of the same species

51
Q

how can phenotypic variation be explained by genetic factors

A

the four different blood groups observed in human populations are due to different individuals within the population having two of three possible alleles for the single ABO gene

52
Q

how is phenotypic variation explained by environmental factors

A

clones of plants with exactly the same genetic information (DNA) will grow to different heights when grown in different environmental conditions

53
Q

what is genetic variation

A

small differences in DNA base sequences between individual organisms within a species population

54
Q

what do monogenic and polygenic show

A

discontinuous variation (e.g. blood group)
continuous variation (e.g. height, mass, skin colour)

55
Q

is discontinuous variation quantitative or qualitative

A

Qualitative differences fall into discrete and distinguishable categories, usually with no intermediates (a feature can’t fall in between categories)

56
Q

is continuous variation quantitative or qualitative

A

Quantitative differences do not fall into discrete categories (unlike in discontinuous variation)
Instead for these features, a range of values exist between two extremes within which the phenotype will fall
For example, the mass or height of a human is an example of continuous variation

57
Q

what causes continuous variation

A

Some phenotypes are affected by multiple different genes or by multiple alleles for the same gene at many different loci as well as the environment

58
Q

what is an additive effect

A

Different genes can have the same effect on the phenotype and these add together to have an additive effect

59
Q

why the variation in phenotype due to genetics is inherited but the variation in phenotype due to environmental factors is not.

A

This is because genetic variation directly affects the DNA of the gametes but variation in phenotype caused by the environment does not.

60
Q

how these stem cells become specialised and develop into heart muscle cells.

A

idea of appropriate stimulus e.g. chemical, hormone
2. idea of activation of some genes ;
3. only the activated genes are transcribed / mRNA
made only at active genes / eq ;
4. mRNA translated (on ribosomes) ;
5. protein made / eq ;
6. which {determines / eq} cell {structure / function}
permanently modifies cell / eq ;
7. reference to cell differentiation

61
Q

advantages of using stem cells from patients and not donor

A

idea of genetically identical cells (to patient) ;
no risk of rejection / eq ;
less risk of infection / eq ;

62
Q

why is it better to produce differentiated cells from ips than pluripotent stem cells

A

that no embryo used and limited supply of embryos
iPS cells can be used in the same individual so no immune response with iPS cells and no risk of infections

ethical and religious objections with embryonic

63
Q

how can you identify totipotent stem cell

A

all genes (potentially) active / as no genes
{switched off / deactivated} / {cell A / cell B}
has genes switched off / eq

therefore it can {give rise
to/differentiate to become} all cell (types)

64
Q

why cant use stem cells from heart to grow cells to repair cornea

A

past day 3-4 so
cells are not totipotent (1)
* therefore some genes have already been activated and deactivated (1)
* therefore, will not be able to specialize into cornea cells (1)

65
Q

how does tissue differ from system

A

tissue is made of one type of cell and system is many different tissues

66
Q

what is polygenic

A

caused by multiple genes at different loci showing continuous variation

67
Q

what is found to the left of the lac operon of the bacterium’s DNA

A

Promoter for regulatory gene

Regulatory gene lacI that codes for the lac repressor protein

68
Q

what is a sex linked disorder

A

(a disorder caused by) a {mutated / faulty } gene (1)
located on the { X / Y} chromosome (1)
therefore (the disorder) is more likely in one gender than another

69
Q

how does epigenetic changes cause difference in characteristics

A

histone modification / dna methylation causes the activation / deactivation of genes effecting enzyme production / metabolism

70
Q

how does epigenetics changes affect development in embryo`

A

DNA (in a chromosome) is wrapped around histones (1)
{acetylation / modification] of the histone affects (binding ofRNA polymerase / chromosome unwinding) (1)
methylation of DNA affects ( transcription of genes /production of mRNA \ (1)
therefore gene expression is altered (1)

71
Q

why is adult stem cell therapy better than embryonic stem cell therapy

A

no destruction of embryos / eq;

embryo has potential to become a human life / eq;

{religious / ethical } objections / eq;

72
Q

propertied of totipotent

A

can {differentiate / give rise) to all cell types (1)
* capable of unlimited cell division (1)

  • can give rise to other totipotent stem cells

Biology Mock AS 2 (23 decks)

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