Differentiation and Variation Flashcards
what is a stem cell
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
what is the ability to differentiate into more specialised cells
potency
what is totipotent
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)
what is pluripotent
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
are stem cells found in adult tissues
Stem cells are also found in some adult tissues but they are much less potent than embryonic stem cells
what is multi potency
gives rise to many different cells. They are adult stem cells that are less potent than embryonic stem cells and are no longer pluripotent
examples of how stem cells are beneficial in medicine
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
what ability does embryonic stem cells have
differentiate into any cell type
What are the two potencies of embryonic stem cells
totipotent - taken in the first 3-4 days after fertilisation
pluripotent- taken on day 5
where are the embryos from that are used in research
waste embryos from in vitro fertilisation
so they have the ability to develop into humans and there is ethical considerations
what can adult stem cells do
divide by mitosis unlimited times but only produce limited type of cells
give examples of adult stem cells
Bone marrow - produce different types of blood cells
Brain - different types of neural and glial cells
why should stem cells produce new cells
for essential processes such as growth , cell replacement, tissue repair
why is adult stem cells less controversial
donor is able to give permission
what is something to look out for when donating adult stem cell
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
why is stem cell use questionable
viable embryo destroyed
what is a disadvantage of adult stem cells
unable to differentiate into specialised cell types
what are tasks regulatory authorities carry out
reviewing proposals
licensing and monitoring
provide guidelines
monitoring developments
up to date information and advice to governments
risks of stem cells
risk of infection and mutations which lead to cancer cells
how do stem cells get specialised
differential gene expression
what is the same in all stem cells of an multicellular organism
same genes and identical genome
similarity between stem cells
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
why is controlling gene expression important
as stem cells can differentiate due to different genes
steps of differentiation
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
what do eukaryotes use to control gene expression
transcription factors
what is a transcription factor
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
what are transcription factors that increase rate known as
Activators work by helping RNA polymerase to bind to the DNA at the start of a gene and to begin transcription of that gene
what are transcription factors that increase rate known as
Activators work by helping RNA polymerase to bind to the DNA at the start of a gene and to begin transcription of that gene
what are transcription factors that decrease rate known as
Repressors work by stopping RNA polymerase from binding to the DNA at the start of a gene, inhibiting transcription of that gene
what does binding of transciption factor to the promotor do
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
what does an operon do
In prokaryotes, control of gene expression often requires the binding of transcription factors to operons
what does operon consist of
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
what is a lac operon
The lac operon controls the production of the enzyme lactase (also called β-galactosidase) and two other structural proteins
what is lactase used for
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
structure of lac operon
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
what does the lac repressor have
two binding sites that allow it to bind to the operator in the lac operon and also to lactose
what happens when lac repressor binds to operator and lactose
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
what happens when lactose is absent
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
what happens when lactose is present
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
what is the levels of regulatory proteins or transcription factors affected by
environmental stimuli such as light, and chemicals
what is epigenetics
control of gene expression by factors other than an individual’s DNA sequence
what does epigenetics involve
Epigenetics involves the switching-on and switching-off of genes, but without changing the actual genetic code
In eukaryotic cells how is nuclear dna sorted
nuclear DNA is wrapped around proteins called histones to form chromatin
can chromatin be modified
Methylation of DNA (chemical addition of -CH3 groups)
Histone modification via acetylation of amino acid tails
what are epigenetic tags
Such modifications are called epigenetic tags and collectively, all the epigenetic tags in an organism is called the epigenome
what does chemical modification of histones and DNA control
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
What is DNA methylation do
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
explain Acetylation of histones
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
how can mutations and epigenetics be differentiated
whilst mutations affect the genetic code itself, by altering nucleotide sequences, epigenetic changes only affect the way the code is read
what is a phenotype
Phenotype - the characteristics of an organism, due to genes of the organism with the environment in which it lives.
what is phenotypic variation
difference in phenotypes between organisms of the same species
how can phenotypic variation be explained by genetic factors
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
how is phenotypic variation explained by environmental factors
clones of plants with exactly the same genetic information (DNA) will grow to different heights when grown in different environmental conditions
what is genetic variation
small differences in DNA base sequences between individual organisms within a species population
what do monogenic and polygenic show
discontinuous variation (e.g. blood group)
continuous variation (e.g. height, mass, skin colour)
is discontinuous variation quantitative or qualitative
Qualitative differences fall into discrete and distinguishable categories, usually with no intermediates (a feature can’t fall in between categories)
is continuous variation quantitative or qualitative
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
what causes continuous variation
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
what is an additive effect
Different genes can have the same effect on the phenotype and these add together to have an additive effect
why the variation in phenotype due to genetics is inherited but the variation in phenotype due to environmental factors is not.
This is because genetic variation directly affects the DNA of the gametes but variation in phenotype caused by the environment does not.
how these stem cells become specialised and develop into heart muscle cells.
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
advantages of using stem cells from patients and not donor
idea of genetically identical cells (to patient) ;
no risk of rejection / eq ;
less risk of infection / eq ;
why is it better to produce differentiated cells from ips than pluripotent stem cells
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
how can you identify totipotent stem cell
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)
why cant use stem cells from heart to grow cells to repair cornea
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)
how does tissue differ from system
tissue is made of one type of cell and system is many different tissues
what is polygenic
caused by multiple genes at different loci showing continuous variation
what is found to the left of the lac operon of the bacterium’s DNA
Promoter for regulatory gene
Regulatory gene lacI that codes for the lac repressor protein
what is a sex linked disorder
(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
how does epigenetic changes cause difference in characteristics
histone modification / dna methylation causes the activation / deactivation of genes effecting enzyme production / metabolism
how does epigenetics changes affect development in embryo`
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)
why is adult stem cell therapy better than embryonic stem cell therapy
no destruction of embryos / eq;
embryo has potential to become a human life / eq;
{religious / ethical } objections / eq;
propertied of totipotent
can {differentiate / give rise) to all cell types (1)
* capable of unlimited cell division (1)
- can give rise to other totipotent stem cells
