3C Differentiation and Variation Flashcards
stem cell
undifferentiated cell with potential to continue to DIVIDE to become specialised cells with one function
differentiated cell
cell with one purpose -> cannot become multiple cells
totipotent
stem cells that can become ALL cells
- embryonic stem cells that can differentiate into any cell type in embryo
- … and extra-embryonic cells (cells that make up placenta and umbilical cord)
“i can totally be pregnant” -> embryonic cells
pluripotent
stem cells that can become MOST cells
- embryonic stem cells that can differentiate into any cell type found in an embryo
- but NOT able to differentiate into cells forming placenta and umbilical cord
(multipotent)
stem cells that can become SOME cells
adult stem cells that have LOST SOME OF POTENCY associated with embryonic stem cells and are no longer pluripotent
explain why some cells do not remain totipotent
during fertilisation and cell division -> become specialised for a purpose
state 3 examples of multipotent stem cells in humans
- nerve cells
- muscle cells
- bone marrow
explain how “potency” of plant and animal cells differ
animal cells: once specialised, it is usually permanent
plant cells: become specialised and unspecialised throughout lifetime
describe potential uses of stem cells in medicine
- used to regrow limbs, organs
- cure degenerative diseases
v useful as no chance of rejection (unlike donor organs)
explain why PLURIPOTENT EMBRYONIC stem cells could be considered more useful than ADULT MULTIPOTENT stem cells
- embryonic stem cells -> can turn into more types of cells than body cells
discuss the ethical views on the use of embryonic stem cells
obtaining stem cells from embryos created via IVF raise ethical issues as procedure destroys viable embryo
FOR:
- embryos will be destroyed anyway
- advancing science with hope of saving lives
AGAINST:
- mothers pressured into donating eggs
- murder? -> on religious grounds
- ppl believe that at moment of fertilisation: genetically unique individual created -> has a right to life
why aren’t stem cells rejected by body?
DNA is from YOU -> not recognised as foreign
what are the dangers of stem cell therapy?
- stem cells becoming cancerous
- body may reject stem cells
- when injecting stem cells -> risk of introducing INFECTION
activators
factors that increase rate of transcription
- help RNA polymerase bind to DNA and begin transcription
repressors
factors that decrease rate of transcription
- prevent RNA polymerase binding to DNA and stopping transcription
where do transcription factors bind to in EUKARYOTES (animals and plants)?
specific DNA sites near START of TARGET GENES (genes they control expression of)
where do transcription factors bind to in PROKARYOTES?
OPERONS
operon
section of DNA that includes…
- cluster of structural genes that are transcribed together (these code for useful proteins e.g. enzymes)
-
control elements -> including a PROMOTER REGION (a DNA sequence that RNA polymerase initially binds to)
-> OPERATOR REGION (where transcription factors bind)
lac operon
controls production of enzyme LACTASE and 2 other structural proteins
where genes that produce enzymes needed to respire lactose are found
promoter
DNA sequence located BEFORE structural genes that RNA POLYMERASE binds to
operator
DNA sequence that TRANSCRIPTION FACTORS bind to
E. coli
bacterium that respires glucose BUT will use lactose if glucose isn’t available
name lac operons structural genes
- lacZ
- lacY
- lacA
they produce proteins that help bacteria digest lactose
potency
ability of stem cells to differentiate into more specialised cell types
how are epigenetic changes to a cell’s gene expression passed on?
- when a cell ÷ and replicates …
- epigenetic changes to its gene expression passed on to daughter cells
- certain genes that are activated / deactivated in o.g cell will also be activated / deactivated in daughter cells
- so daughter cells equipped to deal with changed env in same way as o.g cell was
differentiation
proccess by which a cell becomes specialised
where are totipotent stem cells present?
first few cell ÷ of an embryo
how do stem cells become specialised?
(1 mark)
different genes in their DNA become active and get expressed
how are stem cells specialised in animals and plants?
- when chemical stimulus present -> some genes activated / others inactivated (differential gene expression)
- transcription occurs at active genes
- active mRNA from active genes translated on ribosome to synthesise proteins
- protein modifies cell and determines structure and functions
- changes to cell produced by these proteins cause cell to become specialised
discuss the way society uses scientific knowledge to make decisions about the use of stem cells in medical therapies
(6 marks)
- looking at proposals of research and deciding if they should be allowed -> ethical issues into account
-> ensures research isn’t unnecessarily repeated by diff groups -
licensing and monitoring centres -> ensures only fully trained staff carry out research
-> staff won’t waste precious resources eg. embryos
-> helps avoid unregulated research -
guidelines / codes of practice -> all scientists working in similar manner
-> ensures scientists using acceptable source of stem cells and method to extract cells are controlled (includes max. age of embryo that can be used) -
monitoring developments
-> ensures changes in field regulated appropriately and all guidelines up to date - providing info / advice to governments / professionals
-> helps promote science involved in embryonic research
-> helps society understand what’s involved / why it’s important
adult stem cells can only develop into a limited range of cells whereas embryonic stem cells can develop into all types of specialised cells.
suggest why adult stem cells might be used instead of embryonic stem cells
if patient needs stem cell transplant and own stem cells can be used -> less risk of rejection
as cells are not foreign (‘self’) and doesn’t initiate immune system response
describe how stem cells can be used to treat a range of diseases
- stem cells can differentiate into any cell type -> so can be used to replace damaged tissue in range of diseases
- eg. leukemia (cancer of bone marrow) kills bone marrow stem cells -> so bone marrow transplants given to replace them
what conditions are scientists researching for stem cell treatment?
-
spinal cord injuries
-> stem cells could be used to repair damaged nerve tissue -
heart disease and damage caused by heart attacks
-> replace damaged heart tissue
explain one benefit of using embryonic stem cells instead of adult stem cells
embryonic stem cells can develop into all types of specialised cell
whereas adult stem cells can only develop into a limited range of cells
state 2 reasons why some ppl are opposed to using embryonic stem cells
- believe embryos have a right to life from moment of fertilisation
- believe its wrong to destroy viable embryos
RBCs contain lots of haemoglobin and have no nucleus (to make room for more haemoglobin).
they are produced from a type of stem cell in the bone marrow.
describe how a red blood cell becomes specialised
- stem cell in bone marrow produces new cell where genes for haemoglobin production activated
- other genes (eg. those involved in removing nucleus) activated too
- many other genes activated / inactivated -> leads to specialised RBC
what is the variation in phenotype influenced by?
variation in genotype (genes) and the env
(phenotype produced by interactions of env and genotype)
locus
location of genes on chromosome
explain the type of variation shown by human blood groups
(3 marks)
check this
discontinuous variation
-> blood groups: A, B, AB, O
monogenic characteristics (controlled by one gene) so blood groups show this type of variation
- blood groups only influenced by genotype (not env)
discontinous variation
- when 2 or more distinct categories
- each individ. falls into only 1 category
monogenic characteristics
controlled by one gene
usually show discontinous variation
eg. blood group
polygenic characteristics
polygenic inheritance
controlled by no. of genes at diff loci
usually show continuous variation
eg. height
continous variation
when individ. in pop vary within a range -> no distinct categories
Eg.
- height
- mass
- skin colour
height is a phenotype influenced by both genotype and env.
describe how the env affects the height of an individ.
- height is polygenic (controlled by no. of genes at diff loci)
- and affected by env factors eg. nutrition
- tall parents usually produce tall children (polygenic inheritance)
- BUT if child undernourished: won’t grow to max. height (as protein required for growth)
MAOA is enzyme that breaks down monoamines (chemical) in humans.
describe how the env affects the MAOA of an individ.
- low levels of MAOA linked to mental health problems
- MAOA production controlled by single gene (monogenic)
- BUT taking anti-depressants / smoking can reduce amount produced
risk of cancer is influenced by genotypes and the env.
suggest what env factors influence the risk of cancer
cancer: uncontrolled ÷ of cells -> leads to lumps of cells (tumours) forming
- risk affected by genes
- BUT env factors eg. diet can also influence risk
some arctic animals have dark hair in summer but white hair in winter.
describe how the env interacts with the animals’ genotype to produce this phenotype
- animal hair colour is polygenic
- BUT env plays part in some animals
- env factors eg. decreasing temp trigger this change BUT couldn’t happen if animal didn’t have genes for it
describe how changes to the env can cause changes in gene expression
(4 marks)
in eukaryotes, epigenetic control can determine if certain genes expressed -> altering phenotype
- epigenetic control doesn’t alter base seq DNA
-> works by attaching / removing chemical groups to / from DNA … - … altering how easy it is for enzymes (and other proteins needed for transcription) to interact with and transcribe genes
- epigenetic changes are independent -> modification in 1 area not linked to modification in another
- epigenetic changes to gene expression play role in lots of cellular processes
-> also occur in response to changes to env (pollution, availability of food)
one method of epigenetic control is methylation of DNA.
describe this process
- when methyl group (-CH₃) is added to DNA coding for gene
- group always attaches at a CpG site -> where a cytosine and guanine base are next to each other in DNA
- increased methylation changes DNA structure …
- … so proteins and enzymes needed for transcription (transcription factors) cannot bind to gene
- so gene not expressed (inactivated)
one method of epigenetic control is the modification of histones.
explain why this is the case
histones: proteins that DNA wraps around to form chromatin -> which makes up chromosomes
- adding/removing acetyl groups to chromatin make it highly condensed / less condensed
- how condensed it is affects accessibility of DNA and if proteins and enzymes needed for transcription can bind to it
- so modification of histones affects gene expression
describe the epigenetic modifications of histones
include addition / removal of acetyl groups (COCH₃)
- when histones acetylated -> chromatin less condensed
-> so proteins involved in transcription can bind to DNA
-> so genes can be transcribed (activated) - when acetyl groups removed from histones
-> chromatin highly condensed
-> genes in DNA cannot be transcribed
-> as transcription proteins cannot bind to them
-> so genes repressed - modification of histones REVERSIBLE -> can be diff in diff cell types + varies with age
histone
protein that DNA wraps around to form chromatin (which makes up chromosomes)
epigenome
all epigenetic tags in an organism
