3.8.2 Gene expression and cancer Flashcards
Totipotent stem cells are able to differentiate into..
any type of body cell
multicellular organisms are made up from…
many different types of specialised cells
specialised cells originated from..
stem cells
unspecialised cells that can develop into other cell types are called
stem cells
Two main sources of stem cells can be found..
in the embryo, adult tissues
these types of stem cells are only present in mammals in the first few divisions of the embryo
totipotent (very early embryo)
these types of stem cells are still found in the embryo but have lost their ability to develop into differentiate into placental cells
pluripotent
adult stem cells can be one of two types
- multipotent stem cells
2. unipotent stem cells
these types of stem cells can differentiate into a limited number of stem cells e.g. bone marrow cells can form RBC and WBC
multipotent stem cells
These types of stem cells can only differentiate into ONE type of cell
unipotent
Stem cells specialise because…
different genes are expressed (turned off and on)
All cells contain the same DNA - true or false?
true
Stem cells all contain the same genes - true or false?
true
Molecules which regulate the expression of genes are called..
transcription factors
Where do transcription factors bind to regulate gene expression?
upstream of the gene (promoter region)
What do transcription factors do to regulate gene expression?
encourage binding of RNA polymerase (turn on genes) or prevent RNA polymerase binding (turn off genes)
Where are transcription factors found?
nucleus
When a cell receives a signal to express a gene what does the transcription factor do?
moves from the cytoplasm to the nucleus
Specialised cells all look different - why?
they all express different genes and thus proteins - this determines the cells overall structure
Which stem cell can red blood cells originate from?
bone marrow stem cells
Transcription is when
DNA is copied into mRNA
Translation is when
mRNA is translated into a sequence of amino acids
what are cardiomyocytes?
heart cells
what can stem cells be used for?
treat diseases e.g. paralysis - replace damaged cells/tissues
benefits of using stem cells in medicine?
save life and improve quality of life for many people
iPS cells stands for?
induced pluripotent stem cells
What are iPS cells?
created in the lab - reprogramming adult stem cells to become pluripotent
What are the limitations with adult stem cells?
limited differentiation capacity - they are mulitpotent
Where do we source embryonic stem cells from?
embryos created in the lab from IVF
Embryonic stem cells are classified as one of twp types
- totipotent (very early embryo)
2. pluripotent (early embryo)
Issue surrounding embryonic stem cells?
- ethics surrounding the sourcing of the embryos (embryo will be destroyed)
In all cells which genes will be permanently expressed?
genes involved in respiration
All organisms develop from a fertilised egg - what is the scientific name for this?
zygote
Zygotes divide by what process?
Mitosis
Can specialised cells change into other cell types?
animals - no
plants - yes - shoots/roots
Name a hormone that can regulate transcription
oestrogen
What type of hormone is oestrogen?
steroid hormone
How can oestrogen enter the cell?
lipid soluble and diffused through the phospholipid bilayer
What does oestrogen bind to to regulate transcription?
a binding site/receptor site on the transcription factor
When oestrogen binds to the receptor on the transcription factor what happens?
The DNA binding site on the transcription factor is now able to bind to DNA (transcription activated)
Why is oestrogen able to bind the receptor on transcrption factor?
oestrogen has a complementary shape the the receptor
What property of oestrogen allows it to diffuse through the phospholipid bilayer?
lipid soluble
Who proposed the structure of DNA?
Watson and Crick
What is meant by epigenetics?
heritable changes in gene function without change the base sequence of DNA
What sort of environmental factors might influence phenotype?
stress, sunlight, chemical exposure, diet,
How is your DNA organised into chromosomes?
DNA wrapped around proteins called histones (forming chromatin)
DNA and histones are covered in chemicals known as ..
tags
Tags attached to the DNA and histones form a second layer known as..
the epigenome
What determines the shape of the DNA and histone complex?
epigenome
DNA that is tightly packed, preventing transcription factors binding leads to
gene silencing
DNA that is loosely packed, allowing transcription factors to access the DNA leads to…
gene activation/expression
DNA code is fixed but your epigenome is…
flexible
What does your epigenome respond to?
the environment
Tags attached to DNA are knowns as
methylation
Tags attached to histones are knowns as
actylation
When the association of DNA and histones is weak what does this mean for gene expression?
transcription factors can access the DNA and turn ON a gene
Tight association of DNA and histones affects gene expression - how?
prevents transcription factors binding to the DNA so turns OFF gene expression
tight association of DNA and histones is brought about by..
decreased acteylation and increased methylation
loose association of DNA and histones is brought about by..
increased acteylation and decreased methylation
What does decreased acetylation do to the histone proteins?
increased + charge so more strongly attracted to phosphate in DNA
Why does methylation prevent transcription?
- prevents transcription factors binding to DNA
2. attracts proteins that would condense DNA
increased gene expression is brought about by
more acetylation and less methylation
reduced gene expression is brought about by
less acetylation and more methylation
acetyl group binds to
histones
methyl group binds to
DNA
more acetylation EQUALS
increased gene expression/DNA loosely packed
MORE methylation EQUALS
reduced gene expression/DNA tightly packed
LESS acetylation EQUALS
reduced gene expression/DNA tightly packed
LESS methylation EQUALS
increased gene expression/DNA loosely packed
epigenetics has been associated with what type of disease
cancer
do epigenetic changes alter the DNA base sequence?
NO
Preventing gene expression can also be done at the level of mRNA - how?
mRNA is cut up to prevent it being translated
what type of molecule is involved in silencing mRNA?
siRNA
Once siRNA is formed what does it associate with?
an enzyme
What is unique about the siRNA and the mRNA it is going to silence?
Their base sequences are complementary
enzymes can remove acetyl groups - how would this affect transcription?
less acetylation - reduced gene expression (mRNA not transcribed)
enzymes can remove acetyl groups - how would this affect DNA-histone complex?
tightly packed
All tumours are cancerous - true or false?
false
what is a tumour?
mass of cell caused by uncontrolled cell division
cancer is…?
abnormal mass of cells that invades neighbouring tissues or can break away forming secondary tumours
two types of tumours are?
benign and malignant
Which tumour is cancerous?
malignant
which tumour does not invade neighbouring cells?
benign
How do cancers spread?
blood stream or via lymphatic system
name the two genes that control cell division
proto-oncogenes and tumour suppressor genes
What is the function of a proto-oncogene?
stimulate cell division
what is the function of a tumour suppressor gene?
slow down cell division
what would happen if there was a mutation in a proto-oncogene?
turn into oncogene - uncontrolled cell division
what would happen if there was a mutation in a tumour suppressor gene?
uncontrolled cell division
Mutations in genes that control cell division cause…
cancer
Which type of tumour grows more slowly?
benign
How might tumour cells look compared to normal cells?
different shape
larger/darker nucleus
divide more rapidly
what does methylation do to the DNA?
adds a methyl group to it
In a proto-oncogene what happens to the methylation of the DNA to turn it into a oncogene?
hypomethylation (reduced methylation)
In a tumour suppressor gene what happens to the methylation of the DNA to cause cells to divide out of control?
hypermethylation (increase methylation) - turn gene off
which type of tumour grows rapidly?
malignant
which type of tumour involves using radiotherapy as well as surgery?
malignant
Which type of tumour remains compact
benign
which type of tumour grows finger like projections into surrounding tissue?
malignant
which type of tumour has a capsule?
benign
what are oncogenes?
mutated pro-oncogenes
How to proto-oncogenes stimulate cell growth?
growth factor binds to receptor stimulating cell division
An oncogene can become permanently activated for one of two reasons?
- oncogene codes for a receptor that is permanently activated
- oncogene codes for excessive growth factor
How do tumour suppressor genes work?
they slow down cell division, repair DNA or tell cells to die
what does apoptosis mean?
programmed cell death
Which gene regulates cell division and prevents formation of tumours?
TSG
if a TSG is mutated what is the consequence?
stops inhibiting cell division and cells divide out of control
some cancers are inherited others are…
aquired
what does the TP53 gene code for?
p53 protein
why is p53 important?
p53 protein is important in apoptosis
A mutation in the TP53 will lead to…?
inactive p53 protein and no apoptosis, damaged cells continue to divide
mutation in a proto-oncogene leads to
oncogenes being activated - uncontrolled cell division
mutation in a TSG leads to
TSG being inactivated - uncontrolled cell division
abnormal methylation is common in many tumours - what effect can this have on a TSG?
hypermethylation of a TSG - inactivity - uncontrolled cell division (p53 not made)
what is hypermethylation?
addition on methyl groups on DNA - switching off gene expression
transcription of genes is controlled by protein molecules called?
transcription factors
How do transcription factors move?
from the cytoplasm to the nucleus
Expression of genes can be affected by other molecules e.g. hormones e.g. ….
oestrogen
can epigenetic changes be inherited?
yes!
How would methylation of a TSG lead to cancer?
- Methylation prevents transcription of gene;turns off gene expression
- Protein (p53) not produced that prevents cell division/ causes cell death/apoptosis;
- No control of mitosis; uncontrolled cell growth due to mitosis
Which cancer gene would be inhibited due to increased methylation?
tumour suppressor gene (TSG) - gene not transcribed!
give one way benign tumours differ from malignant tumours
Cells of benign tumours cannot spread to other parts of the body/metastasise
OR
Cells of benign tumours cannot invade neighbouring tissues;
Describe how alterations to TSG can lead to development of tumours
- increased methylation of TSG
- mutations in TSG
- TSG not expressed
- Leading to rapid uncontrolled cell division
