TOPIC 8 - gene expression is controlled by a number of features Flashcards
what is a stem cell?
undifferentiated cells, that can divide indefinitely and turn into other specific cell types
what are the 3 different types of stem cells? define them.
TOTIPOTENT = can develop into any type of cell type including placenta and embryo
PLURIPOTENT = can develop into any cell type excluding placenta and embryo
MULTIPOTENT = can only develop into a few different types of cell
what happens to totipotent cells during embryonic development?
- certain parts of the DNA are selectively translated so that only some genes are ‘switched on’ in order to differentiate the cell into a specific type and form tissues that make up the foetus.
give a unique feature of the pluripotent cells and the use of this feature.
- they can divide in unlimited numbers = used to repair or replace damaged tissue
what is unipotent cell?
- cell that can develop into one type of cell
- happens at the end of specialisation when the cell can only propagate its own type.
eg cardiomyocytes
which type of stem cells are found in embryos?
totipotent and pluripotent
multipotent and unipotent are only found in mature mammals
give some uses of stem cells
medical therapies eg bone marrow transplants, treating blood disorders
drug testing on artificially grown tissues
research eg formation of organs and embryos
how are induced pluripotent stem cells produced?
- unipotent stem cells are treated with transcription factors to make them pluripotent
-modified virus (vector) inserts transcription factor gene from pluripotent cells into DNA of unipotent stem cells - transcription factors are expressed
what is a transcription factor?
- protein that controls the transcription of genes so only certain parts of the DNA are expressed. = allows a cell to specialise
How do transcription factors work?
- Move from cytoplasm into nucleus
- bind to promoter region upstream of target gene
- Activates or represses RNA polymerases ability to bind to gene. This increases or decreases rate of transcription.
give an example of a hormone that affects transcription and explain how it works.
Oestrogen = a steroid hormone
1. diffuses through cell membrane
2. forms oestrogen- oestrogen receptor complex in the cytoplasm
3. complex enters nucleus and acts as transcription factor to facilitate binding of RNA polymerase
what is meant by epigenetics ?
A heritable change in gene function without a change to the base sequence of DNA.
How does increased methylation of DNA affect gene transcription?
- addition of CH3 group to Cytosine bases which are next to guanine
- methylated CpG sites prevents transcription factors from binding =
RNA polymerase cannot bind to the promoter region, leading to gene silencing.
explain what acetylation is.
adding an acetyl (-COCH₃) group to histone proteins.
This reduces the positive charge on histones, weakening their interaction with negatively charged DNA.
Increased acetylation leads to a loosely packed chromatin structure (euchromatin), allowing transcription factors and RNA polymerase to access DNA and promote transcription.
How does decreased acetylation of DNA affect gene transcription?
- positively charged histones bind to negatively charged DNA.
- decreasing acetylation increases the positive charge of histones
- binding becomes too tight and prevents transcription factors from accessing the DNA = gene transcription is suppressed.
How might epigenetic changes affect humans?
They can cause disease either by over activating a gene function (cancer) or by suppressing it.
Give application of Epigenetics.
Treatments of various diseases. Development of ways to reverse epigenetic changes.
What is RNA interference using siRNA?
siRNA = small interfering RNA
- siRNA combines with protein to form siRNA-protein complex.
-siRNA becomes single stranded
- siRNA forms bond with mRNA by complementary base pairing
- siRNA protein-complex breaks down mRNA = prevents translation
What is RNA interference using microRNA?
-miRNA combines with a protein to form a microRNA-protein complex
- binds to mRNA by complementary base pairing
- prevents translation by stopping the ribosomes from attacking
give some charactersitics of benign tumours?
- slow growth
- cells retain function and normal shape
- doesnt spread easily
- easy to treat
give some charactersitics of malignant tumours.
- rapid, uncontrollable growth
- cells do not retain function and often die
- spreads quickly and easily (metastasis)
- difficult to treat
describe the role of tumour-suppressor genes.
- codes for proteins that slow down rate of mitosis or speed up rate of apoptosis
explain how tumour suppressor genes can be involved in developing cancer.
- a mutation in gene could code for non-functional protein. Increased methylation or decreased acetylation could prevent transcription.
- cells will divide uncontrollably resulting in a tumour
describe the role of proto-oncogenes.
Codes for proteins that increases rate of mitosis
if proto-oncogene mutates its called an oncogene.
