epigenetics Flashcards
what is genome sequencing
-identifying the DNA base sequence for a human allows us to work out the amino acid sequence of the polypeptides coded by the DNA
What is the genome
-all of the genetic information in the cells of an organism
what is the proteome
-all of the possible proteins a cell can make
is it possible to directly translate the genome into the proteome
-yes, in simple organisms
-in complex organisms, due to the presence of non-coding regions (VNTRs or STRs), much harder to obtain the proteome
what are the four different types of stem cells
-totipotent, can turn into any cell, including placenta and embryo
-pluripotent, can become most cells, except placental and embryo
-multipotent, can become a few types of cell
-unipotent, can only become one type of cell
What happens to totipotent stem cells during embryonic
development
-only some of the genes are switched on, allows cells to differentiate into a specific type and form the tissues of the foetus
unique feature of pluripotent cells
-they can divide in unlimited numbers, and so can be used to repair damaged tissue
what is a unipotent stem cell and give an example
- a stem cell which can only develop into one type of cell, i.e cardiomyocytes
what is iPS and how are they made
-induced pluripotent stem cells
-from specialised somatic cells, the cell regains capacity to differentiate through the use of proteins
what is a transcription factor
- a protein that controls the transcription of certain genes, so only certain parts of the DNA are expressed
How does a transcription factor work
-moves from cytoplasm to the nucleus
-binds to the promoter region upstream of target gene
-makes it easier or harder for RNA polymerase to bind to gene
-increases or decreases rate of transcription
Give an example of a hormone and how it affects transcription factors
-steroidal hormone oestrogen diffuses through cell membrane (lipid soluble)
-forms a hormone-receptor complex with ER (endoplasmic reticulum)-α receptor in cytoplasm
-complex enters the nucleus and acts as a transcriptional factor to help increase rate of transcription
what is epigenetics
-a HERITABLE change in gene function without a change in the base sequence of DNA
How does methylation of DNA affect gene transcription
-increases de-acetylation
- addition of methyl group onto cytosine bases, which are next to guanine
-prevents transcription factor binding
-so gene transcription is suppressed/gene is silenced
how does de-acetylation of DNA affect gene transcription
-removal of acetyl group from the histone causes it to form a positive charge
-attracted to the negatively charged phosphate groups
-binding becomes too tight and transcription factor cannot bind
-gene silenced
what is siRNA and how does it work?
-small interfering RNA
-mRNA enters the cytoplasm, siRNA binds to the mRNA via complementary base pairing
-molecules is cut into fragments with the enzyme associated with siRNA
-so no TRANSLATION occurs
give the role of tumour suppresser genes
-code for proteins that regulate cell division, and stopping the cell cycle when a cell is damaged
-also program for apoptosis (cell death)
explain how tumour suppressor genes may lead to cancer
-mutation in the TSG could code for non-functional protein
-increased methylation or decreased acetylation will cause silencing of the gene, so no transcription, cells can divide uncontrollably –> tumour
describe the role of proto-oncogenes
control cell division by coding for proteins that stimulate cell division
explain how proto-oncogenes can be involved in developing cancer
-mutation in gene could cause it to become an oncogene
-decreased methylation or increased acetylation can cause excessive transcription
-unregulated cell division which can lead to tumour formation
how does abnormal methylation of genes can cause cancer
-hypermethylation of oncogenes or TSG can impair their function and cause uncontrollable cell division
