8.1-2 Gene Expression Flashcards
What are the 6 types of mutation?
Substitution Addition Deletion Inversion Duplication Translocation
What are the substitution mutations?
Silent - the same amino acid is coded for
Mis-sense - a different amino acid is coded for
Non-sense - a stop codon is coded for
What does addition and deletion mutations result in?
A frame shift
All subsequent codons are altered and therefore every amino acid after that - it can have devastating effects
What is an inversion mutation?
A group of bases is separated and rejoins at the same position but in the reverse order
What is a duplication mutation?
One or more bases are repeated which can result in a frame shift
What is a translocation mutation?
A group of bases is separated in one chromosome and inserted in the base sequence of another chromosome
= significant effects in the phenotype
What causes mutations?
Ionising radiation
Chemical mutagens
Spontaneous errors
How can mutations benefit organisms?
It produces genetic diversity which is necessary for natural selection
What are stem cells?
Undifferentiated cells which can keeping dividing to give rise to other cells
What are the types of stem cells? Order of ability to differentiate
Order of ability to differentiate: Totipotent Pluripotent Multipotent Unipotent
What are totipotent and pluripotent stem cells?
Totipotent - They can form any type of cell as they only translate part of their DNA
Including embryonic stem cells
Pluripotent - they can form any type of cell in the body but not embryonic
They are found in the early stages of an embryo
What are multipotent and unipotent stem cells?
Multipotent - can differentiate into other cell types but are more limited eg bone marrow and umbilical cord
Unipotent - they can only differentiate into one type of cell
How are embryonic stem cells produced?
The inner mass of a blastocyst is removed and isolated once the trophoblast (outer layer of cells) is destroyed using lasers
The embryonic stem cells are cultivated and they can add different growth factors to trigger
What can be produced from unipotent cells?
Induced pluripotent cells (iPS)
By using the appropriate protein transcription factors
What can affect gene transcription?
Oestrogen
siRNA
How does oestrogen affect gene transcription?
It is lipid soluble so it diffuses across the cell membrane
The oestrogen binds to a receptor molecule on the transcription factor
The receptor changes shape which releases the inhibitor and the DNA binding site is exposed
The transcriptional factor binds with the DNA and begins the process of transcription
What is siRNA?
Small interference RNA
Small double stranded sections of RNA cut up
What does siRNA do?
siRNA fragments separate and combine with an enzyme
The siRNA/enzyme complex binds to the mRNA
The mRNA detects this as abnormal and the mRNA is broken down by the enzyme preventing translation
Why is siRNA useful?
To prevent gene mutations from being coded for a carried out into a protein
What are Epigenetics?
The study of changes in organisms caused by modification of gene expression rather than the alteration of the genetic code itself
What is the epigenome?
The shape of the DNA histone complex due to the interaction of chemical tags
The chemicals are attached but not a part of the DNA sequence
What can effect the epigenome?
In utero development
Environmental chemicals
Ageing
Diet
Where do epigenetic factors come from in early development?
From gametes
Then from the mother across the placenta
What is acetylation?
Acetyl molecules are donated from acetyl coA
They bind to the histone tails on heterochromatin to form euchromatin
Euchromatin means the DNA is wrapped less tightly around the histones and is available for a transcriptional factor to access
Why does acetyl have this effect?
The negative acetyl and the negative DNA repel so the attraction between the DNA and histones decreases
Therefore heterochromatin unwinds to euchromatin so DNA can be transcribed
What is methylation?
A methyl group binds to cytosine
The transcriptional factor is no longer complementary and cannot bind to the promoter region
Therefore prevents transcription
How to remember what acetyl and methyl do in the epigenome?
Methyl Masks
Acetyl Allows
What is a benign tumour?
They grow slowly in a capsule and don’t spread
The cells are very specialised
What is a malignant tumour?
Grow rapidly and spread to neighbouring cells (metastasise - through the blood stream or lymphatic system)
Unspecialised cells, dark nucleus and often reoccurring
What is a proto-oncogene?
Stimulate cells to divide (by producing proteins to stimulate cell division)
They allow check points of the cell cycle to be passed
What is a oncogene?
Formed from mutated proto-oncogenes
They are permanently switched on in uncontrolled cell division - either by:
-permanently activating a receptor
-coding for a growth protein
What are tumour suppressant genes?
They cause the cell cycle to stop when damage is detected
They can cause damaged cells to ‘self destruct’ called apoptosis
Describe the role of proto-oncognenes im stimulating DNA replication?
Proto-oncogenes code for: growth factor, receptors, relay proteins and nuclear protein
A growth factor binds to a receptor activating relay proteins
This switches on the nuclear protein which is needed for DNA replication
What mutations can cause cancer?
Mutation of proto-oncogenes (=oncogenes) - overproduction of proteins leading to uncontrolled cell division
Mutation of tumour suppressor genes - you can no longer prevent cell division i.e stop or slow it down
