Section 8 - 20 Gene Expression Flashcards
What is a mutation?
Any change to the quantity or the structure of the DNA of an organism.
What is a gene mutation?
Any change to one or more nucleotide bases, or any rearrangement of the bases, in DNA
What is a substitution mutation?
When a nucleotide in a section of DNA molecule is replaced by another nucleotide that has a different base.
What are three possible consequences of substitution mutation?
- formation of one of the three stop codons that mark the end of a polypeptide chain. - stopped prematurely
- Formation of a codon for different amino acid meaning structure of polypeptide produced would differ in single amino acid. - not correct shape or function
- formation of a different codon but one that produces a codon for the same amino acid - degenerate nature.
What is a deletion mutation?
The loss of a nucleotide base from a DNA sequence
What does a deletion mutation cause?
A frame shift
a reading frame that contains every three letters of the code has been shifted to the left by one letter.
What is addition mutation?
The extra base becomes inserted in the sequence.
Cause a frame shift to the right.
What is duplication mutation?
One or more bases are repeated.
Produces a frame shift to the right.
What is an inversion mutation?
Group of bases become separated from the DNA sequence and rejoin at the same position but in the inverse order.
Base sequence is therefore reversed and affects the amino acid sequence that results.
What is a translocation mutation?
Group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome.
Often having significant effects on gene expression leading to an abnormal phenotype.
These effects include the development of certain forms of cancer and also reduced fertility.
Typically how many natural mutations occur?
One or two mutations per 100000 genes per generation.
What two outside factors affect the basic mutation rate?
- mutagenic agents
- mutagens
What is included in the terms mutagenic agents or mutagens?
- high energy ionising radiation
- chemicals
What is cell differentiation?
The process why which each cell develops into a specialised structure suited to the role that it will carry out.
Another name for a fertilised egg
Zygote
What are totipotent cells?
A fertilised egg which has the ability to give rise to all types of cells.
What do controlling factors do?
ensure that genes for proteins are not expressed.
In what ways do genes prevented from expressing themselves?
- preventing transcription and so preventing the production of mRNA
- preventing translation
At what point can cells no longer specialise into another?
Once cells have matured and specialised they can no longer develop into other cells.
What are stem cells?
Undifferentiated dividing cells that occur in adult animal tissues and need to be constantly replaced.
What are stem cells capable of?
They have the ability to divide to form an identical copy of themselves in a process called self-renewal.
Where do stem cells originate?
- embryonic stem cells
- umbilical cord blood stem cells
- placental stem cells
- adult stem cells
Where are totipotent stem cells found?
In the early embryo.
What are pluripotent stems cells?
Found in embryos
Can differentiate into almost any type of cell.
Examples of pluripotent stem cells
Embryonic stem cells
fetal stem cells
What are multipotent stem cells?
Found in adults
Differentiate into a limited number of specialised cells.
Devlop into cells of a particular type.
Give examples of multipotent stem cells
Adult stem cells
umbilical cord blood stem cells
What are unipotent stem cells?
Can only differentiate into a single type of cell.
Derived from multipotent stem cells and are made in adult tissues.
What are examples of unipotent stem cells?
Heart muscle cells that can divide to produce new heart tissue and so repair damage to heart muscle.
How can you produce induced pluripotent stem cells?
Type of pluripotent cell
produced by unipotent stem sells
How can you make induced pluripotent stem cells?
- Unipotent are almost any body cell
- these cells are genetically altered in a lab making them acquire characteristics of embryonic stem cells which are pluripoetnt
How do iPS and embryonic stem cells different?
iPS - capable of self-renewal - the potential to divide indefinitely to provide a limitless supply
How can pluripotent cells be used?
To regrow tissues that have been damaged in some way - accidents or disease
State the general principles involved in the control of gene expression by controlling transcription
- Genes switched on by specific molecule - transcriptional factors
- Each factor has a specific site to bind to a base sequence
- When bound transcription begins
- mRNA produced and info is translated to a polypeptide
- when genes did not express the site of factor is not active
- If not active then transcription and polypeptide synthesis can not occur.
What is a transcriptional factor?
Molecules that allow genes to be switched on.
This means transcription can occur.
These molecules move from the cytoplasm into the nucleus.
Give an example of a transcriptional factor
oestrogen
How can oestrogen affect genes?
Switch on a gene starting transcription.
Combine with a receptor site on transcriptional factor. - change shape of DNA binding site
- Oestrogen into cell
- Binds to the active site of the receptor molecule of factor. Changes shape so complementary with DNA binding site.
- Factor enters the nucleus through the nuclear pore and binds to base sequence on DNA
- Stimulates transcription of the gene.