Biology notes that will help you get an A*
Notes have been made to cater to the AQA Biology Mark Scheme
Contains everything on the spec for Gene Expression:
- Mutations
- Stem Cells
- Protein Synthesis Regulation
- Epigenetics
- Cancer
- Genome Project
- DNA Fragments
- Recombinant DNA Te...
Mutations
Mutation: a change to the base sequence of DNA
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Mutations can be caused by errors during DNA replication
Types of mutations:
Substitution: one or more bases are swapped for another
Deletion: one or more bases are removed
Addition: one or more bases are added
Duplication: one or more bases are repeated
Inversion: a sequence of bases is reversed
Translocation: a sequence of bases is moved from one location in the genome to another. This could be movement within the same
chromesame or to a different one.
Order of DNA bases in a gene determines the sequence of amino acids in a polypeptide. A mutation changes base order so the sequence
of amino acids in a polypeptide changes.
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This may change the final 3D shape of the protein which could stop it from working
Some mutations cause genetic disorders - inherited disorder cause by abnormal genes or chromosomes. Some mutations increase the
likelihood of developing cancers
If a gamete containing a mutation for a genetic order of or a cancer is fertilised, the mutation will be present in the fetus. These are
called hereditary mutations because they are passed on to the offspring. Not all hereditary mutations one harmful - beneficial hereditary
mutations drive evolution.
Mutations may have no affect because of the degenerate nature of the genetic code. If a mutation doesn't cause a change in the amino
acid order, it's called a silent mutation
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Addition, duplications and deletions will almost always change the amino acid sequence
This is because they change the number of buses in the DNA code
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This causes a frame shift in the base triplets that follow.
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The base triplets that follow on from the mutation are said to to be 'downstream' of the mutation.
Mutagenic agents:
Mutations are random but mutagenic agents can increase the rate of mutations
They can do this by:
Acting as a base: chemicals called base analogs can substitute for a base during replication, changing the base sequence
Altering bases: some chemicals can delete or alter bases
Changing the structure of DNA: radiation can change DNA structure, which causes problems during DNA replication.
, Stem
Stem Cells
Cells
Multicellar organisms are made up from many different cell types that are specialised for their function which originally came from stem
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cells
Stem cells divide to become new cells, which then become specialsed
Embryonic stem cell Adult stem cell
TotipOtent: PluRipOtent: MultipOtent: UnipOtent:
Only present in the first few cell After first few division of Differentiate into a few Differentiate into one
divisions of an embryo.
Can specialise into any type of cell :
embryo, embryonic stem cells
become pluripotent
Can specialise into any cell
different types of cell
Stem cells in bone marrow
can differentiate into red
type of cell
One type of stem cell can only
divide to produce epidermal
except cells that make up and white blood cell skin cells
placenta
Specialisation:
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Stem cells all contain the same genes but during development they only transcribe and translate part of their DNA.
Under the right conditions, some genes are expressed and others are switched off
mRNA is only transcribed from specific genes and then translated into proteins
These proteins modify the cell - they determine the cell structure and control cell processes including the expression of more genes
Changes to the cell produced by these proteins causes specialisation are difficult reverse
Red blood cells are produced from stem cells in the bone marrow. They contain lots of hemoglobin and have no nucleus
The stem cell produces a new cell which the genes for haemaoglobin production and no nucleus are expressed while others are switched
off
Cardiomyocytes:
Cardiomyocytes are heart muscle cells
In mature mammals,it was thought they can't divide to replicate themselves but the heart does have some regenerative capability
Old or damaged cardiomyocytes can be replaced by new ones derived from a small supply of unipotent stem cells in the heart
Some believe it is a really slow process and that some cardiomyocytes are never replaced.
Others think it is more so every cardiomyocytes is replaced several times
Medicine
Bone marrow transplants can be used to replace faulty bone marrow that produce abnormal blood cells. The stem cell in the transplanted
bone marrow divide and specialise to produce healthy blood cells
This can be used to treat leukemia (cancer of blood or bone marrow) and lymphoma (cancer of lymphatic system)
Can also be used to treat genetic disorcles such as sickle-cell anemia and SCID
SCID affects the immune system because white blood cells are defective so sufferers are extremely susceptible to infections.
Bone marrow transplant can be used to treat it
Trials:
Spinal cord injuries: stem cells can replace damaged nerve tissue
Heart disease and damage: stem cells can replace damaged heart tissue
Bladder conditions: stem cells can be used to grow whole bladders to replace diseased ones
Structure Respiratory diseases: donated windpipes can be stripped down to their collagen and then covered with tissue generated by stem
cells to be transplanted
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