Summary AQA A Level Biology - Cornell Style Notes - Unit 8 - The Control Of Gene Expression
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Course
Unit 8 - The Control Of Gene Expression
Institution
AQA
Clear and concise Cornell styled notes for Unit 8 Biology A Level - The Control Of Gene Expression. The notes include diagrams and colours to make revision more visually appealing. The whole course is covered by my notes and is written in a detailed way that is still easily understandable, and each...
Mutations Eve Holland
Key Points: Notes:
Types Of Mutation:
- Addition/subtraction - where one or more bases are added or removed
Types of mutation: from the DNA sequence.
1. Addition - Substitution - where one or more bases are removed in the DNA sequence.
- Inversion - where the order of bases in the DNA sequence are inverted
2. subtraction
(reversed).
3. Substitution - Duplication - where one or more bases are duplicated (repeated) in the
4. Inversion DNA sequence.
5. Duplication - Translocation - where a section of the DNA sequence is moved to another
6. Translocation section of the DNA sequence. This can also happen within and across
chromosomes
Effects of Mutation:
- The sequence of bases in DNA encodes the amino acids that are used in
3 bases code for a amino acid - triplet protein synthesis. If this sequence is altered by mutation, this could
base code or codon influence the proteins an organism produces.
- Three bases encode an amino acid, this called a triplet code or codon
Amino acids bonded with peptide - Amino acids are joined with peptide bonds to form proteins
bonds form proteins
- Mutations give rise to change in the base sequence in DNA
Mutations changes the base sequence - If the amino acids in a protein change then the 3D structure of the protein
may break down
→ amino acids → tertiary structure
- E.g. change in enzyme effects the active site so enzyme is denatured and
→ 3D structure can no longer function
- E.g. Some genetic disorders - Cystic fibrosis is caused by a mutation that
affects proteins in the epithelial cells of the respiratory system.
Degenerate code means that an The Degenerate Code:
amino acid is coded for by more than - Some mutations have no effect on protein structure because of the
degenerate nature of DNA
one base triplet code
- The DNA code is degenerate if some amino acids are encoded by more
than one base triplet code.
Frameshift Mutations:
A frameshift mutation happens when - A frameshift is caused when a base (or multiple bases) is inserted, removed
bases are inserted, removed or or duplicated into the genome.
duplicated which changed the - This type of mutation has altered the number of bases in the DNA
number of bases in the sequence. sequence.
- This means that all the triplet codes downstream from the mutation will
experience a shift.
All triplet codes downstream will shift
Causes of Mutations:
Causes of Mutations: - DNA replication - the bases in the DNA sequence are read and copied.
- DNA replication - There can be errors in the replication process. These errors cause
- Mutagenic agents mutations and these mutations are spontaneous
- Mutagenic agents can increase the rate at which mutations occur
Summary:
, Stem Cells Eve Holland
Key Points: Notes:
Stem cells:
- Stem cells are unspecialised cells. Unspecialised cells are capable of dividing
Stem cells = undifferentiated cells and differentiating into any type of cell. There are four types:
1. Totipotent cells - exist for only a very limited time during embryonic
development in mammals. Totipotent cells are able to produce any type of
body cell, as well as cells of supportive structures such as the placenta. They
are the most unspecialised stem cell and specialise into many different cell
4 types:
types.
1. Totipotent 2. Pluripotent cells develop from totipotent cells in the embryos - Pluripotent
2. Pluripotent cells are able to divide in unlimited numbers and produce any type of cell that
3. multipotent makes up the body. Pluripotent cells can be used to treat human disorders.
4. Unipotent 3. Multipotent cells are found in mature mammals. Multipotent cells can
develop into a limited number of cell types. (e.g. bone marrow)
4. Unipotent cells are found in mature mammals. Unipotent cells can divide to
produce new cells but can only produce one type of cell. (e.g.
cardiomyocytes)
Stem cells become specialised
during embryonic development Specialisation of Stem Cells:
1. Stem cells become specialised during embryonic development. Specialised
When they become specialised only cells only express some of the genes in their DNA.
some genes are activated 1. Totipotent cells become specialised during embryonic development.
2. When the cells become specialised, only some genes are activated.
Only activated genes are expressed 3. Only the activated genes are expressed.
Use of Stem Cells:
Sources of stem cells: Sources:
1. Adult stem cells 1. Adult stem cells (taken from adult body tissues).
2. Embryonic stem cells 2. Embryonic stem cells (taken from embryos).
3. Induced pluripotent stem 3. Induced pluripotent stem cells (iPS).
cells
Advantages:
- Stem cells can be used to reduce preventable deaths. E.g. Stem cells could be
Advantages:
used to grow organs for organ transplants
- Used to grow organ - Stem cells can be used to treat conditions that decrease the quality of life.
transplants E.g. Stem cells could be used to replace the damaged cells in the spinal cord
- Replace damaged cells that cause paralysis.
Disadvantages: Disadvantages:
- Stem cells from embryos is a - There are some disadvantages to using stem cells.
controversial issue for - Obtaining stem cells from embryos is a controversial issue for ethical reasons.
ethical reasons
- iPS cells help avoid this - Somatic (specialised adult cell) cells are converted to
iPS cells by activating genes using appropriate protein transcription factors.
IPS helps avoid this as they are Making somatic cells become unspecialised so they can treat disease.
taken from adult cells and decrease - iPS cells can be made from a patient's own body cells. This also decreases the
the chance of rejection chance of rejection during transplants
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