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8 Control of Gene Expression AQA A-Level Biology 🧬 - Coggle Diagram
8 Control of Gene Expression AQA A-Level Biology 🧬
Gene Mutations
mutations occur in DNA replication spontaneously but the frequency is increased by exposure to mutagenic agents. This can result in different amino acid sequence in primary structure this causes hydrogen and ionic bonds to different locations so a different 3D tertiary structure so could adopt another function or non-functioning protein can result in a mutation that causes cancer.
mutation
- change in the DNA base sequence of a gene
Types of Mutations
Addition
- one extra base added to sequence will cause frameshift
Deletion
- remove a base from sequence will cause frameshift
Substitution
- one base is changed for a different base
Inversion
- DNA detaches re-join inverted section of code in back to front results in different amino acids
Duplication
- duplicates at least one sequence causes frameshift
Translocation of Bases
a group of bases become separated from the DNA sequence on one chromosome and are inserted into the DNA sequence on another chromosome.
Exam Question:
Give two reasons why a substitution mutation could lead to differences in organism?
could affect less replication of cell or could affect less translation/transcription of certain gene to mRNA
Stem Cells
totipotent
- stem cells can divide and produce any type of body cell
mammaliam embryos
pluripotent
- found in embryos can divide into
almost
every cell besides placenta cells can divide unlimited number of times
treat human disorders
stem cells are undifferentiated cells that can continually divide and become specialised
multipotent
- can divide to form a limited number of different cell types e.g bone marrow leukaemia found in mature mammals
unipotent
- capable of giving rise to one type of cell
cardiomyocytes- heart cell tissue
induced pluripotent stem cells
IPS cells can be produces from adult somatic cells using protein transcription factors to do this: the genes switched off to make the cell specialised must be turned back on using transcriptional factors
advantages
done in a single treatment, more long-term, less chance of side-effects from viruses, less chance of rejection by immune response
cell specialisation
is when totipotent cells translate only a part of their DNA
pluripotent cell treatment
can divide in unlimited numbers and can be used to treat human disorders
Gene Therapy vs Stem Cell Transplant- Bone Marrow Sickle Cell Disease
for gene therapy
- less chance of rejection if put in own stem cells, no destruction of bone marrow, donors not required
against gene therapy
- side-effects from harmful virus vector being injected, will still make faulty cells,
Regulation of Transcription & Translation
How is transcription controlled?
Transcription of a gene only occurs when a transcription factor proteins from the cytoplasm enters the nucleus and binds to DNA, each one can bind to different base sequences on DNA stimulating transcription making mRNA to create protein.
If gene is inactive, transcription won't occur, protein won't be made
Role of Oestrogen
is a steroid hormone (lipid-based) which can initiate transcription, since it is lipid soluble it diffuses across cell surface membrane and binds to transcription factor's
receptor
site (which is complimentary) slightly changing shape of
DNA-binding site
changing tertiary structure/shape so it is complimentary to DNA and initiate transcription.
Epigenetics
the heritable change in gene function without changing base sequence of DNA.
Transcription Factors
are proteins with a specific DNA binding site a receptor site of DNA/promoter region which stimulates RNA polymerase
Cancer
Tumour Suppressor Genes/Oncogene Mutation
proto-oncogene produces growth factor and receptor protein, when the growth factor binds to receptor protein on cells it stimulates DNA replication that leads to cell division
Proto-oncogenes-
creates a protein which initiate DNA replication in cell cycle when body needs new cells
stimulate cell division
benign tumour-
which do not metastasise/spread to neighbouring tissues dividing at a slower rate, non-cancerous due to adhesove sticky molecule and in a capsule
malignant tumour-
which does metastasise and spreads to neighbouring cells/tissues in body (via blood stream/lymphatic system) grow large rapidly projections to blood supply (chemotherapy radiotherapy)
cancer
can arise through mutation that causes rapid & uncontrolled mitosis/cell division
Oncogenes-
these are formed from mutated proto-oncogenes and result are permanently switched on resulting in uncontrolled cell division proto-oncogene produces growth factor and receptor protein, when the growth factor binds to receptor protein on cells it stimulates DNA replication that leads to cell division
Abnormal methylation of tumour supressor genes & oncogenes
methylation can cause tumour surpressor gene to turn off resulting in inactive gene resulting in gene being permanatly switched on,
Increased oestrogen concentration
Using Genome Projects
genome
complete set of DNA in an organism is recorded
proteome
complete set of proteins expressed by an organism
Epigenetics & RNA Interference
Epigenetics
- the heritable change in the gene function without changing the base sequence
evaluation question
- only done in non-humans, only done in small amount of time. only done on small sample, no statistical test, no standard deviations, not done in vivo, long-term effects not known
RNA interfrence (RNAi)
an enzyme can cut mRNA into siRNA. One strand of the siRNA then combines with another enzyme. This siRNA-enzyme complex will bind via complementary base pairing to another mRNA molecule thus stop translation of gene to produce protein
Methylation
- increased methylation of DNA inhibits transcription because methyl groups attach to cytosine prevents transcriptional factors from binding and condenses the DNA-histone complex.
Aceylation
- increased acyelation of associated
histones
proteins, if removed from DNA histones become more postive/attacted to the phosphate group of DNA called new chromatin (not tightly coiled)
DNA probe & Gel Electrophoresis
What is a DNA probe?
a single strand of DNA which has a complimentary base sequence to target DNA/gene/allele
Describe how you would use a DNA probe
Extract DNA and use restriction endonuclease to cut gene of interest breaking phosphodiester bonds.
Then separate DNA fragments using gene electrophoresis to form single strands/exposed bases.
Add DNA probe (which is complimentary and binds to start of gene) which has a radioactive probe added to it.
Use autoradiography to show bound probe.
Genetic Fingerprinting
Recombinant DNA Technology
PCR
Denaturation
- This is the first stage, where the DNA double helix is heated (around 94°C) to break hydrogen bonds, separating it into two single strands.
Annealing
- Next, the temperature is lowered (to about 54°C), allowing primers to attach to the single strands, which prevents them from rejoining.
Extension
- Finally, the temperature is raised (to 72°C), and DNA polymerase synthesizes new DNA strands by adding free nucleotides.
doubles each cycle- exponential increase
then after a number of PCR cycles there is no more nucleotides left.