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Section 8 - The control of gene expression - Coggle Diagram
Section 8 - The control of gene expression
20 Gene expression
Gene mutations
Cause of mutations
Mutagenic agents increase the likelihood of mutations occurring during DNA replication
Radiation e.g. X-ray, UV
Chemicals e.g. in tobacco smoke
Mutations arise spontaneously during DNA replication in the cell cycle
Germline mutation - within gametes, is hereditary
Somatic mutation - within body cells, not hereditary
Effects of mutations
Change in one codon
Changes one amino acid
Silent mutation
Same amino acid is coded for
Frameshift
Changes the base triplets in every codon downstream of the mutation
Loss of one or more nucleotide
If a multiple of 3 bases are lost, there is not a frameshift
Types of mutation
Deletion
Loss of one or more nucleotide
If a multiple of 3 bases are lost, there is not a frameshift
Duplication
Bases are repeated
Can cause a frameshift
Addition
Extra bases are added into a gene
Can cause a frameshift
Inversion
Group of bases are reversed in order, completely changing the codons
Translocation
A group of bases move to a different chromosome
Substitution
A nucleotide is changed for a different one, usually changing one codon
May result in a stop codon
May result in the same amino acid due to degenerate nature of the genetic code
May change the amino acid, resulting in a different polypeptide structure
Control of gene expression
Cells
Unipotent stem cells
Can differentiate into one type of cell
Cardiomyocytes
Found in adult tissue
Multipotent stem cells
Found in adult tissue
Can differentiate into some cell types
Bone marrow stem cells and umbilical cord stem cells
Pluripotent stem cells
Can differentiate into almost any type of cell
Found in embryos
Induced pluripotent stem cells
Made from adult somatic cells
Requires transcription factors
Totipotent stem cells
In early embryo
Can differentiate into any type of cell
Totipotent cells only translate some of their DNA
Allows them to specialised into one type of cell e.g. specific proteins for that cells
Cancer
Benign and malignant tumours
Tumour suppressor genes
Slow down cell division
Can mutate and become inactivated
Methylation
Proto-oncogenes
Can mutate to become oncogenes
Oncogenes cause uncontrolled cell division
Oestrogen
Breast cancer
Regulation of translation and transcription
Oestrogen
Breast cancer
Oestrogen binds to a receptor of a transcription factor
Transcription factor can now bind to DNA
Increased transcription and translation of a particular gene e.g. proto-oncogene
Epigenetics
Acetylation of histones
Methylation of DNA
Changes accessibility of DNA
Heritable changes in gene function, without changing the base sequence of DNA
RNA interference
Transcription factors control transcription and expression of particular genes
Using genome projects
Sequencing
Sequencing techniques are constantly improving
Determining the base sequence of the entire genome
Many organisms' genomes have been sequenced, including humans
Application - knowing which genes allow some organisms to tolerate extreme conditions
Proteome
By sequencing the genome of simple organisms, we can determine the proteome of specific cells
Determining the proteome is more difficult in complex organisms
There is lots of non-coding DNA in complex organisms, which makes it more difficult to identify the DNA coding for proteins
Proteome = the complete set of proteins produced by the genome
Application - determining the structure of antigens for vaccines
21 Recombinant DNA technology
Gene technologies
Recombinant DNA technology
Transfer of DNA fragments between organisms
Production of fragments of DNA
Convert mRNA to cDNA by reverse transcriptase
Restriction enzymes to cut DNA at specific positions
Gene machine to create the gene fragment
Amplification of the DNA fragment or gene
Polymerase chain reaction (PCR) is a way of amplifying DNA fragments in vitro
Temperature changes
Requires the DNA fragment, DNA polymerase, nucleotides, primers, and a thermocycler
Transforming cells and culturing them is an in vivo way of amplifying DNA fragments
Need to add promoter and terminator regions to the DNA fragment
Vector transports DNA fragment into host cell e.g. plasmid
Ligases join the plasmid and DNA
Restriction endonucleases cut plasmid to allow insertion of DNA fragment
Complementary sticky ends between plasmid and DNA fragment
Plasmid now has recombinant DNA
Plasmid is introduced into host cells
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Genetic fingerprinting
DNA probes are short, single-stranded DNA sections with a label attached
Hybridisation with DNA
Radioactive or fluorescent labels
Can be used to identify specific alleles, and so can be used to screen for genetic conditions and for personalised medicine
Gel electrophoresis
Separates fragments by size - smallest ones travel furthest
Variable number tandem repeats (VNTRs)
Can determine genetic relationships
Forensic science
Medical diagnosis e.g. Huntingdon's disease
Unique to each person