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SECTION 8 SUMMARY QUESTIONS - Coggle Diagram
SECTION 8 SUMMARY QUESTIONS
WHAT ARE THE DIFFERENT TYPES OF MUTATIONS AND HOW DO THEY ARISE?
SUBSTITUTION
1 base replaced with another base.
No change to AA sequence due to degenerate nature of genetic code.
1 triplet / codon change so 1 amino acid change
DELETION
1 or more bases lost from base sequence.
Frameshift; triplets / codons change downstream of mutation so amino acid sequence changes
If multiple of 3 bases lost – no frameshift, but missing triplets / codons so missing amino acids
ADDITION
1 or more bases added to base sequence.
Frameshift; triplets / codons change downstream of mutation so amino acid sequence changes
If multiple of 3 bases added – no frameshift, but extra triplets / codons so extra amino acids
INVERSION
A sequence of bases is separated from DNA and inserted at the same position, backwards
No frameshift because number of bases stays the same
Triplets / codons in inverted region change so sequence of amino acids encoded by inverted region change
DUPLICATION
A sequence of bases is inserted twice, or multiple times
Frameshift; triplets / codons change downstream of mutation so amino acid sequence changes
If multiple of 3 bases added – no frameshift, but extra triplets / codons so extra amino acids
TRANSLOCATION
Sequence of bases taken out and inserted at a different position on the same, or a different chromosome
Significant impact on gene expression and amino acid sequences at original and new location
WHAT FACTORS AFFECT THE RATE OF MUTATIONS?
MUTAGENIC AGENTS
Increase the rate of gene mutation above the rate of naturally occurring mutations
Examples
Ionising radiation
Carcinogens
Some viruses
WHY DO SOME MUTATIONS HAVE NO IMPACT ON THE PHENOTYPE?
Also, some gene mutations occur in the introns (non-coding sequences within genes) and therefore won’t affect amino acid sequences.
New codon might still code for same amino acid because genetic code is degenerate
Some gene mutations (substitution) change only 1 codon
WHY CAN THE MUTATION OF A SINGLE BASE AFFECT MANY AMINO ACIDS?
A frameshift occurs
This shifts the way the genetic code is read, so all the DNA triplets / mRNA codons downstream from the mutation change
The sequence of amino acids encoded changes accordingly and the effects on the encoded polypeptide are significant
WHAT ARE TOTIPOTENT, PLURIPOTENT, MULTIPOTENT AND UNIPOTENT STEM CELLS AND WHERE ARE THEY FOUND?
MULTIPOTENT
Can divide and differentiate into a limited number of cell types.
Found in mature mammals
UNIPOTENT
Can divide and differentiate into just one cell type
Found in mature mammals
E.g, cardiomycytes
PLURIPOTENT
Found in embryos
Can divide and differentiate into most cell types
TOTIPOTENT
Occur for a limited time in early mammalian embryos
Can divide and differentiate into every cell type in body
WHAT ARE iPS CELLS AND HOW ARE THE FORMED?
Induced Pluripotent Stem Cells
How are they produced?
Produced from adult somatic cells.
Specific protein transcription factors associated with pluripotency put into cells,
causing the cell to express genes associated with pluripotency (reprogrammed).
Cells cultured
= iPS cells
Why are iPS cells used in medical treatment instead of embryonic cells?
No immune rejection as can be made using patient’s own cells
Overcome some ethical issues with using embryonic stem cells e.g. no
destruction of embryo and adult can give permission
HOW DO STEM CELLS BECOME SPECIALISED?
Stimulus e.g, chemical
Causes selective activation of genes – some genes activated while others inactivated
mRNA only transcribed from active genes....translated on ribosomes = proteins
These proteins modify cell permanently and determine cell structure / function
WHAT ARE THE CONSIDERATIONS OF USING STEM CELLS TO TREAT HUMAN DISORDER?
FOR- use of embryonic stem cells
Tiny balls of cells, incapable of feeling pain
Not equivalent to a humans
Would otherwise be destored
Duty to apply knowledge to relieve human suffering
AGAINST- use of embryonic stem cells
Embryos is a potential human; should be given rights
AGAINST- use of induced pluripotent stem cells
Cannto yet reliably reprogram stem cells
Could begin to multiply out of control and cause tumours
WHY ARE STEM CELLS USED IN MEDICINE?
Regrow damaged tissues
Drug testing- used to grow artificial tissues
Development biology research- provide insight into embryological development
WHAT ARE TRANSCRIPTION FACTORS AND HOW DO THEY INFLUENCE THE EXPRESSION OF GENES?
Transcription factors are proteins that control the rate of protein synthesis by switching some genes on and other genes off.
Promoter regions: short sequences of DNA at the start of a gene
Transcription factors move from the cytoplasm into the nucleus.
Binds to the promoter regions.
Activators help RNA polymerase to bind to DNA- GENE IS NOT TRANSCRIBED
Repressors- prevent RNA polymerase binding to DNA so GENE IS NOT TRANSCRIBED