3.8 The control of the gene expression Flashcards
What is a gene mutation?
Change in the base sequences of DNA
When can gene mutations arise?
can arise spontaneously during DNA replication, during interphase of the cell cycle
What is an mutagenic agent?
Things that increase the rate of gene mutation
What are some examples of mutagenic agent?
- Ionising radiation
- Carcinogens
- Some viruses
Name the types of gene mutations
Substitution, Addition, Deletion, Inversion, Duplication and Translocation
Describe the effect on amino acid sequence in the encoded
polypeptide when Substitution happens
- No change due to degenerate nature of genetic code
- 1 tripelt code change -> 1 amino acid change
Describe the effect on amino acid sequence in the encoded
polypeptide when Addition happens
- Frameshift; triplets / codons change
downstream of mutation → amino acid
sequence changes
OR - If multiple of 3 bases added – no frameshift, but
extra triplets / codons → extra amino acids
Describe the effect on amino acid sequence in the encoded
polypeptide when deletion happens
- Frameshift; triplets / codons change
downstream of mutation → amino acid
sequence changes
OR - If multiple of 3 bases lost – no frameshift, but
missing triplets / codons → missing amino acids
Describe the effect on amino acid sequence in the encoded
polypeptide when inversion happens
- No frameshift because number of bases stays
the same - Triplets / codons in inverted region change →
sequence of amino acids encoded by inverted
region change
Describe the effect on amino acid sequence in the encoded
polypeptide when Duplication happens
- Frameshift; triplets / codons change
downstream of mutation → amino acid
sequence changes
OR - If multiple of 3 bases added – no frameshift, but
extra triplets / codons → extra amino acids
Describe the effect on amino acid sequence in the encoded
polypeptide when Translocation happens
- Significant impact on gene expression and
amino acid sequences at original and new
location
Why may some mutations not affect the order of amino acids in a polypeptide?
- new codon might still code for the same amino acid
- due to degenerate nature of the genetic code
- also, some gene mutations occur in the introns and therefore won’t affect amino acid sequences
Explain ‘frameshift’
- occurs when gene mutations change the number of nucleotides by any number not divisible by 3
- codons downstream from the mutation change
- sequence of amino acids encoded changes accordingly and the effects on the encoded polypeptide is significant
What is a stop codon?
Codons that terminate translation
What can a mutation to the stop codon cause?
Premature stop codon
- result in production of shorter and often non-functional polypeptide
How can mutations lead to the production of a non-functional protien/enzyme?
- Change in base / triplet sequence of DNA / gene
- Changes sequence of codons on mRNA
- Changes sequence of amino acids in primary structure of polypeptide
- Changes position of hydrogen / ionic / disulphide bonds in protein tertiary structure
- Changes tertiary structure / shape of protein and in the case of enzymes, the active site
will change shape - In the case of enzymes, the substrate will be unable to bind to active site and form an
enzyme-substrate complex
What is a stem cell?
Unspecialised cell
What are stems cells capable of?
- Self renewal
- Specialisation/Differentiation
How does stem cell specialisation occur generally?
- 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
Name and describe the types of stem cells
Totipotent cells
* Occur for a limited time in early mammalian embryos
* Can divide and differentiate into every cell type in body
Pluripotent cells
* Found in embryos
* Can divide and differentiate into most cell types (every cell type in body but not the cells of the placenta)
Multipotent cells
* Found in mature mammals
* Can divide and differentiate into a limited number of cell types
Unipotent cells
* Found in mature mammals
* Can divide and differentiate into just one cell type
What is an example of a multipotent cell?
- cells in the bone marrow
What is an example of a unipotient cell?
Cardiomyocytes ( cardiac muscle cells)
What is an example of a unipotient cell?
Cardiomyocytes ( cardiac muscle cells)
How are Induced Pluripotent stem cells produced?
- Produced from adult somatic cells (non-pluripotent cells or fibroblasts)
- Specific protein transcription factors associated with pluripotency put into cells, causing the cell to express genes associated with pluripotency (reprogrammed)
- Cells cultured
- = Induced pluripotent stem cells
Why would IPS cells be used over 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
What are the for’s for stem cell treatment?
- embryo are incapable of feeling pain as they are not equivalent to a human being
- embryos would otherwise be destroyed in clincs
- Duty to apply knowlege to relive human suffereing
- Bone Marrow, less likely to be rejected if it comes from patients own body
What are the arguments opposing the use of stem cells in treating human disorders?
Use of embryonic stem cells:
* Embryo is a potential human; should be given rights
Scientific:
* Induced pluripotent stem cells – cannot yet reliably reprogramme stem cells
* Could begin to multiply out of control, and cause tumours
- Can be expensive?
What are transcription factors and how do they work?
- Protiens
- Move from cytoplasm to nucleus
- Bind to DNA at a specific DNA base
sequence on a promotor region - Stimulate (‘activator’) or inhibit
(‘repressor’) transcription ( of target
gene(s) by helping or preventing
RNA polymerase binding
What is Oestrogen?
A steroid hormone initiating transcription
Why can Oestrogen diffuse across the phospholipid bilayer?
Lipid -soluble