Gene Expression Flashcards
What is a mutation?
change to the quantity or the structure of the DNA of an organism
What is a gene mutation?
Any change to one or more nucleotide base
What is the substitution of bases (mutation)?
- new base substituted = stop coding,
- different codon = different amino acid - tertiary structure different,
- different codon = same amino acid.
What is the deletion of bases (mutation)?
- frame shift left - many codons affected (if affecting beginning) or smaller impact (towards the end)
What is an insertion mutation?
- extra base becomes inserted in the sequences- frame shift right
What is a duplication of bases mutation?
- bases are repeated - frame shift right
What is a inversion of bases mutation?
- a group of bases become separated from DNA sequences and rejoin in inverse - affects amino acids sequence produces
What is the Translocation of bases mutation?
- DNA sequence one chromosome is separated and joins another DNA sequence on a different chromosome - abnormal phenotype - cancer, fertility issues
What are Mutagenic agents?
- increase rate of mutations = high ionising radiation - disrupt DNA structure, Chemicals - alter DNA or transcription
What is cell differentiation?
the process through which cells become specialised to perform specific functions
What do mutagenic agents do?
disrupt DNA structure, Chemicals - alter DNA or transcription
Are all genes expressed in a given cell at one time?
not all genes expressed in a given cell at one time -> as they serve different functions
Some genes permanently expressed those gene ….
code for essential processes
What are totipotent cells?
- cells that can mature into any body cell, including the placenta -> e.g cells derived at an early stage from a fertilised egg
What are the stems and what are different types of stem cells?
- Stem cells - have the ability to divide to form an identical copy of themselves
- Stem cells can be found in: Embryos (early - totipotent), umbilical cord (multi-potent), placenta, Adult stem cells (multipotent)
How are genes not expressed?
preventing transcription -> mRNA OR preventing translation
What are pluripotent cells?
differentiate into almost any cell (embryonic) - not the placenta
What are multipotent cells?
limited number of specialised cells (stem cells in bone marrow - blood cells)
What are unipotent cells?
- only differentiate in one cell (cardiomyocytes - heart tissues)
- genetically altered -> to acquire characteristics of embryonic -> include genes and transcriptional factors
What are IPS cells?
- capable of self-renewal - potentially divide indefinitely = more pluripotent cells -> grow tissues that are damaged
What are transcriptional factors?
complementary to the specific base sequence of DNA-> region of DNA begins transcription = mRNA that can attach to the ribosome in the cytoplasm
What is oestrogen?
-Steroid hormones that act as transcription factors
How does oestrogen work?
- Diffuse into membrane -> binds to a receptor site on transcription factor -> DNA binding site changes (tertiary structure change) -> complimentary so can now bind to DNA -> transcription factor enter nucleus through nuclear pore -> bind to specific base sequence in DNA -> transcription occurs
What is the effect of small interfering RNA on gene expression?
- An enzyme cuts large double-stranded molecules of RNA into smaller sections called (siRNA) -> ½ of siRNA strands combine with an enzyme
- The siRNA molecules guide the enzyme to a mRNA molecule by pairing up its bases with complementary ones on a section of the mRNA
- Once in position, the enzyme cuts mRNA into smaller sections -> no longer capable of being translated into polypeptide -> which means the gene has not been expressed
What is a proto-oncogene?
- code for both cell surface receptors and intercellular proteins -> stimulate a cell to divide when growth factors attach to a protein.
What happens if a proto-oncogene mutates into an oncogene?
it becomes permanently activated (switched on) for 2 reasons:
- The receptor protein on the cell-surface membrane is permanently activated so that cell division is switched on even in the absence of growth factors
- The oncogene may code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division
What are tumour suppressor genes?
slow down cell division, repair mistakes in DNA - inhibit cell proliferation or cause apoptosis (opposite role from proto-oncogenes)
What happens if tumour suppressor genes become mutated?
it is inactivated - drops inhibiting cell division and cells can grow out of control
What does hypermethylation result in ?
- Hypermethylation in the promoter region of tumour suppressor gene - tumour suppressor gene inactivated - transcription inhibited - tumour suppressor gene is silenced - increased cell division - formation of tumour
What are the links between oestrogen and cancer?
more oestrogen -> tumour development -> white blood cells drawn to tumour -> increase oestrogen conc
What is epigenetics?
environment factors affecting genetic inheritance - influenced by Lamark
What is an epigenome?
DNA + Histones are covered in chemicals (AKA tags)
What is epigenome silencing and how does it occur?
inactive genes are tightly packed = less accessible - so they are not switched on
What is acetylation?
a process whereby an acetyl group is transferred to a molecule
What is Deacetylation
acetyl group is removed from molecules
What happens when acetylation is decreased?
increases the positive charges of histones - increases attraction to phosphate groups of DNA -> DNA + histones association stronger -> not accessible by transcription factors -> cannot initiate mRNA production -> gene switched off
What is methylation and how does it inhibit transcription of genes?
addition to methyl group (added to cytosine) - normally inhibits the transcription of genes by:
- Preventing the binding of transcriptional factors of the DNA
- Attracting proteins that condense the DNA-histone complex, making inaccessible to transcriptional factors
What is the human genome?
consists of over 3 billion base pairs organised into around 20,000 genes -> this was facilitated by bioinformatics (the science of collecting and analysing complex biological data)
What is a proteome?
all the proteins produced by genome /(in a given type of cell or organism at a given time under specified conditions.)
How does epigenetics work?
An environmental signal stimulates proteins to carry its message into the cell -> passed through proteins in the nucleus -> specific protein attaches to a specific sequence of bases on DNA -> 2 possible effects: Acteylation of histone = Activation or inhibition of genes, methylation of Dna by attracting enzymes that can add or remove methyl groups
