Cellular Control Flashcards
How can mutations arise
They can be spontaneous
They can be from random changes to genetic code
There is an increased frequency from mutagens
What are the 3 types of mutagens
Physical
Chemical
Biological
Give an example(s) of physical mutagens
UV light - Break strands of DNA
X-Ray/Gamma radiation - Cause pyrimidine dimers
Give an example(s) of Chemical mutagens
Deaminating agents - Cytosine to Uracil
Clastogens - eg Benzene cause deletion or addition
Give an example(s) of biological mutagens
Alkylating agents - Attaching an ethyl or methyl group
Base anaglogs - Used in place of a base
Viruses - Inserts itself into the genome
What are the three impacts of a mutation
Neutral
Deleterious
Beneficial
How can a mutation’s impact be neutral
It can be silent due to the degenerate nature of code
It can occur on the non coding DNA (introns)
How can a mutation’s impact be deleterious
There won’t be a protein made
Shorter protein made
Key αα missing
Explain how a mutation leads to cystic fibrosis
Cystic fibrosis is the production of excess mucus
This is due to the deletion of three bases
As a result the protein folds incorrectly
Give an example of a beneficial mutation
Lactose persistence - The ability of adults to digest the lactose in milk
This is a recent mutation
The lactose promoter still works so lactase gene is still transcribed
Avoid osteoporosis
Additional food source
What are the types of chromosome mutations
Deletion - Gene is deleted
Duplication - Gene is duplicated
Translocation - A gene is cut off and attaches to a non homologous chromosome
Inversion - A section of the gene inverts itself
What are the time of point mutations
Original AAA
Substitution - AAT
Deletion - AA
Insertion - AAAA
What is a codon
3 bases that code for an amino acid
What does degenerate code mean
How many possible combinations are there
More than one codon codes for the same amino acid
4^3
What type of mutation is this
TTC TTT
Lys Lys
Silent mutation - A base change still codes for the same amino acid
What type of mutation is this
TTC ATC
Lys Stop
Nonsense - Base change results in the formation of a stop codon
What type of mutation is this
TTC TGC
Lys Thr
Missense - Change in base results in a different amino acid being coded for
Can be conservative or non conservative depending on αα being code
What is a frameshift
Every codon after the mutation is affected
It’s much more harmful then a insertion/deletion of 3n bases
How is gene regulated at a transcriptional level
Genes can be turned permanently on or off
Can be up or down regulated by affecting promoter (transcription factors)
How is gene regulated at a post transcriptional level
Pre mRNA is formed and this undergoes splicing to remove the introns leaving the exons
This is then protected by a modified nucleotide cap and a tail of adenine
Mature mRNA is formed then mRNA editing or further splicing can occur to code for different genes
How is gene regulated at a translational level
Translation can be stopped or started
How is gene regulated at a post transcriptional level
Usually done by phosphorylating proteins to active them
A signalling molecule binds to a complimentary and specific receptor on cell surface membrane
This activates a gene protein which activates adenylyl cyclase
This catalyses the reaction of ATP to form cAMP
This activates protein kinase A (PKA)
Goes to phosphorylates of various proteins
What is an operon
A cluster of genes under the influence of one promoter - energy saving
Describe the lac operon in E.coli if there isn’t lactose present
A regulatory gene at the stand of the operon codes for a repressor protein
This protein binds to an operator region which masks the promoter region
RNA polymerase can’t code for the structural genes
Describe the lac operon in E.coli if there is lactose present
Lactose binds to the repressor protein and it unbinds from the operator region
This unmasks the promoter region and so RNA polymerase can start transcribing the genes
These genes are lactose permease and β galactosidase
What are homeobox genes
Regulatory genes that control body development
Made of 180bp and code for a protein called the homeodomain
They are highly conserved so between species there is very little difference
Involved in mitosis and apoptosis
What are Hox genes
They are a set of homeobox genes only found in animals
They regulate the development of an embryo such as head orientation and limb position
Why do we use fruit flies to look at mutations
They have a short life cycle
Rapid growth rate
Mutations can be observed under a light microscope
How can body plans be controlled
Normal body cells can divide around 50 times - Hayflick limit
Apoptosis is a programmed cell death
Controls body development plans such as separation of fingers, toes and harmful T-lymphocytes
Is the opposite of necrosis
Describe the sequence of events during apoptosis
Enzymes break down the cytoskeleton
Cytoplasm becomes tightly densed with organelles
Blebs form as cell surface membrane changes
Chromatin condense, nuclear envelope breaks down and DNA breaks into fragments
Cells break into vesicles that are ingested by phagocytic cells
What is an internal and external signalling moelcuels
Internal - Hormone
External - Thalidomide
