cellular control Flashcards
What is programmed cell death known as?
Apoptosis.
Distinguish between terms regulatory gene and structural gene.
Regulatory genes produce a regulatory protein/ transcription factor, whereas structural genes produces enzymes.
What is a mutation?
A change in the DNA base sequence of an organism.
What is a point mutation?
Where 1 base is substituted for another base.
What are the three types of point mutation?
- Nonsense.
- Mis-sense.
- Silent.
What is nonsense mutation?
Change results in a stop codon.
What is mis-sense mutation?
Different amino acid is coded for.
What is silent mutation?
Different base occurs in the triplet but it codes for the same amino acid.
What are Indel mutations?
Extra base is added or deleted, leading to frame shift.
What is a mutagen?
Chemical, physical, or biological agent which causes mutations. They increase rate of mutations.
Example of physical, chemical and biological mutagens.
Physical - Ionising radiation.
Chemical - deaminating agents
Biological - viruses, alkylating agents
What are the three stages of controlling a gene expression?
Transcriptional control - Genes switched on and off e.g. Lac Operon.
Post-transcriptional control - mRNA editing e.g. alternative splicing.
Post-translational control - Protein activation.
What are the 2 types of chromatin?
Heterochromatin - Tightly wound DNA causes chromosomes to be visible in cell division, transcription of genes can’t occur as RNA polymerase can’t reach genes.
Eurochromatin - Loosely wound DNA, present during interphase - genes can be freely transcribed.
What are the different effects of histone modification?
- Acetylation and phosphorylation (addition of acetyl/phosphate group) reduces the positive charge on histone, causing DNA to coil less tightly so genes can be transcribed, as RNA polymerase can reach them.
- Methylation (addition of methyl group) causes histones to be more hydrophobic, causing them to bind more tightly to each other making DNA to coil more tightly and therefore genes can’t be transcribed.
What is the Lac Operon?
Group of genes that do similar things.
What are transcription factors and what are they encoded by?
- proteins that bind to sections of DNA to either switch genes on or off.
- they are encoded by regulatory genes.
- TFs can either activate or repress genes.
What 2 genes are expressed in order to digest lactose?
B-galactose : hydrolyses lactose into galactose and glucose.
Lactose permease : A transport protein that becomes embedded into the E.coli membrane to transport more lactose into the cell.
When no lactose is present.
-Repressor protein binds to the operator region and partially covers the promoter region.
-RNA polymerase cant bind to promoter so Z and Y can’t be transcribed.
When lactose is present.
- It acts as an inducer.
- Lactose binds to the repressor protein, stopping it from binding to the operator region.
- Therefore, RNA polymerase can bind to promoter region and transcribe Z and Y.
What happens during post-transcriptional control?
- DNA is split into segments for genes called introns and exons.
- Exons are sequences of DNA for genes that can be expressed (coding).
- Introns are sequences of DNA that do not contain any useful DNA and are not expressed (non-coding DNA).
- Introns are spliced out of the sequence so only exons remain (gene splicing).
What happens during post-translational gene regulation?
- After proteins are produced by translation they can be activated by molecules (e.g. sugars/ hormones) to become functional.
- Folding and shortening of proteins.
- Some of these molecules bind to cell membrane to trigger production of cAMP -> used to alter the 3D shape of proteins by changing active site.
What are homeotic genes?
A set of genes that regulate morphogenesis, the shape that an organism forms (body shape).
What are homeobox genes?
A set of genes that contain a homeobox sequence.
What is homeobox?
An 180 base pair sequence that is highly conserved in plants, animals and fungi.
What is a homeodomain?
A 60 amino acid sequence within a protein.
What are hox genes?
A type of homeobox genes found in clusters in animals that regulate body plan.
What do hox genes do?
They control polarity and where organs are.
These genes show little mutation because they are very important.
They are highly conserved.
Mutation would have a greater effect and alter the body plan causing many other genes to be affected. Any mutation is likely to be lethal and so selected against.
