6.1 - B - Gene Mutations Flashcards
What is a mutation?
A random change to the genetic material
What is a gene mutation?
A change in the base sequence of DNA
What is a mutagen?
List some examples
A physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level.
Tar in tobacco smoke,
Ionising radiation eg: UV light, X-rays and gamma rays.
Which types of mutation are/aren’t associated passed onto offspring?
Mutations associated with mitotic division - not passed into offspring.
Mutations associated with meiosis and gamete formation - may be inherited by offspring.
List and define the 3 types of mutation
Substitution (point mutation) - when one base pair replaces another.
Insertion - when one or more nucleotides are inserted into a length of DNA.
Deletion - when one or more nucleotides are deleted from a length of DNA.
What do insertion and deletion mutations cause?
Define this term
Frameshifts - when the base pairs move left (deletion) or right (insertion).
List and explain the 3 types of substitution mutations
Silent - when a substitution occurs but the triplet code still codes for the same amino acid - it doesn’t change amino acid.
Missense - when a substitution occurs that leads to a change in the amino acid sequence.
Nonsense - when a substitution occurs that turns the amino acid sequence into a termination (stop) sequence.
What is the name for both insertions and deletions?
Indel mutations
In what way can indel mutations not cause a frameshift?
When base pairs are inserted/deleted in multiples of 3, causing there to only be an addition/loss of an amino acid(s).
What does E. coli normally do?
What type of microorganism is it?
It normally metabolises glucose as respiratory substrate.
Bacterium.
What 2 enzymes does lactose produce?
Under what conditions does this occur?
If glucose is absent but lactose is present, lactose induces the production of 2 enzymes:
Lactose permeate - which allows lactose to enter the bacterial cell (coded for by lac Y).
Beta-galactosidase - which hydrolysed lactose to glucose and galactose (coded for by lac Z).
What is an operon?
A length of DNA made out of structural and control (P and Lac O) genes that function together. It’s approx 6,000 base pairs long, containing an operator region lacO next to the structural genes lacZ and lacY that code for the enzymes beta-galactosidase and lactose permease respectively.
Where does RNA polymerase bind on an operon?
What type of biological molecule is it?
What does it do there?
The promoter region, P.
Enzyme.
Begins transcription of the structural genes lacZ and lacY.
What are the control sites of the lac operon?
The operator region and the promoter region
What do structural genes do?
Code for proteins
What do regulatory genes do?
Control the expression of structural genes by switching them on/off - this makes the repressor protein/transcription factors (I) (not part of operon)
What is the operator region?
The region next to structural genes that the repressor binds to lacO
What is the promoter region?
The binding site for RNA polymerase (P).
What do repressor proteins do?
Bind to the operator region, preventing RNA polymerase from binding to the promoter region, therefore preventing transcription.
Where is the regulatory gene found?
What does it do?
It’s found a small distance away from the operon.
Aka: I, it codes for a repressor protein (LacI). When this happens,the repressor protein produced binds to the operator, preventing RNA polymerase from binding to the promoter region.
What happens when lactose isn’t present at the operon?
What happens when lactose is present at the operon?
The lactose binds to the repressor gene made at the regulatory gene, creating an induce-repressor complex that cannot bind to the promoter region, allowing RNA polymerase to bind, which causes enzymes to be synthesised.
With no lactose to stop the repressor gene binding to the regulatory gene, the RNA polymerase can’t bind to it, meaning the enzymes aren’t synthesised.
What is a transcription factor?
Protein or short non-coding RNA that can combine with a specific site on a length of DNA and inhibit or activate transcription of the gene. They slide along a part of the DNA molecule, seeking and binding to their specific promoter regions. They may then aid or inhibit the attachment of RNA polymerase to the DNA, and activate or suppress transcription of the gene.
What is an exon?
The coding, or expressed region of DNA
What is an intron?
The non-coding region of DNA
Why are transcription factors important?
They are essential for the regulation of gene expression in eukaryotes
What do introns do?
Separate exons
Define morphogenesis
Anatomic development
What do homeotic genes do?
They control morphogenesis of organisms
What is a homeobox gene?
A homeobox gene is a homeotic gene that contains a 180 base pair homeobox sequence that codes for a 60 amino‐acid sequence called homeodomain sequence within a protein. These proteins are transcription factors.
Homeobox genes are master genes and regulatory genes ‐ they switch on/off many other genes.
Describe and explain the homeodomain’s shape
The homeodomain sequence’s shape is specific to part of the enhancer region on DNA so it binds to the DNA to initiate/stop transcription to switch genes on or off. This controls the development of the body plan.
What is important about homeobox genes?
They are highly conserved and very similar. They are found in all plant, animal and fungal species from a common ancestor throughout evolutionary history. This is to prevent mutations which would most likely cause death.
What are hox genes?
What do they do?
A type of homeotic genes only found in animals.
They control the formation of anatomical features in the correct locations of the body plan.
What do hox genes do during embryonic development?
In embryonic development Hox genes are expressed one by one along the anterior‐posterior axis which causes the development of particular body parts in this particular order.
How many hox gene clusters do tetrapods have?
4
Suggest 5 characteristics scientists look for in the animals they use in their experiments
Cheap to buy and keep, Reproduce quickly, Small, Large cells, Readily available.
Suggest why information learnt from these model organisms can be applied to humans
All in the same kingdom,
Have shared ancestors,
Similar cells,
Have shared genes and similar embryonic development/similar homeobox/Hox genes.
Explain the link between: homeotic genes, homeobox genes, homeobox sequence, homeodomain sequence and hox genes
Homeotic genes control anatomical development of organisms.
Homeobox genes are a type of homeotic gene that contain a homeobox sequence (180 bp long) that code for a homeodomain sequence (a section of a transcription factor that binds to DNA to control the development of the body plan).
Hox genes are a type of homeobox gene that controls the development of the correct body parts in the right place in animals.
Define apoptosis
Programmed cell death
How are hox genes regulated?
They’re regulated by other genes called gap genes and pair-rule genes. In turn, these genes are regulated by maternally supplied mRNA from the egg cytoplasm.
How is apoptosis different from cell death due to trauma?
Cell death due to trauma involves hydrolytic enzymes
List the sequence of events during apoptosis
Enzymes break down the cell cytoskeleton.
The cytoplasm becomes dense with tightly packed organelles.
The cell surface membrane changes and small protrusions called blebs form.
Chromatin condenses, the nuclear envelope breaks and DNA breaks into fragments.
The cell breaks into vesicles that are ingested by phagocytic cells, so that cell debris does not damage any other cells or tissues. The whole process happens quickly.
How is apoptosis controlled?
Cell signals such as cytokines from cells of the immune system, hormones, growth factors and nitric oxide. Nitric oxide can induce apoptosis by making the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient. Proteins are released into the cytoplasm where they bind to apoptosis inhibitor proteins, allowing apoptosis to occur.
Explain the steps in the post-translational level of gene regulation
A signalling molecule binds to receptor on the plasma membrane of the target cell.
This activates a transmembrane protein which then activates a G protein.
The G-protein then activates adenyl cyclase enzymes.
These enzymes catalyse the formation of many molecules of cyclic AMP from ATP.
cAMP activates PKA (protein kinase A).
PKA catalysts phosphorylation of various proteins, hydrolysing ATP in the process. The phosphorylation activates many enzymes in the cytoplasm.
PKA may phosphorylate another protein.
This then enters the nucleus and acts as a transcription factor.
