19 Flashcards
What is a gene mutation?
A change in the sequence of bases in DNA
What is a change sequence caused by?
Substitution, deletion or insertion of one or more nucleotides within gene
What is a point mutation?
If one nucleotide is affected by
How does substitution of a single nucleotide change primary structure of protein if not a degenerate code?
As this will code for a different amino acid is it is not a degenerate code.
What does degenerate mean?
When more than 1 codon triplet can code for the same amino acid e.g AGC and AGT both code for serine for DNA
What does or deletion lead to?
Insertion or deletion of one or more base pairs results in a complete shift in code called frameshift.
What is a stutter mutation?
When triplets are repeated many times.
What is a silent mutation?
A substitution when a different a different base is used in the base sequence instead of the original base. If the triplet still codes for the same amino acid this is a silent mutation.
How many bases may be removed for a frameshift?
One or two or multiples of them. Cannot be three or multiples of three.
No effect of different mutation
No effect on phenotype of organism because normally functioning proteins are still synthesised
Damaging effect of different mutation
Phenotype of organism is affected in negative way as proteins are no longer synthesised or synthesised proteins are non functional.
Beneficial effect of different mutations
Protein is synthesised and results in new and useful characteristic in phenotype.
What is a mutagen?
Chemical or physical agent which causes mutation
What does a mutagen do?
- causes mutation
- increases rate of mutation
What are the three main mutagens?
Physical
Chemical
Biological
What can the different changes in chromosome structure include?
Deletion
Duplication
Translocation
Inversion
What is chromosome deletion?
A section of chromosome breaks off and is lost within the cell
What is chromosome duplication?
Section gets duplicated on chromosome
What is chromosome translocation?
A section of one chromosome breaks off and joins another non homologous chromosome
What is chromosome inversion?
A section of chromosome breaks off, is reversed, and then joins back onto chromosome
What are housekeeping genes?
Genes that code for frequent enzymes/proteins which are necessary for reactions present in metabolic pathway
What is transcriptional?
Genes can be turned on or off
What is post transcriptional?
mRNA can be modified which regulates translation and the types of proteins produced.
What is translational?
Translation can be stopped or started
What is post translational?
Proteins can be modified after synthesis which changes their function
What are tissue specific genes?
Proteins that are required certain cells at certain times.
What are histones?
Proteins wound around DNA
What is heterochromatin?
Tightly wound DNA causing chromosomes to be visible during cell division
What is euchromatin?
Loosely wound DNA present during interphase
What charge do histones have?
Positive charge
What reduces the positive charge on histones?
Addition of acetyl or phosphate groups.
What is an operon?
A group of genes that are under the control of the same regulatory mechanism and are expressed at the same time.
Are operons more prominently present in prokaryotes or eukaryotes?
Prokaryotes owing to the smaller and simpler structure of their genomes
What is the lac operon?
A group of three genes (lacZ, lacY and lacA)that enable prokaryotes to metabolise lactose if glucose is not present.
What is LacI and what does it do?
It is a regulatory gene and codes for a repressor protein that prevents the transcription of the structural genes in the absence of lactose.
Where does the repressor protein bind to?
Binds to a section on operon called operator.
What do structural genes do?
Code for enzymes and hormones
What do control genes do?
Control the transcription of structural genes
What does it mean if the enzymes are inducible?
Only transcribed when needed
LacZ (B/beta - galactosidase)
Code for enzyme that converts lactase to glucose and galactose, so E coli can carry out aerobic respiration.
LacY (lactose permease code)
The code which makes the bacterial cell more permeable to lactose
LacA (Transacetylase)
Dont need to know much about, just that its a structural genes
What is the operator region?
Used to switch structural genes on and off
What is the promoter region?
RNA polymerase has to bind here to initiate transcription of structural genes.
What is cAMP (cyclic AMP)?
Acts as secondary messenger to increase the amount of enzyme transcription
What happens when glucose is present?
- Low cAMP - no binding to CRP
- DNA doesn’t change shape
-RNA polymerase does not bind
-repressor binds to operator so RNA polymerase cannot attach - enzyme not transcribed
What happens when lactose is present?
- high cAMP
- bind to CRP - shape of DNA changes
-RNA polymerase binds - lactose binds to repressor inhibits
- enzyme transcription is induced by lactose
What is the CRP site?
Region where the protein CRP or cAMP receptor protein binds. It helps bind RNA polymerase to the promoter in order to transcribe genes.
If cAMP is present the CRP attaches to the DNA and allows RNA polymerase to bind
What is an intron?
A non coding section of DNA situated within a gene.
What is an exon?
A section of DNA that encodes a polypeptide.
What is a cap?
A modified nucleotide
What does a cap do?
Help stabilise mRNA and delay degradation in cytoplasm.
Also aids binding of mRNA to ribosomes.
Degradation of mRNA
The more resistant the molecule, the longer it will last in the cytoplasm, that is, a greater quantity of protein synthesised.
What are protein kinases?
Enzymes that catalyse the addition of phosphate groups to protein.
What is post translational control and what can happen?
Involves modification to proteins that have been synthesised
-addition of non protein groups
-modifying amino acids and formation of bonds
-folding or shortening of proteins
-modification by cAMP
What are homeobox genes?
Group of genes which all contain homeobox.
What is homeobox?
Section of DNA 180 base pairs long, coding for a regulator sequence or homeodomain.
They are highly conserved
Switches genes on and off to control body plan
What is a homeodomain?
Binds to DNA and switches other genes on or off
What type of genes are homeobox genes?
Regulatory genes
What are hox genes?
A group of homeobox genes that are only present in animals and are responsible for the correct positioning of body parts.
Diploblastic?
Animals with two primary tissue layers
Triploblastic?
Animals with three primary tissue layers
What are the different types of symmetry?
Radial
Bilateral
Asymmetry
What does apoptosis do?
Leads cells to death that are generally older cells
Apoptosis helps shape body part by removing certain cells.
Internal factors affecting regulatory gene expression?
Hormones
Psychological stress
External factors?
Viruses
Bacteria
Chemicals and drugs
Stress
