Cellular control Flashcards
What is a mutagen?
A mutagen is a chemical physical, or biological agent which causes mutations.
Give an example of a physical, chemical and biological mutagen and what they do.
Physical mutagen- ionizing radiation (X-Ray)- break one or both DNA strands- some breaks can be repaired but mutations can occur in the process.
Chemical mutagen- deaminating agents- chemically alters bases in DNA such as converting cytosine to uracil in DNA, changing the base sequence.
Biological agents-
Alkylating agents- methyl or ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication
Base analogs- incorporated into DNA in place of place of the usual base during replication, changing the base sequence.
Viruses- viral DNA may insert itself into a genome, changing the base sequence.
How do you read a frame of sequences of bases?
The triple code means that sequences of bases are transcribed (or read) consecutively in non-overlapping groups of three.
Each group corresponds to 1 amino acid.
What are some causes of mutation?
- Mutations can occur spontaneously, often during DNA replication, but the rate of mutation is increased by mutagens.
- The loss of a purine base (depurination) or depryrimidisation often occurs spontaneously.
- The absence of a base can lead to the insertion of an incorrect base through complementary base pairing during DNA replication.
What are the effect of different mutations?
No effect- no effect onthe phenotype of an organism because normally functioning protein are still synthesised. Damaging- because proteins are no longer synthesised or protiens synthesised are non- functional (can interfere with essential processes) Beneficial- can result in a new and useful characteristic in the phenotype. E.g. Mutation in a protein present in the cell surface membranes of human cells means that HIV cannot bind and enter these cells. People with this mutation ae immune to infection form HIV.
Give an example of a physical, chemical and biological mutagen and what they do.
Physical mutagen- ionizing radiation (X-Ray)- break 1 or both DNA strands- some breaks can be repaired but mutations can occur in the process.
Chemical mutagen- deaminating agents- chemically alters bases in DNA such as converting cytosine to uracil in DNA, changing the base sequence.
Biological agents-
Alkylating agents- methyl or ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication
Base analogs- incorporated into DNA in place of place of the usual base during replication, changing the base sequence.
Viruses- viral DNA may insert itself into a genome, changing the base sequence.
What are the effects of a silent mutation?
The vast majority of mutations are silent (neutral) meaning they don’t change any proteins, or the activity of any proteins synthesised. Therefore they have no effect on the phenotype of an organism.
They may also result in changes to the primary structure but do not chnage the overall structure or the function of the proteins synthesised.
What are some causes of mutation?
Mutations can occur spontaneously, often during DNA replication, but the rate of mutation is increased by mutagens. The loss of a purine base (depurination) or depryrimidisation often occurs spontaneously. The absence of a base can lead to the insertion of an incorrect base through complementary base pairing during DNA replication.
What are the effect of different mutations?
What are the effect of different mutations?
No effect- no effect onthe phenotype of an organism because normally functioning protein are still synthesised. Damaging- because proteins are no longer synthesised or protiens synthesised are non- functional (can interfere with essential processes) Beneficial- can result in a new and useful characteristic in the phenotype. E.g. Mutation in a protein present in the cell surface membranes of human cells means that HIV cannot bind and enter these cells. People with this mutation ae immune to infection form HIV.
What are the effects of a silent mutation?
The vast majority of mutations are silent (neutral) meaning they don’t change any proteins, or the activity of any proteins synthesised. Therefore they have no effect on the phenotype of an organism.
They may also result in changes to the primary structure but do not chnage the overall structure or the function of the proteins synthesised.
What impact can a change in amino acid have on the function of a biological molecule?
The position and involvement of the amino acid in R group interactions within the protein will determine the impact of the new amino acid on the function of the protien.
E.g.
If the protien is an enzyme and the amino acid plays an important role within the active site, then the protein may no longer act as a biological catalyst.
What impact does addition or deletion of nucleotides have on the reading frame? What is the exception for this rule?
It shifts the reading frame.
This will change every successive codon from the point of mutation.
Except when they’re added or deleted in multiples of 3 ad this is a full codon however the protein formed will still be affected as a new amino acid is added.
What is a mutagen?
A mutagen is a chemical physical, or biological agent which causes mutations.
What is a mutation and what effect does it have on protein synthesis?
A mutation is the change in the sequence in bases of DNA.
Protein synthesis can be disrupted if he mutation occurs within a gene.
What is a mutation caused by?
The change in sequence is caused by the substitution, deletion or insertion of one of more nucleotides (or base pairs) within a gene.
What is a point mutation?
If only one nucleotide is affected it is called a point mutation.
What is the benefit of the degenerate nature of the genetic code?
The degenerate nature of the genetic code means that after substitution of a nucleotide, the new codon may still code for the same amino acid leading to no change in the protien synthesis.
What is the effect of substitution of a nucleotide?
The substitution of a single nucleotide changes the codon in which it occurs.
If the new codon codes for a different amino acid this will lead to a change in the primary structure of the protein.
What type(s) of mutation lead to a frameshift mutation?
Insertion or deletion of a nucleotide.
Where in the DNA do silent mutations occur?
They can occur in the non- coding regions of DNA(introns) or code for the same amino acid due to the degenerate nature of the genetic code.
What is a conservative mutation?
A conservative mutation occurs when the amino acid change leads to an amino acid being coded for which has similar properties to the original, this means the effect of the mutation is less severe.
Give an example of a beneficial mutation?
The ability to digest lactose, is a beneficial mutation.
What effect does a missense mutation have?
Missense mutations result in the incorporation of an incorrect amino acid(s) into the primary structure when the protein is synthesised.
The result depends on the role of the amino acid plays in the structure and therefore function of the protein synthesised.
The mutation could be silent, beneficial, or harmful.
What is the effect of a nonsense mutation?
Nonsense mutations result in a codon becoming a stop codon instead of coding for an amino acid.
The result is a shortened protien being synthesised which is normally non- functional.
These mutations normally have negative or harmful effects on phenotypes.
Where in the DNA do silent mutations occur?
They can occur in the non- coding regions of DNA(introns) or code for the same amino acid due to the degenerate nature of the genetic code.
What are housekeeping genes?
These are genes that code for enzymes which are necessary for reactions present in metabolic pathways like respiration and are constantly required.
What are some changes in the chromosome structure?
Deletion- a section of chromosome breaks off and is lost within the cell.
Duplication- sections get duplicated on a chromosome.
Translocation- a section of one chromosome breaks off and joins another non-homologous chromosome.
Inversion- a section of chromosome breaks off, is reversed and then joins back onto the chromosome.
What categories can mutations be put in?
Amorph
Hypomorph
Hypermorph
What codes for protein- based hormones?
Tissue- specific genes
What effect does a missense mutation have?
Missense mutations result in the incorporation of an incorrect amino acid(s) into the primary structure when the protein is synthesised.
The result depends on the role of the amino acid plays in the structure and therefore function of the protein synthesised.
The mutation could be silent, beneficial, or harmful.
What is a conservative mutation?
A conservative mutation occurs when the amino acid change leads to an amino acid being coded for which has similar properties to the original, this means the effect of the mutation is less severe.
What is a hypermorph mutation?
A mutation that results in a gain in function of a protein.
What is a hypomorph mutation?
A mutation that results in a reduction of function of a protein.
What is a non conservative mutation?
A non conservative mutation is when the amino acid coded for has different properties to the original, this is more likely to have an effect on protein structure, and may cause disease.
What is an amorph mutation?
A mutation that results in the loss of function of a protein.
What is the difference between a gene ad chromosome mutation?
Gene mutations occur in single genes or sections of DNA whereas chromosome mutations affect the whole chromosome or number of chromosomes within a cell.
What is the effect of a nonsense mutation?
Nonsense mutations result in a codon becoming a stop codon instead of coding for an amino acid.
The result is a shortened protien being synthesised which is normally non- functional.
These mutations normally have negative or harmful effects on phenotypes.
What is the impact of gene mutation?
Because gene mutations normally occur during meiosis, they usually lead to developmental difficulties.
Why do protein- based hormones carry out short lived responses?
Protein- based hormones (required for the growth and development of an organism or enzyme) are only required by certain cells at certain time to carry out a short- lived response.
Why does the expression of genes and the rate of synthesis of protein products like enzymes and hormones have to be regulated?
The entire genome of an organism is present in every prokaryotic cell, or eukaryotic cell that contains a nucleus.
This includes genes not required by that cell so the expression of genes and the rate of synthesis of products like enzymes and hormones has to be regulated.
How is the expression and rate of synthesis of protein products regulated?
genes can be turned on or off, and the rate of product synthesis increased or decreased depending on demand.
What are histones modified to do?
DNA coils around histones because they are positively charged and DNA is negatively charged.
Histones can be modified to increase or decrease the degree of packing (or condensation).
What are the 3 genes in the lac operon and what are they involved in?
The lac operon is a group of 3 genes, lacZ, lacY and lacA, involved in the metabolism of lactose.
What are the different ways in which genes are regulated?
Transcriptional- genes can be turned on or off
Post- transcriptional- mRNA can be modified which regulates translation and the types of proteins produced
Translational- translation can be stopped or started
Post translational- Proteins can be modified after synthesis which changes their function
What are the series of reactions that after the binding of the repressor protein called?
This is called down regulation.
What does acetylation or phosphorylation lead to?
The addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduce the positive charge on the histones (making them more negative) and this causes DNA to coil less tightly, allowing certain genes to be transcribed.
