Flashcards in Cellular Control Deck (59)
Define the term “mutation” (umbrella term).
A change in genetic material which may effect the phenotype of the organism.
Define the term “point mutation”.
Changes one base on the triplet codon. May or may not have damaging effects.
Define the term “substitution”.
A mutation where one or more nucleotides are substituted for another in the DNA strands.
Define the term “deletion”.
Mutations where one or more nucleotides are deleted and lost from the DNA strands.
Define the term “frame shift”.
The addition or deletion of a base in a sequence. Causes the whole sequence to shift out of place from the point of addition or deletion, so it is read out of sync. Most damaging.
Define the term “silent mutation”.
A mutation that occurs in the part of the gene that does not code for a protein (the introns). Therefore, it will not effect the phenotype.
Define the term “missense mutation”.
Missense mutatuions result in the incorporation of an incorrect amino acid into the primary structure when the protein is synthesised. Mutation could be silent, beneficial or harmful.
Define the term “nonsense mutation”.
Can result in codon becoming a stop codon instead of coding for an amino acid. The result is a shortened protein being synthesised which is normally non-functional.
These mutations tend to have negative/harmful effects on the phenotype.
Define the term “gene mutation”.
Change in the base sequence which codes for a polypeptide chain/ protein.
Define the term “chromosome mutation”.
Affect the whole chromosome or a number of chromosomes within a cell.
Explain why a change in the sequence of nucleotides of a gene can affect the function of the protein produced from that gene.
A change in the base sequence might change the amino acid that a codon codes for. This would disrupt protein synthesis and therefore the proteins expressed in the phenotype. Potentially very harmful effect i.e. if the active site of an enzyme was not synthesised properly.
Describe how a mutation can have a neutral effect, a harmful effect or a beneficial effect, and give an example of each.
1) Neutral - Normally function proteins are still synthesised. The mutation occurred in the a part of the gene that does not code for a protein.
2) Damaging - the phenotype of an organism is affected in a negative way because proteins are no longer synthesised or the proteins synthesised are non-functional. Can interfere with essential processes.
3) Beneficial - Very rare. A protein is synthesised that results in a new and useful characteristic in the phenotype. i.e. immunity to HIV.
State the 3 types of mutagen and give an example of each.
1) Chemical - deaminating agents - chemically alter bases in DNA.
2) Physical - ionizing radiations (x-ray) - can break one or both of the DNA strands.
3) Biological agents - alkylating agents - methyl or ethyl groups are attached to bases resulting in incorrect pairing of bases during replication.
- base analogs - incorporated into DNA in place of the usual base during replication, changing the base sequence.
- viruses - viral DNA may insert itself into a genome, changing the base sequence.
Name and describe the 4 types of chromosome mutation.
1) Deletion - a section of chromosome breaks off and is lost within the cell.
2) Duplication - sections get duplicated on a chromosome.
3) Translocation - a section of one chromosome breaks off and joins another non-homologous chromosome.
4) Inversion - a section of chromosome breaks off, is reversed and then joins back onto the chromosome.
Describe and explain the possible effects of a substitution mutation.
Would effect the amino acid that a codon codes for as a base in the triplet codon has been changed. This will effect the protein that is synthesised and possibly its functionality. Does not cause a frameshift.
Describe and explain the possible effects of insertion or deletion mutations.
Leads to a frameshift mutation. Every successive codon will be changed after the point of deletion/ insertion. The sequence is therefore read out of sync, the amino acid that each codon codes for being affected. Protein will be synthesised incorrectly.
Define the term “gene expression”.
Information from a gene is used in the synthesis of a functional gene product. Often proteins.
Define the term “epigenetics”.
The control of gene expression by modification of the DNA. -- External control of gene expression.
Name and describe the four levels at which genes (or proteins) are regulated.
1) Transcriptional - genes can be turned off and on.
2) Post-transcriptional - mRNA can be modified which regulates translation and the types of proteins produced.
3) Translational - translation can be stopped or started.
4) Post-translational - proteins can be modified after which changes their functions.
Define the term “chromatin”.
Un-condensed DNA in a complex with histones. Exists like this in nucleus before cell division.
Define the term “heterochromatin”.
Tightly packed DNA during cell division.
Define the term “euchromatin”.
Loosely packed DNA during interphase.
Describe how chromatin remodelling allows the expression of some genes but not others.
- The transcription of genes is not possible when DNA is tightly wound (heterochromatin) because RNA polymerase cannot access the genes. However, genes in loosely packed DNA (eurochromatin) can be freely transcribed.
- You don't want protein sysnthesis to take place during cell division, and it can't because heterochromatin is tightly wound. However, protein synthesis can take place at interphase because eurochromatin is loosely wound.
Simple form of regulation.
Describe how histone modification can affect gene expression.
- Histones can be modified to increase or decrease the degree of packing.
- The addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces the positive charge on histones (and because DNA is negatively charged) it makes DNA to coil less tightly, allowing certain genes to be transcribed.
- The addition of methyl groups (methylation) makes the histones more hydrophobic so they bind more tightly to each other. DNA coils more tightly and prevents transcription of genes.
Define the term “operon”.
A group of genes that are under the control of the same regulatory mechanism and are expressed at the time.
Draw and label a diagram to show the lac operon and its associated regulatory gene.
1) Regulatory gene - a gene that codes for repressor proteins.
2) CAP binding site -
3) Promoter - site of RNA polymerase binding. RNA polymerase will catalyse the formation of phosphodiester bonds between nucleotides.
4) Operator - repressor protein binding site. RNA polymerase will be blocked if a repressor protein binds here.
5) Structural genes - These are transcribed into mRNA and then translated into proteins. They code for the structural genes needed to metabolise lactose.
Define the term “structural gene”.
- Genes that code for structural proteins or enzymes not involved in DNA regulation.
Name the proteins produced from the structural genes in the lac operon.
- Lac Z, beta galactosidase, breaks down glucose.
- Lac Y, lactose permease, brings lactose into the cell.
- Lac A, transacetylase, unknown function.
Describe the roles of the regulatory gene, the structural genes, the operator region and the promotor region of the lac operon for the metabolism of lactose.
- The regulatory gene (lac I) codes for a repressor protein that prevents the transcription of structural genes.
- The structural genes code for three enzymes that involved in the metabolism of glucose. They are transcribed onto a single long molecule of mRNA but are translated into separate proteins.
- RNA polymerase binds the promoter, repressor proteins bind to operator.