Define mutation.
A change to the base (nucleotide) sequence of DNA.
What are the three types of gene mutations?
- SUBSTITUTION
- DELETION
- INSERTION
What is a substitution mutation?
When one or more bases are swapped for another, e.g. ATGCCT becomes ATTCCT
What is a deletion mutation?
When one or more bases are removed, e.g. ATGCCT becomes ATCT
What is a insertion mutation?
When one or more bases are added, e.g. ATGCCT becomes ATGACCT
How does a mutation cause a modification in a protein (3) ?
- The order of DNA bases in a gene determines the order of amino acids in a particular protein.
- If a mutation occurs in a gene, the primary structure of the protein it codes for could be altered.
- This may change the tertiary structure of the protein so it doesn’t work properly, e.g. active sites denatured.
Why can some mutations have a neutral effect on a protein’s function? Give 3 ways.
- Although the base in a triplet changes, the amino acid that the triplet codes for doesn’t change. Some amino acids coded for by more than one triplet. (e.g. TAT and TAC = tyrosine)
- The mutation produces a triplet that codes for a different amino acid, but the amino acid is CHEMICALLY SIMILAR to the original.
- The mutated triplet codes for an amino acid NOT INVOLVED with the protein’s function.
Give an example in which a mutation can have a beneficial effect?
e.g. some bacterial enzymes can be mutated so that it BREAKS DOWN a wide range of antibiotics, so causes bacteria to be resistant to these antibiotics and increases its chance of survival.
Give an example in which a mutation can have a harmful effect?
e.g. cystic fibrosis is caused by a deletion of three bases in the gene that codes for CFTR which means that it beaks down and leads to excess mucus production.
What are the three levels that gene expression can be regulated/controlled?
- TRANSCRIPTIONAL Level
- POST-TRANSCRIPTIONAL level
- POST-TRANSLATIONAL level
What is gene expression controlled by at the transcriptional level?
Transcription Factors
What are Transcription Factors?
Proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription.
What are Transcription Factors that increase the rate of transcription called? And vice versa?
Increases rate of transcription = ACTIVATORS
Decreases rate of transcription = REPRESSORS
How can the shape of a transcription factor that binds to DNA be altered?
What does this mean in terms of the how the synthesis of some proteins are controlled?
By binding of some molecules, e.g. some hormones and sugars
This means the amount of certain molecules in an environment or a cell can control the synthesis of some proteins by affecting transcription factor binding.
How do transcription factors perform in EUkaryotes?
They bind to specific DNA sites near the start of their TARGET genes - the genes they control the expression of.
How do transcription factors perform in PROkaryotes?
They bind to OPERONS
What are operons?
A section of DNA that contains a cluster of STRUCTURAL genes, as well as CONTROL elements,and sometimes a REGULATORY gene.
What is the role of structural genes in an operon?
Codes for USEFUL proteins, e.g. enzymes
What is the role of control elements in an operon?
Includes a PROMOTER ( DNA sequence located BEFORE the structural genes that RNA Polymerase binds to) and an OPERATOR (a DNA sequence that transcription factors bind to)
What is the role of the regulatory gene in an operon?
Codes for an ACTIVATOR or a REPRESSOR.
Describe how gene expression is regulated when lactose is NOT present in E. coli.
- the REGULATORY gene (LacI) produces the lac repressor which is a transcription factor that binds to the OPERATOR site when there’s NO lactose is present.
- This BLOCKS transcription because RNA Polymerase cannot bind to the PROMOTER site.
Describe how gene expression is regulated when lactose IS present in E.Coli.
- Lactose binds to the REPRESSOR, changing the repressor’s shape so that it can no longer bind to the OPERATOR site.
- RNA Polymerase can then begin transcription of the structural genes (i.e. LacZ,LacY,LacA which produces the lactose-digesting enzymes (e.g. lactose permease))
How is gene expression regulated at the POST-transcriptional level in eukaryotic DNA (4)?
- eukaryotic DNA caontain INTRONS which are sections that don’t code for amino acids. EXONS are sections which do code for amino acids.
- When mRNA is produced, both the introns and exons are copied. An mRNA strand that contain introns and exons are called ‘primary mRNA transcripts’ (pre-mRNA)
- Introns are then removed from pre-mRNA by SPLICING. Exons are joined which form MATURE mRNA strands. This all takes place in the nucleus via endonuclease enzymes.
- The mature mRNA then LEAVES the nucleus for translation.
How is gene expression regulated at the post-translational level? (3)
- Some proteins that need to be activated work by binding to cell membranes and trigger the production of cyclic AMP (cAMP).
- cAMP then activates proteins inside the cell by altering its tertiary structure.
- This can then produce an effect, e.g. active site changing to become more/less active.
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Module 5 Section 1 - Communication and Homeostasis0
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Module 5 Section 2 - Excretion0
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Module 5 Section 3 - Animal Responses0
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Module 5 Section 4 - Plant Responses0
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Module 5 Section 5 - Photosynthesis0
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Module 5 Section 6 - Respiration0
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Module 6 Section 1 - Cellular Control35
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Module 6 Section 2 - Patterns of Inheritance2
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Module 6 Section 3 - Evolution0
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Module 6 Section 4 - Manipulating Genomes0
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Module 6 Section 5 - Cloning and Biotechnology0
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Module 6 Section 6 - Ecosystems0
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Module 6 Section 7 - Populations and Sustainability0
