Chapter 19: Genetics of Living Systems Flashcards
Define point mutation.
- When only one nucleotide is affected.
Define frameshift mutation.
- Shift in reading frame of sequence of bases.
- Change in every successive codon from point of mutation.
Outline substitution mutations.
- Change in codon in which mutation occurs.
- Different base substituted into codon.
- Degenerate code –> new codon can still code for the same amino acid.
- Different amino acid coded for –> change in primary structure of protein.
Outline Insertion + Deletion mutations.
- Frameshift mutation.
- Different base inserted or deleted into base sequence.
What is a silent mutation?
- No change in protein or activity of proteins synthesised.
- No effect on phenotype.
- Usually in non-coding regions or DNA or code for same amino acid –> due to degenerate code.
What is a nonsense mutation?
- Codon becomes stop codon instead of amino acid.
- Shorter protein synthesised.
- Non-functional protein with negative effect on phenotype.
What is a missense mutation?
- Incorrect amino acid incorporated into primary structure.
- Could be conservative or non-conservative.
- Conservative = amino acid change leads to similar amino acid being coded for –> less harmful.
- Non-conservative = amino acid has different properties + more likely to have effect on proteins –> more harmful.
Features of transcriptional control
Chromatin Remodelling:
- Heterochromatin –> tightly wound DNA –> causes chromosomes to become visible in prophase.
- Euchromatin –> loosely wound DNA in interphase –> freely transcribed,
- Tightly wound DNA –> RNA polymerase cannot bind to promoter region + access genes –> transcription blocked.
Histone modification:
- Histones –> positively charged + wrapped around DNA which is negatively charge.
- Acetylation/phosphorylation = reduce positive charge on histones –> DNA coils less tightly –> certain genes transcribed.
- Methylation = makes histones more hydrophobic –> bind more tightly to each other –> DNA coils more tightly –> transcription of genes blocked.
Transcription Factors:
- Protein that moves in from cytoplasm and bind to DNA in order to switch genes on/off by increasing/decreasing rate of transcription.
- Activators = start transcription.
- Repressors = stop transcription.
cAMP:
- Secondary messenger that activates proteins by binding of CRP to cAMP –> up regulates transcription.
How does the lac operon work when lactose is present? (transcriptional control)
- Enzyme coded for by lac operon allows lactose to enter bacteria.
- Lactose binds to repressor protein.
- Repressor protein changes shape.
- Transcription unblocked –> RNA polymerase binds to promoter region.
- Enzymes needed to metabolise lactose produced.
Difference between operator + promoter?
- Operator = section of DNA to which repressor protein/transcription factor binds.
- Promoter = section of DNA to which RNA polymerase binds in order to initiate transcription.
Distinguish between structural genes and regulatory genes.
- Structural genes = transcribed onto mRNA + code for proteins/enzymes needed for structure or function.
- Regulatory genes = turn genes on/off; not transcribed; determine which structural genes are expressed; starts/stops transcription.
Outline features of post-transcriptional control.
RNA Processing:
- Pre-mRNA –> modified to form mature mRNA before it binds to ribosomes for protein synthesis.
- Splicing takes place –> introns removed + exons joined together in nucleus.
- Cap added at 5’ end –> aid binding of mRNA to ribosome.
- Tail added to 3’ end.
- Stabilise mRNA + delay degradation in the cytoplasm.
RNA Editing:
- Insertion, deletion, substitution of bases occurs –> change in sequence of mRNA nucleotides.
- Similar to point mutations –> different proteins with different functions synthesised.
- Increases range of proteins that can be synthesised from a single mRNA molecule.
Outline features of translational control.
- Degradation of mRNA in cytoplasm = the more resistant the mRNA molecule the longer it spends in the cytoplasm + the more proteins are synthesised.
- Inhibitory proteins = bind to mRNA to prevent translation.
- Initiation factors = aid binding of mRNA to ribosomes.
Protein Kinases:
- Catalyse phosphorylation of protein to activate proteins.
- Changes tertiary structure of protein + function.
Outline features of post-translational control.
- Modification to proteins after protein synthesis/
- Addition of non-protein groups –> carbohydrates, lipids, phosphates.
- Modification of amino acids + formation of bonds –> disulphide bonds.
- Folding or shortening of protein/polypeptide chains.
- Binding of cAMP to CRP –> in lac operon –> increasing transcription of structural genes.
How does lac operon work when no lactose is present?
- Regulatory gene, Lac I –> codes for repressor protein.
- Repressor binds to operator.
- Prevents binding of RNA polymerase to promoter.
- Prevents transcription of proteins that hydrolyse lactose.
Outline difference between post-transcriptional + post-translational control of gene expression.
Post-transcriptional:
- Affects size/shape/sequence of mRNA.
- Involves editing of primary pre-mRNA –> removal of introns to form mature mRNA.
Post-translational:
- Affects conformation of proteins.
- Involves activation of proteins by cAMP.
State what is meant by a homeobox gene.
- Regulatory gene.
- Homeobox sequence (180 base pairs).
- Code for a homeodomain on a protein.
- Gene products bind to DNA.
- Initiates transcription/switch genes on or off.
- Control development/body plans.
Why is there very little change by mutation in homeobox genes?
- These genes are very important.
- Mutation would have big effects/alter body plan.
- Many genes affected/knock-on effects.
- Mutation most likely lethal/selected against.
Outline the process of apoptosis (programmed cell death regulated by hox genes).
- Enzymes break down cytoskeleton.
- Cytoplasm becomes dense + organelles more tightly packed.
- Cell surface membrane changes –> blebs form.
- Chromatin condenses –> nuclear envelope breaks down DNA into fragments.
- Cell breaks into vesicles taken up by phagocytes which remove the cellular debris.
Evaluate the validity of:
All hox genes are homeobox genes, but not all homeobox genes are hox genes as hox genes are only found in animals.
- Hox genes are one form of homeobox gene.
- Hox genes present in vertebrates in hox clusters.
- Other forms of homeobox genes present in other clusters.
- Hox genes only found in animals but homeobox genes are found in animals, fungi and plants.
- THEREFORE THE STATEMENT IS VALID.
Describe + explain the difference between the functions of RNA polymerase + DNA polymerase.
RNA Polymerase:
- Transcription –> one DNA strand acts as the template for the formation of a new DNA strand.
- Production of mRNA in nucleus.
- Binds to promoter region to initiate transcription.
DNA Polymerase:
- DNA replication.
- Semi-conservative.
- Joins sugar-phosphate backbone before cell division.
Discuss possible effects mutation can have on the structure and function of a protein.
- Different primary/tertiary/secondary structure.
- Protein shorter due to deletion/stop codon or longer due to insertion/duplication.
- Protein unchanged due to silent mutation.
- Function lost/worse/better.
