6.1.1 - Cellular Control (set A - Mutation + Gene Control) Flashcards
What is a mutation, how are they caused?
Change in the sequence of bases in DNA - can disrupt protein synthesis if mutation occurs within gene
- mutation caused by substitution, deletion or insertion of one or more nucleotides within a gene
What is a point mutation?
If only one nucleotide is affected its a point mutation
Outline the effect of deletion or insertion of a nucleotide on the reading frame of a sequence of bases?
Insertion or deletion of a nucleotide/nucleotides leads to a frameshift mutation or introduction of a stop codon
- triplet codes mean sequences of bases are transcribed consecutively in non-overlapping groups of 3 (reading frame of a sequence of bases) - addition or deletion of a nucleotide, shifts the reading frame of the sequence of bases - changes every successive codon from the point of mutation unless number of nucleotides changed is a multiple of 3 (full codon so no change on reading frame) - protein formed is affected due to new amino acid
Outline the effect of substitution on the sequence of bases?
substitution of single nucleotide changes the codon in which it codes (if new codon codes for a different amino acid it will lead to change in primary structure of protein)
- degenerate nature of code means it’s possible that new codon still codes for same amino acid - leading to no change in the protein synthesised
- can cause introduction of stop codon
Outline and explain the 3 types of effects of different mutations??
- no effect/neutral - no effect on phenotype of an organism - normally functioning proteins still synthesised
- damaging - phenotype of organisms is negatively affected - proteins no longer synthesised or synthesised and are non-functional
- beneficial - rarely a mutation can occur resulting in a protein being synthesised with useful characteristics in the phenotype (eg immunity to HIV)
Outline the causes of mutations?
- mutations can occur spontaneously, often during DNA replication but the rate of mutation is increased by mutagens
Mutagen - chemical, physical or biological agent which causes mutations
Outline and provide examples of physical, chemical and biological mutagens?
Physical - ionising radiation (X-ray) - breaks DNA strands which can result in mutations during repair
Chemical - deaminating agents - chemically alter DNA bases eg cytosine to uracil changing base sequence
Biological (viruses ext) - viral DNA may insert itself into genome changing base sequence
Give the 3 types of mutations?
- Insertion
- deletion
- substitution
Outline the 4 stages at which gene expression can be regulated/controlled and the function of each?
- transcriptional control - genes can be turned on or off
- post-transcriptional control - mRNA can be modified which regulates translation
- translation control - translation can be stopped or started
- post-translational control - proteins can be modified after synthesis
Explain the need for gene regulation?
Entire genome of organisms present in every eukaryotic cell (containing a nucleus) includes genes not required by the cell so expression of genes and rate of protein synthesis has to be regulated - genes can be turned on or off and the rate of potential synthesis increased or decreased
- housekeeping genes are those that code for proteins constantly required (eg enzymes for respiration ext)
With focus on chromatin remodelling explain how it affects and regulates the transcription of genes?
DNA is wound around proteins (histones) - heterochromatin is tight wound DNA causing chromosomes to be visible during cell division - transcription of genes is not possible as RNA polymerase cannot access genes
- euchromatin is loosely wound DNA present during interphase - genes can be freely transcribed
simple form of regulation - ensures protein necessary for cell division are synthesised in time and not synthesised during energy-consuming process like when cells dividing
With focus on chromatin remodelling - specificaly histone modification explain how it affects and regulates the transcription of genes?
DNA coils around histones because they are + charged, DNA - charged - histones can be modified to increase or decrease degree of packing
Addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces + charge on histones which causes DNA to coil less tightly allowing certain genes to be transcribed
- addition of methyl groups (methylation) makes histones more hydrophobic so DNA coils more tightly preventing transcription of genes
Outline and explain the groups involved in chromatin remodelling - specificaly histone modification as a mechanism for regulating transcription of genes?
- Addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces + charge on histones which causes DNA to coil less tightly - allowing certain genes to be transcribed
- addition of methyl groups (methylation) makes histones more hydrophobic so DNA coils more tightly preventing transcription of genes
With focus on lac operon explain how it affects and regulates the transcription of genes?
Operon - group of genes under control of same regulatory mechanism/promoter and expressed at the same time (more common in prokaryotes)
- lac operon found in bacteria (E.coli) controls the production of enzymes β- galactosidase, lactose permease and transacetylase
Outline transcription factors in eukaryotes regarding transcriptional control?
proteins which bind to specific DNA sequences at ‘promoter’ regions - correct complex of transcription factors required for transcription to begin
- by increasing or decreasing production of specific transcription factors - we can control transcription of other genes
RNA polymerase not considered to be a transcription factor
Outline and explain the function of parts of lac operon - focus on Operator, Promoter and repressor molecule?
Operator - repressor protein binds here, prevents RNA polymerase binding to DNA (controls switching on and off of genes as RNA polymerase can not bind)
Promoter - section of DNA which is the binding site for RNA polymerase
Repressor molecule - binds to operator, preventing transcription as it partially blocks binding of RNA polymerase (coded for by a regulatory gene) in absence of lactose
Outline 3 mechanisms involved in controlling the transcription of genes at transcriptional level?
- transcription factors
- chromatin remodelling (with focus on histone modification)
- lac operon
Explain RNA processing at a post-transcriptional level?
- product of transcription is pre-mRNA which is modified forming mature mRNA before it can bind to a ribosome and code for proteins
- a cap (modified nucleotide - aids in binding to ribosome) and a tail (long chain of adenine nucleotides) are added to mRNA which help stabilise and protect mRNA - delaying degradation in cytoplasm
splicing occurs - RNA cut a specific points
Explain the process splicing which occurs at a post-transcriptional level?
RNA is cut at specific points - the introns (non-coding DNA) are removed and the exons (coding DNA) are joined together
- both proceeds occur in nucleus
Explain RNA editing at a post-transcriptional level?
Nucleotide sequence of some mRNA molecules can be changed through intentional base addition, deletion or substitution
- same effect as point mutation - result in synthesis of different proteins which may have different function - increases range of proteins produced from single mRNA molecule
Outline and explain fully how the rate of protein synthesis is regulated at a translational level - give the 3 ways?
- degradation of mRNA - more resistant the molecule is, longer it lasts in cytoplasms (addition of a cap and tail to mRNA delays degradation)
- binding of inhibitory proteins to mRNA - prevents mRNA binding to ribosomes and thus inhabiting proteins synthesis
- activation of initiation factors aiding in binding to ribosome - for example eggs of organisms produce large quantities of mRNA which is not required until fertilisation at which point initiation factors are activated
Explain the function of the enzymes protein kinases?
Catalyse addition of phosphate groups to proteins (phosphorylation) - which change tertiary structure and thus function of protein
- important regulators for cell activity - often activated by secondary messenger cAMP
Outline 2 mechanisms involved in controlling the product of transcription at a post-transcriptional level?
- RNA splicing
- RNA editing
Outline and explain fully how the products of protein synthesis are regulated and modified at a post-translational level - give the 4 ways?
- addition of non-protein groups - eg carbohydrate chains, lipids or phosphates
- modifying amino acids and formation of bonds (disulfide bridges
- folding or shortening of proteins
- modification by cAMP - example is lac operon cAMP which binds to cAMP receptor proteins increasing rate of transcription of structural genes
Give the 2 proteins coded by the lac operon?
- beta-galactosidase - breaks downs lactose in 2 simple sugars (glucose and galactose)
- permease - membrane bound protein - which provides route for lactose outside of cel into cell
Explain fully lac operon as an example of transcriptional control?
Group of 3 genes (beta galactosidase and lactose permease and transacetylase) which are transcribed on molecule of mRNA
- regulatory gene lacI located near operon and codes for a repressor protein (prevents transcription of structural genes in absence of lactose)
- repressor protein binds to area called operator - which prevents RNA polymerase binding to DNA and transcription (known as down regulation)
- promoter - section of DNA that is binding site for RNA polymerase
- when lactose is present - it binds to repressor protein causing it to change shape (no longer bind to operator) RNA polymerase can bind to promoter allowing transcription
Define morphogenesis?
Regulation of the pattern of anatomical development
- controlled by specific group of regulatory genes (homebox genes) which can switch genes on and off which allows control of development of the body plan
Explain briefly what homeobox genes are?
Ancient, highly conserved regions of DNA in animals, plants and fungi
- code for homeodomains - protein segments that act as transcription factors
Explain what can be implied through the fact homeobox genes have rarely changed?
Their activity is absolutely fundamental to the development of a body that actually works - any mutation would be fatal and therefore would not be passed on through evolution
Explain what hox genes are, and the role they play?
Specific group of homeobox genes only found in animials
- highly consvered across great evolutionary distances
Explain what body plans are?
Usually represented as cross-sections through the organism
- common feature of animals is that they are segmented - these segments have multiplied and overtime specialised to perform different functions
Define apoptosis?
Programmed cell death essential for shaping organisms
Outline the factors affecting the expression of regulatory genes?
- expression of regulatory genes can be influenced by the environment both internal and external
Outline briefly the stages of apoptosis?
1) cell shrinkage + DAN fragmentation
2) membrane blabbing
3) results in apoptotic bodies
4) phagocytosis of apoptotic bodies
State what is meant by a homeobox gene?
Group of regulatory genes (switch genes on and off) which all contain a homeobox, a section of DNA 180 base pairs long which code for 60 amino acids
