OCR A Level Biology: Cellular Control
Examples of positive effects as a result of mutations
Ability to digest lactose, immunity to HIV, resistance to malaria
Examples of post-translational level regulatory mechanisms
Activation of proteins by cAMP
Biological agents
Alkylating agents, base analogs, viruses
How do alkylating agents lead to mutations?
Attachment of methyl or ethyl groups causes the incorrect pairing of bases in replication
General possible effects of gene mutations
Beneficial, neutral, harmful
How could cofactors play a role in gene regulation?
Bind to proteins that regulate transcription, change binding of proteins to control elements, change rate of transcription
How transcription factors work
Binds at a target sequence, makes it harder or easier for RNA polymerase to bind to the promoter of the gene
How does ionising radiation lead to mutations?
Break one or both DNA strands
Feature of genes that regulate the cell cycle and apoptosis
Can respond to internal and external cell stimuli
Role of beta galactosidase
Catalyses the hydrolysis of lactose to glucose and galactose
Role of lactose permease
Catalyses the transport of lactose into the cell
What can cause stress?
Changes to temperature, changes to light intensity, release of hormones, psychological stress
Mutation
Changes to the amount or arrangement of genetic material
Gene mutation
Changes to the sequence of bases
Nonsense mutations
Codon becomes a stop codon which shortens the protein
Stress
Condition produced when the homeostatic balance within an organism is upset
Types of missense mutation
Conservative, non-conservative
Examples of negative effects as a result of mutations
Cystic fibrosis, phenylketonuria, sickle cell anaemia
Chemical mutagens
Deaminating agents
Mutation responsible for cystic fibrosis
Deletion of one amino acid
Mutation responsible for immunity to HIV
Deletion which changes the receptor molecules' shape
Process of apoptosis
Enzymes break down the cell's cytoskeleton, cytoplasm becomes denser, blebs form, chromatin condenses, nuclear envelope breaks, DNA fragments, cell breaks into vesicles, vesicles taken up by phagocytosis, doesn't damage other cells
Type of mutation that insertion and deletion mutations cause
Frameshift mutations
Homeobox genes
Genes which contain the 180bp homeobox sequence, codes for the homeodomain on transcription factors which binds to DNA to switch genes on or off, control body plan
Feature of homeobox genes
Highly conserved and similar between plants and animals and fungi
Example of the activation of proteins by cAMP
In the lac operon the low glucose concentration increases concentrations of cAMP, cAMP binds to cAMP receptor protein, activates it, binds to the DNA, helps RNA polymerase bind
How do base analogs lead to mutations?
Incorporated into DNA during replication in place of the usual bases
Missense mutations
Incorporation of the wrong amino acids
How do viruses lead to mutations?
Insert viral DNA into a genome
RNA processing
Introns are removed, exons joined together, modified nucleotide cap put on 5' end, polyA tail on 3' end
Physical mutagens
Ionising radiation
Examples of transcriptional level regulatory mechanisms
Lac operon, transcription factors
How the lac operon works when glucose isn't present
Lactose binds to the repressor protein and changes its tertiary structure, can no longer bind to the operator region, RNA polymerase binds to the promoter region, transcription of lacZ and lacY, beta galactosidase and lactase permease are produced in translation
Importance of mitosis and apoptosis in controlling the development of body form
Mitosis increases the number of cells so growth occurs, apoptosis shapes the body by removing unwanted cells, cells doing apoptosis release chemical signals to trigger mitosis to remodel tissues
Hypermorph
Mutation that increases the functioning of a protein
Hypomorph
Mutation that reduces the functioning of a protein
Amorph
Mutation that results in a non-functioning protein
Non-conservative mutation
New amino acid has different properties to the original so has larger effects
Conservative mutation
New amino acid has similar properties to the original so the effect is less severe
RNA editing
Nucleotide sequence of mRNA can be changed from insertion, deletion and substitution mutations, different proteins with different functions synthesised
Where does RNA processing occur?
Nucleus
Role of Hox genes
Only present in animals, control the positioning of body parts, order in which the genes appear is the same as the order they are expressed in, found in gene clusters, control polarity of the body, regulate mitosis and apoptosis
Examples of post-transcriptional level regulatory mechanisms
RNA processing, RNA editing
Morphogenesis
Regulation of the pattern of anatomical development
How the lac operon works when glucose is present
Regulatory gene codes for repressor protein, repressor protein binds to operator region, RNA polymerase can't bind to the promoter region, transcription of lacZ and lacY can't occur, beta galactosidase and lactase permease aren't produced
Blebs
Small bits of cell surface membrane
Role of the cap and tail
Stabilise mRNA, delay degradation in the cytoplasm, cap aids binding of the mRNA to the ribosomes
Factors that affect the expression of regulatory genes
Stress, drugs
Mutation responsible for phenylketonuria
Substitution
Mutation responsible for sickle cell anaemia
Substitution
Mutation responsible for resistance to malaria
Substitution which causes heterozygosity for sickle cell anaemia
Types of gene mutation
Substitution, insertion, deletion
How do deaminating agents lead to mutations?
Switch between bases, switching between cytosine and uracil
Examples of drugs that affect the expression of regulatory genes
Thalidomide
Why are homeobox sequences so similar between plants, animals and fungi?
They're important genes so changes to them are lethal so can't be passed on
Types of regulatory mechanism that control gene expression
Transcriptional, post-transcriptional, post-translational
