OCR A Level Biology: Cellular Control

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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


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