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Year 13 Biology A Level > Cellular Control > Flashcards

Cellular Control Flashcards

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1
Q

Define gene

A
  • A section of DNA which codes for a particular polypeptide
  • Heritable factor
  • Occupies a specific position on a chromosome
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2
Q

How is differentiation of cells brought about?

A
  • Expression of some genes in the genome
  • Other genes are switched off
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3
Q

Define allele

A
  • Various specific forms of a gene
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4
Q

What distinguishes an allele from a gene?

A

An allele is a variety of a gene

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5
Q

How are new alleles formed?

A

By mutation

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6
Q

How many chromosomes are found in human body cells (not including gametes)?

A

23 pairs i.e. 46 chromosomes

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7
Q

Define mutation

A

Random and spontaneous change in the base sequence of a gene

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8
Q

Identify different types of gene mutation

A
  • Base substitution
  • Insertion (causes frameshift)
  • Deletion (causes frameshift)
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9
Q

Define frameshift

A
  • A frameshift mutation is a genetic mutation caused by a deletion or insertion in a DNA sequence that shifts the way the sequence is read.
  • Changes every successive codon from point of mutation
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10
Q

Explain why base substitutions don’t always result in a change in amino acid sequence

A
  • Genetic code is degenerate
  • Multiple codons code for same amino acid
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11
Q

Explain why a change in amino acid sequence can alter protein function

A
  • Each amino acid has different R group
  • R groups interact to determine tertiary structure of protein
  • Different interactions can change protein shape
  • Affects protein function
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12
Q

Describe the different possible effects of mutations

A

No effect
- No change to the phenotype of organism
- Functioning proteins still synthesised

Damaging
- Phenotype altered in negative way
- Functioning proteins no longer synthesised
- Can interfere with essential processes

Beneficial
- Protein synthesised results in new, useful characteristics
- Very rare occurrence
- e.g. mutation in proteins on CD40 cell surface membrane prevents HIV entry

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13
Q

What can cause mutations to occur?

A

Spontaneous mutation
- During DNA replication

Physical mutagens
- Break DNA strands
- e.g. ionising radiation

Chemical mutagens
- Chemically alter DNA bases
- e.g. deaminating agents

Biological agents
- Alter DNA sequence
- e.g. viral DNA inserted into genome

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14
Q

Define chromosome mutation

A
  • Mutations that affect entire chromosome
  • Not just one gene
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15
Q

Describe the different types of chromosome mutation

A

Deletion
- Section of chromosome breaks off and is lost

Duplication
- Section of chromosome duplicated

Translocation
- Section of one chromosome breaks off and joins another non-homologous chromosome

Inversion
- Section of chromosome breaks off and is reversed

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16
Q

Define gene expression

A

Gene expression is the translation and transcription of genetic information. It determines which genes are translated and transcribed and how many.

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17
Q

Outline the various ways that genes are regulated

A

Transcriptional
- Genes can be turned on or off

Post-transcriptional
- mRNA modified to regulate translation

Translational
- Translation can be stopped or started

Post-translational
- Proteins modified after synthesis to change function

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18
Q

Define heterochromatin

A
  • DNA tightly wound around histones
  • Chromosomes become visible under light microscope
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19
Q

Define euchromatin

A
  • DNA loosely wound around histones
  • Present during interphase
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20
Q

Why is transcription of heterochromatin not possible?

A

RNA polymerase cannot access genes

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21
Q

Explain why coiling of DNA around histones occurs

A
  • DNA is negatively charged
  • Histones are positively charged
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22
Q

Describe histone acetylation

A
  • Addition of acetyl group to histone
  • Acetyl groups decrease positive charge of histone
  • DNA coils less tightly
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23
Q

Describe the effects of increased histone acetylation

A
  • Histones are positively charged proteins, DNA is negatively charged
  • Increased acetylation of histones decreases their positive charge, so bind DNA less tightly
  • Transcription factors can access DNA
  • Gene is switched on
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24
Q

Describe the effects of decreased histone acetylation

A
  • Histones are positively charged proteins, DNA is negatively charged
  • Decreased acetylation of histones increases their positive charge, so bind DNA more tightly
  • Transcription factors can no longer access DNA
  • Gene is switched off
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25
Q

Describe histone methylation

A
  • Methyl (CH₃) group added to histone
  • Makes histone more hydrophobic
  • Binds to DNA more tightly
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26
Q

How does histone methylation decrease gene expression?

A
  • Methylation is addition of a CH₃ group to histone
  • Makes histone more hydrophobic
  • Binds to DNA more tightly
  • Prevents binding of transcription factors to DNA
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27
Q

Define epigenetics

A
  • Study of changes in organisms caused by modification of gene expression rather than
    alteration of the genetic code itself
  • Environmental factors can make changes to function of genes which can be inherited
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28
Q

How is gene transcription regulated at a DNA level?

A

By proteins that bind to specific base sequences in DNA

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29
Q

Define promoter

A
  • Non-coding DNA with a function
  • Binding site for RNA polymerase
  • Controls gene expression
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30
Q

Explain how promoters control gene expression

A
  • Every gene has a promoter immediately upstream of the coding sequence
  • Base sequences vary
  • Enables some genes to be transcribed, whilst others are not
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31
Q

Define operator

A
  • Non-coding sequence in prokaryotes
  • Binding site for repressor proteins and transcription factors
32
Q

Define regulatory genes

A

Genes that make regulatory proteins

33
Q

What are regulatory proteins?

A
  • Proteins that bind to DNA sequences outside of promoter region
  • e.g. transcription factors, repressor proteins
34
Q

Define operon

A
  • Group of genes that are under the control of the same regulatory mechanism
  • Expressed at the same time
35
Q

In which type of organisms are operons most common?

A

Prokaryotes

36
Q

What is the advantage of a prokaryotic genome containing operons?

A
  • Efficient
  • If certain gene products not required, all of the genes involved can be switched off
37
Q

What is the role of the lac operon?

A
  • Group of genes in E. Coli
  • Code for proteins that can metabolise lactose
  • Switched on when glucose is not present
38
Q

Define structural genes

A
  • Genes that code for any protein product other than a regulatory factor
  • e.g. enzymes, channel protein
39
Q

Name the structural genes in the lac operon

A
  • lacZ
  • lacY
  • lacA
40
Q

Name the regulatory gene located near the lac operon

A

lacI

41
Q

What does lacI code for?

A
  • Repressor protein
  • Prevents transcription of the lac operon
42
Q

Explain how expression of the lac operon is inhibited

A
  • Repressor protein constantly produced
  • Binds to operator gene (lacO)
  • Prevents RNA polymerase binding to promoter region
43
Q

Explain the changes that occur when lactose is present

A
  • Lactose binds to repressor protein
  • Protein changes shape
  • Can no longer bind to operator
  • RNA polymerase binds to promotor
  • Structural genes transcribed
  • Enzymes synthesised
44
Q

What type of gene regulation is the control of the lac operon?

A

Transcriptional

45
Q

Explain the role of cAMP in the regulation of the lac operon

A
  • cAMP binds to CRP (cAMP receptor protein)
  • Increases rate of transcription of lac operon
46
Q

Explain how an increase in glucose reduces transcription rate of the lac operon

A
  • Glucose decreases level of cAMP
  • Reduces level of active CRP
  • Reduces transcription of lac operon
  • If glucose present, it will be the preferred respiratory substrate
47
Q

Describe the post-transcriptional control of gene expression

A

RNA processing
- Pre-mRNA spliced to remove introns
- Cap added to 5’ end
- Tail added to 3’ end

RNA editing
- Change in nucleotide sequence in mRNA
- Results in synthesis of different proteins
- Increases range of proteins that can be produced from a single gene

48
Q

What is the role of the cap and tail in RNA processing?

A
  • Stabilises mRNA
  • Delay degradation in the cytoplasm
49
Q

Outline the translational control of protein synthesis

A

Degradation of mRNA
- More resistant molecules last longer in cytoplasm
- So greater quantity of protein synthesised

Binding of inhibitory proteins to mRNA
- Prevents binding of mRNA to ribosomes
- Prevents protein synthesis

Activation of initiation factors
- Promote binding of mRNA to ribosomes
- Increases translation rate

50
Q

Explain the role of protein kinases in translational control of protein synthesis

A
  • Enzymes that catalyse addition of phosphate groups to proteins
  • Changes tertiary structure
  • Alters function or activates protein
  • Protein kinases activated by cAMP
51
Q

Outline the post-translational control of gene expression

A
  • Addition of non-protein groups to proteins
  • e.g. carbohydrate chains, lipids
  • Modifying amino acids and formation of intermolecular bonds
  • Folding or shortening proteins
  • Modification by cAMP
  • e.g. increasing rate of transcription of lac operon
52
Q

Define morphogenesis

A

Regulation of the pattern of anatomical development

53
Q

Define homeobox genes

A
  • Regulatory genes
  • All contain 180 base pair (bp) homeobox sequence
54
Q

What type of protein do homeobox genes code for?

A

Regulatory protein

55
Q

Which part of the protein does the homeobox sequence code for?

A

Homeodomain
- Section of protein that binds to DNA

56
Q

What is the role of the homeodomain?

A
  • Switches genes on or off
  • Controls development of body plan
57
Q

Define body plan

A

Position and development of body parts

58
Q

Which organisms are homeobox genes found in?

A
  • Plants
  • Animals
  • Fungi
59
Q

Explain why homeobox genes are highly conserved across a wide range of organisms

A
  • Genes are very important
  • Mutation would alter body plan
  • Many other genes would be affected
  • Mutation likely to be lethal
  • Would be selected against
60
Q

Define Hox genes

A
  • Group of homeobox genes only present in animals
  • Found in gene clusters on different chromosomes
61
Q

What is the role of Hox genes?

A
  • Control correct positioning of body parts
  • Order in which genes appear along chromosome is order which their effects are expressed
62
Q

Define diploblastic animals

A

Animals with two primary tissue layers

63
Q

Define triploblastic animals

A

Animals with three primary tissue layers

64
Q

Define radial symmetry

A
  • No left or right side
  • Only top and bottom
  • Typical in diploblastic animals
  • e.g. jellyfish
65
Q

Define bilateral symmetry

A

Organism have both left and right side and head and tail end
- e.g. humans

66
Q

Define asymmetry

A

No lines of symmetry
- e.g. sponges

67
Q

Outline the role of mitosis in development

A
  • Increases number of cells
  • Leads to growth
68
Q

Define apoptosis

A

Programmed cell death

69
Q

Outline the role of apoptosis in development

A
  • Removes unwanted cells and tissues
  • Reveals shape of body part
70
Q

Outline the role of cell signalling in the shaping of organisms

A
  • Cells undergoing apoptosis release chemicals
  • Stimulate mitosis and cell proliferation
  • Leads to remodelling of tissues
71
Q

Which genes regulate mitosis and apoptosis?

A

Hox genes

72
Q

Define stress

A

Condition produced when homeostatic balance within an organism is upset

73
Q

Give examples of external factors that can cause stress

A
  • Change in temperature
  • Light intensity
74
Q

Give examples of internal factors that can cause stress

A
  • Hormones
  • Psychological stress
75
Q

Why can stress affect growth and development of animals?

A

Influences expression of Hox genes

Year 13 Biology A Level (14 decks)

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