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Biology Paper 2 > Cellular Control > Flashcards

Cellular Control Flashcards

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
Describe histone methylation
- Methyl (CH₃) group added to histone - Makes histone more hydrophobic - Binds to DNA more tightly
26
How does histone methylation decrease gene expression?
- 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
27
Define epigenetics
- 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
28
How is gene transcription regulated at a DNA level?
By proteins that bind to specific base sequences in DNA
29
Define promoter
- Non-coding DNA with a function - **Binding site for RNA polymerase** - Controls gene expression
30
Explain how promoters control gene expression
- Every gene has a promoter immediately upstream of the coding sequence - Base sequences vary - Enables some genes to be transcribed, whilst others are not
31
Define operator
- Non-coding sequence in prokaryotes - **Binding site for repressor proteins and transcription factors**
32
Define regulatory genes
Genes that make regulatory proteins
33
What are regulatory proteins?
- Proteins that bind to DNA sequences outside of promoter region - e.g. transcription factors, repressor proteins
34
Define operon
- Group of genes that are under the control of the same regulatory mechanism - **Expressed at the same time**
35
In which type of organisms are operons most common?
Prokaryotes
36
What is the advantage of a prokaryotic genome containing operons?
- **Efficient** - If certain gene products not required, all of the genes involved can be switched off
37
What is the role of the lac operon?
- Group of genes in E. Coli - Code for **proteins that can metabolise lactose** - Switched on when glucose is not present
38
Define structural genes
- Genes that code for any protein product other than a regulatory factor - e.g. enzymes, channel protein
39
Name the structural genes in the lac operon
- lacZ - lacY - lacA
40
Name the regulatory gene located near the lac operon
lacI
41
What does lacI code for?
- Repressor protein - Prevents transcription of the lac operon
42
Explain how expression of the lac operon is inhibited
- Repressor protein constantly produced - Binds to operator gene (lacO) - **Prevents RNA polymerase binding** to promoter region
43
Explain the changes that occur when lactose is present
- 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
What type of gene regulation is the control of the lac operon?
Transcriptional
45
Explain the role of cAMP in the regulation of the lac operon
- cAMP binds to CRP (cAMP receptor protein) - Increases rate of transcription of lac operon
46
Explain how an increase in glucose reduces transcription rate of the lac operon
- 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
Describe the post-transcriptional control of gene expression
**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
What is the role of the cap and tail in RNA processing?
- Stabilises mRNA - Delay degradation in the cytoplasm
49
Outline the translational control of protein synthesis
**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
Explain the role of protein kinases in translational control of protein synthesis
Enzymes that catalyse addition of phosphate groups to proteins - Changes tertiary structure - Alters function or activates protein Protein kinases activated by cAMP
51
Outline the post-translational control of gene expression
- 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
Define morphogenesis
Regulation of the pattern of anatomical development
53
Define homeobox genes
- Regulatory genes - All contain 180 base pair (bp) homeobox sequence
54
What type of protein do homeobox genes code for?
Regulatory protein
55
Which part of the protein does the homeobox sequence code for?
Homeodomain - Section of protein that binds to DNA
56
What is the role of the homeodomain?
- Switches genes on or off - Controls development of body plan
57
Define body plan
Position and development of body parts
58
Which organisms are homeobox genes found in?
- Plants - Animals - Fungi
59
Explain why homeobox genes are highly conserved across a wide range of organisms
- 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
Define Hox genes
- Group of homeobox genes only present in animals - Found in gene clusters on different chromosomes
61
What is the role of Hox genes?
- Control correct positioning of body parts - Order in which genes appear along chromosome is order which their effects are expressed
62
Define diploblastic animals
Animals with two primary tissue layers
63
Define triploblastic animals
Animals with three primary tissue layers
64
Define radial symmetry
- No left or right side - Only top and bottom - Typical in diploblastic animals - e.g. jellyfish
65
Define bilateral symmetry
Organism have both left and right side and head and tail end - e.g. humans
66
Define asymmetry
No lines of symmetry - e.g. sponges
67
Outline the role of mitosis in development
- Increases number of cells - Leads to growth
68
Define apoptosis
Programmed cell death
69
Outline the role of apoptosis in development
- Removes unwanted cells and tissues - Reveals shape of body part
70
Outline the role of cell signalling in the shaping of organisms
Cells undergoing apoptosis release chemicals - Stimulate mitosis and cell proliferation - Leads to remodelling of tissues
71
Which genes regulate mitosis and apoptosis?
Hox genes
72
Define stress
Condition produced when homeostatic balance within an organism is upset
73
Give examples of external factors that can cause stress
- Change in temperature - Light intensity
74
Give examples of internal factors that can cause stress
- Hormones - Psychological stress
75
Why can stress affect growth and development of animals?
Influences expression of Hox genes

Biology Paper 2 (13 decks)

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