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H2 Biology > Bacteria > Flashcards

Bacteria Flashcards

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1
Q

Describe the structure of a typical bacteria [3]

A

o70S ribosome (as with prokaryotes)
o NO membrane bound organelles/regions
o Plasmid- Small, Circular Extrachromosomal DNA
- May contain genes that confer advantages
e.g Antibiotics resistance

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2
Q

Define Binary Fission

A

Asexual Reproduction that produces genetically identical cells

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3
Q

Why is binary fission beneficial?

A

Selective advantage in stable, favourable environment where it can rapidly replicate & colonise

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4
Q

Describe the process of binary fission [6] (consider the reason for each step)

A
  1. DNA rep. begins at Ori → DNA unzipped by breaking H bonds btwn
    complementary bases to form replication bubble
  2. Semi-conservative replication of DNA as each original strand serves as template for
    synthesis of daughter strands by complementary base pairing
  3. The 2 newly formed Ori moves to opposite poles of cells & attach to plasma membrane
  4. As DNA is circular with no free ends, an interlocking structure formed by 2
    daughter DNA molecule formed when rep. is completed
  5. Topoisomerase cuts, separate & reseal the 2 DNA molecules
  6. Plasma membrane invaginates & new cell wall divides parent cell into 2
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5
Q

Point of comparisons between Binary Fission & Mitosis [5]

A
  1. End products
  2. Amt of DNA formed
  3. When does rep. occur?
  4. Process description (Chr Behaviour)
  5. Spindle Fibre involved?
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6
Q

Define Transformation

A
  1. Uptake of naked,
    foreign DNA from
    surrounding
    environment →
  2. genotype ∆, hence
  3. phenotype ∆
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7
Q

Define Transduction

A
  1. Process of which bacterial DNA from 1 host cell is
  2. introduced into another by a bacteriophage due to
    aberrations in phage reproductive cycle
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8
Q

When does generalised/specialised transduction happen?

A

Specialised: Temperate phage infection…

Generalised: ANY phage

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9
Q

What is a temperate phage in the syllabus?

A

Lambda phage

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10
Q

Describe how does Transformation occur? [4]

A
  1. Foreign DNA
    fragments from
    dead lysed
    bacterial cells
    enter bacterium
  2. Naturally
    competent
    bacteria1 have
    cell-surface
    proteins that
    binds &
    transport DNA
    into cell
  3. Foreign DNA
    incorporated into
    bacterial chr via
    Homologous
    Recombination,
    forming a (con’t)
  4. recombinant bacteria able to express new alleles → permanent ∆ in gen/phenotype
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11
Q

Describe how does generalised tranduction happen?

A
  1. Phage infects
    bacterium, injecting
    its viral genome
    DNA into host cell
  2. Phage enzymes
    degrade bacterial
    DNA into small
    fragments. A small
    fragment of
    degraded host cell
    DNA is randomly
    packaged into
    capsid during
    assembly of phage
    genome
  3. Upon host cell lysis,
    defective phage
    released can infect
    another bacterium,
    injecting previous
    host’s bacterial
    DNA into new host
  4. Foreign bacterial
    DNA can replace
    homologous region
    of new host’s chr as
    homologous
    recombination
    occurs
  5. Recombinant bacteria able to express new alleles → permanent ∆ in gen/phenotype
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12
Q

Describe how does SPECIALISED transduction happen? [6]

A
  1. Temperate phage (lambda)
    infects bacterium,
    injecting its viral
    genome into host
    cell & viral DNA is
    integrated into
    bacterial chr,
    forming prophage
  2. Upon induction,
    Viral DNA may be
    improperly
    excised to include
    adjacent bacterial
    DNA*
  3. Phage-Bacterium
    hybrid DNA may be
    packaged in capsid
    during assembly of
    phage
  4. Upon host cell lysis,
    defective phage
    infect another
    bacterium
  5. New alleles from
    previous host can
    replace
    homologous region
    of new host cell via
    homologous
    recombination (or
    integrase
    incorporate)
  6. Recombinant bacteria able to express new alleles → permanent ∆ in gen/phenotype
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13
Q

Define conjugation [2]

A
  1. Direct transfer of genetic material from
  2. 1 F+
    donor bacteria cell to another through
    mating bridge to another F-recipient
    bacterium
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14
Q

Describe how does conjugation happen? [5]

A
  1. Sex pilus of F+ bacterium makes
    direct contact with F- cell & retracts
    to bring the 2 cells closer
  2. Hollow pilus act as cytoplasmic
    mating bridge btwn 2 cells
  3. 1 of the 2 strands of plasmid DNA is
    nicked & transferred from F+ to F- cell via mating bridge via Rolling
    Circle Replication
  4. SS F plasmid DNA circularises in Fcell & is used as a template to
    synthesize complementary strand
  5. Recombinant bacteria able to express new alleles → permanent ∆ in gen/phenotype
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15
Q

Points of Comparison for Conjugation vs Transformation vs Transduction (General/specialised) vs Conjugation [4]

A
  1. Source of DNA introduced (phage involved?)
  2. Conditions
  3. Type of DNA transferred (random?)
  4. Homo Recombination?
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16
Q

How can a bacteria gain variation? [4]

A
  1. Random mutation
  2. Transformation
  3. Generalised/Specialised Transduction
  4. Conjugation
17
Q

Why does bacteria need to regulate its genes?

A
  1. Unicellular bacteria have limited resources
  2. easily influenced by environment
18
Q

Advantages of regulation? [3]

A

(i) ensure economical use of resources & energy, no wastage,
(ii) allow bacteria to respond & adapt to ∆s,
(iii) Operons can turn on/off as all functionally related protein are synthesized in 1 unit →
selective advantage who can respond & survive better

19
Q

Define operon

A

Cluster of genes with related functions, regulated such that genes in cluster are turned on/off together

20
Q

Define polycistronic mRNA

A

mRNA with multiple stop & start codons , codes for diff p.p that are related to e/o

21
Q

When is Lac operon UPREGULATED?
Is this Positive/Negative Regulation?

A

In ABSENCE of glucose
→ When [glucose] decreases, [cAMP]
increases

Positive regulation

22
Q

When is LAC operon DOWNREGULATED
Is this Positive/Negative Regulation?

A

In ABSENCE of Lactose
No allolactose inducer → lac repressor remains
active → binds to operator → prevent RNA pol.
accessing promoter → prevent transcription

Negative regulation

23
Q

Why is there some activity of Beta-Galactosidase even if the Lac operon is DOWNREGULATED? [4]

A
  1. Basal level of β-galactosidase & permease
    exists due to leaky repression*
  2. Lactose enters cell via permease → converted
    to allolactose by β-galactosidase
  3. Allolactose act as Inducer & bind to Allosteric
    Site of lac repressor → causing conformation
    ∆ & inactivating repressor
  4. Inactive lac repressor unable to bind to
    operator → promoter now available to RNA
    Polymerase to bind* → transcription of
    structural genes occurs
24
Q

Why is repression of Lac operon described as leaky? [2]

A
  1. Interactions btwn repressor & operator are weak
  2. Repressor can dissociate from operator from time to time → basal lvl of permease, β-galactosidase
    → small amt of lactose can enter & converted to allolactose → inactive repressor → transcription
25
Q

Define end-product inhibition [2]

A
  1. A form of feedback inhibition where the
  2. *end product of a metabolic pathway inhibits the enzyme involved in early reactions
26
Q

Describe whether the following operon is repressible/inducible
1. Lac
2. Trp

A
  1. Inducible (cuz its usually INACTIVE due to active repressor produced)
  2. Repressible (cuz its constitutively ACTIVE due to inactive repressor produced)
27
Q

Describe the type of regulation of the Trp Operon

A

Negative Regulation in the form of end-product inhibition

28
Q

When is the Trp operon DOWNREGULATED [2]

A

In presence of HIGH [Trp]
1. Tryptophan acts as co-repressor, binds to
allosteric site of Trp repressor →
activating it
2. Activated Trp repressor binds to Operator in
Promoter → prevents RNA polymerase
from binding to promoter → prevent
transcription of structural genes

29
Q

When is the Trp operon UPREGULATED [2]

A

In presence of LOW [Trp]
1. Low Tryptophan → no co-repressor to
activate repressor → Trp repressor remains
inactive
2. Unable to bind to operator in promoter →
RNA polymerase able to access promoter →
transcription continues → Trp synthesized

30
Q

Given an Lac Operon activity to [glucose] graph, why will there be a delay in increase in activity of Lac operon to utilise Lactose once glucose is fully used up?

A

time needed for transcription & translation of Lac operon given glucose is used up

H2 Biology (20 decks)

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