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Biology > Genetics of Bacteria > Flashcards

Genetics of Bacteria Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

AP: Cell Wall

A
  • peptidoglycan cell wall
  • made up of mucopeptides, glycopeptides and murein (strengthening material)
  • prevents cell from bursting when it absorbs water
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2
Q

AP: Ribosomes

A
  • 70s ribosome

- site for protein synthesis

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3
Q

AP: Cytoplasm

A
  • few organelles ; no membrane-bound organelles
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4
Q

AP: Plasma Membrane

A
  • phospholipid bilayer (Ref. to Cell Structure lect notes)
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5
Q

AP: Nucleoid

A
  • where DNA is generally confined to

- distinct from rest of cell’s interior

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6
Q

SP: Flagellum

A
  • for locomotion/movement
  • hollow cylinder of protein
  • more than 1 can be present in motile bacteria
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7
Q

SP: Pili

A
  • hollow, hairlike structures made of proteins

- allow bacteria to attach to other cells

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8
Q

SP: Capsule / Slime Layer

A
  • protects against chemicals and dessication (extreme drying)
  • stores waste products and protect bacteria from attack by phagocytes
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9
Q

SP: Photosynthetic Membranes

A
  • tubular infoldings of the cell surface membrane

- possess photosynthetic pigments in photoautotrophs

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10
Q

SP: Mesosomes

A
  • foldings of cell surface membrane
  • associated with DNA during cell division and helps with formation of new cell walls
  • site of respiration
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11
Q

SP: Fimbriae

A
  • attachment to other cells or surfaces
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12
Q

SP: Endospores

A
  • survival structures in adverse conditions

- presence of protective multi-layer coat

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13
Q

Describe the structure of prokaryotic genomes.

A
  • bacterial chromosome contains a single DNA molecule (monoploid) several million base pairs long
  • double-stranded DNA molecule associated with a small amount of non-histone proteins, allowing it to coil tightly to form loop domains and subsequently condensed DNA
  • carries genes essential for survival (e.g enzymes for metabolism)
  • in addition, some bacteria may possess plasmids, small circular DNA molecules
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14
Q

What is a plasmid?

A
  • small, autonomously replicating DNA molecule that is separate from the bacterial chromosome
  • carries genes that are not essential to bacteria’s survival but may play important roles in growth and life cycle of bacterial hosts (e.g antibiotic resistance genes)
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15
Q

Differences between Bacterial Chromosome and Eukaryotic Chromosome

A
  1. [Bacterial]
    - not enclosed in membrane-bound nucleus but in nucleoid
    [Eukaryotic]
    - enclosed in membrane-bound nucleus
  2. [Bacterial]
    - highly supercoiled structure, nature of which is unclear
    [Eukaryotic]
    - packaged using histone proteins
  3. [Bacterial]
    - mostly circular although some linear bacterial chromosomes exist
    [Eukaryotic]
    - linear chromosomes
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16
Q

Outline the mechanism of asexual reproduction by binary fission in prokaryotes.

A
  • replication of chromosomal DNA begins at the Origin of Replication (OriR)
  • DNA double helix unwinds and unzips bidirectionally to form 2 separate strands
  • circular DNA has no open ends, forms structure made up of 2 interlocking DNA molecules
  • topoisomerase needed to cut, separate and reseal the 2 DNA molecules by breaking phosphodiester bonds
  • the duplicated molecules are then attached to the plasma membrane and the cell elongates for preparation for cell division
  • during cell division, duplicated DNA is separated and plasma membrane invaginates to form a septum
  • new cell walls formed within the membrane layers, resulting in 2 genetically identical cells that may stay together or separate
17
Q

Advantages of Binary Fission

A
  • allows successful phenotypes to rapidly colonise a habitat (propagate and thrive) in a stable, favourable environment
18
Q

Define “Transformation”

A
  • mode of gene transfer in which a piece of free DNA is taken up by a bacterial cell from the surrounding medium and integrated into the recipient genome
19
Q

Mechanism of Genetic Transformation

A
  • DNA released into environment by cell death or other natural processes
  • as DNA fragment enters cell, one strand may be hydrolysed
  • the other single DNA strand moves across the membrane of a competent bacterial cell ; may pair up with a homologous region of the bacterial chromosome and become integrated
  • this integration requires 2 crossover events (double crossover) to incorporate new DNA into recipient DNA
  • bacterial enzymes degrade remaining DNA
  • resultant cells, transformants, will now express new genes from the new DNA and pass it on to offspring during binary fission
20
Q

Factors affecting Transformation

A
  1. Size of DNA
  2. Competence of recipient cell
  3. Concentration of DNA
  4. Type of DNA
21
Q

Define “Transduction”

A
  • mode of gene transfer in which bacterial DNA is transferred from one bacterium to another by bacteriophages as a result of aberrations in the bacteriophages reproductive cycle
22
Q

Processes of Transduction?

A

Generalised transduction and Specialised transduction

23
Q

Mechanism of Generalised Transduction

A
  • bacteriophages as vectors
  • a bacteriophage infects a bacterium, injecting its phage DNA
  • in the lytic cycle of phage reproduction, host bacterial chromosome is broken into random fragments
  • occasionally, some of the fragments of the host bacterial chromosome are packaged into capsid, forming transducing phages
  • cell lysis releases the transducing phages which may transfer host DNA to the next bacterium they infect
  • the host bacterial DNA may then become integrated into the recipeint bacterial chromosome during homologous recombination
24
Q

Mechanism of Specialised Transduction

A
  • temperate bacteriophages (e.g Lambda phage) as vectors ; able to integrate their genome into bacterial chromosome to form prophage
  • in small percentage of excision events, prophage may imprecisely excise from the bacterial chromosome, carrying with it a small part of the bacterial DNA adjacent to site of prophage integration
  • a bacteriophage carrying this DNA injects another bacterial cell and it may become intergrated ; homologous recombination occurs
25
Q

Criteria for Transduction

A

[only generalised transduction]
- bacteriophage must degrade bacterial chromosome

[generalised and specialised transduction]

  • process of packaging DNA into capsid must not be phage DNA specific
  • genetic recombination through double crossover event
26
Q

Significance of Transduction

A

DNA is protected by capsid coat of bacteriophage, will not be degraded by nucleases in the environment

27
Q

Define “Conjugation”

A
  • mode of gene transfer that involves unidirectional transfer of genetic material from one bacterium to another through the sex pilus as a result of bacterial cell-to-cell contact
28
Q

Mechanism of Conjugation

A
  • F+ cell containing the F factor produces a sex pilus which makes contact with specific receptors on an F- cell
  • temporary cytoplasmic mating bridge formed between the two cells, providing avenue for DNA transfer
  • DNA transferrred from F+ to F- cell ; usually only genes on F factor are transferred
  • transfer initiated when endonuclease cleaves 1 of the DNA strands on the F plasmid at the Origin of Transfer (OriT)
  • one end of nicked DNA separaetes from circle and enters recipient cell
  • replication then takes place on the nicked strand (rolling circle mechanism), producing a circular, double-stranded copy of the F plasmid

Biology (8 decks)

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