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POB 2 > Lecture 7 Prokaryotes (Bacteria) > Flashcards

Lecture 7 Prokaryotes (Bacteria) Flashcards

1
Q

Key Concepts

A

➢ Structural and functional adaptations contribute to prokaryotic success
➢ Genetic diversity:Rapid reproduction, mutation, and genetic recombination
➢ Diverse nutritional and metabolic adaptations
➢ Prokaryotes have both beneficial and harmful impacts on humans

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2
Q

What characteristics enable prokaryotes to reach huge population sizes and thrive in diverse environments

A

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3
Q

THE PROKARYOTIC CELL

A

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4
Q

A. STRUCTURE

A

Essential structure
- cell wall
- cell membrane
- cytoplasm
- nuclear material
Particilar structures
-capsule
-flagella
-pili
-spore

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5
Q

Morphology of Prokaryotic Cells: Shapes

A

● Two types most common
○ Coccus: spherical
○ Rod: cylindrical
● Variety of other shapes
○ Vibrio, spirillum, spirochete
○ Pleomorphic (many shapes)
○ Great diversity often found in low
nutrient environments

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6
Q

Prokaryotic Cell Reproduction

A
  • Binary Fission (figure 12.12)
  • Origin of replication
  • High rate of replication
  • Short generation time (20mn)

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7
Q

Groupings - bacteria divide by binary fission

A

○ Cells often stick together following division
○ Form characteristic groupings
○ Examples:
■ Neisseria gonorrhoeae (diplococcus)
■ Streptococcus (long chains)
■ Sarcina (cubical packets)
■ Staphylococcus - grapelike clusters)

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8
Q

External Organisation

A

▪ Cell Wall
▪ Cell Membrane
▪ Capsule
▪ Flagella
▪ Pilus

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9
Q

1.The Cell Membrane - boundary of the cell

A

○ Phospholipid bilayer embedded with proteins
■ Hydrophobic tails face in; hydrophilic tails face out
○ Serves as semipermeable membrane
○ Proteins serve numerous functions
■Selective gates
■Sensors of environmental conditions

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10
Q
  1. Cell Wall - protection
A

Cell wall is strong, rigid structure that prevents cell lysis
○ Architecture distinguishes two main types of bacteria
■ Gram-positive
■ Gram-negative
○ Made from peptidoglycan (only in bacteria)

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11
Q

The Gram stain

A

Hans Christian Joachim Gram (1853–1938)
● Danish physician working at morgue in Berlin
● Worked for Dr. Carl Friedlander
○ Attempting to identify cause of pneumonia
● Gram was developing methods to stain bacteria
● With one method, bacteria stained unequally
○ Some retained dye, others did not
○ Revealed two different kinds of bacteria
● Basis for modern Gram stain
○ Identifies two major groups of bacteria according to cell wall
structure and chemistry
○ Gram-positive and Gram-negative

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12
Q

The peptidoglycan

A

The strength of the bacterial cell walls is due to a layer of peptidoglycan, a material found only in bacteria

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13
Q

The Gram-Positive and Gram negative

A

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14
Q

Treatment implications

A

● Lipid portions of the lipopolysaccharides in the walls of many gram- are toxic,
causing fever or shock.
● Outer membrane of a gram- helps protect it from the body’s defenses.
● Gram- more resistant to antibiotics - outer membrane impedes the entry of
some drugs.

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15
Q

Antibacterial Substances That Target Peptidoglycan

A

● Peptidoglycan makes good target since unique to bacteria
○ Can weaken to point where unable to prevent cell lysis
● Penicillin interferes with peptidoglycan synthesis
○ Prevents cross-linking of adjacent glycan chains
○ Usually more effective against Gram-positive bacteria than
Gram-negative bacteria
■ Outer membrane of Gram-negatives blocks access
■ Derivatives have been developed that can cross
● Lysozyme breaks bonds linking glycan chain
○ Enzyme found in tears, saliva, other bodily fluids
○ Destroys structural integrity of peptidoglycan molecule

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16
Q

Bacteria That Lack a Cell Wall

A

● Mycoplasma species have extremely variable shape
● Penicillin, lysozyme do not affect
● Cytoplasmic membrane contains sterols that increase
strength

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17
Q
  1. Capsules - adhere to surfaces
A

Gel-like layer outside cell wall that protects or allows attachment to
surface
* Capsule: distinct, gelatinous
* Slime layer: diffuse, irregular
* Most composed of glycocalyx (sugar shell) although some are polypeptides
* Allow bacteria to adhere to surfaces
* Once attached, cells can grow as biofilm (Polysaccharide encased community)
* Example: dental plaque
* Some capsules allow bacteria to evade host immune system

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18
Q
  1. Capsules - adhere to surfaces
A

-Capsule > condensed layers; closely surrounds the bacterium
-slime layer > loosely adherent: nonuniform in density and thickness
-Capsule/slime layer: also called glycoalyx

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19
Q
  1. Capsules - function to adhere to surfaces
A

● Prevents phagocytosis of bacteria
● Attached bacteria to surface

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20
Q
  1. Flagella - involved in motility
A
  • Spin like propellers to move cell
  • Some important in disease
  • Numbers and arrangements help with characterization
  • Peritrichous - distributed over entire surface
  • Polar flagellum: single flagellum at one end of cell
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21
Q
  1. Pili - involved in conjugation
A

● Pili (sing. pilus) are shorter than flagella
● Types that allow surface attachment termed fimbriae
● Twitching motility, gliding motility involve pili
● Sex pilus used to join bacteria for DNA transfer

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22
Q

Internal Organisation

A

▪ Genetic Material
▪ Ribosome
▪ Cytoplasm
▪ Endospore

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23
Q
  1. Genetic Material
A

▪ Chromosome forms gel-like region: the nucleoid
* Single circular double-stranded DNA
* Packed tightly via binding proteins and supercoiling
▪ Plasmids are circular, supercoiled, dsDNA
* Usually much smaller; few to several hundred genes
* May share with other bacteria; antibiotic resistance can
spread this way

24
Q

Specialized membranes

A

slide 26

25
Q

Bacterial chromosome

A
  • Circular chromosome
  • One double-stranded (ds) DNA molecules
    – Vibrio cholera has 2 chromosomes
    – Rhizobium melilotus 3 chromosomes
  • Size ~million base pairs (bp) in length (E.coli ~ 4.6M bp)
    – Human genome ~6 billion bp
  • 90% DNA codes for proteins
    – Human DNA~ only 1% codes for protein
  • Essential genes
26
Q

Plasmids and transposons

A
  • Some bacteria possess a plasmid
  • Small circular DNA molecules
  • One or 2 copies /cell (some have many copies)
  • Non- essential genes
  • Small size ~ thousands bp
  • Function:
    – gene transfer,
    – antibiotic resistance ,
    – killing other bacteria
  • Transposons –
  • moving DNA sequences
27
Q

Theta Replication

A

A plasmid replicates
independently of its
bacterial
chromosome:

Replication begins at the origin of replication (ori) and continues around the circle. In this
diagram, replication is taking place in both directions; in some plasmids, replication is in
one direction only.

slide 29

28
Q

Rolling Circle Replication

A

slide 30

29
Q
  1. Ribosomes - Involved in protein synthesis
A
  • Facilitate joining of amino acids
  • Relative size expressed as S (Svedberg)
  • Reflects density: how fast they settle when centrifuged
  • Prokaryotic ribosomes are 70S
  • Made from 30S and 50S
  • Eukaryotic ribosomes are 80S
  • Important medically: antibiotics
    impacting 70S ribosome do not
    affect 80S ribosome

slide 31

30
Q
  1. Cytoplasm
A

Cytoskeleton: internal protein framework
* Once thought missing in bacteria
* Bacterial proteins similar to eukaryotic cytoskeleton have
been characterized
* Likely involved in cell division and controlling cell shape
Storage granules: accumulations of polymers
* Synthesized from nutrients available in excess
* Carbon, energy storage:
– Glycogen
Gas vesicles: controlled to provide buoyancy
Higher concentration of salts than eukaryotes

31
Q
  1. Endospores - Unique type of dormant cell
A
  • Produced by members of Bacillus, Clostridium
  • May remain dormant for 100 years or longer
  • Extremely resistant to heat, desiccation, chemicals, ultraviolet
    light, boiling water
  • Endospores that survive can germinate to become vegetative cell
  • Found virtually everywhere
32
Q
  1. Endospores - Example of Infections
A

● Anthrax – Bacillus anthracis
● Tetanus – Clostridium tetani
● Botulism – C. botulinum
● Gas gangrene – C. perfringens

33
Q

Sporulation vs Germination

A

▪ Sporulation triggered by carbon, nitrogen limitation
* Starvation conditions begin 8-hour process
* Endospore layers prevent damage
* Exclude molecules (e.g., lysozyme)
* Cortex maintains core in dehydrated state, protects
from heat
* Core has small proteins that bind and protect DNA
* Calcium dipicolinate - protective role
▪ Germination triggered by
heat, chemical exposure

34
Q
  1. Endospores - Medical implications
A

slide 36

35
Q

B. Genetic Change in Bacteria

A

Organisms adapt to changing environments
● Natural selection favors those with greater fitness
● Bacteria adjust to new circumstances
o Regulation of gene expression
o Genetic change
● Change in organism’s DNA alters genotype
o Sequence of nucleotides in DNA
o Bacteria are haploid, so only one copy, no backup
● May change observable characteristics, or phenotype
o Also influenced by environmental conditions
Genetic change in bacteria occurs by two mechanisms:
1. Mutations
2. Horizontal Gene Transfer

36
Q
  1. Mutation
A

Changes the existing nucleotide sequence
* mutation passed on to the progeny (daughter cells)
through vertical gene transfer.
* modified organism and daughter cells = mutants

slide 39

37
Q
  1. Mutation - Antibiotic Resistance
A

slide 40

38
Q
  1. Mutation - MEGA-plate experiment
A

slide 41

39
Q
  1. Genetic Recombination
A

● Horizontal gene transfer
● Movement of DNA from one organism to another.
● changes are passed on to the progeny by vertical transfer.

slide 42

40
Q

Importance

A

Microorganisms commonly acquire genes from other cells,
the process of horizontal gene transfer
Movement of DNA from one cell (the donor) to another (the
recipient) - rapid spread of antibiotic resistance, such as
for Staphylococcus aureus

3 main mechanisms
* Conjugation: direct transfer of DNA from one
bacterium to another
* Transformation: bacterium takes up free DNA
* Transduction: bacterial viruses take DNA from one
bacterium to another

41
Q

Lederberg and Tatum’s
experiment demonstrated
that bacteria undergo
genetic exchange

A

slide 44

42
Q

Davis’s U-tube
experiment demonstrated
that bacterial genetic
exchange requires
direct contact

A

● U-shaped tube that was divided into two
compartments by a filter with fine pores.
● Filter allowed a liquid medium to pass
from one side of the tube to the other,
but the pores of the filter were too small
to allow the passage of bacteria.
● Two auxotrophic strains of bacteria
were placed on opposite sides of the
filter, and suction was applied alternately
to the ends of the U-tube, causing the
medium to flow back and forth between
the two compartments.

slide 45

43
Q

Conjugation

A
  • Direct transfer via connection tube is one-way traffic from
    donor cells to recipient cells.
  • It is not a reciprocal exchange of genetic information.
    3 Requirements
  • F+
    cells: donor cells containing F factor
  • F–
    cells: recipient cells lacking F factor
  • Sex pilus: connection tube
  • Conjugative plasmids direct their own transfer - Replicons
  • F plasmid (fertility) of E. coli – only for transfer
  • Other plasmids encode resistance to some antibiotics
  • Spread resistance easily
44
Q

F plasmid

A

● F plasmid of E. coli - F+
cells have, F–
do not
● Encodes proteins required for conjugation including:
○ Sex pilus (F pilus)
○ Brings cells into contact
○ Enzyme cuts plasmid
○ Single strand transferred
○ Complementary strands synthesized
○ Both cells are now F+

slide 47

45
Q

R plasmids

A

Natural gene transfer and antibiotic resistance
● R plasmids – contain antibiotic resistance genes
● genes located on R plasmids that can be transferred naturally to other bacteri● R plasmids have evolved in the past 60 years since the beginning of
widespread use of antibiotics.
● The transfer of R plasmids is not restricted to bacteria of the same or even
related species.

slide 48

46
Q

The F factor is transferred during conjugation between F+ and F− cells

A

slide 49

47
Q

How do you get chromosomal genes transferred?

A

Hfr cells (high-frequency strains): donor cells with F factor integrated into the donor bacterial chromosome
The F factor is integrated into the bacterial chromosome in an Hfr cell.

At a frequency of only
about 1 in 10,000.
(low frequency)

48
Q

Bacterial genes may be transferred from an Hfr cell to an F− cell in conjugation.

A

slide 51

49
Q

Characteristics of E.Coli cells with different types of F factor

A

slide 52-53

50
Q

Transformation

A

● A bacterium takes up DNA from the medium.
● Recombination takes place between introduced genes
and the bacterial chromosome.
● Competent cells: cells that take up DNA
● Transformants: cells that receive genetic material

Slide 54

51
Q

Transformation can be used to map bacterial genes

A

slide 55

52
Q

Transduction

A

slide 56

53
Q

AB Resistance:
Mutation and horizontal gene transfer

A
  • Rapid reproduction enables bacterial cells
    carrying resistance genes to quickly
    produce large numbers of resistant offspring
  • Resistance genes spread rapidly within
    and among bacterial species by horizontal
    gene transfer
54
Q

Diverse nutritional and metabolic adaptations

A

Prokaryotes can be categorized by how they obtain
energy and carbon:
● Phototrophs obtain energy from light
● Chemotrophs obtain energy from chemicals
● Autotrophs require CO2
or related compounds as a
carbon source
● Heterotrophs require an organic nutrient to make other
organic compounds

55
Q

Diverse nutritional and metabolic adaptations

A

Energy and carbon sources are combined to give 4
major modes of nutrition:
● Photoautotroph
● Chemoautotroph
● Photoheterotroph
● Chemoheterotroph

slide 59

56
Q

The need for oxygen

A

Prokaryotic metabolism varies with respect to O2
● Obligate aerobes require O2
for cellular respiration
● Obligate anaerobes are poisoned by O2
and live by
fermentation or use substances other than O2
for
anaerobic respiration
● Facultative anaerobes can use O2
if it is present or
carry out fermentation or anaerobic respiration if not

57
Q

Impacts on humans and animals

A

● Negative impact - Pathogens (half of human diseases)
● Positive impact
○ Mutualistic Bacteria - intestines (digestion, absorption)
○ Food production (Cheese,yogurt, Beer and wine, sauerkraut)
○ Research and technology (Cloning, recombinant DNA)
○ Medicine (CRISPR-Cas9 system, insulin production)
○ Production - produce natural plastics PHA
○ Bioremediation - remove pollutants from soil, air, or water

POB 2 (25 decks)

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