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1. Microbiology > Structure and Function of Bacterial cells > Flashcards

Structure and Function of Bacterial cells Flashcards

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1
Q

What are the three regions of a bacteria?

A

Surface Appendages

Cell envelope

Cytoplasmic region

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2
Q

What makes up the surface appendage region of bacteria?

A

Either flagella and pili (fimbriae) are attached to cell surfaces

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3
Q

What does the cell envelope consist of?

A

Capsule (glycocalyx)

Outer membrane (only in gram negative cells)

Cell wall

Cytoplasmic membrane

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4
Q

What is the capsule also called?

A

Glycocalyx

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5
Q

What part of the cell envelope is only found in gram negative cells?

A

Outer membrane

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6
Q

What is found in the cytoplasmic region of a bacteria?

3

A

Chromosome (DNA)

Ribosomes

Inclusions

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7
Q

What are pili also called?

A

Fimbriae

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8
Q

What is the function of flagella?

A

Motility

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9
Q

What is the function of pili?

A

Adherence

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10
Q

What type of bacteria are flagella found on?

2

A

On both gram + and - bacteria

On many bacilli but not many cocci

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11
Q

What are the three parts of a flagellum?

A

Filament

Hook

Basal body

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12
Q

What is a filament?

A

A region of the bacterial flagella which is composed of flagellin (protein)

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13
Q

What protein is found in the filament of a flagellum?

A

Flagellin

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14
Q

What is the hook of a flagellum?

2

A

The wider region at the base of the filament

It connects the filament to the motor portion of the flagellum

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15
Q

What is the basal body of a flagellum?

3

A

The motor of a flagellum

It is anchored in cytoplasmic membrane and the cell wall

Consists of four ring shaped proteins stacked around a central rod

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16
Q

What is it called when a bacteria has a single flagellum?

A

Monotrichous

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17
Q

What is it called when a bacteria has flagella all over its surface?

A

Peritrichous

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18
Q

What is it called when a bacteria has a tuft of flagella at one end?

A

Lophotrichous

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19
Q

What is it called when a bacteria has a tuft of flagellum at either end?

A

Amphitrichous

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20
Q

How do flagella move?

4

A

By rotation like a propeller

This causes the bacteria to move in pulses along a line and tumble

A counterclockwise rotation leads to lines

A clockwise rotation leads to a tumbling motion

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21
Q

What are the benefits of being motile to a bacteria?

2

A

Motility serves to keep bacteria in an optimum environment via taxis

Motility assists in bacterial pathogenesis - move through mucous layer - attach to epithelial cells of the mucous membranes

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22
Q

What is taxis?

A

Motile response to an environmental stimulus

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23
Q

How does the flagella move when the bacteria is moving towards a gradient with favourable stimulus or away from an unfavourable one?
(2)

A

The frequency of tumbles is low

Trying to get to the favourable area quickly

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24
Q

How do the flagella move when the bacteria is moving towards an unfavourable stimulus or away from a favourable stimulus?
(2)

A

The frequency of tumbles increases

Allows the cell to reorient itself and move towards a more suitable environment

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25
Q

What are pili?

3

A

Thin filamentous protein structures

They extend from the surface of the bacterial cell

They have a shaft composed of pilin (protein)

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26
Q

On what type of bacteria are pili found?

A

Found on nearly all gram-negative bacteria but not many gram positive bacteria

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27
Q

What protein is found in the shaft of pili?

A

Pilin

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28
Q

What are the two main types of pili?

A

Short attachment pili

Long conjugation pili

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29
Q

What are short attachment pili also called?

A

Fimbriae

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30
Q

Write a note on fimbriae.

4

A

These are organelles of adhesion

They allow bacteria to colonize environmental surfaces or cells and resist flushing

There is an adhesive tip structure at the end of the shaft

These tips have a shape corresponding to specific glycolipid or glycoprotein receptors on a host cell

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31
Q

What is the function of fimbriae?

2

A

They allow bacteria to colonize environmental surfaces or cells

They allow bacteria to resist flushing

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32
Q

What is found at the end of the shaft on fimbriae ?

A

An adhesive tip

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33
Q

What is the role of the adhesive tips on fimbriae?

A

Their shape corresponds to specific glycolipid or glycoprotein receptors on a host cell

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34
Q

Why are fimbriae needed?

A

Since both the bacteria cell and the host cell have negative charges

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35
Q

How do fimbriae work?

A

They enable bacteria to bind to host cells without getting very close (avoid electrostatic repulsion)

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36
Q

What are long conjugation pili also called?

2

A

F pili

sex pili

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37
Q

What is the function of long conjugation pili?

A

They are important in conjugation

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38
Q

What is conjungation?

A

The transfer of genetic material between bacteria through direct cell-to cell contact

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39
Q

What is spread through conjugation?

A

This genetic transfer facilitates the spread of virulence and antimicrobial resistance genes to other bacterial cells

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40
Q

What is the overall role of the glycocalyx?

A

Protection and adherence

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41
Q

What is the overall role of the outer membrane in gram negative bacteria?

A

Structure and permeability

42
Q

What is the overall role of the cell wall?

A

Shape and protection

43
Q

What is the overall role of the cytoplasmic membrane?

A

Transport

44
Q

What is the glycocalyx?

A

A viscous covering of fibres outside of the cell wall

45
Q

When is the glycocalyx called a capsule?

A

If it appears as an extensive tightly bound accumulation of gelatinous material adhering to the cell wall

46
Q

When is the glycocalyx called a slime layer?

A

If it appears unorganized and more loosely attached

47
Q

What are the three functions of the glycocalyx?

A

Protection

Immune evasion

Formation of a biofilm

48
Q

Explain the protection function of the glycocalyx.

A

Shields bacteria from drying out, chemicals and environmental stresses

49
Q

Explain the immune evasion function of the glycocalyx.

A

Capsulated bacteria are difficult to detect by phagocytic cells

e.g. meningitis

50
Q

What is biofilm?

A

A common secreted adhesive matrix

51
Q

What is special about the bacteria in a biofilm?

A

Biofilm allows bacteria to communicate with one another through quorum sensing

The bacteria live a community

52
Q

What are the advantages of biofilm?

4

A

Bacteria are better able to adhere and resist flushing

Bacteria are better able to resist phagocytosis

Bacteria better at trapping nutrients

Bacteria better able to resist antibiotic attacks

53
Q

Give four examples of places where biofilm can form.

A

Catheters/IVs - indwelling lines

Medical implants

Medical devices - endoscope channels

Water supply systems

54
Q

Give three examples of bacteria that form biofilm.

A

Pseudomonas

Enterobacterales

Staphylococcus

55
Q

What are the two main functions of the cell wall?

A

Allow the cell to withstand internal pressure - prevent lysis

Give shape and rigidity to the cell

56
Q

What does the cell wall contain?

A 
A tough mesh of polysaccharide 
 and peptidoglycan (tight-knit complex)
57
Q

What is peptidoglycan also called?

A

Murein

58
Q

What does peptidoglycan do?

A

Gives strength and rigidity to the cell

59
Q

Describe the structure of peptidoglycan.

3

A

A polymer consisting of interlocking chains of identical monomers

Each monomer consists of two joined amino sugars (G and M) with a pentapeptide coming off M

Long sugar chains are joined together by cross links between the peptides off each M

60
Q

Why is peptidoglycan a vulnerability for bacteria?

A

Peptidoglycan is unique to bacteria

Cell wall antibiotics (penicillin) prevent bacteria from forming peptidoglycan

61
Q

How do gram negative cells make up for their lower amounts of peptidoglycan?

A

They have an outer membrane outside the cell wall

62
Q

Where is the layer of peptidoglycan located in the gram negative bacteria?

A

Located in the periplasm which is surrounded by the outer membrane

63
Q

What is the periplasmic space?

2

A

The space either side of the peptidoglycan layer

It is between the cell membrane and the outer membrane

64
Q

What does the outer membrane consist of?

2

A

Consists of a lipid bilayer

Additional polysaccharide

65
Q

What forms the lipopolysaccharide layer (LPS) in gram negative bacteria?

A

Lipid A from the outer membrane and a polysaccharide

66
Q

What are the three main functions of the outer membrane?

A

Structure

Permeability - it is semi-permeable

Pathogenicity

67
Q

How does the outer membrane add to pathogenicity?

2

A

The toxicity of the lipopolysaccharide layer

This LPS acts as an endotoxin and is released when the bacteria lyse

68
Q

What is the cytoplasmic membrane also known as?

2

A

The cell membrane

The plasma membrane

69
Q

What is the cytoplasmic membrane?

A

A thin inner layer that surrounds the bacterial cell constituents

70
Q

What is the main function of the cell membrane?

A

It is the barrier separating the cytoplasm from the environment

71
Q

What happens if the cell membrane is broken?

2

A

The integrity of the cell is destroyed

The cytoplasm will leak out and the cell will die

72
Q

Explain the permeability function of the cell membrane.

4

A

The cytoplasmic membrane is a highly selective permeability barrier

This allows the cell to take in specific metabolites and excrete waste material

It is a phospholipid bilayer (40%) with proteins (60%) suspended at the surface and spanning layers

Materials move across by passive diffusion or active transport using carrier proteins

73
Q

Explain the structure of a phospholipid bilayer.

2

A

The fatty acids point inward to form a hydrophobic environment

The hydrophilic components remain exposed to the aqueous environment

74
Q

Explain the role of the proteins that make up part of the cytoplasmic membrane.

A

Some of these function as selective transport proteins across the membrane

Others function as enzymes during chemical reactions

75
Q

What is the cytoplasmic membrane referred to as due to its ever changing nature?

A

A fluid mosaic

76
Q

What is the cytoplasm in terms of bacteria?

A

Everything enclosed by the cytoplasmic membrane

77
Q

What is the cytoplasm composed of?

A

80% water

78
Q

What is the cytosol?

A

The liquid component of the cytoplasm

79
Q

What is the liquid component of the cytoplasm?

A

The cytosol

80
Q

What does the cytoplasm contain?

6

A

Nucleic acids (DNA and RNA)

Enzymes

Amino acids

Carbohydrates

Lipids

Inorganic ions

81
Q

What two types of metabolic reactions take place in the cytoplasm?

A

Catabolic reactions

Anabolic reactions

82
Q

What do catabolic reactions do in bacterial cells?

A

They break down molecules in order to obtain building block molecules for more complex cellular molecules

83
Q

What do anabolic reactions do in bacterial cells?

A

They synthesize cellular molecules

84
Q

What governs all living process of all cells?

A

Genes

85
Q

What is a gene?

A

A segment of DNA that encodes a protein

86
Q

In what form is the genome present in bacteria?

A

The genome is encoded on one long single double-stranded molecule called a chromosome

87
Q

What is a chromosome also known as?

A

A bacterial nucleoid

88
Q

What does the bacterial chromosome do?

A

Its the genetic control centre of the cell which determines all the properties and functions of the bacterium

89
Q

Why are most prokaryotes haploid?

A

As they usually only have one single chromosome

90
Q

What are plasmids?

A

They are tiny loops of DNA suspended in the cytoplasm

91
Q

What are ribosomes?

2

A

Small dense structures that assemble proteins

They act by translating genetic information into proteins

92
Q

What are inclusions also called?

A

Granules

93
Q

What type of bacteria produce endospores?

A

Gram positive bacteria

94
Q

What is an endospore?

A

A resistant, dormant survival form of the organism

95
Q

List the four main parts of an endospore.

A

Exosporium

Spore coat

Cortex

Core

96
Q

What is the exosporium?

A

The outermost layer of an endospore

97
Q

Where is the spore coat found?

A

Between the exosporium and the cortex

98
Q

Where is the cortex found?

A

Between the spore coat and the core

99
Q

What does the core of an endospore contain?

3

A

A chromosome

Ribosomes

Cellular essentials

100
Q

What are endospores resistant to?

A

High temperatures

Most disinfectant

Antibiotics

Physical agents e.g. radiation, boiling and drying

1. Microbiology (12 decks)

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