Introduction to Bacteria (1) Flashcards by Hannah Maclean

Name bacterial structures A-G

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How would you view a bacteria?

Bacteria are visible using light microscopy but to see the ultrastructure of the cell we need to use an electron microscope

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Do bacteria have a nucleus?

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Describe the cytoplasmic membrane

(aka plasma membrane) is a very thin, elastic and semi-permeable membrane around the bacterial cell contents.

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Describe the cell wall of a bacteria

cell wall -rigid, giving the cell strength and shape but it is permeable.

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Between the plasma membrane and cell wall, which is permeable and semi-permeable?

cell wall - permeable
plasma membrane - semi-permeable

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What component do gram-negative bacteria have?

outer-membrane

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Is this the cell wall of a Gram-negative or -positive bacteria?

positive

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Is this the cell wall of a gram positive or negative bacterium?

negative

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What bacteria has a thin cell wall/peptidoglycan?

Gram-negative

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Which type of bacteria has a cell wall?

Gram-negative

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What is the periplasm?

the space between the inner and outer membrane in Gram-negative bacteria

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Name structures A-C and decide if this is a Gram positive or -negative bacterium

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Name structures A-D and decide if this is a Gram positive or -negative bacterium

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What are the components of the outer membrane of Gram-negative bacteria?

lipopolysaccharides and protein

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What colours in light-microscopy identify a Gram-negative/positive bacterium?

+ purple
- red

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What bacterium appears red in light microscopy?

Negative

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What shape are cocci bacteria?

spherical

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What shape are bacilli?

rod-shaped

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What bacteria are shown here an dhow do they exist?

white cells (multilobed nuclei showing up red) as well as cocci that are in pairs

Gram- positive

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What ways can bacteria exist?

single cells
pairs
chains
clusters

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What bacteria are shown here an dhow do they exist?

cocci in longer chains look under the electron microscope

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Is bacilli Gram-positive or negative?

negative

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Is cocci Gram-positive or negative?

positive

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What bacteria does the red stain indicate here?

see rod shaped bacteria that have stained red so these are Gram-negative rods, also known as Gram-negative bacilli

what is shown in the electron microscopic image?

see rod shaped bacteria that have stained red so these are Gram-negative rods, also known as Gram-negative bacilli

How thick is the cytoplasmic membrane?

5-10 mm thick

What are the components of the cytoplasmic membrane?

phospholipids (40%) and proteins (60%).

What does the cytoplasmic membrane allow?

It allows the passage of water and uncharged small molecules but otherwise forms a barrier

Do charged or uncharged molecules pass through the plasma membrane?

uncharged small molecules

What are the roles of proteins in the plasma membrane?

1. Transport systems for specific nutrients and ions 2. As enzymes involved in processes such as energy generation, cell wall synthesis and DNA replication 3. Sensing proteins that measure concentrations of molecules in the environment

What makes up the cell wall in bacteria?

Made of peptidoglycan

How thick is the cell wall?

10-25mm thick

What are the 2 components of the peptidoglycan?

N-acetylglucosamine acid and N-acetylmuramic acid molecules linked alternately in a chain, with short peptides forming cross-links

Describe the structural features of the peptidoglycan

Thick, strong and relatively rigid- maintains shape

Can antibiotics effect the cell wall peptidoglycan?

YES interfere with construction burst/lysis e.g. penicillin

What happens if the cell wall is weakened or ruptured?

osmosis means the cell will swell and burst –termed lysis

How is the cell wall involved in cell division?

The cell wall plays an important part in cell division ie cross-walls form prior to separating into 2 daughter cells

What is the component of the outer membrane?

lipopolysaccharides LPS

What type of bacteria have lipopolysaccharides?

Gram-negative (small peptidoglycan)

What is the role of the peptidoglycan?

1. Protects peptidoglycan from bile salts (in the gut), also from lysozyme 2. Blocks many antibiotics getting into the cell

What makes Gram-negative bacteria toxic?

Lipid A is a lipid component of an endotoxin held responsible for the toxicity of gram-negative bacteria. It is the innermost of the three regions of the lipopolysaccharide (LPS), also called endotoxin molecule, and its hydrophobic nature allows it to anchor the LPS to the outer membrane. Lipid A (within LPS) forms endotoxin, which, when released into the bloodstream (when multiplying or when lysed), may give rise to endotoxic shock –fever and low blood pressure

What characterises endotoxic shock?

fever and low blood pressure

What lipid is responsible for endotoxic shock?

Lipid A, component of the LPS

What bacteria will cause endotoxic shock?

Gram-negative e.g. cocci

Describe the capsule of bacteria?

usually a hydrated polysaccharide structure that covers the outer layer of the cell wall

Are the LPS layer of Gram-negative bacteria hydrophobic?

YES

What are the 2 types of capsule?

rigid slimy

What is the role of a rigid capsule?

prevent phagocytosis

What is an example of a bacteria with a rigid capsule?

Streptococcus pneumoniae

Describe a slimy capsule

secretory substance secreted by bacteria less well defined, form a slime layer or biofilm

What is the role of a slime layer/slimy capsule?

used to adhere to surfaces provides a protective environment enhanced as bacteria divide and form microcolonies

What is an example of a bacteria forming a slimy capsule?

S. mutans (Gram-positive) form a biofilm on teeth and make plaque

What is the role of the flagella?

movement

Do bacteria always have 1 flagella?

No, can have 1-20

What are the different categories of flagella?

A-Monotrichous Vibrio cholerae (1); B-Lophotrichous Spirillum spp (One point); C-Amphitrichous Rhodospirillum rubrum (both sides); D-Peritrichous (all over)

What type of flagella does V. cholerae have?

monotrichous

What is lophotrichous?

many flagella form one point e.g. Spirillum spp

What is amphitrichous?

flagella form both sides e.g. Rhodospirillum rubrum

What is peritrichous flagella?

flagella all over e.g. E.coli and Salmonella

Why is motility important for bacteria?

increase ability to cause disease pathogenesis

Can flagella be seen with a light microscope?

No - use a staining method

What are fimbriae?

long filamentous polymeric protein structures located at the surface of bacterial cells. They enable the bacteria to bind to specific receptor structures and thereby to colonise specific surfaces. - e.g. adhering to host surfaces - bacterial to bacterial .. conjugation - adherence

Can fimbriae been seen under a light microscope?