Functional Anatomy of Prokaryotic and eukaryotic cells

Prokaryotic

from the Greek words for prenucleus, or

Eukaryotic

from the Greek words for true nucleus.

1. bacteria

2. archaea

examples of prokaryotes: [2]

fungi, protozoa, algae, plants and animals

examples of eukaryotes [5]

Cocci

usually round, but can also be oval, elongated or flattened on one side.

• Diplococci (pairs); e.g. Neisseria meningitidis

pairs of cocci

• Streptococci (chains); e.g. Streptococcus pyogenes

chains of cocci

• Tetrads (groups of four)

groups of four cocci

• Sarcinae (cubes)

cubes of cocci

• Staphylococci (clusters); e.g. Staphylococcus aureus

clusters of cocci

Bacilli (singular: bacillus)

rod-shaped eukaryotic cells

diplobacilli

pairs of bacilli

streptobacilli

Bacilli arranged in chains

coccobacilli

bacilli are more oval shaped and look similar to cocci.

spirals

bacteria with a spiral shape, having one or more twists and are never straight

vibrios

Cells that appear as curved rods

spirillas

Cells that have a helical, corkscrew-like shape and have fairly rigid bodies

spirochetes

Cells that are helical and flexible are celled

• Glycocalyx

• Flagella

• Axial filaments

• Fimbriae and Pili

Among the structures that can be present outside of the bacterial cell wall are the: [4]

glycocalyx

a viscous, gelatinous polymer that consists of polysaccharides and/or polypeptides. The exact chemical composition will vary in different bacteria.

capsule

if glycocalyx is organized and firmly attached to the cell surface, it is caled a

slime layer or an extracellular polymeric substance (EPS).

if glycocalyx is unorganized and loosely attached to the surface

by negative staining. It can also be visualized using TEM

how is capsule seen:

by protecting cells from phagocytosis

how does the capsule contribute to bacterial virulence?

bacterial virulence

the degree to which a pathogen causes disease

biofilms

microbial communities that form as a slime layer on surfaces

enables bacteria to attach and grow on numerous surfaces

protects the cells within a biofilm from dehydration and from harmful compounds such as antibiotics.

functions of the EPS [2]

flagella

long, filamentous structures that some bacteria use for motility.

by enabling the cells to move towards a favourable environment and away from an adverse one.

how do flagella contribute to virulence of pathogens?

H antigen

Among the components of the flagellum is a protein called

different types of Gram-negative serovars 

the H antigen is useful clinically for indentifying what?

serovars 

variations within a species:

Axial filaments

• used by spirochetes for motility.

• They consist of bundles of fibrils that attach to one end of the cell and spiral around the cell beneath an outer sheath

Fimbriae and pili

hair-like appendages that are present on many (but not all) Gram-negative bacteria. They are shorter, straighter and thinner than flagella, and they consist of the pilin protein.

Fimbriae

hair-like appendages that can be found at the poles of a cell or can be evenly distributed over the entire surface

• They function in the attachment of cells to various surfaces, including epithelial surfaces in the body, and they contribute to the formation of biofilms and other aggregates.

fiambriae function how?

by enabling colonization of host surfaces.

how do fimbriae lay an important role in virulence?

[o;o

longer hair-like appendages that are involved in cell motility

conjugation pili (or sex pili),

enable the transfer of DNA from one bacterium to another

 Bacterial ConjugationA key function of the cell wall

the transfer of DNA from one bacterium to another

to protect the cell from bursting in hypotonic environments. It also serves as an anchorage point for flagella.

A key function of the cell wall

it contributes to the ability of some pathogens to cause disease.

• It is also a target of some antibiotics used in the clinic, eg penicillin.

why The cell wall is important clinically [2]

peptidoglycan

The main structural component of the cell wall. a biopolymer composed of repeating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) (the glycan portion) (Fig. 4.12) with attached tetrapeptide side chains (the peptide portion)

chains of NAG and NAM

forms the carbohydrate “backbone” of the peptidoglycan polymer.

the tetrapeptides are directly joined together.

• In the Gram-negative bacterial cell wall, the tetrapeptides are joined how?

• by peptide cross-bridges

• In the Gram-positive cell wall, the tetrapeptides are linked together how?

1. lipoteichoic acids

2. wall teichoic acids

There are two types of teichoic acids

 teichoic acids,

• olymers made of an alcohol (e.g. glycerol) and phosphate in gram positive cellwall

a thick layer of peptidoglycan and teichoic acids

the cell wall of most Gram-positive bacteria consists of:

• Teichoic acids are negatively charged, and thus may bind and regulate the transport of cations (e.g. Ca2+, Mg2+) in and out of the cell.

charge of teichoic acids:

a thin layer of peptidoglycan, an outer membrane, and a periplasm

the Gram-negative cell wall contains [3]

periplasm

gel-like fluid within the periplasmic space 

periplasmic space 

(the space between the outer membrane and plasma membrane).

digestive enzymes and transport proteins.

The periplasm contains [2]

lipopolysaccharide (LPS), lipoproteins, porins and phospholipids.

The outer membrane ofgram negative cell walls is made of [4]

• It has a strong, negative charge, and helps the cells to evade phagocytosis and the actions of complement, which are important components of the host immune response.

how does the gram negative cell wall evade the immune response?

lipoproteins

consist of lipids covalently bonded to proteins. They function as an anchor between the outer membrane and the peptidoglycan.

Porins 

proteins that form channels in the outer membrane. They enable essential nutrients such as nucleotides, disaccharides, peptides, amino acids and iron to cross the outer membrane.

Lipopolysaccharide

a molecule composed of:

• Lipid A

• Core polysaccharide

• O polysaccharide

Lipid A

the lipid portion of the LPS embedded in the top layer of the outer membrane.

It is released when Gram-negative cells multiply and when they die

when is Lipa A released?

functions as an endotoxin and is responsible for the signs and symptoms associated with Gram-negative bacterial infections

Lipa A functions as what?

• Fever, chills

• Dilation of blood vessels

• Shock

• Blood clotting

symptoms associated with Gram-negative bacterial infections: [4]

 core polysaccharide

 is attached to lipid A and is composed of unusual sugars. It functions to provide stability to the LPS.

O polysaccharide

attached to the core polysaccharide and is made of sugar molecules. It functions as an antigen (called the O antigen) and can be used to distinguish different serovars of Gram-negative bacteria.

Members of the genus Mycoplasma

examples of bacteria that lack a cell wall.

mycoplasma

the smallest known bacteria (e.g. 0.33 m diameter) that can replicate outside living host cells. 

• Although they are most closely related to Gram-positive bacteria, they stain pink in the Gram stain due to the absence of a cell wall.

how do mycoplasma stain?

sterols

lipids that help protect the cells from lysis.

Mycobacterium

Acid-fast cell walls are characteristic of members of the genus :

Mycobacterium

bacteria contain a high concentration (60%) of waxy lipids (mycolic acids) in their cell walls

• They are acid-fast and retain the red carbolfuchsin stain due to the presence of the mycolic acids in the cell wall

• The mycolic acids prevent the uptake of dyes using in staining, including the Gram stain.

how do mycobaterium stain?

Lysozyme

present in perspiration, tears, mucus and saliva. It hydrolyzes the bonds between the NAG and NAM residues in peptidoglycan backbone, destroying the peptidoglycan and cell wall

digestive enzymes (eg lysozyme) and chemicals

bacterial cells walls can be damaged by: [2]

β-lactam antibiotics:

 include penicillins. They inhibit the formation of the crosslinks between the tetrapeptides in the peptidoglycan, thus weakening the peptidoglycan and preventing the formation of a functional cell wall

osmotic lysis

rupture due to weakening or loss of the cell wall

the outer membrane inhibits access of these agents to the peptidoglycan layer. Some β-lactam antibiotics can penetrate the outer membrane and are thus effective against Gram-negative bacteria.

gram-negative cells are less susceptible to lysozyme and many β-lactam antibiotics because

• The plasma (cytoplasmic) membrane

• And the cytoplasm and associated components

Structures that are internal to the cell wall include [2]

inner membrane or cell membrane

The plasma membrane that surrounds the cytoplasm of the cell

to serve as a selective barrier and regulate what moves in and out of the cell. In this regard, the plasma membrane exhibits selective permeability.

main function of the inner membrane:

that play an important role in the breakdown of nutrients and in energy generation for the cell.

the inner membrane harbours enzymes that:

• Phospholipids 

• And proteins

The plasma membrane consists of: [2]

They lack sterols

why are bacterial plasma membranes less rigid?

Sterols in the plasma membrane

how do mycoplasma protect cells from lysis?

• Phosphate

• Glycerol

polar head is composed of: [2]

periheral

integral

two types of proteins found in plasma membranes:

Periheral

roteins on the inner or outer surface of the membrane

integral

roteins inserted into the membrane. Some are channels

Fluid mosaic model

This dynamic arrangement of phospholipids and proteins