A detailed functional anatomy of prokaryotic cells and eukaryotic cells in microbiology detail anatomy including structure and function

1. Functional Anatomy of
Prokaryotic and Eukaryotic Cells

2. • General Characteristics:
– Complex, semirigid structure that lies outside
the plasma membrane in almost all bacteria
• Two major functions:
– Maintains characteristic shape of bacteria
– Prevents the cell from bursting when fluids flow
into the cell by osmosis
• Role in bacterial ability to cause disease
• Site of action of some antibiotics
• Very porous and does not regulate passage
of materials into the cell
• Used to differentiate major types of bacteria
The Cell Wall

3. • Peptidoglycan (Murein):
– Made up of a repeating disaccharide
attached by polypeptides to form a lattice.
– Peptidoglycan is one immense covalently
linked molecule, resembling multiple layers
of chain link fence.
• Disaccharide component:
– Made up of two monosaccharides:
• N-acetylglucosamine (NAG)
• N-acetylmuramic acid (NAM)
• Alternating disaccharides (NAG-NAM) are
linked together in rows of 10 to 65 molecules.
The Cell Wall (Composition)

4. Peptidoglycan (Murein):
–Adjacent disaccharide rows are
linked by tetrapeptide
– Parallel tetrapeptide side
chains may be directly linked
together or linked by a
polypeptide cross-bridge.
– Penicillin interferes with the
final linking of peptidoglycan
rows by peptide cross bridges.
The Cell Wall (Composition) Cont.

5. Gram-Positive Cell Wall
• Consist of several layers of peptidoglycan, which form a thick,
rigid structure (20-80 nm).
• Also contain teichoic acids, which are made up of an alcohol
and a phosphate group. Two types:
– Lipoteichoic acids: Span cell wall, linked to cell membrane.
– Wall teichoic acids: Linked to peptidoglycan layer.
• Teichoic acids are negatively charged and:
– Bind to and regulate movement of cations into cell.
– Regulate cell growth and prevent cell lysis.
– Can be used to identify bacteria.

6. Gram-Negative Cell Wall
• Cell wall is thinner, more complex and more susceptible to mechanical
breakage than that of Gram-positive bacteria.
• One or a few peptidoglycan layers and an outer membrane.
• Peptidoglycan is bonded to lipoproteins in:
– Outer membrane
– Periplasmic space:
• Region between outer membrane and plasma membrane.
• Periplasmic space contains degradative enzymes and transport proteins.

7. Gram-Negative Cell Wall
• Outer Membrane (OM) consists of:
– Phospholipid bilayer
– Lipopolysaccharides (LPS) with two components:
• O polysaccharides: Antigens, used to identify bacteria.
• Lipid A: Endotoxin causes fever and shock.
– Porins: Membrane proteins that allow the passage of nucleotides,
disaccharides, peptides, amino acids, vitamins, and iron.
– Lipoproteins
• Functions of Outer Membrane:
– Evade phagocytosis and complement due to strong negative charge.
– Barrier to antibiotics (penicillin), digestive enzymes (lysozyme),
detergents, heavy metals, dyes, and bile salts.

8. Gram-positive Vs Gram-Negative bacteria

9. Gram-positive Vs Gram-Negative bacteria

10. Gram-positive Vs Gram-Negative bacteria

11. Atypical Cell Wall (Acid-Fast Bacteria)
• Cell wall is thick like that of Gram-positive bacteria.
• Contains 60% lipids and much less peptidoglycan.
• Has a waxy consistency.
• Lipids make cells impermeable to many stains, and protect them
from acids, alkalis, and antibiotics.
• Organisms grow slowly because nutrients penetrate inefficiently
and cells spend a lot of energy making lipids.
• Stain as Gram-positive.

12. Atypical Cell Wall (Acid-Fast Bacteria)

13. Atypical Cell Wall (Mycoplasma & Archaebacteria)
Mycoplasma:
– Smallest known bacteria that can grow & reproduce
outside of host cells
– They have no cell wall.
– Pass through most bacterial filters.
– Originally mistaken for viruses.
– Unique plasma membrane contains lipids called
sterols, which protect them from osmotic lysis.
Archaebacteria:
– May lack cell walls or have cell walls without
peptidoglycan
– Instead of peptidoglycan, may have pseudomurein

14. Damage to the Cell Wall
• Bacterial cell wall is made of chemicals unlike those in eukaryotic cells, so:
– Chemicals that damage bacterial cell walls, or interfere with their synthesis, often do not harm the
cells of an animal host
• Cell wall synthesis is the target for some antimicrobial drugs
– Exposure to the digestive enzyme lysozyme
– Present in eukaryotic cells: normal constituent of perspiration, tears, mucus, and saliva
– Active on the major cell wall components of most Gram-positive bacteria
• PROTOPLAST: The wall-less cell whose cellular contents remain surrounded by the
plasma membrane may remain intact if lysis does not occur.
• SPHEROPLAST: Cellular contents, PM, and remaining outer cell wall layer of Gram-Neg.
• Most Gram-negative bacteria are not as prone to penicillin as Gram-positive bacteria
• Because, outer membrane of Gram-negative bacteria forms a barrier