L1: Structure of Bacterial Cell And Targets of Antibiotics Flashcards
What is microbiology?
Microbiology is the study of living organisms (‘microorganisms’ or ‘microbes’); simple in structure and usually small in size (cannot be seen with the naked eye).
What does the study of microbiology include?
They include bacteria, fungi, protozoa, and viruses.
What is the importance of microbiology?
Microorganisms cause many diseases and some microorganisms have been used in the manufacture of antibiotics and foodstuffs.
What are creatures classified into?
- Animalia (Eukaryotic): helminths
- Plantae (Eukaryotic)
- Protista (Eukaryotic): Protozoa
- Fungi (Eukaryotic)
- Monera (Prokaryotic): cellulars like bacteria and acellular like a virus
What is another term for prokaryotic?
Pre-mature
What is the difference between cellular prokaryotic and eukaryotic?
Nuclear membrane: absent - present Chromosomal number: haploid - diploid Histones: absent - present Ribosome: 70s - 80s Peptidoglycan: present - absent Mitochondria: absent - present Mitosis: absent - present Cell wall sterols: absent - present Membrane-bounded organelles: absent - present
What is the size of bacterial cells?
Measured by micron (micron= 1/ 1000 mm).
What is the shape of bacterial cells?
- Cocci or spherical: e.g. Staphylococci.
- Bacilli or cylindrical: e.g. Diphtheria bacilli.
- Spiral:
One curve: e.g. Vibrio.
More than one: e.g. Spirochetes, Spirillum.
What is the habitat of bacterial cells?
a. Parasitic (need host): bacterial flora (commensally) and pathogenic bacteria.
b. Saprophytic: free-living in soil, air, and water.
What is the structure of bacterial cells?
- Surface Structures (bacterial envelope):
● Cell wall.
● Cytoplasmic membrane.
● Capsule or slime layer. - Internal structures:
- Nuclear body
- Flagellae
- Inclusion bodies
- Ribosomes
- Fimbria
- Mesosomes
What are the characters of the cell wall?
It is the rigid layer outside the cytoplasmic membrane.
What is the chemical structure of the cell wall?
Composed of peptidoglycan.
What are the Differences between Gram-positive and Gram-negative cell walls?
Peptydoglycan:
Thick (~ 40 sheets)
Comprising up to 50% of the cell wall.
Thin (One or two sheets)
Comprising only 5–10% of the cell wall.
Special Components:
Teichoicacid:ribitol or glycerol.
Polysaccharides.
- Outer membrane (thick).
Lipoprotein.
Lipopolysaccharide: o Lipid A (the endotoxin). o Polysaccharide (somatic antigen).
2- Periplasmic space
Between cytoplasmic membrane and outer
membrane and contains hydrolytic enzymes and penicillinase.
What is the function of the cell wall?
SPA GTG
- Preservation of the shape of the cell.
- Protectiveagainst high internal osmotic pressure.
- Antigenic character:
In Gram-positive: Teichoic acid.
In Gram-negative: somatic “O” antigen(Polysaccharide). - Toxicity: The lipid A endotoxin of Gram-negative cell wall.
- Cell wall is responsible for Gram staining reaction (Gram-positive bacteria stain violet while Gram-negative bacteria stain pink)
- Cell wall is the target for the action of some antibiotics: penicillin and cephalosporins and vancomycin.
What are the enzymes that attack the cell wall?
The peptidoglycan is hydrolyzed by lysozyme found in tears, saliva, and nasal secretions.
What are the characters of the cell membrane?
It is a very thin elastic membrane that lies immediately under the cell wall.
What is the chemical structure of the cell membrane?
- composed of biphospholipids and proteins.
- prokaryotes have no sterols in the cytoplasmic membrane except for Mycoplasma.
What is the function of the cell membrane?
- Permeability and transport: transport nutrients into and waste products out of the cell.
- Electron transport and oxidative phosphorylation: for energy production (ATP).
- Excretion of hydrolytic enzymes.
- Biosynthetic function: carries enzymes and molecules for the biosynthesis of the cell wall, DNA, and membrane lipids.
- Chemotactic function: contain receptors of binding and repellents.
What are the characters of the capsule?
-Some bacteria can produce a gelatinous layer surrounding the cell outside the cell wall.
Capsule: condensed well-fined layer closely surrounds the cell.
Glycocalyx: polysaccharide-containing material lying outside the cell.
Slim layer: if glycocalyx is loosely surrounding the cell.
What is the chemical structure of the capsule?
Consists of polysaccharides, except in bacillus anthracis(protein polymers).
What is the function of the capsule?
- Virulence factor as it protects the bacterial cell from phagocytosis.
- Protects the cell wall against attack by bacteriophages, complement, and lysozymes.
- Antigenic (K-antigen): used in serodiagnosis or vaccine preparation.
What is the definition of flagella?
Long thread-like, helical filaments.
What are the types of flagellate?
- Monotrichous (single polar flagellum).
- Lophotrichous (multiple polar flagellae).
- Amphitrichous (One flagellum in each pole of the
cell) . - Peritrichous (flagella distributed over the entire
cell) e.g. E.coli.
What is the structure of flagella?
made up of a contractile protein called flagellin.
What are the functions of flagella?
- It is the organ of Motility:
> Movement toward the optimal nutrients.
Movement toward optimal oxygen concentration in aerobic bacteria.
Choosing the locality suitable for colonization.
Assist pathogenic bacteria in penetration through a viscid mucous secretion.
- Highly Antigenic (H-antigens).
What is the color of gram stain in gram-positive and in gram-negative?
Positive: violet
Negative: red
What are the smallest bacteria?
Serratla marcescens
What are nuclear bodies?
- No true nuclei but nucleoid
- No nuclear membrane “prokaryotes”
- They are made of DNA.
” There is a single chromosome that can be seen by E/M very long thin thread folded on itself
What are pili (fimbrae)?
It is a short and rigid appendage formed in gram-negative bacteria
What are pili classified into?
Ordinary and sex pili
What kind of microscope is used to see pili?
EM
How do pili differ from flagella?
-Differs from flagella in the following points:
Occur in motile as well as non-motile strains
> More numerous “100-500” per cell.
> Much shorter and thinner.
more or less straight, flagella are spiral.
> Not originated from the cytoplasm.
What is the function of pili?
- Ordinary pili: adhesion to host cells, and to each other
2 Sex pili: attachment of donor and recipient cells in bacterial conjugation - Antigenic.
- Like capsule, inhibit phagocytosis.
- Ordinary pili are responsible for virulence (colonization Ag, surface virulent-factor
