Bacterial Structures & Morphology Flashcards
Explain the major structures of a bacterial cell and their functions
Cell wall: protection
Nucleoid: section that has the chromosome
no membrane-bound organelles: (can use plasma membrane instead of mitochondria to make ATP/energy)
Ribosomes: 70S (80S in eukaryotes)
Describe the Gram stain procedure
1) crystal violet (gram positive)
2) gram iodine –> fixing step
3) decolorizer (alcohol or acetone)
4) safranin red (gram negative)
Discuss the cell wall structure and chemical components of Gram-positive and Gram-negative bacteria
Gram positive: lysine used for cross-linking to penultimate D-alanine of adjacent peptide; use amino acid bridge; peptidoglycan layer is 3-D
Gram negative: DAP used for cross-linking to penultimate D-alanine of adjacent peptide; peptidoglycan layer is 1 molecule thick
Differentiate Gram-positive and Gram-negative cell walls and their chemical components
Gram positive: lipoteichoic acids transverse cell wall and anchor in membrane; inner membrane is lipid bilayer with integral proteins
Gram negatve: outer membrane bottom leaflet is made up of phospholipid and top layer is made up entirely of lipopolysaccharides – O antigens (outside) and lipid A (anchor); inner membrane is lipid bilayer with integral proteins
Identify bacterial capsule, flagellar arrangement, and endospore position under the light microscope
(practice)
Describe bacterial shapes
- coccus: round
- Bacillus: rod-shaped
- Coccobacillus: round oval
- fusiform bacillus: long oval
- vibrio: curved
- spirillium: wavy, spiral-like
- spirochete: spiral with flagella
Endospore function
- found in Bacillus and Clostridium
- bacterial genome wrapped in thick coat
- dormant form like fungal spores, but not reproductive
- survive harsh environments for years
- induced by harsh conditions
- resist dessication, UV, heat, chemical disinfectants
How do you identify the species from an endospore?
- round or oval
- terminal, subterminal, or central
Somatic pilli function
adhesion to cells
Sex pilli function
hollow tube for sharing genes (conjugation)
Flagella function
- run and tumble
- rotate counterclockwise for movement
- clockwise to tumble
- runs on proton gradient at proton motor
Contrast Spirillum and Spirochete
Spirillum: use flagella for movement, spiral shaped
Spirochete: use internal flagella for movement, wavy (looks like an asterik head on)
What enzyme catalyzes cross-linking?
transpeptidase/penicillin-binding protein
How is cross-linking inhibited?
- B-lactams
- bind penicillin-binding protein
- resemble transition state of reaction
- leads to compromising cell wall structure
What do autolysins do?
remodel cell wall – there is constant turnover
What’s the importance of O antigens?
identify species and strains
Importance of periplasmic space
contain peptidoglycan and enzymes to destroy antibiotics
How does the outer membrane of gram-negative bacteria help protect against disinfectants or antibiotics?
porin proteins channel chemicals into the cell
Describe bacterial arrangements
strepto: chain
staphylo: clusters
diplo: 2
tetrads: 4
sarcinae: 8 (cube-shaped)
Steps of cell wall biosynthesis
1) UDP NAM and NAG are synthesized
2) amino acids added to UDP NAM to form NAM-pentapeptide
3) NAM-pentapeptide transferred to bactoprenol phosphate to generate Lipid I (joined by pyrophosphate bond)
4) UDP transfers NAG to Lipid I to make Lipid II
5) flippase flips Lipid II across the membrane
6) increase Lipid II length by attaching to end of growing peptidoglycan chain
7) bactoprenol-p leaves to other side of membrane to start cycle again (vancomycin can inhibit here)
8) transpeptidation forms peptide cross links between peptidoglycans
