Chapter 3 Flashcards
Cell Envelope
The layers surrounding the contents of the cell:
- Glycocalyx
- Cell Wall
- Cell Membrane
Glycocalyx
A slimy substance that adheres to the outside of the cell wall:
- Protects the cell from dehydration
- Allows bacteria to attach to tissue, which can then be invaded
- Protection against phagocytosis by white blood cells, increasing survival rate
- Retards the staining process
Capsule
A distinct thick gelatinous material that surrounds some types of microorganisms; sometimes required for an organism to cause disease; type of glycocalyx
Slime Layer
Type of glycocalyx that is diffuse (thin) and irregular
Mycoplasma
Genus of bacteria that lack cell walls; pump ions (Na+) out of the cell to keep turgor pressure equal inside and outside - prevents lysis; cell membranes strengthened by cholesterol
Cell Wall
A rigid structure that maintains cell shape and provides protection from the environment (e.g., low levels of heat, chemicals); provides protection from osmotic pressure
Lysis
The swelling and bursting of a cell
Penicillin
Antibiotic that interferes with the synthesis of the peptidoglycan portion of bacterial cell walls; binds to and inactivates the enzymes responsible for resealing breaks in the cell wall, causing lysis
Lysozyme
An enzyme found in tears that digests (breaks down) peptidoglycan
Gram-Positive Cell Wall
Thick, homogenous sheath of petidoglycan (20-80 nm thick) that forms about 90% of the cell wall; retain crystal violet stain (purple)
Peptidoglycan
Macromolecule found only in bacteria that provides strength to the bacterial cell wall; composed of alternating glycan molecules and tetrapeptide chains (4 amino acids long); contains teichoic acid
Glycan Molecules
A simple sugar (glucose) connected to an amino acid (amino sugar)
- NAG (N-acetylglucosamine)
- NAM (N-acetylmuramic acid)
- Forms a mesh-like structure
- Alternating sugars form numerous layers (up to 30 layers thick)
Tetrapeptide Chain
Each layer of carbohydrates are connected by amino acids or peptides (NAM); exact amino acids vary between species (Gram+ cells)
Teichoic Acid
A complex molecule that contains amino acids, sugars, glycerol, and phosphate molecules; used as structural material; travels from the cell membrane through the cell wall, connecting them (Gram+ cells)
Gram-Negative Cell Wall
Thin layer of peptidoglycan (1 layer thick, 5-20% of cell wall) surrounded by an outer membrane; 2 layers - periplasmic space and outer membrane; stain pink
Periplasmic Space
A region between the cell membrane (inner) and the outer membrane in Gram-negative bacterial cells
Periplasm
Gel-like material that fills the periplasmic space
Outer Membrane
Bilayer of Gram-negative cells that surrounds the peptidoglycan layer:
- Layer of phospholipids and macromolecules which serves as a selective barrier for some small molecules to pass
- Layer of Lipopolysaccharides (LPS) which forms the outer sheath of the membrane
Lipopolysaccharide (LPS) or Endotoxins
A molecule formed by bonding lipid to polysaccharide; can be toxic to the human body; different types can be used to identify different strains or species of bacteria
Porin Proteins
Proteins embedded in the outer membrane that allow specific molecules to pass and will shut off when the cell is threatened; makes antimicrobial agents less effective against Gram-negative bacteria
Cell Membrane
Serves as a barrier to molecules (selectively permeable); composed of a phospholipid bilayer (40%) with proteins (60%) embedded in the bilayer; hydrophobic fatty acid tails and hydrophillic phosphate heads
Carrier Protein
Bind to specific substances and transport them across the cell membrane
Channel Protein
Opening which allows small, water soluble substances to go across the cell membrane
Selectively Permeable Membrane
Prevents the entrance or exit of certain molecules (large molecules, molecules not soluble in fat, except for water)
Enzymes Embedded Within the Cell Membrane
Help with:
- Anabolic chemical reactions, including the synthesis of cell wall and appendages
- Catabolic pathways, such as electron transport chain (produces ATP)
Flagella
Long (1-70 nm), thin (20 nm), rigid hair-like appendages composed of protein that must be specifically stained to be seen with a light microscope; rotate 360 degrees at nearly 2000 rpm, causing the cell to slowly spin in the opposite direction providing movement (10X length in a second); important in causing disease
Composition of Flagella
- Filament: the long, tube-like structure
- Hook: where the filament is inserted into
- Two rings: Hook inserted here, provides the anchor for the filament and the hook has one ring attached to the cell membrane and the other to the cell wall
Flagella Arrangements
- None
- Monotrichous (polar flagellation): single flagellum at one end of the cell
- Amphitrichous: single flagellum at each end
- Lophotrichous: a tuft of many flagella at one end
- Peritrichous: flagella located on many sides of the bacterial cell (peri = “around”)
- Present in: all spirilla, half of the bacilli, and few coccus
Appendages for Attachment
Hair-like structures that extend from the cell wall in all directions, but are not used for locomotion; fimbriae and pilus
Fimbriae
Short, but numerous tubes composed of protein that have a tendency to stick to surfaces; adhere to epithelial cells, allowing the cells to invade the tissues (E. coli in the intestines)
Pilus
Long, less numerous, hollow, tubular structures found in gram negative bacteria and some gram positive bacteria; links the cytoplasm of one bacteria with the cytoplasm of another bacteria of the same species; used to exchange plasmids (conjugation)
Bacterial Chromosome
A single, double-stranded, circular piece of DNA containing genes that code for cell maintenance and growth; contains only 3000-4000 genes (25000-32000 in humans); found in the nuclear region of a bacterial cell; attached to the cell membrane
Plasmids
Very small, circular pieces of DNA that are not essential for bacterial growth and cell maintenance; free-floating and not attached to the cell membrane but can incorporate themselves into a bacterial chromosome on occasion
Plasmid Functions
Can provide information that can be helpful to survival, but not essential:
- Resistance to drugs
- Production of toxins
- Production of enzymes
Often transferred to other bacterial cells by conjugation to convey additional resistance
70S Ribosome
Used in protein synthesis; only true organelle found within prokaryotic cells (15000 in protoplasm); ribosomal RNA (rRNA) - 60%, proteins - (40%)
Ribosomal Subunits
Two subunits (S are Svedberg units which weigh molecular units, the higher the value the heavier the unit):
- Bacterial cells: 30S and 50S subunits
- Eukaryotic cells: 40S and 60S subunits
Cytoplasmic Inclusions
Small, membrane bound structures that will contain various substances:
- energy-rich organic substances (glycogen), which are produced in times of plenty and used when the environment is low in energy sources
- gases used in buoyancy and floatation (aquatic systems only)
Granules
Areas within a cell that contain inorganic crystals, but are not membrane bound; store important resources that are essential elements (sulfur, phosphate) in building macromolecules
Endospores
A small, protected, dormant bacteria that will germinate under favorable growth conditions into a new bacterial cell, genetically identical to the cell that produced it:
- only produced by some gram positive rods (Bacillus and Clostridium)
- produced when condition become unfavorable for further bacterial growth and survival is in question (loss of nutrient source, drying of environment)
- produced for survival, not reproduction
- energetically costly
3 Layers of an Endospore
- Spore Coat: outer layer that provides a nearly impervious barrier to many chemicals
- Cortex: Middle layer that contains many calcium salts and dipicolinic acid; keeps core very dry to prevent water from reaching it
- Core: Innermost layer that contains the bacterial chromosome (DNA)
Resistance of Endospores
Very resistant to environmental extremes:
- High temperatures
- Desiccation
- Chemicals and radiation
- Nearly ensures immortality
- Once favorable conditions are sensed, can quickly (1.5 hours) germinate into a bacterial cell
Bacterial Shapes
Vary greatly depending on the cell wall composition and nutritional state or slight differences in genes:
- coccus: sperical
- bacillus: rod
- spirillus: spiral
Bacterial Arrangements
Ways bacteria are found due to cell division and how they stick together after they divide; always to the bacteria by its largest possible:
- di: two
- strep: long chains
- staph: irregular clusters
Coccus Arrangements
- Single cell
- Diplococcus
- Tetrad: clusters of four
- Streptococcus
- Staphylococcus
- Sarcina: clusters of 8, 16, 32 or more cells in a perfect cube shape
Bacillus Arrangements
- Single cell
- Diplobacillus: joined end-on-end
- Streptobacillus: long end-on-end chains
- Palisades: side-by-side arrangement
Spirillus Arrangements
Rarely found in any arrangement but a single cell (can be found in short chains)
