Bacterial Cell Structures and Membrane Functions: A Study Guide

What is the glycocalyx in bacteria?

A gelatinous layer surrounding the cell wall that aids in biofilm formation, increased virulence, and protection against dehydration.

What is the primary function of the bacterial cell wall?

To prevent osmotic lysis and protect the cell membrane.

What is peptidoglycan?

A polymer consisting of repeating disaccharides (N-acetylglucosamine and N-acetylmuramic acid) linked by polypeptides, forming a lattice structure in bacterial cell walls.

What distinguishes gram-positive bacteria from gram-negative bacteria?

Gram-positive bacteria have thick peptidoglycan layers and teichoic acids, while gram-negative bacteria have thin peptidoglycan layers and an outer membrane containing lipopolysaccharides.

What is the role of teichoic acids in gram-positive bacteria?

Teichoic acids link the cell wall to the plasma membrane and help regulate the movement of cations.

What is the periplasmic space?

The space between the outer membrane and the plasma membrane in gram-negative bacteria that contains peptidoglycan.

What is the function of lipopolysaccharides (LPS) in gram-negative bacteria?

LPS serves as an antigen and can act as an endotoxin, contributing to the bacteria's pathogenicity.

What happens during the Gram stain process to gram-positive bacteria?

Alcohol dehydrates the peptidoglycan, preventing the crystal violet-iodine complex from leaving the cell, thus retaining the purple color.

What are protoplasts?

Wall-less gram-positive cells that are susceptible to osmotic lysis.

What are spheroplasts?

Wall-less gram-negative cells that are also susceptible to osmotic lysis.

What is the fluid mosaic model?

A model describing the plasma membrane as a flexible structure with proteins and lipids that can move laterally within the layer.

What is the function of the plasma membrane?

To provide selective permeability, allowing certain molecules to pass while keeping others out, and to house enzymes for ATP production.

What are chromatophores?

Foldings in some bacterial membranes that contain photosynthetic pigments.

What is the effect of penicillin on bacterial cells?

Penicillin inhibits the formation of peptide cross-bridges in peptidoglycan, weakening the cell wall.

What is the significance of mycoplasmas?

Mycoplasmas lack cell walls and have sterols in their plasma membrane, which may protect them from lysis.

What are acid-fast bacteria?

Bacteria with thick peptidoglycan and a waxy lipid (mycolic acid) that resist decolorization by acid-alcohol during staining.

What is the role of lysozyme?

Lysozyme hydrolyzes bonds in the glycan portion of peptidoglycan, weakening the cell wall of gram-positive bacteria.

What is the difference between exotoxins and endotoxins?

Exotoxins are secreted by bacteria and can cause damage to the host, while endotoxins are part of the outer membrane of gram-negative bacteria and can trigger immune responses.

What is the role of peripheral proteins in the plasma membrane?

Peripheral proteins are located on the inner or outer surface of the plasma membrane and play various roles in signaling and structural support.

What is the significance of the outer membrane in gram-negative bacteria?

The outer membrane protects against phagocytes, complement, and antibiotics, and contains porins that allow the passage of certain molecules.

What are L forms?

Wall-less cells that can swell into irregular shapes and are susceptible to osmotic lysis.

What is the function of porins in gram-negative bacteria?

Porins are proteins that form channels through the outer membrane, allowing the passage of small molecules.

What is the action of alcohol in the Gram staining process for gram-negative bacteria?

Alcohol dissolves the outer membrane and creates holes in the peptidoglycan, allowing the crystal violet-iodine complex to wash out, resulting in colorless cells.

What is the role of antibiotics like polymyxin?

Polymyxin damages the plasma membrane of bacteria, causing leakage of cell contents.

What are spheroplasts, protoplasts, and mycoplasms?

Bacterial cells without cell walls.

What is simple diffusion?

The movement of a solute from an area of high concentration to an area of low concentration until equilibrium is reached.

What is facilitated diffusion?

The process where integral membrane proteins assist in the movement of ions or larger molecules across the membrane along the concentration gradient.

What is osmosis?

The net movement of water across a selectively permeable membrane from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration).

What is active transport?

The movement of substances against their concentration gradient (from lower to higher concentration) using energy, typically in the form of ATP.

What is group translocation?

A process that requires a transporter protein and phosphoenolpyruvic acid (PEP), where the substance is altered as it crosses the membrane.

What is the function of the nucleoid?

It contains the bacterial chromosome, which is a circular thread of double-stranded DNA that holds the cell's genetic information.

What are ribosomes?

Cellular structures made of protein and ribosomal RNA, serving as the site of protein synthesis.

What are inclusions in bacterial cells?

Reserve deposits of nutrients, such as metachromatic granules, polysaccharide granules, lipid inclusions, and sulfur granules.

What are endospores?

Resting cells produced by certain bacteria when nutrients are depleted, resistant to harsh conditions, and can survive for thousands of years.

What is sporulation?

The process of endospore formation in bacteria.

What is germination?

The process by which an endospore returns to its vegetative state.

What is osmotic pressure?

The pressure required to stop the net movement of water across a selectively permeable membrane.

What is an isotonic solution?

A solution where solute concentrations are equal inside and outside the cell, resulting in no net movement of water.

What is a hypotonic solution?

A solution where solute concentration is lower outside than inside the cell, causing water to move into the cell.

What is a hypertonic solution?

A solution where solute concentration is higher outside the cell than inside, leading to water moving out of the cell.

What is the plasma membrane's function?

It provides selective permeability, allowing certain molecules to pass while containing enzymes for ATP production.

What are some antimicrobial agents that damage the plasma membrane?

Alcohols, quaternary ammonium compounds (detergents), and antibiotics like polymyxin.

What is the cytoplasm?

The thick, aqueous, elastic substance inside the plasma membrane, consisting of water, proteins, carbohydrates, lipids, and ions.

What are plasmids?

Small, extrachromosomal circles of DNA that carry noncrucial genes and replicate independently of the bacterial chromosome.

What is the significance of ribosomal subunits in prokaryotes?

Prokaryotic ribosomes are composed of 70S subunits, which include a 50S large subunit and a 30S small subunit.

What are metachromatic granules?

Inclusions that serve as phosphate reserves in bacterial cells.

What are gas vacuoles?

Protein-covered cylinders in bacteria that help maintain buoyancy.

What are magnetosomes?

Iron oxide inclusions in bacteria that help destroy hydrogen peroxide.

What is the role of the cytoskeleton in bacterial cells?

It consists of fibers that participate in cell division, maintaining cell shape, growth, and DNA movement.