Microbiology - Bacterial Structure and Function

Exam 1 Review

• The exam covers bacterial cell wall structure (Gram + & Gram -, "Acid fast"), bacterial cellular morphology & arrangement, components of prokaryotic and eukaryotic cells (internal & external), bacterial chemotaxis, endospores, fungi & protozoa, and taxonomy (domains & kingdoms of life).

Bacterial Cell Structure

• Prokaryotic cells are simpler than eukaryotic cells, lacking membrane-bound organelles.
• Bacterial DNA exists as a single, circular chromosome.
• Gram-positive bacteria have a thick peptidoglycan layer in their cell walls and stain purple in Gram staining.
• Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane, and stain pink in Gram staining.
• Acid-fast bacteria have a waxy outer layer, making them resistant to staining.

Bacterial Cellular Morphology & Arrangement

• Bacteria exhibit various shapes (cocci, bacilli, spiral).
• Cell arrangements also vary, forming pairs (diplococci), chains (streptococci), clusters (staphylococci), or other patterns.
• Variations in shape and size of cells within species (pleomorphism) are common depending on nutritional and genetic differences.

Prokaryotic Cell Components

• The image shows a diagram of a typical prokaryotic cell highlighting various components.
• Components include ribosomes, cytoplasm, nucleoid, glycocalyx, cell wall, and cytoplasmic membrane.
• These components play vital roles in cellular structure, function, and activities.
• Inclusions are also found in prokaryotic cells, used for storage.
• Flagella and pili allow for movement and attachment.

Eukaryotic Cell Components

• A eukaryotic cell is much more complex than a prokaryotic cell.
• The image displays a complex diagram of a eukaryotic cell, highlighting various organelles and components.
• Key components include the nucleus, containing chromatin and RNA, the nucleolus, the endoplasmic reticulum (rough and smooth), Golgi body, lysosomes, mitochondria, ribosomes, vacuole, cytoskeleton, and the cytoplasmic membrane.
• Eukaryotic DNA is linear, not circular.

Plasmids

• Plasmids are small, circular, double-stranded DNA molecules, easily manipulated in genetic engineering.
• They are not essential for bacterial growth or metabolism.
• Plasmids are replicated independently from the bacterial chromosome and often carry genes related to antibiotic resistance, tolerance to metals, or production of toxins.

Bacterial Chemotaxis

• Bacteria can move in response to chemical signals (chemotaxis).
• A bacterium's movement towards an attractant (positive chemotaxis) or away from a repellent (negative chemotaxis) involves switching between clockwise (tumbling) and counterclockwise (running) rotation of its flagella.

Endospores

• Endospores are dormant structures formed by some bacteria (mainly bacilli), serving as a survival mechanism under harsh conditions.
• They are highly resistant to heat, drying, and radiation.
• Endospores are not a reproductive mechanism; instead, they allow the cells to survive unfavourable conditions.
• Different bacterial genera form endospores, for example, Bacillus and Clostridium.

Fungi & Protozoa

• Fungi are eukaryotic organisms, including molds (filamentous) and yeasts (unicellular).
• Protozoa are unicellular eukaryotic organisms, exhibiting diverse motility methods (pseudopodia, flagella, cilia).
• Organisms belonging to these two groups are important parts of the various ecosystems.

Taxonomy

• Taxonomy is the science of classifying and naming organisms.
• The three domains of life are bacteria, archaea, and eukarya.
• Each organism is classified based on its evolutionary relationships and shared characteristics at different taxonomic levels, from domains to species.

Glycocalyx

• Glycocalyx is a sugar or protein coating external to a cell wall.
• Its primary function is for attachment, and it protects from phagocytes.
• Two forms exist: capsule (highly organized, tightly attached) and slime layer (loosely attached).

Chemotaxis

• Bacteria can move in response to chemical stimuli.
• Bacteria have mechanisms for movement (rotation of flagella).

Fimbrae & Pili

• Fimbrae are fine hair like bristles on bacterial cell surfaces for attachment and biofilm formation.
• Pili facilitate conjugation (bacterial mating)

Bacterial Mating

• Bacteria exchange genetic material (plasmids) through a process called conjugation.
• Pili are necessary for this conjugation process.

Differential Gram Staining

• Gram staining differentiates bacteria based on cell wall structure.
• A series of steps are involved to stain, decolorise, and counterstain the bacteria.