Major Processes of Living Cells

Four Fundamental Processes

• Growth: Increase in cell size.

• Reproduction: Increase in cell number through division.

• Responsiveness: Ability to react to environmental stimuli.

• Metabolism: Controlled chemical reactions within the organism.

Example: Bacteria growing in nutrient-rich media will divide rapidly, respond to changes in temperature, and metabolize sugars for energy.

Prokaryotic vs. Eukaryotic Cells

Structural and Functional Differences

• Prokaryotic Cells:

  • 70S ribosomes (50S + 30S subunits)

  • No membrane-bound organelles

  • No nucleus; DNA in nucleoid region

  • Includes Bacteria and Archaea

• Eukaryotic Cells:

  • 80S ribosomes (60S + 40S subunits)

  • Membrane-bound organelles (e.g., mitochondria, ER)

  • Membrane-bound nucleus

  • Includes plants, animals, algae, protozoa, fungi

Comparison Table:

Glycocalyces in Bacteria

Types and Relevance to Human Health

• Capsule: Organized, firmly attached layer of repeating organic chemicals; protects bacteria from host immune recognition.

• Slime Layer: Loosely attached, water-soluble layer; aids in adherence to surfaces and biofilm formation.

Example: Streptococcus pneumoniae uses its capsule to evade phagocytosis.

Flagella Structure and Function

Bacterial vs. Eukaryotic Flagella

• Bacterial Flagella: Composed of filament, hook, and basal body; rotates for movement; axial filaments in spirochetes.

• Eukaryotic Flagella: Composed of microtubules (tubulin); anchored by basal body; undulates rather than rotates.

Example: Escherichia coli moves using peritrichous flagella.

Flagellar Arrangements in Bacteria

• Monotrichous: Single flagellum at one end.

• Lophotrichous: Tuft of flagella at one end.

• Amphitrichous: One or more flagella at both ends.

• Peritrichous: Flagella distributed over the entire cell surface.

Fimbriae, Pili, and Flagella

Structural and Functional Differences

• Fimbriae: Short, bristle-like; adherence to surfaces and other cells.

• Pili: Longer than fimbriae, shorter than flagella; involved in DNA transfer (conjugation).

• Flagella: Longest; used for motility.

Bacterial Cell Shapes

• Coccus: Spherical

• Bacillus: Rod-shaped

• Spirochete: Spiral-shaped

Peptidoglycan Structure

Chemical Composition

• Composed of alternating sugars: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)

• Cross-linked by short peptide chains

Gram-Positive vs. Gram-Negative Cell Walls

• Gram-Positive: Thick peptidoglycan, teichoic and lipoteichoic acids, stains purple.

• Gram-Negative: Thin peptidoglycan, outer membrane with lipopolysaccharide (LPS), Lipid A is toxic, stains pink.

Acid-Fast Bacteria

• Contain up to 60% mycolic acid in cell wall

• Resistant to desiccation and many chemicals

Cytoplasmic Membrane Structure and Function

• Phospholipid bilayer

• Semi-permeable; controls entry and exit of substances

• Involved in diffusion, facilitated diffusion, osmosis, active transport, group translocation

Transport Mechanisms

Passive Transport

• Diffusion: Movement of small, lipid-soluble molecules down concentration gradient

• Facilitated Diffusion: Movement via nonspecific or specific protein channels

• Osmosis: Diffusion of water through membrane or aquaporins

Active Transport

• Active Transport: Uses energy (ATP) to move substances against gradient via protein pumps (uniport, symport, antiport)

• Group Translocation: Substance is chemically modified during transport (e.g., glucose phosphorylation)

Osmosis and Cell Responses

• Isotonic Solution: No net water movement

• Hypertonic Solution: Water leaves cell; cell shrinks (plasmolysis)

• Hypotonic Solution: Water enters cell; cell may burst (lysis)

Bacterial Cytoplasm

• Mostly water (cytosol)

• Contains nucleoid (DNA region) and reserve deposits (inclusions)

Endospore Formation and Significance

• Formed in response to unfavorable conditions

• Highly resistant to heat, desiccation, chemicals

• Protected by multiple layers including spore coat

Ribosomes and Cytoskeleton

• Ribosomes: Sites of protein synthesis; composed of rRNA and proteins

• Cytoskeleton: Protein fibers involved in cell shape, division, DNA segregation, and movement

Eukaryotic Organelles

• Non-membranous: Ribosomes, cytoskeleton, centrioles

• Membranous: Nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, chloroplasts (in plants/algae)

Endosymbiotic Theory

• Eukaryotes originated from symbiotic relationships between larger and smaller prokaryotes

• Smaller aerobic prokaryotes became mitochondria; photosynthetic prokaryotes became chloroplasts

Microscopy and Staining

Key Terms and Conversions

• Magnification: Enlargement of an image

• Resolution: Ability to distinguish two close points

• Numerical Aperture: Lens's ability to gather light

• Contrast: Difference between specimen and background

Light vs. Electron Microscopes

Smears and Fixation

• Smear: Spreading specimen on slide

• Fixation: Heat or chemicals used to adhere and preserve cells

Staining Methods

• Simple Stain: Single dye (e.g., crystal violet); reveals size, shape, arrangement

• Differential Stain: Multiple dyes; distinguishes cell types/structures (e.g., Gram, acid-fast, endospore stains)

• Gram Stain Steps: Crystal violet → iodine → alcohol/acetone → safranin

• Acid-Fast Stain: Carbol fuchsin → alcohol → methylene blue

• Endospore Stain: Malachite green → water → safranin

Taxonomy and Classification

• Hierarchy: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

• Three Domains: Bacteria, Archaea, Eukarya

Identification Methods

• Physical Characteristics: Morphology

• Biochemical Testing: Metabolic capabilities

• Serological Testing: Antibody reactions

• Phage Typing: Susceptibility to bacteriophages

• Nucleic Acid Analysis: DNA/RNA sequencing

Dichotomous Key

• Series of paired statements guiding identification

Microbial Metabolism

Catabolism vs. Anabolism

• Catabolism: Breakdown of large molecules; exergonic (releases energy)

• Anabolism: Synthesis of large molecules; endergonic (requires energy)

Oxidation-Reduction Reactions

• Electron transfer between donor and acceptor

• Carrier molecules: NAD+, NADP+, FAD

ATP Phosphorylation Types

• Substrate-Level: Direct transfer of phosphate to ADP

• Oxidative: Uses energy from redox reactions

• Photophosphorylation: Uses light energy

Enzyme Types and Functions

Enzyme Structure and Function

• Enzyme: Biological catalyst

• Apoenzyme: Inactive protein portion

• Holoenzyme: Apoenzyme + cofactors (inorganic ions or organic coenzymes)

• Active Site: Region where substrate binds

• Substrate: Molecule acted upon by enzyme

Factors Affecting Enzyme Activity

• Temperature: High temperatures can denature enzymes

• pH: Extreme pH can denature enzymes

• Substrate Concentration: Activity increases with substrate until saturation

• Competitive Inhibition: Inhibitor binds active site

• Noncompetitive Inhibition: Inhibitor binds allosteric site, changing enzyme shape

Aerobic Respiration Phases

• Glycolysis: Cytoplasm; glucose → 2 pyruvate; substrate-level phosphorylation

• Pyruvate Oxidation: Cytosol (prokaryotes), mitochondria (eukaryotes); pyruvate → acetyl-CoA + CO2

• Krebs Cycle: Cytosol (prokaryotes), mitochondria (eukaryotes); acetyl-CoA → CO2, NADH, FADH2

• Electron Transport Chain: Membrane; electrons transferred, proton gradient formed, ATP produced

Equation for Aerobic Respiration:

Aerobic vs. Anaerobic Respiration

• Aerobic: Oxygen is final electron acceptor

• Anaerobic: Inorganic molecule (not O2) is final electron acceptor

Fermentation

• Occurs when respiration is not possible

• Organic molecule is final electron acceptor

• Produces less ATP than respiration

• Primary types: Beta oxidation and deamination

Alternative Pathways

• Entner-Doudoroff (ED): Only in prokaryotes; yields 1 ATP, 1 NADH, 1 NADPH

• Pentose Phosphate Pathway: Produces NADPH, precursor metabolites; less ATP than glycolysis

• Embden-Meyerhof-Parnas (EMP): Classic glycolysis; yields 2 ATP, 2 pyruvate

Microbial Growth and Nutrition

Essential Elements

• Carbon: Autotrophs (CO2), Heterotrophs (organic compounds)

• Hydrogen: Involved in energy generation

• Oxygen: Essential for aerobes, toxic for obligate anaerobes

• Nitrogen: Needed for amino acids, nucleotides; nitrogen fixation is crucial

• Trace Elements: Required in small amounts

• Vitamins: Growth factors, coenzymes

Organism Classification by Energy and Carbon Source

Oxygen Toxicity and Protection

• Reactive oxygen species (ROS) can damage cells

• Bacteria use antioxidants (e.g., vitamins C and E) and enzymes (e.g., catalase, superoxide dismutase) for protection

Environmental Factors Affecting Growth

• Temperature: Affects protein structure and membrane fluidity

• pH: Neutrophiles (neutral), acidophiles (acidic), alkalinophiles (alkaline)

• Osmotic Pressure: Halophiles tolerate high salt

• Hydrostatic Pressure: Barophiles live under high pressure

Biofilm Formation and Quorum Sensing

• Microbes attach to surfaces, produce extracellular matrix

• Quorum sensing molecules trigger changes in gene expression and behavior

• Channels form for nutrient flow; some cells disperse

Clinical Sample Collection

• Skin: Sterile swab

• Respiratory: Sputum collection

• Reproductive: Sterile swab

• Urinary: Catheter or midstream collection

Microbial Isolation and Culture Media

• Isolation Methods: Streak plate (isolation), pour plate (isolation and enumeration)

• Culture Media Types:

  • Defined (synthetic): Known composition

  • Complex: Unknown composition, supports diverse microbes

  • Selective: Favors/inhibits specific microbes

  • Differential: Visible changes to distinguish microbes

Preservation of Cultures

• Refrigeration: Short-term

• Deep-freezing: Years

• Lyophilization: Decades

Binary Fission and Bacterial Growth

• One cell divides into two; exponential (logarithmic) growth

• Generation Time: Time for one cell to divide

Growth Equation:

Where = number of cells at time t, = initial number of cells, = number of generations

Bacterial Growth Curve Phases

• Lag Phase: Adaptation, no division

• Log (Exponential) Phase: Rapid division

• Stationary Phase: Nutrient depletion, growth rate = death rate

• Death (Decline) Phase: Cells die faster than they divide

Chemostat

• Open system; continuous addition of fresh medium and removal of old

• Maintains constant growth rate and cell density

Methods for Counting Bacteria

Additional info: Some details (e.g., specific enzyme names, advanced microscopy types) were inferred for completeness and clarity.