Prokaryotic and Eukaryotic Cell Structure, Function, and Metabolism: Study Guide

Overview of Cell Types and Structure

Unicellular vs. Multicellular Organisms

Organisms can be classified based on the number of cells they possess:

• Unicellular: Consist of a single cell (e.g., most bacteria, archaea, some protists).

• Multicellular: Composed of multiple cells (e.g., plants, animals, fungi).

Cell Theory

Cell theory is a foundational concept in biology, stating:

• All living organisms are composed of cells.

• The cell is the smallest unit capable of life.

• All cells arise from pre-existing cells (rejecting spontaneous generation).

Basic Functions of Cells

• Growth

• Maintenance

• Reproduction

• Waste removal

• Respiration

Structural Components of All Cells

• Plasma membrane

• Cytoplasm

• DNA

• Ribosomes

Types of Cells

• Prokaryotic: Cells without a nucleus (e.g., bacteria, archaea).

• Eukaryotic: Cells with a nucleus (e.g., plants, animals, fungi, protists).

Prokaryotic Cells

Types of Prokaryotes

• Archaea

• Bacteria

Archaea and bacteria are both prokaryotes but have significant differences in their cell wall composition, membrane lipids, and genetic machinery.

Cell Morphology

• Common Shapes:

  • Coccus (spherical)

  • Bacillus (rod-shaped)

  • Spirillum (spiral-shaped)

  • Other arrangements: Strepto- (chains), Staphylo- (clusters), Tetrad (groups of four), Sarcina (cubical packets)

Cell Arrangements

Arrangement is determined by the pattern of cell division and whether cells remain attached after division.

External Structures

• Capsules and Slime Layers:

  • Capsules: Organized, tightly bound layers outside the cell wall; not present in all bacteria.

  • Slime layers: Loosely attached, unorganized layers.

  • Functions: Protection from desiccation, phagocytosis, and can aid in adherence to surfaces.

  • Role in biofilms: Capsules and slime layers help bacteria form biofilms, which are communities of microorganisms attached to surfaces.

• Flagella:

  • Long, whip-like appendages used for motility.

  • Arrangements: Monotrichous (single), Lophotrichous (tuft at one end), Amphitrichous (one at each end), Peritrichous (all over surface).

  • Movement: Flagella rotate to propel the cell (taxis).

• Pili and Fimbriae:

  • Pili: Longer, involved in conjugation (DNA transfer).

  • Fimbriae: Shorter, used for attachment to surfaces.

Cell Wall Structure

• Gram-Positive Bacteria:

  • Thick peptidoglycan layer

  • Teichoic acids present

  • Stain purple in Gram stain

• Gram-Negative Bacteria:

  • Thin peptidoglycan layer

  • Outer membrane containing lipopolysaccharide (LPS)

  • Stain pink/red in Gram stain

• Atypical Cell Walls:

  • Mycoplasma: Lack cell walls

  • Archaea: May lack peptidoglycan; have unique cell wall components

Table: Comparison of Gram-Positive and Gram-Negative Cell Walls

Feature	Gram-Positive	Gram-Negative
Peptidoglycan Thickness	Thick	Thin
Teichoic Acids	Present	Absent
Outer Membrane	Absent	Present (contains LPS)
Gram Stain Color	Purple	Pink/Red

Internal Structures

• Cytoplasm: Gel-like matrix inside the cell.

• Nucleoid: Region containing the bacterial chromosome (not membrane-bound).

• Ribosomes: Sites of protein synthesis; prokaryotic ribosomes are 70S (composed of 50S and 30S subunits).

• Inclusions: Storage granules for nutrients, gases, or other substances.

• Endospores: Highly resistant, dormant structures formed by some bacteria (e.g., Bacillus, Clostridium).

Bacterial Growth and Reproduction

Binary Fission

Bacteria reproduce asexually by binary fission, a process in which a single cell divides into two identical daughter cells.

Phases of Bacterial Growth

• Lag Phase: Adaptation, little to no cell division.

• Log (Exponential) Phase: Rapid cell division and population growth.

• Stationary Phase: Growth rate slows as resources become limited; cell death equals cell division.

• Death Phase: Nutrient depletion and waste accumulation lead to cell death.

Metabolism and Enzymes

Characteristics of Enzymes

• Biological catalysts that speed up chemical reactions by lowering activation energy.

• Highly specific for their substrates.

• Affected by temperature, pH, and concentration of substrate and enzyme.

Enzyme Inhibition

• Competitive Inhibitors: Compete with substrate for active site.

• Non-competitive Inhibitors: Bind elsewhere, changing enzyme shape and function.

Metabolism

• Sum of all chemical reactions in an organism.

• Divided into catabolism (breakdown of molecules, releases energy) and anabolism (synthesis of molecules, requires energy).

ATP: The Energy Currency

• ATP (adenosine triphosphate) stores and transfers energy for cellular processes.

• ATP is generated by substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation.

Nutritional Classification of Organisms

Organisms are classified based on their energy and carbon sources:

• Energy Source:

  • Photo-: Light

  • Chemo-: Chemical compounds

• Carbon Source:

  • Auto-: CO2

  • Hetero-: Organic compounds

Examples: Photoautotrophs (e.g., cyanobacteria), Chemoheterotrophs (e.g., most bacteria, animals).

Cellular Respiration and Fermentation

ATP Production Pathways

• Aerobic Respiration: Uses oxygen as the final electron acceptor.

• Anaerobic Respiration: Uses inorganic molecules other than oxygen as the final electron acceptor.

• Fermentation: Organic molecules serve as both electron donors and acceptors; does not require oxygen.

Glycolysis

First step in glucose catabolism; occurs in the cytoplasm and produces pyruvate, ATP, and NADH.

Krebs Cycle (Citric Acid Cycle)

Series of reactions that generate ATP, NADH, and FADH2 from acetyl-CoA.

Electron Transport Chain (ETC)

Located in the plasma membrane of prokaryotes; uses electrons from NADH and FADH2 to generate ATP via oxidative phosphorylation.

Fermentation

Occurs when oxygen is absent; regenerates NAD+ for glycolysis. End products include lactic acid, ethanol, and other compounds.

Origin of Mitochondria and Chloroplasts

Mitochondria and chloroplasts are believed to have originated from endosymbiotic events, where ancestral prokaryotes were engulfed by a host cell and evolved into organelles.

• Both contain their own DNA and ribosomes.

• Replicate independently of the host cell.

• Support the endosymbiotic theory of eukaryotic evolution.

Key Terms and Definitions

• Prokaryote: Organism lacking a nucleus and membrane-bound organelles.

• Eukaryote: Organism with a nucleus and membrane-bound organelles.

• Peptidoglycan: Polymer forming the cell wall of most bacteria.

• Endospore: Dormant, resistant structure formed by some bacteria.

• Biofilm: Community of microorganisms attached to a surface.

• ATP: Adenosine triphosphate, main energy carrier in cells.

Sample Equations

• General Equation for Aerobic Respiration:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$

• ATP Hydrolysis:

$ATP + H_2O \rightarrow ADP + P_i + \text{energy}$

Summary Table: Prokaryotic vs. Eukaryotic Cells

Feature	Prokaryotic	Eukaryotic
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Cell Wall	Usually present (peptidoglycan)	Present in plants/fungi (cellulose/chitin)
Ribosome Size	70S	80S (cytoplasm), 70S (mitochondria/chloroplasts)
DNA Structure	Circular	Linear

Additional info:

• Some details, such as the specific arrangement of flagella or the full list of metabolic pathways, were inferred based on standard microbiology curricula.

• Tables and figures referenced (e.g., "Coloring Book Plate 11") are not included but their content has been summarized in the notes above.