Cellular Energetics and Structure: Study Guide for Cell Biology Exam 1

Overview to Cellular Energetics

Cell Theory

The cell theory is a fundamental concept in biology, stating that all living organisms are composed of cells, cells are the basic unit of life, and all cells arise from pre-existing cells.

• Key Points:

  • All organisms are made of one or more cells.

  • The cell is the basic structural and functional unit of life.

  • Cells arise only from pre-existing cells by division.

Macromolecules of the Cell

Types of Macromolecules

Cells contain four major types of macromolecules: proteins, nucleic acids, polysaccharides (carbohydrates), and lipids. Each is built from specific monomers and linked by characteristic bonds.

• Proteins: Polymers of amino acids, linked by peptide bonds.

• Nucleic Acids: Polymers of nucleotides, linked by phosphodiester bonds.

• Polysaccharides: Polymers of monosaccharides (e.g., glucose), linked by glycosidic bonds.

• Lipids: Not true polymers; composed of fatty acids and glycerol, linked by ester bonds.

Monomers and Bonds:

• Amino acids (proteins): Peptide bonds

• Nucleotides (nucleic acids): Phosphodiester bonds

• Monosaccharides (polysaccharides): Glycosidic bonds

• Fatty acids & glycerol (lipids): Ester bonds

Properties: Each macromolecule has unique chemical properties, such as hydrophobicity (lipids), charge (proteins, nucleic acids), and structural roles (carbohydrates).

Protein Structure

Proteins have four levels of structure, each stabilized by specific interactions.

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape, stabilized by hydrophobic interactions, ionic bonds, hydrogen bonds, and disulfide bridges.

• Quaternary structure: Association of multiple polypeptide chains.

Example: Hemoglobin is a quaternary protein composed of four polypeptide subunits.

Enzymes

Enzymes are biological catalysts, mostly proteins, but some are RNA molecules (ribozymes).

• Active Site: Region where substrate binds; composed of amino acids that may not be adjacent in primary structure.

• Induced-fit model: Substrate binding induces conformational changes in the enzyme, enhancing catalysis.

• Enzyme Inhibition:

  • Competitive: Inhibitor binds to active site, blocking substrate.

  • Noncompetitive: Inhibitor binds elsewhere, altering enzyme activity.

• Regulation:

  • Substrate-level: Direct interaction with substrate.

  • Feedback: End product inhibits earlier step.

  • Allosteric: Effector binds to site other than active site, changing activity.

  • Covalent modification: Addition/removal of chemical groups (e.g., phosphorylation); can be reversible or irreversible.

Equation:

$\text{E} + \text{S} \rightleftharpoons \text{ES} \rightarrow \text{E} + \text{P}$

E: enzyme, S: substrate, ES: enzyme-substrate complex, P: product

Cells and Organelles

Types of Cells

Cells are classified as bacterial, archaeal, or eukaryotic (plant and animal).

• Bacterial and Archaea: Prokaryotic, lack membrane-bound organelles.

• Eukaryotic: Have membrane-bound organelles (nucleus, mitochondria, etc.).

Major Differences:

• Bacteria: No nucleus, circular DNA, cell wall of peptidoglycan.

• Eukaryotes: Nucleus, linear DNA, complex organelles.

Major Organelles and Cell Structures

Organelles perform specialized functions and may be membrane-bound.

• Nucleus: Contains genetic material; membrane-bound.

• Mitochondrion: Site of aerobic respiration; membrane-bound.

• Chloroplast: Site of photosynthesis in plants; membrane-bound.

• Endomembrane System: Includes ER, Golgi, lysosome, endosome; involved in protein sorting and transport.

• Peroxisome: Detoxifies harmful substances; membrane-bound.

• Vacuole: Storage and structural support in plants; membrane-bound.

• Ribosome: Protein synthesis; not membrane-bound.

• Cytoskeleton: Structural support and movement; not membrane-bound.

• Cell wall/Extracellular matrix: Structural support outside plasma membrane.

Similarities between Bacteria, Mitochondria, and Chloroplasts: All have circular DNA, ribosomes, and can divide independently.

Composition of Virus

Viruses are composed of genetic material (DNA or RNA) surrounded by a protein coat (capsid); some have a lipid envelope.

Membranes and Membrane Transport

Biological Membranes and Fluid Mosaic Model

Biological membranes are lipid bilayers described by the fluid mosaic model, where proteins and lipids move laterally within the layer.

• Lipids: Phospholipids, glycolipids, cholesterol; composition affects fluidity.

• Fluidity: Characterized by melting temperature (Tm); depends on lipid composition (saturated vs. unsaturated fatty acids).

• Membrane Asymmetry: Different lipid and protein composition on inner and outer leaflets.

Membrane Proteins:

• Integral: Span the membrane; hydrophobic regions.

• Peripheral: Attached to membrane surface.

• Lipid-anchored: Covalently attached to lipids.

• Chemical Properties: Hydrophobicity, glycosylation (addition of carbohydrate groups).

Transport Across Membranes

Transport mechanisms allow solutes to cross membranes, often involving proteins.

• Simple Diffusion: Movement of small, nonpolar molecules down concentration gradient; no protein required.

• Facilitated Diffusion: Movement of larger or polar molecules via channel or carrier proteins; down concentration gradient.

• Active Transport: Movement against concentration gradient; requires energy (ATP) and transport proteins.

Examples:

• Simple diffusion: O2, CO2

• Facilitated diffusion: Glucose via GLUT transporter

• Active transport: Na+/K+ pump

Cellular Energetics

Metabolic Pathways

Metabolism consists of anabolic (building up) and catabolic (breaking down) pathways.

• Anabolic: Synthesis of complex molecules; requires energy.

• Catabolic: Breakdown of molecules; releases energy.

Organism Types

• Aerobic: Require oxygen for metabolism.

• Anaerobic: Do not require oxygen; may be harmed by it.

• Facultative: Can switch between aerobic and anaerobic metabolism.

Glucose Catabolism

Glucose is broken down to generate ATP, NADH, and other intermediates. The process occurs in distinct steps, each localized in specific cellular compartments.

• Glycolysis: Occurs in cytosol; breaks glucose into pyruvate, generating ATP and NADH.

• Pyruvate Catabolism: Depends on oxygen availability.

ATP Yield:

• Glycolysis: 2 ATP, 2 NADH per glucose

• Aerobic respiration: Up to 36-38 ATP per glucose

• Anaerobic fermentation: 2 ATP per glucose

Cellular Localization:

• Glycolysis: Cytosol

• Pyruvate oxidation, TCA cycle, oxidative phosphorylation: Mitochondria

Fate of Pyruvate

• Anaerobic: Fermentation pathways produce lactate (animals) or ethanol + CO2 (yeast).

• Aerobic: Pyruvate undergoes oxidative decarboxylation, enters citric acid cycle, and proceeds to oxidative phosphorylation.

Equation for Glycolysis:

$\text{Glucose} + 2\text{NAD}^+ + 2\text{ADP} + 2\text{P}_i \rightarrow 2\text{Pyruvate} + 2\text{NADH} + 2\text{ATP} + 2\text{H}_2\text{O}$

Aerobic Respiration

• Pyruvate Oxidation: Pyruvate converted to acetyl-CoA.

• Citric Acid Cycle (TCA/Krebs): Acetyl-CoA oxidized, generating NADH, FADH2, and ATP.

• Oxidative Phosphorylation: Electron carriers transfer electrons through respiratory complexes, creating a proton gradient (chemiosmosis) and driving ATP synthesis.

Equation for Aerobic Respiration:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy (ATP)}$

Catabolism of Fatty Acids (β Oxidation)

Fatty acids are broken down by β oxidation to generate acetyl-CoA, NADH, and FADH2, which enter the citric acid cycle and oxidative phosphorylation.

• Location: Mitochondria

• Products: Acetyl-CoA, NADH, FADH2

Equation for β Oxidation:

$\text{Fatty Acid} + \text{CoA} + \text{NAD}^+ + \text{FAD} \rightarrow \text{Acetyl-CoA} + \text{NADH} + \text{FADH}_2$

Summary Table: Cell Types and Organelles

Cell Type	Key Features	Organelles Present
Bacterial	No nucleus, circular DNA, cell wall	Ribosome, cell wall
Archaea	No nucleus, unique membrane lipids	Ribosome, cell wall
Eukaryotic (Animal)	Nucleus, linear DNA, complex organelles	Nucleus, mitochondria, ER, Golgi, lysosome, cytoskeleton
Eukaryotic (Plant)	Nucleus, chloroplasts, cell wall	Nucleus, mitochondria, chloroplast, ER, Golgi, vacuole, cytoskeleton

Additional info: Table entries inferred for clarity and completeness.

Summary Table: Membrane Transport Modes

Transport Mode	Protein Required	Directionality	Example
Simple Diffusion	No	Down gradient	O2, CO2
Facilitated Diffusion	Yes	Down gradient	Glucose (GLUT)
Active Transport	Yes	Against gradient	Na+/K+ pump

Additional info: Table entries inferred for clarity and completeness.