뒤로Cell Structure, Membrane Function, and Energy Processes in General Biology
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Cell Structure and Function
Main Organelles and Their Functions
Cells contain specialized structures called organelles that perform distinct functions necessary for cellular life.
Nucleus: Contains genetic material (DNA); controls cell activities.
Mitochondria: Site of cellular respiration; produces ATP.
Chloroplasts: Found in plant cells; site of photosynthesis.
Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).
Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
Lysosomes: Contain digestive enzymes; break down waste.
Vacuoles: Storage of substances; large central vacuole in plant cells.
Differences between Eukaryotes and Prokaryotes:
Eukaryotic cells: Have a nucleus and membrane-bound organelles; examples include animal, plant, fungi, and protist cells.
Prokaryotic cells: Lack a nucleus and membrane-bound organelles; examples include bacteria and archaea.
Animal vs. Plant Cells: Plant cells have cell walls, chloroplasts, and large vacuoles; animal cells do not.
Cell Membrane Structure and Function
Composition, Permeability, and Function
The cell membrane is a selectively permeable barrier composed mainly of a phospholipid bilayer with embedded proteins.
Phospholipid bilayer: Provides fluidity and flexibility.
Proteins: Serve as channels, carriers, receptors, and enzymes.
Cholesterol: Stabilizes membrane fluidity.
Permeability: Allows selective passage of substances.
Concept of Tonicity
Tonicity refers to the relative concentration of solutes in the solution outside the cell compared to inside the cell.
Hypotonic: Lower solute concentration outside; water enters cell.
Hypertonic: Higher solute concentration outside; water leaves cell.
Isotonic: Equal solute concentration; no net water movement.
Transport Across the Cell Membrane
Types of Transport
Cells move substances across membranes using various mechanisms:
Diffusion: Passive movement of molecules from high to low concentration.
Osmosis: Diffusion of water across a selectively permeable membrane.
Facilitated Diffusion: Passive transport via membrane proteins.
Active Transport: Movement against concentration gradient using energy (ATP).
Bulk Transport: Includes endocytosis (into cell) and exocytosis (out of cell).
Aquaporins: Channel proteins that facilitate water movement.
Cellular Biochemical Processes
Redox Reactions
Oxidation is the loss of electrons; reduction is the gain of electrons. These reactions are central to energy transfer in cells.
Catabolic and Anabolic Reactions
Catabolic reactions: Break down molecules, releasing energy (e.g., cellular respiration).
Anabolic reactions: Build complex molecules, requiring energy (e.g., photosynthesis).
Spontaneity of reactions: Determined by changes in free energy ().
Concept of Change in Delta G ():
: Reaction is spontaneous (exergonic).
: Reaction is non-spontaneous (endergonic).
Enzymes and Activation Energy
Enzyme Function and Regulation
Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy barrier.
Active site: Region where substrate binds.
Substrate: Molecule upon which the enzyme acts.
Inhibitors: Molecules that decrease enzyme activity.
ATP synthase: Enzyme that synthesizes ATP during cellular respiration and photosynthesis.
Cellular Respiration and Photosynthesis
Overview and General Steps
Cellular respiration and photosynthesis are key energy-transforming processes in cells.
Cellular respiration: Converts glucose and oxygen into ATP, carbon dioxide, and water.
Photosynthesis: Converts light energy, carbon dioxide, and water into glucose and oxygen.
Major Steps and Their Importance
Electron flow: Movement of electrons through chains (electron transport chain in respiration; light reactions in photosynthesis).
Energy storage: ATP and NADPH are produced and used for cellular work.
General familiarity: Direction of electron flow, major reactants and products.
Energy source: Glucose (respiration); light (photosynthesis).
Photosynthetic pigments: Chlorophyll absorbs light; different pigments absorb different wavelengths.
Krebs Cycle (Citric Acid Cycle): Series of reactions in mitochondria that generate electron carriers for ATP production.
Calvin Cycle: Series of reactions in chloroplasts that fix carbon dioxide into glucose.
Comparison Table: Cellular Respiration vs. Photosynthesis
Process | Main Reactants | Main Products | Location | Energy Source |
|---|---|---|---|---|
Cellular Respiration | Glucose, O2 | CO2, H2O, ATP | Mitochondria | Chemical (glucose) |
Photosynthesis | CO2, H2O, Light | Glucose, O2 | Chloroplasts | Light |
Oxygen's Role
Cellular respiration: Oxygen is the final electron acceptor in the electron transport chain.
Photosynthesis: Oxygen is produced as a byproduct during the splitting of water.
General Differences Between C3 and C4 Plants
C3 and C4 plants differ in their photosynthetic pathways and adaptation to environmental conditions.
Feature | C3 Plants | C4 Plants |
|---|---|---|
First Product of CO2 Fixation | 3-carbon compound (3-phosphoglycerate) | 4-carbon compound (oxaloacetate) |
Photorespiration | High | Low |
Adaptation | Cool, moist environments | Hot, dry environments |
Fermentation
Concept and Cellular Location
Fermentation is an anaerobic process that allows cells to produce ATP without oxygen.
Occurs in the cytoplasm.
Produces less ATP than aerobic respiration.
Common types: lactic acid fermentation (in muscle cells) and alcoholic fermentation (in yeast).
Additional info:
ATP synthase is crucial for ATP production in both cellular respiration and photosynthesis.
Photosynthetic pigments include chlorophyll a, chlorophyll b, and carotenoids.
Photorespiration is a process that can decrease the efficiency of photosynthesis in C3 plants.
