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

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.

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.