Cellular Structure, Membrane Transport, Metabolism, and Photosynthesis: Study Guide

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Cellular Membranes and Transport

Phospholipid Bilayer Structure

The phospholipid bilayer forms the fundamental structure of cell membranes, providing a semi-permeable barrier between the cell and its environment.

Phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
They arrange themselves in two layers, with tails facing inward and heads facing outward.
This arrangement creates a flexible, fluid barrier.

Fluid Mosaic Model

The fluid mosaic model describes the structure of cell membranes as a mosaic of components (phospholipids, proteins, cholesterol, and carbohydrates) that gives the membrane a fluid character.

Fluid: The lipid and protein molecules can move laterally within the layer, allowing flexibility.
Mosaic: The membrane is composed of various proteins and other molecules embedded in or attached to the bilayer.

Membrane Transport Mechanisms

Cells regulate the movement of substances across their membranes using several mechanisms:

Simple diffusion: Movement of small, nonpolar molecules (e.g., O2, CO2) directly through the lipid bilayer from high to low concentration.
Facilitated diffusion: Movement of larger or polar molecules (e.g., glucose, ions) via specific transport proteins, still down their concentration gradient.
Osmosis: Diffusion of water across a selectively permeable membrane.
Active transport: Movement of substances against their concentration gradient using energy (usually ATP) and transport proteins.

Isotonic, Hypotonic, and Hypertonic Solutions

These terms describe the relative concentration of solutes in solutions inside and outside the cell, affecting water movement:

Isotonic solution: Solute concentration is equal inside and outside the cell; no net water movement.
Hypotonic solution: Lower solute concentration outside the cell; water enters the cell, which may swell or burst (lysis in animal cells, turgor in plant cells).
Hypertonic solution: Higher solute concentration outside the cell; water leaves the cell, causing it to shrink (crenation in animal cells, plasmolysis in plant cells).

Osmotic lysis occurs when a cell bursts due to excessive water intake in a hypotonic environment.

Cellular Metabolism

Endergonic and Exergonic Reactions

Metabolic reactions are classified based on energy changes:

Endergonic reactions: Require energy input (e.g., synthesis of macromolecules).
Exergonic reactions: Release energy (e.g., breakdown of glucose in cellular respiration).

Anabolism and Catabolism

Anabolism: Biosynthetic pathways that build complex molecules from simpler ones; usually endergonic.
Catabolism: Degradative pathways that break down complex molecules into simpler ones; usually exergonic.

Enzymes and Enzyme Activity

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.

Enzyme activity can be affected by temperature, pH, substrate concentration, and inhibitors.
Enzymes are specific to their substrates and often regulated by allosteric sites.

Enzyme Inhibition

Competitive inhibition: Inhibitor competes with substrate for the active site.
Non-competitive inhibition: Inhibitor binds to an allosteric site, changing enzyme shape and function.
Increasing substrate concentration can overcome competitive but not non-competitive inhibition.

Redox Reactions in Metabolism

Oxidation and Reduction

Redox reactions involve the transfer of electrons:

Oxidation: Loss of electrons.
Reduction: Gain of electrons.
In cellular respiration, glucose is oxidized and oxygen is reduced.

Example equation:

Cellular Respiration

Overview and Steps

Cellular respiration is the process by which cells extract energy from glucose to produce ATP.

Glycolysis: Occurs in the cytoplasm; breaks glucose into pyruvate, producing ATP and NADH.
Pyruvate oxidation: Converts pyruvate to acetyl-CoA, producing NADH and CO2.
Krebs cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix; produces ATP, NADH, FADH2, and CO2.
Electron Transport Chain (ETC): Occurs in the inner mitochondrial membrane; uses NADH and FADH2 to generate a proton gradient for ATP synthesis.
Oxidative phosphorylation: ATP is produced as protons flow back through ATP synthase.

Key Molecules

NADH and FADH2: Electron carriers that transfer electrons to the ETC.
ATP: Main energy currency of the cell.
Oxygen: Final electron acceptor in the ETC, forming water.

ATP Yield

Total ATP produced per glucose: ~30-32 ATP (varies by cell type and conditions).
Most ATP is produced during oxidative phosphorylation.

Fermentation

When oxygen is absent, cells use fermentation to regenerate NAD+ and produce ATP.

Lactic acid fermentation: Produces lactate (in animals).
Alcoholic fermentation: Produces ethanol and CO2 (in yeast).
Fermentation yields much less ATP than aerobic respiration.

Photosynthesis

Overview

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy (glucose).

Occurs in chloroplasts, mainly in the thylakoid membranes and stroma.
Two main stages: Light-dependent reactions and Calvin cycle (light-independent reactions).

Light-Dependent Reactions

Take place in the thylakoid membranes.
Chlorophyll absorbs light, exciting electrons.
Water is split to provide electrons, releasing O2 as a byproduct.
Electron transport chain generates ATP and NADPH.

Calvin Cycle (Light-Independent Reactions)

Occurs in the stroma of the chloroplast.
Uses ATP and NADPH to fix CO2 into glucose.
Key enzyme: Rubisco (catalyzes carbon fixation).

Electron Flow in Photosynthesis

Electrons flow from water to NADP+, forming NADPH.
Oxygen is produced from the splitting of water.

Order of Photosynthetic Events

CO2 fixation
ATP production
Glucose production
Chlorophyll excitation and electron transfer
Water splitting to produce oxygen
NADPH production

Key Structures and Functions

Chlorophyll: Main pigment absorbing light energy.
Thylakoid membrane: Site of light-dependent reactions.
Stroma: Site of Calvin cycle.
Photosystems I and II: Protein complexes that capture light energy and transfer electrons.

Summary Table: Comparison of Cellular Respiration and Photosynthesis

Process	Location	Reactants	Products	Energy Conversion
Cellular Respiration	Mitochondria (mainly)	Glucose, O2	CO2, H2O, ATP	Chemical energy (glucose) to ATP
Photosynthesis	Chloroplasts	CO2, H2O, light	Glucose, O2	Light energy to chemical energy (glucose)

Additional info: Some explanations and context have been expanded for clarity and completeness, as the original file contained only question prompts.