Notes on Chloroplasts and Mitochondria

Chloroplasts and Mitochondria Study Guide

Part I: Chloroplasts

A. Structures of the Chloroplast

  • Stroma

    • The fluid-filled space surrounding the thylakoids inside a chloroplast. It contains enzymes, chloroplast DNA, and ribosomes.

  • Thylakoid

    • Membrane-bound structures where the light-dependent reactions of photosynthesis occur. They contain chlorophyll and are stacked in structures called granum.

  • Granum

    • A stack of thylakoids that facilitates the arrangement of light-absorbing pigments to maximize light absorption during the light-dependent reactions.

  • Stromal Lamellae

    • Connecting thylakoids that link grana together, providing structural support in the chloroplast.

  • Inner Membrane

    • A highly selective membrane that contains transport proteins that regulate the passage of materials in and out of the chloroplast.

  • Outer Membrane

    • A permeable membrane that allows small molecules and ions to pass freely. It is made of a lipid bilayer similar to other membranes in the cell.

B. Role of Structures in Photosynthesis

  • Photosynthesis occurs in two main stages:

    1. Light-dependent reactions

    • Location: Thylakoid membranes

    • Description: Use light energy to produce ATP and NADPH while splitting water molecules to release oxygen.

    1. Calvin Cycle (Light-independent reactions)

    • Location: Stroma

    • Description: Uses ATP and NADPH from the light-dependent reactions to fix carbon dioxide into glucose through a series of enzymatic steps.

  • Role of Chlorophyll

    • Chlorophyll is the green pigment found in thylakoids and is essential for absorbing light energy, which drives the light-dependent reactions. It primarily absorbs blue and red light, reflecting green light, which is why plants appear green.

Part II: Mitochondria

A. Structures of the Mitochondria

  • Outer Membrane

    • Smooth membrane that encloses the mitochondrion, allowing for the passage of ions and small molecules.

  • Inner Membrane

    • Contains numerous folds known as cristae that increase surface area for chemical reactions. It is where the electron transport chain occurs.

  • Cristae

    • Folded structures of the inner membrane, creating a large surface area that facilitates the processes of oxidative phosphorylation.

  • Ribosomes

    • Small structures found within mitochondria that synthesize some of the proteins needed for mitochondrial function.

  • Mitochondrial DNA

    • Circular DNA located in the mitochondria, responsible for coding essential proteins for mitochondrial function and replicating independently of nuclear DNA.

B. Reactions in Cellular Respiration

  • Cellular Respiration consists of three main reactions:

    1. Glycolysis

    • Purpose: Converts glucose into pyruvate, producing a small amount of ATP and NADH in the cytoplasm of the cell.

    1. Krebs Cycle (Citric Acid Cycle)

    • Purpose: Processes pyruvate in the mitochondria to produce ATP, NADH, FADH₂, and carbon dioxide, further driving energy production.

    1. Electron Transport Chain

    • Purpose: Utilizes electrons from NADH and FADH₂ to convert ADP to ATP while moving protons across the inner membrane, resulting in a proton gradient used for ATP synthesis through chemiosmosis.