Untitled Quiz

Main Functions of Intercellular Compartments

• Cytosol: Protein synthesis, many metabolic pathways
• Nucleus: Contains genome (DNA, RNA), and ribosome assembly
• Endoplasmic Reticulum (ER): Synthesis of lipids and proteins
• Golgi Apparatus: Protein modification, packaging of proteins and lipids
• Lysosomes: Degradation of cellular material
• Endosomes: Sorting and recycling
• Mitochondria: ATP synthesis, apoptosis
• Chloroplasts: Photosynthesis, ATP synthesis
• Peroxisomes: Oxidation of toxic molecules

Origin of Eukaryotic Cells: The Endosymbiotic Theory

• The endosymbiotic theory is an evolutionary theory of eukaryotic cell origin from prokaryotes.
• It was first proposed by Konstantin Mereschkowski and later supported by Lynn Margulis with microbiological evidence.
• This theory suggests that eukaryotic organelles evolved from symbiotic relationships with individual single-celled prokaryotes (bacteria and archaea).
• Symbiosis describes a close and long-term biological interaction.
• The theory proposes that organelles like mitochondria and chloroplasts were once free-living prokaryotes that were engulfed by another prokaryote.
• Evidence supporting this theory includes:
  • Binary fission of mitochondria and chloroplasts, which is similar to bacteria
  • Circular DNA inside these organelles is similar to bacterial DNA

The Big Leap: Energy Supply

• Aerobic Respiration: Converts energy stored in food molecules (e.g., glucose) into chemical energy stored in ATP in the presence of oxygen. A byproduct is carbon dioxide.
• Photosynthesis: Uses energy from sunlight to build carbohydrates from carbon dioxide and water. Oxygen is released as a byproduct.

Mitochondria: Structure and Function

• Aerobic Respiration: Converts energy stored in food (glucose) into ATP in the presence of oxygen. Carbon dioxide is a byproduct.
• Outer Mitochondrial Membrane (OMM): Contains enzymes with diverse metabolic functions, including those that break down monoamines (e.g., dopamine, serotonin). Also contains porins, which are permeable to molecules like ATP and sucrose.
• Inner Mitochondrial Membrane (IMM): Has a high protein-to-lipid ratio (3:1). Folds called cristae increase the membrane surface area and contain machinery for aerobic respiration and ATP production. Rich in cardiolipin, a phospholipid characteristic of bacterial membranes.

Mitochondria and Cellular Respiration

• Cellular Respiration: Uses chemical energy of carbohydrates and lipids to produce ATP.
• Aerobic Respiration: Cellular respiration in the presence of oxygen.
• Substrate-level Phosphorylation: Releases enough energy to drive phosphorylation of ADP to ATP during reactions like glycolysis. Glycolysis breaks down glucose to pyruvate.
• Oxidative Phosphorylation: Transfers chemical energy to electron carriers, creating a gradient that powers ATP synthesis.

Coenzymes/Electron Carriers

• Some coenzymes can exist in oxidized or reduced states that accept or donate electrons.
  • Examples: NAD+ (oxidized), NADH (reduced); FAD (oxidized), FADH2 (reduced)

Mitochondrial Oxidative Phosphorylation

• Oxidative phosphorylation — is the fourth stage of cellular respiration in animal cells.
• It involves two main steps:
  • Step 1: Transfer of electrons through complexes I-IV (the electron transport chain), which pumps protons resulting in an electrochemical gradient.
  • Step 2: Movement of protons down the gradient through ATP synthase drives ATP synthesis.