Cell Respiration Notes

Cell Respiration

AP Ch. 7

Overview of Cell Respiration

• Cell respiration involves breaking down carbohydrates to store energy in the chemical bonds of the terminal phosphate group of ATP.

Stages of Cell Respiration

• Glycolysis:
  • Takes place in the cytosol of the cell.
  • Has an efficiency of only 3.5%.
• Krebs Cycle (Citric Acid Cycle):
  • Occurs in the mitochondrial matrix.
  • Requires oxygen to proceed.
• Electron Transport Chain:
  • Takes place on the inner membrane of the mitochondria.
  • Produces about 36-38 ATP molecules from one glucose molecule.
  • Has an efficiency of 66%.

Anaerobic Respiration (Fermentation)

• Occurs when oxygen is not present and is only 3.5% efficient
• Since Krebs cycle needs oxygen, pyruvate is converted to:
  • Lactic acid
  • Ethanol (alcohol)
  • Both are types of fermentation

Key Molecules in Cell Respiration

• Glucose:
  • Reactant from food.
• O2 (Oxygen):
  • Reactant that diffuses into the cell for aerobic respiration.
• CO2 (Carbon Dioxide):
  • Product made from carbon atoms in glucose.
• H2O (Water):
  • Product produced in the last steps of the electron transport chain, where H+ and electrons join with O2.
• NAD+ (Nicotinamide Adenine Dinucleotide):
  • Organic coenzyme that assists enzyme activity in the transfer of electrons.
  • Generates 3 ATP per 2 electrons during the electron transport chain.
• FAD (Flavin Adenine Dinucleotide):
  • FADH+ adds electrons into the electron transport chain to generate 2 ATP.
• ATP (Adenosine Triphosphate):
  • Molecule that stores energy from organic food molecules.
  • Used to accomplish work.
  • Approximately 36 ATP molecules are produced from one glucose molecule.

Glycolysis

• First part of the equation:
  • Glucose is converted using 2 ADP to 2 ATP and 2 NAD+ to 2 NADH and produces 2 pyruvic acid molecules.
  • $Glucose + 2ADP + 2NAD^+ \rightarrow 2ATP + 2NADH + 2 \text{ Pyruvic acid}$

Krebs Cycle

• Pyruvic acid (C☺☺) loses $CO_2$ to become Acetyl-CoA.
• Acetyl-CoA combines with a 4-carbon compound to form citric acid.
• Citric acid goes through a series of redox reactions, releasing $CO_2$, NADH, FADH2 and ATP and regenerating the 4-carbon compound.

Electron Transport and Chemiosmosis

• Electron donors pass high-energy electrons along a series of electron carriers (cytochromes) embedded in the ion-permeable inner mitochondrial membrane.
• Electrons and starter energy come from food.
• H+ ions are passed across the membrane.

Oxidative Phosphorylation

• Energy released from electrons as they pass to different carriers is used to build ATP from ADP.
• Uses oxygen and involves adding phosphate to ADP.
• ATP = Adenosine Triphosphate.
• ADP = Adenosine Diphosphate Key Processes

Electron Transport Chain and ATP Synthase

• As ATP synthase rotates, it grabs a low-energy ADP, attaching a phosphate, forming high-energy ATP.

Electron Transport Chain Details

• Series of carriers moving high energy electrons to a state of low energy finally passing them to $H_2O$
• $NADH$ donates electrons to the chain, and $FADH_2$ donates electrons at a lower energy level.
• Electrons are passed down the chain, releasing energy to pump $H^+$ ions into the intermembrane space, creating a concentration gradient.
• $H^+$ ions flow down the concentration gradient through ATP synthase, driving the synthesis of ATP from ADP and phosphate.
• Oxygen acts as the final electron acceptor, combining with electrons and $H^+$ ions to form water.

Key Parts of the Cellular Components

• Cell Membrane:
  • Glucose and $O_2$ pass through.
• Cytoplasm/Cytoskeleton:
  • Site of glycolysis.
  • Location of enzymes.
• Mitochondria:
  • Outer membrane: Materials pass through into the inner membrane.
  • Inner Membrane: Location of cytochromes (electron acceptors) and ATP Synthase.
  • Matrix: Krebs cycle location; also location of Mitochondrial DNA, tRNA, Ribosomes, etc.

Cytochromes

• A class of hemoproteins found in the mitochondria that transports electrons or hydrogen ions during cell respiration or photosynthesis.
• Cytochromes are found in the inner membrane of mitochondria.
• The “chrome” refers to color through which they are divided into groups based on their ability to absorb or transmit certain colors of light
• Examples:
  • NADH
  • Cytochrome B/C
  • Cytochrome oxidase

ATP Synthase (ATPase)

• Uses concentration gradient of H+ ions across the membrane as an energy source to make ATP.
• Overall Equation: $C<em>6H</em>{12}O<em>6 + 6O</em>2 \rightarrow 6H<em>2O + 6CO</em>2 + ATP$
• Overall yield is around 36-38 ATP per glucose molecule.

Misconceptions and Reminders

• Oxygen Purpose:
  • Accept electrons and remove electrons to forms $H_2O$.
• Electrons:
  • Power electron transport chain. Makes ATP (food with more H have more calorie/energy).
• Glycolysis:
  • Takes energy to make energy
  • Remakes NADH.
• Oxidative Phosphorylation:
  • Using oxygen to make ATP.
• Redox:
  • Reduction (gain electrons) / Oxidation (lose electrons).
• Bonds:
  • Make a bond (get energy) / Break (release energy).