Biology 102

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Biology 102

• Cellular respiration

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Lecture Outline

• Glucose metabolism Overview
• Glycolysis The first step in capturing energy
  in glucose
• Cellular respiration How additional energy is
  generated from glucose
• Krebs cycle
• Electron transport system

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1. Glucose metabolism Overview

• Why focus on glucose?
• All cells do it!
• Relatively simple
• Most other compounds enter the glucose metabolism
  pathway when being broken down
• Pathways go both ways
• Example fat from sugar

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1. Glucose metabolism Overview

• The formula! (You know this!)
• The major reactions
• Glycolysis
• No oxygen needed
• Generates 2 net ATP and 2 NADH per glucose
  molecule
• 3-C molecule, pyruvate, formed that enters other
  reactions depending upon presence/absence of O2
• Cellular respiration
• requires O2
• Includes two parts
• Krebs cycle
• Electron transport

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Location of different reactions

• Glycolysis cytoplasm of cell
• Krebs cycle matrix of mitochondrion
• Electron transport inner membrane of
  mitochondrion

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2. Glycolysis

• Two steps
• Activation (This gets the reaction over that
  activation energy hump! 2 ATP used.)
• Energy harvest (4 ATP and 2 NADH produced)
• Electrons and protons (H) also harvested!
• NET result 2 ATP, 2 NADH and 2 pyruvate
  molecules (3-carbon chain) per glucose molecule

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It is actually a bit more complicated, but you
dont need to memorize these details
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• SIDE NOTE G3P is the same high-energy 3-carbon
  compound that directly builds the glucose
  molecule in the Calvin-Benson cycle!

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What happens to the pyruvate formed during
glycolysis?

• Used in fermentation (if oxygen absent)
• Lactic acid (lactate) formed OR
• Alcohol (ethanol) formed
• In both cases, electrons and H from NADH are
  given to the pyruvate so NAD can be recycled
  and continue to carry out its function in
  glycolysis

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What happens to the pyruvate formed during
glycolysis?

• Used in cellular respiration (if oxygen present)
• Oxygen is the final acceptor for the electrons
  and H stripped from the glucose!
• Water is formed!
• Think back to photosynthesis, where water was the
  source for electrons and H, and O2 was formed!

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3. Cellular respiration

• The net result
• LOTS of ATP generated (34-36 ATP)
• CO2 is formed as C-C bonds are broken
• Organic back to inorganic
• Water is formed when oxygen serves as an electron
  (and H) acceptor
• Remember how it serves as a donor for these
  things in photosynthesis?

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Focus Krebs cycle

• Transition from Glycolysis
• Pyruvate transported to mitochondrial matrix
• One CO2 breaks off
• NADH formed
• 2-C molecule (acetyl Co A) enters..
• Krebs cycle
• Small amount of ATP generated
• C-C bonds are broken, releasing 2 CO2
• Electrons and H to NAD and FAD to form NADH and
  FADH2.
• Remember that electrons carry their energy with
  them.

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Focus Electron transport/ chemiosmosis

• NADH and FADH2 carry the electrons, H (and
  associated energy) to an electron transport
  system on the inner membrane of the mitochondria
• Electron transport from high to low energy
  carriers is coupled to the synthesis of ATP
• Creates and utilizes H gradients to do this.
• Oxygen serves as the final electron and H
  acceptor, so that water is formed

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Membrane proteins involved in electron transport

• ATP synthesizing enzyme
• H ion channel is key part
• Electron transport system
• Series of specific proteins imbedded in membrane

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Electron transport

• Electrons from NADH and FADH2 deposit electrons
  to the system
• Electrons move from high to low energy compounds
• The energy released is used to transport H ions
  from the matrix to the intermembrane compartment

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Formation of ATP

• The H gradient drives the production of ATP

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Summary Energy harvested from glucose