Lab2

Metabolic pathways: An overview of cellular respiration and fermentation
Chapter 6

Cellular respiration, photosynthesis occur in eukaryotic organelles (mitochondria, chloroplasts)

CELLULAR RESPIRATION
GLUCOSE
1 2 GLYCOLYSIS 1

PYRUVATE OXIDATION2

KREBS CYCLE
3 2

ELECTRON TRANSPORT 4 CHAIN 2

NET ATP PRODUCED = 36
Nelson, 2003

Redox Reactions
• Reduction-oxidation reactions
– Transfer electrons from donor to acceptor atoms

• Donor is oxidized as it releases electrons
• Acceptor is reduced as it accepts electrons

Cellular Respiration Series of chemical reactions and electron exchanges that convert glucose into ATP C6H12O6 + 6O2 6CO2 + 6H2O + ATP + heat
Aerobic respiration – involving oxygen Anaerobic respiration – no oxygen

Cellular Respiration Series of chemical reactions and electron exchanges that convert glucose into ATP

Fig 6.5

Can transfer more of the energy stored in glucose into ATP if it is done in a series of steps instead of one step.

REDOX Reactions Loss and addition (transfer) of electrons REDOX RED = reduction (reaction involving gaining electrons) OX = oxidation (reaction involving losing electrons)
“LEO the lion says GER” LEO = lose electrons, oxidized GER = gain electrons, reduced
IN TEXTBOOK acronym– oxidation is loss, reduction is gain (OILRIG)

See your grade 12 chemistry notes for review.

REDOX Reactions
Electrons travel with protons. Therefore, addition or removal of hydrogen associated with REDOX reactions.
Becomes oxidized

C6H12O6 + 6O2 6CO2 + 6H2O + ATP + heat
Becomes reduced

Electron Carrier in cellular respiration
NAD+ Nicotinamide adenine dinucleotide “Collects” or “accepts” electrons from the stepwise breakdown (series of chemical reactions) of glucose Electrons “collected” by NAD+ used in the production of ATP. NAD+ + 2e- + 2H+  NADH + H+

Oxidized form

Reduced form

Electron Carrier in cellular respiration
FAD Flavin adenine dinucleotide FAD +
Oxidized form

2e- + 2H+  FADH2
Reduced form

FADH2 used in electron transport chain to produce ATP

Cellular Respiration
Glycolysis
Pyruvate oxidation Citric acid cycle or Kreb’s cycle Electron transport chain and chemiosmosis

KNOW Mitochondrion Anatomy
Raven et al., (2008) Biology 8th edition. McGraw Hill.

Cristae (inner membrane), intermembrane, and matrix involved in cellular respiration.

Cellular Respiration – per 1 glucose
Component
Glycolysis I (energy needed) Glycolysis II (ATP made) Pyruvate Oxidation Citric Acid Cycle Electron Transport Chain (ETC) Chemiosmosis

Where Occurs
Cytoplasm Cytoplasm Mito. matrix Mito. matrix Mito.

# ATP # NADH # NADH # FADH 2 used produced used produced

#FADH # ATP produced 2 used

2 2 2 6 10
2 10 10 2

4

2 2

2 32
2 38

Same as ETC

TOTALS

38 ATP produced – 2 ATP used = net yield of 36 ATP per 1 glucose

CELLULAR RESPIRATION
GLUCOSE
1 2

GLYCOLYSIS

1

PYRUVATE OXIDATION 2

KREBS CYCLE
3 2

ELECTRON TRANSPORT 4 CHAIN 2

NET ATP PRODUCED = 36
Nelson, 2003

Glycolysis

glucose + 2 ADP + 2 Pi + 2 NAD+ → 2 pyruvate + 2 NADH + 2 H++ 2 ATP

Net ATP?

Substrate-level phosphorylation

E.g., via phosphoglycerate kinase enzyme

Glycolysis
The following slides outline the series of molecular changes that occur during glycolysis and the enzymes that are involved. Your are NOT expected to memorize every molecule, enzyme, and the order in which they occur.

Understand that through a series of chemical reactions, involving enzymes, glucose is modified into other 6 carbon molecules and then 3 carbon molecules, resulting in two pyruvate (3 carbon) molecules. Know the significance and placement (where occurs approx during glycolysis) of glucose, glyceraldehyde-3-phosphate, and pyruvate. Be able to recognize what has occurred from one molecule to the next.

Glycolysis (ATP invested phase)

Glycolysis (ATP invested phase)

Glycolysis (ATP invested phase)

Glycolysis (ATP invested phase)

1 glucose converted to 2 G3P

Glycolysis (ATP produced phase)

Glycolysis (ATP produced phase)

Glycolysis (ATP produced phase)

Glycolysis (ATP produced phase)

Glycolysis (ATP produced phase)

Glycolysis Summary
All 6 carbons of glucose used in two molecules of pyruvate. NO CARBON LOST. CHANGE IN POTENTIAL ENERGY.

2 ATP are invested (used) 4 ATP are produced 2 NADH are produced

Cellular Respiration
Glycolysis
Pyruvate oxidation Citric acid cycle or Kreb’s cycle Electron transport chain and chemiosmosis

Components of Cellular Respiration
Glycolysis

Pyruvate oxidation Citric acid cycle or Kreb’s cycle
Electron transport chain and chemiosmosis

Pyruvate Oxidation
2 pyruvate converted into 2 acetyl-CoA via enzyme catalyzed reactions 2 NADH produced (1 per pyruvate conversion) 2 CO2 released (1 per pyruvate conversion)

To ETC

To Kreb’s

Components of Cellular Respiration
Glycolysis
Pyruvate oxidation

Citric acid cycle or Kreb’s cycle Electron transport chain and chemiosmosis

Citric acid cycle (aka Krebs cycle, TCA cycle)

1 acetyl-CoA + 3 NAD+ + 1 FAD + 1 ADP + 1 Pi + 2 H2O → 2 CO2 + 3 NADH + 1 FADH2 + 1 ATP + 3 H+ + 1 CoA

Citric Acid Cycle

Citric Acid Cycle or Kreb’s Cycle
• 8 enzyme catalyzed reactions.
• MUST END WITH WHAT YOU STARTED!! Per Acetyl CoA molecule: • 1 ATP produced • 3 NADH produced • 1 FADH2 molecule • 2 CO2 molecules

Citric Acid Cycle or Kreb’s Cycle
1 2

Acetyl group (2 carbons) added to oxaloacetate (4 carbons) to create citrate (6 carbons)

CoA (acetyl CoA) added back into the cycle later

Citric Acid Cycle or Kreb’s Cycle
2

Citrate (6C) molecule rearranged into isocitrate (6C)

Note: CoA-SH is represented as CoA in your textbook

Citric Acid Cycle or Kreb’s Cycle
3+4 2

2 electrons and protons transferred to NAD+ to create NADH. 1 carbon is released as CO2 CoA-SH (cleaved from acetyl CoA) added.

4 2

Citric Acid Cycle or Kreb’s Cycle
5 2

CoA-SH is released and a phosphate added (Pi) to the carbon molecule (not shown). Phosphate passed to GDP to create GTP. Phosphate pass from GTP to ADP to create ATP

Citric Acid Cycle or Kreb’s Cycle
6 2

2 electrons and 2 hydrogen transferred to FAD to produce FADH2

Citric Acid Cycle or Kreb’s Cycle
7 2

Addition of water (OH plus H added) and rearrangement of bonds 2 electrons and hydrogen transferred to NAD+ to produce NADH Oxaloacetate re-created
8

Components of Cellular Respiration
Glycolysis
Pyruvate oxidation

Citric acid cycle or Kreb’s cycle Electron transport chain and chemiosmosis

Electron Transport Chain
Series of integral membrane proteins, located in the inner membrane of a mitochondrion Involved in transferring protons (H+) from the matrix to the intermembrane space. Creating/maintaining the proton concentration gradient

Raven et al., (2008) Biology 8th edition. McGraw Hill.

Making ATP during cellular respiration
1. Substrate Phosphorylation
Enzyme catalyzes transfer of phosphate from high energy substrate to ADP.

2. Oxidative Phosphorylation
ATP is created with ADP and inorganic phosphate by ATP synthase.

Electron Transfer System and Oxidative Phosphorylation

Electron Transport Chain
Electrons from NADH and FADH2 are transported through the series of membrane bound proteins, to fuel the transfer of protons (H+) from the matrix to the intermembrane space.

I UQ II III Cyt c IV

= complex 1 = ubiquinone = complex 2 = complex 3 = Cytochrome c = complex 4

Complexes composed of various proteins including cytochromes

Oxygen is the final electron acceptor.

Oxidative Phosphorylation and Chemiosmosis
• ATP synthase catalyzes ATP synthesis using energy from the H+ gradient across the membrane (chemiosmosis)

• ATP synthase – Embedded in inner mitochondrial membrane with electron transfer system

Chemiosmosis
• ATP synthase composed of multiple components
• H+ enter stator (following concentration gradient) and attach to binding site on rotor, causing a conformational change.

• shape change causes rotor to spin • spinning activates catalytic sites in knob, and production of ATP catalyzed. ADP + Pi  ATP

Electron Transport Chain and Chemiosmosis

Proton concentration gradient created by ETC used by ATP synthase for ATP production (chemiosmosis)

Oxidation of Carbohydrates, Fats, and Proteins

Very simplistically

Electrons are pulled from our food, and used to power the machinery involved in creating a proton concentration gradient which drives the production of most of our ATP.

Cell Respiration Video http://media.pearsoncmg.com/bc/bc_0media_bio/bioflix/cells/cell_resp.html

Anaerobic Cellular Respiration & Fermentation

Alcohol (Ethanol) Fermentation

Glycolysis ONLY
Pyruvate converted to ethanol 2 ATP per glucose molecule

Occurs in bacteria and yeast

Lactic Acid Fermentation

Glycolysis ONLY Lactate created 2 ATP per glucose molecule

Lactate

Lactic acid

H+ + CH3CH(OH)CO2  CH3CH(OH)CO2H

Occurs in bacteria, yeast, and animals (e.g. human muscle cells)

How efficient is cellular respiration?

No

Figure 25 from “Biology 12” by Di Giuseppe et al. Nelson Publishing.

Figure 6.19 from “Biology: Exploring the Diversity of Life” by Russell et al. 1st Canadian ed. Nelson Publishing.

Misunderstanding of e- transfer mechanisms? (NADH in cytosol transfers e- to membrane–bound acceptors in mitochondria. “Shuttle pathways” facilitate.)

NB: These are estimates, and yields vary between cells, different conditions, etc.

Control of Cellular Respiration

Metabolic pathways: An overview of Photosynthesis
Chapter 7