Lecture 4, Ch. 9

Lecture #4 • Chapter 9~ Cellular Respiration: Harvesting Chemical Energy

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Intr oducti on t o Meta bo lism  

 Complex substances are broken down for energy, required metabolites, structural components, etc.  Cells must synthesize new complex substances.  

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 These rxns occur with a minimum of side products, energy loss or undesired interferences and at reasonable temperatures, pH and pressure.  All of these rxns must be controlled or regulated for optimum

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Def initi ons:

Catabolism = the breakdown of complex substances.   Anaboli sm = the synthesis of complex substances from simpler ones. ******************************************************** ***

Principles of Energy Harvest • Catabolic pathway √ Fermentation √Cellular Respiration C6H12O6 + 6O2 ---> 6CO2 + 6H2O + E (ATP + heat)

• http://www.northland.cc.mn.us/biology/Biology1111/anima

Glycolysis: Specific tissue functions • RBC’s – Rely exclusively for energy

• Skeletal muscle – Source of energy during exercise, particularly high intensity exercise

• Adipose tissue – Source of glycerol-P for TG (glycerol phosphate) synthesis – Source of acetyl-CoA for FA synthesis

• Liver – Source of acetyl-CoA for FA synthesis – Source of glycerol-P for TG synthesis

ATP • Adenosine triphosphate Adenine

Ribose

3 Phosphate groups

• The molecule that living organisms use for energy • After it is formed, energy is released once the chemical bonds are broken.

Types of cellular respiration C e l l u la r R e s p i r a t i o n t h e r e le a s e o f e n e r g y a n a e r o b ic t h e r e le a s e o f e n e r g y W I T H O U T o x y g e n

a e r o b ic t h e r e le a s e o f o x y g e n u s i n g o x y g e n

p a r t ia l b r e a k d o w n o f g lu c o s e

c o m p le t e b r e a k d o w n o f g lu c o s e

li t t le e n e r g y e x r t r a c t e d ( 2 A T P - n e t)

m a x im u m e n e r g y e x tr a c te d ( 3 6 A T P - n e t)

P r o t i s t s a n d b a c t e r ia

H um ans

Fermentation • A type of anaerobic respiration where energy is released and end products such as ethyl alcohol, CO2 (yeast) and lactic acid (bacteria)

Anaerobic respiration The release of energy without oxygen

glycolysis • The breaking of glucose • Another name for anaerobic respiration

Glycolysis Glucose

The happenings: 2. 2 ATP needed to start the reaction 3. Glucose is broken down to 2 pyruvic acids and 4 ATP are produced (2 go back into the reaction)

2 Pyruvic acid

To the electron transport chain

The math of glycolysis 4 ATP made 2 ATP needed for the reaction 2 ATP made in profit

Fermentation • A type of anaerobic respiration where energy is released

And bacteria

Aerobic respiration Release of energy by using oxygen Glucose completely broken down In the mitochondria

Importance of oxygen • Cells that can use oxygen can extract the energy remaining from the end products of anaerobic respiration • The end products have almost as much energy as the glucose molecule • Oxygen is the final hydrogen acceptor (forming water)

Flowchart Cellular Respiration

Glucose (C6H1206) + Oxygen (02)

Glycolysis

Krebs Cycle

Electron Transport Chain

Carbon Dioxide (CO2) + Water (H2O)

The Kreb cycle • Pyruvic acid undergoes fruther breakdown and energy is released • Carbon dioxide is released during these reactions • 2 ATP made

Want to see something scary? • I had to memorize this in class. Structures and all!

The Electron Transport Chain • Enzyme reactions that take place after the Krebs Cycle • Produces 32 ATP • Water formed because oxygen is the final hydrogen acceptor •

http://www.sp.uconn.edu/~terry/images/anim/ETS_slow.html

The math of aerobic respiration • 2 ATP from glycolysis • 2 ATP from Krebs Cycle • 32 ATP from the electrom transport chain • 36 ATP total

Redox reactions • Oxidation-reduction • LEO says GER (adding e- reduces + charge)

• Oxidation is e- loss; reduction is e- gain • Reducing agent: donor • Oxidizing agent: acceptor

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Oxidizing agent in respiration • NAD+ (nicotinamide adenine dinucleotide) • Removes electrons from food (series of reactions) • NAD + is reduced to NADH • Enzyme action: dehydrogenase • Oxygen is the eventual eacceptor

Electron transport chains • • •

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Electron carrier molecules (membrane proteins) Shuttles electrons that release energy used to make ATP Sequence of reactions that prevents energy release in 1 explosive step Electron route: food---> NADH ---> electron transport chain ---> oxygen

Cellular respiration • Glycolysis: cytosol; degrades glucose into pyruvate • Kreb’s Cycle: mitochondrial matrix; pyruvate into carbon dioxide • Electron Transport Chain: inner membrane of mitochondrion; electrons passed to oxygen

Glycolysis • • •

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1 Glucose ---> 2 pyruvate molecules Energy investment phase: cell uses ATP to phosphorylate fuel Energy payoff phase: ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation Net energy yield per glucose molecule: 2 ATP plus 2 NADH; no CO2 is released; occurs aerobically or anaerobically

Kreb’s Cycle • •

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If molecular oxygen is present……. Each pyruvate is converted into acetyl CoA (begin w/ 2): CO2 is released; NAD+ --> NADH; coenzyme A (from B vitamin), makes molecule very reactive From this point, each turn 2 C atoms enter (pyruvate) and 2 exit (carbon dioxide) Oxaloacetate is regenerated (the “cycle”) For each pyruvate that enters: 3 NAD+ reduced to NADH; 1 FAD+ reduced to FADH2 (riboflavin, B vitamin); 1 ATP molecule

Electron transport chain •

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Cytochromes carry electron carrier molecules (NADH & FADH2) down to oxygen Chemiosmosis: energy coupling mechanism ATP synthase: produces ATP by using the H+ gradient (proton-motive force) pumped into the inner membrane space from the electron transport chain; this enzyme harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation)

Review: Cellular Respiration •

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Glycolysis: 2 ATP (substrate-level phosphorylation) Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose

Related metabolic processes • Fermentation: alcohol~ pyruvate to ethanol lactic acid~ pyruvate to lactate • Facultative anaerobes (yeast/bacteria) • Beta-oxidation lipid catabolism