Cellular Respiration !

Welcome to your first boring powerpoint…

Jeff Jewett

American College of Sofia, Sofia Bulgaria

Version 2.0, posted 6 December 2009

Fig 8.5 Energy, Spontaneous Change, Work Capacity

ATP

Figures 8.8 & 8.9 Campbell & Reece

Fig 8.10

The Big Idea

• “with the help of enzymes, a cell systematically degrades complex organic molecules that are rich in potential energy to simpler waste products that have less energy. Some of the energy taken out of chemical storage can be used to do work; the rest is dissipated as heat.” P163 CR

Types of Respiration

• Aerobic Respiration (with oxygen)– Usually just call “respiration”

C6H12O6 + O2 6H2O + 6CO2 + energy

• Energy is captured as 36-38 (ADP + P) 36-38 ATP

• Anaerobic Respiration / Fermentation (without Oxygen)

Fig 9.2

• Energy flows (in from sun, out as heat)

• Matter/nutrients cycle

ReDox Reaction

• Oxidation & Reduction• A reaction where an electron (or a partial

charge) is transferred from one compound to another

• Reduction – gains electrons (and energy)• Oxidation – loses electrons (and energy)• Oxidizing Agent = gets reduced• Reducing Agent = gets oxidized

– (I know, that’s confusing…)

• H2 + O2 H20 + energy (fuels space shuttle, “fuel cells”)• Electrons equally shared on H-H bond (non-polar), but mostly

on O in H-O bond (polar)• Means H “lost” most of an electron, and lost energy• H was oxidized, O was reduced

Partial Charge ReDox

• The more electronegative the atom, the more energy it requires to pull an electron away from it.

• An electron loses potential energy when it moves from a less e-neg atom to a more electronegative atom.

• Stairstep photo, Fig 9.5b

Electron Carriers

• Explosions inside body = bad • Gradual release of energy = good • Nicotinamide Adenine Dinucleotide (NAD+)

• NAD+ NADH

• FAD FADH2

• Dehydrogenase reaction on p 164

Fig 9.4

Fig 9.6 Overview of cellular Respiration

Fig 9.8 Glycolysis

• The breaking of sugar pyruvate

• In the cytoplasm

• Does not require O2

• Net gain of 2 ATP

• COO- groups are low in energy (compared to H-C-OH in sugars), are fully oxidized

Krebs Cycle (Citric Acid Cycle)

• Glycolysis releases less than ¼ of energy in glucose (most of the rest is in pyruvate)

• O2 is required to extract the rest of energy• Pyruvate moves into mitochondria (active

transport) for Krebs Cycle• 1. Pyruvate to acetyl-CoEnzymeA

– This is first decarboxylation step (CO2 removed)– Oxidize the 2C remaining to form Acetate/Acetic Acid– Store energy by reducing NAD+ NADH– Acetate joins to CoEnzyme A (from B Vitamin– Acetyl-CoA has high potential energy / very reactive

Krebs Cycle (summary)

• A “metabolic furnace” oxidizing organic fuel (pyruvate), releasing CO2

A closer look – Krebs Cycle

• Pay attention to “start” of cycle (where pyruvate enters)

• Decarboxylation• Energetic compounds:

4 NADH, 1 FADH2, 1 ATP

• Waste compound: 3 CO2

• Regeneration of oxaloacetate (cycle)

The Citric Acid Cycle (“Krebs” Cycle / TCA Cycle)

• In Mitochondria• Decarboxylation (pyruvate CO2)• 1 ATP is produced• Most energy of pyruvate is stored in Electron

Carriers (NAD+/FAD) which were reduced

• FAD (oxidized) FADH2 (reduced)

• 4 NAD+ oxidized 4 NADH (reduced)

• This step does not require O2, but will not occur unless O2 available for next step

After Glycolyis & Krebs…

• All carbon from sugar converted to CO2 (exhaled)

• 4 ATP produced so far– 2 from glycolysis, 2 from Krebs (2 pyruvates)• Most energy stored in electron carriers

• Time to “cash ‘em in” (take NADH/FADH2 to “battery exchange”)

• We need OXYGEN!

• Glycolysis occurs in cytoplasm

• Krebs Cycle occurs in mitochondria (MATRIX)

• Oxidative Phosphorylation occurs in mitochondria (on and across inner membrane)

Folds of inner membrane known as “cristae”

Oxidative Phosphorylation: Electron Transport Chain (ETC) and Chemiosmosis

Intermembrane Space (“outside”)

Mitochondrial Matrix (“inside”)

Corrected Slide!

Electron Transport Chain:

gradual release of energy as e- travel from food to oxygen

• Electron Carriers (NADH, FADH2) donate 2 e- to series of molecules embedded in inner mitochondrial membrane

• NADH, FADH2 are oxidized to NAD+ and FAD

• “bucket brigade” passing e- down ETC, reducing each “downhill” molecule

• Final electron acceptor is oxygen (O2) (very electronegative)

• O2 + 2e- + 2H+ (protons from solution) H20

Moving electrons = electricity

• Electrons traveling down ETC made to do work

• Use flow of e- from NADH/FADH2 to pump H+ out of mitochondrial matrix (to “intermembrane space”

• H+ conc. matrix: low,

• H+ conc. in intermembrane space: high

Chemiosmosis (1978 Nobel Prize): use H+ gradient to do cellular work

• Charge/pH difference across membrane creates potential energy

• Flow of H+ across membrane used to power ATP Synthase

• ATP Synthase phosphorylates ADP ATP (endergonic reaction)

• 1 FADH2 used to create ~2 ATP

• 1 NADH used to create ~3 ATP

Chemiosmosis

• “Energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work.” (CR p176)

• H+ gradient “proton-motive force”

ATP Synthase

• Like a hydropower turbine

• It spins!

• Smallest rotary motor in nature

• ATP Synthase provides the only place H+ can diffuse back into matrix

• Read p175 (good summary)

Movies!

• Campbell Reece Animation #1

• “Californication” remix

• ATP Synthase Animation

3 steps of respiration (with Oxygen)

• Glycolyis: sugar split in two, 2 pyruvates produced, 2 ATP and 2 NADH

• Krebs: 2 pyruvates oxidized into CO2. 2 ATP, 6 CO2, 8NADH, 2FADH2 produced in mito matrix.

• Oxidative Phosphorylation: NADH/FADH2

transfer energy (electrons) to ETC, which gradually releases energy from food to oxygen. – Energy is used to pump protons (H+) out of matrix,

creating proton gradient (proton-motive force).– Proton-motive force used to power ATP synthesis

(chemiosmosis) as H+ diffuse back into matrix.

Counting ATP (more fun than counting sheep…)

• 2 ATP from glycolysis, 2 ATP from Krebs

• Each NADH powers production of ~3 ATP

• Each FADH2 powers production of ~2 ATP

• 10 NADH creates up to 30 ATP

• 2 FADH2 creates up to 4 ATP

• 36-38 ATP total

• ~40% efficient (rest of energy lost as heat)

Got Oxygen??? (Nope…)

• Fermentation animation (textbook)• Without oxygen, NADH is waste, must re-

generate NAD+ to keep glycolysis going• Fermentation = glycolysis + NAD+

regeneration• Alcholic Fermentation• Lactic Acid Fermentation• Only get ~5% of energy out of glucose

(compared to aerobic respiration)

Alcoholic Fermentation

• Many bacteria, yeast

• Pyruvate CO2 and Ethanol

– 2 NADH 2NAD+

http://glasscooking.files.wordpress.com/2007/09/fermentation.jpg

Lactic Acid Fermentation

• Some fungi/bacteria make yogurt/cheese

• Human muscles

• Pyruvate lacate

• 2NADH 2NAD+

Energy Pathways

Pathway Duration Running Distance

ATP / Creatine Phosphate(100g/120g)

2-3 seconds of ATP + 6-8 seconds of CP

<200m

Glycolysis / lactate (anaerobic)

A few minutes <800m

Aerobic Hours >1600m