INTRODUCTION TO CELLULAR RESPIRATION Copyright © 2009 Pearson Education, Inc.

Photosynthesis and cellular respiration provide energy for life  Energy is necessary for life processes –Why? –Growth- transport- manufacture –Movement- reproduction- other –This energy ultimately comes from the sun through photosynthesis light energy is converted into chemical energy –Organisms break down food gradually to release the chemical energy as ATP Copyright © 2009 Pearson Education, Inc.

Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts Glucose Cellular respiration in mitochondria H2OH2O CO 2 O2O2  (for cellular work) ATP Heat energy

Photosynthesis and cellular respiration provide energy for life  Cellular respiration - organisms use O 2 to harvest the energy in glucose (to make ATP!) and release CO 2 and H 2 O  All eukaryotic organism use cellular respiration to obtain energy glucose + oxygen  carbon + water + energy dioxide C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++

C 6 H 12 O 6 + 6O2O2 Glucose Oxygen 6 CO 2 Carbon dioxide + 6 H2OH2O Water + ATPs Energy

Cellular Respiration – the big picture: reactants: glucose (or some other fuel source) oxygen products: energy (ATP) carbon dioxide water

Why do we breathe?  supplies oxygen to our cells for cellular respiration  Also removes carbon dioxide  Cellular respiration uses O 2 to help harvest energy from glucose and produces CO 2 in the process  It is an aerobic process (requires oxygen) Copyright © 2009 Pearson Education, Inc.

What is the overall purpose of cellular respiration?  To get the energy in glucose and convert it into ATP molecules  ATP is energy that an be used by cells Copyright © 2009 Pearson Education, Inc.

Overview: Cellular respiration occurs in three main stages  Stage 1: Glycolysis - anaerobic  Stage 2: Krebs (citric acid cycle) - aerobic  Stage 3: Electron Transport Chain - aerobic Copyright © 2009 Pearson Education, Inc.

–Starts with  glucose (6 carbons) –Glucose is split into 2 molecules of pyruvate (3 carbons) –Glycolysis requires the input of energy –Not much energy is generated  only 2 ATP for every glucose –Also shuttles some electrons (in the form of NADH) to the electron transport chain (the final step in the process) –occurs in the cytoplasm  involves many steps (each catalyzed by its own enzyme) Copyright © 2009 Pearson Education, Inc. glucose      pyruvate 2x2x 6C 3C Stage 1: Glycolysis

pyruvate       CO 2 NEXT… If oxygen is present…  pyruvate enters mitochondria where enzymes of Krebs cycle finish the breakdown of sugar to CO 2 3C 1C If oxygen is NOT present… fermentation occurs – we will review this later

Stage 2: The Krebs (citric acid) cycle –First the pyruvate is converted into acetyl CoA which is then broken down into carbon dioxide  the Krebs cycle gives off CO 2 –occurs in the mitochondria –Produces a small amount of ATP, more electron carriers (NADH and another electron carrier called FADH 2 ) –that means more electrons to the ETC (electron transport chain)! Copyright © 2009 Pearson Education, Inc.

 The conversion of pyruvate and the Krebs cycle produces large quantities of electron carriers. NADH FADH 2 NADH

Glycolysis occurs in the cytosol.  glucose is broken down into two molecules of pyruvate.  Produces ATP and NADH Krebs cycle occurs in the mitochondria  Breaks down pyruvate to carbon dioxide.  Produces ATP, NADH, and FADH 2  NADH and FADH 2 pass electrons to the electron transport chain

Stage 3: The Electron Transport Chain (Oxidative phosphorylation) –NADH and FADH 2 (the energy carriers)are finally used to make lots of ATP –The electrons are shuttled through the electron transport chain in the inner mitochondrial membrane –ADP is converted into ATP as electrons are transported down the chain –Only occurs in the presence of oxygen – oxygen is the final electron acceptor Copyright © 2009 Pearson Education, Inc.

 As the ETC passes electrons down the energy staircase, it also pumps hydrogen ions (H + ) across the inner mitochondrial membrane into the intermembrane space creating a concentration gradient.  The concentration gradient sets up the flow of H + back into the matrix through ATP synthase (enzyme in the membrane) and ATP is produced Copyright © 2009 Pearson Education, Inc.

Where do the electrons end up?  Electrons from NADH or FADH 2 ultimately pass to oxygen.  THIS IS WHY WE MUST BREATHE!!!!  What if you don’t????? No oxygen means no ATP (energy) and cells die leading to the death of the organism!

Review: Each molecule of glucose yields many molecules of ATP –total yield of about 36 ATP molecules per glucose molecule –This is about 40% of a glucose molecule potential energy –water and CO 2 are also produced Copyright © 2009 Pearson Education, Inc.

Summary of cellular respiration  Where did the glucose come from?  Where did the O 2 come from?  Where did the CO 2 come from?  Where did the CO 2 go?  Where did the H 2 O come from?  Where did the ATP come from?  What else is produced that is not listed in this equation?  Why do we breathe? C 6 H 12 O 6 6O 2 6CO 2 6H 2 O ~38 ATP  +++

Pyruvate is a branching point Pyruvate O2O2 O2O2 mitochondria Kreb’s cycle aerobic respiration fermentation anaerobic respiration

Fermentation enables certain cells to produce ATP without oxygen  Fermentation is an anaerobic (without oxygen) energy-generating process –Still uses glycolysis to produce 2 ATP molecules but can’t go on to Krebs and ETC without oxygen –Still starts with glucose but occurs when NO oxygen is present –2 types: –Alcohol fermentation –Lactic acid fermentation Copyright © 2009 Pearson Education, Inc.

 alcohol fermentation –Used by some bacteria and yeasts (single-celled fungi) –converts pyruvate to CO 2 and ethanol –Important in baking and winemaking industry Copyright © 2009 Pearson Education, Inc.

 lactic acid fermentation –Used by your muscle cells and certain bacteria –converts pyruvate to lactic acid –Both types of fermentation produce just a little ATP (2) but can occur when there is no oxygen available Copyright © 2009 Pearson Education, Inc.