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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
Photosynthesisin chloroplasts
Glucose
Cellular respirationin mitochondria
H2O
CO2
O2
(for cellular work)
ATP
Heat energy
Photosynthesis and cellular respiration provide energy for life
Cellular respiration - organisms use O2 to harvest the energy in glucose (to make ATP!) and release CO2 and H2O
All eukaryotic organism use cellular respiration to obtain energy
glucose + oxygen carbon + water + energydioxide
C6H12O6 6O2 6CO2 6H2O ATP+ + +
C6H12O6 + 6 O2
Glucose Oxygen
6 CO2
Carbondioxide
+ 6 H2O
Water
+ ATPs
Energy
Cellular Respiration – the big picture:
reactants: glucose (or some other fuel
source)oxygen
products:energy (ATP)carbon dioxidewater
Why do we breathe?
supplies oxygen to our cells for cellular respiration
Also removes carbon dioxide
Cellular respiration uses O2 to help harvest energy from glucose and produces CO2 in the process
It is an aerobic process (requires oxygen)
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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
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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
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– 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)
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glucose pyruvate2x 6C 3C
Stage 1: Glycolysis
pyruvate CO2
NEXT…If oxygen is present…
pyruvate enters mitochondria where enzymes of Krebs cycle finish the breakdown of sugar to CO2
3C 1C
If oxygen is NOT present…fermentation occurs – we willreview 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 CO2
– occurs in the mitochondria
– Produces a small amount of ATP, more electron carriers (NADH and another electron carrier called FADH2 )
– that means more electrons to the ETC (electron transport chain)!
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The conversion of pyruvate and the Krebs cycle produces large quantities of electron carriers.
NADHNADH NADH
NADHNADH
NADHNADH
NADH
NADH
FADH2
FADH2
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 FADH2
NADH and FADH2 pass electrons to the electron transport chain
Stage 3: The Electron Transport Chain (Oxidative phosphorylation)
– NADH and FADH2 (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
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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
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Where do the electrons end up?
Electrons from NADH or FADH2 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 CO2 are also produced
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Summary of cellular respiration
Where did the glucose come from?
Where did the O2 come from?
Where did the CO2 come from?
Where did the CO2 go?
Where did the H2O come from?
Where did the ATP come from?
What else is produced that is not listed in this equation?
Why do we breathe?
C6H12O6 6O2 6CO2 6H2O ~38 ATP+ + +
Pyruvate is a branching point
Pyruvate
O2O2
mitochondriaKreb’s cycle
aerobic respiration
fermentationanaerobic
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
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alcohol fermentation
– Used by some bacteria and yeasts (single-celled fungi)
– converts pyruvate to CO2 and ethanol
– Important in baking and winemaking industry
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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
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