Cellular Respiration – Guided Notes
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Autotrophs: self-feeders
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Photosynthesis
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Producers
Heterotrophs: other eaters
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Consumers
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Cellular Respiration: chemical process that uses oxygen to convert chemical energy stored in
organic molecules into another form of energy
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Kinetic energy: energy of motion
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Potential energy: energy that is stored due to an object’s position or arrangement
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Thermal energy: (heat) total amount of energy associated with the random movement of
atoms and molecules in a sample of matter
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Chemical energy: potential to do work due to the arrangement of atoms with the molecules
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calorie: amount of energy required to raise the temperature of 1 gram of water by 1o Celsius
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A calorie is such a tiny unit of energy so people usually express the energy in food in kilocalories
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1 kilocalorie= 1000 calories
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ATP: adenosine triphosphate
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The triphosphate tail is the business end of ATP…it is the source of energy used for most cellular
work
Examples of Cellular Work
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Chemical work: building large molecules such as proteins
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Mechanical work: contraction of a muscle cell
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Transport work: pumping solutes across a cell membrane
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ATP is continuously converted to ADP as your cells do work
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ATP is “recyclable”!!
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ADP can be converted back to ATP by adding a third phosphate group…this requires energy…the
source of energy is the organic molecules in food
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This cycle is fast repeating…a working muscle cell recycles all of its ATP molecules about once
each minute!! (that’s 10,000,000 ATP molecules spent and regenerated per second
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Cellular respiration is an aerobic process…it requires oxygen!
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Respiration is used to describe breathing
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Breathing for a whole organism is not the same as cellular respiration, but the two processes are
related
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Why does the process of cellular respiration release energy?
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An atom’s positively charged nucleus exerts an electrical “pull” on negatively charged electrons
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When an electron “falls” toward the nucleus, potential energy is released
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Oxygen attracts electrons very strongly…it is sometimes called an “electron grabber”
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Carbon and hydrogen atoms exert much less pull on electrons
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Cellular respiration is a controlled fall of electrons…like a step-by-step “walk” of electrons down
an energy staircase
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Cellular respiration unlocks the energy in glucose in small, manageable amounts…the formation
of ATP molecules
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Oxygen only comes in as an electron acceptor at the end
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Structure of mitochondria
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All the chemical processes that take place in cells make up the cell’s metabolism…cellular
respiration is one type of chemical process
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Cellular respiration consists of a series of reactions and is referred to as a metabolic pathway
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Stage I: Glycolysis
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Glycolysis is the chemical break down of a glucose molecule
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Splitting of sugar
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Takes place outside the mitochondria in the cytoplasm of the cell
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Two ATP molecules are used as an “investment”
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Glucose is split into two three-carbon sugars, each with a phosphate group
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Each of these pyruvate molecules then transfers electrons and hydrogen ions to a
carrier molecule called NAD+
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NAD+ is converted to NADH
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Pyruvates lose the phosphate groups to form two pyruvic acids
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Four new ATP molecules are produced…a net gain of two ATP molecules (“payment”)
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Fermentation
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Fermentation= cellular process of making ATP without oxygen
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Makes ATP entirely from glycolysis… remember that glycolysis does not use oxygen
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Doesn’t seem very efficient, but if enough sugar is burned, fermentation can regenerate enough
ATP molecules for short bursts of activity
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Lactic acid is a waste product of fermentation
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Temporary build up of lactic acid in muscles contributes to fatigue after exercising
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Our bodies consume oxygen to convert lactic acid back to pyruvic acid
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We gain the oxygen supply by breathing heavy or stop exercising
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Fermentation can be yummy!!
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Anaerobic= without oxygen
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Yeast are forced to ferment sugar when they are placed in an anaerobic environment
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Fermentation in yeasts produces alcohol, alcoholic fermentation, and carbon dioxide
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Bread, beer, wine, etc.
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Some bacteria found in stagnant ponds or deep in the soil are actually poisoned if they come
into contact with oxygen
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All of their ATP is generated by fermentation
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Stage II: The Krebs Cycle
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Hans Krebs 1930s
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Krebs Cycle finishes the breakdown of pyruvic acid molecules to carbon dioxide
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More energy is released
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The fluid matrix in the inner membrane of the mitochondrion contains the enzymes for the
Krebs cycle
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The pyruvic acid molecules diffuse into the mitochondrion
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They then lose a CO2 molecule…the resulting molecule is then converted to a two-carbon
compound called acetyl coenzyme A (also known as acetyl CoA)
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The acetyl CoA then enters the Krebs Cycle
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Once in the Krebs cycle, each acetyl CoA joins a four-carbon acceptor molecule
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The Krebs cycle produces two CO2 molecules and one ATP molecule per acetyl CoA molecule
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But…electron carriers trap most of the energy
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At the end of the cycle the four-carbon acceptor molecule has been regenerated and the cycle
can continue
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Since each turn of the Krebs cycle breaks down one acetyl CoA molecule, the cycle actually turns
twice for each glucose molecule, producing a total of four CO2 molecules and two ATP molecules
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Stage III: Electron Transport Chain and ATP Synthase Action
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Final stage of cellular respiration
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Occurs in the inner membrane of mitochondria
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Electron transport chain= sequence of electron carrier molecules that transfer electrons and
release energy during cellular respiration
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Carrier molecule (NADH) transfers electrons from the original glucose to an electron transport
chain
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Electrons are transported through the chain being pulled to oxygen at the end of the chain
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At the end of the chain the oxygen and hydrogen ions combine to form water
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Each transfer in the chain releases a small amount of energy
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This energy is used to pump hydrogen ions across the membrane
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This pumping action stores potential energy
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Mitochondria have protein structures called ATP synthases
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Hydrogen ions pumped by electron transport rush back through the ATP synthase
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The ATP synthase uses energy from the flow of hydrogen ions to convert ADP back to ATP
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Generates up to 34 ATP molecules for every one glucose molecule
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This process is similar to how a dam works!
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Adding up the ATP molecules
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Glycolysis
= 2 ATP
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Krebs cycle
= 2 ATP
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ATP synthase = 34 ATP
Total
38 ATP