Ch 9- Cellular Respiration

Ch 9- Cellular Respiration
• How do we get the energy we need?
– Food
– What in food gives us the energy we need?
• Cellular Respiration- process that releases energy
by breaking down food molecules in the presence
of oxygen
– Made up of glycolysis, Krebs cycle, and the electron
transport chain
• Equation for cellular respiration
– 6 O₂+ C₆H₁₂O₆→ 6 CO₂+ 6 H₂O + Energy
Main Stages of Cellular Respiration
• Each stage captures some of the chemical energy available in food
molecules and uses it to produce ATP
• Glycolysis- process in which one molecule of glucose is broken in
half, producing two molecules of pyruvic acid- 3-carbon compound
• Glycolysis needs 2 ATP molecules to begin process
• What happens during glycolysis?
– 2 molecules of pyruvic acid, 2 molecules of ATP, and 2 molecules of
NADH are produced
• One of reactions of glycolysis removes 4 high energy electrons and
passes them to NAD⁺-electron carrier
– Each NAD⁺ accepts a pair of high energy electrons and transfers them
to other molecules
– Allows energy from glucose to be passed to other pathways in cell
• Cellular Respiration
• Releases energy from food molecules by
producing ATP in the absence of oxygen
• What happens during fermentation?
– NADH is converted back to NAD⁺ by passing high
energy electrons back to pyruvic acid
– Allows glycolysis to produce steady supply of ATP
• Anaerobic
• 2 main types of fermentation- alcoholic
fermentation and lactic acid fermentation
• Alcoholic fermentation- uses pyruvic acid and
NADH to produce ethyl alcohol, carbon
dioxide and NAD⁺
– Used by yeasts and few other microorganisms
• Lactic Acid- uses pyruvic acid and NADH to
produced lactic acid and NAD⁺
– Produced in muscles during rapid exercise when
body cannot supply enough oxygen to tissues
– Unicellular organisms produce lactic acid as waste,
as result prokaryotes are used in array of food
Sec 2- Krebs Cycle and Electron
• 90% of chemical energy still available in
glucose after glycolysis, locked up in high
energy electrons of pyruvic acid
• Oxygen is required for final steps of cellular
respiration- aerobic
Krebs Cycle
• Oxygen must be present
• Also known as Citric Acid Cycle
• During cycle, pyruvic acid is broken down into carbon
dioxide in a series of energy extracting reactions
• Citric Acid Production
– Pyruvic acid enters mitochondrion, carbon is removed
forming CO₂, electrons are removed, changing NAD⁺ to
– Coenzyme A joins the 2 carbon molecule, forming acetylCoA. Acetyl- CoA adds the 2 carbon acetyl group to a 4carbon compound forming citric acid
• Energy Extraction
– Citric acid is broken down into 5-carbon
compound and then into 4-carbon compound
– 2 more molecules of CO₂ are released and
electrons join NAD⁺ and FAD, forming NADH and
FADH₂, one molecule of ATP is generated
– Energy output from one molecule of pyruvic acid=
4 NADH, 1 FADH₂, and 1 molecule of ATP
• CO₂ released is source of all carbon dioxide we
• ATP produced in Krebs cycle is used for cellular
Electron Transport Chain
• Krebs cycle generates high energy electrons that are
passed to NADH and FADH₂
• Electrons are passed from carriers to electron transport
• Uses high energy electrons from Krebs cycle to convert
• Takes place in mitochondrion
• Steps of Electron Transport Chain
– High energy electrons passed along chain from one carrier
protein to next. At end of chain, enzyme combines these
electrons with hydrogen ions and oxygen to form water
– Oxygen serves as final acceptor, it is essential for getting
rid of low energy electrons and hydrogen ions-the wastes
of cellular respiration
• Every time 2 high energy electrons transport
down chain, energy is used to transport
hydrogen ions across the membrane
• Inner membrane of mitochondria contain
protein spheres called ATP synthases, as H⁺
ions escape through channels, into these
proteins, ATP synthases spin and grab a low
energy ADP and attaches a phosphate,
forming high energy ATP
• On average, each pair of high energy electrons
produces 3 molecules of ATP from ADP
• Glycolysis produces 2
ATP molecules
• Krebs cycle and Electron
Transport Chain
produce roughly 36 ATP
molecules, 18 times
more than glycolysis

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