Download Ch 9 Cellular respiration

Ch. 9 Cell Respiration
Title: Oct 15 ­ 3:24 PM (1 of 53)
Essential question:
How do cells use stored chemical energy in organic molecules and to generate ATP?
Title: Oct 15 ­ 3:28 PM (2 of 53)
Title: Oct 19­9:29 AM (3 of 53)
Review of how ATP drives cellular work
Title: Oct 19­9:31 AM (4 of 53)
Where do organic compounds store their energy?
in their arrangement of atoms (potential energy)
by using enzymes, breakdown molecules to do work and produce heat (catabolic pathways)
two methods:
fermentation­partial degrading of sugars without using oxygen
cellular respiration­degrading of sugars with the use of oxygen
Title: Oct 15 ­ 3:31 PM (5 of 53)
Cellular respiration Overall Reaction
organic + oxygen CO2 + water + energy
compounds
organic compounds that can be used are carbs, proteins, and fats, use glucose as example
6 2
C H O + O 6CO + 6H O + energy (ATP 2
2
6 12 6
+ heat)
is exergonic = G = ­686kcal/mol
also uses redox reactions
Title: Oct 15 ­ 3:36 PM (6 of 53)
becomes oxidized
C H O + 6O 6CO + 6H O + energy
2
2
6 12 6
2
becomes reduced
hydrogen is transferred from glucose to oxygen; by oxidizing glucose, respiration gives off stored energy from glucose to make ATP
enzymes lower the activation energy needed to make this happen
Title: Oct 15 ­ 3:52 PM (7 of 53)
In cellular respiration , hydrogen atoms are not transferred directly to oxygen­ are passed to coenzyme called NAD+ (nicotinamide adenine dinucleotide) is an electron acceptor, an oxidizing agent
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dehydrogenases remove a pair of hydrogen atoms (2 e­, 2p+) from sugar (oxidizing it)
dehydrogenase gives 2 e­ and 1 p+ to NAD+, the other p+ is released into surrounding solution
­becomes NADH
Title: Oct 19­9:36 AM (9 of 53)
To finally get electrons to oxygen, need an electron transport chain (proteins imbedded in inner membrane of mitochondrion)
electrons (from food) are shuttled by NADH to the top of the ETC (high energy end)
At the bottom (lower energy end) oxygen captures the electrons with hydrogen protons to form water
Oxygen is the final electron acceptor
Title: Oct 15 ­ 6:18 PM (10 of 53)
Electron transport chains
Title: Oct 19­9:37 AM (11 of 53)
Overview of Cellular respiration
Title: Oct 15 ­ 6:46 PM (12 of 53)
Stages of Cellular respiration:
Glycolysis
Citric Acid cycle (Kreb's cycle)
Oxidative phosphorylation: Electron transport chain and chemiosmosis
Title: Oct 15 ­ 6:47 PM (13 of 53)
Glycolysis= "splitting of sugar"
­catabolic pathway
­occurs in cytosol
­glucose (6 C sugar) is split into 2 three C sugars which are then oxidized and rearranged to form 2 molecules of pyruvate
­consists of 10 steps (each requires an enzyme)
­some steps use energy (ATP)
­some steps form ATP
net yield = 2 ATP + 2 NADH + 2 pyruvate
Title: Oct 15 ­ 6:49 PM (14 of 53)
Energy input and output of glycolysis
Title: Oct 19­9:40 AM (15 of 53)
­no CO2 is released in glycolysis
­glycolysis occurs with (aerobic) or without (anaerobic) presence of oxygen
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Glycolysis ­ energy investment phases
Title: Oct 19­9:43 AM (17 of 53)
Energy payoff phase of glycolysis
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Citric Acid Cycle
­catabolic pathway
­takes place in mitochondrion matrix
­starts by having pyruvate transported inside mitochondrion
Title: Oct 15 ­ 6:59 PM (19 of 53)
Step 1
­pyruvate's carboxyl gp. is removed as CO2 and released by cell
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Step 2
­remaining 2 C fragment is oxidized to form acetate, an enzyme transfers e­ to NAD+ to become NADH
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Step 3
­coenzyme A (derived from a B vitamin) is attached to acetate (makes this gp. reactive)­ Acetyl CoA; acetyl gp. then goes into citric acid cycle for more oxidation
Title: Oct 19­9:47 AM (22 of 53)
Citric acid cycle = tricarboxylic acid cycle = Kreb's Cycle
pathway figured out by Hans Krebs in 1930s
http://nobelprize.org/nobel_prizes/medicine/laureates/1953/krebs­bio.html
Title: Oct 15 ­ 7:11 PM (23 of 53)
2
overview: (per pyruvate ­ actually 2 going in )
pyruvate is broken down into:
3 CO2 1 ATP formed via substrate level phosphorylation 4 NAD+ are reduced to 4 NADH
1 FAD is reduced to FADH 2
4 NADH and 1 FADH go to ETC from 2
here
*FAD = flavin adenine dinucleotide (derived from riboflavin ­ a B vitamin)
Title: Oct 15 ­ 7:12 PM (24 of 53)
­has 8 steps, each catalyzed by an enzyme
step 1 ­ acetyl gp is added to oxaloacetate to make citrate (condensation reaction)
steps 2­7 citrate is decomposed and converted back to oxaloacetate
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Citric acid cycle
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Summary of Kreb's Cycle
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What happens to the electrons being carried by NADH and FADH ?
2
Oxidative phosphorylation ­ The production of ATP generated by redox reactions in the Electron Transport Chain
Title: Oct 15 ­ 7:28 PM (28 of 53)
Electron Transport Chain
­in inner membrane of mitochondrion ­ has increased surface area (cristae) for lots of ETCs
­mostly made of proteins ­ multiprotein complexes #I­IV
­prosthetic gps. are attached to these proteins ­ nonprotein ­ needed for catalysis by enzymes
­during chain­electron carriers alternate between reduced and oxidized states as they gain and lose electrons
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Free energy change during electron transport
Title: Oct 15 ­ 7:37 PM (30 of 53)
In ETC:
NADH
passes electrons
flavoprotein
iron­sulfur protein
ubiquinone (not a protein)
series of cytochromes
cytochrome a3
oxygen (final electron acceptor)
Title: Oct 15 ­ 7:38 PM (31 of 53)
cytochromes have an iron group that accepts and donates electrons, each has a different heme grp.
oxygen then picks up two hydrogens from solution to form water
FADH adds electrons to the ETC at complex II (a lower energy 2
level than NADH) ­ makes 1/3 less energy for ATP synthesis than NADH
*ETC makes no ATP ­ its purpose is to ease the fall of electrons to release energy in small amounts at a time or otherwise would be explosive
Title: Oct 15 ­ 7:47 PM (32 of 53)
Chemiosmosis
=an energy coupling mechanism that uses stored energy in the form of a hydrogen ion gradient across a membrane to drive cellular work
­in inner mitochondrion membrane
­ATP synthase is a enzyme used to make ATP from ADP and inorganic phosphate
ATP synthase uses a concentration gradient of hydrogen ions to power ATP synthesis
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chemiosmosis couples electron transport chain to ATP synthesis
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ATP synthase
four parts made of polypeptides
a. rotor ­ within membrane spins when hydrogen ions flow past it down gradient
b. stator­ anchored in membrane, holds knob stationary
c. rod ­ extends into knob and spins, causing a conformational change and activating catalytic sites in the knob
d. knob ­ stationary, has three catalytic sites that join inorganic phosphate to ADP to make ATP
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ATP synthase
Title: Oct 19­9:58 AM (36 of 53)
How does the hydrogen ion gradient get produced?
from electron transport chain
­certain steps in ETC cause H+ to be taken up and released into the surrounding solution
­H+ is accepted from mitochondrial matrix and deposited in intermembrane space
­H+ gradient = proton­motive force
Title: Oct 15 ­ 8:03 PM (37 of 53)
ATP yield per molecule of glucose at each stage in cellular respiration
Title: Oct 15 ­ 8:16 PM (38 of 53)
each NADH generates 3 ATP
each FADH generates 2 ATP
2
net result = 36 or 38 ATP per molecule of glucose (depends on variables)
40% of energy in glucose is transferred to ATP, the rest is lost as heat
Title: Oct 15 ­ 8:18 PM (39 of 53)
How can a cell make ATP if there is no oxygen present?
Fermentation
Title: Oct 15 ­ 10:02 PM (40 of 53)
Fermentation generates ATP by substrate level phosphorylation as long as there is enough NAD+ (get enough because in anaerobic conditions,electrons are transferred from NADH to pyruvate)
­pyruvate is electron acceptor for oxidizing NADH back to NAD+ and can then be reused in glycolysis
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two types of fermentation:
1.alcohol fermentation (yeast & bacteria)
2. lactic acid fermentation (yeast/ fungi used in dairy industry, and human muscle cells)
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Alcohol fermentation
end product = ethanol
­makes 2 ATP, 2 carbon dioxide
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Lactic Acid Fermentation
­end product is lactate (ion form of lactic acid)
­2 ATP made
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So: Both fermentation and cellular respiration:
­use glycolysis to oxidize glucose
­produce 2 ATP by substrate level phosphorylation
­NAD+ is oxidizing agent that accepts electrons from food in glycolysis
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Differences:
­fermentation final electron acceptor = pyruvate or acetaldehyde
­respiration final electron acceptor = oxygen
­respiration has citric acid cycle
­respiration can make more ATP per sugar molecule
facultative anaerobes are yeasts or bacteria that can make enough ATP to survive using either fermentation or respiration
our muscle cells are like facultative anaerobes
Title: Oct 15 ­ 10:27 PM (46 of 53)
glycolysis is important in evolution
­ before oxygen was present in the atmosphere organisms could use glycolysis to make ATP
­is the most widespread metabolic pathway ­because happens in cytosol is also evidence it evolved early
Title: Oct 15 ­ 10:32 PM (47 of 53)
Types of molecules that can be used for glycolysis:
1. carbohydrates: if dissaccharides, polysaccharides, first need to be hydrolyzed to glucose and other monosaccharides
2. proteins: must be hydrolyzed to amino acids, then converted by enzymes to intermediates in glycolysis and citric acid cycle (amino gps must be removed first=deamination)
3. Fats:digested to glycerol and fatty acids, glycerol is converted to glyceraldehyde ­3­phosphate (intermediate in glycolysis)
fatty acids undergo beta oxidation to get 2 C fragments that can enter the citric acid cycle as acetyl CoA
Title: Oct 15 ­ 10:36 PM (48 of 53)
How different molecules are involved in Cellular respiration
Title: Oct 19­10:04 AM (49 of 53)
Anabolic pathways that are used by organisms are related to glycolysis and citric acid cycle
­some intermediates of glycolysis and citric acid cycle can be used to synthesize other compounds
­can make amino acids using compounds from citric acid cycle
­glucose made from pyruvate
­fatty acids made from acetyl CoA
Title: Oct 15 ­ 10:45 PM (50 of 53)
feedback inhibition regulates cellular respiration
­end product inhibits an enzyme that catalyzes part of the pathway
ex. phosphofructokinase (allosteric enzyme with receptor sites for specific inhibitors and activators)
if ATP high ­ gets inhibited, slows glycolysis
if AMP high ­ gets stimulated
if citrate is high in mitochondria, some gets in cytosol and inhibits enzyme
if citrate is low, glycolysis increases
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Control of cellular respiration
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Title: Oct 22­11:45 AM (53 of 53)