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Chapter 7- How Cells Harvest Energy
Terms in this set (44)
Organism that converts radiant energy from the sun into chemical energy; 10% of all organisms
Organism that lives off of the chemical energy autotrophs produce; include animals, fungi, and most eubacteria and protists (90% of all organisms)
all chemical reactions in a cell
specific sequence reactions leading from precursor molecules to product molecules
synthesis pathway involving growth & repair, building molecules up; usually endergonic
provide energy for anabolic reactions
: involved with decreasing molecular order & complexity as the reaction proceeds
-cells do catabolism to get energy for anabolism (usually in form of ATP), to get building block molecules, to recycle cellular components
(Aerobic) cellular respiration
-An ATP-producing catabolic (complex to simple) process (exergonic)
-ultimate electron acceptor is an inorganic molecule, such as oxygen
organic compounds +oxygen --> carbon dioxide + water + energy.
-Carbohydrates, proteins and fats can all be metabolized as fuel, but cellular respiration is most often described as the oxidation of glucose
*Consider: C6H12O6 + 6O2 --> 6CO2 +6H20 +energy
Complete oxidation of glucose to CO2. Most ATP made by oxidative phosphorylation during which energy stored in chemical bonds is used for this synthesis. Oxygen utilized in cellular respiration shows up as H2O.*
When an inorganic molecule other than oxygen is final electron acceptor
Adenosine triphosphate (energy currency of cell with energy stored in linked, charged phosphate groups)
Uses for ATP
-activities that require work
-drive endergonic reactions
How ATP drives endergonic reactions
Enzyme that catalyzes endergonic reaction has two binding sites, one for reactant and one for ATP. ATP site splits ATP, freeing
change of free energy = -7.3 kcal/mol
catabolism of glucose
Consider: While from a chemical viewpoint, catabolism of glucose (cellular respiration) and burning glucose are very similar (same total energy), more energy is released as heat (not useable to pay for cell work) when glucose is burned rather than catabolized. So it makes sense to convert glucose potential energy (in a cell as high as 720 kcal/mol) into ATP, thereby minimizing lost energy (unsuable) in the form of heat.
cellular respiration pathways
1. glycolysis 2. pyruvate oxidation 3. Krebs (citric) cycle 4. electron transfer thru electron transport chain
(ADP +Pi --> ATP)
glycolysis: glucose (6carbon) + 2ATP (glucose priming) + 2NAD+ --> 2 pyruvate (3carbon) + 2NADH + 4ATP (4-2 (ATP used for glucose priming)= 2ATP net thru substrate phosphorylation)
Consider: Glycolysis is a process common to all living organisms and will occur in the presence or absence of oxygen.
glucose + oxygen --> CO2 + water + ATP + heat
4 major pathways in oxidative respiration:
2.pyruvate oxidation ( pyruvate -> AcetlyCoA)
3. Krebs cycle
-1st stage of cellular respiration
-brakes down glucose to form ATP
-2 molecules of pyruvate are formed
-occurs in cytosol (no molecular oxygen used; no mitochondrion participation; catalyzing enzymes are in cytoplasm)
-10 enzyme catalyzed reactions/pathways that extract energy from glucose to produce ATP.
-the oldest part of cellular respiration
pyruvate + NAD + CoA----> acetyl-CoA + NADH + CO2
~the pyruvate continues to the mitochondria matrix where the multi-enzyme complex is (pyruvate dehydrogenase).
~ goes to fermentation (anaerobic)
-Pyruvate looses an electron (3 carbon to 2 carbon molecule) and produces CO2 and acetyl-CoA.
- For each molecule, one of NAD+ reduces to NADH (this later carriers electron to make ATP during Krebs cycle)
Krebs/Citric Acid Cycle Stages
1. the acetyl-CoA (from the oxidation of the pyruvate) is combined with
2. acetyl-CoA + pyruvate --> citric acid
3. citric acid gets oxidizes into many electron carries that will later be used in the ETC.
in consideration of ONE pyruvate
Process goes by, reduction of coenzyme electron carries..
NAD+ --> NADH...(x3)
ADP + Pi---> ATP..(1) (substrate level phosphorylation)
THIS IS FOR ONE PYRUVATE
there is 2 pyruvates
products at end of glycolysis, pyruvate oxidation, and Krebs Cycle
6 CO2 (4 CO2 in kreb cycle + 2 CO2 in acetly-CoA)
4 ATP (2 ATP kreb cycle + 2 ATP glycolysis)
10 NADH (6 NADH kreb cycle + 2 NADH pyruvate oxidation + 2 NADH glycolysis)
2 FADH2 ( kreb cycle)
Cytochrome = type of protein molecule that contains a heme prosthetic group and that functions as an electron carrier; the iron of cytochromes that transfer electrons
Heme group = Prosthetic (A tightly bound, specific non-polypeptide unit ) group composed of four
organic rings surrounding a single iron atom.
allow electrons carried through here to reduce oxygen into water
Enzyme that catalyzes synthesis of ATP by using energy stored in gradient of protons that is built across membranes (plasma membrane of prokaryotes; inner membranes of mitochondria or chloroplasts)
Consider: Theoretical eukaryote total yield per glucose = 36 ATP (4 ATP through substrate phosphorylation before Electron Transport Chain and 32 ATP generated from oxidative phospolylation and chemiosmosis after Krebs Cycle)
How does ATP synthase operates?
ATP synthase is embedded in membrane; forms channel for proton movement down concentration gradient (diffusion force similar to osmosis, therefore called chemiosmosis); energy released causes component rotation; mechanical energy converted into terminal chemical bond that holds 3rd phosphate group
change in G of glucose oxidation
-compound that has highest free energy and produces most ATP per molecule
feedback inhibition of aerobic respiration
- citrate (produced during Krebs Cycle) inhibits phosphofructokinase during glycolysis - NADH (produced during Krebs Cycle) inhibits Pyruvate dehydrogenase during glycolysis
catabolism of proteins and fats
fatty acid tails are converted to acetyl groups by ß- oxidation (beta oxidation); amino acids undergo deamination to remove amino group and remainder of amino acid converted into molecule that enters glycolysis or Krebs cycle
glycolysis net (end product)
2 ATP (~2% of chemical energy of glucose) & 2 NADH
Recycling of NADH under anaerobic conditions
the high energy e- is dumped back into the pyruvate creating
lactate or ethanol
giving us NAD+ back.
Lactate (lactic acid fermentation)
Muscle cells experiencing heavy exercise have limited oxygen reserves, so they resort to lactic acid fermentation (anaerobic metabolism of glucose) for energy production.
Glucose to pyruvate reacts with NADH + H+ lactate + NAD+
Consider: Whether fermentation produces ethanol or lactate, it always produces NAD+.
oxidation without oxygen
- methanogens use CO2 (final electron acceptor), reducing it to CH4 (methane) - sulfur bacteria use inorganic sulphate, SO4 (final electron acceptor), reducing it to H2S
how many NADH and FADH2 (both reduced electron carriers) are produced?
10 (8 NADH and 2 FADH2)
NAD+, FAD function
become reduced and carry hydrogen atoms (electrons) and free energy from compounds being oxidized to give hydrogen atoms and free energy to compounds being
electron carrier that is used in harvesting energy from glucose molecules in a series of gradual steps
- the conversion of glucose to pyruvate and the subsequent utilization of pyruvate to regenerate NAD+
comparison between aerobic and anaerobic
Both cellular respiration (aerobic) and anaerobic
1. begin with glycolysis (oldest process in terms of evolution)
2. oxidize glucose to pyruvate
3. both produce NADH as high-energy intermediates.
(energy investment)- 2 ATP are used to start the process of glucose oxidation. (ATP is broken down, phosphate is attached to molecule) they are added to a 6-carbon molecule glucose. The final is a 6-carbon molecule with 2 phosphates.(-2 ATP)
- The 6-carbon molecule splits into 2 3-carbon sugar phosphate. ( glyceraldehyde-3-phosphate) (G3P)
- 2 NAD+ picks up electrons and hydrogen ions forming NADH
-energy is released when NAD+ binds to the molecule forming a phosphate group which is attached to the molecule.
-ADP + Pi--> ATP for each of the 4 total phosphate groups. (-2 ATP + 4 ATP produced = 2 ATP in total) (0 NADH + 2 NADH= 2NADH)
- stays with 2 3-carbon pyruvate
a 3-carbon molecule that is the end product of glycolysis.
multi-enzyme complex that removes CO2 from pyruvate
-its one of the largest enzymes known!
- result= pyruvate is oxidized
decarboxylation of pyruvate
takes place in mitochondrion and produces the CO2, acetylCoA, and NADH
the link between glycolysis and Krebs
Krebs/Citric Acid Cycle
-Acetyl-CoA is cycled thru 9 reactions; enzymes are located in matrix of mitochondria
-1 glucose drives 2 Krebs cycle
-Krebs Cycle takes place in mitochondria matrix
6 carbon glucose is completely broken down into 6 CO2
TOTAL AMOUNT PRODUCED IN KREB CYCLE.
Oxidative phosphorylation/ Electron Transport Chain
-located in the inner mitochondrial membrane;
- electrons are transported and eventually form ATP.
Oxidative phosphorylation/ Electron Transport Chain Stages
After glycolysis/krebs, you are left with 10 NADH and 2 FADH2.
1. NADH---> NAD+ +H+ +
(oxidation of NADH)
formed go through a series of protein complexes (electron carriers) to release energy from a high energy level state to a low energy level state.
Eventually reducing oxygen into water
THEY ENTER THE CYTOCHROME OXIDASE COMPLEX (THE LAST PROTEIN BEFORE ATP SYNTHASE) WHICH ALLOWS THEM TO OXIDIZE OXYGEN INTO WATER
3.They use this energy that is released to pump protons (H+) from the matrix on to the outer membrane of the mitochondria.
4.They create a proton gradient (a difference between inner and outer concentration) and want to go back in and they go through
5. When the protons enter ATP synthase, it uses it as an energy source to drive the axel to spin. While the axel is spinning, ADP and phosphate groups are being squished together forming ATP.
What percent is cellular respiration efficient in capturing glucose energy?
32% efficient in capturing glucose energy in form of 36 ATP
cellular respiration is ~32% efficient in capturing glucose energy in form of 36ATP
Where does 1.glycolysis 2. pyruvate oxidation 3. krebs 4. ETC take place?
3. mitochondria matrix
4. inner membrane space of mitochondria
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