Lecture 7 Flashcards
Cell Respiration
Sugars are broken down and oxidized to produce CO2 and water
the energy is captured in form of high energy chemical bonds.
Explanation: The energy released during these reactions is captured in the form of “high-energy” chemi- cal bonds—covalent bonds that release large amounts of energy when hydrolyzed—in activated carriers such as ATP and NADH. These carriers in turn serve as portable sources of the chemical groups and electrons needed for biosynthesis
Activation
Molecules require a boost over an energy barrier to undergo chemical reaction, this boost is activation energy
The controlled, stepwise oxidation of sugar in cells captures useful energy, unlike the simple burning of the same fuel molecule
The direct burning of sugar in nonliving conditions releases
a large amount of energy all at once. This quantity is too large to be captured by
any carrier molecule, and all of the energy is released as heat.
In a cell, enzymes catalyze the breakdown of sugars via a series of small steps, in which a portion of the free energy released is captured by the formation of activated carriers—most often ATP and NADH.
Each step is catalyzed
by an enzyme that lowers the activation- energy barrier that must be surmounted by the random collision of molecules at the temperature of cells (body temperature),
so as to allow the reaction to occur
Catabolism
breakdown of molecules into smaller subunits.
In animals, the breakdown
of food molecules occurs in three stages.
Stage 1: Breakdown of large food molecules to simple subunits.
Stage 2: Breakdown of simple subunits to Acetyl CoA; Limited amounts of ATP and NADH produce. Glycolysis.
Stage 3: Complete oxidation of the Acetyl group in the acetyl coA to H2O and CO2; Large amount of ATP produced on the inner mitochondrial membrane. Stage 3 of catabolism takes place entirely in mitochondria.
NET RESULT FOOD+O2–» ATP+NADH+CO2+H2O
Gycolysis
TAKES PLACE IN THE CYTOSOL AND DOES NOT REQUIRE OXYGEN.
Produces ATP and NADH
Oxidation reaction (loss of an electron).
Glycolysis can be divided into
-Energy investment
-Energy production
Includes: Substrate level
phosphorylation
The final metabolite produced by glycolysis is
Pyruvate.
Enzymes of the glycolytic pathway
Include:
Kinase –»» A kinase transfers a phosphate group from ATP to a substrate in steps 1 and 3; other kinases transfer a phosphate to ADP to form ATP in steps 7 and 10.
Isomerase —-»» Isomerases in steps 2 and 5 prepare molecules for the chemical alterations to come.Catalyzes the rearrangement of bonds within a single molecule.
Dehydrogenase—–»» catalyzes the oxidation of a molecule by removing a hydrogen atom plus an electron. The enzyme glyceraldehyde 3-phosphate dehydrogenase generates NADH in step 6
Mutase—–»» The movement of phosphate by phosphoglycerate mutase in step 8 helps prepare the substrate to transfer this group to ADP to make ATP in step 10. Catalyzes the shifting of a chemical group from one position to another within a molecule
Glycolysis general steps
Invest one molecule of glucose, an energy investment to be repaid later.
fructose 1,6- bisphosphate—»> cleavage of the six-carbon sugar to two three-carbon sugars —–»»> two molecules of glyceraldehyde 3-phosphate—-»> energy generation—-»> two molecules of pyruvate.
Glycolysis steps 1-4
Step 1: Glucose is phosphorylated by ATP, forming a sugar-phosphate glucose 6-phosphate.Done by Enzyme Hexokinase. A kinase
Glucose+ATP—»> glucose 6-phos +ADP+Hplus. A hexokinase does this.
Step 2: phosphoglucose isomerase reorganizes the chemical structure from a ring form to an open-chain form, forming fructose 6-phosphate.
Step 3: phosphofructokinase adds a phosphate group. Becomes fructose 1,6 bisphosphate.
Step 4: The six-carbon sugar is cleaved to produce two three-carbon molecules. Only the glyceraldehyde 3-phosphate can proceed immediately through glycolysis. Done by Aldolase.dihydroxyacetone phosphate and glyceraldehyde 3-phosphate are made.
Glycolysis steps 5-10
Step 5: dihydroxyacetone phosphate, is isomerized to form a second molecule of glyceraldehyde 3-phosphate. Done by Trisoe phosphate isomerase.
Step 6: glyceraldehyde 3-phosphate oxidation, energy generation phase of glycolysis beings.
NADH and a new high-energy linkage to phosphate formed.
1,3-bisphosphoglycerate and NADH is created.
step 7: The transfer to ADP of the high-energy phosphate group that was generated in step 6 forms ATP. Done by the phosphoglycerate kinase. Creating ATP and 2-phosphoglycerate.
Step 8: 3-phosphoglycerate becomes a 2-carbon sugar. Done by Mutase.
Step 9: Water is removed from 2- 2-phosphoglycerate by enolase, creating h02 and a high-energy enol phosphate linkage.
Step 10: the transfer for ADP to the high-energy phosphate group generated in step 9 form ATP. This is done by Pyruvate kinase. phosphoglycerate becomes pyruvate when the phosphate group is removed from it and added to adp by proyvuate kinease.
Net Result of Glycolysis
For every one molecule of glucose
Two moles of pyruvate are made.
Two moles of ATP is made.
Two moles of NADH is made.
CITRIC ACID CYCLE STEPS
Occurs in the mito, the starting molcules is Acetyl CoA. Product carriers are 3NADH, GTP,FADH2.
Porduct 2 CO2, Oxaloacate.
Step 1: Citrate synthase removes CH3 from acetyl CoA. Now oxaloacetate is attracted to the negatively charged CH2 on coA, oxaloacetate forms a bond to CH2. This causes a loss of coenzyme A by hydrolysis, this drives the reaction forward.
acetyl CoA+ oxaloacetate–» Water is added+ Citrate+coenzymeA+ H+.
Step 2: isomerization reaction, water removed then added. Citrate becomes Isocitrate.
Step 3: isocitrate, NAD+ becomes NADH+H+ —» α-ketoglutarate formed.
Step 4: α-ketoglutarate dehydrogenase complex, catalyzes ozidation of NADH,CO2 and a high energy coenzyme A (CoA). NADH formed and CO2 released
α-ketoglutarate+CoA–»> succinyl CoA.
Step 5: succinyl CoA becomes succinate + HS CoA. this is done with P is added. GDP becomes GTP.
Step 6: Oxidation step GAD accepts two hydrogen atoms from succinate. Becomes FADH2 and Furmarate.
Step 7: Water added to fumarate giving us Malate. fumarase
Step 8: In the last of four oxidation steps in the cycle, the carbon carrying the hydroxyl group is converted to a carbonyl group, regenerating the oxaloacetate needed for step 1.
malate–»» NAD+ NADH then it creates –»> oxaloacetate.
Citric Acid Cycle overview
The two carbons from acetyl CoA that enter this turn of the cycle. will be converted to CO2 in subsequent turns of the cycle: the two carbons in the starting oxaloacetate. will be converted to CO2 in this cycle.
Each turn of the citric acid cycle produces? net result
NET RESULT: ONE TURN OF THE CYCLE PRODUCES THREE NADH, ONE GTP, AND ONE FADH2, AND RELEASES TWO MOLECULES OF CO2
