Kaplan MCAT Biology 03
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45 terms
Terms | Definitions |
|---|---|
 Cellular Metabolism | - the sum total of all chemical reactions that take place in a cell - either anabolic (require energy) or catabolic (release energy) |
| Autotrophic | - green plants - convert sunlight into bond energy stored in the bonds of organic compounds (glucose) in the anabolic process of photosythesis - don't need an exogenous supply of organic compounds |
| Heterotrophic | - obtain energy catabolically - break down organic nutrients that must be ingested |
| Net reaction of photosynthesis | 6CO₂ + 2H₂O + energy --> C₆H₁₂O₆ + 6O₂ |
| Energy Carriers | - molecular carriers used by the cell to shuttle energy between reactions - ATP, NAD⁺, FAD |
| ATP | - adenosine triphosphate - cell's main energy currency - synthesized during glucose catabolism - composed of nitrogenous base adenine, sugar ribose and three weakly linked phosphate groups - energy of ATP is stored in these covalent bonds (high-energy bonds) |
| ADP | - adenosine diphosphate - Pi: inorganic phosphate - ATP --> ADP + Pi + 7 kcal/mole - the 7 kcal/mole provides energy for endergonic/endothermic reactions like muscle contraction, motility and active transport across plasma membranes |
| AMP | - adenosine monophosphate - PPi: phyrophosphate - ATP --> AMP + PPi + 7 kcal/mole |
| Carrier Coenzymes | - NAD⁺, FAD, NADP⁺ - transport the high energy electrons of the hydrogen atoms to a series of carrier moelcules on the inner mitochondrial membrane (electron transport chain) |
| NAD⁺ | nicotinamide adenine dinuclotide |
| FAD | flavin adenine dinucleotide |
| NADP⁺ | - nicotinamide adenine dinucleotide phosphate - the reduced form, NADPH, is found in plant cells only |
| Oxidation | - loss of an electron - NAD⁺, FAD, NADP⁺ are referred to as oxidizing agents because they cause other molecules to lose electrons and undergo oxidation (while they're reduced NADH, FADH₂, NADPH) |
| Reduction | - gain of electrons |
| Glucose Catabolism | occurs in two stages: a) glycolysis b) cellular respiration |
| Glycolysis | - series of reactions that lead to the oxidative breakdown of glucose into two molecules of pyruvate, the production of ATP and reduction of NAD⁺ into NADH - occurs in cytoplasm - mediated by specific enzymes |
| Glycolytic Pathway | - fructose 1,6-diphosphate is split into dihydroxyacetone and glyceraldehyde 3-phosphate (PGAL) - dihydroxyacetone is isomerized into PGAL - two molecules of PGAL is formed per molecule of glucose - 1 glucose = 2 pyruvate - net production of 2 ATP/mole of glucose (4 generated, 2 used up) |
| Substrate Level Phosphorylation | - ATP synthesis is directly coupled with the degradation of glucose without the participation of an intermediate molecule like NAD⁺ |
| Net Reaction for Glycolysis | glucose + 2ADP + 2Pi + 2 NAD⁺ --> 2 pyruvate + 2ATP + 2NADH + 2H⁺ + 2H₂O |
| Fate of Pyruvate | - anaerobic: pyruvate is reduced through fermentation - aerobic: pyruvate is further oxidized during cell respiration in mitochondria |
| Fermentation | - regeneration NAD⁺ to continue glycolysis without O₂ - reduce pyruvate to ethanol or lactic acid - fermentation produces only 2 ATP per glucose molecule |
| Alcohol Fermentation | - occurs in yeast and bacteria only - pyruvate produced in glycolysis is decarboxylated to acetaldehyde, then reduced by NADH in step 5 of glycolysis to yield ethanol - pyruvate --> acetaldehyde --> ethanol |
| Lactic Acid Fermentation | - occurs in certain fungi and bacteria and in human muscle cells during strenuous activity - happens when oxygen supply to muscle cells lags behind the rate of glucose catabolism - pyruvate generated is reduced to lactic acid, which can lower blood pH if accumulated, eventually becomes muscle fatigue - oxygen debt: the amount of oxygen needed to oxidize lactic acid back to pyruvate and enters cellular respiration |
| Cellular Respiration | - most efficient catabolic pathway to harvest energy stored in glucose - occurs in mitochondrion and catalyzed by reaction specific enzymes - produces 36-38 ATP - aerobic, O₂ acts as the final acceptor of electrons that are passed from carrier to carrier during the final stage of glucose oxidation - three stages: pyruvate decarboxylation, citric acid cycle and electron transport chain |
| Pyruvate Decarboxylation | - pyruvate formed during glycolysis is transported from the cytoplasm into the mitochondrial matrix where it is carboxylated (lost a CO₂), and the remaining acetyl group is transfered to coenzyme A to form acetyl CoA. - in process, NAD⁺ is reduced to NADH - pyruvate + coenzyme A -- acetyl CoA |
| The Citric Acid Cyle (TCA Cycle) | - known as the Krebs cycle or the tricarboxylic acid cycle (TCA cycle) - begins when the two carbon acetyl group from acetyl CoA combines with oxaloacetate, a four carbon molecule, to form the six carbon citrate - 2CO₂ are released, oxaloacetate is regenerated to use for another turn of the cycle - 1 cycle = 1 ATP produced by substrate level phosporylation via GTP intermediate - electrons are transferred to NAD⁺ and FAD, generating NADH and FADH₂, which transport electrons to electron transport chain |
| The Citric Acid Cyle continued | - electrons are transferred to NAD⁺ and FAD, generating NADH and FADH₂, which transport electrons to electron transport chain, where ATP is produced via oxidative phosporylation - each molecule of glucose = 2 pyruvates 2x3 NADH --> 6 NADH 2x1 FADH₂ --> 2 FADH₂ 2x1 GTP (ATP) --> 2 ATP |
| Oxidative Phosphorylation | - ATP is produced when high energy potential electrons are transferred from NADH and FADH₂ to oxygen by a series of carrier molecules located in the inner mitochondrial membrane - as the electrons are transferred from carrier to carrier, free energy is released - later this energy is used to form ATP |
| Net reaction of Citric Acid Cycle per glucose molecule | 2 Acetyl CoA + 6 NAD⁺ + 2 FAD + 2 ATP + 2Pi + 4H₂O --> 4 CO₂ + 6 NADH + 2 FADH₂ + 2 ATP + 4 H⁺ + 2 CoA |
| Electron Transport Chain (ETC) | - a complex carrier mechanism located on the inside of the inner mitochondrial membrane - two parts: electron transfer and ATP generation + the proton pump |
| Cytochromes | - most of the molecules of the ETC - electron carriers that resemble hemoglobin in structure of their active site - functional unit contains a central iron atom, which is capable of undergoing a reversible redox reaction |
| FMN (flavin mononuclotide) | - first molecule of the ETC - reduced when it accepts electrons from NADH, therefore oxidizing NADH to NAD⁺ |
| Cytochrome a₃ | - last carrier of the ETC - passes its electron to the final eectron acceptor, O₂ - in addition, O₂ picks up a pair of hydrogen ions from the surrounding medium and forms water - 2H⁺ + 2e⁻ + ½ O₂ --> H₂O |
| ETC without )₂ | - without oxygen, ETC becomes backlogged with electrons and NAD⁺ can't be regenerated to continue glycolysis without lactic acid fermentation occuring - Cyanide and dinitrophenol works the same way. - Cyanide blocks the transfer of electrons from Cytochrome a₃ to O₂ - Dinitrophenol uncouples the electron transport chain from the proton gradient established across the inner mitochondrial membrane |
| Electron Carriers | - categorized into three large protein complexes: a) NADH dehydrogenase b) the b-c₁ complex c) cytochrome oxidase |
| ATP Generation and the Proton Pump | - there are energy losses as electrons are transferred from one complex to the next, this energy is then used to synthesize 1 ATP per complex - since we have 3 complexes, we generate 3 ATP - NADH delivers its electrons to NADH dehydrogenase complex, so for each NADH = 3 ATP - FADH₂ bypasses the NADH dehydrogenase complex and delivers directly to carrier Q (ubiquinone), which is between complex 1 and 2, so each FADH₂ = 2 ATP |
| Proton Gradient | - as NADH passes its electrons to the ETC, free H⁺ are released and accumulate in mitochondrial matrix - ETC pumps these ions out of the matrix, across the inner mitochondrial membrane and into intermembrane space at each of the three protein complexes - the continuous translocation of H⁺ creates a positively charged acidic environment in the intermembrane space |
| Proton-Motive Force | - from proton gradient - drives H+ back across inner membrane and into the matrix - membrane is impermeable to ions, so H⁺ must flow through specialized channels provided by enzyme complexes called ATP synthetases - as H⁺ pass through ATP synthetases, energy is released to allow for the phosphorylation of ADP to ATP - oxidative phosphorylation: coupling of oxidation of NADH with phosphorylation of ADP |
| Glucose Catabolism - event and location | Event --> Location glycolysis -- cytoplasm fermentation -- cytoplasm pyruvate to acetyl CoA -- mitochondrial matrix TCA cycle -- mitochondrial matrix ETC - inner mintochondrial matrix |
| Review of Glucose Catabolism | - Net amount of ATP = ATP by substrate level phosphorylation + ATP by oxidative phosphorylation - Substrate level = 1 glucose = ATP from glycolysis + (1 ATP x 2 turn of Citric Acid Cycle) ---> 4 ATP - Oxidative = 32 ATP - Total = 36 ATP |
| Alternate Energy Sources | - when glucose supplies run low, the body uses these (in order): carbohydrates, fats and proteins - these are first converted to either glucose or glucose intermediates, which can be degraded in the glycolytic pathway and TCA cycle |
| Carbohydrates | - disaccharides are hydrolyzed into monosaccharides - then converted into glucose or glycolytic intermediates - glycogen in the liver can be converted into glucose 6-phosphate, a glycolytic intermediate |
| Fats | - stored in adipose tissue in the form of triglyceride - when needed, they are hydrolyzed by lipases to fatty acids and glycerol, and are carried by the blood to other tissues for oxidation - glycerol can be converted into PGAL - a fatty acid must be "activated" first in the cytoplasm, this requires 2 ATP - on active, it is transorted into mitochondrion and taken through a series of "beta-oxidation cycles" that convert it into two carbon fragments, then converted to acetyl CoA, which enter TCA cycle. - each round of beta oxidation generates 1 NADH and 1 FADH₂ -fats yield the most ATP per gram |
| Proteins | - the body degrades amino acids only when there isn't enough carbs available - most amino acids undergo a transamination reaction where they lose an amino group to form an alpha-keto acid - carbon atoms of most amino acids are converted into acetyl CoA, pyruvate or one of the intermediates of the citric acid cycle |
| Metabolic Map | ... |
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