cellular respiration

cellular respiration

process that transfers energy from molecules (carbohydrates, proteins & fats) and makes it available for cellular use.

ATP

- adenine, ribose and 3 phosphates • Cellular work comes from the breakdown of ATPADP (adenosine diphosphate), which produces energy for muscular contraction, active transport, etc. - resynthesized (reattach a phosphate group) via phosphorylation

glycolysis continued.....summarization

1. Glucose enters the cell by facilitated diffusion and is phosphorylated to glucose-6-phosphate, essentially trapping glucose within the cell. 2. Glucose enters glycolysis, an anaerobic process that occurs in the cytosol. a. In phase 1 of glycolysis, sugar activation, glucose is phosphorylated in a series of steps to fructose-6-phosphate to provide the activation energy for events that occur later in the pathway. b. In phase 2 of glycolysis, sugar cleavage, fructose-6-phosphate is split into two three-carbon fragments: glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. c. In phase 3 of glycolysis, sugar oxidation and ATP formation, the pair of 3-carbon fragments produced in phase 2 are oxidized to transfer hydrogen to NAD+, and the oxidized fragments are phosphorylated, creating bonds that can be used to transfer energy to ATP synthesis. d. The final products of this series of reactions are two pyruvic acid molecules, two molecules of NADH, and four molecules of ATP, although two ATPs were consumed at the beginning of the process. The two pyruvic acid molecules can follow two distinct pathways, depending on the availability of oxygen. a. If adequate oxygen is present in the cell, glycolysis continues, and NADH delivers its electrons to the electron transport chain. b. If there is not adequate oxygen available, NADH returns its hydrogen to pyruvic acid, forming lactic acid, which allows NAD+ to continue to act as an electron acceptor. c. Once enough oxygen is available within the cell, lactic acid is oxidized back to pyruvic acid and enters aerobic pathways.

glycolysis

Basically, cellular respiration is taking our food breaking it down in the presence of oxygen and making ATP out of it. • Glucose (carbohydrate: toast, hashbrowns) enters cells via facilitated diffusion • Glycolysis is an anaerobic stage that breaks down 6 carbon glucose molecule to pyruvic acid in the cytoplasm of the cell Glycolysis (Glycolytic Pathway) • Aerobic/anaerobic pathways begin here • 10-step (10 enzyme catalyzed reactions) pathway • Anaerobic phase (occurs despite presence/absence of O2) • Occurs in cytosol • 6 carbon glucose 2 pyruvic acid molecules • Three major events or phases - Sugar activation, sugar cleavage, sugar oxidation and ATP formation

catabolism

Catabolism - hydrolysis (breakdown using water) of complex structures to simpler ones; releases energy • Ex. Proteins amino acids breaks down larger molecules into smaller ones via hydrolysis Hydrolysis (an example of catabolism) (water + break): decomposes carbohydrates, lipids and proteins (reverse of dehydration synthesis). A water molecule is used for every bond that is broken. I.e., Disaccharide 2 monosaccharides where 1 H2O supplies 1 hydrogen atom, which is added to one sugar group and a hydroxyl group (HO) is added to the other. Breaks down carbohydrates to mono; fats to glycerol & fatty acids; proteins to amino acids; nucleic acids to nucleotides.

Enzyme Action

Enzymes speed metabolic reactions by a million or more •Required in small amounts because they are not consumed or alteredfunction repeatedly •Enzymes act only on specific molecules called the enzyme's substrate (the substrate is formed into one or more products) Each enzyme must be able to recognize its specific substrate - shape dependent • Enzyme-catalyzed reactions (some reversible) - Substrate + Enzyme Enzyme-Substrate ComplexProduct + Enzyme (unchanged) • Some enzymes catalyze only a few reactions per second, while others 100,000's Specific enzymes control hundreds of different chemical reactions in cellular metabolism • Enzyme controlled reactions, metabolic pathways, lead to synthesis or breakdown of particular biochemicals - every cell has 100's of different enzymes - enzyme name = substrate + "ase" (lipase=lipid splitting, protease=protein splitting, sucrase=sucrose splitting)

final products of glycolysis

Final products of glycolysis - 2 (3 carbon) pyruvic acid (C3H4O3) - 2 NADH (Electron carrier) + H+ (reduced NAD+) - Net gain of 2 ATP (notice 4 ATP produced, but 2 are used in the priming process) - Notice: no O2 is used in glycolysis (hence, anaerobic pathway) • For glycolysis to continue, NAD+ must be present to accept hydrogen atoms (NADH + H+)

glycolysis continued...

Much more of the energy in glucose is conserved in the form of high-energy electrons carried in pairs by the electron shuttler's: NADH and FADH2, which are generated in glycolysis and CAC. • NAD+ is an oxidizing agent (accepts/carries electrons). This reaction forms NADH, which can then be used as a reducing agent to donate electrons. • FAD accepts 2 electrons and 2 protons to become FADH2, which can then be oxidized to FADH by donating 1 electron and 1 proton. Three Events of Glycolysis • Sugar oxidation and ATP formation - NADH is produced, ATP is synthesized and 2 3-carbon pyruvic acid molecules result. - Six steps; two major events • Two 3-carbon fragments oxidized (reducing NAD+) • Inorganic phosphate groups (Pi) attached to each oxidized fragment - Phosphate group cleavage 4 ATP formed by substrate-level phosphorylation The 6-carbon sugar glucose is broken down in the cytosol into two 3- carbon pyruvic acid molecules with a net gain of 2 ATP and the release of high-energy electrons.

CAC continued

Products of each turn of CAC (Krebs) cycle: - 3 NADH + H+, 1 FADH2, 2 CO2, 1 ATP • So, 1 glucose 2 pyruvic acid molecules two turns of Krebs cycle final products - 6 NADH + H+, 2 FADH2, 4 CO2, 2 ATP • Adding products of transitional phase, final products of CAC: - 8 NADH + H+, 2 FADH2, 6 CO2, 2 ATP • Does not directly use O2 - NADH molecules must be oxidized in electron transport chain for Krebs cycle to continue • Cycle intermediates may be used as building materials for anabolic reactions

how ATP is made

Substrate Level Phosphorylation - during glycolysis and CAC, a substrate directly hands a phosphate to ADP to become ATP (substrate, substance acted upon by an enzyme, donates the phosphate) this represents only a small fraction of the energy in each glucose mole that passes through these pathways. • Electron Transport or Oxidative Phosphorylation - uses an electrochemical or chemiosmotic gradient of protons (H+) across the inner mitochondrial membrane to generate ATP from ADP in ETC, which is a key difference from substrate-level phosphorylation. ATP is produced from the flow of protons through channel proteins and ATP synthase

glycolysis continued

Sugar activation - Glucose phosphorylated (2 phosphate groups are added to a glucose molecule) by 2 ATP ("primes" or activates) fructose-1,6- bisphosphate - Energy investment phase • Provides activation energy for later reactions Sugar cleavage - Fructose-1,6-bisphosphatetwo 3-carbon fragments; isomers • Dihydroxyacetone phosphate - Quickly reverses to glyceraldehyde 3-phosphate • Glyceraldehyde 3-phosphate

oxidation (glucose example)

The term "oxidation," in fact, refers to any reaction where oxygen is combined with another molecule, which is then said to be oxidized. Glucose oxidation is an aerobic process, a chemical reaction that requires oxygen. During the process, one glucose molecule combines with six oxygen molecules to produce six carbon dioxide molecules, six water molecules, and adenosine triphosphate (ATP), a molecule that cells use to store or transfer energy.

stages of metabolism

Three stages in processing nutrients - Stage 1: Digestion, absorption, and transport to tissues - Stage 2: Cellular processing (in cytoplasm) • Anabolism/synthesis of lipids, proteins, and glycogen, or • Catabolism (glycolysis) into pyruvic acid and acetyl CoA - Stage 3: Oxidative (mitochondrial) breakdown of intermediates into CO2, water, and ATP

anabolism

synthesis (build) of large molecules from small ones; require energy • Ex. Amino acids proteins provides all the materials a cell needs for maintenance, growth & repair Dehydration synthesis (a type of anabolic process) joins simple sugars (mono to poly), glycerol & fatty acids (fat), amino acids (proteins), and nucleotides (nucleic acids), where the reactions result in: H2O & storage of energy in the bonds of largest mole - Metabolic Processes: Anabolism • Simple sugars: 2 monosaccharides are joined to form a disaccharide, which yield 1 H2O molecule - Repeated to form polysaccharideslarger molecules of glycogen=store energy • Glycerol & 3 fatty acids: join to form 1 fat molecule and yields 3 H2O molecules • 2 Amino acids: join to form a peptide bond (dipeptide, polypeptide) molecule yields 1 H2O molecule • Nucleotides join to form nucleic acids

Glycogenesis and Glycogenolysis

• Because the cell cannot store large amounts of ATP, other processes are used to handle glucose in excess of what can be used in ATP synthetic pathways. • Glycogenesis is the body's way of storing glucose in the form of a polysaccharide. This is a long chain of glucose molecules that can be compactly stored in cells. The type of bond connecting the glucose molecules is very easily degraded, so glycogen can quickly be converted to glucose when blood sugar levels get low. • this process occurs mostly in the liver and skeletal muscle. Glycogenolysis • Glycogenolysis is the process of converting stored glycogen (polysaccharide) into glucose for the body to use as energy when needed. - Glycogen breakdown via glycogen phosphorylase in response to low blood glucose

Summary of Cellular Respiration ATP Production

• Complete oxidation of 1 glucose molecule • Glycolysis + Krebs cycle + electron transport chain CO2 + H2O 32 molecules ATP - By both substrate-level and oxidative phosphorylation • But, energy required to move NADH + H+ generated in glycolysis into mitochondria final total ~ 30 molecules ATP - Still uncertainty on final total

Athletes and Carbohydrates

• Complex carbohydratesmore glycogen storage in muscle; more effective than high-protein meal for intense muscle activity • Carbo loading - Carbohydrate-rich diet for 3-4 days; decreased activity muscles store more glycogen - improved performance and endurance

cellular respiration...

• Consists of three, interconnected, series of reactions called carbohydrate metabolism • Complete glucose catabolism (releases energy) requires 3 pathways: - Glycolysis, the citric acid cycle (Kreb's cycle) and electron transport chain (oxidative phosphorylation) • Products of these reactions are - CO2, H2O, and energy (ATP: 50% lost as heat/50%) • Is either aerobic (needs O2 molecules) or anaerobic (needs no O2 molecules) • 1 glucose molecule = up to 38 moles of ATP

lactic acid

• For glycolysis to continue, NADH + H+ must be able to deliver electrons to the ETC • In the presence of O2, it does and will continue processing electrons and recycling NAD+ (ETC) • Under anaerobic conditions, ETC has nowhere to unload its electrons and can no longer accept new electrons from NADH. • For glycolysis to continue, NADH + H+ can give its electrons and hydrogens back to pyruvic acid in a reaction that forms lactic acid (NAD). Lactic acid build up inhibits glycolysisATP. (Liver later converts back to pyruvic acid) • Run to bus, sprint hard....hit wall, legs burn.

Electron Transport Chain and Oxidative Phosphorylation

• Is aerobic/directly uses oxygen • Produces greatest amount of ATP • Overview - NADH + H+ and FADH2 (from glycolysis and Krebs cycle) deliver hydrogen atoms - Hydrogen atoms split H+ + electrons - Hydrogen atoms combined with O2water - Electrons passed along chain to final electron acceptor - oxygen • Oxygen has greatest pull on electrons - Released energy harnessed ATP by oxidative phosphorylation Electron Transport Chain and Oxidative Phosphorylation • Theelectrontransportchainistheoxygen-requiring process of aerobic respiration involving the pickup of hydrogens removed from food fuels during oxidation by O2, resulting in the formation of water, a process called oxidative phosphorylation. • Involveschainofproteins(electroncarriers)boundon inner mitochondrial membrane. The ETC is essentially a series of carriers (proteins) arranged in four distinct complexes, which are embedded in the mito membrane and are called electron-carrier complexes I-IV. • Theenergyreleasedasthehighenergyelectrons (glycolysis/CAC via electron carriers NAD/FAD) are passed from carrier to carrier moves hydrogen ions across the mito membrane, from the mito matrix to the intermembrane space, which creates a concentration gradient of hydrogens. Electron Transport Chain and Oxidative Phosphorylation • Theresultinggradientisaformofstoredenergy,which phosphorylates ADP to ATP via a complex of proteins called ATP synthase. • Ashydrogensmovedownthegradient(from intermembrane space back to the matrix) the energy released is used by ATP synthase complex, which catalyzes ATP synthesis (phosphorylates ADP to ATP). • ATPsynthasecomplex(2parts:channel/phosphorylater) rotates and ADPATP. **Each rotation=3 ATP's • FADH2canultimatelyproduce2molesofATP,NADH can produce 3.

CAC overview

• PAleavescytosolandentermitochondria • Fueledby2,3-carbonpyruvicacids(PA)(glycolysis)enter separately • EachPAlosesacarbonCO2andreleasesmore high energy electrons (ETC) - the CO2 then combines with a coenzyme to form a 2-carbon, acetyl coenzyme A (acetyl CoA) 4- carbon oxaloacetic acid, which forms 6-carbon citric acid. For each citric acid, 2 CO2's (go to cytosol, exit cell, to bloodstream) and 1 ATP are generated, as well as more release of high energy electrons (ETC). Two turns of cycle per one glucose mole.

Citric acid cycle (Krebs cycle)

• Transitional phase converts each pyruvic acid to acetyl CoA in three steps: • Decarboxylation - removal of 1 C to produce acetic acid and CO2 • Oxidation - High-energy electron release; H atoms removed from acetic acid; picked up by NAD+ NADH + H+ • Formation of acetyl CoA - Acetic acid + coenzyme A acetyl coenzyme A (acetyl CoA) • Coenzyme A takes acetic acid to Krebs cycle - Combined with 4-carbon oxaloacetic acid 6-carbon citric acid (hence citric acid cycle) • During eight steps acetic acid decarboxylated and oxidized to keto acid intermediatesNADH + H+ and FADH2 • In final step, oxaloacetic acid regenerated