Chapter 13 How Cells Obtain Energy PDF

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Full lecture notes on chapter 6 of cell biology with christine rigsby....

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Chapter 13: How Cells Obtain Energy Sunday, October 11, 2020

11:07 AM

Cell Food: Sugars (carbohydrates, mainly glucose) - Cells require constant energy (chemical bond energy) - Plants make their own, animals have to obtain - Energy is stored in high energy bonds in carrier molecules (ATP,NADPH, NADH, FADH2, acetyl CoA) - Fatty acids and proteins can serve as sources too Stepwise functions allows energy released to be stored in carriers molecules rather than being released as heat ATP Synthesis: Lots of energy because huge -G - Coupled reactions in cytoplasm (anaerobic)/mitochondria matrix (aerobic) (glycolysis/Krebs) - Activated carrier molecules are used in mitochondria (oxidative phosphorylation) on inner mitochondria membrane *ADP +Pi --> ATP (reaction is energetically unfavorable)

Three Stages of Catabolism 1. Breakdown of large macromolecules to simple subunits (proteins to amino acids, polysaccharides to simple sugars, fats to fatty acids and glycerol) - Digestion: Occurs outside cells or within lysosomes; because you have to have enzymes to break it down but to avoid breaking itself down enzymes separated outside cell (lining is there to protect cells from digesting itself) 2. Glycolysis: occurs in cytoplasm (inside cell) - Focusses on glycose but amino acids and fats can enter; glucose is broken down into pyruvate - Breakdown of simple subunits to acetyl CoA: accompanied by production of limited amounts of ATP and NADH 3. Citric Acid Cycle occurs in mitochondria matrix, and ETC used to drive oxidative phosphorylation - Complete oxidation of acetyl CoA To H2O and CO2: accompanied by production of large amounts of ATP in mitochondria

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Glycolysis: the breakdown of glucose Other sugars can be used after being converted to one of the intermediates in the pathway Anaerobic (O is not consumed or necessary for the reaction to occur Occurs in the cytosol of most cells End products: 2 pyruvates, 2 net ATP, 2 NADH Substrate level phosphorylation synthesizes ATP NADH is reduced in ETC and NAD+ is used for glycolysis again

*Will ask enzymes, reactants and products in all the steps in glycolysis and Krebs on exam all or nothing questions* Panel

- In organisms that live in low oxygen or cant live in oxygen (Anaerobic) undergo fermentation, glycolysis is the source of ATP - Pyruvate and NADH stay in cytosol because they don’t need to be transported to matrix for Krebs. They are converted into products that are excreted like lactate and ethanol/CO2 (byproducts of glycolysis becomes fermentation products) - NADH is converted back to NAD+ for sustaining glycolysis (to keep glycolysis going to keep ATP production) - Involves ETC embedded in a membrane with a molecule other than oxygen as an electron acceptor *Cells cant excrete pyruvate so it will build up; using it for fermentation allows NADH to be converted back to NAD+

• Enzymes couple oxidation to Energy Storage - Allows for favorable and unfavorable reactions to occur

Pyruvate is actively pumped into the mitochondrial matrix Pyruvates dehydrogenase complex assist in converting Pyruvate to Acetyl Co-A and NADH and Co2 Acetyl CoA is the molecules that will enter Citric Acid Cycle *In presence of O Acetyl CoA is made and in presence of enzyme converted to citric acid*

Mitochondrial Structure - Outer mitochondrial membrane (outer boundary) - Inner mitochondrial membrane has two interconnected domains (inner boundary membrane, cristae- where the machinery for ATP is located) - Mitochondrial matrix (contains a circular DNA molecule, ribosomes, and enzymes) (RNA and proteins can be synthesized in the matrix) *Know where things are moving to (in/out matrix, intermembrane space) and where reactions are taking place; understand spaces and localization of reaction

Fatty acids are an alternative for fuel: Fatty acids can be converted to Acetyl CoA in the mitochondria matrix (like pyruvate) NADH and FADH2 are generated in Krebs Some amino acids are also transported into the mitochondria i. Some converted into acetyl CoA and others turned into Krebs intermediates In aerobic bacteria, catabolic processes take place in cytosol

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Citric Acid Cycle Requires abundant O for cycle and ETC Also called Tricarboxylic acid, TCA, and Krebs End products: 3 NADH, 1 GTP, 1 FADH2, (energy carriers) 2 CO2 (waste) In the mitochondrial matrix Explain its discovery and how we know it’s a cycle (how we know pg. 436-437)

*oxaloacetate at the end of the cycle combines with acetly CoA to produce citrate under enzyme citrate synthase - Acetly CoA is not oxidized directly; transferred to oxaloacetate and forms citric acid via citrate synthase. This is the first step in the cycle - Citrate is gradually oxidized and the energy is captured by formation of carrier molecules - Oxaloacetate is regenerated to start the cycle again *Energy stored in NADH and FADH2 are used to produce ATP in oxidative phosphorylation (drives the ETC). Transfer of electrons drives a pump embeded in the intermitochondrial membrane to drive transfer of protons across the matrix to the intermembrain space to create electrochemical gradient to drive production of ATP. - Oxidative phosphorylation is the only step in oxidation of food molecules that requires O from atmosphere CO2 released in ETC are from hydrolysis of water not atmospheric oxygen O2 used in oxidative phosphorylation are reduced to water not incorporated into CO2

Biosynthetic Pathways- Anabolic - Many intermediates are utilized in other anabolic pathways in the cell - Form amino acids, nucleotides, lipids, and other small molecules for the cell - Ex: Oxalocetate ---> aspartate, a-ketoglutarate ---> glutamate i. Both aspartate and glutamate are building blocks for proteins (both are amino acids)

Electron Transport Chain - Last stage in oxidation of food molecule - Chemical energy is released - Chain of electron carriers embedded in inner mitochondrial membrane (plasma membrane for bacteria) - Energy released is used to drive protons across the membrane into the intermembrane space, generating a transmembrane gradient - H+ gradient drives ATP synthase to phosphorylate ADP (coupled to gradient to drive unfavorable phosphorylation) - Electrons are added to oxygen and protons to form water - Appox. 30 molecules of ATP are produced from one complete oxidation of glucose/ 17 ATP per pyruvate

Feedback Regulation • Gluconeogenesis - Mechanism to generate glucose from pyruvate • Step 1,3, and 10 are irreversible • Must bypass • Must utilize 4 ATP and 2 GTP • Occurs mainly in liver • Regulation depends on buildup or lack of metabolites (when ATP is in abundance) Presence of ATP inhibits phosphofructokinase (inhibits the production of ATP, glycolysis) It activates fructose 1,6-bisphosphatase (activate gluconeogenesis)

Gluconeogenesis is not efficient because it uses GTP and ATP Glucose is stored glycogen (branched polymer of glucose) - Glycogen stored in liver and muscle *Metabolites regulating enzymatic function is allosteric regulation - When ATP is needed, cells breakdown glycogen into glucose 1-phosphate via glycogen phosphorylase which is converted to glucose 6-phosphate for glycolysis pathway (can enter and be an intermediate for glycolysis) - Glycogen synthase is the opposite enzyme to build glycogen - Both enzymes are regulated by glucose 6-phosphate but in opposite directions - Also regulated by signaling pathways and hormones: insulin, adrenaline, glucagon, growth hormones regulate the production/breakdown of glycogen

*If glucose 6-phosphate is building up (because its not being broken down by glycolysis (bc too much ATP being produced) glycogen synthase is activated to form glycogen to store glucose and glucose 6-phosphate Other food storage: FAT - Important because of higher energy yields - Glycogen stored for about 1 day because it needs high water content to accompany glycogen - Fat can be stored for at least one month i. Normally stored as droplets in cells (adipocytes) as triacyclglycerols - Can release fatty acids for other purpose like glycolysis - Animal cells can readily convert sugars to fats; fats cannot convert fatty acids to sugars

Plants convert some photosynthesis end products into starch (similar to glycogen) - Fats in plants are similar to animals (just differ in fatty acids that make them up)

- Seeds of plants are embryos so they store a lot of fats and starches (makes seeds major food source) - Fats and starches stored in chloroplast in plants (also where photosynthesis is carried out)

*More membranes = more surface area for chemical reactions* Compartments means the ability to create gradients (drives transport and reactions)...