NNNNooootttteeeebbbbooooooookkkk::::MCB 150CCCCrrrreeeeaaaatttteeeedddd::::10/9/2012 11:14 PMUUUUppppddddaaaatttteeeedddd::::10/15/2012 3:55 PMTTTTaaaaggggssss::::MCB 150, Study GuideUUUURRRRLLLL::::https://www.google.com/search?q=delta+greek+letter&ie=utf-8&oe=utf-8&aq=t&rls…Exam II Study Guide9/17/2012Things to know:- Why does the cell do this?- Tools to do this?- What are we going to use this for? Lecture Notes:- The energy needs of a cell are spectacularly high: where does that energy come from?- METABOLISM - the sum of all chemical activity in the cell -- thousands of individual reactions - Catabolism - takes MCs (food) and breaks them down - releases energy (-∆G; exergonic) - final products used as precursors for new MCs - Biosynthesis - takes precursors and makes macroMCs - biosynthetic reactions require energy, and get it from catabolic reactions - HOW??- How do we get the energy from our food to use in biosynthesis? - The Carbon and Hydrogen in food molecules are not in most stable form, which makes them reactive - Most stable form of carbon is: CO2 (carbon dioxide) - BYPRODUCT OF METABOLISM - Most stable form of hydrogen is: H2O (water) - So, in a series of steps (reactions), large organic MCs (glucose) are broken down to CO2 and H2O by combining w/ O - The C and H are OXIDIZED - called an Oxidation Reaction = very EXERGONIC process - spread out over multiple reactions (~20) to harness more of the energy (so its not dissipated as heat) - each oxidation rx is controlled by a specific enzyme- Oxidation reactions involve the REMOVAL of electrons!! - electron are NOT lost; instead they are transferred to a MC which is REDUCED - OIL RIG; Leo the Lion says Ger - oxidation and reduction reactions must balance - In bio, most electrons transferred in redox reactions are in the form of 2 H atoms (2 e-s and 2 protons) - ENERGY IS HELD IN THE TRANSFERRED ELECTRONS- recipients of e-s in redox reactions are often special molecules associated with enzymes called COFACTORS or COENZYMES - UPS truck - Molecular UPS trucks - these coenzymes are only temporary carriers - 2 main coenzymes in bio. oxidation (accepts 2H) - NAD+ ---> reduced to NADH (actually accepts 2 electrons and 1 H+) - Nicotinamide Adenine Di=Nucleotide - FAD ---> reduced to FADH2 (accepts 2 H) - BOTH REDUCTION REACTIONS ARE REVERSIBLE!!!- So, if cofactors don't "keep" the energy, what happens to it?- Ultimately, all the energy harnessed from the oxidation of food sources is used to make ATP - ATP = Adenosine Tri-Phosphate = most common energy "currency" for the cell- Where does the energy in ATP come from? - Phosphate groups are unstable (the NEGATIVE charges repel each other!!) - Hydrolysis of ATP to ADP, Pi, Energy - ATP <--> ADP + Pi - ∆G = -7 kcal/mol ---- Exergonic and Reversible- Side notes: 1. Energy currency MC 2. Put it in a growing RNA chain (down) w/ an RNA polymerase enzyme- How does ATP drive energy-requiring reactions? - ATP hydrolysis is COUPLED to the endergonic reaction - The reaction that requires energy uses the energy provided upon hydrolysis of ATP - "one of them pays for the other" - A common ex: - Glucose --> Glucose-6-Phosphate => ∆G = +3 - ATP --> ADP + Pi => ∆= -7 - Net of these coupled reactions => ∆G= -4 -----(whatever is left over is released as heat) - Coupled reactions often showed as: (insert lecture notes example here:)- So how does the energy from food get to ATP? = CELLULAR RESPIRATION! :) / :( - Breakdown of glucose to CO2 and H2O - Multiple reactions in 3 distinct pathways (phases) - Glycolysis- Pyruvate Oxidation and the Krebs (or Citric Acid) Cycle - Electron Transport Chain and Oxidative Phosphorylation - Let's follow the path of energy and molecules from glucose to ATP1. Glycolysis- First pathway in breakdown of glucose - "glyco" (sugar) + "lysis" (splitting) - 10 steps - glucose --> 2 3carbon MCs (pyruvates)- Pathway is actually ENDERGONIC up to production of first 3 Carbon MCs (uses cell's store of ATP)- Occurs in the CYTOPLASM of all living cells --> essential and least different- end goal = MAKE ATP!!- 2 steps are endergonic- 3 steps are exergonic - Net Result: - 2 ADP --> 2 ATP : 4 ATP, but "net yield" is 2 - 2 NAD+ --> 2 NADH - Glucose --> 2 Pyruvate - Energy from the first endergonic step harnessed by the transfer of e- to NAD+ (Energy not used to directly synthesize ATP, but its "saved" and used later)- Energy from other exergonic reactions is in the form of Pi, which is used to phosphorylate ADP --> SLP (Substrate-Level Phosphorylation)- Where's the source of Energy?? 1. Coupled reaction to a pathway reaction = SUBSTRATE LEVEL PHOSPHORYLATION - Stealing a Pi from this substrate to do it 2. Oxidative Phosphorylation- Problems at the end of Glycolysis 1. Still aren't at lowest energy state 2. NAD+ is used up but not recycled, and is still holding on to a lot of our energy- Three things to think about: 1. How is energy in pyruvate released? 2. How is NAD+ replaced? 3. How is energy in NADH transferred to ATP? - W/Oxygen = Aerobic Respiration - W/out Oxygen = Anaerobic Respiration (Fermentation)Aerobic Respiration- Carbon source (2 MCs of Pyruvate) completely converted to CO2 - only happens in the presence of oxygen - pyruvate molecules are converted to acetyl-CoA, which then enters the Krebs (or Citric Acid) Cycle = "pyruvate shuttle" :) - all C-H bonds converted to C-O bonds (6 CO2 released) - energy transferred to NAD+ and FAD (makes more NADH and FADH2)- another SLP reaction in Krebs cycle (GTP is ATP analog) ?????- Where does aerobic respiration take place? - Eukaryote --> Mitochondria - Prokaryotes --> Cytoplasm and Plasma Membrane- Parts of the Mitochondria: - 2 membranes and 4 leaflets - Levels of organization from outer to inner - Outer Membrane - typical protein/lipid distribution (about 50-50) - PORINS - a protein; like a MC straw (not selective) - Inter-Membrane Space - composition of ions and small MCs - is same as cytoplasm - Inner Membrane - Principle site of ATP generation - >70% protein! - ETC (Electron Transport Chain) proteins -