Cell Biology Chapter 13 Flashcards
What are activated carriers, what are they used for, why are they important and how is energy stored in them? Does the formation of energy and the breakdown to gain that energy has + or – ΔG in each case?
Activation carriers provide energy for non-spontaneous reaction through their chemical bonds. This energy is key for non-spontaneous reactions. The formation of them have a + ΔG, and their breakdown have a -ΔG; For the most part, their creation are related to catabolic reactions and are used to anabolic reactions; NADPH operates chiefly with enzymes that catalyze anabolic reactions, supplying the high-energy electrons needed to synthesize energy-rich biological molecules; NADH has a special role as an intermediate in the catabolic system of reactions that generate ATP through the
oxidation of food molecules
Focus on those key steps, what is being reduced and oxidized
Respiration will be considered in five stages: The glycolytic pathway; Pyruvate is oxidized to generate acetyl CoA (acetyl coenzyme A); Acetyl Co A enters the citric acid cycle, where it is completely oxidized to CO2; Electron transport, the transfer of electrons from reduced coenzymes to oxygen coupled to active transport of protons across a membrane; The electrochemical proton gradient formed in step 4 is used to drive ATP synthesis (oxidative phosphorylation)
What requires oxygen and what doesn’t. What role does Oxygen play in these reactions? Which reactions depend on Oxygen directly or indirectly and why is this? Think about how things can be regulated because of the presence or
absence of oxygen.
Glycolysis and fermentation do not require oxygen; Citric Acid Cycle (indirectly) and Oxidative Phosphorylation in the Electron Transport Chain require oxygen (directly); In aerobic respiration, the terminal electron acceptor is oxygen, and the reduced form is water; If no oxygen is present, pyruvate is not allowed to enter the Citric Cycle and it is further oxidized to produce
lactic acid; Oxygen is the final acceptor of electrons in the electron transport chain; Without oxygen, the electron transport chain becomes jammed with electrons; Consequently, NAD cannot be produced, thereby causing glycolysis to produce lactic acid instead of pyruvate, which is a necessary component of the Citric Cycle; Thus, the Citric Cycle is heavily dependent on oxygen, considering it an aerobic process
Know why cells resort to Fermentation and what are the end products in different organisms.
Primary purpose: Oxidation of NADH NAD+; Replenish cytosolic NAD+ to enable glycolysis to continue; Results in conversion of pyruvate to; Lactate (muscle cells); Ethanol + CO2 (yeast); NO ENERGY PRODUCED in fermentation! It is REQUIRED for glycosylation to continue in the ABSENCE of oxygen!
What do cancer cells do? Why?
Cancer cells consume glucose more rapidly than normal cells; Many cancer cells get their energy mainly by fermenting glucose to lactate, even in the presence of oxygen! This is called aerobic glycolysis; Despite its inefficiency, it allows cancer cells to outgrow normal cells; The cancer cells dramatically increase the amount of glucose consumed; They also display an increase in activity of nutrient transporters; Cancer cells carry out aerobic glycolysis mainly to produce carbon skeletons for biosynthesis of substances in
high demand by proliferating cells; They do not primarily use aerobic glycolysis for energy production
Intermediate step: In the mitochondria Matrix (after glycolysis and before Citric Acid Cycle)
2 pyruvate to Acetyl-CoA (from 3Cs to 3 Cs); Decarboxylates pyruvate (removal of CO2 = waste); Generates NADH (1 per pyruvate molecule, therefore 2NADH (reduction NAD+ to NADH); Acetyl group combines with Coenzyme A to produce Acetyl-CoA;
Citric Acid cycle is a cycle, what makes it a cycle? What needs to happen in it so that process can continue?
3 water molecules are required for each cycle; Complete oxidation of Acetyl-CoA ; Occurs within the mitochondrial matrix; Each Acetyl-CoA oxidized results in: 1 GTP (equivalent to ATP), 3 NADH, 1 FADH2, 2 CO2, Since 2 Pyruvates are formed from 1 glucose, then 2 Acetyl-CoA are formed which then forms 2 GTP, 6 NADH, 2FADH2 and 4 CO2; Key products are high energy electron carriers NADH and FADH
Know how the proton gradient works (key players) in relation to making ATP and where in the cell is happening, how are those protons moving from where to where?
Electron transport and ATP generation are not independent processes; they are functionally linked to each other: Electron Transport Chain (ETC); Conversion of energy from electron carriers to proton electrochemical gradient across inner mitochondrial membrane; ETC embedded in inner mitochondrial membrane; Chemiosmosis; ATP synthase; Use of proton gradient to power ATP synthase for the production of ATP
ETC
Oxidizes NADH ->NAD+ and FADH2 ->FAD
NADH ->NAD+ in complex 1
FADH2 -> FAD in; Generates proton gradient (in the intermembrane space); Forms water; O2 final electron acceptor; 4 electrons + 4 protons + O2 2 H2O; Complexes I, III, and IV are found in the inner mitochondrial membrane; For each pair of electrons transported through complexes I, III, and IV, 10 protons are pumped from the matrix into the intermembrane space
Differences between Substrate level phosphorylation and Oxidative Phosphorylation
Substrate-level phosphorylation – directly
transfer energy to form phosphodiester bond that forms ATP; Formation of ATP during glycolysis and Citric Acid Cycle (CAC or Tricarboxylic acid (TCA) cycle or the Krebs cycle); Other phosphorylation events ; Oxidative phosphorylation – activated carriers transfer energy through indirect mechanisms to drive ATP production; Responsible for majority of ATP produced in Aerobic Respiration
Glycolysis: 2 ATP, 2 NADH Pyruvate to Acetyl-CoA: 2 NADH Acetyl-CoA Oxidation: 2 GTP, 2 FADH2, 6 NADH
NADH from Cytosol: 1.5 ATP/NADH (less ATP due to permeability of the mitochondria membrane)
NADH in Mitochondria: 2.5 ATP/NADH
FADH2 in Mitochondria: 1.5 ATP/FADH2
So we have: 2 ATP; 2 GTP –> 2 ATP; 2 NADH (Cytosol) * 1.5 = 3 ATP; 8 NADH (Mitochondria) * 2.5 = 20 ATP; 2 FADH2 (Mitochondria) * 1.5 = 3 ATP; Total: 30 ATP
Eukaryotic Cardiac Muscle Cells and Hepatocytes have an efficient transport mechanism of NADH from glycolysis to also enter the ETC as other NADH, so they also produce 32 ATP per glucose.
The number 36 comes from rounding to 2 ATP/FADH2 and cytoplasmic NADH, and 3 ATP/NADH
For Bacteria/Hepatocytes/Cardiac Muscle Cells, this number would be 38.
