Class Notes (806,745)
Canada (492,424)
Biology (116)
BIOL 1010 (39)

Chap 9 - Cellular Respiration.docx

9 Pages
Unlock Document

University of Lethbridge
BIOL 1010
Brent Sellinger

Reece et al, 9 Ed 1 Chapter 9 Cellular Respiration: Harvesting Chemical Energy I. Introduction Chemical elements essential to life are recycled but energy is not (remember the Laws of Thermodynamics). Energy flows into the ecosystem as sunlight and back out as heat (Figure 9.2) • Organic compounds store energy in their arrangements of atoms. • Catabolic pathways systematically degrade complex organic molecules (rich in energy) to simpler waste products, which store less energy. In the process, energy is transferred from the energy rich nutrient molecules to energy rich molecules (e.g.,ATP) that can be used directly by the cell to perform work. • These catabolic pathways include both anaerobic processes (e.g., fermentation and anaerobic respiration) and aerobic respiration. • Technically cellular respiration includes both aerobic and anaerobic respiration but historically the term cellular respiration originated from the study of aerobic respiration. This course will focus on aerobic respiration. Aerobic Respiration • Organic compounds are degraded in the presence of oxygen to produce carbon dioxide, water and usable forms of energy (i.e.,ATP) Organic Compounds + O ▯ CO + H O + Energy (work + heat) 2 2 2 Organic compounds that can be used in aerobic respiration • carbohydrates (e.g., glucose) • fats • proteins C 6 O12 66O ▯ ▯ ▯2▯ ▯ 6 CO + 62H O + En2rgy (ATP + Heat) ∆G = - 686 kcal/mol of glucose Where does aerobic respiration occur? II. What is Cellular Respiration? 1* Cellular respiration is how many cells transfer the energy stored in complex organic molecules (“food”) to ATP. 2* Aerobic respiration happens to be the most prevalent and efficient catabolic pathway – it is used by most eukaryotic and many prokaryotic species. ▯ 2 How do catabolic pathways that decompose glucose and other energy rich organic molecules yield energy for the cell? 3* Cellular respiration is a controlled stepwise oxidation of organic molecules in a cell • Enzymes catalyze oxidation via a series of small steps. Free energy is transferred via electrons to carrier molecules (most often but not alwaysATP and NADH). The relocation of electrons releases energy stored in organic molecules and this energy is ultimately used to synthesizeATP What is Oxidation? • During catabolism of organic molecules, electrons and the potential energy associated with the electrons are relocated to different molecules. Ultimately, this free energy is used to drive the synthesize ofATP (and generate heat). • Transfer of one or more electrons (e ) from one reactant to another occurs in many chemical reactions. - • These e transfers are oxidation-reduction reactions or redox reactions. Note: redox reactions always occur together (i.e., reduction can’t occur without oxidation also occurring!) oxidation - loss of electrons (e ) by a substance - reduction - gain of e by a substance Xe + Y ▯ X + Ye - reducing agent ▯ electron donor (X) oxidizing agent ▯ electron acceptor (Y) Note: Not all redox reactions involve the complete transfer of electrons from one substance to another. Some redox reactions involve changing the degree of sharing of electrons in covalent bonds. oxidation C 6 12 66 O ---->26 CO + 6 H O 2 Usable2form of Energy reduction ▯ Reece et al, 9 Ed 3 Chapter 9 Electrons lose potential energy as they shift from a less electronegative atom to a more electronegative atom. This potential energy is released and can be used to perform work. In general – molecules rich in hydrogen are excellent fuels III. Aerobic Respiration • While glucose is typically used to teach anaerobic respiration, it is important to know that many other energy rich organic molecules can be used to drive this catabolic process • Aerobic respiration of glucose is the cumulative function of three metabolic stages: 1. Glycolysis 2. CitricAcid Cycle (also known as Krebs cycle, Tricarboxylic acid cycle – TCA cycle) 3. Oxidative Phosphorylation: Electron Transport and chemiosmosis 1. Glycolysis (“splitting of sugar”) • Technically not part of aerobic respiration but most cells deriving energy from glucose use glycolysis to prepare starting material for the citric acid cycle • occurs in the cytosol (for eukaryotic and prokaryotic cells) • oxygen is not required and CO is 2ot released during this stage.All of the carbon atoms from one glucose molecule are found in 2 molecule of pyruvate!!! • 10 enzymatic steps (Figures 9.8 and 9.9 – You are not expected to memorize the steps in Fig 9.9 – just have a look at the steps. We will talk about several key steps in lecture.) For 1 molecule of glucose (C H 6 )12n6ering glycolysis, it goes through 10 chemical reactions divided into two phases A. Energy investment phase • first 5 steps • uses 2ATP • produces 2 glyceraldehyde phosphate (this is a 3 carbon molecule) B. Energy payoff phase • last 5 steps • produces 4 ATP 2 NADH (nicotinamide adenine dinucleotide) 2 pyruvate (all of the carbon atoms from glucose are found in pyruvate) 2 H 2 ▯ 4 How are the 4ATP produced during glycolysis? Substrate-level phosphorylation:. ATP produced in glycolysis is generated by substrate level phosphorylation: when an enzyme (i.e., a kinase) transfers a phosphate group from a substrate molecule toADP (Figure 9.7). Check out steps 7 and 10 in Figures 9.9. How are the 2 NADH produced during glycolysis? See step 6 in Figure 9.9 + - - + Dehydrogenases remove 2 H and 2 e from the substrate (fuel molecule) and transfer 2 e and 1 H to nicotinamide adenine dinucleotide (NAD ). NAD is a coenzyme. Energy is transferred along with the electrons to NAD . The other proton is released as H into the surrounding solution. (Figure 9.4) dehydrogenase | | + + H-C-OH + NAD C=O + NADH + H | | If oxygen is present then energy stored in NADH can be used to generateATP by oxidative phosphorylation (Electron transport and chemiosmosis) – see stage 3 of aerobic respiration Approximately 25% of the energy stored in glucose is released during glycolysis. How is this energy released? Where is the remaining energy that was stored in glucose? 2. CitricAcid Cycle (also known as Krebs cycle or the tricarboxylic acid cycle) • described by Hans Krebs - 1930s If oxygen is present then pyruvate is actively transported into the mitochondrion and oxidation is completed. But what about prokaryotic organisms – where does this process occur?? ▯ Reece et al, 9 Ed 5 Chapter 9 Prior to the citric acid cycle there is a junction step that links Glycolysis and the CitricAcid Cycle (Figure 9.10) Conversion of pyruvate ▯ acetyl CoA (catalyzed by a multi-enzyme pyruvate dehydrogenase complex). This conversion involves the following three steps a) Removal of pyruvate’s carboxyl group generating CO 2 b) The remaining two carbon molecule is oxidized forming an acetyl group (-COCH ). In the p3ocess, the + extracted electrons are transferred to NAD thereby storing energy in NADH and a H are produced c) The acetyl group is attached to coenzymeA(a sulfur containing compound derived from a B vitamin) forming a reactive product called acetyl CoA CitricAcid Cycle (Figure 9.11, 9.12) • 8 enzyme catalyzed steps (in eukaryotes, all enzymes are found in the mitochondrial matrix, except for the enzyme that catalyzes step 6, it is found in the inner mitochondrial membrane) • 2 carbon enter the cycle as an acetyl group and 2 different carbon leave as 2 CO 2 • The citric acid cycle is a cyclical process • In the first step, acetyl (-COCH )3is added to oxaloacetate (4 carbon atoms) forming citrate (6 carbon atoms) Every acetyl (-COCH ) e3tering the citric acid cycle results in •
More Less

Related notes for BIOL 1010

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.