Lecture Chapter 6. Cellular Respiration

Transcription

1 Lecture Chapter 6 Cellular Respiration

2 How do marathon runners and sprinters differ? Long-distance runners have many SLOW FIBERS in their muscles Slow fibers break down glucose for ATP production aerobically (using oxygen) These muscle cells can sustain repeated, long contractions

3 Sprinter s muscles have more FAST FIBERS - Fast fibers make ATP without oxygen anaerobically - They can contract quickly and supply energy for short bursts of intense activity

4 The dark meat of a cooked turkey is an example of slow fiber muscle Leg muscles support sustained activity The white meat consists of fast fibers - Wing muscles allow for quick bursts of flight

5 INTRODUCTION TO CELLULAR RESPIRATION Nearly all the cells in our body break down sugars for ATP production Most cells of most organisms harvest energy aerobically, like slow muscle fibers The aerobic (+O 2 ) harvesting of energy from sugar is called cellular respiration Cellular respiration yields CO 2, H 2 O, and a large amount of ATP

6 Cellular respiration breaks down glucose molecules and banks their energy in ATP The process uses O 2 and releases CO 2 and H 2 O Glucose Oxygen gas Carbon dioxide Water Energy Breathing supplies oxygen to our cells and removes carbon dioxide O 2 CO 2 BREATHING Lungs CO 2 Bloodstream O 2 Muscle cells carrying out CELLULAR RESPIRATION

7 MITOCHONDRION Mitochondria use the energy in sugars, fats and proteins to make ATP

8 Cellular respiration oxidizes sugar and produces ATP in three main stages: GLYCOLYSIS occurs in the cytoplasm The KREBS CYCLE (TCA) and the ELECTRON TRANSPORT CHAIN occur in the mitochondria Fig High-energy electrons carried by NADH Glucose GLYCOLYSIS Pyruvic acid KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Cytoplasmic fluid Mitochondrion

9 Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid Glucose Pyruvic acid

10 Details of glycolysis Read and think about each step so that you can see the big picture Memorize and understand the NET REACTIONS Steps 1 3 A fuel molecule is energized, using ATP. Step 4 A six-carbon intermediate splits into two three-carbon intermediates. Step 5 A redox reaction generates NADH. Step Glucose Glucose-6-phosphate PREPARATORY PHASE (energy investment) Fructose-6-phosphate Fructose-1,6-diphosphate Glyceraldehyde-3-phosphate (G3P) ENERGY PAYOFF PHASE 1,3-Diphosphoglyceric acid (2 molecules) Steps 6 9 ATP 3-Phosphoglyceric acid and pyruvic acid 7 (2 molecules) are produced. 8 2-Phosphoglyceric acid (2 molecules) 2-Phosphoglyceric acid (2 molecules) See Figure Pyruvic acid (2 molecules per glucose molecule)

11 6.7 Using Coupled Reactions to Make ATP Glycolysis is the first stage in cellular respiration Takes place in the cytoplasm Occurs in the presence or absence of oxygen Involves ten enzyme-catalyzed reactions These convert the 6-carbon glucose into two 3-carbon molecules of pyruvate Priming reactions Cleavage reactions Energy-harvesting reactions 1 6-carbon glucose (Starting material) 2 ATP 2 3 P P P P 6-carbon sugar diphosphate 6-carbon sugar diphosphate P P P P 3-carbon sugar3-carbon sugar phosphate phosphate 3-carbon sugar phosphate NADH 2 ATP 3-carbon sugar phosphate NADH 2 ATP Fig carbon pyruvate 3-carbon pyruvate

12 6.8 Harvesting Electrons from Chemical Bonds The oxidative stage of aerobic respiration occurs in the mitochondria Fig It begins with the conversion of pyruvate into acetyl coa Depending on needs

13 The Krebs Cycle Takes place in the mitochondria It consists of nine enzyme-catalyzed reactions that can be divided into three stages 1 Acetyl CoA binds a 4-carbon molecule producing a 6-carbon molecule 2 Two carbons are removed as CO 2 3 The four-carbon starting material is regenerated Krebs cycle enzymes strip away electrons and H + from each acetyl group generating many NADH and FADH 2 molecules 1 CoA (Acetyl-CoA) carbon molecule (Starting material) 6-carbon molecule 6-carbon molecule NADH 4-carbon molecule (Starting material) NADH CO 2 FADH 2 4-carbon molecule 5-carbon molecule 4-carbon molecule Fig ATP NADH CO 2

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15 6.9 Using the Electrons to Make ATP Energy Transfer in the Mitochondria

16 6.9 Using the Electrons to Make ATP Glucose is entirely consumed in the process of cellular respiration Glucose is converted to six molecules of CO2 used to buffer the ph of blood breathe out as waste The glucose energy is transformed to 4 ATP molecules 10 NADH electron carriers 2 FADH2 electron carriers THE REDUCING POWER IN THESE ELECTRON CARRIERS IS USED TO MAKE 32 ATP MOLECULES IN THE ELECTRON TRANSPORT CHAIN

17 6.9 Using the Electrons to Make ATP Pyruvate from cytoplasm H + H + Intermembrane space NADH e H + Acetyl-CoA Krebs cycle NADH 1. Electrons are harvested and carried to the transport system. FADH 2 e e 2. Electrons provide energy to pump protons across the membrane. H 2 O 3. Oxygen joins with protons to form water. 1 O H + O 2 CO 2 2 ATP 32 ATP H + Mitochondrial matrix 4. Protons diffuse back in, driving the synthesis of ATP. ATP synthase Fig An overview of the electron transport chain and chemiosmosis

18 The electrons carried by NADH and FADH 2 are donated to the electron transport chain Energy released by the electrons is used to pump H + into the space between the mitochondrial membranes In chemiosmosis, the H + ions diffuse through ATP synthase complexes, which capture the energy to make ATP Fig. 6.25

19 Chemiosmosis in the mitochondrion Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.12

20 Other Sources of Energy Food sources, other than sugars, can be used in cellular respiration These complex molecules are first digested into simpler subunits Polysaccharides can be hydrolyzed to monosaccharides and then converted to glucose for glycolysis Proteins can be digested to amino acids, which are chemically altered and then used in the Krebs cycle Fats are broken up and fed into glycolysis and the Krebs cycle

21 Fig How cells obtain energy from foods

22 Anaerobic Respiration The use of inorganic terminal electron acceptors other than oxygen Organism Methanogens Archaea Sulfur bacteria Terminal electron acceptor CO 2 SO 4 Sulfate Reduced Product CH 4 Methane H 2 S Hydrogen sulfide

23 Fermentation The use of organic terminal electron acceptors The electrons carried by NADH are donated to a derivative of pyruvate This allows the regeneration of NAD + that keeps glycolysis running Two types of fermentation are common among eukaryotes Lactic fermentation and Ethanolic fermentation Fig Occurs in animal muscle cells Occurs in yeast cells

24 Sunlight energy BIG PICTURE Life from the Sun Nearly all the chemical energy that organisms use comes ultimately from sunlight CO 2 + H 2 O Chloroplasts, site of photosynthesis Mitochondria sites of cellular respiration Glucose + O 2 This is a VERY IMPORTANT cycle (for cellular work) Heat energy