Chapter 8 HOW CELLS RELEASE ENERGY HOW CELLS RELEASE ENERGY (hyperlink on title) Jill before teaching inbed these hyperlinks

Define CR: ] it is all the biochemical pathways necessary to extract energy from nutrient molecules in the presence of oxygen – leaving CO 2 as a metabolic WASTE ] Who does it? F ALL living organisms!! Even those without a respiratory system, including plants and fungus F Anyone who has mitochondria and EVEN if they DON’T ] Reverse of photosynthesis – moving energy from carbs into ATP

All cells (prokaryotic & eukaryotic) require energy to: combat entropy carry out day-to-day functions repair/replace worn out organelles reproduce What form of energy do cells use? ATP Link on picture

How do cells obtain ATP? All cells must make their own ATP from nutrients they have either synthesized (autotrophs) or consumed (heterotrophs). Most cells break down nutrients to make ATP in TWO ways: Cellular respiration (aerobic process) Fermentation (anaerobic process)

General equation for Aerobic cellular respiration of glucose: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + 30 ATP General wquation for Fermentation (anaerobic cellular respiration) Not so well defined!

Cellular respiration occurs in 3 stages: Glycolysis Krebs Cycle Electron Transport Chain Eukaryotic cells Cytoplasm Mitochondria Prokaryotic cells Cytoplasm Cell membrane

Cool Stuff ] When ATP  ADP, 7.5 kcal/mole of energy released. How does this compare to the peanut? ] Extra Credit: F calculate kcal/gram for ATP F Consider peanut: 1.5 to 2.5 Kcal/g F How many ATP’s per peanut? F Formula for ATP C 120 H 16 N 70 O 208 P 93

WHY a biochemical pathway – why not realease energy in ONE step ? ] Glucose molecule = 686 Kcal/mole F This is 3.81 Kcal/g (more than twice as much as in an entire peanut!) F Instant cell death!!!

Efficient? ] Not very! ] Each step will loose some energy via heat ] Not all bad – this helps maintain internal temperature of organism

Glycolysis (“glucose-splitting”) (hyperlink in pink)glucose-splitting F Glucose (6C) is split into two pyruvate (3C) molecules. (aka pyruvic acid) does not require oxygen energy harvested/glucose: 2 ATP (via substrate-level phosphorylation) 2 NADH (actively transported into mitochondria of eukaryotic cells for use by the electron transport chain) 1 st half: activates glucose – 2 ATP’s used – no ATP gained 2 nd half: extracts a little energy Takes place in cytoplasm (cytosol) Adding phosphates prevent glucose from migrating out f the cytoplasm

First half of glycolysis activates glucose by investing 2 ATP molecules.

Second half of glycolysis extracts energy by releasing 4 ATP molecules.

Where the big stuff happens!

Intermediary step required before Kreb can happen: Pyruvic acid must be converted to Acetyl CoA before it can enter Krebs cycle. PA moves into mitochondrial matrix. PA looses a CO 2 (when NAD reduced to NADH) and becomes Acetyl CoA ( 2 Carbon molecule)

2. Krebs Cycle (aka. citric acid cycle)Krebs Cycle Acetyl Co A enters the Kreb and combines with oxaloacetate to form citric acid. cells use carbon skeletons of intermediates to produce other organic molecules (amino acids). Enormous quantities of CO 2 produced energy harvested per acetyl CoA: Per GLUCOSE molecule (half each cycle) 2 ATP (via substrate-level phosphorylation) 6 NADH 2 FADH 2

Thus far, how much useable energy has been produced from the breakdown of 1 glucose molecule? 4 ATPs The electron transport chain is needed to harvest the potential energy in NADHs & FADH 2 s.

Electron Transport Chain (ETC)Electron Transport Chain Series of proteins & electron carriers embedded in the cristae,inner mitochondrial membrane (eukaryotes) or cell membrane (prokaryotes). O 2 is the final electron acceptor Uses the energy trapped in NADH and FADH 2 in other steps (become NAD and FAD) H 2 O is the final product (electrons + H ions + O = water) Meantime the H ion released from NADH and FADH begin to fill the intermembrane compartment (space between outer mictochondrial membrane and the cristae)

] Electron Transport, con’t Hydrogen ions (protons) slide into a channel of ATP synthase When channel is stimulated, ADP is phosphoralated to produce ATP. Net ATP varies hugely – estimates are around 26 energy harvested/NADH: 2.5 ATPs (via chemiosmotic phosphorylation) energy harvested/FADH 2 : 1.5 ATPs (via chemiosmotic phosphorylation)

How many ATPs can 1 glucose yield?

Can cells use proteins & lipids to produce energy?

Fermentation F Biochemical pathways that try to extract energy from nutrients, in the absence of oxygen. F Glycolysis produces pyruvic acid which is broken down in fermentation Alcoholic fermentation F Pyruvic acid is broken down to ethanol and carbon dioxide. F Ex. yeast (used in production of baked goods & alcoholic beverages)

NET ATP???

Lactic acid fermentation Pyruvic acid is broken down to lactic acid. Examples: certain bacteria (used in production of cheese & yogurt) human muscle cells in oxygen debt

Photosynthesis, glycolysis & cellular respiration are interrelated.

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