2.A.2 Organisms Capture and Store Energy Part II (Cellular Respiration) Organisms capture and store free energy for use in biological processes Organisms capture and store free energy for use in biological processes.

Cellular respiration uses free energy available from sugars to phosphorylate ADP, producing the most common energy carrier, ATP.

The free energy available in sugars can be used to drive metabolic pathways vital to cell processes.

Cellular respiration involves a series of enzyme-catalyzed reactions that harvest free energy from simple carbohydrates.

Cell respiration is a catabolic pathway that yields energy by oxidizing organic fuels.

The breakdown of organic molecules is exergonic (  G >0); the energy released can be harnessed to phosphorylate ADP  ATP.

The Three Steps of Cellular Respiration Glycolysis Krebs Cycle Electron Transport Chain

Glycolysis: the breakdown of one glucose molecule into two pyruvate. It occurs in the cytoplasm and is anaerobic.

Glycolysis: Energy Investment Phase Glucose, a six carbon sugar, is split into two 3-carbon molecules. Requires 2 ATP

Glycolysis: Energy Payoff Phase The two 3-carbon molecules are converted into two pyruvate. Produces 2 NADH and 4 ATP

Glycolysis: Summary Investment: Glucose 4 ATP formed – 2 ATP used 2 NAD + Payoff: 2 Pyruvate 2 ATP 2 NADH Oxidation Reaction

Pyruvate is transported from the cytoplasm to the mitochondrion, where it is converted to Acetyl CoA.

Transition Reaction: Investment: 2 Pyruvate Payoff: 2 Acetyl Coenzyme A 2 NADH 2 CO 2 (waste product)

The Krebs Cycle (Also known as the Citric Acid Cycle or the TCA Cycle)

The Krebs Cycle occurs in the matrix of the mitochondria. Matrix

The Krebs Cycle produces 2 ATP through substrate-level phosphorylation. (Must occur twice for one glucose to be consumed).

The Krebs Cycle produces 2 ATP through substrate-level phosphorylation.

During the Krebs Cycle, coenzymes NAD + and FADH each receive high energy electrons and become NADH and FADH2.

The Krebs Cycle Summary: Investment: 2 Acetyl CoA Payoff: 2 ATP 6 NADH 2 FADH 2 4 CO 2 (waste) Substrate-Level Phosphorylation

The Electron Transport Chain is imbedded in the inner mitochondrial membrane.

Electrons that were extracted in the Krebs cycle are carried by NADH and FADH 2 to the Electron Transport Chain.

The electrons are passed from one carrier to the next until they are ultimately accepted by oxygen, forming water. (Oxygen is the final electron acceptor.)

The energy from the electrons is used to pump protons into the intermembrane space, forming an electrochemical gradient.

The electrons diffuse through ATP synthase (chemiosmosis), which uses the energy of the gradient to synthesize ATP from ADP. This type of ATP synthesis is called Oxidative Phosphorylation.

The Electron Transport Chain occurs on the cell membrane of prokaryotes.

The Electron Transport Chain Summary: Investment: 10 NADH 2 FADH 2 Oxygen Payoff: 28 ATP H 2 O Oxidative Phosphorylation

Cellular Respiration Summary: Investment: 1 glucose oxygen Investment: 1 glucose oxygen Payoff: Water CO ATP Payoff: Water CO ATP Yields 686 kcal energy per mole of glucose oxidized!

Cellular respiration also occurs in plants, along with photosynthesis.

Endotherms can decouple oxidative phosphorylation from the electron transport to produce more body heat instead of ATP.

Different energy-capturing processes use different types of electron acceptors: NADP+ for photosynthesis Oxygen for cellular respiration NADP+ for photosynthesis Oxygen for cellular respiration

In the absence of oxygen, ATP production can continue. This is called fermentation.

There are two types of fermentation: Fermentation Lactic Acid Fermentation Animals Ethanol Fermentation Yeast

Fermentation produces ATP through substrate-level phosphorylation when the ETC cannot run due to lack of oxygen.

Lactic Acid Fermentation

Ethyl Alcohol Fermentation

Fermentation Summary: Investment: 1 glucose Payoff : 2 ATP 2 CO 2 Anaerobic

Heterotrophs may metabolize carbohydrates, lipids and proteins by hydrolysis as sources of free energy. Hydrolysis:

Photosynthesis and Cellular Respiration are mirror reactions. Photosynthesis: Cellular Respiration:

Learning Objectives LO 2.4 The student is able to use representations to pose scientific questions about what mechanisms and structural features allow organisms to capture, store and use free energy. [See SP 1.4, 3.1] LO 2.5 The student is able to construct explanations of the mechanisms and structural features of cells that allow organisms to capture, store or use free energy. [See SP 6.2]