Energy Flow and Chemical Recycling in Ecosystems The

Energy Flow and Chemical Recycling in Ecosystems The chemical elements of life are recycled but energy is not – it flows into an ecosystem as light and leaves as heat

Electrons “fall” from organic molecules to oxygen during cellular respiration • C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O + energy Oxidation of C 6 H 12 O 6 coupled to the reduction of O 2. Controlled release of energy to form ATP. The remainder of the energy is released as heat. This process is called oxidative phosphorylation.

Overview of Cellular Respiration

Glucose glycolysis → 2 ATP 2 Pyruvate Overview of Cellular Respiration The first step is called glycolysis. It occurs in the cytosol. During glycolysis, a glucose molecule (6 carbons) is converted to two pyruvate molecules (3 carbons each). It does not require oxygen (it is anaerobic). A total of 2 ATP are gained as a result of these reactions.

The Glycolytic Pathway

Summary of Glycolysis glucose (C 6) 2 ATP 4 ATP produced 2 ADP 2 C 3 2 ADP - 2 ATP consumed 2 NAD+ 2 ATP net 2 NADH 2 ATP 2 NADH are also produced 2 ADP 2 ATP 2 pyruvate (C 3)

Efficiency of Glycolysis • Compare the kilocalories of glucose with the kilocalories in the ATP that is made. • The 2 ATP molecules made during glycolysis account for only 2% of the energy in glucose • Where does the rest go? • It’s still in pyruvic acid • This small amount of energy is enough for bacteria, but more complex organisms need more of glucose’s energy.

Fermentation • If there is no oxygen some cells can convert pyruvic acid into other compounds and get more NAD+ • No ATP is made, but the NAD+ can keep glycolysis going to make a little ATP • 2 kinds of fermentation: Lactic acid fermentation and Alcoholic Fermentation

Anaerobic Aerobic

Evolutionary Significance of Glycolysis • Glycolysis is the most widespread pathway, so it probably evolved early. • The first prokaryotes evolved over 3. 5 billion years ago, before there was much O 2 in the atmosphere. • Glycolysis occurs in the cytosol and does not require membrane-bound organelles. • Eukaryotic cells with organelles probably evolved about 2 billion years after prokaryotic cells.

A transport protein built into the membrane facilitates the movement of pyruvate into the mitochondrion

Overview of Cellular Respiration

The Krebs Cycle

• The conversion of pyruvate to acetyl Co. A and the Krebs cycle produce large quantities of electron carriers.

The inner mitochondrial membrane couples electron transport to ATP synthesis Proton-motive force Oxidative phosphorylation

• A protein complex, ATP synthase, in the cristae actually makes ATP from ADP and Pi. • ATP used the energy of an existing proton gradient to power ATP synthesis. – This proton gradient develops between the intermembrane space and the matrix.

Feedback mechanisms control cellular respiration

How are food molecules other than glucose oxidized to ATP?

RESPIRATION PROTEINS CYTOPLASMGL YCOLOSIS HAPPENS HERE! CARBO’S (SUGARS) FATS (LIPIDS) AMINO ACIDS GLUCOSE C 6 H 12 O 6 GLYCOLOSIS IN CYTOPLASM NO OXYGEN! ATP TOTALS GLYCOLOSIS=2 PYRUVIC ACID RESPIRATION=34 BOTH=36! MAKES 2 ATPS ACETYL-Co. A CO 2 IS RELEASED O 2 ENTERS HERE MITOCHONDRIARES PIRATION HAPPENS IN THIS ORGANELLE! KREBS CYCLE AND ELECTRON TANSPORT MAKES 34 ATPS