Review  What are the 4 macromolecules?  What is an enzyme?  What is a polymer?  What is a monomer?  What is the name of the process that breaks polymers?  What is the name of the process that joins polymer?

Enzymes

Cellular Respiration Harvesting Chemical Energy

Cellular Respiration  the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen  It is the reverse of photosynthesis.  C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O

3 main stages – each captures some of the chemical energy available in food molecules and uses it to produce ATP  Glycolysis  Krebs's Cycle  Electron Transport Chain (ETC)(mitochondria)

Glycolysis  Happens in the cytoplasm  net gain of 2 ATP per glucose molecule  main purpose is to produce pyruvic acid to be used in the Kreb’s Cycle and to create NADH to transport high energy electrons to the electron transport chain  NAD + – high energy electron carrier like NADP + in photosynthesis  NAD + accepts a pair of high energy electrons forming a molecule called NADH which holds the electrons until they can be transferred to other molecules. NADH carries electrons to the electron transport chain  Glycolysis does not require oxygen and can, therefore, supply chemical energy to cells when oxygen is unavailable.  If oxygen is not present, pyruvate is converted to lactic acid in the cytoplasm -- anaerobic respiration

Kreb’s Cycle (citric acid cycle) At the end of glycolysis, 90% of the energy from glucose is still unused – locked in the high energy electrons of pyruvic acid. The main purpose of this cycle is to produce NADH and FADH 2 – high energy electron carriers – these carriers carry electrons to the electron transport chain.

Electron Transport Chain  The electron transport chain uses high energy electrons from the Kreb’s Cycle to convert ADP to ATP. Water is a waste product of the ETC (and of cellular respiration) just as oxygen is in photosynthesis.

Electron Transport Chain

When oxygen is not present …. Glycolysis is followed by a different pathway!  Fermentation

Fermentation  Fermentation releases energy from food molecules by producing ATP in the absence of oxygen.  Cells convert NADH to NAD + by passing high energy electrons back to pyruvic acid.  This allows glycolysis to continue producing a steady supply of ATP  Called anaerobic because it does not require oxygen.  Two types: alcoholic fermentation and lactic acid fermentation.

Alcoholic Fermentation  Produces carbon dioxide and alcohol  This is what causes bread dough to rise – when yeast runs out of oxygen it ferments, giving off carbon dioxide gas which creates the air spaces in a slice of bread.  The alcohol evaporates.

Lactic Acid Fermentation  Lactic acid is produced in the muscles during rapid exercise when the body cannot supply enough oxygen to the tissues.  Without oxygen the body is unable to produce all the ATP required.  Muscle cells begin producing ATP by lactic acid fermentation.  The build-up of lactic acid causes a painful, burning sensation – sore muscles

Comparing Photosynthesis and Cellular Respiration PhotosynthesisCellular Respiration FunctionEnergy captureEnergy release LocationChloroplastsMitochondria and Cytoplasm Who does it?“green” cells – plant, algaeALL living cells ReactantsCO 2 & H 2 OC 6 H 12 O 6 & O 2 ProductsC 6 H 12 O 6 & O 2 CO 2 & H 2 O Equation 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 C 6 H 12 O 6 +6O 2  6CO 2 + 6H 2 O OrderHappens firstHappens second