Respiration: Harvesting Chemical Energy

Living organisms ______(break down) organic molecules within their cells and use the energy released to manufacture ______by phosphorylating ADP. Many prokaryotes and virtually all eukaryotes phosphorylate ____either through ______(anaerobic) or ______(aerobic). Both of these processes involve oxidation of glucose, yet only the latter requires oxygen.

Glycolysis

During glycolysis, the potential energy of glucose, is released during a series of chemical reactions which occur in the______. Some of the energy released when ______are broken, is used to phosphorylate ______,and some is transferred to a ______,NAD+, which is reduced to NADH. No oxygen is used during glycolysis. ______, a product of glycolysis may either be converted to lactate or ______(fermentation) or be converted to an acetyl group for further processing during the Krebs cycle.

Fermentation

In the absence of ______, many cells use fermentation to produce ATP by ______. Pyruvate, the end-product of glycolysis, serves as an electron acceptor for oxidating ______back to ______. In the first process, the pyruvate resulting from glycolysis is converted to ______then ethanol; in the second, the pyruvate is converted to ______.

Kreb’s Cycle

The Kreb’s cycle, which occurs in the ______is the second major stage in cellular respiration It is an eight step cycle that completes the metabolic breakdown of glucose molecules to carbon dioxide. The first event to occur is oxidation of pyruvate to acetyl, which then combines with ______to yield acetyl CoA. Next, coenzymeA delivers the acetyl group to ______a four carbon compound already present in the mitochondrion, with which the 2 carbon acetyl group combines to form ______This step initiates the "first turn" of the Krebs Cycle. At the end of the Krebs Cycle, oxaloacetate has once again been formed. A second acetyl coA combines with it, initiating the second turn of the Krebs Cycle.

After the second cycle has been completed, the original glucose has been turned into a total of______CO2 molecules yet no oxygen has been used. Only______ATP molecules have been netted.

Oxidative Phosphorylation

This process occurs on the plasma membrane of prokaryote cells and on the ______membrane of the mitochondrion; quantitatively, it is the most important way that ______is made by aerobic cells. During the process, the coenzymes (____ and FADH2) which have accumulated during previous processes transfer hydrogen atoms to components of the ______. During transport, hydrogens and electrons are transferred to acceptors in such a way that protons are pumped across the inner mitochondrial membrane. This results in an ______which is later used to phosphorylate ADP (make ATP) as protons diffuse back across the membrane. Hence, oxidative phosphorylation results from a process of ______(energy-coupling mechanism that uses energy stored in the form of H+ gradient across a membrane to drive cellular work). In the final step of this sequence, electrons are transferred to oxygen and used in the formation of ______.

Word bank

catabolize

ATP

pyruvate

oxaloacetate

water

coenzyme

NADH

oxygen

inner

electrochemical gradient

lactic acid

respiration

bonds

coenzyme a

6

citric acid

electron transport chain

chemiosmosis

substrate level phosphorylation

ADP

NAD+

fermentation

cytoplasm

ethanol

acetaldehyde

mitochondrial matrix

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