Download Overview of Cellular Respiration

Overview of Cellular Respiration
Organic compounds such as glucose store energy in their ________________________. These molecules are broken
down and their energy extracted in _______________________. The first stage of cellular respiration occurs in the
_______________, while the second and third stages occur in ____________________. In cellular respiration,
electrons are transferred from ________________ to ________________ such as NAD+ and finally to
______________; the energy released by this relocation of electrons is used to make _____. Carbon dioxide and
water are given off as _______________.
Glycolysis is a series of steps in which a glucose molecule is broken down into two molecules of
__________________. As the chemical bonds in glucose are broken, ______________ (and ______________ ions) are
picked up by __________, forming _________. Glucose is __________________ and NAD + is __________________. A
net output of two ATP molecules are also produced in glycolysis for every glucose molecule processed. But most of
the energy released by the breakdown of glucose is carried by the electrons attached to NADH.
The pyruvate molecules are modified as they enter the mitochondrion, releasing ______________________. The
altered molecules enter a series of reactions called the ___________________________. More carbon dioxide is
released as the citric acid cycle completes the ____________________________________. Two ATPs are formed per
glucose, but most of the energy released by the oxidation of glucose is carried by NADH and FADH2.
Almost all of the ATP produced by cellular respiration is banked in the final phase—
______________________________. The NADH and FADH2 molecules produced in __________________ and the
_______________________ donate their electrons to the electron transport chain. At the end of the chain,
________________ exerts a strong pull on the electrons, and combines with them and hydrogen ions (protons) to
form _______________. The electron transport chain converts chemical energy of moving electrons to a form that
can be used to drive oxidative phosphorylation, which produces about 34 ATP molecules for each glucose molecule
consumed.
Glycolysis
Glycolysis, which begins the breakdown of glucose, is a series of ______ enzyme-catalyzed chemical reactions that
can be divided into two main phases.
In the _____________________ phase, some ATP energy is used to start the process of glucose oxidation. By the end
of this phase, a 6-carbon molecule (glucose) has been split into two 3-carbon molecules of glyceraldehyde-3phosphate.
The 3-carbon glyceraldehyde-3-phosphate molecules now enter the ______________________ phase. Chemical
bonds are broken, and NAD+ picks up electrons and hydrogen ions, forming NADH. The energy released is used to
attach ___________________ groups. The phosphates are transferred to ADP, finally making some ATP. This way of
making ATP is called ____________________________ phosphorylation. A couple more reactions rearrange the
atoms in the 3-carbon molecules. More ATP is generated in the final reaction that yields ______________________.
For each glucose molecule broken down during glycolysis, a net of two ATPs are formed, along with two NADH
molecules.
Citric Acid Cycle (also known as the “Krebs Cycle”)
The oxidation of glucose continues in the citric acid cycle. ________________ molecules formed during glycolysis
diffuse from the ____________ into the ____________________, but pyruvate itself does not enter the citric acid
cycle. A reaction occurs that removes a carbon atom, releasing it in ____________________. Electrons are
transferred to an NADH molecule, storing energy. __________________, or CoA, joins with the 2-carbon fragment,
forming ______________.
One molecule of acetyl CoA enters the citric acid cycle. The 2-carbon fragment of acetyl CoA attaches to the 4carbon molecule ______________________ in the first reaction of the cycle. This forms _____________. In a series
of steps, bonds break and reform. Two carbon atoms are released, one at a time, in molecules of carbon dioxide.
Electrons are carried off by molecules of NADH and FADH2. One step produces an ATP molecule by
__________________________ phosphorylation. A 4-carbon oxaloacetate molecule is ________________________.
Since two acetyl CoA molecules are produced for each glucose molecule broken down, a second acetyl CoA enters
the citric acid cycle. The same series of reactions occurs, releasing carbon dioxide and producing more NADH,
FADH2, and ATP.
The cell has gained two ATPs that can be used directly. However, most of the energy originally contained in the
bonds of glucose is now carried by the NADH and FADH2 molecules.
Oxidative Phosphorylation
Most of the energy harvested from organic molecules during glycolysis and the citric acid cycle is stored in
__________ and ___________. These molecules give up their high-energy electrons in the third phase of cellular
respiration—_________________________________—where most of the cell's ATP fuel is produced.
The electron transport chain is an array of molecules—mostly _______________— built into the inner membrane of
the ______________________. NADH gives up its high-energy electrons to the first complex in the electron transport
chain. The electrons move from one member of the chain to the next, giving up their energy as they are pulled from
NADH toward highly __________________________ oxygen. The energy given up by the flow of electrons is used to
pump hydrogen ions from the mitochondrial _____________ into the ______________________ space. Oxygen
captures the electrons in the very last step in electron transport. The last complex adds a pair of electrons to an
oxygen atom and two hydrogen ions, forming ___________.
The electron transport chain has used the energy of moving _____________ to pump ____________________ into
the intermembrane space. This buildup of hydrogen ions— like water behind a dam— stores the
________________________ that was originally in the bonds of glucose molecules.
The backed-up hydrogen ions give up their energy when they diffuse through a special protein in the membrane
called ____________________. As hydrogen ions flow down their _____________________________, ATP synthase
captures their energy to make ATP. This mode of ATP production is called oxidative phosphorylation because it is
powered by the transfer of electrons to oxygen.
Under normal conditions, almost all the ATP produced in the process of cellular respiration is manufactured by
electron transport and oxidative phosphorylation— about _____ ATPs for every glucose consumed.
Summary of Cellular Respiration
Glycolysis and the citric acid cycle produce a small amount of ATP via substrate-level phosphorylation, but most of
the cell's ATP is made via oxidative phosphorylation, when NADH and FADH2 produced in glycolysis and the citric
acid cycle give up to oxygen the electrons obtained from organic molecules.
Fermentation
All cells are able to synthesize ATP via the process of glycolysis. In many cells, if oxygen is not present, pyruvate
(pyruvic acid) is metabolized in a process called ________________________. By oxidizing the NADH produced in
glycolysis, fermentation regenerates __________, which can take part in glycolysis once again to produce more ATP.
The net energy gain in fermentation is 2 ATP molecules per molecule of glucose. Fermentation complements
________________ and makes it possible for ATP to be continually produced in the absence of _________________.
There are two types of fermentation. Alcohol fermentation which occurs in _____________, results in the
production of ethanol and carbon dioxide. Lactic acid fermentation, which occurs in _______________, results in
the production of ___________ (lactic acid).
The Relationship between Glycolysis and Alcohol Fermentation
Glycolysis produces NADH, ATP, and pyruvate (pyruvic acid). If oxygen is not present, NADH cannot be oxidized in
the electron transport chain. Without fermentation, the cell would run out of NAD+, bringing _________________ to
a halt. In alcohol fermentation, the pyruvate (pyruvic acid) from glycolysis loses one carbon in the form of carbon
dioxide and the product is then reduced to ________________ by NADH. With the formation of ethanol, NADH is
oxidized and becomes NAD+. With a continuous supply of NAD+, glycolysis can continue, producing more ATP. During
fermentation, the NADH produced by glycolysis is oxidized, ensuring a continuous supply of NAD+ for glycolysis.
Alcohol fermentation occurs in yeast cells.
The Relationship between Glycolysis and Lactic Acid Fermentation Glycolysis produces NADH, ATP, and pyruvate (pyruvic acid). If oxygen is not present, NADH cannot be oxidized in
the ______________________________. Without fermentation, the cell would run out of _________, bringing
glycolysis to a halt. In lactic acid fermentation, the pyruvate (pyruvic acid) from glycolysis is reduced to
_________________________ by NADH. With the formation of lactate (lactic acid), NADH is oxidized and becomes
NAD+. With a continuous supply of NAD+, glycolysis can continue, producing more ATP. During fermentation, the
NADH produced by glycolysis is oxidized, ensuring a continuous supply of NAD+ for glycolysis. Lactic acid
fermentation occurs in muscle cells.