chapter 13

Would you expect fatty acids found in cells to most commonly have an even or an odd number of carbon atoms?

Even number because the oxidation of fatty acids breaks the carbon chain into two carbon units that become attached to CoA. Conversely, fatty acids are constructed by linking together acetyl groups

a high-energy electron carrier produced by reduction of FAD during the breakdown of molecules derived from food, including fatty acids and acetyl CoA.

FADH2

Because glycolysis is only a prelude to the oxidation of glucose in mitochondria, which yields 15-fold more ATP, glycolysis is not really important for human cells.

False, because in the absence of oxygen, glycolysis is the main producer of ATP; glycolysis also provides intermediates

nucleoside triphosphate used in the synthesis of RNA and DNA. it serves as an activated carrier in some energy transfer reactions. also has a special role in microtubule assembly, protein synthesis, and cell signaling.

GTP

Yeast cells can grow both in the presence of O2 and in its absence. Under which of the two conditions could you expect the cells to grow better? Explain your answer.

In the absence of O2 because it allows for more ATP to be produced.

In cells that can grow both aerobically and anaerobically, fermentation is inhibited in the presence of O2. suggest a reason for this observation.

In the presence of molecular oxygen, oxidative phosphorylation converts most of the cellular NADH to NAD+. since fermentation requires NADH, it is severely inhibited by the availability of oxygen gas.

central metabolic pathway found in aerobic organisms, which oxidizes acetyl groups derived from food molecules to CO2 and H2O. In eukaryotic cells it occurs in the mitochondria.

Krebs cycle;citric acid cycle

activated carrier widely used in the energy-producing breakdown of sugar molecules

NADH

C6H12O6 (glucose) + 6O2 --> 6CO2 + 6H2O + energy the reaction supplies the cell with essential water

false, because although the reaction produces water it is not essential to the reaction

C6H12O6 (glucose) + 6O2 --> 6CO2 + 6H2O + energy None of the produced energy is in the form of heat

false, because entropy has to increase, and most of these reactions are accomplished by releasing heat

C6H12O6 (glucose) + 6O2 --> 6CO2 + 6H2O + energy all of the energy produced is in the form of heat

false, because no chemical energy would be harvested in a useful form such at ATP; about 50% is in the form of heat

C6H12O6 (glucose) + 6O2 --> 6CO2 + 6H2O + energy many steps in the oxidation of sugar molecules involve reaction with oxygen gas

false, molecular oxygen is only used in the very last step of the reaction

energy storage lipids in cells that are composed of triacylglycerols (fatty acids esterified with glycerol).

fat

refer to study guide question 3. give an general explanation for this observation.

fatty acids have more bonds than sugars. the bonds contain chemical potential energy and yield when oxidized. fatty acids will yield more energy than sugars when they are oxidized because they have more bond energy stored in them.

a form of metabolic control in which the end product of a chain of enzymatic reactions reduces the activity of an enzyme early in the pathway

feedback regulation

the breakdown of organic molecules without the involvement of molecular oxygen, this form of oxidation yields less energy than aerobic cell respiration

fermentation

Explain why cells growing in the absence of oxygen could not simply discard pyruvate as a waste product. Which products derived from glucose would accumulate in cells unable to generate either lactate or ethanol by fermentation?

fermentation allow NAD+ to be recycled because it is important in glycolysis. in the absence of oxygen, glycolysis is the only way to produce ATP. If this doesn't happen, step 6 won't happen and 3PG will accumulate.

this is produced in step 3 of glycolysis by the enzyme phosphofructokinase;

fructose 1,6 biphosphate

it removes the phosphate from fructose 1,6 bisphosphate to produce fructose 6-phosphate

fructose 1,6 bisphosphatase

set of enzyme- catalyzed reactions by which glucose is synthesized from small organic molecules such as pyruvate, lactate, or amino acids, in effect, the reverse of glycolysis

gluconeogenesis

polysaccharide composed exclusively of glucose units used to store energy in animal cells. Granules of it are especially abundant in liver and muscle cells.

glycogen

the major enzyme in glycogenolysis, leading to the release of glucose-1-phosphate from glycogen. This enzyme is activated by phosphorylation from ATP by glycogen phosphorylase kinase, activated by cAMP-dependent protein kinase or by Ca2+ via calmodulin, or inhibited by hydrolysis of the phosphate by glycogen phosphatase.

glycogen phosphorylase

Ubiquitous metabolic pathway in the cytosol in which sugars are partially metabolized to produce ATP.

glycolysis

a gel-like material that resembles bacterial cytoplasm that contains the enzymes that are responsible for the citric acid cycle reactions. The matrix also contains dissolved oxygen, water, carbon dioxide, the recyclable intermediates that serve as energy shuttles,

mitochondrial matrix

metabolic intermediate. Couples with acetyl coA to form citrate, i.e. The entry point of the tricarboxylic acid cycle. Formed from aspartic acid by transamination.

oxaloacetate

process in bacteria and mitochondria in which ATP formation is driven by the transfer of electrons from food molecules to molecular oxygen.

oxidative phosphorylation

the enzyme that regulates the entry of sugars into glycolysis

phosphofructokinase

three-carbon metabolite that is the end product of the glycolytic breakdown of glucose; provides a crucial link to the citric acid cycle and many biosynthetic pathways

pyruvate

where pyruvate is rapidly decarboxylated by a giant complex of three enzymes, (CO2, NADH, acetyl CoA

pyruvate dehydrogenase complex

polysaccharide composed exclusively of glucose units, used as an energy store in plant cells

starch

C6H12O6 (glucose) + 6O2 --> 6CO2 + 6H2O + energy in cells, the reaction takes place in more than one step

true

C6H12O6 (glucose) + 6O2 --> 6CO2 + 6H2O + energy some cells that grow in the absence of O2 produces CO2

true

the reactions of the citric acid cycle do not directly require the presence of oxygen

true

refer to question 13-15. assume the oxaloacetate containing radioactive 14C in its keto group is added to the extract. Where should the 14C atom be located after precisely one turn of the cycle?

14C label would be quantitively recovered in oxaloacetate. its also no longer in the keto group but in the methylene group of oxaloacetate.

Molecules that serves as the principal carrier of energy in cells; this nucleoside triphosphate is composed of adenine, ribose, and three phosphate groups; Activated carrier widely used in the energy-producing breakdown of sugar molecules

ATP and NADH

Humans are unable to synthesize all 20 amino acids. in this course of a day when do you suppose humans make net amounts of new proteins? Explain your answer.

After a big meal, the amino acids that we can't make are available to work with what amino acids we already have producing protein synthesis.

For question 13-2, suggest why arsenate is a compound of choice for murderes, but not for cells. formulate your explanation in terms of the step in glycolysis at which 1,3-bisphophoglycerate is converted to 3-phosphoglycerate, generating ATP.

Arsenate becomes attached in step 6 of glycolysis to form 1-arseno-3-phosphoglycerate. the product of hydrolysis, 3-phosphoglycerate, is the same product normally formed in step 7 by the action of phosphoglycerate kinase; the energy required to break the high energy bond will not be able to harness energy for the conversion of ATP, if Arsenate was used.

When enzymes convert the large polymeric molecules in food into simpler monomeric subunits; it occurs either outside cells or in specialized organelles within cells called lysosomes

digestion

series of electron carrier molecules along which electrons move from a higher to a lower energy level to a final acceptor molecule.

electron transport chain

Refer to question 13-15. Assume that pyruvate containing radioactive 14C in its carboxyl group is added to a cell extract that can support oxidative phosphorylation. Which of the molecules produced should contain the vast majority of the 14C that was added?

Pyruvate is converted to acetyl CoA, and the labeled 14C atom is released as 14CO2 gas

the form of ATP synthesis that takes place in steps 7 and 10 in glycolysis that occurs by the transfer of a phosphate group directly from a substrate molecule to ADP

Substrate level phosphorylation

Refer to question 13-11. Why is this a useful compound to store energy? Justify your answer with the information shown in Figure 13-8.

The amount of free energy stored in the phosphate bond in creatine phosphate is larger than that of the anhydride bonds in ATP. It also has a high conversion rate, which allows for it to rapidly go in the right direction without wasting a lot of energy.

a cyclic reaction pathway requires that the starting material be regenerated and available at the end of each cycle. if compounds of the citric acid cycle are siphoned off as building blocks to make other organic molecules via a variety of metabolic reactions, why does the citric acid cycle not quickly grind to a halt?

The pathways are bi-directional. while things are exiting, more things are coming in.

"the oxygen consumed during the oxidation of glucose in animal cells is returned as part of CO2 to the atmosphere." How could you support your answer experimentally?

This statement is false because CO2 does not contain those specific oxygen atoms that were consumed as part of the oxidative phosphorylation process and converted into water. 18O isotope show this by being used instead of 16O isotope because the oxygen atoms in the released CO2 molecules do not come directly come from the atmosphere but from organic molecules.

C6H12O6 (glucose) + 6O2 --> 6CO2 + 6H2O + energy some organisms carry out the reverse reaction

True

activated carrier that donates the carbon atoms in its readily transferable acetyl group to many metabolic reactions, including the citric acid cycle and fatty acid biosynthesis; the acetyl group is linked to coenzyme A by thioester bond that releases a large amount of energy when hydrolyzed.

acetyl CoA

series of enzyme-catalyzed reactions by which large biological molecules are synthesized from smaller subunits; usually requires an input of energy

anabolic pathways

is respiration without oxygen; the process uses a respiratory electron transport chain but does not use oxygen as the electron acceptors.

anaerobic respiration

A molecule that plays a role in transporting electrons through the electron transport chain. they are usually proteins bound to a nonprotein group; they can undergo oxidation and reduction relatively easily, thus allowing electrons to flow through the system.

carrier molecules

set of enzyme-catalyzed reactions by which complex molecules are degraded to simpler ones with release of energy; intermediates in these reactions are sometimes called catabolites

catabolism

specialized organelle in algae and plants that contains chlorophyll and serves as the site in which photosynthesis takes place.

chloroplasts

linked pair chemical reactions in which free energy released by one reaction serves to drive the other reaction

coupled reaction