Unit 2 Bio 1A (Ch. 9)

Front 1

In general terms, distinguish between fermentation and cellular respiration.

Back 1

--One catabolic process, fermentation, is a partial degra- dation of sugars or other organic fuel that occurs without the use of oxygen.

-- However, the most efficient catabolic pathway is aerobic respiration, in which oxygen is consumed as a reactant along with the organic fuel (aerobic is from the Greek aer, air, and bios, life). The cells of most eukaryotic and many prokaryotic organisms can carry out aerobic respiration.

Front 2

2. Write the summary equation for cellular respiration.

Back 2

Organic compounds + Oxygen --> Carbon dioxide + Water + Energy

Front 3

Write the specific chemical equation for the degradation of glucose

Back 3

C6H12O6 + 6O2 --> 6CO2 + 6H2O + Energy (ATP + Heat)

Front 4

Define oxidation and reduction

Back 4

In many chemical reactions, there is a transfer of one or more electrons (e-) from one reactant to another. These electron transfers are called oxidation-reduction reactions, or redox reactions for short.

OXIDATION: In a redox reaction, the loss of electrons from one substance is called oxidation

REDUCTION: the addition of electrons to another substance is known as reduction

Front 5

4. Explain in general terms how redox reactions are involved in energy exchanges.

Back 5

Energy must be added to pull an electron away from an atom, just as energy is required to push a ball uphill. The more electronegative the atom (the stronger its pull on electrons), the more energy is required to take an electron away from it. An electron loses potential energy when it shifts from a less electronegative atom toward a more electronegative one,

-- A redox reaction that moves electrons closer to oxygen, such as the burning (oxidation) of methane, therefore releases chemical energy that can be put to work.

Front 6

5. Describe the role of NAD+ in cellular respiration.

Back 6

Therefore, the electrons transferred from glucose to NAD+, which is thus reduced to NADH, fall down an energy gradient in the electron transport chain to a far more stable location in the electronegative oxygen atom. Put another way, oxygen pulls electrons down the chain in an energy-yielding tumble analogous to gravity pulling objects downhill.

Front 7

6. Be able to draw and label all the component s of a mitochondria.

Back 7

TBD

Front 8

Name the three stages of cellular respiration and state the region of the eukaryotic cell where each stage occurs.

Back 8

glycolysis: cytosol

citric acid cycle: matrix of the mitochondria

electron transport: inner membrane of the mitochondrian

Front 9

8. Describe how the carbon skeleton of glucose differ from pyruvate .

Back 9

TBD

Front 10

9. Explain why ATP is required for the preparatory steps of glycolysis.

Back 10

TBD

Front 11

11. Describe where pyruvate is oxidized to acetyl CoA, what molecules are produced, and how this process links glycolysis to the citric acid cycle.

Back 11

--Upon entering the mitochondrion via active transport, pyruvate is first converted to a compound called acetyl coenzyme A, or acetyl CoA

--This step, linking glycolysis and the citric acid cycle, is carried out by a multienzyme complex that catalyzes three reactions: 1 Pyruvate’s car- boxyl group (—COO-), which is already fully oxidized and thus has little chemical energy, is removed and given off as a molecule of CO2. This is the first step in which CO2 is released during respiration. 2 The remaining two-carbon fragment is oxidized, forming acetate (CH3COO-, which is the ionized form of acetic acid). The extracted electrons are transferred to NAD+, storing energy in the form of NADH.

Front 12

12. List the products of the citric acid cycle(numbers of NADH and FADH2). Explain why it is called a cycle.

Back 12

--the total yield per glucose from the citric acid cycle turns out to be
6 NADHs, 2 FADH2s, and the equivalent of 2 ATP

--Citrate is the ionized form of citric acid, for which the cycle is named. The next seven steps decompose the citrate back to oxaloacetate. It is this regeneration of oxaloacetate that makes the process a cycle.

Front 13

14. Distinguish between substrate level phosphorylation and oxidative phosphorylation.

Back 13

--Substrate-level phosphorylation is directly phosphorylating ADP with a phosphate and energy provided from a coupled reaction. ...

--Oxidative phosphorylation is when ATP is generated from the oxidation of NADH and FADH2 and the subsequent transfer of electrons and pumping of protons. ((oxidative phosphorylation, which uses energy
released by the electron transport chain to power ATP synthesis.))

Front 14

15. In general terms, explain how the exergonic “slide” of electrons down the electron transport chain is coupled to the endergonic production of ATP by chemiosmosis. (RE-CHECK)

Back 14

The electron transport chain makes no ATP directly. Instead, it eases the fall of electrons from food to oxygen, breaking a large free-energy drop into a series of smaller steps that release energy in manageable amounts, step by step. How does the mitochondrion (or the plasma membrane, in the case of prokaryotes) couple this electron transport and energy release to ATP synthesis? The answer is a mechanism called chemiosmosis.

Front 15

16.Explanine in detail chemiosmosis(be able to draw a labeled diagram).

Back 15

This process, in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesis of ATP, is called chemiosmosis (from the Greek osmos, push). In general terms, chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of an H+ gradient across a membrane to drive cellular work.

Front 16

18. Summarize the net ATP yield from the oxidation of a glucose molecule by constructing an ATP

Back 16

+2 ATP by substrate level phosphorylation (glycolysis)

+2 ATP by substrate level phosphorylation (citric acid cycle)


+ about 26 or 28 ATP by oxidative phosphorylation, depending one which shuttle transports electrons from NADH in cytosol

= about 30 or 32 ATP (MAX per glucose)

Front 17

19. Explain why it is not possible to state an exact number of ATP molecules generated by the oxidation of glucose.

Back 17

-- There are three reasons we cannot state an exact number of ATP molecules generated by the breakdown of one molecule of glucose. First, phosphorylation and the redox reactions are not directly coupled to each other, so the ratio of the number of NADH molecules to the number of ATP molecules is not
a whole number. We know that 1 NADH results in 10 H+ being transported out across the inner mitochondrial membrane, but the exact number of H+ that must reenter the mi- tochondrial matrix via ATP synthase to generate 1 ATP has long been debated.

--Second, the ATP yield varies slightly depending on the type of shuttle used to transport electrons from the cytosol into the mitochondrion. The mitochondrial inner mem- brane is impermeable to NADH, so NADH in the cytosol is segregated from the machinery of oxidative phosphoryla- tion. The 2 electrons of NADH captured in glycolysis must be conveyed into the mitochondrion by one of several elec- tron shuttle systems. Depending on the kind of shuttle in a+ particular cell type, the electrons are passed either to NAD or to FAD in the mitochondrial matrix. If the electrons are passed to FAD, as in brain cells, only about 1.5 ATP can result from each NADH that was originally generated in the cytosol. If the electrons are passed to mito- chondrial NAD+, as in liver cells and heart cells, the yield is about 2.5 ATP per NADH.

-- A third variable that reduces the yield of ATP is the use of the proton-motive force generated by the redox reactions of respiration to drive other kinds of work.

Front 18

20. State the basic function of fermentation.

Back 18

Fermentation is a way of harvesting chemical energy without using either oxygen or any electron transport chain—in other words, without cellular respiration

Front 19

21. Compare the fate of pyruvate in alcohol fermentation and lactic acid fermentation.

Back 19

--In alcohol fermentation, pyruvate is converted to ethanol (ethyl alcohol) in two steps.

-- During lactic acid fermentation, pyruvate is reduced directly by NADH to form lactate as an end product, with no release of CO2.

Front 20

22. Compare the processes of fermentation and cellular respiration.

Back 20

--In fermentation, the final electron acceptor is an organic molecule such as pyruvate (lactic acid fermentation) or acetaldehyde (alcohol fermentation). In cellular respiration, by contrast, electrons carried by NADH are transferred to an electron transport chain, which regenerates the NAD+ required for glycolysis.

-- Fermentation yields 2 molecules of ATP, produced by substrate-level phosphorylation. In the absence of an electron transport chain, the energy stored in pyruvate is un- available. In cellular respiration, however, pyruvate is com- pletely oxidized in the mitochondrion. Most of the chemical energy from this process is shuttled by NADH and FADH2 in the form of electrons to the electron transport chain.

-- Thus, cellular respiration harvests much more energy from each sugar molecule than fermentation can. In fact, aerobic respiration yields up to 32 molecules of ATP per glucose molecule—up to 16 times as much as does fermentation.

Front 21

23. Describe the evidence that suggests that glycolysis is an ancient metabolic pathway.

Back 21

The role of glycolysis in both fermentation and respiration has an evolutionary basis. Ancient pro- karyotes are thought to have used glycolysis to make ATP long before oxygen was present in Earth’s atmosphere. The oldest known fossils of bacteria date back 3.5 billion years, but appreciable quantities of oxygen probably did not begin to accumulate in the atmosphere until about 2.7 billion years ago.

Front 22

24. Describe how food molecules other than glucose can be oxidized to make ATP.

Back 22

Glycolysis can accept a wide range of carbohydrates for catabolism. In the digestive tract, starch is hydrolyzed to glucose, which can then be broken down in the cells by glycolysis and the citric acid cycle. Similarly, glycogen, the polysaccharide that humans and many other animals store in their liver and muscle cells, can be hydrolyzed to glucose between meals as fuel for respiration. The digestion of di- saccharides, including sucrose, provides glucose and other monosaccharides as fuel for respiration. Most of the energy of a fat is stored in the fatty acids. A metabolic sequence called beta oxidation breaks the fatty acids down to two-carbon frag- ments, which enter the citric acid cycle as acetyl CoA.

Front 23

25. Explain how glycolysis and the citric acid cycle can contribute to anabolic pathways.

Back 23

Compounds formed as intermediates of glycolysis and the citric acid cycle can be diverted into anabolic pathways as precursors from which the cell can synthesize the molecules it requires

Front 24

26. Explain how ATP production is controlled by the cell and describe the role that the allosteric enzyme phosphofructokinase plays in the process. (RE-CHECK)

Back 24

Phosphofructokinase is an allosteric enzyme with receptor sites for specific inhibitors and activators.