Biochemistry Test 4 Study Guide

(A) Where in an earlier chapter have we encountered something comparable to the action of the acylcarrier protein (ACP) of fatty-acid synthesis? (B) What is a critical feature of the action of the ACP?

(a) the lipoate "swinging arm" of the pyruvate dehydrogenase complex (b) the "arm" or ACP carries the group to be acted on from one enzyme to another (avoiding a diffusion-limited process and also positioning key groups correctly). In the case of the ACP, the group to be acted on (beta-carbon) is always the same distance from the ACP, regardless of the length of the growing fatty acid, and thus the critical group is always in proximity to the active sites of the several pertinent enzymes.

4. What is the order of events in b-oxidation? hydration oxidation yielding FADH2 cleavage oxidation yielding NADH

2 hydration 1 oxidation yielding FADH2 4 cleavage 3 oxidation yielding NADH

Why is it advantageous to tropical plants to use C4 rather than the C3 fixation pathway?

3 reasons come to mind. (1) light energy is usually not limiting (2) the plants have small pores to prevent water loss, but this also limits CO2 uptake. (3) the C4 pathway allows for increasing the CO2 concentration in the inner chloroplast, which would not be otherwise possible with the small pores.

Why does the degradation of palmitic acid to eight molecules of acetyl-CoA require 7 rather than 8 rounds of beta-oxidation process?

7 carbon-carbon bonds are broken in the course of beta-oxidation.

6. Draw a transmembrane glycoprotein in a lipid bilayer. Indicate which face of the membrane is intracellular and which face is extracellular. Label the regions of amino acids that would be hydrophilic and hydrophobic. Label the carbohydrate group.

A transmembrane protein should traverse the lipid bilayer with a portion extending into the extracellular space and into the intracellular space. The amino acids in the bilayer (near the fatty acid tails) will consist of hydrophobic amino acids, and the portions extending into the aqueous cytoplasm and extracellular space will be hydrophilic. Carbohydrate groups (the glyco part of the glycoprotein) will only be found on the extracellular portion of the protein.

Can ATP production take place in chloroplasts in the absence of light? Give the reason for your answer.

ATP can be produced by chloroplasts in the absence of light if some way exists to form a proton gradient.

What structural feature do all steroids have in common? What are the biosynthetic implications of this common feature?

All steroids have a characteristic fused-ring structure, implying a common biosynthetic origin.

Suggest a reason why the cell membranes of bacteria grow at 20C tend to have a higher proportion of unsaturated fatty acids than the membranes of bacteria of the same species grown at 37C. In other words, bacteria grown at 37C have a higher proportion of saturated fatty acids in their cell membranes.

At the lower temperature, the membrane would tend to be less fluid. The presence of more unsaturated fatty acids would tend to compensate by increasing the fluidity of the membrane compared to one at the same temperature with higher proportion of saturated fatty aids.

A drug that reduces blood cholesterol has the effect of stimulation the production of bile salts. How might this result in lower blood cholesterol? (2 ways)

Bile Salts are made from cholesterol, and cholesterol is taken from the body into the intestine in the bile fluid.

Suggest a reason why inorganic ions, such as K+, Na+, Ca2+, and Mg2+, do not cross biological membranes by simple diffusion.

Biological membranes are highly nonpolar environments. Charged ions tend to be excluded from such environments rather than dissolving in them, as they would have to do to pass through the membrane by simple diffusion.

2. Individuals with abnormally low levels of carnitine in their muscles suffer from muscle weakness, particularly when their carbohydrate stores get low. In addition, their muscles have increased levels of triacylglycerols. Explain these effects.

Carnitine is required to metabolize fatty acids. Once activated, fatty acids are transferred to carnitine to be transported into the mitochondrial matrix in order to undergo b-oxidation to generate acetylCoA that can be used in the citric acid cycle. If no carnitine is available, then fats could not be used for energy and fatigue woud result, particularly when carbohydrates were not available for energy metabolism. Triacylglycerols would build up because they are not being metabolized.

Egg yolks contain a high amount of cholesterol, but they can also contain a high amount of lecithin. From a diet and health standpoint, how do these 2 molecules complement each other?

Cholesterol is not very water-soluble, but lecithin is a good natural detergent, which is actually part of lipoproteins that transport the less soluble fats through the blood.

What is the advantage to plants to have the option of both cyclic and noncyclic pathways for photophosphorylation?

Cyclic photophosphorylation can take place when the plant needs ATP but does not have a great need for NADPH. Noncyclic photophosphorylation can take place when the plant needs both.

Uncouplers of oxidative phosphorylation in mitochondria also uncouple photoelectron transport and ATP synthesis in chloroplasts. Give an explanation for this observation.

Electron transport and ATP production are coupled to each other by the same mechanism in mitochondria and chloroplasts. In both cases, the coupling depends on the generation of a proton gradient across the inner mitochondrial membrane or across the thylakoid membrane, as the case may be.

Why might a person who is an alcoholic have a "fatty liver"?

Ethanol is converted to acetaldehyde and then to acetic acid. Humans can use that acetic acid only for energy, or they can convert it to fatty acids and other lipids.

Calculate the net ATP yield from the complete processing of a saturated fatty acid containing 17 carbons. Consider the beta-oxidation steps, processing of acetyl-CoA through the citric acid cycle, and electron transport.

From 7 cycles of beta-oxidation: 7 acetyl-CoA, 1 propionyl-CoA, 7 FADH2, 7 NADH,. From the processing of 7 acetyl-CoA in the citric acid cycle: 7 FADH2, 21 NADH, and 7 GTP. From the processing of the propionyl-CoA: -1 ATP for conversion to succinyl-CoA, -1 GTP from the citric acid cycle, and 1 NADH and 1 FADH2 from the citric acid cycle. From reoxidation of all FADH2 and NADH: 22.5 ATP from 15 FADH2, and 72.5 ATP from 29 NADH. From 8 GTP: 8 ATP. Subtotal: 103 ATP. Subtract a 2-ATP equivalent used in activation step and 1-ATP equivalent used in the conversion to succinyl-CoA for a grand total of 100 ATP.

Calculate the ATP yield for the complete oxidation of one molecule of palmitic acid (16 carbons). How does this figure differ

From 7 cycles of beta-oxidation: 8 acetyl-CoA, 7 FADH2, and 7 NADH. From the processing of 8 acetyl-CoA in the citric acid cycle: 8 FADH2, 24 NADH, and 8 GTP. From reoxidation of all FADH2 and NADH: 22.5 ATP from 15 FADH2, 77.5 ATP from 31 NADH. From 8 GTP: 8 ATP. Subtotal: 108 ATP A 2-ATP equivalent was used in the activation step. Grand total: 106 ATP The grand total for stearic acid was: 120 ATP.

If photosynthesizing plants are grown in the presence of CO2, is every carbon atom of the glucose that is produced labeled with the radioactive carbon? Why or why not?

Glucose synthesized by photosynthesis is not uniformly labeled because only one molecule of CO2 is incorporated into each molecule of ribulose-1,5-biphosphate, which then goes on to give rise to sugars.

What is the energetic driving force for the formation of phospholipid bilayers?

Hydrophobic interactions among the hydrocarbon tails are the main energetic driving force in the formation of lipid bilayers.

Why might a doctor smell the breath of a person known to have diabetes who just passed out?

If the reason for passing out is uncontrolled diabetes, the doctor expects to smell acetone on the breath, since the otherwise unused sugars are being converted to fats and ketone bodies.

Suppose that you are studying a protein involved in transporting ions in and out of cells. Would you expect to find the nonpolar residues in the interior or the exterior? Why?

In a protein that spans a membrane, the nonpolar residues are the exterior ones; they interact with the lipids of the cell membrane. The polar residues are in the interior, lining the channel through which the ions enter and leave the cell.

A larger proton gradient is required to form a single ATP in chloroplasts than in mitochondria. Suggest a reason why. (hint: ions can move across the thylakoid membrane more easily than across the inner mitochondrial membrane.)

In mitochondria, both a proton gradient (chemical) and an electrochemical gradient (based on charge) are formed, both contributing to the total potential energy. In chloroplasts, only a proton gradient is formed, because ions move across the the thylakoid membrane and neutralize charge. The proton gradient alone is considerably less efficient.

Given the nature of the hormonal activation of lipases, what carbohydrate pathways would be activated or inhibited under the same conditions?

In the liver, glycogen breakdown and gluconeogenesis would occur. In the muscle, glycogen breakdown and glycolysis would occur.

How many cycles of beta-oxidation are required to process a fatty acid with 17 carbons?

It would take 7 cycles of beta-oxidation to release 14 carbons as acetyl-CoA, with the last 3 being released as propionyl-CoA.

1. In severe, uncontrolled diabetes, ingested glucose is not taken into cells. Therefore it continues circulating in the blood and is partially excreted in the urine. One danger for diabetics is the build-up of ketones. Why would ketones build-up in the blood and urine of diabetics? How are ketones formed, and why are they dangerous if they build-up?

Ketones are metabolites of fatty acid metabolism that build up when more acetylCoA is being made than is being used by the citric acid cycle. If glucose is not available, cells will begin to metabolize fatty acids to fuel ATP synthesis. This will generate a lot of acetylCoA. Excess acetylCoA will be converted to acetoacetate which is a keto-acid. As this acid builds up in the blood, it can generate more protons than the blood can buffer, thus lowering the pH of the blood. In an effort to balance this change, the kidney will begin to excrete protons, excreting salts and water with them. This can result in severe dehydration.

Why does the American Heart Association recommend the use of canola oil or olive oil rather than coconut oil in cooking?

Less heart disease is associated with diets low in saturated fatty acids.

Give a reason for the toxicity that can be caused by overdoses of lipid-soluble vitamins.

Lipid-soluble vitamins accumulate in fatty tissue, leading to toxic effects. Water-soluble vitamins are excreted, drastically reducing the chances of an overdose.

Crisco is made from vegetable oils, which are usually liquid. Why is crisco a solid?

Many of the double bonds have been saturated. Crisco contains "partially hydrogenated vegetable oils."

3. Explain why nonpolar toxins tend to accumulate within fatty tissues. Why can't these toxins be excreted like polar toxins can?

Nonpolar toxins are not soluble in water (only polar substances are soluble in water), but are soluble in lipid (fat). Therefore, they will tend to be stored in fatty tissues. Urine is mostly water, so nonpolar substances cannot be excreted in the urine.

Why must cholesterol be packaged for transport rather than occurring freely in the bloodstream?

One oxygen atom from O2 is need to form epozide. The NADPH is needed to reduce the other oxygen atom to water.

Suggest a reason why plants containt light-absorbing pigments in addition to chlorophylls a & b.

Only a relatively small portion of the visible spectrum is absorbed by chlorophylls. The accessory pigments absorbed light at additional wavelengths. As a result, most of the visible spectrum can be harnessed in light-dependent reactions.

What is the evolutionary advantage to organisms that the calvin cycle has a number of reactions in common with other pathways?

Organisms would need only a few mutations giving rise to the enzymes unique to the Calvin cycle. The rest of the pathway is already in place.

Would you expect H2O or CO2 to be the source of the oxygen produced in photosynthesis in chloroplasts. Why is this likely to be so?

Oxygen produced in photosynthesis comes from water. The oxygen-evolving complex is part of the series of electron-transfer reactions from water to NADPH. Carbon dioxide is involved in the dark reactions, which are different reactions that take place in another part of the chloroplast.

Suggest a reason why partially hydrogenated vegetable oils are used so extensively in packaged foods.

Partially hydrogenated vegetable oils have the desired consistency for many foods, such as oleomargarine and components of TV dinners.

Which is more hydrophilic, cholesterol or phospholipids?

Phospholipids are more hydrophilic than cholesterol. The phosphate group is charged, and the attached alcohol is charged or polar. These groups interact readily with water. Cholesterol has only a single polar group, an -OH.

What is implied about the energy requirements of photosystems 1 and 2 by the fact that there is a difference in the minimum wavelength of light needed for them to operate (700 nm for photosystem 1 and 680 nm for photosystem 2)?

Photosystem II requires more energy than photosystem I. The shorter wavelength of light means a higher frequency. Frequency, in turn, is directly proportional to energy.

2. Rice is a C3 plant. Would you expect rice to grow well in Hawaii? Why or why not? Sugar cane is a C4 plant. Why does it grow well in Hawaii?

Rice would not grow well in Hawaii because it would have to keep its stomata closed to reduce water loss. This would trap oxygen in the leaf and prevent carbon dioxide from entering the leave. The Rubisco would begin to bind oxygen instead of carbon dioxide, participating in photorespiration. In photorespiration ATP is used to neutralize phosphoglycolate, a potentially toxic substance to the plant. This reduces the efficiency of photosynthesis by about 25-30%. This reduction in energy production would lead to stunted growth. On the other hand, sugar cane is a C4 plant that is adapted to minimize photorespiration. In C4 plants, carbon is fixed in mesophyll cells that contain PEP carboxylase, not Rubisco. This ultimately generates malate which is pumped into bundle sheath cells containing Rubisco. Malate is decarboxylated, liberating carbon dioxide. Since there are fewer bundle sheath cells than mesophyll cells in these plants, carbon dioxide is accumulated in bundle sheath cells. Rubisco will bind to carbon dioxide and initiate the Calvin cycle to make glucose.

4. Saturated fats are solid at room temperature, but unsaturated fats are liquid at room temperature. Why?

Saturated fats consist of saturated (each internal carbon has 2 hydrogens), straight chain fatty acids that can pack closely together at room temperature (or colder) and form van der Waals interactions that limit mobility and form a solid. Unsaturated fats consist of unsaturated (one or more carbons do not have 2 hydrogens, thus have double-bonds with a neighboring carbon), kinked fatty acid tails that cannot pack closely together, remaining mobile at room temperature, thus forming a liquid.

Why do we refer to the conversion of 6 molecules of CO2 (6 carbon atoms) to one molecule of glucose (also 6 carbon atoms) as a net reaction?

Six molecules or carbon dioxide fixed in the Calvin cycle do not end up in the same glucose molecule. However, labeling experiments show that six carbon atoms are incorporated into sugars for every six carbon dioxide molecules that enter the Calvin cycle.

Which statements are consistent with the fluid-mosaic model of membranes? a- all membrane proteins are bound to the interior of the membrane b- both proteins and lipids undergo transverse (flip-flop) diffusion from the inside to the outside of the membrane. c- some proteins and lipids undergo lateral diffusion along the inner or outer surface of the membrane d- carbohydrates are covalently bonded to the outside of the membrane e- the term mosaic refers to the arrangement of the lipids alone

Statements (c) and (d) are correct. Transverse diffusion is only rarely observed [statement (b)], and the term 'mosaic' refers to the pattern of distribution of proteins in the lipid bilayer [statement (e)]. Peripheral proteins are also considered part of the membrane [statement (a)].

Which statements are consistent with the known facts about membrane transport? a- active transport moves a substance from a region in which its concentration is lower to one in which its concentration is higher. b- transport does not involve any pores or channels in membranes. c- transport proteins may be involved in bringing substances into cells.

Statements (s) and (c) are correct; statement (b) is not correct because ions and larger molecules, especially polar ones, require channel proteins.

Suggest a reason why animals that live in cold climates tend to have higher proportions of polyunsaturated fatty acid residues in their lipids than do animals that live in warm climates.

The higher the percentage of unsaturated fatty acids in membranes in cold climates is an aid to membrane fluidity.

It is frequently said that camels store water in their humps for long desert journeys. How would you modify this statement based off of the information you have learned in this chapter?

The humps of camels contain lipids that can be degraded as a source of metabolic water, rather than water as such.

In preparation of sauces that involve mixing water and melted butter, egg yolks are added to prevent separation. How do the egg yolks prevent separation? (hint: egg yolks are rich in phosphaticdylcholine, aka lecithin)

The lecithin in the egg yolks serves as an emulsifying agent by forming closed vesicles. The lipids in the butter (frequently triacylglycerols) are retained in the vesicles and do not form a separate phase.

Why might some food companies find it economically advantageous to advertise their product (for example, triaglycerols) as being composed of polyunsaturated fatty acids with trans-double bonds?

The public is attuned to the idea of polyunsaturated fats as healthful. The trans configuration gives a more palatable consistency. Recently, however, concerns have arisen about the extent to which such products mimic saturated fats.

5. Describe the structure of triglycerides, phospholipids and cholesterol. How are they the same, how are the different? Why are they all considered lipids? What biological roles do each of these types of lipids have?

Triglycerides are a glycerol with three fatty acids...completely nonpolar and hydrophobic. Serves to store energy and insulate organs Phospholipids are a glycerol with two fatty acids and one phosphate ester containing an additional alcohol attached to it. The fatty acid portion is nonpolar and hydrophobic, while the phosphate ester is charged, polar and hydrophilic. Serves to make up cell membranes Cholesterol consists of 7 hydrocarbon rings, with a single -OH group. Most of the molecule is nonpolar and hydrophobic, but the -OH, when present, is hydrophilic. Cholesterol esters have a fatty acid in the place of the -OH, making cholesterol esters completely hydrophobic. Serves as a precursor for a number of steroid hormones and is an important part of membranes - maintains fluidity They are considered lipids because they contain hydrocarbon portions (they all have that in common). They differ in their solubilities in water.

Albert Szent-Gyorgi, a pioneer in early photosynthesis research, stated, "What drives life is a little electric current, kept up by the sunshine." What did he mean by this?

With very few exceptions, life directly or indirectly depends on photosynthesis. The electric current is the flow of electrons from water to NADP+, a light-requiring process. The "current" continues in the light-independent reactions, with electrons flowing from NADPH to bi-phosphoglycerate, which ultimately yields glucose.

6. In what order are triglycerides built? a fatty acid is added to make diacylglycerol phosphate DHAP is converted to glycerol-3-phosphate a fatty acid is added to make lysophosophatidate phosphate group is removed yielding diacylglycerol a third fatty acid is added to make a triacylglycerol

_3____a fatty acid is added to make diacylglycerol phosphate _1____DHAP is converted to glycerol-3-phosphate _2____a fatty acid is added to make lysophosophatidate _4____ phosphate group is removed yielding diacylglycerol _5____a third fatty acid is added to make a triacylglycerol

11. Which of the following is true of photorespiration? a) Occurs when Rubisco binds to oxygen instead of carbon dioxide b) Makes photosynthesis more efficient c) Would occur in cold, wet climates d) Occurs only in the dark

a

If you presented 14C-labeled carbon dioxide to a C4 plant, which of the following would you expect to find containing the 14C-label? Circle all that apply. a) Oxaloacetate b) 3-phosphoglycerate c) NADPH d) glucose e) ATP

a b d

3. During fatty acid anabolism, what molecules are used as to build the new fatty acid? Circle all that apply a) Malonyl-CoA b) Succinyl-CoA c) Acetyl-CoA d) Carnitine

a) Malonyl-CoA c) Acetyl-CoA

1. Paraquat is an herbicide that was used extensively to destroy marijuana fields. It acts by accepting electrons from ferredoxin before they can get to the NADP+ reductase complex. The electrons are then donated to an irrelevant molecule that takes them away from the process. a. What would be the effects of Paraquat on the ATP production of chloroplasts via noncyclic electron flow? Why? b. What would be the effects of Paraquat on the glucose production of chloroplasts? Why?

a- ATP production would not change as the electron transport chain is not disturbed. (Since paraquat accepts the electron, it allows electron flow to continue, only prohibiting NADPH production) b- Glucose production would stop since the Calvin cycle requires NADPH, and no NADPH would be made in the presence of Paraquat.

10. In C3 plants, which enzyme is accomplishes carbon fixation? a) Chlorophyll b) Rubisco c) PEP carboxylase d) Ferredoxin e) None of the above

b

12. What molecule reduces ferrodoxin in photosystem I? a) Chlorophyll P680 b) Chlorophyll P700 c) Chlorophyll b d) Plastoquinone

b

8. Which of the following is NOT involved in cholesterol synthesis? Circle all those that apply. a) AcetylCoA b) SuccinylCoA c) Mevalonate d) Isoprene e) Squalene

b

5. Fatty acid anabolism yields ______ and all other fatty acids are made from that. a) Lineolate b) Ethanolamine c) Palmitate d) Diacylglycerol

c

7. Which of the compounds above can also be used in phospholipids synthesis? a) Lysophosphatidate b) Diacylglycerol c) Diacylglycerol phosphate d) Triacylglycerol

c

9. The formation of mevalonate from acetylCoA is inhibited by a) Mevalonate b) acetylCoA c) cholesterol d) LDL e) Phosphatidate

c

13. Photophosphorylation a) Is the production of ATP using the energy from light b) Involves chemiosmosis c) Uses ATP synthase d) Occurs in chloroplasts e) All of the above

e