nutr 455 exam 2

The majority of energy in the typical American diet comes from:

Carbohydrates

A ketopentose is a carbohydrate containing \_____ carbons and a \_____ group

5

ketone

When compounds with 1 or more chiral carbon atoms and the same formula are arranged as mirror images they are said to be \_____.

enantiomers

What is the nutritional significance of stereoisomers?
a.Some isomers cannot cyclize.
b.Certain metabolic enzymes require a
particular structure.
c.Certain isomers cannot polarize light.
d.Some isomers have no anomeric
carbon.

B

Name the model that depicts cyclized monosaccharides as lying in a horizontal plane with the hydroxyl groups pointing down or up from the plane.

Haworth

What are the major dietary energy sources that are composed of two simple sugars?

disaccharides

What is the most common digestible homopolysaccharide existing as both amylose and amylopectin

starch

Which of the following homopolysaccharides made of glucose contributes the most energy to the ordinary diet?
a. amylose
b. amylopectin
c. glycogen
d. cellulose

B

A homopolysaccharide that is important in human diets is \_____ and the end product formed from the complete digestion of this homopolysaccharide is \_____.

starch

glucose

In what form do carbohydrates enter the bloodstream?

monosacchaireds

What is the key enzyme in digestion of polysaccharides?

α-amylase

Which of the following carbon bonds is digested by α-amylase?
a. α (1-4)
b. α (1-6)
c. β (1-4)
d. β (1-6)

A

Which of the following is the predominant monosaccharide produced by the digestion of all dietary carbohydrates?
a. ribose
b. fructose
c. galactose
d. glucose

D

The enzyme needed to hydrolyze the α (1,6) bond of amylopectin is \_____, which is secreted from the \_____.

isomaltase

enterocyte

The disaccharidases are synthesized by the \_____.

enterocyte

Sucrose digestion is initiated in the \_____.

duodenum

The final molecules that are absorbed from the digestion of the carbohydrate in spaghetti (noodles) and a cream sauce are \_____.

glucose and galactose

Choose the best description of the main method of glucose absorption.
a. passive diffusion down a concentration gradient
b. active transport with fructose
c. facilitated transport
d. active transport with sodium

D

What is a likely reason that large quantities of fructose may cause gut discomfort?
a. Diffusion of fructose only occurs from low to high concentrations.
b. Facilitated diffusion is slower than active transport.
c. Active transport is saturable.
d. Pinocytosis reverses fructose and releases it to the gut.

D

The glucose transporter that is sensitive to insulin is

GLUT4

Which hormonal changes occur in response to a fall in blood glucose concentration?
a. increased insulin, decreased glucagon
b. decreased insulin, increased glucagon
c. decreased insulin, decreased glucocorticoids
d. increased insulin, increased glucagon

B

Glycemic load considers the \_____ in the food.

quantity and quality of carbohydrate

People with type 1 diabetes have
a. slow translocation of GLUT4 receptors from the Golgi body.
b. lack of mRNA synthesis for GLUT4 receptors in adipocytes or myocytes.
c. increased glycogenesis in myocytes after a meal.
d. below-normal glucokinase activity because of low insulin levels.

D

Insulin is an anabolic hormone. Which process does insulin stimulate?
a. lipolysis
b. gluconeogenesis
c. glycogenesis
d. ketogenesis

C

Due to a lack of the enzyme glucose-6-phosphatase, which tissue capable of glycogenesis cannot contribute to blood glucose levels between meals?
a. liver
b. muscle
c. brain
d. kidney

B

Glycolysis is a process involving:
a. synthesis of fatty acids.
b. reactions that convert glucose to glycogen.
c. reactions that convert glucose to pyruvate.
d. reactions that convert glycogen to protein.

C

The major end products of cellular oxidation of carbohydrate include:
a. carbon, nitrogen, and hydrogen.
b. water, carbon dioxide, and energy.
c. glucose and amino acids.
d. dietary fiber and ammonia.

B

In what part of the cell does glycolysis occur?

cytosol

In which cellular site is most of the energy released when carbohydrates are oxidized to carbon dioxide and water?

mitochondrion

Two hormones that stimulate glycogenolysis in the muscle and liver, respectively, are \_____.
a. cortisol and epinephrine
b. epinephrine and glucagon
c. insulin and epinephrine
d. glucagon and insulin

B

In what organelle are the enzymes that catalyze the citric acid cycle located?

Mitochondrion

In the \_____ galactose is eventually converted to \_____.

hepatocyte

glucose

Under anaerobic conditions within a cell, how many net ATPs are formed from one glucose molecule by substrate-level phosphorylation?

B

In the complete oxidation of 1 mol of glucose, how many ATPs are formed?

32-38

When oxygen is present in a tissue, less glucose is metabolized to pyruvate. Why?
a. Less lactate can accumulate in the presence of oxygen.
b. ATP accumulates and inhibits phosphofructokinase.
c. Metabolism slows in the presence of oxygen.
d. More glucose is converted to glycogen.

B

Alcohol in beverages is degraded mainly in the liver cytosol with the production of one NADH for each ethanol molecule. Predict what effect consumption of alcohol would have on the activity of the liver malate-aspartate shuttle.

Increase

The formation of ATP by compounds with a more negative phosphate group transfer potential than -7,300 cal is called \_____.

Substrate Level Phosphorylation

During the end reaction of the electron transport chain, molecular oxygen becomes \_____.

reduced to water

Electron flow through Complexes I, III, and IV is accompanied by the translocation of protons
a. from the matrix into the intermembrane space.
b. from the iron-sulfur centers into the cytosol.
c. from cytochrome c to cytochrome c1.
d. from cytochrome b to the iron-sulfur center.

A

Electrons carried by one mole NADH + H+ enter the electron transport chain at Complex I and generate \_____ mole(s) ATP as they are sequentially oxidized.

2.5

The enzyme ATP synthase is believed to catalyze the formation of ATP, as described by the \_____ theory.

chemiosmotic

The purpose of the hexose monophosphate shunt is to produce

pentose phosphates and NADPH

Which tissue has the least activity of the pentose phosphate pathway?
a. liver
b. adrenal cortex
c. mammary gland
d. skeletal muscle

D

Gluconeogenesis is essentially the reversal of which pathway?
a. glycogenesis
b. glycolysis
c. TCA cycle
d. lipogenesis

B

All of the following are substrates for gluconeogenesis EXCEPT
a. fatty acids.
b. lactate.
c. glycerol.
d. glucogenic amino acids.

A

Muscle lactate is converted to glucose in the liver and returned to the muscle by means of the \_____.
a. malate-aspartate shuttle
b. electron transport chain
c. Cori cycle
d. pentose phosphate pathway

C

If an individual with no blood sugar abnormalities when eating regularly presented with severe hypoglycemia after 30 hours of fasting, which enzyme would you suspect might be malfunctioning?
a. phosphofructokinase
b. pyruvate kinase
c. fructose-1,6-bisphosphatase
d. glucose-6-phosphatase

C

All of the following enzymes are negatively regulated (allosterically inhibited) by increasing levels of ATP EXCEPT \_____.
a. phosphofructokinase
b. pyruvate dehydrogenase complex
c. hexokinase
d. citrate synthase

C

Glucagon stimulates hepatic gluconeogenesis and suppresses glycolysis by reducing the concentration of \_____, a positive modulator of phosphofructokinase.
a. fructose-2,6-bisphosphate
b. fructose-1,6-bisphosphate
c. glucose-6-phosphate
d. glucose-1-phosphate

A

T/F The abundance of GLUT4 is increased by induction in response to a high-CHO meal.

F
traslocation, not induction

T/F The purpose of the pentose phosphate pathway is to generate ribose, for nucleic acid synthesis, and NAD, for oxidizing power.

F
it generates NADPH for reducing power

T/F Phosphorylation of a protein always results in its inactivation, whereas dephosphorylation activates it.

F

(Phosphorylation can sometimes inactivate a protein/enzyme (e.g., glycogen synthase) and sometimes activate a protein/enzyme (e.g., glycogen phosphorylase), with dephosphorylation respectively activating and inactivating these enzymes)

T/F Glucose is transported from the lumen into the enterocyte by active transport using SGLT1 protein, which also requires Na as a co-transporter.

T

T/F The process of gluconeogenesis occurs partially in the mitochondria, and partially in the cytosol.

T

T/F The muscle is an important tissue in gluconeogenesis, because it can use amino acids from protein breakdown and convert them to glucose, which it then secretes into the circulation for other tissues.

F
The muscle cannot convert amino acids to glucose and then secrete it because of a lack of glucose-6-phosphatase.

T/F The signal for glycogenolysis to occur in liver and muscle is glucagon, which is secreted by the pancreas in response to low blood glucose levels.

F

The signal is glucagon for the liver, epinephrine for muscle.

T/F The reason we require the malate-aspartate shuttle is because NADH cannot enter the mitochondria to donate its electrons to the electron transport chain.

T

T/F The Cori cycle would be active under anaerobic conditions, such as excessive muscle exertion.

T

T/F Although many enzymes in a given pathway are bidirectional, often the key enzymes are unidirectional (i.e., only work in one direction).

T

T/F Because they do not have mitochondria, red blood cells generate a lot of lactate from glycolysis, which they in turn must convert into glucose to meet their energy needs.

F

The lactate must travel from the RBC via the blood to the liver; in the liver, lactate is converted into glucose (via gluconeogenesis), which is then secreted back into the bloodstream.

T/F All cells have mitochondria, which act as the main site for ATP production.

F

RBCs do not have mitochondria; hence, they rely on glycolysis for energy needs and produce a lot of lactate.

T/F Active transport requires energy for the Na-K pump to transport Na out of the cell, thereby driving the transport of something else (e.g., glucose) when the Na re-enters the cell down its concentration gradient.

T

Match the enzymes with the pathway in which they function in carbohydrate metabolism.

phosphofructokinase:

glycolysis

Match the enzymes with the pathway in which they function in carbohydrate metabolism.

Pyruvate Carboxylase:

glyconeogenesis

Match the enzymes with the pathway in which they function in carbohydrate metabolism.

glycogen phosphorylase:

glycogenolysis

Match the enzymes with the pathway in which they function in carbohydrate metabolism.

glucose-6-phosphate dehydrogenase

pentose phosphate pathway

Match the enzymes with the pathway in which they function in carbohydrate metabolism.

branching enzyme:

glycogenesis

A homopolysaccharide that is important as a storage compound in human body is \_____, which can be enzymatically dismantled to produce \_____.

glycogen

glucose

When dietary intake of carbohydrate is reduced or blood glucose concentration declines, the pathway that is stimulated in the liver by glucagon and corticosteroids is called \_____. Four non-carbohydrate precursors that

glycogenesis

pyruvate

lactate

glycerol

Glucokinase located in the \_____ is induced by insulin, and hexokinase located in the \_____ is inhibited by glucose-6-phosphate.

liver (and pancreas)

muscle

ADP can positively modulate the activity of the rate-limiting allosteric enzyme in glycolysis, \_____.

phosphofructokinase

Pyruvate dehydrogenase is positively modulated by \_____ and \_____.

AMP
NAD-

Which statement is true?
a. The use of high-fructose corn syrup in U.S. products increased between 1970 and 1998, but has since leveled off.
b. Between 2000 and 2010, use of high-fructose corn syrup in the U.S. food supply was about twice the use of table sugars.
c. High-fructose corn syrup and corn syrup are two names for the same product.
d. All high-fructose corn syrup sold in the U.S. is made from corn.

A

The fructose : glucose ratio of high-fructose corn syrup is approximately \_____.

a. 100:1
b. 80:20
c. 50:50
d. 25:75

C

Which tissue metabolizes fructose?
a. muscle
b. adipose tissue
c. liver
d. all of these

C

When fructose-sweetened beverages are consumed in research studies, plasma triglycerides levels are:
a. always elevated.
b. sometimes elevated.
c. never elevated.
d. elevated only in women.

B

Dietary fiber is currently defined as
a. carbohydrates and lignin that are nondigestible by human enzymes and are intact and intrinsic in plants.
b. carbohydrates that are nondigestible by human enzymes, have been isolated, extracted or manufactured, and have been shown to have beneficial physiological effects in humans.
c. crude fiber.
d. the same as functional fiber.

A

Functional fiber is currently defined as
a. carbohydrates and lignin that are nondigestible by human enzymes and are intact and intrinsic in plants.
b. carbohydrates that are nondigestible by human enzymes, have been isolated, extracted or manufactured, and have been shown to have beneficial physiological effects in humans.
c. all dietary fiber.
d. the same as crude fiber.

B

Dietary fibers are mainly provided by
a. proteins that have been heated with sugars.
b. plant cell walls.
c. chitin and chitosan.
d. plant gums.

B

Processed foods that may have cellulose purified from wood added to them include all of the following EXCEPT \_____.
a. canned green beans
b. cake mixes
c. sandwich spreads
d. fruit juice mixes

A

Which group of high-fiber foods contains the greatest quantities of hemicellulose?
a. legumes
b. whole-grain cereals and bran
c. fruits
d. vegetables

B

Which fiber component is provided primarily by the outer layers of cereal grains?
a. lignin
b. pectin
c. fructans
d. cellulose

D

Pectins are part of the cell wall and middle lamella and are \_____.
a. water soluble
b. gel forming
c. stable at acidic pHs
d. all of the above

D

What is the primary noncarbohydrate component of fiber?
a. gums
b. hemicellulose
c. lignin
d. cellulose

c

Name a water-soluble, gel-forming fiber that functions in the plant as intracellular cement and that is used commercially to make jellies and to provide fiber in enteral formulas.
a. lignin
b. gum
c. pectin
d. cellulose

c

What are the hydrocolloids that are secreted at a site of injury on a plant or surround the endosperm of some seeds and that are used as thickening agents?
a. lignin
b. cellulose
c. pectins
d. gums

D

What are the homopolymers of glucopyranose found in cereal brans such as oats and barley that are effective in reducing serum cholesterol?
a. beta-glucans
b. fructans
c. fructooligosaccharides
d. chitin

A

Common food sources of fructans are \_____.
a. strawberries, apples, and citrus fruits
b. whole grains
c. chicory, onions, and Jerusalem artichokes
d. legumes

C

Which of the following fibers stimulate the growth of bifidobacteria and thus are considered prebiotics?
a. lignins
b. fructans
c. beta-glucans
d. cellulose

B

What type of resistant starch is formed during food processing such as the cooking and cooling of starchy foods?
a. RS1
b. RS2
c. RS3
d. RS4

C

Which of the following is NOT a form of resistant starch?
a. natural starch in cell walls of steel-cut oats
b natural starch in hot corn starch pudding
c. starch crystals in cooled, cooked foods, such as potatoes
d. chemically modified starch, such as cross-bonded starch

B

The predominant source of dietary chitin is \_____.
a. supplements
b. bran
c. vegetables
d. fruits

A

When fibers form viscous gels in the stomach, which of the following occurs?
a. Gastric emptying is delayed or slowed.
b. Satiety is decreased significantly.
c. Digestion of fats and carbohydrates increases.
d. The nutrient diffusion rate is increased.

A

Glycemic control is \_____ in response to foods rich in fiber or to fiber supplements.

Improved

Which of the following high-fiber foods are most effective in lowering serum cholesterol?
a. corn and wheat
b. chitosan and chitin
c. rice bran and wheat bran
d. oat bran and legumes

D

Which fiber type is poorly fermentable?
a. lignin
b. pectin
c. gums
d. resistant starch

A

Which volatile short-chain fatty acid is believed to lower serum cholesterol by acting as an inhibitor of cholesterol biosynthesis?
a. acetic
b. butyric
c. propionic
d. palmitic

C

. What characteristics of fiber may protect against developing colon cancer?
a. Fibers adsorb primary bile acids to promote their excretion.
b. Fibers increase fecal bulk and dilute carcinogen concentrations.
c. Fibers can be fermented to butyric acid, which may slow proliferation of cancer cells.
d. All of the above

D

Which of the following is NOT a typical gastrointestinal response to ingestion of dietary fiber?
a. increased glucose absorption
b. delayed gastric emptying
c. increased bile-acid excretion
d. increased fecal bulk

A

Fiber lowers serum cholesterol concentrations by all of the following mechanisms EXCEPT \_____.
a. decreased transit time
b. increased excretion of bile acids in the feces
c. a shift of bile acid pools toward chenodeoxycholic acid, which inhibits HMG-CoA reductase
d. production of propionic acid from gut fermentation of fiber

A