Biochem 21 Flashcards

The major disaccharide in natural sweeteners, fruits, and vegetables is:

A. Lactose
B. Maltose
C. Sucrose
D. Trehalose

Natural sweeteners, fruits, and vegetables also contain small amounts of:

A. Glucose and galactose
B. Fructose and mannose
C. Maltose and lactose
D. Ribose and xylose

Dietary fiber cannot be digested primarily because humans lack the necessary:

A. Transporters
B. Glycosidases
C. Lipases
D. Peptidases

The principal polymer for dietary fiber is:

A. Amylopectin
B. Cellulose
C. Glycogen
D. Lignin

Disaccharides are converted to monosaccharides by:

A. Isomerases
B. Glycosidases
C. Oxidases
D. Transferases

Glycosidases hydrolyze which bond type?

A. Peptide bonds
B. Ester bonds
C. Glycosidic bonds
D. Phosphodiester bonds

Undigested carbohydrates that reach the colon are commonly:

A. Oxidized by hepatocytes
B. Fermented by bacteria
C. Excreted unchanged only
D. Absorbed by villi

Alpha-amylase is best classified as an:

A. Exoglycosidase
B. Endoglycosidase
C. Transaminase
D. Isomerase

Alpha-amylase hydrolyzes which bonds within polysaccharides?

A. Beta-1,4 bonds
B. Alpha-1,6 bonds
C. Alpha-1,4 bonds
D. Beta-1,6 bonds

Alpha-amylase cleaves its target bonds at:

A. Terminal residues only
B. Random internal intervals
C. Branch points exclusively
D. Brush-border membranes only

The shortened polysaccharide chains generated by alpha-amylase are termed:

A. Limit dextrins
B. Alpha-dextrins
C. Maltotetroses
D. Glycoproteins

Pancreatic alpha-amylase continues hydrolysis of:

A. Lactose and sucrose
B. Glycogen and starch
C. Fiber and cellulose
D. Trehalose and lactose

Which product is formed by pancreatic alpha-amylase?

A. Free galactose
B. Maltose
C. Sucrose
D. Fructose

Which additional product is formed by pancreatic alpha-amylase?

A. Trimaltotriose
B. Lactulose
C. Cellobiose
D. Trehalose

The oligosaccharides formed by pancreatic alpha-amylase are also called:

A. Alpha-dextrins
B. Limit dextrins
C. Glycolipids
D. Proteoses

Glucoamylase is best classified as an:

A. Endoglycosidase
B. Exoglycosidase
C. Oxidoreductase
D. Isomerase

Glucoamylase is specific for which bond?

A. Alpha-1,4
B. Alpha-1,6
C. Beta-1,4
D. Beta-1,6

Glucoamylase hydrolysis primarily releases:

A. Maltose
B. Galactose
C. Glucose
D. Fructose

Glucoamylase is found in the:

A. Stomach lumen
B. Brush border
C. Pancreatic acini
D. Colonic crypts

The sucrase-isomaltase complex provides almost all intestinal hydrolysis of:

A. Beta-1,4 bonds
B. Alpha-1,6 bonds
C. Alpha-1,2 bonds
D. Beta-1,6 bonds

Sucrase-isomaltase accounts for what share of intestinal sucrose hydrolysis?

A. About half
B. About two thirds
C. About 80%
D. Essentially all

Sucrase-isomaltase accounts for about what share of small-intestinal maltose hydrolysis?

A. 20%
B. 40%
C. 80%
D. 100%

Trehalase hydrolyzes glycosidic bonds in:

A. Lactose
B. Maltose
C. Sucrose
D. Trehalose

Trehalose is composed of:

A. Glucose plus galactose
B. Two glucosyl units
C. Glucose plus fructose
D. Galactose plus fructose

The beta-glycosidase complex is also known as:

A. Sucrase-maltase
B. Lactase-glucosylceramidase
C. Glucoamylase-isomaltase
D. Maltase-phosphorylase

The beta-glycosidase complex hydrolyzes the bond between glucose and galactose in lactose. That bond is:

A. Alpha
B. Beta
C. Ester
D. Peptide

The beta-glycosidase complex hydrolyzes certain glycolipids containing glucose or galactose linked to:

A. Cholesterol
B. Ceramide
C. Bilirubin
D. Lecithin

The catalytic site responsible for that beta-glycosidase complex activity is called:

A. Enterokinase
B. Phlorizin hydrolase
C. Lactulose synthase
D. Sucrase core

Sucrase-isomaltase and beta-glycosidase activities are highest in the:

A. Duodenum
B. Jejunum
C. Ileum
D. Colon

Glucoamylase activity rises along the intestine and is highest in the:

A. Duodenum
B. Jejunum
C. Ileum
D. Cecum

Congenital lactase deficiency follows which inheritance pattern?

A. Autosomal dominant
B. X-linked recessive
C. Mitochondrial
D. Autosomal recessive

In congenital lactase deficiency, the deficient enzyme activity is:

A. Trehalase
B. Lactase
C. Sucrase
D. Glucoamylase

An infant develops diarrhea, weight loss, and dehydration soon after breast-feeding begins. The best diagnosis is:

A. Secondary lactase deficiency
B. Congenital lactase deficiency
C. Sucrase-isomaltase deficiency
D. Glucose-galactose malabsorption

The best treatment for congenital lactase deficiency is:

A. High-sucrose diet
B. Gluten restriction
C. No lactose diet
D. High-fiber supplementation

In adult hypolactasia, lactase levels are:

A. Completely absent
B. Increased markedly
C. Decreased less severely
D. Replaced by sucrase

Lactase deficiency caused by villous injury is termed:

A. Congenital deficiency
B. Primary deficiency
C. Secondary deficiency
D. Isolated deficiency

Acute lactose intolerance developing after a GI infection most strongly suggests:

A. Congenital lactase loss
B. Secondary lactase deficiency
C. Trehalase excess
D. Fructose malabsorption

In mucosal injury, lactase activity is characteristically:

A. Last lost, first recovered
B. First lost, last recovered
C. Unchanged throughout
D. Permanently absent always

Secondary lactase deficiency is expected to recover because lactase activity:

A. Never returns
B. Always increases permanently
C. Usually comes back
D. Converts to sucrase

Dietary fiber is beneficial in diverticular disease because it helps:

A. Acidify stool
B. Harden stool
C. Soften stool
D. Sterilize stool

Colonic bacteria metabolizing soluble fiber generate gases and:

A. Long-chain fatty acids
B. Short-chain fatty acids
C. Ketone bodies
D. Bile acids

The short-chain fatty acids formed in the colon are absorbed by:

A. Hepatocytes
B. Pancreatic ducts
C. Colonic epithelial cells
D. Gastric chief cells

After absorption, these short-chain fatty acids are used primarily for:

A. Hemoglobin synthesis
B. Energy
C. Urea production
D. Ketogenesis only

Which soluble fibers reduce cholesterol levels?

A. Cellulose and inulin
B. Pectins and beta-glucan
C. Lignin and glycogen
D. Lactose and trehalose

The cholesterol-lowering effect of Pectins and beta-glucans acts at the level of:

A. Chylomicrons
B. Bile acids
C. GLUT transporters
D. Lactase activity

Pectin can help in diabetes mainly by:

A. Increasing fructose uptake
B. Slowing simple sugar absorption
C. Blocking insulin release
D. Stimulating glucagon secretion

GLUT5 is located on the luminal side of intestinal epithelial cells and transports:

A. Glucose
B. Galactose
C. Fructose
D. Mannose

Which transporter is found in human erythrocytes and in the brain?

A. GLUT1
B. GLUT2
C. GLUT3
D. GLUT4

GLUT1 is characterized by:

A. Low affinity
B. High capacity
C. High affinity
D. Insulin dependence

Which transporter is found in liver, kidney, pancreatic beta cells, and the serosal surface of intestinal mucosal cells?

A. GLUT1
B. GLUT2
C. GLUT3
D. GLUT5

GLUT2 is best described as:

A. High affinity, low capacity
B. Insulin sensitive, high affinity
C. High capacity, low affinity
D. Neuron specific, high affinity

Which transporter is found only in neurons?

A. GLUT1
B. GLUT2
C. GLUT3
D. GLUT4

GLUT3 is characterized by:

A. High affinity
B. Low affinity
C. Low capacity
D. Insulin responsiveness

Which transporter is found in adipose tissue, skeletal muscle, and cardiac muscle?

A. GLUT1
B. GLUT2
C. GLUT4
D. GLUT5

GLUT4 is best described as:

A. Fructose specific
B. Insulin sensitive
C. Neuron specific
D. Erythrocyte specific

In skeletal muscle, which additional stimulus increases GLUT4 numbers?

A. Fasting
B. Exercise
C. Glucagon
D. Lactose

GLUT4 has:

A. High affinity
B. Low affinity
C. No tissue specificity
D. No insulin response

Which transporter is found in intestinal epithelium and spermatozoa?

A. GLUT2
B. GLUT3
C. GLUT4
D. GLUT5

The presence of GLUT5 in spermatozoa is linked to their use of:

A. Galactose
B. Fructose
C. Glycogen
D. Lactate

The hypoglycemic response results from decreased glucose supply to the:

A. Liver
B. Pancreas
C. Brain
D. Kidney

The majority of dietary carbohydrate calories in many diets comes from which plant starch polysaccharides found in grains, tubers, and vegetables?

A. Lactose and trehalose
B. Amylopectin and amylose
C. Glycogen and cellulose
D. Sucrose and lactose

Amylose is best described as a polymer of glucosyl residues linked mainly by:

A. α-1,6 bonds
B. β-1,4 bonds
C. α-1,2 bonds
D. α-1,4 bonds

Amylopectin contains a main chain of α-1,4 bonds with branches formed by:

A. β-1,6 bonds
B. α-1,6 bonds
C. β-1,4 bonds
D. α-1,2 bonds

Sucrose is a disaccharide composed of:

A. Glucose and galactose
B. Glucose and fructose
C. Fructose and galactose
D. Two glucose units

The glycosidic linkage in sucrose is:

A. β-1,4
B. α-1,6
C. α-1,2
D. β-1,2

Lactose is the major animal carbohydrate and is composed of:

A. Glucose and fructose
B. Glucose and galactose
C. Fructose and galactose
D. Two glucoses

The glycosidic linkage in lactose is:

A. β-1,4
B. α-1,2
C. α-1,4
D. α-1,6

α-Amylase hydrolyzes which bonds?

A. Internal α-1,4 bonds
B. Terminal α-1,6 bonds
C. Internal β-1,4 bonds
D. Terminal β-1,6 bonds

Salivary amylase is:

A. Digested by pepsin only
B. Inactivated by stomach acid
C. Blocked by bile salts
D. Removed by enterocytes

Which statement about amylase substrate specificity is correct?

A. It hydrolyzes α-1,4 and α-1,6
B. It hydrolyzes only α-1,4-linked glucose polymers
C. It hydrolyzes all glucose polymers
D. It hydrolyzes β-1,4 cellulose bonds

Acarbose lowers postprandial glucose primarily by inhibiting pancreatic α-amylase and:

A. Lactose transporters
B. Brush-border α-glucosidases
C. Hepatic glycogenolysis
D. Colonic fermentation

Acarbose is used mainly in patients with:

A. Type 1 diabetes
B. Celiac disease
C. Type 2 diabetes
D. Hereditary fructose intolerance

Acarbose is not used often mainly because it commonly causes:

A. Constipation and nausea
B. Flatulence and diarrhea
C. Hemolysis and rash
D. Bradycardia and edema

Brush-border glycosidases are collectively referred to as:

A. Small-intestinal disaccharidases
B. Pancreatic oligosaccharidases
C. Gastric exoglycosidases
D. Hepatic glucanases

Which of the following is one of the four brush-border glycosidases discussed?

A. Enterokinase
B. Glucoamylase
C. Ptyalin
D. Hexokinase

Which listed enzyme is another brush-border glycosidase from this set?

A. Sucrase-isomaltase complex
B. Pepsin
C. Glycogen phosphorylase
D. Trypsin

Which listed enzyme is another brush-border glycosidase from this set?

A. Trehalase
B. Pepsin
C. Glycogen phosphorylase
D. Trypsin

Which listed enzyme is another brush-border glycosidase from this set?

A. B-glucosidase complex
B. Pepsin
C. Glycogen phosphorylase
D. Trypsin

Glucoamylase is a long polypeptide chain that forms:

A. One catalytic barrel
B. Two globular domains
C. Three transmembrane subunits
D. Four proteolytic chains

Each glucoamylase globular domain contains:

A. A lipid anchor
B. A catalytic site
C. An ATPase core
D. A bile-binding loop

Glucoamylase is protected from digestion because it is heavily:

A. Sulfated
B. Phosphorylated
C. Glycosylated
D. Ubiquitinated

Glucoamylase is an exoglycosidase specific for:

A. α-1,6 bonds
B. β-1,4 bonds
C. α-1,2 bonds
D. α-1,4 bonds

Glucoamylase begins digestion from the:

A. Reducing end
B. Nonreducing end
C. Branch point only
D. Middle of chain

The sucrase-isomaltase complex protrudes into the lumen and is clipped into two subunits by an:

A. Hepatic enzyme
B. Intestinal protease
C. Pancreatic lipase
D. Salivary esterase

After cleavage, the two sucrase-isomaltase subunits remain attached through:

A. Disulfide bonds only
B. Noncovalent interactions
C. Peptide crosslinks
D. Tight junctions

Both subunits of the sucrase-isomaltase complex contain:

A. A catalytic site
B. A transporter pore
C. A chloride channel
D. A kinase domain

The isomaltase-maltase site accounts for almost all intestinal hydrolysis of:

A. β-1,4 bonds
B. α-1,6 bonds
C. α-1,2 bonds
D. β-1,6 bonds

A brush-border enzyme sequentially removes glucose from linear starch fragments but cannot cleave branch points. Which bond does it hydrolyze?

A. β-1,4 bond
B. α-1,4 bond
C. β-1,6 bond
D. α-1,6 bond

An oligosaccharide branch point persists until acted on by isomaltase. Which linkage required isomaltase?

A. α-1,2 linkage
B. β-1,4 linkage
C. α-1,4 linkage
D. α-1,6 linkage

After debranching, a remaining linear glucan bond can be hydrolyzed by either glucoamylase or isomaltase. Which bond is this?

A. α-1,4 linkage
B. α-1,1 linkage
C. β-1,4 linkage
D. β-1,6 linkage

Trehalose is best described as a disaccharide composed of:

A. Glucose and fructose
B. Glucose and galactose
C. Two glucose molecules
D. Two galactose molecules

Trehalase hydrolyzes which bond in trehalose?

A. α-1,1 linkage
B. α-1,4 linkage
C. β-1,4 linkage
D. α-1,6 linkage

Trehalase is notable for having:

A. Two catalytic domains
B. No membrane anchor
C. Three active sites
D. One catalytic site

Which large brush-border glycoprotein has two catalytic sites and also functions as lactase?

A. Trehalase
B. β-glucosidase complex
C. Glucoamylase
D. Sucrase-isomaltase

The β-glucosidase complex is attached to the membrane through its carboxyl end by a:

A. Sulfate bridge
B. Cholesterol anchor
C. Peptide tether
D. Phosphatidylglycan anchor

The lactase site of the β-glucosidase complex hydrolyzes which bond in lactose?

A. α-1,4 bond
B. β-1,4 bond
C. α-1,2 bond
D. α-1,6 bond

The second catalytic site of the β-glucosidase complex hydrolyzes a bond between a sugar and:

A. Ceramide
B. Cholesterol
C. Glycerol
D. Sphingomyelin

Phlorizin hydrolase activity refers to cleavage of a β-glycosidic bond in:

A. Sucrose
B. Trehalose
C. Glycolipids
D. Amylopectin

In the small intestine, sucrase-isomaltase activity is highest in the:

A. Jejunum
B. Duodenum
C. Ileum
D. Colon

Overall brush-border glycosidase activity is highest in the:

A. Ileum
B. Jejunum
C. Colon
D. Stomach

Glucoamylase activity reaches its highest level in the:

A. Duodenum
B. Jejunum
C. Cecum
D. Ileum

Along the small intestine, glucoamylase activity generally increases toward the:

A. Ileum
B. Duodenum
C. Stomach
D. Pylorus

Which carbohydrate is more resistant to digestion because it is less well hydrated?

A. Trehalose
B. Lactose
C. Glycogen
D. Amylose-rich starch

In the colon, undigested sugars are rapidly metabolized by bacteria to gases, lactate, and:

A. Ketone bodies
B. Bile acids
C. Short-chain fatty acids
D. Amino acids

Which set lists the major gases formed by colonic bacterial sugar metabolism?

A. Oxygen, nitrogen, helium
B. H2, CO2, CH4
C. CO, O2, H2S
D. NH3, CO2, N2

Incomplete sugar digestion causes diarrhea primarily by increasing:

A. Gastric motility
B. Colonic water retention
C. Pancreatic secretion
D. Bile acid synthesis

In lactose intolerance, unabsorbed lactose is converted by colonic bacteria to gas and:

A. Ethanol
B. Acetone
C. Lactic acid
D. Urea

Lactase activity normally peaks at about:

A. One month after birth
B. One year after birth
C. Birth
D. Puberty

Lactase activity usually declines to adult levels by approximately:

A. 1 to 2 years
B. 3 to 4 years
C. 10 to 12 years
D. 5 to 7 years

Adult hypolactasia is associated with which phenotype?

A. Persistence phenotype
B. Malabsorption phenotype
C. Nonpersistence phenotype
D. Hypersecretion phenotype

In lactose intolerance, diarrhea reflects the osmotic effects of lactose and:

A. Lactic acid
B. Histamine
C. Bicarbonate
D. Uric acid

Which set contains only insoluble dietary fibers?

A. Pectins, gums, mucilages
B. Cellulose, hemicellulose, lignins
C. Mucilages, cellulose, gums
D. Lignins, pectins, gums

Which set contains only soluble dietary fibers?

A. Lignins, cellulose, gums
B. Cellulose, mucilages, lignins
C. Pectins, mucilages, gums
D. Hemicellulose, pectins, lignins

Which fiber type is most readily digested by colonic bacteria to produce gas and short-chain fatty acids?

A. Soluble fiber
B. Insoluble lignin
C. Resistant ceramide
D. Brush-border starch

Which set lists the major short-chain fatty acids formed by colonic bacterial sugar metabolism?

A. Lactic, pyruvic, citric
B. Acetic, succinic, fumaric
C. Butyric, oxaloacetic, lactic
D. Acetic, propionic, butyric

Flatulence from carbohydrate malabsorption is caused mainly by bacterial generation of:

A. Bile salts
B. H2, CO2, CH4
C. Lactase and trehalase
D. Acetylcholine and gastrin

A patient with chronic constipation is advised to increase soluble fiber that can also lower serum cholesterol by binding bile acids. Which fiber is this?

A. Cellulose
B. Pectins
C. Lignins
D. Hemicellulose

The glycemic index of a food refers to:

A. Intestinal glucose uptake capacity
B. Amount of carbohydrate absorbed
C. Postprandial insulin secretion
D. Rate blood glucose rises

Which carbohydrate has one of the highest glycemic indices?

A. Glucose
B. Fructose
C. Lactose
D. Pectin

Which additional sugar has one of the highest glycemic indices?

A. Sucrose
B. Fructose
C. Maltose
D. Galactose

On the luminal side of enterocytes, glucose is absorbed primarily by:

A. Na-dependent transporters
B. Facilitated diffusion only
C. Passive paracellular flow
D. H+-coupled cotransport

The low intracellular sodium concentration that drives luminal glucose uptake is maintained by the:

A. Na/H exchanger
B. Na-K ATPase
C. Ca ATPase
D. H/K ATPase

Glucose exits enterocytes across the serosal membrane primarily by:

A. Na-coupled cotransport
B. Secondary active transport
C. Endocytosis
D. Facilitative transporters

Glucose movement from enterocyte to blood normally requires:

A. ATP hydrolysis directly
B. Luminal sodium entry
C. No direct energy use
D. Brush-border peptidases

Which structural feature is shared by all GLUT transporters?

A. Two catalytic subunits
B. Six membrane domains
C. Twelve membrane domains
D. An ATP-binding site

Galactose absorption from lumen into enterocytes occurs by the same mechanism as:

A. Glucose
B. Fructose
C. Mannose
D. Lactate

Galactose exits enterocytes into blood primarily by:

A. Na-dependent cotransport
B. Facilitative transporters
C. Endocytic vesicles
D. Chloride exchange

Fructose enters enterocytes from the lumen by:

A. Na-dependent uptake
B. Secondary active transport
C. Endocytosis
D. Facilitated diffusion

In most cells, glucose uptake is usually not the rate-limiting step because GLUTs generally have:

A. Low Km or high abundance
B. High Km only
C. ATPase activity
D. Sodium coupling only

Glucose crossing from blood into extracellular CSF at the blood-brain barrier primarily uses:

A. GLUT2
B. GLUT4
C. GLUT5
D. GLUT1

Transport of glucose from blood into brain tissue is primarily mediated by:

A. GLUT1
B. GLUT2
C. GLUT3
D. GLUT4

A lactose-intolerant patient avoiding dairy should pay particular attention to replacing:

A. Calcium
B. Iron
C. Potassium
D. Phosphate

A diabetic is advised to eat oatmeal, beans, and apples because gel-forming fibers can:

A. Delay gastric emptying
B. Stimulate insulin release
C. Raise glycemic index
D. Block fructose uptake

The same gel-forming fibers also help by:

A. Increasing starch hydrolysis
B. Enhancing bile secretion
C. Slowing sugar absorption
D. Accelerating gastric emptying

A patient suspected of carbohydrate malabsorption should undergo which test after a sugar load?

A. D-xylose test
B. Hydrogen breath test
C. Schilling test
D. Secretin stimulation test

In cholera, the organism first:

A. Invades enterocytes deeply
B. Destroys villi directly
C. Attaches to brush border
D. Blocks lactase synthesis

Cholera toxin binds irreversibly to which cell-surface receptor?

A. GLUT5
B. GM1 ganglioside
C. SGLT1
D. CFTR

Cholera toxin then catalyzes:

A. Protein dephosphorylation
B. DNA strand cleavage
C. Glycolipid hydrolysis
D. ADP-ribosylation

Increased enterocyte cAMP in cholera most directly decreases intestinal:

A. Glucose transport
B. Peptide hydrolysis
C. Potassium secretion
D. Na/anion/water absorption

Cholera toxin also directly stimulates intestinal:

A. Calcium absorption
B. Bicarbonate loss
C. Chloride secretion
D. Lactase synthesis