EXAM #1: BIOCHEMISTRY OF THE GI TRACT

Question 1

What enzymes are contained in the mouth that begin the breakdown of food?

Answer 1

1) Alpha-amylase

2) Lingual lipase

Question 2

What is the function of alpha-amylase?

Answer 2

Breakdown of starch in the mouth

Question 3

What is the function of lingual lipase?

Answer 3

Breakdown of TAGs in the mouth

Question 4

What macronutrient is NOT brokendown in the mouth?

Answer 4

Protein

Question 5

What are the components of gastric juice that breakdown food?

Answer 5

1) HCl

2) Pepsin

Question 6

What is the inactive zymogen form of pepsin?

Answer 6

Pepsinogen

Question 7

What converts pepsinogen into its active form?

Answer 7

Secretion of HCl that lowers the pH of the gastric juice

Question 8

What are the three functions of HCl in the stomach?

Answer 8

1) Initial breakdown of protein
2) Activation of pepsinogen to pepsin
3) Kill microorganisms

Question 9

What enzymes are produced by the pancreas?

Answer 9

Amylase
Lipase
Peptidase

Question 10

In addition to enzymes, what else does the pancreas secrete?

Answer 10

NaCl

NaHCO3

Question 11

What pancreatic enzyme is secreted in its active form?

Answer 11

Pancreatic alpha-amylase

Question 12

What is the function of bile acids?

Answer 12

Emulsificaiton of aggregated lipids to make them more accessible for lipid digestion enzymes

Question 13

What form must carbohydrates be absorbed in in the small intestine?

Answer 13

Monosaccharide

Question 14

What are the common sources of glucose?

Answer 14

Honey
Fruit
Corn syrup

Question 15

What are the common sources of fructose?

Answer 15

Honey

Fruit

Question 16

What is the common source of sucrose?

Answer 16

Table sugar

Question 17

What is amylose?

Answer 17

Plant carbohydrate/ starch with alpha 1,4 glycosidic bonds

Question 18

What is amylopectin?

Answer 18

Plant carbohydrate/starch with alpha 1,4 glycosidic bonds AND alpha 1,6 branches

Question 19

What is the specific molecular function of alpha-amylase?

Answer 19

Hydrolysis of non-terminal alpha-1,4 linkages

Question 20

What is the function of pancreatic alpha-amylase?

Answer 20

Conversion of branched polysaccharides into oligosaccharide units in the small intestine

Question 21

What are the end products of pancreatic alpha-amylase digestion?

Answer 21

1) Maltose
2) Maltotriose
3) alpha-limit dextrins

Question 22

What is cellulose? Why can’t humans breakdown cellulose?

Answer 22

Polysaccharide plant cell wall component with BETA 1,4 GLYCOSIDIC BONDS

**Humans don’t have BETA 1,4 ENDOGLYOCSIDASES to breakdown cellulose

Question 23

What is Chitin? Why can’t humans breakdown Chitin?

Answer 23

Polymer of N-acetyl-glucosamine with Beta 1,4 Glycosidic bonds that we do not have the enzymes to breakdown

Comes from fungi and arthropods*

Question 24

How are the oligosaccharides made by alpha-amylase broken down into monosaccharides?

Answer 24

Membrane bound glycosidases on the luminal side of small intestine enterocytes

Question 25

What is lactose hydrolyzed into via lactase?

Answer 25

1) Glucose | 2) Galactose

Question 26

What is maltose hydrolyzed into via maltase?

Answer 26

2x Glucose

Question 27

What is sucrose hydrolyzed to via sucrase/isomaltase?

Answer 27

1) Glucose | 2) Fructose

Question 28

What transporter transports glucose across the membrane of the enterocyte for absorption?

Answer 28

Na+/Glucose cotransporter SGLT1

Question 29

What transporter transports fructose across the enterocyte membrane for absorption?

Answer 29

Facilitated diffusion transporter, GLUT5

Question 30

What is the role of Na+/K+ ATPase pumps in the absorption of monosaccharides?

Answer 30

- Cotransporters use Na+ as the driving force | - Concentration gradient is maintained by Na+/K+ ATPase

Question 31

Which monosaccharide transporter requires ATP? Which does NOT?

Answer 31

``` SGLT1= ATP GLUT5= NO ATP ```

Question 32

Once monosaccharides are in the enterocyte, how do they get into the circulation?

Answer 32

Facilitated diffusion transporter, GLUT2

Question 33

Where does protein digestion begin? What enzyme?

Answer 33

Stomach via pepsin

Question 34

What activates pepsinogen into pepsin?

Answer 34

Low pH from HCl secreted via parietal cells

Question 35

What is the specific molecular function of pepsin?

Answer 35

Pepsin breaks proteins into large fragments

Question 36

What happens to proteins in the small intestine?

Answer 36

Further breakdown into amino acids, dipeptides, and tripeptides

Question 37

What pancreatic enzymes breakdown proteins in the small intestine?

Answer 37

Chymotrypsin Trypsin Carboxypeptidases Elastase

Question 38

What enzymes are produced by enterocytes of the small intestine to breakdown proteins?

Answer 38

Aminopeptidase Dipeptidase Endopeptidase

Question 39

Which enzymes are zymogens, pancreatic proteases or small intestine proteases?

Answer 39

Pancreatic

Question 40

What is the difference between an Endoprotease and an Exoprotease? Which pancreatic proteases are Endoproteases and which are Exoproteases?

Answer 40

Endoprotease= hydrolyze internal peptide bonds - Trypsin - Chymotrypsin - Elastae Exoprotease= hydrolyze only terminal peptide bonds - CARBOXYPEPTIDASE

Question 41

What enzyme in the small intestine enterocyte beings conversion of pancreatic zymogens to active proteases?

Answer 41

Enteropeptidase

Question 42

What is the function of enteropeptiase?

Answer 42

Conversion of Trypsinogen to Trypsin

Question 43

What is the general role of the pancreatic proteases? What is the follow-up role of the proteases produced by the small intestine enterocytes?

Answer 43

Pancreatic= large fragments into oligopeptides Small intestine= oligopeptides into di/tripeptides and amino acids

Question 44

Where does the further digestion of di/tripeptides occur?

Answer 44

Intracellularly i.e. in the enterocyte

Question 45

What prevents Trypsin activation in the pancreas?

Answer 45

Trypsin inhibitor in the pancreas

Question 46

What happens when pancreatic ducts are blocked i.e. how does this lead to acute pancreatitis?

Answer 46

Blocked ducts lead to an accumulation of Trypsinogen that overwhelms inactivating enzymes; activation occurs in the pancreas and leads to tissue damage

Question 47

What disease of the pancreas is associated with CF?

Answer 47

Pancreatic insufficiency

Question 48

How does CF lead to pancreatic insufficiency?

Answer 48

1) CFTR mutation= decreased Sodium Bicarboante 2) Dehydrates pancreatic juice/ thickens it 3) Thickened pancreatic juice reduces production of pancreatic digestive enzymes

Question 49

What is the manifestation of pancreatic insufficiency?

Answer 49

Insufficient digestion of: 1) Lipids 2) Proteins 3) Carbohydrates Plus symptoms excess FAT in the large intestine

Question 50

Describe the etiology of Celiac Disease.

Answer 50

- Exact cause is unknown, but there is a peptidase defect - Small peptides are present in the intestine that are toxic to mucosal cells - Ingestion of gluten causes an inflammatory response

Question 51

What transporter is present on the luminal membrane of the intestine and facilitate the uptake of amino acid, di and tripeptides?

Answer 51

SLC type transporters

Question 52

What disease does a defect in SLC3A1/7A9 result in?

Answer 52

Cystinuria

Question 53

Describe the etiology of Cystinuria.

Answer 53

- Defect in the amino acid transporter that catalyzes the reuptake of cystine in the kidney - Cystine accumulates in the urine - Cytine is insoluble and forms kidney stones

Question 54

What do TAGs need to be digested into for uptake?

Answer 54

2x fatty acids | 1x glycerol

Question 55

What three enzymes facilitate TAG digestion? Which does the bulk of the work?

Answer 55

1) Lingual lipase 2) Gastric lipase 3) Pancreatic lipase* *Pancreatic lipase does most of the digestion of lipids in the small intestine

Question 56

What happens to lipids in the small intestine?

Answer 56

Emulsifiaction by bile acids to prevent the formation of large lipid droplets

Question 57

What prevents pancreatic lipase from being denatured by bile acids?

Answer 57

Binding to colipase in the small intestine

Question 58

What reaction is catalyzed by pancreatic lipase?

Answer 58

Hydrolysis of 2 fatty acids from TAG to form: - Monoglycerol - 2x fatty acids

Question 59

Where are bile acids formed, stored, and secreted?

Answer 59

- Formed= liver from cholesterol - Stored= gallbladder - Secreted= duodenum

Question 60

Where are bile acids reabsorbed for intrahepatic circulation/ recycling?

Answer 60

Ileum

Question 61

What happens to fatty acids once they are absorbed into enterocytes?

Answer 61

Resynthesis to TAG in the endoplasmic reticulum

Question 62

What happens to TAGs in the enterocyte, once they have been re-synthesized?

Answer 62

Packaging into Chylomicrons

Question 63

What apolipoprotein facilitates the packacking of TAGs into chylomicrons?

Answer 63

Apo B-48

Question 64

Where are chylomicrons secreted once formed in the enterocytes?

Answer 64

Lymphatic system

Question 65

What is Steatorrhea?

Answer 65

Lipid malabsorption resulting in increased lipids in the feces

Question 66

What are the causes Steatorrhea?

Answer 66

1) Disruption in delivery of bile acids to the duodenum 2) Compromised pancreas function e.g. CF 3) Defective intestinal mucosa 4) Products such a Olestra, a fat substitute that cannot be digested