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Gastrointestinal Biology > GB 9. Digestion and Absorption of Proteins and Carbohydrates > Flashcards

GB 9. Digestion and Absorption of Proteins and Carbohydrates Flashcards

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1
Q

What is the main process/mechanism of digestion?

A

Complex Dietary Molecules digested via enzymes into Small Molecules
- through the process of hydrolytic cleavage

complex dietary molecules = protein, fat, carbohydrates

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2
Q

What are proteins made of? What makes them special?

A
  • they are made up of amino acids

- they are the only macronutrient that contains nitrogen

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3
Q

What are the principle sites that protein digestion occurs in?

A

[1] Stomach

[2] Small Intestine

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4
Q

Which type of enzymes are released to aid in protein digestion? Where is it released from?

A

Proteolytic Enzymes

  • secreted into stomach
  • released from pancreas into small intestine
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5
Q

What is the 1st step in digestion?

A

Chewing - Mechanical Breakdown

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6
Q

What is the function of saliva?

A
  • aids in swallowing to get food down esophagus
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7
Q

In the stomach, what is present to help break protein down?

A

Gastric Juices

  • hydrochloric acid
  • pepsin
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8
Q

To be specific, what type of enzyme is present in the stomach to help digest proteins? What is the optimum pH?

A

Pepsinogen released by chief cells

  • pepsinogen converted to pepsin by HCl
  • pepsin = an endopeptidase
  • pH = 2.0
  • enzymes are proteases

*note: endopeptidases are proteases

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9
Q

What are the 2 major pancreatic enzymes that are released by the pancreas to help digest proteins as it goes from the stomach to the small intestine?

A

[1] Chymotrypsin
[2] Trypsin

++ small intestinal cells secrete additional enzymes that break apart into amino acids

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10
Q

What may occur to the amino acids (that came from proteins) in the lower parts of the small intestine?

A
  • amino acids may go from the intestines to the blood
  • (nutrients are absorbed)
  • this requires special transport proteins + ATP!!
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11
Q

What are the enzymes released by the pancreas called?

A

Zymogens

- an inactive substance which is converted into an enzyme when activated by another enzyme

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12
Q

What is the active form of Trypsinogen?

A

trypsin

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13
Q

What is the active form of Chymotrypsinogen?

A

Chymotrypsin

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14
Q

What is the active form of Proelastase?

A

Elastase

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15
Q

What is the active form of Procarboxypeptidase?

A

Carboxypeptidase

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16
Q

How is trypsinogen converted to trypsin?

A

enteropeptidase

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17
Q

How is chymotrypsinogen converted to chymotrypsin?

A

trypsin

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18
Q

How is proelastase converted to elastase?

A

trypsin

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19
Q

How is procarboxypeptidase converted to carboxypeptidase?

A

trypsin

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20
Q

What are the enzymes that are endopeptidases and have a serine protease mechanism?

A
  • trypsin
  • chymotrypsin
  • elastase
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21
Q

What are the enzymes that are carboxypeptidases and have a metalloprotease (Zn2+) mechanism?

A
  • carboxypeptidase A

- carboxypeptidase B

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22
Q

What is the cleavage specificity of trypsin?

A

peptide bonds adjacent to BASIC amino acids

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23
Q

What is the cleavage specificity of chymotrypsin?

A

peptide bonds adjacent to HYDROPHOBIC amino acids

24
Q

What is the cleavage specificity of elastase?

A

peptide bonds adjacent to SMALL amino acids

25
Q

What is the cleavage specificity of carboxypeptidase A?

A

HYDROPHOBIC amino acids at C-TERMINUS

26
Q

What is the cleavage specificity of carboxypeptidase B?

A

BASIC amino acids at C-TERMINUS

27
Q

What are the products of protein digestion?

A

[1] Tetra-Peptides
[2] Tri-Peptides
[3] Amino Acids

28
Q

Why do amino acids go from the blood to the liver?

A
  • liver is the checkpoint for amino acid distribution
  • ammonia is produced by the metabolism of amino acids
  • NH3 is then converted into urea in liver
  • urea is excreted into urine by kidney
29
Q

What is the structure and solubility of urea?

A
  • urea contains 2 nitrogens

- highly soluble in water

30
Q

1 gram of carbohydrate provides how many calories?

A

4 calories

31
Q

What is the general structure of carbohydrates? What are the 3 groups of carbohydrates?

A

Carbohydrates:

  • carbon
  • hydrogen
  • oxygen

Carbohydrates consist of 3 Main Groups:
[1] simple carbohydrates (monosaccharides)
[2] disaccharides
[3] complex carbohydrates (starch, glycogen and fiber)

32
Q

What are the principal sites of digestion for carbohydrates?

A

[1] Mouth

[2] Intestinal Lumen

33
Q

Where does digestion of carbohydrates begin?

A
  • starts in mouth
  • chewing
  • salivary alpha amylase
  • hydrolyses random alpha (1 to 4) bonds
34
Q

What happens to the salivary alpha amylase in the stomach?

A

the LOW PH inactivates the salivary amylase

35
Q

What are the GROUPS of pancreatic enzymes involved with digesting carbohydrates in the small intestine?

A

[1] Endoglycosidases
- an enzyme that releases oligosaccharides from glycoproteins or glycolipids

[2] Disaccharidases
- enzymes the break down complex sugars (like lactose) into simple sugars (like glucose) so that the intestine can absorb the nutrients

[3] Oligosaccharidases
- break down oligosaccharides

36
Q

What does maltose and maltotriose get broken down into in the small intestine?

A

glucose + glucose

37
Q

What enzyme breaks down maltose and maltotriose in the small intestine?

A
  • glucoamylase
  • sucrase
  • maltase
38
Q

What does sucrose get broken down into in the small intestine?

A

glucose + fructose

39
Q

What enzyme breaks down sucrose in the small intestine?

A

sucrase

40
Q

What does lactose get broken down into in the small intestine?

A

galactose + glucose

41
Q

What enzyme breaks down lactose in the small intestine?

A

lactase

42
Q

What does trehalose get broken down into in the small intestine?

A

glucose + glucose

43
Q

What enzyme breaks down trehalose in the small intestine?

A

trehalase

44
Q

What are the products generated from the digestion of carbohydrates?

A 
[1] maltose
[2] maltotriose
[3] alpha-limit dextrins
[4] glucose
[5] galactose
[6] fructose
45
Q

Why does lactose intolerance arise? What happens in lactose intolerance?

A

[1] insufficient amount of lactase leads to no breakdown of lactose

[2] the undigested lactose goes to the large intestine where the bacteria digests it

[3] the bacterial digestion produces gases (symptoms of diarrhea, bloating + abdominal cramps)

46
Q

What is lactose intolerance severity dependent on?

A

depends on the amount of consumed lactose and the degree of lactase deficiency

47
Q

Which population type does lactose intolerance mainly affect?

A
  • adults

- often associated with race

48
Q

What are enterocytes?

A
  • they are the villus that is covered by simple columnar epithelium
  • site of absorption
49
Q

List the enzymes that are anchored to the microvilli.

A
  • aminopeptidase
  • endopeptidase
  • carboxypeptidase
  • dipeptidase
  • disaccharidases
  • oligosaccharidases
50
Q

Where is most substances absorbed?

A
  • in the proximal small intestine

- almost all by the time the chyme reaches the jejunum

51
Q

What is the rate of transport proportional to?

A

Rate of Transport is proportional to the Surface Area

52
Q

What are the 3 main absorption mechanisms?

A

[1] Passive Diffusion
[2] Facilitated Diffusion
[3] Active Transport
- energy dependent membrane proteins in the enterocyte

53
Q

Explain the process of peptide absorption (its entry into the enterocyte).

A
  • form in which majority of protein is absorbed
  • more rapid than absorption of free amino acids

Steps:

  • coupled to H+ gradient
  • as peptide enters, H+ enters the cell
  • the Na+/H+ maintains the gradient (Na+ enters cell, H+ exits the cell)
  • protein is metabolized into free amino acids in enterocyte
54
Q

Are proteins absorbed into the blood?

A

No, only free amino acids are absorbed into the blood

55
Q

How are peptides transported across the basolateral membrane?

A
  • they are released into the interstitial fluid by FACILITATED DIFFUSION and CO-TRANSPORT
  • transported to the liver via hepatic portal vein
  • GLUTAMATE and ASPARTATE are utilized as energy and not trasnported out of the enterocyte!
56
Q

How is monosaccharides absorbed into the enterocyte?

A
  • by passive diffusion (very SLOW)
  • by membrane associated transporters:
  • – Na+/glucose co-transporter (SGLT1)
  • – Na+ independent transporter (GLUT5)
57
Q

Explain the process by which monosaccharides are transported into and out of the enterocyte.

A

[1] glucose + sodium bind to common transporter SGLT (sodium-dependent glucose transporter) on luminal membrane

[2] sodium moves down electrochemical gradient

[3] sodium actively pumped out of cell into basolateral space in exchange for potassium

[4] glucose transported by GLUT (glucose transporter) into interstitial fluid

[5] the energy technically comes from the utilization of ATP by the sodium/potassium ATPase which keeps sodium concentrations within the epithelial cells low this giving the sodium in the lumen a high potential energy

Gastrointestinal Biology (15 decks)

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