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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

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
What is the cleavage specificity of carboxypeptidase A?
HYDROPHOBIC amino acids at C-TERMINUS
26
What is the cleavage specificity of carboxypeptidase B?
BASIC amino acids at C-TERMINUS
27
What are the products of protein digestion?
[1] Tetra-Peptides [2] Tri-Peptides [3] Amino Acids
28
Why do amino acids go from the blood to the liver?
- 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
What is the structure and solubility of urea?
- urea contains 2 nitrogens | - highly soluble in water
30
1 gram of carbohydrate provides how many calories?
4 calories
31
What is the general structure of carbohydrates? What are the 3 groups of carbohydrates?
Carbohydrates: - carbon - hydrogen - oxygen Carbohydrates consist of 3 Main Groups: [1] simple carbohydrates (monosaccharides) [2] disaccharides [3] complex carbohydrates (starch, glycogen and fiber)
32
What are the principal sites of digestion for carbohydrates?
[1] Mouth | [2] Intestinal Lumen
33
Where does digestion of carbohydrates begin?
- starts in mouth - chewing - salivary alpha amylase - hydrolyses random alpha (1 to 4) bonds
34
What happens to the salivary alpha amylase in the stomach?
the LOW PH inactivates the salivary amylase
35
What are the GROUPS of pancreatic enzymes involved with digesting carbohydrates in the small intestine?
[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
What does maltose and maltotriose get broken down into in the small intestine?
glucose + glucose
37
What enzyme breaks down maltose and maltotriose in the small intestine?
- glucoamylase - sucrase - maltase
38
What does sucrose get broken down into in the small intestine?
glucose + fructose
39
What enzyme breaks down sucrose in the small intestine?
sucrase
40
What does lactose get broken down into in the small intestine?
galactose + glucose
41
What enzyme breaks down lactose in the small intestine?
lactase
42
What does trehalose get broken down into in the small intestine?
glucose + glucose
43
What enzyme breaks down trehalose in the small intestine?
trehalase
44
What are the products generated from the digestion of carbohydrates?
``` [1] maltose [2] maltotriose [3] alpha-limit dextrins [4] glucose [5] galactose [6] fructose ```
45
Why does lactose intolerance arise? What happens in lactose intolerance?
[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
What is lactose intolerance severity dependent on?
depends on the amount of consumed lactose and the degree of lactase deficiency
47
Which population type does lactose intolerance mainly affect?
- adults | - often associated with race
48
What are enterocytes?
- they are the villus that is covered by simple columnar epithelium - site of absorption
49
List the enzymes that are anchored to the microvilli.
- aminopeptidase - endopeptidase - carboxypeptidase - dipeptidase - disaccharidases - oligosaccharidases
50
Where is most substances absorbed?
- in the proximal small intestine | - almost all by the time the chyme reaches the jejunum
51
What is the rate of transport proportional to?
Rate of Transport is proportional to the Surface Area
52
What are the 3 main absorption mechanisms?
[1] Passive Diffusion [2] Facilitated Diffusion [3] Active Transport - energy dependent membrane proteins in the enterocyte
53
Explain the process of peptide absorption (its entry into the enterocyte).
- 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
Are proteins absorbed into the blood?
No, only free amino acids are absorbed into the blood
55
How are peptides transported across the basolateral membrane?
- 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
How is monosaccharides absorbed into the enterocyte?
- by passive diffusion (very SLOW) - by membrane associated transporters: - -- Na+/glucose co-transporter (SGLT1) - -- Na+ independent transporter (GLUT5)
57
Explain the process by which monosaccharides are transported into and out of the enterocyte.
[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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