Chapter 15: Carbs + Proteins Flashcards Preview

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Flashcards in Chapter 15: Carbs + Proteins Deck (44):
1

What are examples of macronutrients?

Carbohydrates, proteins, lipids, water

2

Are carbohydrates essential nutrients?

No, but they supply energy

3

What are the functions of carbohydrates?

Glucose = major energy substrate

4

What are major sources of carbohydrates?

Fruits and vegetables

Grain products

Milk + milk products

Refined sugars

5

Differentiate amongst monosaccharides, disaccharides, and polysaccharides?

Monosaccharides = 1 unit (glucose, galactose, fructose)

Disaccharides = 2 sugar units

Polysaccharides = chains = starch or glycogen

6

What is starch?

A mixture of large polymers composed of alpha-linked glucose molecules in plants

7

Define dietary fiber, added/functional fiber, and total fiber.

Dietary fiber = nondigestible carbohydrates + lignin that are intrinsic and intact in plants

Added/functional fiber = isolated nondigestible carbohydrates that have proven beneficial physiological effects in humans

Total fiber = sum of dietary + added fiber

8

Differentiate between soluble and insoluble fiber and give examples of foods that contain each

Soluble fiber = found in foods like oat bran, barley, nuts, seeds, beans, fruits, strawberries

Insoluble fiber = whole wheat and grain products, vegetables and wheat bran

9

What are two principles of carbohydrate digestion?

1) intestine can only absorb monosaccharides

2) enzymatic digestion by glucosidases occurs in two phases:
Luminal digestion by salivary + pancreatic enzymes
Brush-border digestion via membrane-bound enzymes

10

What pH inactivates amylases?

Acidic pH
(Especially salivary vs. pancreatic amylase)

11

Which amylase is the major digestive enzyme for starch?

Pancreatic amylase

12

What is the MOA of amylase?

Chews up polysaccharide into maltose, maltotriose, and alpha-limit dextrin

13

Where is the brush border located?

Apical membrane of small intestinal epithelial cells

14

What are substrates of brush border?

Sucrose, lactose
Linear glucose oligomers
Alpha-limit dextrins

15

Describe the brush border hydrolysis of glucose oligomers.

Glucoamylase and sucrase/isomaltase enzymes hydrolyze short chain glucose (example: maltose, maltriose) to glucose

16

Describe brush border hydrolysis of alpha-limit dextrins

Sucrase/isomaltase (one enzyme w/ two activities) can hydrolyse both alpha-1,6 and alpha-1,4 bonds, allowing digestion of alpha-limit dextrins

17

Describe brush border digestion of lactose

Cleaved by a single, brush border enzyme called lactase (or LPH) to yield glucose and galactose

Low activity of lactase

18

What is the RLS for digestion and absorption of lactose?

Hydrolysis

Malabsorption is common = lactose intolerance

19

Describe brush border digestion of sucrose

Cleaved by brush border enzyme sucrase/isomaltase to yield glucose and fructose

Rate of hydrolysis >>> rate of uptake (RLS)

20

Name 3 monosaccharide transporters in the intestine

Sodium-glucose cotransporter = SGLT-1

Glucose/hexose transporter = GLUT-2

Glucose/hexose transporter = GLUT-5

21

What is sucrose?

Table sugar

= glucose + fructose

22

What is lactose?

Milk sugar

Glucose + galactose

23

What is maltose?

Product of starch digestion

Glucose + glucose

24

What transporter brings in glucose after brush border hydrolysis of glucose oligomers?

SGLT 1

25

What transporter brings in glucose and galactose after brush border digestion of lactose?

SGLT1

26

What transporters bring in fructose and glucose after brush border digestion of sucrose?

SGLT1

GLUT5q

27

Describe SGLT-1

Symporter = secondary active transport -Glucose and galactose

Cotransport of sodium and monosaccharide

Expressed at apical surface of small intestinal epithelial cells

28

Describe GLUT-2

Uniporter for transport of glucose and fructose (basolateral side)

When there's High glucose/fructose levels = inserts on apical side

Sodium independent

29

Describe GLUT-5

Uniporter for fructose

Sodium-independent

30

Where is GLUT-2 found?

Intestine, liver, pancreas, kidney

31

Where is GLUT-5 found?

Intestine, kidney

32

What is villous atrophy?

Celiac disease

Loss of brush border hydrolases = intestinal malabsorption

33

What features of protein digestion and absorption are similar to carbohydrates digestion?

Luminal digestion to oligopeptides with limited digestion to free amino acids

Brush border digestion to yield tri- and dipeptides and free amino acids

Pancreatic digestive enzymes quantitatively most important

34

What general features about protein digestion/absorption are different from carbohydrate absorption?

Oligomers (tri- and dipeptides) can be transported into enterocytes

Cytotoxic digestion occurs

Greater diversity of substrates and products requires many more peptidases and transporters

Additional digestive enzymes from stomach (pepsin), not salivary glands

35

Describe features of gastric proteolysis

Mediated by pepsin

Products mainly large, non-absorbable peptides = help to stimulate gastrin secretion by G cells in Antrim

Not essential for normal protein digestion

36

What are features of pepsin?

+ stored and secreted by chief cells as inactive precursor (called pepsinogen)

+ cleavage of peptide at acid pH yields active form

+ inactivated at pH >4.5 (in small intestine)

37

What are the most abundant peptidases in the small intestine's lumen?

Trypsin

Carboxypeptidase

38

Describe alterations of protein digestion and absorption

Pancreatic insufficiency: cystic fibrosis, pancreatitis, malignancy

Intestinal malabsorption: villous atrophy

Genetic defects: deficiencies in AA transporters

39

Compare monomers of carbs vs. proteins

Glucose, galactose, fructose

Amino acids

40

Compare luminal hydrolysis in carbs vs. proteins

Salivary + pancreatic amylase

Gastric pepsin, pancreatic proteases (trypsin...)

41

Compare bush border digestion in carbs vs proteins

Lactase, sucrase/isomaltase, glucoamylase

Multiple endo and ecto peptidases

42

Compare uptake characteristics in carbs vs. proteins

Monomers

Monomers and oligomers (di and tripeptides)

43

Compare apical epithelial uptake in carbs vs. proteins

SLGT -1 (glucose, galactose)
GLUT5 (fructose)
***conditionally GLUT2 (glucose, fructose)

Multiple AA transporters
PEPT1

44

Compare basolateral release of carbs vs. proteins

GLUT2

Multiple AA transporters