Carbohydrates Flashcards
(69 cards)
1
Q
What are the 2 major steps of carbohydrate digestion?
A
- Intralumenal hydrolysis
- Membrane digest
2
Q
What is the CHO ratio for carbohydrate
A
1:2:1 ratio, c:h:o
3
Q
What is the RDA for carbohydrates?
Normal population
A
130g a day for brain function
4
Q
How many grams of fiber should one be consuming, if 1000kcals are consumed?
A
14g
5
Q
Whats the AMDR for carbohydrates
A
45-65%
6
Q
What are the monosaccrides and their differences
A
- Glucose - OH facing down on C4
- Galatose - OH group facing up on C4
- Fructose - 5 carbon ring
7
Q
Explain how a glycosidic bond forms
A
- Condensation reaction
- Hydroxyl froup on one glucose and Hydrogen group on the other
- Form an alpha(1,4) glycosidic bond and water
8
Q
What’s the difference between an alpha and beta glycosidic bond?
A
Alpha- between 1,4 and facing down
Beta between 1,4 and facing up
9
Q
Difference between the reducing end and non reducing of a sugar?
A
The reducing end has a unsubstituted anomeric carbon
10
Q
What’s the clinical significance of the Millard reaction?
A
The increase in sugar in the blood can lead to the formation of aminoketoses which can form advance glycation products. Those products can then collect in collagen tissue, this can form glycoproteins
11
Q
What are the starches?
A
Amylose & amylopectin
12
Q
What type of glycosidic bond does amylose have?
A
A1,4 —> spiral
13
Q
What type of glycosidic bond does amylopectin have?
A
A1,4 and A1,6 —> branched
14
Q
What type of glycosidic bond does cellulose have?
A
B1,4 and hydrogen —> crystalline structure
15
Q
What types of bonds are in glycogen?
A
A1,6 and A1,6 —> dense, shorter branching
16
Q
What determines if a polysaccharide can be broken down by enzymes?
A
The physiochemical properties and the structure
17
Q
What polysaccharide only has A1,4 linkages and is makes up 30% of starch?
A
Amylose
18
Q
What polysaccharide has A1,4 and A1,6 bonds
A
Amylopectin
19
Q
What polysaccharide has B1,4 bonds and H bonds?
A
Cellulose
20
Q
What polysaccharide has A1,4 and A1,6 bonds that animals make
A
Glycogen
21
Q
Describe the steps of digestion for amylose
A
- Salivary glands going to release A-amylase —> breakdown the a1,4 glycosidic bonds to form dextrins
- Salivary a-amylase is deactivated by high pH of stomach
- Pancreas will release pancreatic a-amylase which will breakdown the a1,4 bonds of the dextrin into maltose
- BBM will release Maltase into lumen to breakdown maltose into glucose
22
Q
Describe the steps for amylopectin digestion
A
- Salivary glands will release a-amylase to breakdown amylopectin into dextrins
- Food goes into stomach where salivary a-amylase is destroyed
- Pancreas will release pancreatic a-amylase which will hydrolyze the a1,4 glycosidic bonds into maltose and limit dextrins
- BBM will release maltase to break down maltose into free glucose. A-dextrinase will break down limit dextrins into glucose
23
Q
What are the final products of amylose hydrolysis?
A
Maltotriose and maltose
24
Q
What are the final products of of amylopectin?
A
Maltotriose, maltose and limit dextrins
25
In what stage are poly/oligosacchrides broken down
Intralumenal hydrolysis —> stage 1
26
In what stage are only oligosacchrides broken down?
During stage two —> BBM
Tri, di, and monosaccharides (absorbed) formed
27
What end is the glucose released from?
The non reducing end (exoglucosidase)
28
Do lactose and sucrose have products after intraluminal hydrolysis?
No
29
Do lactose and sucrose have products after BBM hydrolysis?
Yes, glucose+ galactose—> lactose
Glucose + fructose —> sucrose
30
What’s sugar has the only B1,4 bond
Lactose
31
Where are the transporter located for the monosaccharides?
Apical membrane of the small intestine via villous epithelial cells
32
How are glucose and galactose transported to the portal vein?
They need energy requiring active transport
33
How is fructose transported to the portal vein?
Thru facilitated diffusion high concentration to low concentration
34
Explain how is glucose and fructose transported into the bloodstream, if the meal is low sugar
1. Fructose is transported into the cell via GLUT5, glucose is transported into the cell with SGLUT 1 transporter
2. GLUT 2 vesicles transport glucose and fructose to the other side to the bloodstream
35
Explain how is glucose and fructose transported into the bloodstream, if the meal is high in sugar
1. SGLUT 1 and GLUT 5 transporter and saturated with glucose and fructose, respectively
2. Recruitment of GLUT 2 occurs to triple rate of action
3. GLUT 2, bring to the other side of cell to enter the blood stream
36
What does the rate of CHO assimilation depend on?
1. Enzyme hydrolysis at BBM
2. Transport of sugar
37
Explain the malabsorption of lactose
1. Lactose goes into the intestinal lumen but there in no lactase to break it down
2. Bacteria ferments the lactose to product short chain fatty acids
3. The s.F.a bring in fluid, which cause water diarrhea and increases gut distension
38
What is the definition of fibre
- Edible 3 carbohydrates polymers that are non digestible by enzymes
- naturally derived by food sources
- obtained from food material and have a physiological effect
- synthetic carbohydrate material that have a physiological effect
39
Humans lack the enzymes to digest which type of bond?
B1,4
40
Where are the digestible carbs in a plant
In the cell lumen
41
Where are the non digestible carbs of the plant
In the plant wall
42
Name a couple insoluble fibres
Cellulose and hemicellulose
43
Name a couple soluble fibers
Pectins and gums
44
What contributes to total fibre
Dietary fibre and functional fibre
45
What is dietary fibre
Intrinsic and intact from plants
46
What is functional fibre
Isolated indigestible fibre that has physiological benefit (can be from plants, animals, extracted or synthesized)
47
What percent of starch is indigestible
5-20%
48
Why would resistant starch be inaccessible to enzymes
- Compostion of food (high fibre, lots of fat)
- starch structure (granule, processed, dense, uncooked)
- Fermentable by bacteria
49
What are the different ways resistant starches can form?
Heat, cooling, baking and storage and processing
50
How are amylose and amylopectin different in how they retrograde?
Amylose is more prone to irreversible retrograde and amylopectin retrograde process can be reversed
51
How can fibre decrease kcal intake
Fibre increases bulk which stretch receptors, leading to increased satiety and decrease kcal intake
52
What classifies different fibre?
Composition (types of bonds) and physical properties such as fermentation, solubility and viscosity
53
Describe the properties of soluble fibre
- hold onto water and are viscous
- increase transit time, delay gastric emptying, decrease postprandial glucose levels, delay nutrient absorption and are more fermentable to insoluble fibre
54
Soluble fibre examples foods
hemicelluloses, pectins, b-glucans, gums, polysaccharides
- oat bran, kidney beans , carrot broccoli
55
Describe the properties of insoluble fibre
- decrease transit time and increase bulk
- don’t dissolve in water, so they remain intact speeding up transit time
- poorly fermentable
- act as a laxative
56
Examples of insoluble fibres
lignin, cellulose, some hemicelluloses
57
Describe the water binding capabilities of soluble fibre
- Soluble fibres can hold several times their weight
- slows down gastric emptying and increases satiety
- not much mixing of contents which mean decreases enzyme interaction
- decrease nutrient diffusion rates and decrease glycemic index response
58
How can fibre decrease serum cholesterol concentration
- Fibres bind to F.a, bile acids and cholesterol to prevent the formation of micelles
- decrease formation of lipids = decreased formation of micelles
- increase fecal acid excretion and decrease serum cholesterol levels
59
Explain fibre and fermentability
Different fibres can be broken down by different bacteria’s —> specific bacterial proliferation
60
What short chain fatty acids are fermented to contribute to energy
Acetate, butyrate and propionate
61
Increased Short Chain Fatty Acid (SCFA) production has net effect of…
| Degradation + Fermentatbility
- increased Water & sodium absorption in colon
- increased Mucosal cell proliferation
- Provision of energy
- Acidification of luminal environment —> increased Excretion of bile: decreased solubility of free bile acids, decreased calcium binding which leads to decreased rate of conversion of primary bile acids to secondary bile acids (activity of bacterial 7 α dehydroxylase at pH 6–6.5)
62
Explain fibres relationship to fecal bulk
- increased Fecal bulk decreased frequency of defecation decreased intestinal transit time decreased
intraluminal pressure
63
Explain detoxification and fibre
Mix of fibres that increased bulk & bacterial mass that leads to diluting effect on toxins & decreased contact time with intestinal wall
– Certain colonic bacteria scavenge toxins decreased carcinogenic substance formation & inhibit tumor cell formation
64
What are prebiotics
resistance to digestion/ absorption in SI, partial or complete fermentation by microbiota in the colon, & ability to stimulate growth of select bacteria
65
Where does glycolysis occur
In the cytoplasm
66
What enzyme breaks down sucrose?
| Name final monoscchrides
sucrase --> glucose + fructose
67
What enzyme breaks down lactose?
| + Final monosacchrides
Lactase
Glucose and galactose
68
What enzyme breaks down maltose?
| + monosacchrides
Maltase or A-glucosidase
2 glucose
69
