7. Carbohydrates Flashcards
1
Q
Major Monosaccharides in diet (4)
A
glucose
fructose
ribose
galactose
2
Q
Major Disaccharides in diet (3)
A
sucrose
maltose
lactose
3
Q
Major Polysaccharides in diet (2)
A
starch + glycogen (amylose, amylopectin)
fiber + resistant starch (cellulose, pectin, hemicellulose)
4
Q
What is the dominant natural isomer of monosaccharides in the diet?
A
D isomer (D-glucose) (L-glucose is synthesized)
5
Q
What are raffinose, stachyose, and verbascose? How are they digested?
A
They are oligosaccharides that are fermented by bacteria in the colon (gives you gas)
6
Q
Amylose
A
- straight chain glucose polymer
- alpha 1-4 linkages
- forms helical coils
- STARCH
7
Q
Amylopectin
A
- branched chain glucose polymer
- alpha 1-4 linkages and 1-6 branch linkages
- branches (doesn’t coil)
- forms colloidal suspensions in water
- branches every 24-30 residues
- STARCH
8
Q
Glycogen
A
- large, branched glucose polymer
- alpha 1-4 linkages and 1-6 branched linkages
- branches every 8-12 residues
- found in the liver and muscle tissues
9
Q
Dietary Fiber
A
- plant material
- both polysaccharide and lignin
- RESISTANT TO HUMAN DIGESTIVE ENZYMES
10
Q
Why is dietary fiber indigestible?
A
Humans don’t produce the enzymes required to break beta 1-4 linkages
11
Q
Lignin
A
- made of aromatic polymers and composed of coumaryl, coniferyl, and sinapyl
- gives plants a “woody” characteristic
12
Q
Cellulose
A
- straight chain polysaccharide with repeating glucose subunits
- INSOLUBLE (has BETA 1-4 linkages; body can’t break these down
13
Q
Pectin
A
- Homopolysaccharide with methylgalactosyluronic acid subunits
- has jelly-like consistency
- found in fruits and vegetables
- SOLUBLE (fermentable)
14
Q
Hemicellulose
A
- made of pentoses and hexoses covalently bonded
- contains side chains
- some units include xylose, mannose, and galactose
- found in plant cell walls
- INSOLUBLE
15
Q
What are the proposed health beneficial effects of fiber? How do they occur?
A
- fiber binds to cholesterol in the small intestine and carries it out with waste
- it binds to metals, increasing fecal bulk and alters the viscosity of intestinal contents
- reduces the risk of diabetes by slowing sugar absorption as well as normalizing blood lipid levels
16
Q
What are the major enzymes involved in carbohydrate digestion, and where are they located?
A
- Salivary amylase (in saliva; first enzyme to break down carbs)
- Alpha amylase (located in small intestine; secreted by pancreas)
- Maltase, Sucrase, Lactase, and Alpha-dextrinase (break down disaccharides into their monomers; found in microvilli in small intestine)
17
Q
What kinds of carbohydrates are absorbable?
A
Carbs must be broken down into mono and disaccharides before they’re absorbable
18
Q
What is Resistant Starch?
A
- not completely hydrolyzed by amylases in upper digestive tract
- considered a type of fiber in small intestine (aren’t broken down)
- metabolized by bacteria in large intestine
19
Q
How are monosaccharides absorbed? What is the major energy source?
A
- Fructose binds to a protein carrier for absorption
- Absorptive cells in the small intestine use sodium gradient, ATP, and SGLT1 as energy sources to absorb glucose and galactose
20
Q
Glycemic response
A
degree and duration to which blood glucose level is elevated after consuming a portion of food that would provide 50 grams of digestible carbs and measured for 2 hours
21
Q
Glycemic index
A
comparison of glycemic response to a food standard, based on studies of healthy people
22
Q
Glycemic load
A
glycemic index normalized to actual serving standards
23
Q
6 major glucose transporters
A
- GLUT1 (insures uptake during hypoglycemia)
- GLUT2 (found in pancreas, intestine, and liver cells)
- GLUT3 (main transporter in neurons)
- GLUT4 (insulin regulated to help regulate hyperglycemia)
- GLUT5 (the FRUCTOSE transporter)
- GLUT7 (transports glucose out of endoplasmic reticulum after gluconeogenesis is complete)
24
Q
What does Km of GLUT transporters tell you about its function?
A
- Km tells you when the transporter is most active
- High Km (low affinity) - most active when high concentrations of glucose are present
- Low Km (high affinity) - protein is active during hypoglycemia (low glucose concentrations)
25
Describe how blood glucose causes insulin production
- high amount of blood glucose causes glucose uptake via GLUT2
- ATP formation through glucose utilizes inactivated potassium channels
- Beta cell membrane becomes depolarized due to accumulation of potassium ions
- calcium channels open and calcium diffuses into the cell
- calcium promotes fusing of insulin secretory vesicles with plasma membrane
- insulin is then released
26
Describe how insulin causes glucose uptake
- insulin causes an increase of the number of glucose transporters at the plasma membrane face in adipose and muscle tissues
- increased glucose entry occurs by increasing the activity of glucokinase
- once glucose enters, it is phosphorylated by glucokinase (maintains entry of glucose into cell)
27
major hormones and stress signals (4) involved in glucose metabolism
- Insulin (increases uptake of glucose into adipose and muscle tissues; LOWERS BLOOD SUGAR)
- Glucagon (increases glycogen breakdown in liver; RAISES BLOOD SUGAR)
- Epinephrine (increases glycogen breakdown in liver and skeletal muscles; aids in glucose uptake)
- Cortisol (increases blood sugar through gluconeogenesis; antagonize insulin)
28
Inputs of glycolysis
glucose
2 ATP
2 NAD+
2 ADP+P
29
Outputs of glycolysis
2 Pyruvic Acid
NADH+H
4 ATP (2 net gain)
30
How is glycogen synthesized (starting material and how its activated)?
- glycogen synthesis starts with UDP-glucose and is formed from Glycogen Synthase
- When chain reaches 11 or more glucose monomers, branching enzymes form a branch from an oligomer of about 6-8 monomers
31
Glycogenolysis
- the breakdown of glycogen into glucose-1-phosphate and glucose via glycogen phosphorylase
- important role in fight-or-flight response and regulation of glucose levels in blood
32
What is the input into the Pentose Phosphate Pathway and what are the outputs?
The PPP generates NADPH and pentose via two distinct phases (oxidative and non-oxidative phases)
33
Gluconeogensis
- the formation of glucose from carbon substrates (ex: pyruvate, lactate, glycerol, gluconeogenic amino acids, and odd-chain fatty acids)
- glucose is formed when the body is low on blood glucose levels and requires energy
34
Which organ is dependent on glucose?
the liver (synthesizes into glycogen for storage)
35
What is the current recommendation for fiber intake? Whole grains?
- fiber intake: 25-40 g per day
| - whole grain: 3-5 16 g servings per day
36
Whole Grain vs. Fiber
Whole grain - contains fiber but is made up of bran, germ, and endosperm (so it contains more nutrients than just fiber)
Fiber - indigestible part of whole grain (mostly contained in bran)
37
Multigrain vs. Whole Grain
Multigrain - made of refined grains (not as healthy as whole grains)
Whole grains - use entire grain (versus just the endosperm)
38
Metabolism of Fructose vs. Glucose
Fructose
- no insulin response
- doesn't suppress hunger hormone
- goes through unregulated metabolism in liver
39
Consuming too much dietary fructose
increases liver fat
increases circulating triglycerides
40
HFCS (high fructose corn syrup) vs. sucrose
they are pretty similar
41
How has carbohydrate intake changed over the past 100 years in the US?
Cholesterol, Salt, and Sugar consumption has all increased
