Transcript complete

Chapter 4 Carbohydrates
Objectives:
•
Learn the major sources of dietary carbohydrates.
– What are these digested to and absorbed as?
– What are the major types of glucose transporters and where are they found?
How are these transporters regulated?
•
Understand how the major carbohydrates are utilized metabolically by your
cells
– Understand the basic processes involved in glycolysis, glycogenesis,
glycogenolysis, gluconeogenesis, and the hexosemonophosphate shunt
– Understand how fructose and galactose enter these pathways
•
Learn how these pathways are regulated by insulin and glucagon
– What are the major ways that regulation takes place (mechanisms of regulation)?
•
Learn how ethanol consumption impacts the metabolic pathways for
carbohydrates
–
–
–
–
•
Acetaldehyde toxicity
High NADH:NAD+ ratio
Substrate competition
Induced metabolic tolerance
Learn how some diseases are associated with carbohydrate metabolism
– Diabetes
– Hypoglycemia
Enzymes involved in carbohydrate digestion and metabolism are stereospecific for
D sugars
Reference
molecule
Chiral carbon?
Anomeric carbon?
Fig. 4-2, p. 74
Pentoses?
Reducing sugars?
Oligosaccharides?
Table 4-1, p. 75
Fig. 4-5a, p. 77
Fig. 4-6, p. 78
Table 4-2, p. 81
Golgi
Apparatus
Glucose
Transport
Vesicle-bound
transporters
Translocation
Synthesized
transporters
from ribosomes
Insulin
Insulin
receptor
Fig. 4-8, p. 82
(a) Glucose
(reference food)
(b) Low glycemic index
(c) Fasting baseline
Hours
Glucose meal
Fig. 4-9, p. 83
Cereals
Snacks
Pasta
Beans
All Bran
51
chocolate bar
49
fettucini
32
baked
44
Bran Buds + psyll
45
corn chips
72
linguini
50
black beans, boiled
30
Bran Flakes
74
croissant
67
macaroni
46
butter, boiled
33
Cheerios
74
doughnut
76
spagh, 5 min boiled
33
cannellini beans
31
Corn Chex
83
graham crakers
74
spagh, 15 min boiled
44
garbanzo, boiled
34
Cream of Wheat
66
jelly beans
80
Soups/Vegetables
kidney, boiled
29
Frosted Flakes
55
pizza, cheese & tom
60
carrots, fresh, boil
49
kidney, canned
52
Grapenuts
67
Pizza Hut, supreme
33
corn, sweet
56
lentils, green, brown
30
muesli, natural
54
popcorn, light micro
55
parsnips
97
lima, boiled
32
potato chips
56
peas, fresh, boil
48
navy beans
38
pinto, boiled
39
Fruit
apple
38
Power bars
58
Drinks
apricots
57
pretzels
83
apple juice
40
red lentils, boiled
27
banana
56
saltine crakers
74
colas
65
soy, boiled
16
cantalope
65
Cereal Grains
Gatorade
78
Breads
cherries
22
barley
25
orange juice
46
bagel, plain
72
dates
103
basmati white rice
58
Milk Products
baquette, Frnch
95
grapefruit
25
bulgar
48
ice cream, van
60
pita
57
grapes
46
couscous
65
ice milk, van
50
pizza, cheese
60
kiwi
52
skim milk
32
Fig. 4-10, p. 84
Fig. 4-11a, p. 85
Glycogen synthase – active when dephosphorylated,
inactive when phosphorylated; insulin vs. glucagon
Fig. 4-11b, p. 85
Glycogenolysis – activated by glucagon and epinephrine through action on glycogen
phosphorylase (phosphorylase a, phosphorylated – active; phosphorylase b,
dephosphorylated - inactive
Fig. 4-12, p. 86
Fig. 4-13, p. 87
Fig. 4-14, p. 88
1. Citrate synthase
2. Aconitase
3. Isocitrate
dehydrogenase
4. a ketoglutarate
dehydrogenase
5. Succinyl thiokinase
6. Succinate
dehydrogenase
7. Fumarase
8. Malate
dehydrogenase
Fig. 4-15, p. 91
Fig. 4-16, p. 91
Fig. 4-17, p. 93
Used when
nucleic acids
are needed
Used when
NADPH is
needed
Fig. 4-19, p. 95
Brain, neurons, and RBCs are dependent on glucose as a
nutrient. When dietary intake of glucose is decreased and
glycogen stores are depleted, we can make new glucose
from alternative fuel sources in a process called
gluconeogenesis
Fuels used to make new glucose include
• amino acids,
• lactate,
• Glycerol
Organ which most often performs gluconeogenesis is the
liver
Irreversible rxn
Fig. 4-21, p. 97
Four Mechanisms for Regulating Blood Glucose
• Allosteric modulation by compounds within the
pathways
• Hormonal activation of covalent modification of specific
enzymes
• Directional shifts in reversible reactions by changes in
reactant or product concentrations
• Translocation of enzymes within the cell
•
Citrate synthase
•
Aconitase
•
Isocitrate
dehydrogenase
 a ketoglutarate
dehydrogenase
•
Succinyl thiokinase
•
Succinate
dehydrogenase
•
Fumarase
•
Malate
dehydrogenase
Regulated by NADH/NAD+
Regulated by ATP/ADP
Fig. 4-15, p. 91
Fig. 4-22, p. 101
Ethyl Alcohol: Metabolic Impact
• Ethyl alcohol most closely resembles a carbohydrate
• It has caloric value, and is a common dietary component of alcoholic
beverages
• Each gram of alcohol yields 7kcal of energy
– May account for 10% of total energy intake in moderate consumers
– May account for 50% of total energy intake in alcoholics.
• Ethanol is absorbed throughout the digestive tract and is transported
in the blood.
• It is then oxidatively degraded, mostly in the liver, to acetaldehyde
and then to acetate. Acetate eventually is converted to acetylcoA
– Alcohol dehydrogenase
– MEOS or cytochrome P-450
– catalase
ethanol + NAD+ ----> acetaldehyde + NADH
Acetaldehyde is toxic
reactive with amino groups and may interact with proteins
competes for the plasma carrier of pyridoxal (vitamin B6)
acetaldehyde + NAD+ ----> acetic acid + NADH
Acetic acid can lead to acidosis
Because the two reactions require NAD+, NADH can build up. What problems
might this cause?
anaerobic metabolism to regenerate NAD+
lack of pyruvate for gluconeogenesis - hypoglycemia
Fig. 4-23, p. 102
Metabolic consequences
•
•
•
•
Acetaldehyde toxicity
Elevated NADH:NAD+ ratio
Metabolic competition
Induced metabolic tolerance
• Elevates HDL in
serum and lowers
serum lipoproteins
• Slowing development
of smooth muscles in
atherosclerosis
Diseases of Carbohydrate Metabolism
• Diabetes
• Hypoglycemia