Ch.20Pt.2_000

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Transcript Ch.20Pt.2_000

Phosphate Ester Formation
• Hydroxyl group + H3PO4 --> Phosphate Ester
• Phosphate esters are important compounds in
carbohydrate metabolism.
Phosphate ester formation
-D-glucose-1-phosphate
Sugar and phosphate combinations are the basis for
nucleotides involved in DNA / RNA,
energy carrying molecules (ADP & ATP),
and chemical messengers (cAMP)
Amino Sugar Formation
• Hydroxyl group is replaced by an amino group -->
Aldosamine
– Important in cartilage polysaccharides and red blood cell
markers (ABO)
– There are 3 important, naturally-occurring amino sugars.
• In each the amino group is on C#2.
Amino sugar formation
Glucosamine and hyaluronic acid
act as the backbone for the
formation of proteoglycans
found in the structural matrix
of joints
Glycosidic bonds:
The hydroxyl group and a hydroxyl group
of another sugar or other compound can join together,
splitting out water to form a glycosidic bond.
Acting hemiacetal
Acting as an alcohol
R-OH + HO-R'  R-O-R' + H2O
glycosidic linking helps form disaccharides,
oligosaccharides, and polysaccharides
from rings of monosaccharides
Disaccharide formation
Alpha () or beta () describes
the –OH orientation on C #1.
The numbers represent the C #
connections on the Haworth projection
Disaccharides
• Formation of disaccharides is like glycoside
formation (condensation rxn)
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•
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•
•
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– Monosaccharide + alcohol --> glycoside + H2O
Monosaccharide + monosaccharide --> disaccharide + H2O
Disaccharide glycosidic linkage Reducing? Human Digestion
Maltose
(1-4)
yes
easily
Cellobiose (1-4)
yes
no
Lactose
(1-4)
yes
usually
Sucrose
(1-2) no
yes
Common Disaccharides:
Sucrose: -Glucose and -Fructose
,  (12) glycosidic linkage
Milk sugar:
galactose and glucose
connected
(14) glycosidic linkage of 2 D-Glucose molecules
Polysaccharides (glycan)
• Variations
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–
–
–
Homopolysaccharides vs. Heteropolysaccharides
Length of chain
Type of Glycoside Linkage
Degree of Branching
• Properties
–
–
–
–
NOT sweet
No positive Tollens or Fehling’s test
Limited water solubility
Colloids form readily
Storage Polysaccharides
energy source
(homopolysaccharides)
Starch (plants)
amylose (15-20%)
straight-chain
-glucose polymer
(~1000 G)
amylopectin (80-85%)
branched chain (~100,000 G)
glucose polymer
(~100,0000 G)
Starch + H2O --> glucose
Nutritional value
Glycogen (animals)
Highly branched
glucose polymer
(~1,000,000 G)
Glucose <==> Glycogen
(stored in liver
& muscle)
Cellulose
Structural Polysaccharides
(homopolysaccharides)
Cellulose (cell wall)
straight chain -glucose
polymer
Chitin (exoskeleton)
N-acetyl amino derivative of
glucose
Cotton and wood are primarily cellulose
(14) glycosidic bonds of two glucose rings
create linear but angled bonding.
Our enzymes cannot match
this bond angle structure
to hydrolyze cellulose into cellobiose subunits or
break that down to glucose
Acidic Polysaccharides
(heteropolysaccharides)
• Hyaluronic acid
– Joint lubricant
Hyaluronic acid: heteropolysaccharide –
2 different glucose derivatives:
Glucuronic acid plus
N-acetyl--D-Glucosamine
Alternates (13) and (14) linkage
• Heparin
– Anticoagulant
Acidic polysaccharides associated with the
connective tissue of joints give hurdlers such
as these the flexibility needed to accomplish
their task.
Glycolipids & Glycoproteins
• These form when glycosidic linkages
connect monosaccharides with lipids
&/or proteins.
• Very important molecules for cell
recognition processes
Dietary Considerations
• A balanced diet ~ 60% carbohydrate
– Simple carbs = mono & disaccharides
– Complex carbs = polysaccharides
– Starch
– Cellulose
• Natural vs. Refined Sugars
– Natural: a mixture of sugar and other compounds
– Refined: 100% sugar molecules
• Glycemic effect: due to the rate of carbohydrate
digestion
– Glycemic index
Glycemic Index:
Measures the rate that specific
carbohydrates are hydrolyzed into
glucose.
Slow release of glucose into blood = good
Quick release of glucose into blood /
overproduction of insulin = bad