SOIL ORGANIC MATTER Biomolecules Organic Acids; Carbohydrates; Other Humic Substances
Carbohydrates (saccharides) Organic biomolecules: 1.Carbohydrates 2.Lipids 3.Proteins 4.Nucleic...
-
date post
21-Dec-2015 -
Category
Documents
-
view
231 -
download
0
Transcript of Carbohydrates (saccharides) Organic biomolecules: 1.Carbohydrates 2.Lipids 3.Proteins 4.Nucleic...
Carbohydrates(saccharides)
Organic biomolecules:
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic acids
Functions of carbohydrates
• Energy: metabolism and storage
• Structural and protective
• Precursors for other biomolecules
• Cell recognition and regulation
• Components of DNA and RNA units
Look for these functions in the chapter: - which molecules that we discuss fit which category?
Terminology
• Basic building block: monosaccharides– Polyhydroxyaldehydes (figure 18.1)– Polyhydroxyketones (figure 18.2)
• Bigger units constructed of monosaccharides: polysaccharides– Disaccharides– Oligosaccharides– Polysaccharides
Important points of monosaccharides:
• Biologically important sugars are generally 3-6 C’s in length
• Number from nearest the carbonyl end• The stereochemistry of important hexoses in
biology is ____ at the next-to-terminal carbon
• Carbohydrate = carbo + hydrate
Sugar terminology: -ose
• Aldoses = • Ketoses =
• Triose, tetrose, pentose, hexose:
• Note: sugars have several identities so what terminology you use depends on what identity you are addressing
Important monosaccharides:
• Hexoses:– D-glucose = blood sugar, dextrose– D-fructose = levulose– D-galactose:– D-mannose:
• Pentoses:– D-ribose (deoxyribose –at C2 - in DNA)– D-xylose
Construct sugar model
• Furanose = 5 membered ring
• Pyranose = 6 membered ring
• Construct D-glucose as open chain, then convert to cyclic form
Conversion of D-glucose to its cyclic forms:
•Pyranose or furanose?
•Anomers: differ in configuration at the hemiacetal carbon (C1 here)
(Fischer projection)
(Haworth projections)
Anomers:
Hexoses and pentoses form stable hemiacetals which are 5 or 6 membered rings
Each hemiacetal structure is one of two possible anomers (alpha or beta)
Practice converting Fischer projections into Haworth projections
Monosaccharide properties
• Sweetness• Very water soluble • Crystalline at RT • Not soluble in nonpolar solvents
– Slightly soluble in EtOH, MeOH
• Undergo mutarotation to rapid equilibration in water between anomeric forms– Each sugar has its own characteristic equilibrium
ratio; we have the example of glucose– Positive Benedict’s test because ___________
Check your lab results:
• Monosaccharides:– Solubility in water– Benedict’s test– Crystalline at RT
• Diastereomers with characteristic m.p.’s
– Optical rotation• Diastereomers with
unique optical activity
Disaccharides
• Dehydration reaction between a hemiacetal and an alcohol forms a glycoside ( = an acetal of a carbohydrate)
• This linkage is made through a stereospecific enzyme-catalyzed reaction in biological systems– The difference in starch vs. cellulose: digestibility by
humans is an example of structure → function
Cellobiose = from partial hydrolysis of cellulose, by enzyme cellulase
Reducing sugar = Benedict’s test results: _____
Polysaccharides• Storage
– Starch– glycogen
• Structural– Cellulose– Chitin
• Recognition– Glycolipids– glycoproteins
Essentially nonreducing sugars:
Benedicts ____mutarotation____
Starch: shown here is a small unit
What type of glycosidic linkage is shown between glucose units?_________
Amylose (10-30%) linear, long chains
Cellulose: Glycosidic linkage is _________
Planar formation of chainsNeed cellulase to cleave this linkage: provided by microorganisms of ruminantsFiber for humans
Cell recognition
The ABO blood groups are major sugars, expressed on cell membranes, called antigens
Antibody response to these particular sugar attachments is expressed early in life, presumably due to similar environmental immunogens exposures; so everybody has the antibodies appropriate to their blood type.
Frequency of ABO phenotype in US population
White Black AsianNative American
O 45 49 43 79
A 41 27 27 16
B 10 19 25 4
AB 4 4 5 <1
Frequency of ABO phenotypes worldwide
About 21% of worldwide population has A allele.
Distribution in native populations worldwide
About 63% of world population is type O
Distribution in native populations worldwide
http://anthro.palomar.edu/vary/images/map_of_A_blood_allele.gif
Other antigens
• D-antigens: a different sugar chain attached to the cell membrane
• If you have D-antigen, you are Rh+• If you don’t express D-antigen, you are
Rh-
• Ratio of people who are Rh+ : Rh- – White Americans: 85:15– Black Americans: 92:8
More on antigens
• Duffy antigens (Fya and Fyb) provide a recognition site for parasite plasmodium vivax to dock and enter cell
White Americans: 65% Fya+; 80% Fyb+
(Or <1% Fya- and Fyb- )
Black Americans: 10% Fya+; 23% Fyb+
(Or 68% Fya- and Fyb- )
• So who is genetically more resistant to this particular malarial parasite?
This end is an inositol sugar
A malarial parasitic glycosylphosphatidylinositol (GPI); a parasitic sugar that helps initiate malarial infection.
1. Identify the first four sugars2. What are the glycosidic linkages
between the sugar units?
OH
OH
H
O
OH
HH
OH
O P
O
OH
O
NH2
OH
OH
H
O
HH
OH
CH2OH
H
OH
OH
H
O
OH
HH
OH
H
OH H
O
H
NH2H
OH
CH2OH
H
H OH
H
OH
HH
O
HOH
H OH6
5 4
3
21
PHO
OO
SH