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Biochemistry
THEME – STRUCTURE DICTATES FUNCION
Main Ideas - 1)
2)
3)
Ch. 10 – Carbohydrates
10.1 Introduction to Carbohydrates –
Carboyhydrates –
Structure
- either polyhhydroxyaldehyde or a polyhydroxyketone
Mono-
Roles
di-
oligo-
poly-
saccharides
- metabolism of carbohydrates provides energy
- serve as structural and protective materials
- precursor molecules for biosynthesis of proteins, lipids, and nucleic acids
- attached to proteins and lipids in cell membranes to help in cell recognition and
specific molecules, triggering physiological processes
- ribose and deoxyribose are the sugars in DNA and RNA
10.2 Monosaccharides
Classification 1) ketone/aldehyde containing
2) carbon chain length
3 C’s
4 C’s
5 C’s
6 C’s
Build it!
KEY: Be sure to understand that when you “thought” you built glucose it’s highly likely that most
people built a stereoisomer of glucose.
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Stereoisomerism - aldoses & ketoses <<Figures 10.1 and 10.2>>
Isomerism Summary from Ch. 9
Isomers
(Connectivity Differences)
(Connectivity Differences)
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Recognizing structural relations:
For each of the following pairs of compounds, indicate whether the pair consists of different
compounds that are (1) constitutional isomers or (2) stereoisomers that are enantiomers or (3)
stereoisomers that are diasteromers or (4) not isomers.
(a) D-Glucose and D-mannose
(b) D-ribose and D-xylulose
(c) D-fructose and D-arabinose
(d) D-sorbose and L-sorbose
Practice
(e) D-sorbose and D-fructose
Sugar
Cyclic
#
Shape
Stereoisomers
Important Monosaccharides
aldopentose
glucose
aldotetrose
fructose
ketotetrose
galactose
ketohexose
2-deoxy-D-ribose
D-ribose
10.3 Cyclic Hemiacetal Structures
To convert acyclic structure to cyclic structure.
• Draw the fischer projection of the acyclic structure and then turn it sideways.
• Rotate the bond between C4 and C5 to bring the C5-OH group close to the carbonyl group.
• Add the alcohol – OH to the carbonyl group: break the O-H bond, and then bond the H of the –OH
to the carbonyl O and bond the O of the –OH to the carbonyl C.
• aldoses exist predominantly as _______________.
• aldhexoses take the shape of a _______________.
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• Ketoses exist predominantly as ___________________.
• Ketopentoses take the shape of a ___________________.
Practice Drawing Fischer and Haworth projections:
Draw the cyclic structure of a-D-galactose, referring only to figure 10.1. Indicate how this task is
simplified if you are allowed to directly refer to both figures 10.1 and 10.3
10.4 Chemical and Physical Properties of Monosaccharides
Monosaccharides -
solubility in water ________________
phase at room temp. ________________
highly concentration solutions are ____________
solubility in alcohols ________________
solubility in ethers & hydrocarbons ________________
taste ________________
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Box 10.1 How Sweet Is It?
• Taste depends on _____________, ______________, and _______________.
saccharin
cyclamates
aspartame
acesulfame K
sucralose
Artificial sweeteners are “calorie-free” because___________________________________________
Oxidation of the Aldehyde Group/ Benedicts Test
Aldose
+
Cu2+
 carboxylic acid + Cu2O
• ____________________________ are considered “reducing sugars.”
• Reducing sugars bring about the ____________ of another substance while they get _____________.
• In order to test positively the sugar must be in the _____________ form.
• -hydroxy ketones like fructose are converted to aldoses in the alkaline Benedicts soln, thus give a
__________ test.
Reducing Sugars
NOT Reducing sugars
Acetal Formation: The Production of Glycosides
Hemiacetal (aldose/ketose) + alcohol  acetal
Acetal NOTE: the
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10.5 Disaccharides
Maltose
Understanding the notation:
• the  in (14)- indicates
• the first number in (14)indicates
• the second number in
(14)- indicates
Cellobiose
Lactose
Sucrose
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Ex. 10.5 –Drawing the structure of a disaccharide
Melibiose, a disaccharide found in some plants, contains D-galactose linked to D-glucose by an
(16)-glycosidic linkage – an a-glycosidic linkage from C1 of D-galactose to C6 of D-glucose.
Draw the structure of melibiose and indicate whether it is a reducing sugar. Does it undergo
mutarotation?
Digestion and Absorption of Carbohydrates
• Only ________________ are small enough to pass through the intestinal wall into the blood stream.
sucrose
lactose
maltose
10.6 Polysaccharides – starch, glycogen, cellulose
Polysaccharides differ structurally several ways:
1. In the monosaccharide(s) that constitute(s) the residues.
2. In the –OH group(s) that participate(s) in linking the monosaccharide residues.
3. In the glycosidic linkage ( or ), when one of the –OH groups is the hemiacetal –OH (as is
usual).
4. In the presence or absence of branching in the polysaccharides.
Starch –
10-30%
30-90%
Glycogen
structurally similar to _______________
Digestion:
Storage:
When needed:
Starch
glucose + glucose
glycogen
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Cellulose:
• gives the plant ______________ and ______________
• structure:
Stable conformation:
Digestion:
Humans
Grazing Animals
Iodine Test:
Box 10.4 Dietary Fiber
Dietary Fiber –
•
•
•
Soluble
vs.
Insoluble
Cell Recognition: Glycolipids and Glycoproteins
Cell Recognition – cells recognize one another due to ____________________ attached to the cell
surface (usually ________ saccharides).
- saccharides are present as
1)
2)
Ex.
Egg – sperm
Blood types
Other Ex’s
10.7 Photosynthesis
Plants can convert carbohydrate to
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