Lecture 4 - carbs Flashcards
what are carbohydrates
- source of energy
o diet
o endogenous
▪ stored form of energy - structural components
o cell membrane
o RNA and DNA
o cell walls of bacteria and plants - Glucose
o Major clinically significant carbohydrate
4 structural properties may be used to classify carbohydrates:
- The size of the base carbon chain (number of carbons in the molecule)
- Location of the CO group
- Number of sugar units
- The stereochemistry \
C L A S S I F I C A T I O N ( C A R B O N N U M B E R )
basic formula where n is the number of carbon
3-triose- glyceraldehyde
dihydroxyacetone
4- tetrose - erythrose
5-pentose - rib or deoxyribose
6-hexose- glucose galactose
7-heptose-sedoheptulose
A L D O - HEX - O S E F A M I L Y
- ALDO
– aldehyde group where the carbonyl group is found on the end C so C=O on terminal C
-carbs from aldehydes are called aldoses - HEX
– 6 carbons - OSE
– carbohydrate - 3 naturally occurring forms
– D-glucose
– D-galactose
– D-mannose - Chemical formula: C6H12O6
THE K E T O - HEX - O S E F A M I L Y
- KETO
– ketone group where the carbonyl group C=O is found on a C that is in the middle
-carbs from ketones is called ketoses - HEX
– 6 carbons - OSE
– carbohydrate - 1 naturally occurring form
– D-fructose - Chemical formula: C6H12O6
what are isomers
- Isomers
o compounds with the same molecular formula but different structures
▪ identical number of atoms and atomic elements - difference in configuration around one specific C atom
o glucose, fructose, galactose, mannose C6H12O6 (epimer)
what is a Stereoisomers
o compounds identical in composition and differ only in spatial configuration
* D- and L- configuration
D- -OH on the right
L- -OH on the left
o most sugars in humans are of the D form with OH on the right
enantiomers
Non-superimposable mirror images are called enantiomers
(optical isomers)
– they have a “chiral” carbon
what is a M O N O S A C C H A R I D E S
simple sugar
* a single polyhydroxy aldehyde or ketone unit that cannot be
hydrolyzed to a simpler form
–c=o and -oh groups form a ring structure (with the chiral carbon) through intramolecular hemiacetal or hemiketal linkage
-when an aldehyde and alcohol come together a ring structure is formed through INTRAMOLECULAR HEMIACETAL OR HEMIKETAL LINKAGES
in a HEMIACETAL FORM (alde+alco) - THE HYDROXYL forms a bridge between c1 and c5 and the carbonyl forms alcohol
makes a carboxylic acid OH-C-OR
the anomeric carbon is the c attached to C=O
carbonyl
c=O
carboxyl
COOH
ketone and alcohol reaction - hemiketal
It is the =O (carbonyl group) that reacts with the –OH (alcohol or
“hydroxyl” group)
The H+ from the alcohol group moves positions to form a new OH and the remaining O (from the alcohol) forms the “bridge
fructose
❑ Carbonyl group (at C2 - anomeric carbon) and chiral carbon (at C5) form the hemiketal linkage to form the ring structure
❑ Hemiketal linkage: between the carbonyl group (-C=O) and the chiral carbon
❑ Chiral carbon is the highest numbered carbon with 4 different “groups
A and B isomers
Two chiral ring forms are possible
o MUTAROTATION alters the equilibrium between the three forms
* spontaneous opening and closing of the hemiacetal or hemiketal structure
* carbon about which this rotation occurs is the anomeric carbon
o (-OH group down) and (-OH group up) anomers
chemical properties of monosacc
- some carbohydrates are reducing substances
– free aldehyde or ketone group required - the anomeric carbon must remain unaltered
- the ring must be able to open up!
– Cu2+ or Fe3+ ions can be reduced by reducing sugars
* the resulting oxide is red
* lab application:
o Urinalysis: clinitest tablets with Benedicts reagent /clinitest (Copper 2 Sulphate reduced to copper 1 oxide)
if testing water or egg white the result will be blue or negative but if testing glucose or other sugars the test will be red or post
what are disacc
-two monosaccharides joined covalently by a glycosidic bond,
with a formation of h2o
o aldehyde or ketone group of one monosaccharide joins to alcohol or aldehyde or ketone group of another
o Cx(H2O)y
- physiologically important disaccharides
maltose = glucose + glucose
lactose = glucose + galactose
sucrose = glucose + fructose
how does disaccharide act as a reducing sugar
-can be a reducing sugar only if there is a free aldehyde or ketone group
- When the anomeric carbon has a hydroxyl group available to participate, it is considered “reducing”
- If the anomeric carbon is involved in the linkage, then it cannot be a reducing sugar
so if the anomeric carbon is axial or equatorial alone thats okay but if its joined like \o/ then no
what happens when a sugar is reducing
- it reduces another compound and is oxidized i.e the carbonyl group is oxidized to a carboxyl group
- All monosacccharides are reducing sugars because they are capable of opening up the ring form
- The reducing end of the disaccharide is the monosaccharide with a free anomeric carbon that is not involved in a glycosidic bond and is capable of converting to the open chain form.
how are disaccharides hydrolyzed
intestinally by disaccharidases like maltASE, lactase, sucrase
o monosaccharides are absorbed and transported to liver
o the only CHO to be directly used for energy or stored as glycogen is glucose
- fructose and galactose cannot be used until they are converted to glucose
what is starch
polysaccharides
o Storage form of carbohydrate in plants
o Composed of two polymers:
* Amylose
▪ linear chain of alpha-1,4-linked glucose units more than a 1000 glucose will make an amylose
- Amylopectin
▪ highly branched chain: with alpha 1-4 and alpha1-6 links
▪ up to 1 million glucose units
what is Glycogen
polysaccharides
o animal storage form of carbohydrate
* liver (hepatocytes)
* muscle
o similar to amylopectin, more highly branched (every 8-12 units)
* enhanced solubility
what is Cellulose
polysaccharides
structural polysaccharide in plants
o high tensile strength from beta-1,4 linkages look like ////
o humans do not have cellulases
-purest form of cellulose is in
cotton
what are two major hormones that help maintain glucose levels between 4.1-5.6 mmol/l
- Insulin:
▪ Increases glycogenesis and glycolysis
▪ Increases lipogenesis
▪ Decreases glycogenolysis - Glucagon:
▪ Increases glycogenolysis
▪ Increases gluconeogenesis
o Regulatory hormones:
* Insulin, Glucagon, Epinephrine, Cortisol, Growth hormone, ACTH
o Disorders of carbohydrate metabolism:
* Hyperglycemia (high blood glucose), Hypoglycemia (low blood glucose)
Glycogenesis
pathway in glucose metabolism
- converts glucose to glycogen for storage
- occurs when blood glucose is high resulting in a lowered blood glucose
- mainly in liver hepatocytes, influenced by insulin
