Carbohydrates Flashcards
Carbs overview
- most abundant organic molecules in nature
- wide range of functions
- major energy source
- stores energy
- cell membrane component for intracellular com.
- only on outer surface of lipid bi layers - structural component
- in cell walls
- exoskeleton
- fibrous cellulose of plant walls - (CH2O)n—-ratio C:H:O= 1:2:1
Types of carbohydrates
- based on number of monomers
- monosaccharides (1 unit)
- Disaccharides (2 monosaccharide units)
- oligosaccharides(3-10 monosaccharide units)
- polysaccharides (more than 10)
Monosaccharide classification
- according to the number of carbons they contain
2. according to the type of their most oxidized functional group (Aldoses or Ketoses)
Structural Isomers
-compounds that have the same chemical formula but different structures (glucose, fructose, mannose)
Epimers
- compounds that differ in configuration around only ONE SPECIFIC CARBON ATOM
- glucose and galactose
Enantiomers
- pairs of structures that are mirror images to each other.
- D-glucose (naturally occurs in human body) and L-glucose
Monosaccharide cyclization
- 99% of monosaccharide with 5 or more carbons exist in a ring
- keto or aldehyde group reacts with an alcohol group on same the same sugar
- creates an anomeric carbon that can exist in alpha or beta form (alpha=hydroxyl group on same sideas O)(beta=opposite side)
- ENZYMES ARE SPECIFIC TO ONE OF THE ANOMERIC FORMS
- RINGS ARE MORE STABLE
- RINGS AND NON RINGS ARE IN EQUILIBRIUM
Disaccharide types of bonds
-bonds that link monosaccharides by GLYCOSIDIC bonds.
Naming: geek letter for alpha or beta, numbering is according to connected carbon
Lactose
glucose + galactose (Beta 1-4)
Sucrose
glucose +fructose (Alpha 1-2)
Maltose
Glucose+ glucose (Alpha 1-4)
Reducing Sugar
- all monosaccharides are, but not all disaccharides
- if the OH group on the anomeric carbon in a ring is NOT linked to another compound by a glycosidic bond, the ring can open
- then it can act as a reducing agent
- when they open, more open, and react and open more.
- you should not find reducing sugars in urine
Glycogen
- highly branched polymer of glucose
- alpha 1-4 and 1-6 linkage
- energy storage in liver and muscle cells
Amylose
- form of starch in plants
- unbranched alpha 1-4 glycosidic linkage
Amylopectin
- form of starch in plants
- branched BUT NOT AS BRANCHED AS GLYCOGEN
- alpha 1-4 and 1-6 linkage
Cellulose
- unbranched
- humans can’t digest
- Beta 1-4 linkage
Complex carbohydrates
-carbohydrates attached to noncarbohydrate structures
noncarbo structure examples
purines and pyrimidines
Aromatic rings
Proteins
Lipids
Complex carbohydrate bonds
N-glycosidic link and O-glycosidic link
Glycoside hydrolyses
- enzyme for complex carbo digestion
- breaks down glycolytic bonds
Salivary alpha amylase
Role-breaks large insoluble cab molecules into smaller ones
Specificity-hydrolysis of alpha 1-4 bonds ONLY
Substrates-any carb with 1-4 bonds, starch, glycogen, maltose
Products: short branched and unbranched oligosaccharides
pH-7
MOUTH
Pancreatic alpha amylase
Role-break down carbs
Specificity- hydrolysis of alpha 1-4 ONLY
substrates-things with 1-4 bonds, starch, glycogen
Products-unbranched oligosaccharides and disaccharides
pH-7
INTESTINAL LUMEN
Digestion in the mucosal cells
- all enzymes are transmembrane proteins on luminal surface
- sucrase-1 protein with 2 subunits. cleave 1-2 in sucrose and 1-6 in isomaltose
- maltase-1 protein with 2 activities. cleave 1-4 in maltose and 1-4 in dextrins
- Lactase- cleave 1-4 bonds in lactose
- Trehalase-cleaves 1-1 bonds in trehalase (mushrooms)
Absorption of monosaccharides
- monosaccharides only are sugars absorbed
- absorbed in duodenum and upper jejunum
Mechanism of monoasccharide absorption
from lumen into cells
- transporter proteins are highly specific for each monosaccharide
- sodium-dependent (SGLT-1)-glucose and galactose active transport
- sodium independent(GLUT-5)-fructose passive transport
From cells into the portal circulation
- GLUT-2
- passive transport
- galactose, glucose, fructose
Abnormal degradation of disaccharides
- disaccharides present in large intestines
- cause osmotic imbalance
- act as substrates for the intestinal microbiota
- measure H2 gas in breath to determine amount of carbs not absorbed by the body
Lactase Deficiency
- lactose intolerance
- you don’t have lactase
- congenital deficiency is rare
- avoid milk, dumbass
Sucrase-isomaltase complex deficiency
- sucrose intolerance
- autosomal recessive disorder
- more common in europeans
- avoid sucrose/ take replacement enzymes
- do a tolerance test with individual disaccharides
