Chpt 11- Carbohydrates Flashcards
Carbohydrates Definition
- an aldehyde or ketone derivative of a polyhydroxyl compound (having more than one hydroxyl group)
- Old def-hydrate of carbon (CH2O)n
Counting Saccharides
Saccharide=Sugars (-ose) 3 Carbons- trios 4 Carbons- Tetrose 5 Carbons- Pentose 6 Carbons- Hexose 7 Carbons- Heptose 8 Carbons- Octose
Function of Carbohydrates
- energy source (glucose or sucrose)
- energy storage molecules (starch in plants, glycogen in animals
- structural components (DNA and RNA)
- Cell signaling molecule
- Cell to cell recognition (Glycosylation of proteins and other biomolecules)
Isomer
Molecules with identical molecular formulas but different structural formulas
Enantiomer
- Differ in configuration around one chiral carbon
- mirror images
- D or L (living systems contain D)
Epimer
- one of two optical isomers that differ from each other only in the configuration about one asymmetric carbon aton
- during cyclization
- alpha or beta
Diasteromer
-one of two or more optical isomers of a component that are not enantiomers (possible due to multiple asymmetric carbons)
Different ways of Classifying Carbohydrates
- Classified by repeating Structural element
- Monosaccharides are classified as Aldose or Ketose
- Cyclized Monosaccharides are classified as Alpha or Beta
- Monosaccharides are classifies as Furanose and Pyranose
Classification of Carbohydrates:
Repeating Structural element
- Monosaccharide (one)
- disaccharide (two)
- Oligosaccharide (more than 9)
- polysaccharide (ALOT)
Classification of Carbohydrates:
Monosaccharides as Aldose and Ketose
Aldose-contains an aldehyde group
Ketose-contains a ketone group
D-Aldoses and D-ketoses you need to know:
D-Aldoses: (-ose)
1) D-Glyceraldehyde (3 Carbons)
2) D-erythrose (4 Carbons also D-ketoses)
3) D-ribose (5 Carbons and also D-ketose)
4) D-glucose (6 carbons)
5) D-mannose (6 carbons)
6) D- galactose (6 carbons)
D-Ketoses (-ulose)
1) Dihydroxyacetone (3 Carbons)
2) D-erythrulose (4 carbons also D-Aldose)
3) D-ribulose (5 carbons also D-Aldose)
4) D-fructose (6 carbons)
Classifying Carbohydrates:
Cyclized Monosaccharides are classified as Alpha or Beta
> 5 carbons cyclize into ring form
-in vivo <1% exist in linear form
Cyclization produces anomeric carbon-new chiral carbon
Alpha HYDROGEN Above
Beta HYDROGEN Below
Hemiacetal
formed by reacting aldehyde with an alcohol
5-membered ring (furanose)
Hemiketal
formed by reacting ketone with an alcohol
6 membered ring (Pyranose)
Classifying Carbohydrates:
Monosaccharides are classified as Furanose and Pyranose
Furanose- 5 membered ring
Pyranose- 6 membered ring
*Fructose can form both Furanose and Pyranose rings
Cyclic Conformations of 6 membered ring
Chair conformation is more stable than boat conformations due to steric hindrance
- Axial-nearly perpendicular to the average plane of the ring (stick straight up or down)
- Equatorial- atoms nearly parallel to the average plane of the ring (stick slightly up or down)
- Furanose rings assume envelope form
- C-2 or C-3 out of plane on the same side as C-5
Monosaccharides Mofications
- Hydroxylation- O glycosidic bonds
- Amine groups attach through N linked glycosidic bonds
- Phosphorylated (PO32) ***
Phosphorylation of Carbohydrates
Key metabolic intermediates
Sugars become negatively charges (anionic)
-“Locks” the intermediates into the cell or other membrane bound compartment
-activates the intermediate
Reducing vs NonReducing Sugars
Reducing sugars have a free aldehyde group or are capable of forming an aldehyde through ring opening, isomerization, or tautomerization
-some ketone groups may through tautomerization be reducing
Tests for reducing sugars
Benedicts Reagent (CuSO4/Citrate)
Fehling’s Solution (CuSO4/tartrate)
-reducing sugars reduce copper (II) to copper (I). The produce, copper (I) oxidize, forms a red precipitate
Tollen’s Test (silver mirror test)
Tollen’s reagent precipitates silver metal when exposed to free aldehydes
Glycosidic Bonds
- Connects monosaccharides into: dimers, trimers, oligosaccharides, or polysaccharides
- Condensation (dehydration) reaction
- Two orientations: alpha or Beta
What are the disaccharides we need to know?
Maltose
Lactose
Sucrose
Maltose
Disaccharide
(alpha-D-glucopyranosyl-1,4-alpha-D-glucopyranose)
Glucose alpha-1,4-Glucose
Breakdown produce to glycogen/starch
Lactose
Disaccharide
(B-D-galactopyranosyl-1,4-alpha-D-glucopyranose)
Galactose B-1,4-Glucose
Mammals milk sugar
Sucrose
Disaccharide
(alpha-D-Glucopyranosyl-1,2-B-D-fructofuranoside)
Glucose alpha 1,2 fructose
table sugar
Polysaccharides we need to know for class?
Glycogen
Starch
Cellulose
Glycogen
Polysaccharide
Monomer-Glucose
Bond-connect alpha-1,4- with alpha 1,6 branches
Function-animal energy (glucose) storage and stored in liver and muscle
Starch
Polysacchardie
Monomer- glucose
Bond-connected alpha-1,4 with alpha 1,6 branches
Function: Plant energy (glucose) storage
Cellulose
Polysaccharide
Monomore-glucose
Bond: connected B-1,4 linear polymer of glucose
function: plant structural fiber
Structure of Glycogen and Starch
Both are branched polymers of glucose connected by alpha 1,4 glycosidic bonds with alpha 1,6 branches
Glycogen has more branches than starch
Proteoglycans
are glycosolated proteins that serve as joint lubricants and structural components in connective tissue
Glycosaminoglycans
are the carbohydrate component of proteoglycans
-repeating disaccharides of amino sugars
Mucopolysaccharidoses
diseases caused by the inability to degrade glycosaminoglycans (carbohydrate component of proteolglycans)
Skeletal deformities and reduced life expectancy
Osteoarthritis
Disease caused by breakdown of proteoglycans
Glycosyltransferases
class of enzymes that catalyzes the formation of glycosidic bonds -use sugar nucleotide intermediates
the genes for specific glycosyltransferases are inherited in the Mendelian Pattern
ABO blood types
due to different carbohydrates on the surface of RCBs
O antigen group is foundation
- contain four carbohydrates (fucose, 2 copies of Galactose, N-actetylglucosamine)
- modified to form A and B antigens
A antigen
-added N-acteylgalactosamine
B antigen
-added galactose
Proteins Modification in relation to carbohydrates
Proteins are modified by Attachment of carbohydrates
1) N linked carbohydrates are attached to the R group of asparagine
2) O linked carbohydrates are attached to the R group of Serine or Threonine
For both:
-Glycosylation sites identified by consenses sequences
Asn-X-Ser or Asn-X-Thr, where X can’t be proline
N-linked Oligosaccharides
Extensive modification leads to vast array of molecular shapes
EPO
Erythropoietin
Function-stimulates the production of RBCs
-Glycoprotein hormone; secreted kidney
Structure:
- 165 amino acids
- 3 N-linked groups
- 1 O-linked Group
Uses:
- Treats anemia cancer patients
- Performance enhancement by athletes (Lance Armstrong)
Cellular Localization:
N-linked Carbohydrates
Glycoproteins
O-linked carbohydrates
N-linked carbohydrates:
- are attached/modified in thee lumen of the Endoplasmic Reticulum
- are modified in the lumen of the golgi
Glycoproteins:
-are usually found on cell surface
O-linked carbohydrates:
-are attached in Golgi and cytoplasm
N Linked Carbohydrates Synthesization
are synthesized as a performed unit and transferred to newly synthesized proteins
-assembled on a Dolichol phosphate in Lumen of ER
Lectins:
Function and Structure
specific carbohydrate binging proteins
Legere (to select)
Function- cell to cell interaction
Structure: classified based on:
amino acid homology and biochemical properties
Digestion of Carbohydrates
1) Mouth
Mastification mixes salivary alpha amylase with dietary starch
2) Stomach
digestion halts (inhibits alpha amylase) due to low PH
3) small intestine
-acid neutralized by bicarbonate (from pancreas)
-alpha amylase (from pancreas-continues digestion)
4) Mucosal lining of upper jejunum
-Disaccharidases, oligosaccharidases-isomaltase, maltase, sucrase
-secreted by luminal side of the brush border of intestinal mucosal cells
