non energy role of carbohydrates
TRANSCRIPT
Digested Absorbed
Diet Monosaccharide Portal circulation Enters
systemic Glucose Liver circulation Enters Converted
Mainly meant for energy .
There are other special functions of this molecule .
FATE OF GLUCOSE & ITS UTILISATION
OXIDATION STORAGE LIPOGENESIS CONVERSION CONVERSION
-GLYCOLYSIS GLYCOGEN INTO AMINO INTO OTHER
-HMP SHUNT ACIDS CARBOHYDRATES
-URONIC ACID PATHWAY
-RAPOPORT LUEBERING CYCLE
GLUCOSE
HEXOSE MONO PHOSPHATE (HMP) SHUNT
Alternate oxidative pathway for GLUCOSE Mainly meant for production of NADPH and PENTOSE
SUGARS Occurs in special tissues for special function eg :- Liver,
RBC, Adrenal cortex, Lactating mammary gland.
1. NADPH Used as electron donor in many reductive synthesis in the
body . eg:- -Extra mitochondrial de novo fatty acid synthesis. -Synthesis of Cholesterol - To keep Glutathione in reduced state ( RBC, Lens) -Phagocytosis
Role of HMP pathway in Lens
10% of glucose is oxidized in this pathway to produce NADPH to keep G-SH in reduced form ,which is necessary for maintenance of lens proteins.
Ribonucleotide reductase
Ribonucleotide Deoxyribonucleotide
Thiroredoxine Thiroredoxine (Red ) (Oxi )
NADP NADPH + H+
HMP
2. TO PROVIDE PENTOSE
For Nucleotide and Nucleic acid synthesis
In denovo synthesis , purines are built on R-5-P molecule to form nucleotides .
Component of important molecules like ATP ,ADP, cAMP ,cGMP
and co enzymes like NAD, NADP ,FMN , FAD . CoA
Uronic acid pathway
Biomedical importance
Production of D-Glucuronic acid ------mainly utilised for detoxification of foreign substances
(Xenobiotics) ----also used for synthesis of MPS
Functions of Glucuronic acid1. Conjugation UDP Glucuronic acid is a active form
Conjugation takes place in liver & enzyme which catalises is Glucuronyl transferase
various Xenobiotics like drugs ,chemicals , pollutants ,food additives , carcinogens & endogeneous hormones . are converted into corresponding Glucuronides which are more polar & soluble , excreted in urine .
Eg :- Bile pigments (bilirubin )—mono & diglucuronoides
Aromatic amino acids -----Benzoic acid Drugs & other xenobiotics------ First hydroxylated by
mono oxygenase Cyt P450 system & then conjugated with D-Glucuronic acid .
Hormones-----Thyroid hormones ,derivatives of certain steroid hormones are detoxified by D-Glucuronic acid .
2. Synthesis of MPS-composed of amino sugars and uronic acid .-amino sugar may be glucosamine or galactosamine
which is acetylated .-uronic acid may be D-glucuronic acid or L-iduronic
acid-some may contain only galactose with glucosamine
Eg:- Hyaluronic acid , Chondroitin sulphate ,Keratan sulphate , Heparin .
Functions of MPSAs a constituents of extra cellular matrix interacts
with collagens and elastins
Acts as polyanions ---binds to polycations and cations (Na+, K+ ) ,thus attracts water by osmotic pressure into extra cellular matrix contributing to its turgor .
Acts as a barrier in tissues ---Hyaluronic acid –permits metabolites to pass through but resists penetration of bacteria and other infective agents .Also acts as lubricant and shock absorber .
Heparin acts as a anticoagulant and also as co- enzyme for Lipoprotein lipase enzyme
Dermatan sulphate present in sclera of the eye maintains the overall shape of the eye .
Keratan sulphate present in cornea of the eye and lie between the collagen fibrils and play an important role in maintaining corneal transperancy .
Functions of 2,3 BPG
2,3 BPG is the most abundant organic phosphate in RBC ,where its concentration is roughly equals to that of Hb
One molecule of 2,3 BPG binds to a pocket in the center of the deoxy Hb tetramer ,formed by the 2β
globin chains .This preferrential binding stabilises the taut form. This reduces the affinity of Hb for oxygen thus
enables Hb to release oxygen at tissue level .
Glycoproteins
Located on the extracellular side of plasma membrane
2%-10%------are contributed by the sugar residues of their glcoproteins
Membrane bound glycoproteins participate in a broad range of cellular phenomena including cell surface recognition , cell adhesion , blood group antigens .
GLYCOPHORINS
Transmembrane protein with carbohydrate coat . Single polypeptide chain with 16 attached oligosaccharide units .These carbohydrate units are rich in sialic acid a
negatively charged sugar .The carbohydrate units of glycophorins give RBC a
very hydrophilic , anionic coat , which enables them to circulate with out adhering to other cells and vessel walls .
Cell-Cell recognition1. Eg:- Asialoglycoprotein receptor
Many newly synthesized glycoprotein , such as immunoglobulin , peptide hormones contain carbohydrate units with sialic acid residues .
In course of hours or days ,depending upon the particular protein, these groups are removed by SIALASES protruding from the surface of blood vessels .
The exposed galactose residues from the trimmed glycoprotein is detected by ASIALOGLYCOPROTEIN RECEPTOR in the plasma membrane of the liver cells .
The complex of the glycoprotein and receptor is then internalised by the liver cells
ABO Substances
These are glycosphingolipids and glycoproteins sharing common oligosaccharide chains .
On RBC membrane –oligosaccharide that determines the specific nature of ABO substance is present in glycosphingolipid .
In secretions ----the same oligosaccharide is present in glycoprotein .
H substance is the biosynthetic precursor of both A and B substance .
Fucose -Gal-GlaNAc-R A
GalNAcFucose-Gal-GlaNAc-R H
Fucose-Gal-GlaNAc B Gal
Glycosides
Glycosides are formed when hemiacetal or hemiketal hydroxyl group ( of anomeric carbon ) of a carbohydrate reacts with a hydroxyl group of another carbohydrate or a non carbohydrate ( aglycone )
Aglycone can be ---methanol , glycerol , sterol , phenol , or bases like adenine .
They are important in medicine due to their action on cardiac muscle . ( steroids as aglycone )
Cardiac glycosideUsed in cardiac insufficiency .Steroids as aglycone .Derivatives of Digitalis ,strophanthus , squill plants .Eg:-Digitonin 4Galactose +Xylulose + Digitogenin(aglycone )
OuabainInhibits active transport of Na+ in cardiac muscle
(sodium pump inhibitor )
Sucrose
If introduced parentally cannot be utilised , but changes osmotic condition of the blood and causes a flow of water from the tissue into the blood .
Thus can be used in edema like cerebral edema .
Homopolysaccharides
Inulin -polymer of D Fructose . -Used in renal function test to determine GFR .
Cellulose -polymer of D Glucose . -not digested in humans . -adds bulk to the intestinal substance and stimulate peristalsis and elimination of indigested food residues .
Dextrins - partial hydrolysed product of starch . - used as mucilages .
Dextrans - polymer of D Glucose ( alpha 1-6 ,1-4 , 1-3 linkages in each unit ) -molecular weight 75000 -used as plasma expander due to their high viscosity , low osmotic pressure, slow disintegration,
utilisation and elimination .
Agar -made up of repeated units of Galactose which is
sulphated . -purified agar dissolves in hot water and on cooling
it sets like a gel which is used in agar plates for culture of bacteria .
Agarose -Galactose combined with 3,6 anhydro galactose
units -used as a support medium in Electrophoresis .
Conversion into aminoacids
Synthesis of non essential amino acidsby transamination reaction .
Eg:-pyruvate alanine oxaloacetate aspartate
C skeletons of nonessential aminoacids are derived from glucose or its metabolites .