Carbohydrates Flashcards
(22 cards)
Carbs
Monomers joined by glycosidic bonds
Highly Oxidisable
Store potential energy (starch, glycogen)
Structural and Protective functions (cellular matrices)
Cell-cell Communication
*Anomeric Carbon
Its the only oxidisable residue
Stabilises the glucose structure
Lactose and Maltose are named reducing sugars since an anomeric carbon is present in glucose??
Homopolysaccharides
Heteropolysaccharides
Single monomeric species
2 or more monomer species
Starch
Glucose polymer
Amylose + Amylopectin which form A-Helices
Many non reducing ends and few reducing ends
Amylose
20-25% of Starch
D-Glucose residues (a1-4 linkage)
Amylopectin
75-80% Starch
Branched
Glycosidic (a1-4) bonds join glucose in chains but branches at (a1-6) every 24-30 residues
Glycogen
Polymer of glucose (a1-4) linked subunit with (a1-6) branches every 8-12 residues
More Extensively branched than Starch
Many reducing ends which speed up degradation
90% in liver and skeletal muscles
Polymers exist bc?
Polymers form hydrated gels which are
Osmotically inactive
Glycosaminoglycans GAGs
Function: Mucus and synovial fluid
Un-branched polymers made from
Repeating units of hexurinic acid and amino sugar
Proteoglycans
GAGs covalently attaching to proteins
Macromolecules found in cell surface / bw cells in extracellular matrix
Part of the connective tissue
Carbs»_space; Protein
Glycoproteins
Protein»_space; Carbs
Outer Plasma Membrane
ECM
Blood
Mucopolysaccharidoses
Malfunction or Absence of enzymes required for Glycosaminoglycans breakdown
GAGs build up in connective tissue, blood and cells
Damages cellular architecture and function
Dementia, Heart, Endothelial function, Inflamed joints
Hurler Syndrome
Clouding and degradation of cornea
Arterial Wall Thickening
CSF buildup, Ventricular space enlargement - Dementia
Developmental Abnormalities
Carbohydrate Digestion
Mouth: Salivary amylase hydrolyses a1-4 bonds
Duodenum: Pancreatic Amylase a1-4 bonds
Jejunum -
Isomaltase: Hydrolyses a1-6 bonds
Glucoamylase: removes Glc sequentially from non-reducing ends
Sucrase Hydrolyses Sucrose
Lactase: Hydrolyses Lactose
Cellulose and Hemicellulose
Oligosaccharides
Cannot be digested - Increase faecal bulk
Lactose Intolerant
Lactose is osmotically active draining water in small intestine - diarrhoea
Bacteria in gut break down undigested lactose causing gas to build up
Absorbed Glucose
Glc diffuses through intestinal epithelium to blood and liver where is phosphorylated into G6P by hepatocytes
G6P cannot diffuse out of cells since GLUT cannot recognise it
Glucokinase
Hexokinase
High Km and Vmax (When Glc is high in concentration it quickly phosphorylates to G6P in *liver)
Low Km and Vmax (When Glc is low in concentration it quickly phosphorylates to G6P in tissues, it is easily satisfied-efficient)
Where is G-6-P (GLYCOGEN) found?
Liver
Skeletal muscles form lactate from G-6-P in Glycolysis
Glycogen Synthase
Glycogenin covalently binds Glc from Uracil Diphosphate (UDP)-Glc to form chains of 8Glc Recidues
Glucose Synthase extends the Glc chains
Glycogen Branching Enzyme breaks chains
Glycogen Degradation
1) Glc monomers are removed one at a time from the non-reducing ends as G1P by Glycogen Phosphorylase
2) Transferase activity of de-branching enzyme removes a set of 3Glc Residues and attaches them to the nearest non-reducing end via (a1-4) bond
3) Glycosidase removes final Glc by breaking (a1-6) linkage to release free Glc
McArdles’s Disease
Skeletal Muscle Phosphorylase Deficiency
Cramps, High muscle Glycogen
