Carbohydrates Flashcards
What are the functions of carbohydrates?
Energy source
Energy storage
Structural component
Immune function
Intracellular communication
What is the general formula of carbohydrates?
(CH2O)n
What is a 1 sugar carbohydrate?
Monosaccharide
What is a 2 sugar carbohydrate?
Disaccharides
What are 3-10 sugar carbohydrates?
Oligosaccharides
What are 11-100 sugar carbohydrates?
Polysaccharides
How do classify monosaccharides based on number of carbons?
3- trioses
4- tetroses
5- pentoses
6-hexoses
7- heptoses
8- nonoses
What is the aldose functional group?
O
II
R1-C-H
What is the ketose functional group?
O
II
R1-C-R2
What are isomers?
Compounds that have the same chemical formula but different structures
What are epimers?
Carbohydrate isomers that differ in configuration around only one specific carbon atom
What are enantiomers?
Pair of structures that are mirror images of each other
D - OH group on the right of the chiral carbon
L - OH group on the left of the chiral carbon
What is a pyranose ring?
5 carbon atoms a and 1 oxygen atom
What is a furanose ring?
4 carbon atoms and 1 oxygen atom
What are the three main disaccharides made from?
Sucrose = glucose + fructose = a-D-glucopyranosyl-(1–>2)-B-D-fructofuranoside
Maltos = glucose + glucose = a-D-glucopyranosyl-(1–>4)-B-d-glucopyranose
Lactose = galactose + glucose = B-d-galactopyranosyl-(1–>4)-B-D-glucopyranose
Cellulose
Structural polysaccharide
B1-4 glycosidic bonds between glucose and glucose
Humans do not have the enzyme to hydrolyse this bond so humans cannot digest cellulose
Major constituent of plant walls
Starch
Storage eplysaccharide
A1-4 glycosidic bonds between glucose and glucose
Amylose - unbranded only a1-4 linkages
and amylopectin - branched(every 20-30 residues) a1-4, a1-6
Glycogen
Branched polymer (every 8-10 residues)
Mainly a1-4 linkages, also a1-6 linkages
How are carbohydrates digested?
Mouth - salivary a-amylase hydrolysing a1-4 bonds - maltose and dextrin
Small intestine - pancreatic a-amylase - maltose and dextrin
Upper jejunum - brush border membrane-associated oligosaccharides and disaccharides of intestinal mucosal cells - glucoses, fructose, galactose- (enzymes - dextrinase, glucoamylase)
What are the enzymes involves in carbohydrate digestion?
Isomaltase - isomaltose into glucose
Maltase - maltose into glucose
Sucrase - sucrose into glucose and fructose
Lactase - lactose into galactose and glucose
Glucoamylase - cuts of single glucose molecules
Amylase - starch to maltose and dextrin
How are carbohydrates absorbed?
Monosaccharides are absorbed by intestinal muscle cells.
1. Glucose, galactose = taken up together by Na-dependent glucose cotranporter 1 (SCLT-1) into enterocyte. Na exchanged with K.
2. Fructose = taken up by Na-independent monosaccharide transporter (GLUT-5).
3. All 3 monosaccharides transported from intestinal cells into GLUT-2.
Deficiencies in carbohydrates degradation?
Hereditary deficiency of individual disaccharidases
Lactose intolerance -70-80% of population
Isomlatose/sucrose intolerance - 10% of greenlands Eskimos, 2% of North American’s are heterozygous
Symptoms - osmotic diarrhoea (underinvested carbs pass into large intestine, abdominal cramps, flactulence (bacterial fermentation of carbs produces large volumes of CO2 and H2)
Metabolism of glucose?
Glycogenesis - Glucose to glycogen
Glycogenolysis - glycogen to glucose
Pentode phosphate pathway - glucose to NADPH + Ribulose-5-P - ribulose-5-P then goes back to NADPH giving off Ribose-5-P
Glycolysis - glucose + 2ATP + 2NADH = 4ATP + pyruvate
Gluconeogenesis - pyruvate to glucose
Anaerobic glycolysis - pyruvate to lactate
Pyruvate to acetyl-CoA (2NADH = 6ATP)
Acetyl CoA to CO2 (2GTP, 6NADH=18ATP, 2FADH2=4ATP)
Catabolic or anabolic pathways?
Catabolic pathways - NADH - making energy
Anabolic pathways - NADPH - synthesising new molecules
