III - Carbohydrates Flashcards
Most abundant organic molecules in nature
Carbohydrates
Empiric Formula: (CH2O)n - hydrates of carbon
Carbohydrates
Functions of Carbohydrates
energy source, storage form of energy, part of cell membranes, structural components
Polymers of repeating sugar units
Carbohydrates
One sugar unit
monosaccharide
Two sugar units
disaccharide
3-10 sugar units
oligosaccharide
> 10 sugar units
polysaccharide
How many sugar units do monosaccharides have?
One
How many sugar units do disaccharides have?
Two
How many sugar units do oligosaccharides have?
3-10
How many sugar units do polysaccharides have?
> 10
The simplest and most basic form of carbohydrate hence cannot be hydrolyzed further
monosaccharide
From fruit juices, hydrolysis of cane sugar, maltose and lactose
Glucose
The “sugar of the body”, carried by the blood, principal sugar used by the tissues
Glucose
Present in urine in DM owing to its high levels in the blood
Glucose
Found in fruit juices, honey, hydrolysis of cane sugar and inulin (from the Jerusalem artichoke)
Fructose
Can be changed to glucose in the liver and so used in the body
Fructose
Hereditary _____ intolerance leads to _____ accumulation and hypoglycemia
Fructose
From the hydrolysis of lactose
Galactose
Can be changed to glucose in the liver and metabolized, synthesized in the mammary gland to make the lactose of milk, a constituent of glycolipids and glycoproteins
Galactose
Failure to metabolize _____ leads to cataracts
Galactose
from the hydrolysis of plant mannans and gums
Mannose
A constituent of many glycoproteins
Mannose
Monosaccharide found in nucleic acids
Ribose
Monosaccharides found in glycoproteins
Xylose, Arabinose, Mannose
Monosaccharide found in proteoglycans
Neuraminic Acid
Monosaccharide found in cardiac tissue
Lyxose
Ribose is found in
nucleic acids
Xylose is found in
glycoproteins
Arabinose is found in
glycoproteins
Mannose is found in
glycoproteins
Neuraminic Acid is found in
proteoglycans
Lyxose is found in
cardiac tissue
Condensation product of two monosaccharide units, linked by glycosidic bonds
disaccharide
Glucose + Glucose
Maltose - α(1→4)
Glucose + Galactose
Lactose - β(1→4)
Glucose + Fructose
Sucrose - α1→β2
From germinating cereals, malt, digestion by amylase or hydrolysis of starch
Maltose
From milk, found in urine during pregnancy
Lactose
From sorghum, pineapples, carrots, cane and beet sugar
Sucrose
From fungi and yeasts, the major source of insect hemolymph
Trehalose
Condensation product of 3-10 monosaccharides, most are not digested by human enzymes, maltotriose
Oligosaccharide
Condensation product of >10 monosaccharides, may be linear or branched, easily digested
Polysaccharide
Homopolymer of glucose forming an α-glucosidic chain called glucosan or glucan
Starch
Most important dietary source of carbohydrate in cereals, potatoes, legumes and other vegetables
Starch
Storage polysaccharide in animals (“animal starch”)
Glycogen
More highly branched structure than amylopectin with chains of 12-14 α-D-glucopyranose residues with α(1→4) glycosidic linkage with branching via α(1→6) glycosidic bonds
Glycogen
Polysaccharide of fructose used to determine the GFR
Inulin
Chief constituent of plant cell walls, fiber, cannot be digested
Cellulose
Insoluble and consists of β-D-glucopyranose units linked by β(1→4) bonds to form long, straight chains strengthened by cross-linking H-bonds
Cellulose
Also known as mucopolysaccharides
Glycosaminoglycans
Complex carbohydrates containing amino sugars and uronic acids
Glycosaminoglycans
May be attached to a protein molecule to form a proteoglycan
Glycosaminoglycans
Also known as mucoproteins, found in cell membranes
Glycoproteins
Proteins containing branched or unbranched oligosaccharide chains
Glycoproteins
Compounds that have the same chemical formula but different structures
Isomers
Compounds that differ in configuration around only one specific carbon atom with the exception of the carbonyl atom
Epimers
Pairs of structures that are mirror images of each other
Enantiomers/Stereoisomers/Optical Isomers - Dextro- (R), Levo- (L)
More common configuration of sugars in the body (D vs. L)
Dextro- (R)
Compounds that differ in configuration (linear/ring)
Anomers
More common configuration of sugars in the body (linear vs. cyclic)
Cyclic
Linear form of sugars
Fischer Projection
Cyclic form of sugars
Haworth Projection
5C Ring
Furan
6C Ring
Pyran
α and β forms of sugar spontaneously interconvert through a process called
Mutarotation
Physical digestion in the mouth
Mastication
Amylase can only digest _____ glycosidic bonds
α(1→4) - glycogen
Facilitates diffusion for all sugars, found in the basement membrane
GLUT-2 Transporter
Facilitates diffusion for all sugars, found in the lumen of the SI
GLUT-5 Transporter
A secondary active transporter for glucose and galactose (needs Na-K-ATPase), Na/hexose symporter, for glucose and galactose
SGLT-1 Trasporter
Tells how fast a carbohydrate is absorbed compared to glucose and galactose
Glycemic Index
Fast Absorption: GI _ 1
GI > 1
Slow Absorption: GI _ 1
GI < 1
Food with ___ GI is beneficial for DM.
low GI
Disaccharidase deficiency found in Asians
Lactose Intolerance / Lactase Deficiency
Disaccharidase deficiency found in Greenland Eskimos
Isomaltase-Sucrase Deficiency
Acquired enzyme deficiency occurs during _____ where enzymes are removed in stool.
severe diarrhea
Sum of all the chemical reactions in a cell, tissue or the whole body
Metabolism
Synthesis of compounds from smaller raw materials
Anabolic Metabolism
An endergonic and divergent process
Anabolic Metabolism
Breakdown of larger molecules
Catabolic Metabolism
An exergonic and convergent process, usually oxidative
Catabolic Metabolism
Produces reducing equivalents and ATP mainly via the ETC
Catabolic Metabolism
Crossroads of metabolism, links anabolic and catabolic pathways
Amphibolic Metabolism
Regulators of Metabolism: signals from within the cell
substrate avaiability, product inhibition, allosteric activators/inhibitors
Regulators of Metabolism: communication between cells
gap junctions (direct contact), neurotransmitters (synaptic signaling), hormones (endocrine signaling)
Regulators of Metabolism: second messenger systems
calcium/inositol triphosphate (ITP), adenylyl cyclase system (cAMP), guanylate cyclase system (cGMP)
Inositol Triphosphate System: G Protein
Gq
Inositol Triphosphate System: Substrate
Phosphatidylinositol - found in the cell membrane, acted on by phospholipase C
Inositol Triphosphate System: 2nd Messengers
Diacyl glycerol (DAG) - activates protein kinase C, Inositol Triphosphate (ITP) - release intracellular Ca
Membrane-bound enzyme that converts ATP to cyclic AMP (cAMP) in response to hormones
Adenylyl cyclase
Hydrolyzes cAMP to 5’-AMP
cAMP phosphodiesterase
Adenylyl Cyclase System: G Protein
Gs - stimulates, increase cAMP, Gi - inhibits, decrease cAMP
Adenylyl Cyclase System: Substrate
ATP
Adenylyl Cyclase System: 2nd Messengers
cAMP - activates protein kinase A
GLUT-1 is found in
erythrocytes, brain, kidneys, colon, placenta
GLUT-2 is found in
liver, pancreatic β-cells, small intestines, kidneys
GLUT-3 is found in
brain, kidneys, placenta
GLUT-4 is found in
heart and skeletal muscle, adipose
GLUT-5 is found in
small intestines
GLUT Transporter in erythrocytes, brain, kidneys, colon, placenta
GLUT-1
GLUT Transporter in liver, pancreatic β-cells, small intestines, kidneys
GLUT-2
GLUT Transporter in brain, kidneys, placenta
GLUT-3
GLUT Transporter in heart and skeletal muscle, adipose
GLUT-4
GLUT Transporter in small intestines
GLUT-5
Function of GLUT-1
uptake of glucose
Function of GLUT-2
rapid uptake and release of glucose
Function of GLUT-3
uptake of glucose
Function of GLUT-4
insulin-stimulated uptake of glucose
Function of GLUT-5
absorption of glucose
Major pathway for glucose metabolism that converts glucose into 3C compounds to provide energy
Glycolysis
Glycolysis: Location
Cytoplasm, all cells
Glycolysis: Substrate
Glucose
Glycolysis: End-Product
Pyruvate or Lactate - depends on the availability of oxygen or mitochondria
Glycolysis: Rate-Limiting Step
fructose 6-phosphate → fructose 1,6-bisphosphate
Glycolysis: Rate-Limiting Enzyme
Phosphofructokinase 1
Occurs in cells with mitochondria in the presence of oxygen to produce Pyruvate
Aerobic Glycolysis
Occurs in cells without mitochondria without oxygen to produce Lactate
Anaerobic Glycolysis
3 Irreversible Steps in Glycolysis
Step 1: phosphorylation of glucose, Step 3: phosphorylation of fructose 6-phosphate, Step 10: formation of pyruvate
Glycolysis: Step 1
glucose → glucose 6-P
Phosphorylates glucose in the first step of glycolysis
Hexokinase or Glucokinase
Phosphorylates glucose in most tissues with low Km (high affinity) and low Vmax, inhibited by glucose 6-P
Hexokinase
Phosphorylates glucose in liver parenchyma and pancreatic islets with high Km (low affinity) and high Vmax, inhibited by fructose 6-P, induced by insulin
Glucokinase
Glucose phosphorylator that is saturated in the liver and acts in a constant rate to provide glucose 6-P to meet the cell’s need
Hexokinase
Glucose phosphorylator that removes glucose from the blood following a meal providing glucose 6-P in excess requirements for glycolysis which is used for glycogenesis and lipogenesis
Glucokinase
Glycolysis: Step 3
fructose 6-phosphate → fructose 1,6-bisphosphate
Phosphofructokinase 1 converts fructose 6-P to _____
fructose 1,6-BP
Converts fructose 6-P to fructose 1,6-BP
PFK1 - Phosphofructokinase 1
Phosphofructokinase 1 activators
fructose 2,6-BP, AMP
Phosphofructokinase 1 inhibitors
ATP, Citrate
Phosphofructokinase 2 converts fructose 6-P to _____
fructose 2,6-BP
Converts fructose 6-P to fructose 2,6-BP
Phosphofructokinase 2
Phosphofructokinase 2 activators
well-fed state - high insulin, low glucagon
Phosphofructokinase 2 inhibitors
fasting state - low insulin, high glucagon
Glycolysis: Step 10
phoshoenolpyruvate (PEP) → pyruvate
Forms pyruvate from PEP in glycolysis
Pyruvate kinase
Pyruvate kinase activator
fructose 1,6-BP - feedforward mechanism
Pyruvate kinase inhibitors
glucagon + cAMP = phosphorylation
ATP Consumption in Glycolysis
glucose → glucose 6-P (hoxokinase or glucokinase), fructose 6-phosphate → fructose 1,6-bisphosphate (phosphofructokinase 1)
ATP Production in Glycolysis
1,3-biphosphoglycerate → 3-phosphoglycerate (phosphoglycerate kinase), phosphoenolpyruvate → pyruvate (pyruvate kinase)
NADH Production in Glycolysis
glyceraldehyde 3-phosphate → 1,3-bisphosphoglycerate (glyceraldehyde 3-phosphate dehydrogenase)
Aerobic Glycolysis: Pyruvate
enters the Citric Acid Cycle
Aerobic Glycolysis: ATP Yield
6 or 8