Carbohydrates Flashcards
What are is the function of carbohydrates
Highly oxidizable - major metabolic process
Store potential energy - glycogen
Structural/protective - ECM of cells
Contribute to cell-to-cell communication - ABO blood groups
What are monosaccharides
Carb with one sugar subunit
3 hexoses (6C sugars) - Glucose (Glc), Galactose (Gal), Fructose (Fru)
What are disaccharides
Monosaccharide monomers, linked by glycosidic bond
3 important - Maltose, Lactose, Sucrose
What is a glycosidic bond
Covalent bond between hydroxyl group and anomeric carbon
What is an anomeric carbon
Different anommers are mirros images
C 1 on Glc residue
Stabilises Glc structure
Only residue that can be oxidised
Describe maltose
Anomeric C-1 can be oxidised
Reducung sugar
Describe Lactose
Glycosidic bond between galactose and glucose
Anomeric C on glucose is oxidised, reducing sugar
Describe Sucrose
No free anomeric C-1
no oxidiation site
non-reducing sugar
Descibre Polysaccharides
Long chain carbs, many monosaccharide monomers
Homopolysaccharides - single monomeric species
Heteropolysaccharides - Two or more monomeric species
Descibe Starch
Two types of Glc polymers:
Amylose (20-25%) - (α1→4) join glucose chains
Amylopectin (75-80%) - (α1→6) create branches
Many non-reducing ends, few reducing
Describe Oligosaccharides
Polymer with small numbers of monsaccharides
Cell regeneration and cell adhesion
Lack in diet lead to poor health
Describe the digestion of Carbs
Mouth - Salivary amylase hydrolyses (α1→4) bonds of starch
Stomach - no carb digestion
Small intestines
Describe the digestion of carbs in small intestines
Isomaltase - hydrolyses (α1→6) bonds
Glucoamylase – removes Glc sequentially from non-reducing ends
Sucrase – hydrolyses sucrose
Lactase – hydrolyses lactose
Describe the absorbtion of glucose
- Absorbed indirectly by ATP into epithelial cells
- Glucose and Na+ transported at same time down Na+ conc. gradient
- Works continually even when blood glucose is high
Describe the absorbtion of Galactose
Similar to glucose, using conc. gradients to facilitate transport
Describe the absorbtion of Fructose
Binds to channel protein GLUT5
Moves down conc. gradient, high in gut lumen low in blood
Fate of absorbed glucose
Absorbed by intesine epithelial cells into blood towards liver
Phosphorolated to glucose-6-phosphate by hepatocytes
G6P cannot diffuse out cell
What enzymes catalysts are there for glucose absorbtion
Glucokinase (liver)
Hexokinase (other tissues)
Describe Glucokinase
Blood Glc is high
High glucokinase Vmax can phosphorylate Glc quickly
Most absorbed Glc trapped in liver
Describe hexokinase
Hexokinase low Km means at low Glc, tissues can absorb effectively
Hexokinase low Vmax, tissues “easily satisfied”, don’t keep absorbing Glc
What is the function of glycogen
Energy storage
90% in:
Liver - replenishes blood glucose when fasting
Skeletal muscle - catabolism produces ATP for contraction
Describe glycogen synthesis
Step 1:
- Glygogenin (enz) covalently bonds Glc from (UDP)-glucose to chains of 8 Glc
- Glycogen synthase extends Glc chains
Step 2:
- Glycogen chains broken by glycogen-branching enzyme and re-attached by (α1→6) bonds to give branch points
What is the process of glycolysis
1 - Phosphorylation of Glc - hexokinase, 1 ATP used
2 - G-6-P to F-6-P
3 - F-6-P to F-1,6-bisP
6 - Oxidation of Glyceraldehyde-3-P to 1,3-bisPGlycerate - 2 NADH produced
7 - Pi transfer from 1,3-bisPG to ADP = 3-PG, 2 ATP produced
10 - Transfer of Pi from PEP to ADP = Pyruvate, 2 ATP produced
What happens to pyruvate
- Ethanol
- Lactate
- CO2
