MONOSACCARIDE
Carbohydrates are the body's primary source of energy. Carbohydrates play a crucial role in a healthy, balanced diet. For example, without carbohydrates, our body would lack a key fuel source.
Types of carbohydrate:
1. Monosaccharides
2. Oligosaccharides ( formed when few monosaccharides are linked)
3. Polysaccharides ( formed when many monosaccharides are bonded together)\
Ex: glycogen, starch, cellulose
Note: The reaction that adds monosaccharide units to a growing carbohydrate involved the loss of one H2O to each new link formed, accounting on the difference general formula
Monosaccharide
Dihydroxyacetone (ketotrise)
Carbohydrates are the body's primary source of energy. Carbohydrates play a crucial role in a healthy, balanced diet. For example, without carbohydrates, our body would lack a key fuel source.
Types of carbohydrate:
1. Monosaccharides
2. Oligosaccharides ( formed when few monosaccharides are linked)
3. Polysaccharides ( formed when many monosaccharides are bonded together)\
Ex: glycogen, starch, cellulose
Note: The reaction that adds monosaccharide units to a growing carbohydrate involved the loss of one H2O to each new link formed, accounting on the difference general formula
Monosaccharide
- General formula: (CH2O) , n ≥ 3
- Can be polyhydroxy aldehyde (aldose) or polyhydroxy ketone (ketose)
- Simplest monosaccharides contain 3 carbon atoms are called trioses
Dihydroxyacetone (ketotrise)
- Most common sugars are aldoses rather than ketoses
- D-glucose: adehyde group is written at 'top' and designated as C-1
- D-fructose: ketone group becomes C-2, the C atom next to the 'top'
- no. of Carbon atoms are numbered in sequence from the 'top'
- the designated of the configuration as L or D depends on the arrangement at the chiral carbon with highest number.
chiral carbon is a carbon that attach to 4 difference types of atom / 4 different groups of atoms
- D configuration: hydroxyl group (-OH) is on the right of the highest number of chiral carbon
- L configuration: hydroxyl group (-OH) is on the left of the highest number iif the chiral carbon
Based on figure 2.0
- diastereomers: nonsuperimposable, nonmirror-image stereoisomers. Ex: D-Erythrose and D-Threose
- epimers: diastereomers that differ from each other in the configuration at only one chiral carbon. Ex: D-Erythrose, D-Threose
Based on Figure 3.0
- Aldopentoses have 3 chiral carbons and have 8 possible stereoisomers- 4 D forms, 4 L forms.
- Aldohexoses have 4 chiral carbons and have 8 possible stereoisomers- 8 D forms, 8 L forms
How do monosaccharides react?
1. Oxidation and reduction reactions of sugars play key roles in biochemistry.
2. Oxidation of sugars provides energy for organism to carry out their life processes
3. Highest yield of carbohydrate occurs when sugars are completely oxidized to carbon dioxide and water in aerobic processes.
4. The reverse of complete oxidation of sugars is the reduction of Carbon dioxide and water to form sugars (photosynthesis)
1. Oxidation and reduction reactions of sugars play key roles in biochemistry.
2. Oxidation of sugars provides energy for organism to carry out their life processes
3. Highest yield of carbohydrate occurs when sugars are completely oxidized to carbon dioxide and water in aerobic processes.
4. The reverse of complete oxidation of sugars is the reduction of Carbon dioxide and water to form sugars (photosynthesis)
POLYSACCHARIDE
When many monosaccharides linkes together, the result is polysaccharides. Polysaccharides that occur in organism are usually composed of a very few types of monosaccharide components.
Polymer that consist of one type of monosaccharide: homopolysaccharide
polymer consist of more than one type of monosaccharide: heteropolysaccharide4
STARCH
Figure 4.0 shows that
When many monosaccharides linkes together, the result is polysaccharides. Polysaccharides that occur in organism are usually composed of a very few types of monosaccharide components.
Polymer that consist of one type of monosaccharide: homopolysaccharide
polymer consist of more than one type of monosaccharide: heteropolysaccharide4
STARCH
- starches are polymers of α-D-Glucose that occur in plant cells
- Note that there is an alpha linkage in starch, in contrast with the beta linkage in cellulose.
- The types of starches can be distinguish from one another by their degree of chain branching
Figure 4.0 shows that
- amylose and amylopectin are the two forms of starch
- Note that the linear linkage of amylose is alpha (1 to 4), but the branches in amylopectin are alpha (1 to 6)
- Branches om polysaccharides can involve any of the hydroxyl group on the monosaccharide components
- Amylopectin is highly branch structure.
GLYCOGEN
- Glycogen is a branched-chain polymer of α-D-Glucose
- Like amylopectin, Glycogen cosist of chain of alpha (1 to 4) linkages and alpha (1 to 6) linkages at branch points
- Differences of amylopectin and glycogen is that glycogen are more highly branched
CHITIN
- Chitin is polysaccharide that is similar to cellulose in both structure and function.
- Chitin is homopolysaccharides which all the residues linked in beta (1 to 4) glycosidic bonds
- Chitin differs from cellulose in the nature of the monosaccharide units; in cellulose, the monomer is β-D-Glucose; in chitin, the monomer is N-acetyle-β-D-Glucosamine
Mary K. Campbell, Shawn O. Farrel. Biochemistry: fifth edition. THOMSON, United States of America. 2006
carbohydrate metabolism
Catabolism
Oligosaccharides and/or polysaccharides are typically cleaved into smaller monosaccharides by enzymes called glycoside hydrolases. The monosaccharide units then enter monosaccharide catabolism. Organisms vary in the range of monosaccharides they can absorb and use and they can also vary in the range of more complex carbohydrates they are capable of disassembling.
Metabolic pathways
- Carbon fixation, or photosynthesis, in which CO2 is reduced to carbohydrate.
- Glycolysis - the oxidation metabolism of glucose molecules to obtain ATP and pyruvate
- Pyruvate from glycolysis enters the Krebs cycle, also known as the citric acid cycle, in aerobic organisms after moving through pyruvate dehydrogenase complex.
- The pentose phosphate pathway, which acts in the conversion of hexoses into pentoses and in NADPH regeneration. NADPH is an essential antioxidant in cells which prevents oxidative damage and acts as precursor for production of many biomolecules.
- Glycogenesis - the conversion of excess glucose into glycogen as a cellular storage mechanism; this prevents excessive osmotic pressure buildup inside the cell
- Glycogenolysis - the breakdown of glycogen into glucose, which provides a glucose supply for glucose-dependent tissues.
- Gluconeogenesis - de novo synthesis of glucose molecules from simple organic compounds. An example in humans is the conversion of a few amino acids in cellular protein to glucose.
Energy productionTypically, a breakdown of one molecule of glucose by aerobic respiration (i.e. involving both glycolysis and Kreb's cycle) is about 33-35 ATP.[1] This is categorized as:
- Anaerobic breakdown by glycolysis - yielding 8-10 ATP
- Aerobic respiration by kreb's cycle - yielding 25 ATP
GLUCOREGULATION
Glucoregulation is the maintenance of steady levels of glucose in the body; it is part of homeostasis, and so keeps a constant internal environment around cells in the body.
The hormone insulin is the primary regulatory signal in animals, suggesting that the basic mechanism is very old and very central to animal life. When present, it causes many tissue cells to take up glucose from the circulation, causes some cells to store glucose internally in the form of glycogen, causes some cells to take in and hold lipids, and in many cases controls cellular electrolyte balances and amino acid uptake as well. Its absence turns off glucose uptake into cells, reverses electrolyte adjustments, begins glycogen breakdown and glucose release into the circulation by some cells, begins lipid release from lipid storage cells, etc. The level of circulatory glucose (known informally as "blood sugar") is the most important signal to the insulin-producing cells. Because the level of circulatory glucose is largely determined by the intake of dietary carbohydrates, diet controls major aspects of metabolism via insulin. In humans, insulin is made by beta cells in the pancreas, fat is stored in adipose tissue cells, and glycogen is both stored and released as needed by liver cells. Regardless of insulin levels, no glucose is released to the blood from internal glycogen stores from muscle cells.
The hormone glucagon, on the other hand, has an effect opposite to that of insulin, forcing the conversion of glycogen in liver cells to glucose, which is then released into the blood. Muscle cells, however, lack the ability to export glucose into the blood. The release of glucagon is precipitated by low levels of blood glucose. Other hormones, notablygrowth hormone, cortisol, and certain catecholamines (such as epinepherine) have glucoregulatory actions similar to glucagon.