Carbohydrate – sugars, encompasses the monomers, called monosaccharides, small polymers called oligosaccharides, and large polymers called polysaccharides
5.1 Sugars as Monomers
1. How Monomers Differ
a. Monosaccharide – simple sugar, monomer
i. Carbonyl group serves as a distinguishing feature 1. At end of molecule, forms an aldehyde sugar (aldose) 2. In middle of molecule, forms a ketone sugar (ketose) ii. Presence of a carbonyl group along with multiple hydroxyl groups provides an array of functional groups in sugars iii. Number of carbons also varies in monosaccharides 3. Trioses (3), pentoses (5), hexose (6)
iv. Differences of structure is responsible for differences in function
v. Rare to see sugars exist in linear forms
4. Tend to form rings in aqueous solution
5.2 Structure of Polysaccharides
a. Polysaccharides – polymers formed when monosaccharides are linked together i. Disaccharide – simplest polysaccharide of two sugars b. Simple sugars polymerized through condensation reactions between two hydroxyl groups, forming a glycosidic linkage through a covalent bond c. Since glycosidic linkages form between hydroxyl groups and every monosaccharide contains at least two hydroxyl groups, location and geometry of glycosidic linkages varies widely between polysaccharides d.
α- linkages are easy for enzymes to break while β-linkages are difficult to break 2. Starch: A Storage Polysaccharide in Plants
e. Starch is made up of α-glucose monomers joined by glycosidic linkages ii. Mixture of unbranched amylose and branched amylopectin 3. Glycogen: A Highly Branched Storage Polysaccharide in Animals f. Glycogen performs the same storage role in animals that starch does in plants iii. Polymer of α-glucose
4. Cellulose: Structural Polysaccharide in Plants
g. Cellulose is a major component of the cell wall in plants iv.
Polymer of β-glucose monomers
1. Generates linear molecule rather than helix in α-glucose, and permits hydrogen bonding between adjacent, parallel strands of cellulose 5. Chitin: Structural Polysaccharide in Fungi and Animals h. Similar to cellulose, except of glucose, its made of “NAc” v. Also has β-linkages
6. Peptidoglycan: Structural Polysaccharide in Bacteria
i. Peptidoglycan gives bacteria cell wall strength and stiffness j.
Most complex of polysaccharides so far
k. Linked by β-glycosidic linkages
l. Chain of amino acids is attached to one of the two sugar types vi. Peptide bonds link amino acid chains to others on adjacent strands
5.3 What Do Carbohydrates Do
1. Role of Carbs as Structural Molecules
a. Cellulose and chitin, along with modified peptidoglycan, are key structural compounds i. Form fibers that give organisms strength and elasticity ii. Made of β-glycosidic linkages
b. Almost all organisms have enzymes to break α-linkages but only a few organisms have enzymes to break β-linkages iii. Shape and orientation of β-linkages make them difficult to break 2. Role of Carbs in Cell Identity
c. Polysaccharides do not store information, but do display it.
d. Glycoprotein is a protein that in covalently bonded to a carb, usually the relatively short chain of sugars call oligosaccharides e. Each cell of your body has glycoproteins on its surface that identify it as a part of your body f. The identification information displayed by glycoproteins helps cells recognize and communicate with each other 3. Role of Carbs in Energy Storage
g. Carbohydrates store and provide chemical energy in cells iv. Photosynthesis converts the kinetic energy in sunlight into chemical energy stored in the bonds of carbohydrates h. Both carbs and fats are used as fuel in cells, but fats store twice as much energy per gram compared to carbs i. Starch and glycogen are efficient energy-storage molecules because they polymerize via α-linkages v. α- linkages are readily hydrolyzed while β-linkages resist enzymatic degradation vi. Phosphorylase is the most important enzyme in catalyzing the hydrolysis of α-linkages in glycogen 1. Most of your cells contain phosphorylase
vii. Amylase is the enzyme involved in breaking α-linkages in starch j. When cells need energy, exergonic reactions lead to the breakdown of glucose and capture the released energy through synthesis of ATP viii. CH2O + O2 + ADP + P CO2 + H2O + ATP
ix. For example, carbohydrates are like water piled up behind a dam and ATP is the electricity generated at the dam. 2. Carbohydrates store chemical energy while ATP uses it.
Read more: Benedict’s Test Cellulose
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