Lesson 5 Carbohydrates PDF

Carbohydrates What Are Carbohydrates? Carbohydrates are used by organisms as Sources of energy Building material Cell-surface markers Cell communication They contain the elements carbon, hydrogen and oxygen in...

Carbohydrates What Are Carbohydrates? Carbohydrates are used by organisms as Sources of energy Building material Cell-surface markers Cell communication They contain the elements carbon, hydrogen and oxygen in a 1:2:1 ratio Types of  Carbohydrates Carbohydrates are classified into three groups Monosaccharides Simplest sugar Contains only one group Oligosaccharides Sugars containing several simple sugars attached to one another Polysaccharides Sugars containing several hundred to several thousand subunits Monosaccharides  Monosaccharides can be distinguished based on two features The length of their carbon chain (how many carbons are attached) The positioning of the carbonyl group Ketone (C=O) Aldehyde (HC=O) Most Common Monosaccharides Monosaccharides act as isomers Recall, isomers are molecules with the same chemical formula but a different  arrangement of atoms The most common monosaccharides are glucose, fructose and galactose All have the formula C6H12O6 Glucose and galactose are an aldehyde Fructose is a ketone Note: Fructose is the only 5-carbon ring Forms of Glucose There are two forms of glucose α-glucose Hydroxyl group at carbon 1 lies above the plane of the ring  β-glucose Hydroxyl group at carbon 1 lies below the plane of the ring Oligosaccharides Oligosaccharides contain two or three simple sugars together Often referred to as disaccharides The sugars are bonded through a glycosidic linkage This is a type of covalent bond, with a condensation reaction The most common disaccharides are maltose, sucrose and lactose  Maltose has a two α-glucose 1-4 glycosidic linkage Sucrose has α-glucose + α-fructose 1-2 glycosidic linkage Lactose has α-glucose + β-galactose 1-4 glycosidic linkage Disaccharides  Polysaccharides Polysaccharides are composed of hundreds to thousands of monosaccharides They serve two important functions in the cell Energy storage Most common polysaccharides are Starch and glycogen Structural support  Most common polysaccharides are Cellulose and Chitin Cellulose Cellulose is the most abundant polysaccharide found in plants This is what makes up the building material for plants exterior This is known as the cell wall It cannot be broken down Cellulose is made from the glycosidic linkage of β-glucose through a 1-4 glycosidic linkage Cellulose Cont’d  Cellulose can never branch It always remains as a straight chain As a result, the hydroxyl groups of parallel molecules can form many hydrogen bonds This produces tight bundles called microfibrils This is what makes cellulose tough Humans do not have enzymes to break this down Instead we consume plants for dietary roughage which means that it can scrape any waste in our stomach We get no nutritional value though Chitin  Chitin is found on the exoskeleton of insects and crustaceans It is a cellulose-like polymer of N-acetylglucosamine It has a nitrogen attached to the second carbon Like cellulose, it cannot be broken down Glycogen  When there is excess glucose in the body, they combine to form glycogen This acts as a storage unit in the liver and muscle cells Unfortunately, this form of energy depletes in a day if not used The structure contains α-glucose 1-4 linkage α-glucose 1-6 linkage between branches Starch Starch acts as the main storage unit in plants There are two types of starch  Amylose Amylopectin Unbranched chain Branched chain Simplest form More complex α-glucose 1-4 linkage α-glucose 1-4 linkage 1-6 linkage between branches Homework Complete Questions Pg.38, #2-3, 5