Lecture 5: Carbohydrates (BIOL2000)
Lecture 5: Carbohydrates (BIOL2000) 200001
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This 6 page Class Notes was uploaded by Olivia Sutton on Wednesday February 17, 2016. The Class Notes belongs to 200001 at Boston College taught by Danielle Taghian in Spring 2016. Since its upload, it has received 37 views. For similar materials see Molecules and Cells in Biology at Boston College.
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Date Created: 02/17/16
Lecture 5: Intro to Carbohydrates Feb 3, 2016 Key Concepts Sugars and other carbs are variable in structure Monosaccharides are monomers that polymerize to form polysaccharides through different glycosidic linkages Carbs perform a variety of functions, from energy storage to formation of structures An Intro to Carbs Contain a carbonyl and several hydroxyl functional groups o Carbonyl: reacts to make the carb a large molecule o Hydroxyl: makes the carbs soluble in water Contain many carbon-hydrogen (C-H) bonds Difference between aldehydes and ketones is the location of the carbonyl group Monosaccharaides Vary in structure through: o Placement of carbonyl group o Different # of carbons o Hydroxyl group arrangements o Alternative ring forms (alpha or beta) Carbonyl Group Aldehyde sugar (aldose0: carbonyl is at the end of the molecule Ketone sugar (ketose): carbonyl is in the middle of carbon chain Number of Carbon Atoms Varies between: o Three – triose o Five – pentose o Six – hexose Directionality: carbon atoms are numbered starting at the end closest to the carbonyl group “Ose” is the suffix for carbohydrate “Ase “ is the subject for enzyme Arrangement of Hydroxyl Group Glucose vs. Galactose Same chemical formula but different structures = different functions Hydroxyl groups are what cause the condensation reactions when forming linkages between monosaccharides Alternative Ring Forms Sugars in aqueous solutions form ring structures Ex: Glucose When the cyclic structure forms in glucose, the C-1 carbon forms a bond with oxygen in the C-5 hydroxyl, and its carbonyl group becomes a hydroxyl group. Structure of Polysaccharides Simple sugars polymerize when condensation reactions occur between two hydroxyl groups Because glycosidic linkages form between hydroxyl groups, and every monosaccharide has at least 2 OH groups, the location and geometry of glycosidic linkages can vary widely among polysaccharides Multiple hydroxyl groups yield diverse molecules. This differs from protein and nucleic acid polymerization Starch Used for energy storage in plants (such as potatoes) Amylose: an alpha helical ring Amylopectin: has a branch point with another segment of monomer (1-6 linkage) Branches when an alpha-1,6 glycosidic bond forms between monomers of two strands About 1 in 30 glucose molecules contain these enzymes Glycemic Index: ratio of amylose to amylopectin in food o Amylose is good for longer duration because they take longer digest o Amylopectin is good for a short amount of time Glycogen Used for energy storage in animal cells (such as liver and muscles) Alpha-1,4 glycosidic linkages Similar to amylopectin except with more branches Cellulose Used for structural support in cell walls of plants and algae Beta-glucose monomers Linear strands (not helical) Long parallel strands held together by H bonds Chitin Used for structural support in fungi cell walls and component of insect and crustacean cytoskeleton Like cellulose, except monomers = N-acetyl glucosamine o Subunits form H bonds between adjacent strands -> results in tough, stiff sheet for protection Can be combined with calcium carbonate in exoskeleton of crustacean or with sclerotin in arthropods Peptidoglycan Used for structural support in bacterial cell walls Complex—long backbone w/ 2 types alternating monosaccharaides o Beta-1,4 glycosidic linkages Peptide bonds form between amino acids of adjacent strands *In cellulose, chitin, and peptigoglycan, the beta-1,4 glycosidic linkages resist enzymatic digestions How do penicillin and cephalosporin kill bacteria? Both bind tightly to enzymes that catalyze the formation of cross- link between individual strands within peptidoglycan Causes cell wall to weaken and break down Very few side effects in humans and very specific Bacteria have evolved enzymes to break these antibiotics down!!! Big resistance problems!! What Do Carbs Do? Important building blocks in the synthesis of other molecules: RNA and DNA act as “carbon skeletons” Also indicate cell identity, store chemical energy, and form fibrous structural materials that protect cells The Role of Carbohydrates in Cell Identity Although polysaccharides are unable to store information, the display information on the outer surface of cells form glycoproteins — proteins with covalent bonds to carbohydrates Many monosaccharaides = many unique oligosaccharides All of our brain cells pretty much run on carbs. Athletes who do low-carb diets run out of fuel pretty quickly Glycoprotein: carb attached to a protein. The Role of Carbohydrates in Energy Production and Storage In chemical evolution, the storage of energy in the chemical bonds of H 2O and HCN was the key step to the creation of complex organic molecules, including sugars When you break/make bonds, you exchange energy The electrons in C–H bonds are shared more equally and held less tightly than they are in C–O bonds. o Molecules with a long of C-H bonds store lots of energy Carbohydrates participate in exergonic reactions to produce ATP. o Exergonic: liberating energy The free energy in ATP is used to drive endergonic reactions and perform cell work o Endergonic: requiring energy Which is the best energy source? Glucose is an excellent energy source because there is a great decrease in free energy when it is oxidized by oxygen to yield carbon dioxide and water. How do Carbohydrates Store Energy? Phosphorylase: catalyzes hydrolysis of alpha-glycosidic linkages in glycogen Amylase: catalyzes hydrolysis of alpha-glycosidic linkages in starch Glucose is then converted into energy and the released glucose subunits can then be used in the production of ATP