Carbohydrates, Lipids, & Proteins

Carbohydrates, Lipids, & Proteins http://bioweb.wku.edu/courses/biol115/wyatt/biochem/carbos.htm http://schools.nashua.edu/myclass/marshalll/anatomy/Pictures/Forms/DispForm.aspx?ID=32 Topic 3.2

Overview: The Molecules of Life • All living things are made up of four classes of large biological molecules: • Carbohydrates • Lipids • Proteins • Nucleic acids • Macromolecules - large molecules of thousands of covalently connected atoms • Molecular structure and function are inseparable

Concept 5.1: Macromolecules are polymers, built from monomers • Polymer - long molecule consisting of many similar building blocks called monomers • Three of the four classes of life’s organic molecules are polymers • Carbohydrates • Proteins • Nucleic acids

Organic compounds contain carbon and are found in living organisms.

Not all compounds that contain carbon are considered “organic”. They are referred to as “inorganic” HCO3- Na2HCO3 CO CO2 Oxides of carbon Hydrogen carbonates CO32- CaCO3 Na2CO3 Carbonates

If given the name could you draw the structure, or if given the structure could you give it a name?

The Synthesis and Breakdown of Polymers • A dehydration reaction occurs when two monomers bond together through the loss of a water molecule • Polymers are disassembled to monomers by hydrolysis, the reverse of the dehydration reaction Hydrolysis breaks bonds Condensation makes bonds Water splitting Water releasing Catabolic reactions are those which break down molecules (e.g. digestion) Anabolic reactions are those which build molecules (e.g. protein synthesis) All of these reactions require enzymes – biological catalysts.

Animation: Polymers Right-click slide / select “Play”

(a) Dehydration reaction: synthesizing a polymer Figure 5.2 1 2 3 Short polymer Unlinked monomer Dehydration removesa water molecule,forming a new bond. 1 4 2 3 Longer polymer (b) Hydrolysis: breaking down a polymer 4 2 3 1 Hydrolysis addsa water molecule,breaking a bond. 2 3 1

Figure 5.2a (a) Dehydration reaction: synthesizing a polymer 2 1 3 Unlinked monomer Short polymer Dehydration removesa water molecule,forming a new bond. 4 2 1 3 Longer polymer

Figure 5.2b (b) Hydrolysis: breaking down a polymer 4 2 1 3 Hydrolysis addsa water molecule,breaking a bond. 2 1 3

Concept 5.2: Carbohydrates serve as fuel and building material • Carbohydrates include sugars and the polymers of sugars • Simplest carbs are monosaccharides (single sugars) • Polysaccharides - carbohydrate macromolecules (polymers) composed of many sugar building blocks

Sugars • Monosaccharides have molecular formulas that are usually multiples of CH2O • Glucose (C6H12O6) is the most common monosaccharide • Monosaccharides are classified by • The location of the carbonyl group (as aldose or ketose) • The number of carbons in the carbon skeleton

Aldoses (Aldehyde Sugars) Ketoses (Ketone Sugars) Figure 5.3 Trioses: 3-carbon sugars (C3H6O3) Glyceraldehyde Dihydroxyacetone Pentoses: 5-carbon sugars (C5H10O5) Ribose Ribulose Hexoses: 6-carbon sugars (C6H12O6) Fructose Glucose Galactose

In aqueous solutions many sugars form rings • Monosaccharides: • Major fuel for cells • Raw material for building molecules

Figure 5.4 6 6 1 2 5 5 3 4 1 4 1 4 2 2 5 3 3 6 (a) Linear and ring forms of glucose 6 5 4 1 2 3 (b) Abbreviated ring structure

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A disaccharide - formed from dehydration reaction joining two monosaccharides • This covalent bond is called a glycosidic linkage

Animation: Disaccharide Right-click slide / select “Play”

Monosaccharides are the monomers of polysaccharides: condensation maltose + glucose glucose + water (disaccharide)

Polysaccharides • Polysaccharides, the polymers of sugars, have storage and structural roles • The structure and function of a polysaccharide are determined by its: • Sugar monomers • The positions of glycosidic linkages

Polysaccharides (such as starches) are polymers (more than two molecules). These structures are usually very long and may be branched. Glycosidic bonds can be 1-4 or 106 (carbon links) http://www.fas.org/irp/imint/docs/rst/Sect20/A12.html

State one function of glucose, lactose, and glycogen in animals, and of fructose, sucrose and cellulose in plants.

Storage Polysaccharides • Starch, a storage polysaccharide of plants, consists entirely of glucose monomers • Plants store surplus starch as granules within chloroplasts and other plastids • The simplest form of starch is amylose

Figure 5.6 Starch granules Chloroplast Amylopectin Amylose (a) Starch: a plant polysaccharide 1 m Glycogen granules Mitochondria Glycogen (b) Glycogen: an animal polysaccharide 0.5 m

Figure 5.6a Chloroplast Starch granules 1 m

Glycogen is a storage polysaccharide in animals • Humans and other vertebrates store glycogen mainly in liver and muscle cells

Figure 5.6b Glycogen granules Mitochondria 0.5 m

Structural Polysaccharides • Cellulose - a major component of the tough wall of plant cells • Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ • The difference is based on two ring forms for glucose: alpha () and beta ()

Animation: Polysaccharides Right-click slide / select “Play”

Concept 5.3: Lipids are a diverse group of hydrophobic molecules • Lipids - the one class of large biological molecules that do not form polymers • The unifying feature of lipids is having little or no affinity for water • Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bonds • The most biologically important lipids are fats, phospholipids, and steroids

Fats • Fats - constructed from glycerol and fatty acids • Glycerol - three-carbon alcohol with a hydroxyl group attached to each carbon • Fatty acid - a carboxyl group attached to a long carbon skeleton

Figure 5.10 Fatty acid(in this case, palmitic acid) Glycerol (a) One of three dehydration reactions in the synthesis of a fat Ester linkage (b) Fat molecule (triacylglycerol)

Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats • In a fat, three fatty acids are joined to glycerol by a dehydration (condensation) reaction creating an ester linkage, creating a triacylglycerol, or triglyceride

Figure 5.10b Ester linkage (b) Fat molecule (triacylglycerol)

Fatty acids vary in length (number of carbons) and in the number and locations of double bonds • Saturated fatty acids - the maximum number of hydrogen atoms possible and no double bonds • Unsaturated fatty acids - one or more double bonds

(b) Unsaturated fat – Usually plant fats & fish fats Figure 5.11 Saturated fat – most animal fats Structuralformula of asaturated fatmolecule Structuralformula of anunsaturated fatmolecule Space-fillingmodel of stearicacid, a saturatedfatty acid Space-filling modelof oleic acid, anunsaturated fattyacid Cis double bondcauses bending.

A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits • Hydrogenating vegetable oils (adding hydrogen) also creates unsaturated fats with trans double bonds • Trans fats may contribute more than saturated fats to cardiovascular disease

Phospholipids • Phospholipid - two fatty acids and a phosphate group are attached to glycerol • The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head

Figure 5.12 Choline Hydrophilic head Phosphate Glycerol Fatty acids Hydrophobic tails Hydrophilichead Hydrophobictails (a) Structural formula (b) Space-filling model (c) Phospholipid symbol

Phospholipids added to water form into a bilayer (think cell membrane), with the hydrophobic tails pointing toward the interior • Phospholipids are the major component of all cell membranes

Steroids • Steroids are lipids characterized by a carbon skeleton consisting of four fused rings • Cholesterol, an important steroid, is a component in animal cell membranes • High levels of cholesterol may contribute to cardiovascular disease

Carbohydrates, Lipids, & Proteins