Lecture 2: Macromolecules
Sugars & Lipids

Cells Contain 4 Major Types of Giant Molecules (Macromolecules, Polymers)

• Proteins
• Polysaccharides
• Nucleic Acids
• Some Lipids: molecules not as big as the other groups- some quite small

Biological Polymers are Made From About 60 Small Building Blocks

• Cells contain thousands of types of giant molecules (macromolecules, polymers)
• Polymers are macromolecules made from a single building block molecule
• Most of the macromolecules are made from about 60 types of small building block molecules
• Most macromolecules are linear: building blocks linked head to tail- a few have branches (some polysaccharides)
• This is what you would get if you heated cells in hydrochloric acid overnight at 110 degrees C:

Building Blocks	Number of Kinds	Polymers
Amino Acids	20	Proteins
Fatty Acids	10	Storage Lipids/Membranes
Sugars & Relatives	10	Polysaccharides/Nucleic Acids
Nucleotides	5	Nucleic Acids
Others	15	All of Above

Making Macromolecules Involves Dehydration and Requires Energy

• Macromolecules naturally break down into their building blocks
• Hooking the building blocks together to make polymers requires energy from ATP
• ATP is the "energy currency of the cell" (a little like the dollar)
• Each time a bond is formed to make a macromolecule water is removed (dehydration)
• When macromolecules break down spontaneously they take up water (hydrolysis); this is what happens in digestion
  

Polysaccharides are Made from Small Sugar Molecules

• Carbohydrates are small sugars and sugar polymers (polysaccharides)
• Most of the sugars have 3-7 carbons; 6 is the most common
• Hydrate refers to water.
• Notice that most of the carbons in carbohydrates have OH (hydroxyl) on one side and H on the other. If you put the OH and H together you will get water. If you take common cane sugar (sucrose) and treat it with concentrated sulfuric acid it will pull the water off and you will see the black carbon left behind.
• Each small sugar molecule contains either an aldehyde group or a keto group (the 3 below all have aldehyde groups at one end- to see keto groups look at the formulas for fructose or ribulose in your textbook)

Glucose	Deoxyribose	Ribose

• These are 3 biological carbohydrates that are good to know. Glucose is the major source of energy in our bodies (and in the bodies of most organisms). It has 6 carbons and in the process of glycolysis is split into two 3 carbon pyruvic acids. If the cell is aerobic it is eventually oxidized in the Krebs cycle to CO2 and water. Can you spot the aldehyde and hydroxyl groups?
• The other 2 sugars have 5 carbons. They are found in the molecules of heredity, DNA (deoxyribose) and RNA (ribose). Notice that deoxy ribose is missing the oxygen at the second position.
• These 3 sugars are monosaccharides (1 sugar). Two sugars attached together = disaccharide (example = cane sugar or sucrose)
• Sugars usually curl up into rings in water solutions. Here are the ring forms of deoxyribose and ribose:

Deoxyribose (ring form)	Ribose (ring form)

Polysaccharides are Used for Structure and Energy Storage

• Glycogen: energy storage in animals (4 Calories/gram)
• Starches: energy storage in plants
• Cellulose: forms plant cell walls
• Chitin: forms exoskeleton (external skeleton) of arthropods- contains amono group
• Some sugars are attached to membrane proteins (example: ABO blood groups)

Different Polysaccharides Have Different Bonds Between the Sugars

• In polysaccharides the sugars are linked at different positions; also the links may have different orientations
• Both starch and cellulose are polymers of glucose, with the number 1 carbon of one sugar attached to th e number 4 carbon of the next sugar.
  • Orientation of the bonds is different -> quite different properties
  • We can use starch for food but not cellulose: we do not have digestive enzymes to split cellulose

Lipids are a Group of Hydrophobic Molecules

• Lipids have no common structure. They are a group of compounds that do not like to associate with water, that is, they are hydrophobic. If you put them into a test tube containing oil and water they will go into the oil (oil/water partition test).
  
  
• Oil/water partition tests:
  • L tube: a layer of oil floats above layer of water
  • Middle tube: red hydrophobic dye moves into oil
  • R tube: blue hydrophilic dye goes into water
• Some lipids are amphipathic- have both hydrophobic and hydrophilic ends; these molecules will accumulate at boundary of oil & water (act like detergents)
• Two important groups of lipids, phospholipids and triglycerides, are based upon glycerol and fatty acids. Glycerol and phosphate are not in themselves lipids, but are parts of large lipid molecules.
• Fatty acids sometimes have double bonds between 2 or more carbons
  • This puts a kink in the chain (see text figure 5.12)
  • Such fatty acids are unsaturated (fewer hydrogen atoms)
  • Unsaturated fats are more liquid than saturated fats (they don't pack together as well)
  • Membranes made with unsaturated fats are more permeable than those made with saturated fats

Fatty Acid (usally 16-18 carbon atoms)	Glycerol	Phosphate

• If you attach a fatty acid to each of the 3 hydroxyl (OH) groups in glycerol you get a triglyceride (sometimes called a neutral fat):

Triglyceride (Neutral Fat)

• This is the fat that we store around our waists. Hibernating and migrant animals store lots of triglycerides for energy reserves. It is the best way to store energy for long-term use because you get 9 Calories per gram instead of only 4 Calories per gram when you store carbohydrates. We store enough fat to provide energy enough to walk about 1000 miles.
• Phospholipids are like triglycerides except that only 2 fatty acids are attached to the glycerol. The third position is attached to phosphate and other polar (water-loving) molecules. This gives phospolipids both hydrophobic and hydrophilic sides and this structure is ideal for forming cell membranes.
• Steroids have 4 rings, which makes the molecule very flat and stiff. The best known steroid is cholesterol. Too much cholesterol causes clogging of the arteries, but in the right amount it is very useful. It is essential for cell membranes (it keeps them from falling apart) and is a precursor for several hormones, including cortisone, aldosterone and both male and female sex hormones.

Cholesterol

Estradiol (female sex hormone)	Testosterone (male sex hormone)

• Notice that the male and female sex hormone are very similar. They differ by only a hydroxyl group (OH), a methyl group (CH3) and a couple of double bonds in the ring. Do you appreciate the power of chemistry?

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