The Chemistry of Living Systems CHAPTER 18 The Chemistry of Living Systems 18.1 Fats and Carbohydrates

Reactants → Products ∆H In a chemical reaction molecules are converted into new ones, and energy is either absorbed (DH > 0) or released (DH < 0). Reactants → Products ∆H Chemical reactions occur in the body and in nature and are responsible for life Nature uses fat and carbohydrate molecules for energy and for structural purposes

Our bodies break down carbohydrates for energy, and the excess is stored away Polar bears have a diet that is rich in fats. More energy is stored in fats than in carbohydrates. Trees use cellulose, a type of carbohydrate, to grow tall without falling over Nature uses fat and carbohydrate molecules for energy and for structural purposes

Carbohydrates Carbohydrates are polymers, and the monomers are called monosaccharides Glucose Fructose One monosaccharide Another monosaccharide

From Chapter 17.2 Glucose 6-membered ring Fructose 5-membered ring

Simple carbohydrates Monosaccharides are individual sugar units Galactose Monosaccharides are individual sugar units Oligosaccharides contain 2-10 monosaccharides linked together Sucrose

Complex carbohydrates Monosaccharides are individual sugar units Oligosaccharides contain 2-10 monosaccharides linked together Polysaccharides contain more than 10 monosaccharides Starches, glycogen and cellulose are examples of polysaccharides

Remember: Optical isomers are stereoisomers that contain a carbon bonded to four different groups, and they rotate light differently chiral carbon

Ring structures Remember: Optical isomers are stereoisomers that contain a carbon bonded to four different groups, and they rotate light differently Our bodies can only metabolize the “D” form of glucose

Ring structures The position of the hydroxyl group is also important in carbohydrate chemistry

Condensation polymerization Units of a-D-glucose are linked together through condensation polymerization to form starch

Condensation polymerization Sucrose (or table sugar) is a disaccharides with two different monomers glucose fructose

Carbohydrates in our diet Simple carbohydrates are digested faster and get in the bloodstream quickly. Complex carbohydrates are digested slower (they keep us feeling full longer), and contain more fiber, vitamins and minerals.

Carbohydrates in our diet If you keep a piece of bread in your mouth, why does it begin to taste sweet?

Carbohydrates in our diet If you keep a piece of bread in your mouth, why does it begin to taste sweet? That is because enzymes in saliva begin to break down the complex carbohydrates into simple carbohydrates

Carbohydrates in our diet Our bodies use carbohydrates for energy. Excess carbohydrate is stored in the body in the form of glycogen in the liver and muscles. Glycogen can easily be reconverted to glucose if you need more energy. Only so much excess is stored as glycogen. The rest is converted to fat, which is more difficult to break down. Overeating carbohydrates will increase your body fat!

Nature uses carbohydrates for energy and structure Monosaccharides are individual sugar units Oligosaccharides contain 2-10 monosaccharides linked together Polysaccharides contain more than 10 monosaccharides Simple carbohydrates Complex carbohydrates Nature uses carbohydrates for energy and structure

Fats and oils Fats are solid at room temperature while oils are liquids. The formation of fats and oils is an efficient way for animals and plants to store energy. More energy per gram can be extracted from fats compared to carbohydrates.

Fats and oils Saturated fats are solid at room temperature, and stay solid in our bodies. They are dangerous because they can cause blockages in our arteries. Saturated fats are also more difficult to break apart than unsaturated fats Recall from Chapter 17.1:

Fats and oils Some fat molecules are necessary for our health Multiple sclerosis is a disease of the myelin, a fatty coating on nerve cells. In this scan of normal fat distribution in a human body the adipose tissue is yellow

The carboxylic group reacts with glycerol Fat molecules A fat molecule consists of a glycerol molecule attached to fatty acids a fatty acid chain The carboxylic group reacts with glycerol Fat molecules are nonpolar because of the long hydrocarbon chain on fatty acids glycerol

Triglycerides A triglyceride molecule is made of one glycerol molecule and three long-chain fatty acids glycerol 3 fatty acids 16 to 18 carbons in humans The fatty acid chains do not have to be identical

Triglycerides A triglyceride molecule is made of one glycerol molecule and three long-chain fatty acids glycerol 3 fatty acids With different fatty acids, fat molecules have a melting range rather than a single melting point

Fatty acids The first double bond is the third carbon-carbon bond from the end of the chain Omega-3 fatty acid Carboxylic acid head group

Fatty acids Omega-3 fatty acid unsaturated fatty acid Omega-3 fatty acid Unsaturated fatty acids tend to be liquids at room temperature and are better for your health

How do fat molecules travel in our body? glycerol 3 fatty acids A nonpolar molecule Our blood and body fluids are mostly water, which is polar. How do fat molecules travel in our body?

We need something that is polar and nonpolar. glycerol 3 fatty acids A nonpolar molecule Our blood and body fluids are mostly water, which is polar. We need something that is polar and nonpolar.

We need something that is polar and nonpolar. Replace a fatty acid chain with a polar group glycerol polar nonpolar Our blood and body fluids are mostly water, which is polar. We need something that is polar and nonpolar.

Phospholipids A phospholipid molecule consists of one glycerol molecule attached to two fatty acids and a phosphate group phosphate group (polar) 2 fatty acid chains (nonpolar)

Phospholipids Hydrophilic head (“likes water”) Hydrophobic tails (“fears water”)

interacts with lipid (fat) Phospholipids A phospholipid molecule is often represented like this: Hydrophobic tails interacts with lipid (fat) Hydrophilic head interacts with water

Phospholipids Lipoprotein in blood Phospholipids can form a small sphere called a micelle This way, they keep the hydrophobic tails away from the surrounding water Lipoproteins are micelle structures that also contain proteins on the surface

Phospholipids Phospholipids can also be used to separate two aqueous regions by forming a phospholipid bilayer. Cell membranes are made up of phospholipid bilayers Hydrophobic Hydrophilic

Unsaturated fatty acids (with double bonds) are better for your health Triglyceride Phospholipid hydrophobic glycerol 3 fatty acids hydrophilic Unsaturated fatty acids (with double bonds) are better for your health phospholipid bilayer