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

2. 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

3. 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

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

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

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

7. 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

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

9. 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

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

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

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

13. 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.

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

15. 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

16. 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!

17. 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

18. 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.

19. 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:

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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?

27. 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.

28. 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.

29. 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)

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

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

32. 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

33. 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

34. 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