1. 2.2 How Do Atoms Form Molecules?

2. 2.3 Why Is Water So Important To Life?
Many molecules dissolve easily in water.
Water is an excellent solvent, capable of dissolving a wide range of substances because of its positive and negative poles.
NaCl dropped into H2O
The positive end of H2O is attracted to Cl–.
The negative end of H2O is attracted to Na+.
These attractions tend to push apart the components of the original salt.

3. 2.3 Why Is Water So Important To Life?
Water as a solvent
Cl–
Na+ H
Na+
Cl– O H
Cl–
Na+
Fig. 2-8

4. 2.3 Why Is Water So Important To Life?
Water molecules tend to stick together.
Surface tension: water tends to resist being broken
Cohesion: water molecules stick together
Fig. 2-9

5. 2.3 Why Is Water So Important To Life?
Water can form ions.
Water spontaneously becomes H+ and OH–.
Acid solutions have a lot of H+ (protons).
Alkaline solutions have a lot of OH– (hydroxyl ions).
A base is a substance that combines with H+, reducing their numbers.
pH measures the relative amount of H+ and OH– in a solution.

6. 2.3 Why Is Water So Important To Life?
A water molecule is ionized.
(–)
(+) O O + H H H H
water
(H2O)
hydroxide ion (OH–)
hydrogen ion (H+)
Fig. 2-10

7. 2.3 Why Is Water So Important To Life?
pH measures acidity.
Acids have a pH below 7.
Bases have a pH above 7.
Neutral solutions have a pH of 7.
Buffers are substances that maintain a constant pH in a solution.

8. 2.3 Why Is Water So Important To Life?
The pH scale
stomach acid (2) lemon juice (2.3)
vinegar, cola (3.0)
1 molar hydrochloric acid (HCl)
black coffee (5.0)
normal rain (5.6) urine (5.7)
orange (3.5) tomatoes beer (4.1)
water from faucet milk (6.4) pure water (7.0)
household ammonia (11.9) washing soda (12)
drain cleaner (14.0) 1 molar sodium hydroxide (NaOH)
blood, sweat (7.4)
phosphate detergents chlorine bleach (12.6)
seawater (7.8–8.3)
baking soda (8.4)
oven cleaner (13.0)
toothpaste (9.9) 1 2 3 4
pH value 5 6 7 8 9 10 11 12 13 14
(H+ > OH–)
(H+ < OH–)
neutral (H+ = OH–)
100
10–1
10–2
10–3
10–4
10–5
10–6
10–7
10–8
10–9
10–10
10–11
10–12
10–13
10–14
increasingly acidic
increasingly basic
H+ concentration in moles/liter
Fig. 2-11

9. 2.3 Why Is Water So Important To Life?
Water interacts with many other molecules.
Oxygen released by plants during photosynthesis comes from water.
Water is used by animals to digest food and thus breakdown large biomolecules – hydrolysis reactions.
Water is produced in chemical reactions that combine small biomolecules forming larger, more complex ones – dehydration synthesis reactions.

10. 3.2 How Are Biological Molecules Joined Together Or Broken Apart?
Dehydration synthesis
The construction of large molecules yields water.
Small molecules are joined together to form large molecules.
During the joining of small molecules, water is released.
This water-releasing reaction is called dehydration synthesis.

11. 3.2 How Are Biological Molecules Joined Together Or Broken Apart?
Dehydration synthesis
dehydration synthesis + O HO O H HO OH HO OH O H H
(a)
Dehydration synthesis
Fig. 2-12a

12. 3.2 How Are Biological Molecules Joined Together Or Broken Apart?
Hydrolysis reactions
During the breakdown of large molecules, covalent bonds are broken, separating the subunits

13. 3.2 How Are Biological Molecules Joined Together Or Broken Apart?
Hydrolysis
hydrolysis + O HO OH HO O H HO OH O H H
(b)
Hydrolysis
Fig. 2-12b

14. 3.1 Why Is Carbon So Important To Life?
An organic molecule is one that contains carbon.
This is possible because carbon has four electrons in its outermost shell, leaving room for four more electrons from other atoms.
Therefore, carbon can form many bonds with other atoms.

17. 3.3 What Are Carbohydrates?
Carbohydrates are molecules composed of carbon, hydrogen, and oxygen in the ratio of 1:2:1.
They can be small single sugar molecules or long chains of single sugar molecules strung together.

18. 3.3 What Are Carbohydrates?
A simple sugar
CH2OH H O H H H O H H H H 6 5 4 3 2 1 H C C C C C C H HO OH H OH O O O H O O H H H H H OH
(a)
Glucose, linear form
(b)
Glucose, ring form
Fig. 2-13

19. 3.3 What Are Carbohydrates?
Monosaccharide: a carbohydrate consisting of one sugar molecule
Disaccharide: two sugars linked together
Polysaccharide: three or more sugars linked together

21. 3.3 What Are Carbohydrates?
Simple sugars, such as glucose, provide important energy sources for organisms.
Sucrose, such as table sugar, is a disaccharide containing one glucose molecule attached to a fructose molecule.

22. 3.3 What Are Carbohydrates?
Manufacture of a disaccharide
glucose
fructose
sucrose
CH2OH
CH2OH O
HOCH2 O O
HOCH2 O H H H H H H H H +
dehydration synthesis OH H H HO OH H O H HO HO O H HO
CH2OH HO
CH2OH H OH OH H H OH OH H O H H
Fig. 2-14

23. 3.3 What Are Carbohydrates?
A variety of simple sugars occurs in organisms.
Disaccharides store energy and are two simple sugars bonded together by a dehydration synthesis reaction, such as lactose (milk sugar) and sucrose (table sugar).
Polysaccharides store energy for long periods of time or can be structural. Starch in plants and glycogen in animals are energy storage molecules. Chitin (lobster shells) and cellulose (plant call walls) are polysaccharides which are structural.

24. 3.3 What Are Carbohydrates?
Cellulose structure
wood is mostly cellulose
plant cell with cell wall
close-up of cell wall
Hydrogen bonds cross-linking cellulose molecules
CH2OH H OH
CH2OH H OH O O H H H H H O OH H H O OH H O OH H H O OH H H O H H H H
individual cellulose molecules
bundle of cellulose molecules
cellulose fiber O O H OH
CH2OH H OH
CH2OH
Fig. 2-15

25. Molecular characteristics of lipids
3.4 What Are Lipids?
Molecular characteristics of lipids
Lipids are molecules with long regions composed almost entirely of carbon and hydrogen.
The nonpolar regions of carbon and hydrogen bonds make lipids hydrophobic and insoluble in water.

26. 3.4 What Are Lipids? Lipid classification
Group 1: Oils, fats, and waxes (Triglycerides)
Group 2: Phospholipids
Group 3: Steroids

28. Group 1: Triglycerides (continued)
3.4 What Are Lipids?
Group 1: Triglycerides (continued)
Fats and oils form by dehydration synthesis from three fatty acid subunits and one molecule of glycerol.
etc.
CH2
CH2
CH2 H O CH H C OH HO C
CH2
CH2
CH2
CH2
CH2
CH2
CH2 CH O H C OH + HO C
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
etc. O H C OH HO C
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
etc. H
glycerol
fatty acids
Fig. 2-16

29. Group 1: Triglycerides (continued)
3.4 What Are Lipids?
Group 1: Triglycerides (continued)
Fats and oils formed by dehydration synthesis are called triglycerides.
Triglycerides are used for long-term energy storage in both plants and animals.
etc.
CH2
CH2
CH2 O H O CH + H H H C O C
CH2
CH2
CH2
CH2
CH2
CH2
CH2 CH O O + H H H C O C
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
etc. O O H C O C
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
etc. + H H H
3 water molecules
triglyceride
Fig. 2-16

30. Group 1: Triglycerides (Fats) (continued)
3.4 What Are Lipids?
Group 1: Triglycerides (Fats) (continued)
Fatty acids of fats are said to be saturated and are straight molecules that can be stacked.
(a)
Beef fat (saturated)
Fig. 2-18a

31. Group 1: Triglycerides (Oils) (continued)
3.4 What Are Lipids?
Group 1: Triglycerides (Oils) (continued)
Unsaturated fatty acids have bends and kinks in fatty acid chains and can’t be stacked.
(b)
Peanut oil (unsaturated)
Fig. 2-18b

32. 3.4 What Are Lipids? Group 2: Phospholipids
Phospholipids have water-soluble heads and water-insoluble tails.
They are found in cell membranes in a double layer.
They are like oils except one fatty acid is replaced by a phosphate group attached to glycerol.

33. Group 2: Phospholipids (continued)
3.4 What Are Lipids?
Group 2: Phospholipids (continued)
The phosphate end of the molecule is water soluble; the fatty acid end of the molecule is water insoluble.
CH3
CH2
CH2
CH3 O–
CH2
CH2
CH2
H3C - N+ -
CH2 -
CH2 - O - P - O -
CH2 O
CH2
CH2 CH
CH3 O HC - O - C -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 - CH O
H2C - O - C -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH2 -
CH3
polar head
glycerol
fatty acid tails
(hydrophilic)
(hydrophobic)
Fig. 2-19

34. 3.4 What Are Lipids? Group 3: Steroids
Steroids contain four carbon rings fused together.
Various functional groups protrude from the basic steroid “skeleton”.
Cholesterol is a steroid found in cell membranes.

35. 3.4 What Are Lipids? Group 3: Steroids
Testosterone and estrogen are male and female reproductive hormones, respectively, and are steroids. OH
CH3
CH3 HC
CH3
CH2 HO
CH2
(b)
Estrogen
CH2 HC
CH3 OH
CH3
CH3
CH3
CH3 HO O
(a)
Cholesterol
(c)
Testosterone
Fig. 2-20

36. 3.5 What Are Proteins? Functions of proteins
Proteins act as enzymes to catalyze many biochemical reactions.
They can act as energy stores.
They are involved in carrying oxygen around the body.
They are involved in muscle movement.

37. 3.5 What Are Proteins?
Some proteins are structural and provide support in hair, horns, spider webs, etc.
Fig. 2-21

39. Proteins are formed from chains of amino acids.
3.5 What Are Proteins?
Proteins are formed from chains of amino acids.
All amino acids have the same basic structure:
A central carbon
An attached amino group
An attached carboxyl group
An attached variable side group

41. 3.5 What Are Proteins? Amino acid structure variable group R H O
amino group
carboxylic acid group N C C H O H H
hydrogen
Fig. 2-22

42. 3.5 What Are Proteins?
More and more individual amino acids are added to the peptide until a polypeptide (protein) is formed.
amino acid
amino acid
peptide
water H R O H R O H R O H R O N C C + N C C N C C N C C + O H H O H H H O H H H H O H H H
amino group
carboxylic acid group
amino group
peptide bond
Fig. 2-23

43. Three-dimensional shapes give proteins their functions.
3.5 What Are Proteins?
Three-dimensional shapes give proteins their functions.
Long chains of amino acids fold into three-dimensional shapes in cells, which allows the protein to perform its specific functions.
When a protein is denatured, its shape has been disrupted and it may not be able to perform its function.

44. Structure of nucleic acids
3.6 What Are Nucleic Acids?
Structure of nucleic acids
Nucleic acids are long chains of similar, but not identical, subunits called nucleotides.

45. Structure of nucleic acids (continued)
3.6 What Are Nucleic Acids?
Structure of nucleic acids (continued)
All nucleotides have three parts.
A five-carbon sugar (ribose or deoxyribose)
A phosphate group
A nitrogen-containing molecule called a base

46. Deoxyribose nucleotide
3.6 What Are Nucleic Acids?
Deoxyribose nucleotide
base
NH2
phosphate C N C N OH HC O C CH N HO P O
CH2 N O
sugar H H H H OH H
Fig. 2-25

47. 3.6 What Are Nucleic Acids? Types of nucleotides
Those that contain the sugar ribose.
Those that contain the sugar deoxyribose.
Nucleotides string together in long chains as nucleic acids with the phosphate group of one nucleotide bonded to the sugar group of another.

48. 3.6 What Are Nucleic Acids? Nucleotide chain base sugar phosphate
Fig. 2-26

49. DNA and RNA, the molecules of heredity, are nucleic acids.
3.6 What Are Nucleic Acids?
DNA and RNA, the molecules of heredity, are nucleic acids.
There are two types of nucleic acids.
Deoxyribonucleic acid (DNA): contains the genetic code of cell
Ribonucleic acid (RNA): is used in the synthesis of proteins