1. Chapter 3 Molecules of Life (Sections 3.4 - 3.6)

2. 3.4 Lipids
Cells use lipids as major sources of energy and as structural materials
lipid
Fatty, oily, or waxy organic compound
All are hydrophobic (nonpolar), or have regions that are hydrophobic

3. Types of Lipids
Phospholipids are the main structural component of cell membranes
Waxes are lipids that are part of water-repellent and lubricating secretions

4. Key Terms
fat
Lipid that consists of a glycerol molecule with one, two, or three fatty acid tails

5. Saturated and Unsaturated Fats
Animal fats are saturated
Tend to remain solid at room temperature because their saturated tails pack tightly together
Most vegetable oils are unsaturated
Kinked tails do not pack tightly, so unsaturated fats are typically liquid at room temperature
Partially hydrogenated vegetable oils have a trans double bond that allows them to pack tightly, like saturated fats
Solid at room temperature

6. Fatty Acids

7. Trans and Cis

8. Phospholipids phospholipid
Lipid with a highly polar phosphate group in its hydrophilic head, and two nonpolar, hydrophobic fatty-acid tails
Main part of cell membranes
Opposing properties of a phospholipid molecule give rise to cell membrane structure
Two layers of lipids (lipid bilayer)
Hydrophobic tails sandwiched between hydrophilic heads

9. Phospholipids and Cell Membranes
Head is hydrophilic –tails are hydrophobic
Lipid bilayer— the structural foundation of all cell membranes
Figure 3.10 Phospholipids as components of cell membranes. Left, the head of a phospholipid is hydrophilic, and the tails are hydrophobic. Right, a double layer of phospholipids—the lipid bilayer—is the structural foundation of all cell membranes.

10. hydrophilic head one layer of lipids one layer of lipids
two hydrophobic
tails
Figure 3.10 Phospholipids as components of cell membranes. Left, the head of a phospholipid is hydrophilic, and the tails are hydrophobic. Right, a double layer of phospholipids—the lipid bilayer—is the structural foundation of all cell membranes.
Fig. 3.10, p. 42

11. Waxes
wax
Water-repellent mixture with long fatty-acid tails bonded to long-chain alcohols or carbon rings
Functions:
Covers exposed surfaces of plants
Protects and lubricates skin and hair
Honeycomb

12. Key Concepts
Lipids
Lipids function as energy reservoirs and as waterproofing or lubricating substances
Lipids are the main structural component of all cell membranes

13. 3.5 Proteins— Diversity in Structure and Function
Structurally and functionally, proteins are the most diverse molecules of life
The shape of a protein is the source of its function
protein
Organic compound that consists of one or more chains of amino acids (polypeptides)

14. Amino Acids
Cells make thousands of different kinds of proteins from only twenty kinds of monomers (amino acids)
amino acid
Small organic compound that is a subunit of proteins

15. Amino Acids
Generalized structure of amino acids: Twenty amino acids are used in eukaryotic proteins
Figure 3.12 Generalized structure of amino acids. Appendix V has models of all twenty of the amino acids used in eukaryotic proteins.

16. Building Proteins
Protein synthesis (making proteins) involves covalently bonding amino acids into a chain polypeptide linked by peptide bonds
peptide bond
Bond that joins the amine group of one amino acid and the carboxyl group of another amino acid in a protein
peptide
Short chain of amino acids linked by peptide bonds
Polypeptide
Longer chain of amino acids linked by peptide bonds
Primary structure of a protein

17. Polypeptide Formation
Condensation: A peptide bond forms between the carboxyl group of the methionine and the amine group of the serine (condensation and functional groups again!)
Additional amino acids are added to the carboxyl end to make the polypeptide longer
Figure 3.13 Polypeptide formation. Chapter 9 offers a closer look at protein synthesis.

18. Protein Structure
Polypeptides (primary structure) twist into loops, sheets, and coils (secondary structure) that can pack further into functional domains (tertiary structure)
Many proteins, including most enzymes, consist of two or more polypeptides (quaternary structure)
Fibrous proteins aggregate into much larger structures

19. Primary and Secondary Structure
Primary structure (polypeptide) twists into secondary structure
Figure 3.14 Protein structure.

20. Tertiary and Quaternary Structure
Tertiary structure forms functional domains
Hemoglobin has quaternary structure (4 globin chains)
Figure 3.14 Protein structure.

21. Aggregate Proteins
Many proteins aggregate by thousands into much larger structures, such as keratin filaments that make up hair
Figure 3.14 Protein structure.

22. Polypeptide Formation
A protein’s primary structure consists of a linear sequence of amino acids (a polypeptide chain). Each type of protein has a unique primary structure. 1
glycine
lysine
arginine
Polypeptide Formation 2
Secondary structure arises as a polypeptide chain twists into a coil (helix) or sheet held in place by hydrogen bonds between different parts of the molecule. The same patterns of secondary structure occur in many different proteins. 3
Tertiary structure occurs when a chain’s coils and sheets fold up into a functional domain such as a barrel or pocket. In this example, the coils of a globin chain form a pocket. 4
Some proteins have quaternary structure, in which two or more polypeptide chains associate as one molecule. Hemoglobin, shown here, consists of four globin chains (green and blue). Each globin pocket now holds a heme group (red). 5
Many proteins aggregate by the thousands into much larger structures, such as the keratin filaments that make up hair.
Figure 3.14 Protein structure.
Stepped Art
Fig , p. 45

23. Combined Proteins Enzymes often attach sugars or lipids to proteins
Glycoproteins allow a tissue or body to recognize its own cells
Lipoproteins carry fats and cholesterol through the bloodstream
Low-density lipoprotein (LDL)
High-density lipoprotein (HDL)

24. 3.6 Importance of Protein Structure
A protein’s structure dictates its function so, if a protein unravels (denatures), it loses its function
denature
To unravel the shape of a protein or other large biological molecule
Caused by shifts in pH or temperature, exposure to detergent or some salts that disrupt hydrogen bonds, and other molecular interactions responsible for protein shape

25. Key Concepts
Proteins
Structurally and functionally, proteins are the most diverse molecules of life
They include enzymes and structural materials
A protein’s function arises from and depends on its structure

26. 3.7 Nucleic Acids
Nucleotides are small organic molecules consisting of a sugar, a phosphate group, and a nitrogen-containing base
nucleotide
Monomer of nucleic acids; has five-carbon sugar, nitrogen-containing base, and phosphate groups

27. A Nucleotide Monomer
ATP, a nucleotide monomer of RNA, and also an essential participant in many metabolic processes

28. Nucleic Acids
Nucleotides are monomers of DNA and RNA, which are nucleic acids
nucleic acid
Single- or double-stranded chain of nucleotides joined by sugar–phosphate bonds; for example, DNA, RNA

29. A Nucleic Acid A chain of nucleotides is a nucleic acid
The sugar of one nucleotide is covalently bonded to the phosphate group of the next, forming a sugar–phosphate backbone
Figure 3.17 Nucleic acid structure.

30. DNA and RNA DNA (Deoxyribonucleic acid)
DNA encodes heritable information that guides the synthesis of RNA and proteins
Consists of two nucleotide chains twisted in a double helix
RNA (Ribonucleic acid)
RNAs interact with DNA and with one another to carry out protein synthesis

31. DNA
DNA consists of two chains of nucleotides, twisted into a double helix
Hydrogen bonding maintains the three-dimensional structure

32. Other Nucleotides Some nucleotides have additional functions
Example: ATP energizes many kinds of molecules by phosphate-group transfers
ATP Adenosine triphosphate
Nucleotide that consists of an adenine base, a five-carbon ribose sugar, and three phosphate groups

33. Key Concepts Nucleic Acids
Nucleotides are the building blocks of nucleic acids
Some have additional roles in metabolism
DNA and RNA are part of a cell’s system of storing and retrieving heritable information