UNIT A: Cell Biology

Chapter 2: The Molecules of Cells: Sections 2.7, 2.8

Chapter 3: Cell Structure and Function

Chapter 4: DNA Structure and Gene Expression

Chapter 5: Metabolism: Energy and Enzymes

Chapter 6: Cellular Respiration

Chapter 7: Photosynthesis

In this chapter, you will learn how basic chemistry is used in biology.

What life processes might be affected by a problem with protein structure?

How are biological molecules involved in energy use in the body?

UNIT A Chapter 2: The Molecules of Cells

TO PREVIOUS SLIDE

Chapter 2: The Molecules of Cells

2.7 Proteins

Proteins are composed of monomers of amino acids. Each amino acid contains a central carbon atom bonded to

•an amino group

•a carboxyl group

•a hydrogen

•an R group that determines the type of amino acid it is

Figure 2.21 Representative amino acids.

UNIT A Chapter 2: The Molecules of Cells Section 2.7

TO PREVIOUS SLIDE

Proteins

Proteins perform numerous functions. For example,

•They transport molecules across the plasma membrane

•One category of proteins, called enzymes, catalyze cell reactions

•They provide structural support (for example, keratin in nails and collagen in tendons and ligaments)

•Some act as cell messengers, influencing metabolic activity

UNIT A Chapter 2: The Molecules of Cells Section 2.7

TO PREVIOUS SLIDE

Peptides

Polypeptides are polymers of amino acids joined by peptide bonds.

•Peptide bonds are polar covalent bonds, allowing hydrogen bonding between amino acids. This influences the three-dimensional shape of proteins.

Figure 2.22 Synthesis and degradation of a dipeptide.

UNIT A Chapter 2: The Molecules of Cells Section 2.7

TO PREVIOUS SLIDE

Levels of Protein Organization

There can be up to four levels of structural organization in proteins.

•Primary structure: amino acid sequence

•Secondary structure: polypeptide orientation, such as alpha helix or beta pleated sheet

•Tertiary structure: three-dimensional shape of a polypeptide chain (protein). This shape is held together by covalent, ionic, and hydrogen bonds between R groups on different amino acids (for example, disulfide linkage S−S between two cysteine amino acids)

UNIT A Chapter 2: The Molecules of Cells Section 2.7

TO PREVIOUS SLIDE

Levels of Protein Organization

• Quaternary structure: three-dimensional arrangement of polypeptide chains for proteins with two or more chains

The final shape of a protein is very important for its function. Proteins that become denatured undergo an irreversible change in shape. This causes them to no longer be active or to be only partially active.

UNIT A Chapter 2: The Molecules of Cells Section 2.7

TO PREVIOUS SLIDE

UNIT A Chapter 2: The Molecules of Cells Section 2.7

TO PREVIOUS SLIDE

Figure 2.23 Levels of protein organization.

UNIT A Chapter 2: The Molecules of Cells Section 2.7

TO PREVIOUS SLIDE

Check Your Progress

1. List some of the functions of proteins.

2. Describe the structure of an amino acid.

3. Compare and contrast the four levels of protein structure.

UNIT A Chapter 2: The Molecules of Cells Section 2.7

TO PREVIOUS SLIDE

The two types of nucleic acids are

•DNA (deoxyribonucleic acid), which carries the genetic information of an organism

•RNA (ribonucleic acid), which consists of different types of molecules such as mRNA, tRNA, and rRNA

UNIT A Chapter 2: The Molecules of Cells Section 2.8

TO PREVIOUS SLIDE

2.8 Nucleic Acids

Structure of DNA and RNA

UNIT A Chapter 2: The Molecules of Cells Section 2.8

TO PREVIOUS SLIDE

• Nucleotides in DNA contain the sugar deoxyribose and four different types of bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

• Nucleotides in RNA contain the sugar ribose and the same bases as DNA except uracil (U) replaces thymine.

Nucleic acids are polymers of nucleotides, which contain a phosphate group, a pentose sugar, and a nitrogen-containing base.

Figure 2.24 Structure of a nucleotide.

Structure of DNA and RNA

Nucleotides form a linear molecule, called a strand. A strand has a backbone of alternating sugar and phosphate groups with bases projecting to one side.

•DNA is double-stranded, with the strands twisted about each other in a double helix. The strands are held together by hydrogen bonding between bases (C to G and T to A)

•RNA is single-stranded

Figure 2.25 Overview of DNA structure.

UNIT A Chapter 2: The Molecules of Cells Section 2.8

TO PREVIOUS SLIDE

Structure of DNA and RNA (Summary)

UNIT A Chapter 2: The Molecules of Cells Section 2.8

TO PREVIOUS SLIDE

ATP (Adenosine Triphosphate)

ATP is a nucleotide that also acts as a source of energy for

• Chemical work: ATP supplies energy for synthesis of macromolecules

• Transport work: ATP supplies energy used to pump substances across the plasma membrane

• Mechanical work: ATP supplies energy for processes such as muscle contraction and flagella movement

Figure 2.26 ATP reaction.

UNIT A Chapter 2: The Molecules of Cells Section 2.8

TO PREVIOUS SLIDE

The ATP Cycle

Figure 2.27 The ATP cycle.

UNIT A Chapter 2: The Molecules of Cells Section 2.8

TO PREVIOUS SLIDE

Energy is stored in the chemical bonds of the phosphates.

•Energy is released when the bonds between phosphate groups are broken

•Usually, the last phosphate is cleaved to form ADP + Pi, and energy is used for a reaction

•ATP can be remade from ADP and Pi

UNIT A Chapter 2: The Molecules of Cells Section 2.8

TO PREVIOUS SLIDE

Check Your Progress

1. Describe the structure of nucleic acids.

2. Describe how energy is stored in ATP.

UNIT A Chapter 2: The Molecules of Cells Section 2.8

TO PREVIOUS SLIDE