Molecules of Life IICHAPTER 3Molecules of Life IICHAPTER 3

Proteins• Amino Acid Monomers

• Polypeptide (protein) Polymers

• Levels of Protein Structure

• Importance of Structure to Function

Nucleic Acids• Nucleotides

• Polymers

• DNA vs.. RNA

Proteins

• A protein is a polymer constructed from amino acid monomers.

• Proteins perform most of the tasks the body needs to function:

• Structural Support

• Storage

• Movement

• Transport

• Body or Cellular Defense

• Docking and Reception

• Catalysis (Enzymes)• Chemical messaging (hormones)• Sensing

• Regulation and Control

Figure 3.19

Examples of Some Types of Proteins and Their Functions

The Monomers: Amino Acids

• All proteins are constructed from a common set of 20 kinds of monomers known as amino acids or peptides

• Each amino acid consists of:

2. An amino (NH2) group, which is basic and polar

3. A carboxyl ( ) group, which is acidic and polar

4. A side group that can be either hydrophobic or hydrophylic

1. A central carbon atom bonded to four covalent partners

Figure 3.1

Example of An Amino Acid Which Allegedly Makes One Sleepy

Proteins as Polymers

• Cells link amino acids together by dehydration reactions, forming peptide bonds between them

• Your body has tens of thousands of different kinds of protein.

– The kind and arrangement of amino acids makes each one different.

Protein Polymers (Polypeptides) are Highly Variable

– Once an amino acid chain is built inside a cell, the chain folds up into a unique shape

– Because structure gives rise to function, two proteins with even slightly different structure fold differently and behave differently

– Any chemical or type of stress that changes the folded structure of a protein ruins its functionality

Protein Structure Introduction

Molecules of Life IICHAPTER 3Molecules of Life IICHAPTER 3

Proteins• Amino Acid Monomers

• Polypeptide (protein) Polymers

• Levels of Protein Structure

• Importance of Structure to Function

Nucleic Acids• Nucleotides

• Polymers

• DNA vs.. RNA

1. Primary (1o) structure

• The specific kinds of amino acids and their sequence in a polypeptide (protein chain)

• A slight change in the primary structure of a protein affects its ability to function.

Four Levels or Degrees of Protein Folding

Primary Protein Structure

Four Levels or Degrees of Protein Folding

• The polypeptide chain folds into an alpha helix, sustained by H-bonds.

(b) Secondary Structure

• The polypeptide chain folds into a pleated sheet, sustained by H-bonds

2. Secondary (2o) structure

Four Levels or Degrees of Protein Folding

3. Tertiary (3o) structure

• The alpha helices and pleated sheets then fold among each other

• New level of structure is supported by hydrogen, ionic, disulfide, and non-polar bonds

Tertiary Structure

Four Levels or Degrees of Protein Folding

3. Quaternary (4o) structure

• Several polypeptide chains join together to form a protein complex with subunits

Unfavorable temperature and pH changes can cause a protein to unravel and lose its shape (denature) and thereby lose functionality

(d) Quaternary structure

Molecular Reconstruction of a Quaternary Structured Protein

The Strength of Spider and Silkworm Protein

• Especially strong because of multiple pleated sheet structures

•These proteins are five times as strong as steel, twice as elastic as nylon, waterproof, and stretchable

Hydrogen bonds

Molecules of Life IICHAPTER 3Molecules of Life IICHAPTER 3

Proteins• Amino Acid Monomers

• Polypeptide (protein) Polymers

• Levels of Protein Structure

• Importance of Structure to Function

Nucleic Acids• Nucleotides

• Polymers

• DNA vs. RNA

Nucleic Acids

• Nucleic acids are information storage molecules.

– They provide the directions for building proteins.

• Nucleic acids are build of monomers called nucleotides

– Ribonucleotides are used in making the polymer called ribonucleic acid (RNA)

– Deoxyribonucleotides are used in making the polymer called deoxyribonucleic acids (DNA)

Nucleotides are Composed of a Phosphate, Sugar, and Nitrogenous Base

Nitrogenous Bases Contain Either One or Two Rings

• Nucleotide monomers are linked into long chains.

– These chains are called polynucleotides, or DNA strands.

– A sugar-phosphate backbone joins them together.

DNA and RNA Structure

Nucleic Acids Are Polymers of Nucleotides

RNA is a simple chain of ribonucleotides

DNA is a Double Stranded Molecule Held Together By Hydrogen Bonds

DNA Molecule as a Ladder: Two Rails Held Together By Rungs

The DNA Molecule is twisted into a spiral in 3-dimensional space

Evolution Connection: DNA and Proteins as Evolutionary Tape Measures

• Evolutionary relationships between organisms can be assessed.

– Molecular genealogy extends to relationships between species.

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

Figure 3.30

Genetic and Evolutionary Relatedness Can Be Determined From DNA and Protein Similarities

Molecules of Life IICHAPTER 3Molecules of Life IICHAPTER 3

Proteins• Amino Acid Monomers

• Polypeptide (protein) Polymers

• Levels of Protein Structure

• Importance of Structure to Function

Nucleic Acids• Nucleotides

• Polymers

• DNA vs.. RNA