Download 4 MolLife2

Molecules of Life II
CHAPTER 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
• Docking and Reception
• Storage
• Catalysis (Enzymes)
• Movement
• Transport
• Chemical messaging
(hormones)
• Sensing
• Body or Cellular Defense
• Regulation and Control
Examples of Some Types of Proteins and Their Functions
Figure 3.19
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:
1. A central carbon atom bonded to four covalent partners
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
Example of An Amino Acid Which Allegedly Makes One Sleepy
Figure 3.1
Proteins as Polymers
• Cells link amino acids together by dehydration
reactions, forming peptide bonds between them
Protein Polymers (Polypeptides) are Highly Variable
• Your body has tens of thousands of different kinds
of protein.
– The kind and arrangement of amino acids makes
each one different.
– 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 II
CHAPTER 3
Proteins
• Amino Acid Monomers
• Polypeptide (protein) Polymers
• Levels of Protein Structure
• Importance of Structure to Function
Nucleic Acids
• Nucleotides
• Polymers
• DNA vs.. RNA
Four Levels or Degrees of Protein Folding
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.
Primary Protein Structure
Four Levels or Degrees of Protein Folding
2. Secondary (2o)
structure
•
The polypeptide
chain folds into an
alpha helix,
sustained by Hbonds.
•
The polypeptide
chain folds into a
pleated sheet,
sustained by Hbonds
(b) Secondary 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 nonpolar 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
(d) Quaternary structure
Unfavorable temperature and pH changes can cause a protein to unravel
and lose its shape (denature) and thereby lose functionality
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 II
CHAPTER 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:
The DNA Molecule is twisted into a
Two Rails Held Together By Rungs
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
Genetic and Evolutionary Relatedness Can Be Determined From DNA and Protein Similarities
Figure 3.30
Molecules of Life II
CHAPTER 3
Proteins
• Amino Acid Monomers
• Polypeptide (protein) Polymers
• Levels of Protein Structure
• Importance of Structure to Function
Nucleic Acids
• Nucleotides
• Polymers
• DNA vs.. RNA