Lecture # 3

Proteins always contain nitrogen, as well as
carbon, hydrogen and oxygen, and sometimes
sulfur and phosphorus.

There are two types of proteins:
1. structural proteins
examples: keratin, collagen, and extensin

2. Enzymes, which are metabolic catalysts

The two types of protein differ in function. 
In terms of structure, they are similar
in that they are all made of monomers
called amino acids.

Basic structure of an amino acid

20 amino acids are commonly found in
proteins

Proteins differ in the relative proportions
of the amino acids that make them up.

Two amino acids linked together is called a
dipeptide.

Three amino acids linked together is called a
tripeptide.

tetrapeptide
pentapeptide
hexapeptide

oligopeptide

Polypeptide is the same as protein

Primary structure is the sequence
of the amino acids.

Secondary structure is looping of the chain of
amino acids back on itself.

Tertiary structure is the folding of the looped
chain in three dimensions.

Quaternary structure describes how one
protein molecule interacts with another.

When in a solution, proteins maintain a
complex but stable structure.  This is
called the native state of the protein.

The disruption of the native state of
a protein is called denaturation.

Denaturation inactivates enzymes.

Species Specificity of Proteins

Rejection of transplanted organs can be
due to protein incompatibility.

Essential amino acids cannot be synthesized
by an animal and must be included in the diet.

There are two major types of nucleic acids:

Ribonucleic Acid   RNA

Deoxyribonucleic Acid  DNA

Nucleic acids are made of monomers called
nucleotides.

Each nucleotide is made of a phosphate group,
a simple sugar and one nitrogenous base.

The phosphate always has the same structure.

The simple sugar can be either ribose or
deoxyribose.

There are four possible nitrogenous bases

in RNA.

Purines: Adenine        A      

               Guanine         G

Pyrimidines:

                Cytosine     C

                Uracil         U

In DNA, thymine occurs instead of uracil.

There are no types of DNA.

There are three types of RNA:
Messenger RNA    m-RNA
Transfer RNA         t-RNA
Ribosomal RNA     r-RNA

DNA and RNA carry information in the
sequence of their nucleotides.

The most important molecule in all
biological systems is water.

Water is important because it:
1. is a good solvent
2. has a high heat capacity
3. has a high heat of vaporization
4. has high heat conductivity
5. is a good lubricant
6. at the molecular level is a product or
reactant in many biochemical reactions

Hydrolysis is the destruction of a polymer
by putting water back into its structure.

If you mix something in water, you get
one of three things:

1. true solution.  The dissolved solute is
very small, < 1 nanometer (nm) in diameter.

The dissolving liquid is called the solvent.

A true solution is transparent and stable.

Most acids, alkalis, salts, sugars and small
proteins form true solutions in water.

2. Suspension.  The suspended particles are
> 100 nm in diameter.

Suspensions are generally opaque and
are not stable.

3. Colloid.  The dispersed particles are > 1 nm, but
< 100 nm in diameter.

Colloids generally are transparent and stable.

Colloids exist in two physical states:
Liquid state called a sol
Solid state called a gel

The properties of a cell are determined by the
cell’s contents being a colloid.