Download Lecture 5: Powerpoint

Biology 102
Lecture 5: Biological Molecules
(cont.)
Lecture outline
1. Proteins
 Functions
 Structure
2. Nucleic acids
 Functions
 Structure
Proteins

Key functions:
 Structure

Skin (collagen); hair and nails (keratin)
 Movement


Proteins in muscle (actin and myosin)
Defense

Antibodies
 Signals



Several hormones (growth hormone, insulin)
Receptors for neurotransmitters
Channels in membranes
 Catalysis

Enzymes
Amino acids are the monomers of
proteins

Composition
 Amino
group
 Carboxylic acid group
 “R”-group: variable
Properties of particular amino acids are
based on their R-groups
There are 20 total amino acids
• Here are a few examples
Protein synthesis

Proteins are formed when amino acids link
together with a dehydration synthesis
reaction
 Note
where they link together
 Note the formation of water: dehydration synthesis
Four levels of protein structure
Primary structure of proteins

The primary
structure of proteins
is its particular
sequence of amino
acids
Secondary structure of
proteins

Secondary structure
occurs due to
regularly spaced
hydrogen bonds

The structural properties of silk are due
to beta pleated sheets.
The
presence of so many hydrogen bonds
makes each silk fiber stronger than steel.
Fig. 5.21
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Tertiary structure of a protein

Results from various interactions
between R groups.
hydrogen
bonds among polar and/or
charged areas
ionic bonds between charged R groups,
Hydrophobic interactions among
hydrophobic R groups.
Disulphide bridges that form strong, stable
bonds between parts of the molecule
Tertiary structure (cont.)
Quaternary structure


Results from interactions of two or more
polypeptide chains
Hemoglobin is the interactions of two different types
of chains (alpha and beta), with two of each per
molecule
Importance of tertiary and
quarternary structure

Shape of the protein is tied to its function
 Example:
Lock and key fit of an enzyme and the
reactants (substrates) that it brings together

Higher levels of protein structure are directly
tied to the amino acid sequence (primary
structure)
 Change
in primary structure can drastically alter
protein function


Example: Hemoglobin/sickle cell anemia
Denaturation: IF secondary and higher level
structure destroyed, protein can no longer
function
Nucleic acids

Functions of nucleic acids
Molecules
of heredity (DNA, RNA)
Second messengers inside the cell (cAMP)
Short-term energy carriers (ATP)
Coenzymes
Monomers of nucleic acids are
nucleotides
Nucleotides can bond together
to form nucleic acids

As with all other
polymers, the
reaction is a
dehydration
synthesis
 Phosphate
group of
one nucleotide bonds
with the sugar of the
adjacent nucleotide