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Organic Macromolecules: Proteins and
Nucleic Acids
I.
Levels of Protein Structure
A. Proteins are polymers made up of
monomers called amino acids.
Amino Acids – an organic compound of
the general formula H2N-CHR-COOH
where R can be one of 20 side
proteins
An illustration of how the atoms in a CARBOXYL group
are arranged would be:
Note: The “R” shows represents where the carboxyl group
attaches to an amino acid (also where it would attach to
carbohydrates, lipids, and nucleic acids)
1. Amino acids have different R (“residue”)
groups that can alter the functions of
the amino acid chain simply by changing
how it interacts with other amino acids.
2. There are 20 different amino acids (with
20 different R-groups) that can form
long chains called polypeptides.
Polypeptides – a large molecule made
up of many amino acids; joined by
peptic linkages (peptide bonds)
B. Protein structure can be discussed on 4 basic levels:
primary (1o), secondary (2o), tertiary (3o), and
quaternary (4o).
Primary Structure – The specific sequence of amino
acids in a protein that is determined by your DNA.
Secondary Structure – localized regularities of
structure (H-bonds between amino acids effect
secondary structure)
Tertiary Structure – the relative locations in space of
all atoms in the molecule
Quaternary Structure – the arrangement of
polypeptide chains (in proteins with multiple
polypeptide chains)
II. How Protein Structure is determined
A. The simplest level of protein structure is
the primary level (1o).
1. This level of protein structure describes
the specific order of amino acids
dictated by mRNA during protein
synthesis.
2. Since mRNA is transcribed (“written”)
directly off of a DNA strand then the
information for primary protein
structure comes directly from DNA.
3. Amino acids are joined together through a
dehydration synthesis forming peptide bonds
between the amino acids
Peptide bond (peptic linkage) – a covalent bond
formed between two amino acids when the
carboxyl group of one amino acid reacts with the
amine group (NH2) group of another amino acid
and a molecule of water is released.
B. The next level of protein structure is the
secondary (2o) level.
1. This level of protein structure is determined
by how the amino acids interact with each
other.
2. The interactions depend on the location and
types of amino acids in the polypeptide chain.
3. When certain amino acids are placed in a
specific order, Hydrogen bonds form between
them causing the polypeptide chain to twist
and bend.
C. The third level of protein structure is the
tertiary level (3o)
1. The folding of the secondary level
causes the polypeptide to take on an
overall three dimensional shape.
2. This level of protein structure is used to
classify proteins because the 3-D shape
of proteins determines the protein’s
purpose within the body.
3. Proteins usually form structures (will
have rigid shapes) or are functional (will
have twisted shapes)
D. The Fourth level of protein structure is
the quaternary level (4o).
1. Not all proteins can be described at this
level because not all proteins are
composed of more than one polypeptide
chain.
2. At this level proteins containing more
than one polypeptide chain join
together like pieces to a puzzle to form
the final product.
3. A common protein with quaternary
structure is hemoglobin.
III. Enzymes
A.
Enzymes are protein catalysts that help speed
up chemical reactions in living things only.
Enzyme – a type of protein in all living
things that speed up the rate of
chemical reactions
1. Enzymes work by manipulating
substrates
Substrate – a reactant that an enzyme
acts on to speed up a chemical
reaction
2. An enzyme can speed up chemical
reactions by:
•
Twisting and breaking bonds to make the
number of products greater than the
number of substrates.(catabolic)
•
Holding substrates together making the
number of products less than the
number of substrates.(anabolic)
B. The shape of the enzyme is unique and only
specific substrates will fit into its active site.
Active site – the part of an enzyme where
manipulation of the substrate occurs
1. Once an enzyme acts on a substrate the
enzyme is free to act on another substrate
until it is metabolized (chemically destroyed).
2. If during protein synthesis amino acids are not
placed in the proper order then the enzyme
will have the wrong shape which means the
substrate won’t fit into the active site.
*Cause of many recessive traits and genetic
disorders.
I.
Nucleic Acids
A. Nucleic Acids are polymers made up of
monomers called nucleotides.
Nucleotides – unit of a nucleic acid that
is made up of a 5-carbon sugar, a
phosphate group, and a nitrogenous
base (which varies)
B. There are two basic kinds of nucleic acids:
RNA - Ribonucleic Acid contain nucleotides
with 5-carbon sugar ribose
DNA – Deoxyribonucleic acid contains
nucleotides with the 5-carbon sugar
deoxyribose
C. Nucleotides can only form base pairs with a
complementary nucleotide.
1. Two DNA molecules are held together by Hydrogen
bonds that form between the nitrogenous bases.
2. When mRNA is being translated, the nucleotides
form Hydrogen bonds with the complementary
DNA nucleotide.
3. The 5-carbon sugars form covalent bonds through
dehydration synthesis to form the sugar-phosphate
backbone of the nucleic acid molecule.
D. The only function of nucleic acids is to store
and transmit genetic information.