Cell Biology:
Cell Compounds and Biological Molecules
Lesson 4 – Proteins and Nucleic Acids (Inquiry into Life pg. 37-41)
Today’s Objectives

Analyze the structure and function of biological molecules in
living systems, including carbohydrates, lipids, proteins, nucleic
acids






List the major functions of proteins
Draw a generalized amino acid and identify the amine, acid
(carboxyl), and R-groups
Identify the peptide bonds in dipeptides and polypeptides
Differentiate among the different levels of protein organization with
respect to structure and bond type, including: primary, secondary,
tertiary, quaternary
Name the four bases in DNA and describe the structure of DNA
using the following terms: nucleotide (sugar, phosphate, base),
complementary base pairing, double helix, hydrogen bonding
Relate the general structure of the ATP molecule and its role as
“energy currency”
2.7 - Proteins

Proteins have many functions:







Proteins such as keratin and collagen have structural
roles.
Proteins are also enzymes that speed up the chemical
reactions of metabolism.
Proteins such as hemoglobin are responsible for the
transport of substances within the body.
Proteins transport substances across cell membranes.
Proteins form the antibodies of the immune system that
defend the body from viruses and disease.
Proteins such as insulin are hormones that regulate cellular
function.
Contractile proteins such as actin and myosin allow parts
of cells to move and muscles to contract.
What are proteins?




Contain carbon, hydrogen, oxygen, and nitrogen
Also often contain sulfur, and sometimes phosphorus
and iron
The basic structure of a protein is a chain of amino
acids (polypeptides)
There are about 20 different amino acids
What are amino acids?




Proteins are polymers with amino acid monomers
An amino acid has a central carbon atom bonded to a
hydrogen atom and three groups:
One of the three groups is an amino group (-NH2),
One of the groups is an acidic group (-COOH)



Hence called an amino acid!
The third group is called an R Group
Amino acids differ from one another by their R group
What are R groups?



An R group is a variety of atoms attached to amino acids
R group = radical group or remainder group
An R group distinguishes one amino acid from another
Examples of amino acids
Formation of Proteins




An amino acid can be referred to as a peptide
Dehydration synthesis of amino acids result in the
bonding of amino acids together and the release of water
molecules
When two amino acids bond together, they produce a
dipeptide
Example: amino acids glycine and alanine bond to form
the dipeptide gly-ala
Formation of proteins

The bond that connects amino acids is called a peptide
bond





A dipeptide has one peptide bond holding together two
amino acids
A Tripeptide would have two peptide bonds holding together
three amino acids
A polypeptide would have numerous peptide bonds holding
together numerous amino acids
A polypeptide is a single chain of amino acids
The order or combination of these amino acids
determines which protein is produced
Dehydration synthesis of amino acids
Dehydration synthesis of amino acids
Dehydration synthesis of amino acids
Formation of proteins
This process when repeated form long
sequences of amino acids, or proteins
 These sequences take on specific features and
characteristics of the individual amino acids
that are bonded together

Protein Structure

There are three to four levels of protein structure




Primary structure – sequence of amino acids (polypeptide)
Secondary structure – orientation of polypeptide
Tertiary structure – final 3-D shape of polypeptide
Quaternary structure* - arrangement of multiple
polypeptides
 *not all proteins have multiple polypeptides
Primary Structure



Simply the sequence of amino
acids
Because there are twenty
amino acids, it is easy to see
that there are literally millions
of different possible amino acid
sequences
Consequently, there are
millions of proteins
Secondary Structure



As the amino acid chains
(polypeptides) get longer,
they begin to twist or fold
This is a result of stress on
the peptide bonds
Two types of secondary
structure:



Alpha helix – like a spiral
Beta pleated sheet – like
folded paper
The alpha helix is most
common
Secondary Structure – alpha helix



As the polypeptide bends into a spiral, hydrogen bonds
form between the hydrogen of one amino acid and an
oxygen further down the chain
This hydrogen bond helps the alpha helix hold its shape
An alpha helix contains 3.6 amino acids per spiral
Secondary Structure – Beta pleated sheet

Hydrogen bonds can form between parallel lengths of
the polypeptide chain creating beta pleated sheets
Secondary Structure
Tertiary Structure




The third level of protein structure or tertiary structure
is described as the bending and folding of the alpha
helix
As the helix gets longer there are some amino acids that
cannot fit the configuration and therefore cause kinks
New bonds will form to hold it into a three
dimensional (3-D) shape
These bonds can be ionic, covalent, and/or hydrogen
bonds
Tertiary Structure
Alpha
helix
Quaternary Structure


Only occurs in proteins with more than one
polypeptide
The quaternary structure is where different 3-D
(tertiary) configurations are associated with and function
with each other


Imagine multiple kinked helixes tied up with each other in
knots
An example of a protein with quaternary structure is
hemoglobin which transports substances through our
body in our blood
Quaternary Structure
Levels of Protein Structure
More about Protein Functions

Enzyme proteins speed up chemical reactions in our
body






Reactions that normally would take several hours will take
only a fraction of a second
Proteins such as hemoglobin transport nutrients and
other substances through our body
Antibody proteins fight infections and attack viruses
The protein keratin is the main structural component
of fingernails and hair
Collagen makes up the connective tissues in our
muscles
Actin/myosin make up muscle fibers that allow for
movement
2.8 Nucleic Acids


Nucleic Acids are polymers made up of monomers
called nucleotides
There are two types of nucleic acids:



DNA – deoxyribonucleic acid
RNA – ribonucleic acid
Some functions of Nucleic Acids:




They form genetic material and are involved in the
functioning of chromosomes and protein synthesis
DNA stores genetic information
DNA codes for the order of amino acids in a protein
RNA is an intermediary in the sequencing of amino acids
into a protein
What are Nucleotides?

Nucleotides are made from a pentose sugar, a
phosphate group, and a nitrogen containing base
Nucleotides


There are five basic nucleotides:
Adenine and Guanine


Cytosine, Uracil, and Thymine


Double ring structure purines
single ring structure pyrimidines
These bases are found in DNA and RNA


DNA contains A,G,T and C
RNA contains A,G,U and C
DNA structure compared to RNA structure
Nucleotides


The bases found in DNA
form complementary
base pairs (the same two
bases always bond with
each other)
The structure of DNA is a
double helix (we will talk
more about DNA later this
year
Complementary Base Pairs in DNA
ATP (Adenosine Triphosphate)




One particularly important nucleic acid is the modified nucleotide
known as ATP
ATP is an RNA nucleotide with an adenine (A) base (adenine +
ribose = adenosine) attached to 3 phosphate groups
ATP is a very high energy molecule
When ATP undergoes hydrolysis, large amounts of energy are
released
ATP: The energy currency of cells



ATP is a high energy molecule because the last two phosphate
bonds are unstable and easily broken
A lot of energy is required to maintain these bonds
If the bonds are broken, this energy is released





When an ATP molecule loses a phosphate, it becomes the molecule
ADP (adenosine diphosphate) and a phosphate molecule
With the addition of energy, this process can be reversed, creating
the ATP cycle
Muscle cells use the energy for muscle contraction
Cells use the energy to synthesize carbohydrates and
proteins
More on this later in the year
ATP Cycle
Pop Quiz!











An amino acid is a central hydrogen atom attached to a
hydrogen atom and what?
What are the monomers called that make up proteins?
Describe primary protein structure
Describe secondary protein structure
What are the two main types of secondary structure
Describe tertiary protein structure
Describe quaternary protein structure
What are 3 main functions of proteins?
What are the monomers called that make up nucleic acids?
How do cells get energy from the hydrolysis of ATP?
What are the 4 bases found in DNA?