Proteins and nucleic acids are important macromolecules that make up cells. Proteins are composed of amino acids and perform critical functions like structure and catalysis. The four levels of protein structure are primary, secondary, tertiary, and quaternary. Nucleic acids DNA and RNA contain nitrogenous bases and sugars. DNA provides genetic instructions and replicates, while RNA has roles in protein synthesis. ATP is an energy-carrying molecule made from RNA nucleotides.

1. Proteins and Nucleic Acids
BIO 351
Human Anatomy and
Physiology I

2. Proteins: Characteristics
 Make up 10 to 30% of cell mass.
 Basic structural material of the body.
 Play vital roles in cell functioning.
 All contain carbon, hydrogen, oxygen,
and nitrogen. Some contain sulfur or
phosphorus also.
 All proteins are made up of building
blocks called amino acids.

3. Muscle tissue
contains the proteins
myosin and actin.
Muscles

4. Amino Acids
 20 commonly occur in nature, 8 of these are
essential AA (can’t be synthesized by
human body, must be included in diet)
 Two important functional groups—the amino
group (can act as a base and accept
protons) and the carboxyl group (can act as
an acid and donate protons).
 All amino acids are identical except for the R
group—the R groups are what make each
amino acid different and chemically unique.

5. Basic Amino Acid Structure

6. R Groups Highlighted

7. Protein Formation
 Proteins are formed from amino acids
by dehydration synthesis.
 The bonds between adjacent amino
acids are called peptide bonds.
 Most proteins contain over 100 amino
acids and are truly macromolecules.
Some contain up to 10,000 amino
acids.

8. Organization of Proteins - 4
Structural Levels of Proteins
 Primary structure– the linear sequence of
amino acids in the chain.
 Secondary structure—formed by coiling of
the primary chain into an alpha helix (with
hydrogen bonds maintaining the coiled
structure) or a beta pleated sheet (hydrogen
bonds hold primary polypeptide chains side
by side in a pleated structure like an
accordion).

10. Structural Levels of Proteins
 Tertiary structure—achieved when an
alpha helix or beta pleated sheet folds
in a three dimensional way to produce
a globular molecule.
 The structure is maintained by both
hydrogen and covalent bonds.

12. Structural Levels
 Quaternary structure—happens when
two or more polypeptide chains
aggregate in a regular manner to form
a complex protein.
 The shape of a protein determines its
function. Anything that causes the
protein to unfold will result in the
protein being unable to perform its job.

13. Hemoglobin

15. Fibrous Proteins
 Strand-like
 Also called structural proteins.
 Most exhibit secondary structure only but some
have quaternary structure as well (collagen is an
example of a protein with quaternary structure).
 Insoluble in water
 Very stable
 Provide mechanical support and tensile strength.
 Examples include collagen and keratin (both of
which are present in skin), and the muscle proteins
actin and myosin

16. Globular Proteins
 Spherical and compact
 Tertiary structure; some with quaternary
structure as well
 Water soluble
 Chemically active
 Examples are enzymes and antibodies
 Also called functional proteins
 Susceptible to denaturing

18. Protein Denaturation
 The activity of functional proteins depends on their
three dimensional structure.
 The hydrogen bonds responsible for maintaining the
structure are fragile and can be broken by changes
in both the physical and chemical environment.
 Hydrogen bonds begin to break when the pH
changes or the temperature rises above normal.
 The proteins unfold and lose their biological activity.

19. Enzymes
 Enzymes are globular proteins that act
as biological catalysts.
 Each enzyme is chemically specific.
 Enzymes work by lowering the
activation energy of a reaction.
 Enzymes act on substrates and trigger
chemical reactions in the body.

20. Enzyme Activity

21. Nucleic Acids
 Contain carbon, hydrogen, oxygen, nitrogen,
and phosphorus
 Two types—DNA and RNA
 DNA is the genetic material of the cell and is
found in the nucleus.
 It replicates itself in order for cell division to
occur.
 It provides instructions for protein synthesis.
 There are 3 major types of RNA
(messenger, transfer and ribosomal). Each
has a different function.

23. DNA
 DNA is coiled like a spiral staircase or
ladder, known as a double helix
 The 2 “backbones” are composed of
alternating sugar and phosphate groups
 Each “rung” of the ladder is composed of 2
nitrogenous bases hooked together by
hydrogen bonds
 Chromosomes are formed from DNA.
Genes are sections of chromosomes. Taken
together, all of the genetic material in a
cell’s nucleus is known as a genome

24. Nucleotides
 The structural units of nucleic acids
 Each nucleotide has three components
 N-containing base
 5-carbon sugar (a pentose)
 Phosphate group
(Note: A nucleoside consists of just a base plus a
pentose sugar without the phosphate)

25. N-containing Bases
 There are 5 different N-containing bases
found in nucleic acids. These are divided
into 2 types, purines and pyrimidines.
 They follow these base-pairing rules:
 Adenine pairs with thymine
 Cytosine pairs with guanine
 Uracil replaces thymine in RNA
 Adenine and guanine are purines. They
each contain 2 rings.
 Cytosine, uracil, and thymine are
pyrimidines. They each have a single ring
structure.

26. The nucleic
acids are the
largest
molecules in
the body.

27. DNA
 DNA replicates itself before cell division and
provides instructions for making all of the
proteins found in the body.
 The structure of DNA is a double-stranded
polymer containing the nitrogenous bases A,
T, G, and C, and the sugar deoxyribose.
 Bonding of the nitrogenous bases in DNA is
very specific; A bonds to T (via 2 hydrogen
bonds), and G bonds to C (via 3 hydrogen
bonds)
 The bases that always bind together are
known as complementary bases.

29. DNA polymerase III adds one nucleotide at a time to the 3’
end of the newly formed strand following base pairing rules

30. RNA
 The major types of RNA are produced inside
the nucleus, and then transported into the
cytoplasm, where they are used to make
proteins according to the instructions
provided by the DNA.
 The structure of most types of RNA is a
single-stranded polymer containing the
nitrogenous bases A (adenine), G (guanine),
C (cytosine), and U (uracil), and the sugar
ribose.
 In RNA, G bonds with C, and A bonds with
U.

32. Genetic Code

34. ATP
 ATP is the energy currency used by the cell.
 ATP is an adenine-containing RNA
nucleotide that has two additional phosphate
groups attached.
 The additional phosphate groups are
connected by high energy bonds.
 Breaking the high energy bonds releases
energy the cell can use to do work.