1) Proteins are made of amino acids joined by peptide bonds and folded into complex shapes that determine their function. There are four levels of protein structure: primary, secondary, tertiary, and quaternary. 2) Nucleic acids are made of nucleotides and transmit hereditary information by determining which proteins are produced. DNA contains genes and is located in the nucleus, while RNA participates in protein synthesis. 3) Biological macromolecules include proteins, nucleic acids, carbohydrates, and lipids, all composed of monomers joined by covalent bonds. These complex molecules have essential functions in cells and living organisms.

1. Introduction to Biology
(BIO 110)
Dr. Saira Justin
BIOLOGICAL
MACROMOLECULES

2. PROTEINS
DEFINITION
Extremely complex long chain/s of amino acid residues joined by peptide bonds.
• contain nitrogen, & usually sulphur, as well as carbon, hydrogen & oxygen.
• most versatile cell components
FORMS
Protein shape is critical to its function, which is maintained by many different
types of chemical bonds.
• Globular protein e.g., hemoglobin
• Fibrous protein e.g., collagen .
Terms ‘polypeptide’ & ‘protein’ can be used interchangeably,
but when a polypeptide is about 50 amino acid residues long it
is generally agreed to have become a protein

3. a. AMINO ACID
• Amino acids have a central asymmetric carbon to which an amino group, a
carboxyl group, a hydrogen atom, and a side chain (R group) are attached.
• All proteins are made up of different arrangements of the same 20 types of
amino acids
https://wou.edu/chemistry/
The name "amino acid" is derived
from the fact that they contain both
amino group and carboxyl acid
group in their basic structure.

4. Lippincott’s Biochemistry 6th Edition
AMINO ACID
• Non-polar/Hydrophobic
• Polar/Hydrophilic
• Acidic/Negative/ COO-/ Hydrophilic
• Basic/Positive/NH3+/ Hydrophilic

5. b. PEPTIDE BOND
• amino acids are joined covalently by peptide bonds
• these are amide linkages between carboxyl group of one amino acid &
amino group of another.
Linkage of many amino acids through peptide bonds results in an unbranched chain
called a polypeptide. Each component amino acid in a polypeptide is called a “residue”
Biology by S.B Martin, 9th Edition

6. NAMING PEPTIDE BOND FEATURESPEPTIDE BOND
Lippincott’s Biochemistry 6th Edition

7. PROTEINS - LEVELS OF ORGANIZATION
The structure of large molecules can be described at several levels of complexity,
arranged in a kind of conceptual hierarchy.
Lehninger Principles of Biochemistry, 7th Edition

8. 1. PRIMARY STRUCTURE
DEFINITION
• sequence of amino acid residues
• covalent bonds link amino acid residues in a polypeptide chain.
SIGNIFICANCE
• folds up into its unique 3D structure, & in turn determines function of the protein.
• spatial arrangement of atoms in a protein/part of a protein is called its conformation.
• functional conformation of protein is called its native state.
https://wou.edu/chemistry/
What will happen if the primary structure
of a protein is changed??

9. 2. SECONDARY STRUCTURE
Secondary structure refers to stable, short-range, periodic folding elements that
are common in proteins.
• Regular arrangements of amino acids that are located near to each other in the
linear sequence.
EXAMPLES
1. α-helix
2. β-sheet
3. β-bend (β-turn)
Lippincott’s Biochemistry 6th Edition

10. A. α-HELIX
• spiral structure
• tightly packed, coiled polypeptide backbone
core
• side chains of component amino acids
extending outward …….?????
• rigidity is determined by number of
hydrogen & disulfide bonds
• Each turn of an α-helix contains 3.6 amino
acids.
Several different polypeptide helices are found in
nature, but the α-helix is the most common.
Lippincott’s Biochemistry 6th Edition

11. B. β - SHEET
• polypeptide backbone is nearly fully extended into a zigzag
strand
• all of the peptide bond components are involved in
hydrogen bonding (hydrogen bonds are perpendicular to the
polypeptide backbone)
• arrangement of several β strands side-by-side forms a
planar type structure called a β sheet (a.k.a., β pleated sheet)
• when illustrations are made of protein structure, β-strands
are often visualized as broad arrows
Lippincott’s Biochemistry 6th Edition

12. PARALLEL SHEETS ANTI-PARALLEL SHEETS
polypeptide chains or segments of
polypeptide chains arranged parallel to each
other (with all the N-terminal of the β-strands
at one end).
polypeptide chains or segments of polypeptide
chains arranged anti-parallel to each other (with
N-terminal and C-terminal ends of the β-strands
alternating).
Lippincott’s Biochemistry 6th Edition

13. C. β-BENDS (REVERSE TURNS, β-TURNS)
Secondary structure elements that link successive
runs of  helix or β conformation where
polypeptide chain reverses direction in space
• β turns, are usually found on the surface of
protein molecules (commonly globular protein),
and often include charged residues.
• β-bends are stabilized by the formation of
hydrogen and ionic bonds.
β-Bends were given this name because they often connect successive strands of anti-parallel β-sheets
Lippincott’s Biochemistry 6th Edition

14. 3. TERTIARY STRUCTURE
Overall three-dimensional arrangement of all atoms in a protein.
• long-range aspects of the fold of a protein
• interactions between isolated elements of secondary structure.
• both noncovalent and covalent interactions are included.
“Tertiary” refers both to the folding of domains (the basic units of structure and
function), and to the final arrangement of domains in the polypeptide.
The primary structure of a polypeptide chain determines its tertiary structure.
Lippincott’s Biochemistry 6th Edition

15. A. INTERACTIONS - Stabilizing Tertiary Structure
Interactions b/w amino acid side chains guide folding of polypeptide/s to form a
compact structure.
Following four types of interactions cooperate in stabilizing the tertiary structures
a) Disulfide Bonds
b) Hydrophobic Interactions
c) Hydrogen Bonds
d) Ionic Interactions
https://wou.edu/chemistry/

16. B. PROTEIN FOLDING
Interactions between side chains of amino acids determine how a
long polypeptide chain folds into 3-D shape of functional protein.
• occurs within cell in seconds to minutes
• amino acid side chains are attracted and repulsed according to their
chemical properties.
https://www.youtube.com/watch?v=yZ2aY5lxEGE
https://www.youtube.com/watch?v=gFcp2Xpd29I
process of “trial and error” tests many, but not all, possible
configurations, seeking a compromise in which attractions
outweigh repulsions. This results in a correctly folded protein.
Lippincott’s Biochemistry 6th Edition

17. 4. QUATERNARY STRUCTURE
Refers to the contacts between, and overall arrangement in 3D space of the individual
subunits of a multi-subunit protein.
POLYPEPTIDE CHAINS
• two or more polypeptide chains
• structurally identical or totally unrelated.
• held together by various interactions (hydrogen bonds, ionic bonds, & hydrophobic)
• subunits function independently of each other or may work cooperatively.
• example…….????
Lippincott’s Biochemistry 6th Edition

18. FIBROUS & GLOBULAR PROTEINS
Globular Proteins
• spherical or globular shape.
• often function as regulatory proteins
& enzymes.
• hydrophobic side chains are buried
in the interior, whereas hydrophilic
groups are generally found on
surface.
Fibrous Proteins
• elongated and fibrous or sheet like
• mechanically strong & water
insoluble
• often structural proteins
Biology by S.B Martin, 9th Edition

19. BENEFITS OF PROTEINS
Biology by S.B Martin, 9th Edition

20. NUCLEIC ACIDS
DEFINITION
Nucleic acids transmit hereditary information & determine what proteins a cell manufactures.
• made of nucleotides, joined by phosphodiester linkages
• large, complex molecules.
• acidic in nature
CLASSES
Two classes of nucleic acids are found in cells
1. Deoxyribonucleic acid
2. Ribonucleic acid
Were first identified, by Swiss biochemist Friedrich Miescher in 1870, in the nuclei of pus cells.
Biology by S.B Martin, 9th Edition

21. NUCLEOTIDE COMPOSITION
1. five-carbon sugar: deoxyribose (in DNA) or ribose (in RNA);
2. one or more phosphate groups: make/s the molecule acidic
3. nitrogenous base: a ring compound that contains nitrogen.
• double-ring purine & single-ring pyrimidine.
Biology by S.B Martin, 9th Edition Biology by C.J Clegg

22. NUCLEOSIDE VS NUCLEOTIDE
Nucleoside: nucleobase/nitrogenous base + five-carbon sugar (ribose or 2'-deoxyribose)
Nucleotide: nucleobase + a five-carbon sugar + one or more phosphate groups.
NUCLEOTIDE FORMATION
Condensation reaction forms a nucleotide with the formation of 2 molecules of water.
Biology by C.J Clegg
Since any one of the bases can be
selected, five different types of
nucleotide can be formed.

23. NUCLEOTIDES BECOME NUCLEIC ACID
Nucleotides condense together, one nucleotide at a
time, to form nucleic acids or polynucleotides.
• very long, thread-like macromolecules
• joined by phosphodiester linkages
• alternating sugar & phosphate molecules form the
‘backbone’- uniform and unvarying.
• attached to each of the sugar molecules is a base
• Since bases vary, they represent a unique sequence
that carries the coded information held by the nucleic
acid.
Biology by C.J Clegg

24. DNA
Two nucleotide chains held together by
hydrogen bonds & entwined around each
other in a double helix
• composes genes, hereditary material of
cell
• remains in the nucleus
• contains instructions for making all the
proteins, & all the RNA the organism
needs.
• pairing: adenine (A) with thymine (T),
& cytosine (C) with guanine (G),
• sugar deoxyribose, and phosphate.
RNA
RNA is usually composed of one
nucleotide chain
• participates in protein synthesis.
• types:
• mRNA (messenger)
• tRNA (transfer)
• rRNA (ribosomal)
• pairing: adenine (A) with uracil (U), &
cytosine (C) with guanine (G),
• sugar ribose, and phosphate.
Biology by S.B Martin, 9th Edition

25. DNA
THE DOUBLE HELIX
Biology by C.J Clegg

26. RNA
RNA can fold upon itself, with the folds stabilized by
short areas of complementary base pairing within the
molecule, forming a three-dimensional structure.

27. RECOMMENDED BOOKs
Biology by S.B Martin, 9th Edition
Biology by C.J Clegg
Biology, OpenStax College
ADDITIONAL READ
https://www.youtube.com/watch?v=YO244P1e9QM
&ab_channel=AmoebaSisters
https://www.youtube.com/watch?v=0Elo-
zX1k8M&ab_channel=AmoebaSisters
27