The central dogma of molecular biology, the basic structure of nucleic acids, Genetic code, 4 levels of protein structure, Revision question with answers

1. Slides prepared by Dr.Lakshmi
Structure and Function of
Large Biological Molecules-
Proteins and nucleic acids
Molecules of Life 2-
Biomolecules (2)

2. Learning Objectives
1. State the central dogma of molecular biology
2. Introduce the elements, type of bonds ,functional groups present in
proteins and nucleic acids.
3. For each group of biomolecules learn the name of its generic
monomer (simple unit) and polymer (complex structure) and their
function.
4. Identify the chemical elements and functional groups in proteins
5. Recognize the structure of an amino acid and the peptide bond that
connects di-, tri, and polypeptides.
6. Identify their chemical elements and components of a nucleotides in
nucleic acid.
7. Describe the function of DNA
8. Compare and contrast the 2 types of nucleic acids: DNA and RNA.
Slides prepared by Dr.Lakshmi

3. Look at yourself, the muscles, bones and the skin
are all made of cells, whose structure and
functions are determined by millions of proteins
in you.
The instructions for making all these proteins are "written" in a cell’s
DNA in the form of genes.
The central dogma of molecular biology
describes the two-step process:
1. Transcription
2. Translation
Thus information in genes flows into proteins:
DNA → RNA → protein

4. Transcription :is the synthesis of an RNA copy of a
segment of DNA.
mRNA (messenger RNA) is synthesized by the
enzyme RNA polymerase.
Translation: This mRNA comes out from cell
nucleus and goes to Ribosomes (protein making
factories).
Information in mRNA is decoded by ribosomes
and specific Amino acids are picked up from
cytoplasm and assembled to form polypeptides
which later fold into active protein to perform its
function
Two main process in protein synthesis (making)
Translation

5. Chemical Structures and Functions of Nucleic Acids
• Nucleic acids are polymers specialized for the storage,
transmission, and use of genetic information.
• They carry information inside the cells just as a disk in a computer
• DNA = deoxyribonucleic acid
• RNA = ribonucleic acid
• Nucleic acids are composed of monomers called nucleotides.
• Nucleotides consist of a pentose sugar, a phosphate group, and a
nitrogen-containing base.
• Molecules made of pentose sugar + nitrogenous base BUT No
phosphate is called nucleoside

6. Chemical Structures and Functions of Nucleic Acids
• Deoxyribonucleic acid (DNA): makes up
hereditary material of the cell (genes) and
contains instructions for making proteins
and RNA
• Ribonucleic acid (RNA): used in processes
that link amino acids to form polypeptides
• Pentose sugar:
• DNA = deoxyribonucleic acid (contains
deoxyribose)
• RNA = ribonucleic acid (contains ribose)

7. RNA and DNA:
Complementary base pairing can also
occur between DNA & RNA
C + G will still pair,
A will pair with U instead of T

8. • The “backbone” of DNA and RNA is a chain of sugars and phosphate
groups, bonded by a condensation reaction - phosphodiester linkages.
Chemical Structures and Functions of Nucleic Acids
The phosphate groups link
carbon 3′ in one sugar to
carbon 5′ in another sugar.

10. 3 RNA involved in protein synthesis

11. PROTEINS
 Proteins are linear polymers made with
more than 20 different amino acids
 Amino acids contain a basic amino group (-
NH2) and an acidic Carboxyl group (-
COOH) so they function as both base
(amino because it takes H) and acid
(carboxyl because it gives H).
 The unique character of each amino acid is
determined by the nature of the R group

12. There are genetic codes for specific Amino acids
GENETIC CODE SPECIFIES 20 AMINO ACIDS (AA):
• All 20 Amino acids are encoded by nucleotide triplets
called codons
• Codon is a 3 letter genetic code (AUG)
• Genetic codon is Redundant meaning several AA are
specified by multiple codons
Slides prepared by Dr.Lakshmi

13. Structure of Amino acids
 All Amino acids are monomers of protein.
 All amino acids have two functional groups attached to the
carbon (alpha - α carbon):
 carboxyl (COOH) and 2. amino groups (NH2)
 The α carbon atom is asymmetrical because it is bonded to four
different atoms/groups
 The side chains or R-groups also have functional groups.
 Hydrogen

14. Slide 14
• A condensation reaction (loss of water) forms a peptide bond
between two amino acids
• The N-terminus and the C-terminus are separated from each other at
each amino acid, but the N-terminus is made to firmly bind to the C-
terminus of another amino acid and the C-terminus to the N-
terminus of another amino acid.
• The important point is that the bond itself is in the same format as –
COOH vs. NH2 – both right and left. This results in a peptide bond of
(the amide group)-CONH-.
Formation of Peptide Bonds
The peptide bond is inflexible—no rotation is possible.

15. • Dipeptide: a molecule containing two amino acids joined by a
peptide bond.
• Tripeptide: a molecule containing three amino acids joined by
peptide bonds.
• An oligopeptide, or peptide (oligo-, "a few"), consists of two
to twenty amino acids and can include dipeptides,
tripeptides, tetrapeptides, and pentapeptides.
• Polypeptide: a macromolecule containing many amino acids
joined by peptide bonds(more than 50).
• Protein: a biological macromolecule of molecular weight 5000
g/mol or greater, consisting of one or more polypeptide
chains.
Different types of peptides

16. Slide 16
Break down of Peptide Bonds
• A dehydration reaction occurs when two monomers bond
together through the loss of a water molecule

17. There are four levels of protein structure
• The shape of the protein determines
its function.
• protein part with many nonpolar
amino acids tend to fold into the
interior of the protein
• Primary = sequence of Amino acids
• Secondary = forms pleated sheet,
helix, or coil
• Tertiary = entire length of Amino
acids folded into a shape
• Quaternary = several amino acids
sequences linked together

19. Functions of Proteins
1. •Enzymes—catalytic proteins (speed up the biochemical
reactions
2. Defensive proteins (e.G., Antibodies)
3. • signaling proteins - control physiological processes
(hormones)
4. Membrane transporters – regulate passage of substances
across cellular membranes
5. Receptor proteins—receive and respond to molecular signals
6. •Storage proteins store amino acids for later use
7. • Structural proteins provide physical stability and movement.
8. • Transport proteins carry substances within the organism
(e.G., Hemoglobin).
9. • Genetic regulatory proteins regulate when, how, and to what
extent a gene is expressed.

20. Quick revision
Q1. The reaction in the diagram shows
hydrolysis of protein
1. True
Q2. The diagram below
shows……………level of protein
structure 2.Quaternary
Q.3 The amino acid in below diagram is hydrophilic or
hydrophobic in nature
3. hydrophobic

21. 1. Oil and butter are Non polar substances cannot form
hydrogen bonds with water and are hydrophobic.
1. Name the monomer of a protein…
3. How many amino acids participate in a condensation
reaction by removing water to form a single peptide bonds
4. List all the 4 biological macromolecules
5. Carboxyl group is usually…...in nature and amino group is
usually in …..in nature
6. Monomer Alanine + Monomer glycine = dipeptide
7. Breaking of a peptide by removing water is called hydrolysis
( 1. True or False)
2. Amino acids
(3)2 reactants
4. Carbohydrates, proteins,
fats, nucleic acids
5. Acidic
Amino is basic
7. Yes
8. Yes
Quick Revision of past lectures

22. Recap
• List key differences between DNA & RNA
• List differences between pyrimidines & purines
• How do purines & pyrimidines pair up in complementary
base pairing?
• What are the differences between DNA replication &
transcription?