LOGO
Lecture 10
Nucleic acids and protein synthesis
Organic Chemistry – FALL 2015
Course lecturer :
Jasmin Šutković
CHAPTER OUTLINE
International University of Sarajevo
Book chapter 22
22.1 Nucleosides and Nucleotides
22.2 Nucleic Acids
22.3 The DNA Double Helix
22.4 Replication
22.5 RNA
22.6 Transcription
22.7 The Genetic Code
22.8 Translation and Protein Synthesis
22.9 Mutations and Genetic Diseases
22.10 Recombinant DNA
22.11 FOCUS ON HEALTH & MEDICINE:
Viruses
Introduction
 WHETHER you are tall or short, fair-skinned or dark-complexioned,
blue-eyed or brown-eyed, your unique characteristics are determined
by the nucleic acid polymers that reside in the chromosomes of your
cells.
 The nucleic acid DNA stores the genetic information of a particular
organism, while the nucleic acid RNA translates this genetic
information into the synthesis of proteins needed by cells for
proper function and development.
 Even minor alterations in the nucleic acid sequence can have
significant effects on an organism, sometimes resulting in
devastating diseases like sickle cell anemia and cystic fibrosis.
NUCLEOSIDES AND NUCLEOTIDES
 Nucleic acids are unbranched polymers composed of repeating
monomers called nucleotides.
 There are two types of nucleic acids.
1. DNA, deoxyribonucleic acid, stores the genetic information of an
organism and transmits that information from one generation to another.
2. RNA, ribonucleic acid, translates the genetic information contained in DNA
into proteins needed for all cellular functions.
The nucleotide monomers that compose DNA and RNA consist of three components—a
monosaccharide, a nitrogen-containing base, and a phosphate group.
About DNA
 Found in Chromosomes
 Humans have 46 – other species have
different numbers
 Chromosomes are divided into genes
 A gene is a portion of the DNA molecule
responsible for the synthesis of a single
protein.
NUCLEOSIDES—JOINING A MONOSACCHARIDE
AND A BASE
The nucleotides of both DNA and RNA contain a five-membered ring
monosaccharide, often called simply the sugar component.
• In RNA, the monosaccharide is the aldopentose D-ribose.
• In DNA the monosaccharide is D-2-deoxyribose, an aldopentose that
lacks a hydroxyl group at C2.
Bases
Only five common nitrogen-containing bases are present in nucleic
acids.
• Three bases with one ring (cytosine, uracil, and thymine) are
derived from the parent compound pyrimidine.
• Two bases with two rings (adenine and guanine) are derived from
the parent compound purine.
Each base is designated by a one-letter abbreviation.
NUCLEOTIDES—JOINING A NUCLEOSIDE
WITH A PHOSPHATE
 Nucleotides are formed by adding a
phosphate group to the 5'-OH of a
nucleoside.
 Ribonucleotides are derived from ribose, while
deoxyribonucleotides are derived from 2deoxyribose.
NUCLEIC ACIDS
Nucleic acids—both DNA and RNA—are polymers of
nucleotides, formed by joining the 3'-OH group of one
nucleotide with the 5'-phosphate of a second nucleotide in
a phosphodiester linkage.
THE DNA DOUBLE HELIX
 Our current understanding of the structure
of DNA is based on the model proposed
initially by James Watson and Francis
Crick in 1953
 DNA consists of two polynucleotide
strands that wind into a right-handed
double helix.
The double helix is stabilized by hydrogen bonding between the bases
of the two DNA strands as shown in Figure 22.4. A purine base on one
strand always hydrogen bonds with a pyrimidine base on the other
strand.
Two bases hydrogen bond together in a predictable manner, forming
complementary base pairs.
• Adenine pairs with thymine using two hydrogen bonds, forming an A–T
base pair.
• Cytosine pairs with guanine using three hydrogen bonds, forming a C–
G base pair.
Central Dogma
 What comes after ...how we synyhesise the protein then?
 Each chromosome contains many genes, those portions
of the DNA molecules that result in the synthesis of
specific proteins.
 We say that the genetic message of the DNA molecule is
expressed in the protein. Only a small fraction (1–2%) of
the DNA in a chromosome contains genetic messages or
genes that result in protein synthesis.
REPLICATION
RNA
While RNA is also composed of nucleotides, there are important
differences between DNA and RNA.
 In RNA, The sugar is ribose.
 U (uracil) replaces T (thymine) as one of the bases.
 RNA is single stranded.
RNA molecules are much smaller than DNA molecules
 Ribosomal RNA (rRNA)
 Messenger RNA (mRNA)
 Transfer RNA (tRNA)
Types of RNA molecueles
 Ribosomal RNA, the most abundant type of RNA, is found in the ribosomes
in the cytoplasm of the cell. Each ribosome is composed of one large subunit
and one small subunit that contain both RNA and protein. rRNA provides the
site where polypeptides are assembled during protein synthesis.
 Messenger RNA is the carrier of information from DNA (in the cell nucleus)
to the ribosomes (in the cytoplasm). Each gene of a DNA molecule
corresponds to a specifi c mRNA molecule. The sequence of nucleotides in
the mRNA molecule determines the amino acid sequence in a particular
protein.
 Transfer RNA, the smallest type of RNA, interprets the genetic information
in mRNA and brings specific amino acids to the site of protein synthesis in
the ribosome. Each amino acid is recognized by one or more tRNA
molecules, which contain 70–90 nucleotides..
TRANSCRIPTION
 The conversion of the information in DNA to the synthesis of proteins
begins with transcription— that is, the synthesis of messenger
RNA from DNA.
The genetic code
 From DNA to RNA ....so how can small
mRNA make a protein ?
Its because the GENETIC CODE
For example, the codon UAC in an mRNA molecule codes
for the amino acid serine, and the codon UGC codes for the
amino acid cysteine. The same genetic code occurs in
almost all organisms from bacteria to whales to humans.
TRANSLATION AND PROTEIN
SYNTHESIS
The translation of the information in messenger RNA to protein synthesis
occurs in the ribosomes.
Each type of RNA plays a role in protein synthesis.



mRNA contains the sequence of codons that determines the order of amino
acids in the protein.
Individual tRNAs bring specifi c amino acids to add to the peptide chain.
rRNA contains binding sites that provide the platform on which protein
synthesis occurs.
Each individual tRNA contains an anticodon of three nucleotides that is
complementary to th codon in mRNA and identifi es individual amino acids.
For example, a codon of UCA in mRNA corresponds to an anticodon of AGU
in a tRNA molecule, which identifi es serine as the amino acid.
Celluloze
Trabslation phases
 Initiation- mRNA binds to ribosome and starts
with AUG codon (coding for Methionine).tRNA
brings anticodone that codes for one specific
amino acid
 Elongation – next tRNA brings another amino
acid and attaches to the first a.a(methionine)
 Termination – when the stop codon comes
(UAE,UAG or UGA) then the traslation stops
Mutations