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Course lecturer : Jasmin Šutković

Organic Chemistry – FALL 2015

Lecture 10Nucleic acids and protein synthesis

CHAPTER OUTLINE International University of Sarajevo

22.1 Nucleosides and Nucleotides22.2 Nucleic Acids22.3 The DNA Double Helix22.4 Replication22.5 RNA22.6 Transcription22.7 The Genetic Code22.8 Translation and Protein Synthesis22.9 Mutations and Genetic Diseases22.10 Recombinant DNA22.11 FOCUS ON HEALTH & MEDICINE:Viruses

Book chapter 22

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 MONOSACCHARIDEAND 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 are formed by adding a phosphate group to the 5'-OH of a nucleoside.

Ribonucleotides are derived from ribose, while deoxyribonucleotides are derived from 2-deoxyribose.

NUCLEOTIDES—JOINING A NUCLEOSIDEWITH A PHOSPHATE

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.

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.

TRANSLATION AND PROTEIN SYNTHESIS

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