Section A: DNA as the Genetic Material CHAPTER 16 THE MOLECULE BASIS OF INHERITANCE

Watson and Crick discovered the double helix by building models to conform to X-ray data In April 1953, James Watson and Francis Crick shook the scientific world with an elegant double-helical model for the structure of deoxyribonucleic acid or DNA. In April 1953, James Watson and Francis Crick shook the scientific world with an elegant double-helical model النموذج الحلزونى المزدوج for the structure of deoxyribonucleic acid or DNA. Watson and Crick began to work on a model of DNA with two strands, the double helix. Watson and Crick began to work on a model of DNA with two strands, the double helix الحلزونى المزدوج.

The amino acid sequence of a polypeptide is programmed by a gene.The amino acid sequence of a polypeptide is programmed by a gene. A gene is a small region in the DNA.A gene is a small region in the DNA. Nucleic acids store and transmit hereditary information.Nucleic acids store and transmit hereditary information المعلومات الوراثية. There are two types of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).There are two types of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Organisms inherit DNA from their parents.Organisms inherit تتوارث DNA from their parents. –When a cell divides, its DNA is copied and passed to the next generation of cells. –When a cell divides تنقسم, its DNA is copied and passed to the next generation of cells. DNA : Introduction

Structures of nucleic acids (DNA & RNA) o H H H H H CH 2 o P o o o Base o P o o o o H H H H H CH 2 Base DNA nucleotide Bases Thymine (T) Adenine (A) Cytosine (C) Guanine (G) Purine Pyrimidine Deoxyribose Phosphate group

Fig. 16.3, Page 290 The PO 4 group of one nucleotide is attached to the sugar of the next nucleotide in line فى صف مستقيم.The PO 4 group of one nucleotide is attached to the sugar of the next nucleotide in line فى صف مستقيم.

Nitrogenous bases القواعد النيتروجينية Sugar-phosphate backbones Thymine (T) Adenine (A) Cytosine (C) Guanine (G) Purine Pyrimidines Hydrogen bonds Nitrogenous bases Uracil (U)

Adenine (A) would form 2 hydrogen bonds only with thymine (T) Adenine (A) would form 2 hydrogen bonds only with thymine (T) Guanine (G) would form 3 hydrogen bonds only with cytosine (C). Guanine (G) would form 3 hydrogen bonds only with cytosine (C). Fig. 16.6, Page 292 DNA

DNA & RNA o H H H H H CH 2 Deoxyribose sugar ( O on C2 is missed ) o OH H H H H CH 2 Ribose sugar (no missed O) R ibo- N ucleic- A cid D eoxiribo- N ucleic- A cid Single stranded nucleic acid Double stranded nucleic acid Bases: A, G, C, T Bases: A, G, C, U

Nucleic acids consist of تتكون من nucleotides.Nucleic acids consist of تتكون من nucleotides. Each nucleotide consists of three parts ثلاث اجزاء: a nitrogen base قاعدة نتروجينية, a pentose sugar سكر خماسي, and a phosphate group.Each nucleotide consists of three parts ثلاث اجزاء: a nitrogen base قاعدة نتروجينية, a pentose sugar سكر خماسي, and a phosphate group. The nitrogen bases come in two types: Purines and Pyrimidines.The nitrogen bases come in two types: Purines and Pyrimidines. The pentose sugar joined to المرتبط بـ the nitrogen base is ribose in nucleotides of RNA and deoxyribose in DNA.The pentose sugar joined to المرتبط بـ the nitrogen base is ribose in nucleotides of RNA and deoxyribose in DNA. The only difference الفرق بينbetween the sugars is the lack نقص of an oxygen atom ذرة on carbon 2 in deoxyribose.The only difference الفرق بينbetween the sugars is the lack نقص of an oxygen atom ذرة on carbon 2 in deoxyribose. Nucleic acids الاحماض النووية

phosphodiesterSugars of one nucleotide join ترتبط the phosphate of the next with a phosphodiester bond. Genes are normally hundreds to thousands of nucleotides long. الترتيب التتابعى يُحدد ترتيب الأحماض الأمينيةThe linear order الترتيب التتابعى of bases in a gene specifies يُحدد the order of amino acids ترتيب الأحماض الأمينية ( the monomers of a protein ).

The flow of genetic information is from DNA mRNA protein. –Protein synthesis occurs in Ribosomes. Fig. 5.28

An RNA molecule is single polynucleotide chain (single strand).An RNA molecule is single polynucleotide chain (single strand). DNA molecules have two polynucleotide strands (double strand) that spiral around to form a double helix حلزون مزدوج.DNA molecules have two polynucleotide strands (double strand) that spiral around تدور حلزونيا to form a double helix حلزون مزدوج. Inheritance is based on replication of the DNA double helix Fig. 16.5, Page 291

–Adenine (A) always pairs with thymine (T) and guanine (G) with cytosine (C). If we know the sequence of bases تتابع القواعد on one strand الخيط, we know the sequence on the opposite strand.If we know the sequence of bases تتابع القواعد on one strand الخيط, we know the sequence on the opposite المقابل strand. The two strands are complementary.The two strands are complementary مكملين لبعضهما.

Repeated Sugar - Phosphate Sugar–Phosphate-BaseSugar–Phosphate-Base PolynucleotidePolynucleotide DNA backbone One nucleotide DNA Molecule DNA Double stranded RNA single stranded TCGATAG AGTCTAC UUmRNA DNA