Section A: DNA as the Genetic Material

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

2. 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 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 الحلزونى المزدوج.

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

4. Bases 3 5 o o H H DNA nucleotide Adenine (A) CH2 CH2 Base Base 5 H H Purine H H H H H H 4 1 Guanine (G) 3 2 o o o o o o P P Cytosine (C) o o Pyrimidine Thymine (T) 5 3 Structures of nucleic acids (DNA & RNA) Phosphate group Deoxyribose 3

5. The PO4 group of one nucleotide is attached to the sugar of the next nucleotide in lineفى صف مستقيم. Fig. 16.3, Page 290

6. 5 3 Hydrogen bonds Cytosine (C) Guanine (G) Nitrogenous bases Thymine (T) Adenine (A) Purine Pyrimidines 5 3 Sugar-phosphate backbones Nitrogenous basesالقواعد النيتروجينية Uracil (U)

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

8. o H CH2 H Deoxyribose sugar (O on C2 is missed) H Ribose sugar (no missed O) H o H CH2 H H H H OH Single stranded nucleic acid Double stranded nucleic acid Bases: A, G, C, U Bases: A, G, C, T DNA & RNA Deoxiribo-Nucleic-Acid Ribo-Nucleic-Acid

9. Nucleic acids الاحماض النووية • 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. • 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 only difference الفرق بينbetween the sugars is the lack نقص of an oxygen atom ذرة on carbon 2 in deoxyribose.

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

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

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

13. 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 المقابل strand. • The two strands are complementary مكملين لبعضهما.

14. DNA backbone One nucleotide DNA Molecule A G C T A T C U U T C G A T A G Repeated Sugar - Phosphate Sugar–Phosphate-Base Polynucleotide DNA Double stranded RNA single stranded DNA mRNA