1. Chapter 10 Part - 1 Molecular Biology of the Gene - DNA Structure and Replication

2. DNA Structure and Function James Watson and Francis Crick –discovered the chemical structure of DNA in 1953. –It allowed the researchers to understand the fundamental processes in genetics.

3. DNA Structure and Function Watson’s and Crick’s research –was aided by the work of others, including Rosalind Franklin, who was using X- ray Crystallography to learn about DNA’s structure.

4. Nucleic Acids: - They are a special group of chemicals in cells concerned with the transmission of inherited information - They have the capacity to store the information that controls cellular activity

5. Kinds of nucleic acids There are two kinds of nucleic acids: Deoxyribonucleic acid (DNA) – Is a major component of chromosomes and in found in the nucleus Ribonucleic acid (RNA) – is involved in the “reading” of the DNA information

6. Nucleotides All nucleic acids made up of simple repeating units (monomers) called Nucleotides, link together to form chains or strands, often of great length

7. Nucleotides The strands vary in the sequence of the bases found on each nucleotide. It is this sequence which provides the “genetic code”.

8. Each nucleotide –is made up of a 5 – carbon sugar (monosaccharide), a phosphate group, and four types of nitrogenous bases.

9. Nitrogenous Bases Nitrogenous bases –received their name because they all contain nitrogen The principal bases of DNA - Purines Adenine (A) Guanine (G) - Pyrimidines Cytosine (C) Thymine (T)

10. Nitrogenous Bases The principal bases of RNA –Purines Adenine (A) Guanine (G) –Pyrimidines Cytosine (C) Uracil (U) Please note that in RNA Thymine (T) is replaced by Uracil (U)

11. Base pairing rules Nucleotides link according to strict base pairing rules; A = T A always pairs with T) G = C (G always pairs with C) Base pairs are joined to each other in the middle by hydrogen bonds.

12. The Molecular Structure of DNA In 1953, Watson and Crick figured out that DNA molecule has two strands twisted into a double helix (corkscrew shape) each made of a series of repeating subunit nucleotides. A DNA molecule looks like a twisted ladder or spiral staircase

13. The Molecular Structure of DNA The sides of the ladder or the “handrails” or “backbone” are made up of sugar and phosphate groups. The steps, or “rungs” of the ladder are formed by nitrogenous bases. Each rung is made up of a complimentary base pair (either A-T or G-C) held together by hydrogen bonding.

14. RNA Structure and Function Structure –a single stranded structure with the base Uracil instead of Thymine –contains the 5-carbon sugar (Ribose instead of the Deoxyribose as in the case of DNA) Function - The primary function of RNA is to carry the instructions from DNA to the cytoplasm and to direct the synthesis of protein.

15. DNA and RNA Similarities and Differences Similarities – Both are nucleic acids Both composed of nucleotides Both have a sugar- phosphate backbone Both have four different types of nitrogen bases.

16. Differences DNA RNA 1.Found in nucleus 1. Found in nucleolus, nucleus and Cytoplasm 2. The genetic material 2. Helper to DNA 3. Sugar is a 5-carbon Deoxyribose 3. 5-carbon sugar is Ribose 4. Bases are A,, C, G and T 4. Bases are A, C, G and U 5. Double stranded (chain) 5. Single stranded (chain) 6. Is transcribed (to give mRNA) 6. Is translated (to give proteins) 7. One type 7. Three types: - mRNA - tRNA - rRNA

17. Types of RNA mRNA –Carries genetic information from chromosomes to the ribosomes and directs the synthesis of protein (in cytoplasm) tRNA –Transfer amino acids to the ribosomes, where they are joined (in cytoplasm) rRNA –Is found within the ribosomes (in cytoplasm). It is a structural component of ribosomes

18. DNA Replication For the information in DNA to be passed on, it must first be copied. This coping of DNA is known as DNA replication (it is making a copy of itself) The duplication of DNA, occurs during the Interphase stage of the cell cycle Replication of DNA is the initial step for cell division (both mitosis and meiosis) This process creates two sister chromatids that are found in chromosomes that are held together by a common centromere

19. Steps in DNA Replication DNA replication requires energy and enzymes Each of the two original strands serves as a template (or pattern) for creation of a new matching strand

20. Step 1 Unwind the DNA molecule –The hydrogen bonds between the paired bases break –The double helix unwinds or “unzips” a short segment of the DNA, exposing its base by a enzyme called helicase. –Nucleotides on each of two single strands are now available to form base pair with their compliment from a new free- floating nucleotide.

21. Step 2 Make new strands –DNA polymerase “reads” the exposed strand, and assembles complementary bases across from them. –The addition and matching of new bases as catalyzed by DNA polymerase. – DNA polymerase is also responsible for editing out any mismatches.

22. Step 3 Enzyme DNA Ligase seals ‘sugar Phosphate’ backbone of the small DNA segmented pieces. The new helices are composed of half old (original) and half newly joined nucleotides (Semi-conservative model)

23. DNA Replication Process

24. Mutation Mutation – Permanent alteration in cell’s DNA base sequence A permanent change in a gene may cause a change in phenotype Error rate minimized by DNA polymerase proof reading Mutations often have no ill effect on the organism. Point Mutation – a permanent mistake in a particular location in the genome.

25. Mutation

26. Chromosomal Mutations Mutation –may lead to the proliferation of cells resulting in cancerous growth. Mutation rate is low, but after decades of accumulated mutations, cells can become malignant Heritable mutation –occur in germ-cells (cells that divides to make sperm and egg) –also create genetic diversity