DNA and RNA Nucleotide Structure

• DNA and RNA are nucleic acids composed of nucleotide chains.
• Nucleotides contain nitrogenous bases: adenine (A), cytosine (C), guanine (G), or thymine (T).
• The sequences of nucleotides are vast.

Nucleotide Structure

• Nucleotides have a nitrogenous base, a sugar, and a phosphate group.
• Nucleotides are linked by covalent bonds between the sugar of one nucleotide and the phosphate of the next.
• This forms a sugar-phosphate backbone, with nitrogenous bases projecting from it.
• A single nucleotide consists of a phosphate group, a sugar (deoxyribose), and a nitrogenous base.
• The phosphate group features a phosphorus atom surrounded by four oxygen atoms.
• Deoxyribose has five carbon atoms, and lacks an oxygen atom compared to ribose.
• DNA stands for deoxyribonucleic acid.

Nitrogenous Bases

• Nitrogenous bases are basic
• Each contains a single or double ring structure made of nitrogen and carbon atoms with functional groups attached.
• These functional groups affect the molecule's function by participating in chemical reactions.
• The NH2 group on cytosine can form a hydrogen bond with the C═O group on guanine.
• This specificity in chemical groups is responsible for the specific base pairing in DNA.
• Pyrimidines are single-ring structures (thymine and cytosine).
• Purines are double-ring structures (adenine and guanine).

RNA vs. DNA

• RNA's sugar is ribose, containing an -OH group that deoxyribose lacks.
• RNA contains Uracil instead of Thymine.
• RNA polynucleotide chains are chemically alike to DNA polynucleotide chains.

DNA and RNA Comparison

• Both are polymers of nucleotides with a sugar, a nitrogenous base, and a phosphate.
• RNA has ribose, DNA has deoxyribose.
• Both have A, G, and C Bases, but DNA has T whereas RNA has U.
• Nucleotides are a building block of nucleic acids, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and one or more phosphate groups.
• Polynucleotides are a polymer made up of many nucleotide monomers covalently bonded together
• The Double helix DNA form has two adjacent polynucleotide strands interwound into a spiral shape.

DNA Structure Discovery

• James D. Watson and Francis Crick first discovered DNA structure.
• Watson saw an X-ray image of DNA taken by Rosalind Franklin.
• The image suggested a helical shape with a uniform diameter and nitrogenous bases stacked like plates

Watson and Crick's Model

• The model featured sugar-phosphate backbones on the outside of the helix and nitrogenous bases on the interior.
• A double-ring base (purine) pairs with a single-ring base (pyrimidine) for consistent thickness.
• Adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C).
• These pairings are complementary.

Chargaff's Rules

• Adenine (A) levels equal thymine (T) levels, and guanine (G) levels equal cytosine (C) levels
• This is because A always pairs with T and G always pairs with C on DNA’s polynucleotide chains.
• The DNA double helix model is like a twisted rope ladder.
• The sides are sugar-phosphate backbones, the rungs nitrogenous base pairs connected by hydrogen bonds.
• C-G pairs form three hydrogen bonds, while A-T pairs form two.

Watson, Crick and Wilkins

• Watson, Crick, and Maurice Wilkins received the Nobel Prize in 1962
• Rosalind Franklin had passed away in 1958 and was not eligible for the prize.
• Genetic information is encoded in the nucleotide sequence of DNA.

DNA Replication

• DNA encodes and stores genetic information.
• It is the molecular basis of heredity.
• During cell division, genes are passed from one cell to the next.
• Complementary base pairing allows DNA to be copied.
• A pairs with T, and G pairs with C
• Parental DNA strands separate, and each serves as a template for assembling a complementary strand.
• Enzymes link nucleotides to form new DNA strands.
• Daughter DNA molecules are identical to the parental DNA.

DNA Replication Model

• Each daughter molecule has one old strand from the parental molecule and one new strand.
• This semiconservative model means half of the parental molecule is conserved in each daughter molecule.
• The process requires many enzymes and proteins.

DNA Synthesis Accuracy

• E. coli replicates in under an hour and human cells in a few hours.
• The process has only about one incorrect DNA nucleotide per several billion.
• When the two strands of the double helix separate, free nucleotides can base-pair along each strand, leading to the synthesis of new complementary strands.