Molecular Basis of Inheritance

• General Animal Biology (Zool-109) discusses the molecular basis of inheritance
• The course utilizes the textbook "Campbell Biology" (10th edition)

Molecular Basis of Inheritance

• Watson and Crick discovered the double helix structure of DNA by building models based on X-ray data.
• In April 1953, James Watson and Francis Crick revealed an elegant double-helical model for DNA structure.
• Watson and Crick began working on a model of DNA with two strands, the double helix.

DNA: The Genetic Material

• The amino acid sequence of a polypeptide is programmed by a gene.
• A gene is a small region in DNA.
• Nucleic acids store and transmit hereditary information.
• The two types of nucleic acids are ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
• DNA directs mRNA synthesis, controlling protein synthesis.
• Organisms inherit DNA from their parents.
• Each DNA molecule is very long, consisting of hundreds to thousands of genes.
• When a cell divides, its DNA is copied and passed to the next generation of cells during meiosis.
• mRNA interacts with ribosomes to direct the synthesis of amino acids in a polypeptide (protein).

Structure of DNA

• DNA and RNA are composed of nucleotides.
• Nucleotides include a base, a sugar portion and a phosphate group.
• The bases in DNA are Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
• Adenine and Guanine are purines.
• Cytosine and Thymine are pyrimidines.
• One nucleotide's phosphate group links to the sugar of the next, forming a sugar-phosphate backbone.
• The sugar-phosphate backbone consists of alternating phosphates and sugars, from which the bases start.
• Bases are attached to this backbone.
• Cytosine, Guanine, Thymine, Adenine, and Uracil are nitrogenous bases.
• Cytosine and Guanine form three hydrogen bonds.
• Thymine and Adenine form two hydrogen bonds.

DNA vs RNA

• DNA contains deoxyribose sugar (one less oxygen atom).
• RNA contains ribose sugar.
• DNA is a double-stranded nucleic acid, while RNA is single-stranded.
• DNA uses the bases A, G, C, and T, while RNA uses A, G, C, and U (Uracil).

Nucleic Acid Polymer

• Nucleic acids are polymers of nucleotide monomers.
• Each nucleotide has three parts: a nitrogenous base, a pentose sugar, and a phosphate group.
• Nitrogenous bases (carbon and nitrogen rings) are either purines or pyrimidines.
• The pentose sugar is ribose in RNA and deoxyribose in DNA.
• The only difference between the sugars is an oxygen atom's absence on carbon-2 in deoxyribose.
• Polynucleotides are synthesized by connecting the sugar of one nucleotide to the next nucleotide's phosphate via a phosphodiester link.
• A sugar-phosphate backbone with nitrogenous bases as appendages is created.
• A DNA or mRNA polymer's nitrogen base sequence is unique for each gene.
• Genes can be hundreds to thousands of nucleotides.
• The linear order of bases in a gene dictates the amino acid order which creates a protein.
• The flow of genetic information is from DNA to mRNA to protein (at the ribosome).
• Protein synthesis is carried out by ribosomes.
• In eukaryotes, DNA resides in the nucleus, but most ribosomes are in the cytoplasm with mRNA serving as an intermediary.
• RNA is a single polynucleotide chain.
• DNA molecules are composed of two polynucleotide strands (double strand) spiraling into a double helix.
• The sugar-phosphate backbones of DNA are on the helix's exterior.
• Pairs of nitrogenous bases connect the chain using hydrogen bonds.
• DNA molecules have thousands to millions of base pairs.
• Base pairing occurs when Adenine (A) always pairs with Thymine (T), and Guanine (G) with Cytosine (C).
• Two identical copies of the original double-stranded DNA molecule are produced.
• The copies are distributed to the daughter cells by meiosis.
• The process ensures that genetic information is transmitted.