Molecular Basis of Inheritance: DNA Structure Lecture Notes Fall 2024

1 1 2 2 3 3 4 4 5 5  Eukaryotic Cell - Animal 6 6  The Nucleus: Information Central Nucleus is usually most conspicuous organelle Nuclear membrane encloses nucleus and is a double me...

1 1 2 2 3 3 4 4 5 5  Eukaryotic Cell - Animal 6 6  The Nucleus: Information Central Nucleus is usually most conspicuous organelle Nuclear membrane encloses nucleus and is a double membrane – Each membrane consists of a lipid bilayer The nucleus contains most of the DNA in an eukaryotic cell 7 7  Overview: Life’s Operating Instructions Hereditary information is encoded in DNA and reproduced in all body cells DNA program directs the development of biochemical, anatomical, physiological, and (to some extent) behavioural traits Ribosomes use the information from the DNA to make proteins 8 8  Concept : Nucleic acids store, transmit, and help express hereditary information The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene Genes are made of DNA, a nucleic acid made of monomers called nucleotides 9 9  The Roles of Nucleic Acids There are two types of nucleic acids – Deoxyribonucleic acid (DNA) – Ribonucleic acid (RNA) Two roles of DNA 1. DNA provides directions for its own replication 2. DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis 10 10  The central dogma of molecular genetics is that DNA makes RNA, which makes proteins 11 11  DNA RNA Protein In eukaryotic cell …. DNA replication occurs in the nucleus Transcription – forming of mRNA happens in the nucleus Translation – forming protein/polypeptide happens in the cytoplasm © 2014 Pearson Education Ltd. 12 12  DNA makes 3 major types of RNA by Transcription mRNA – decoded message from gene/DNA – is translated rRNA – structural component of ribosome – is not translated tRNA – transports amino acid during translation – is not translated 13 13 Fig. 14.7 Watson and Crick 1953 Nobel prize 1956 14 14  DNA Structure James Watson and Francis Crick, 1953 – proposed a double helix structure – Two strands of DNA wrapped onto each other in a helical fashion 15 15  The Components of Nucleic Acids Nucleic acids are polymers called polynucleotides Each polynucleotide is made of monomers called nucleotides 16 16  The Components (monomers) of Nucleic Acids Nucleoside = nitrogenous base + sugar Nucleotide = nucleoside + phosphate group Figure 5.25b 17 17  The Nitrogen bases of nucleotide Two types of nitrogenous bases Pyrimidines (cytosine, thymine, uracil) single six- membered ring Purines (adenine, guanine) six-membered ring fused to five- membered ring Figure 5.25c1 18 18  The sugar In DNA, the sugar is deoxyribose component of In RNA, the sugar is ribose nucleotide 19 19  The Structures of DNA Molecule DNA is a double helix and shows complimentarity and antiparallel nature 20 20 20  5 end The structure of DNA Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm 5 end (a) Key features of DNA structure (b) Partial chemical structure 21 21 21  Linking two nucleotides Adjacent nucleotides are joined by covalent bonds formed between -OH group on 3’ carbon of one nucleotide and phosphate on 5’ carbon on next 22 22  1. Links create Nucleotide 5’ PO4 Polymers sugar-phosphate backbone with 3’ OH nitrogenous bases as appendages 2. Sequence of bases in a DNA or mRNA polymer is unique for each gene 3. A DNA molecule includes many genes 23 23 24 24  …… and … so the DNA structure looks like this !!!!! 25 25  What does the RNA look like????? 26 26  Structural comparison of the genome components of eukaryotes, prokaryotes, and viruses 27 27  Structural comparison of the genome components of eukaryotes, prokaryotes, and viruses 28 28 28 29 29  Structural comparison of the genome components of eukaryotes, prokaryotes, and viruses 30 30  From DNA to Chromosome 31 31  The Human Karyotype (arrangement of paired chromosomes in decreasing order of length) 32 32  Khatam 33 33