Nucleic Acids PDF

Nucleic Acids 21.1 Components of Nucleic Acids Nucleic Acids The transfer of necessary genetic information to new cells by the means of these biomolecules Classified into two categories: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), both are polymers consisting of...

Nucleic Acids 21.1 Components of Nucleic Acids Nucleic Acids The transfer of necessary genetic information to new cells by the means of these biomolecules Classified into two categories: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), both are polymers consisting of long, linear molecules. Ribonucleic acid (RNA) found mainly in the cytoplasm of living cells sugar component: D-ribose Deoxyribonucleic acid (DNA) found primarily in the nuclei of cells sugar component: D-deoxyribose (as it lacks one oxygen atom at the second position of the heterocyclic ring) Both sugars of the nucleic acids occur in β-configuration Nucleotides The repeating structural units, or monomers of the nucleic acids Composed of three simpler components: heterocyclic base, sugar, and phosphate Heterocyclic compounds can be classified as either pyrimidine or purine Uracil, Thymine, Cytosine (U,T,C) - three pyrimidine bases Adenine and Guanine (A,G) - two purine bases Adenine, Guanine & Cytosine - both in DNA and RNA Uracil - only RNA Thymine - only DNA Phosphate the third component of nucleotides derived from phosphoric acid (𝐻3𝑃𝑂4), which under cellular pH conditions exists in ionic form: 21.2 The Structure of DNA DNA molecules largest molecules known contain between 1 million and 100 million nucleotide units linkages are referred to as phosphodiester bonds Nucleic acid backbone sugar-phosphate chain that is common to all nucleic acids Constant throughout the entire DNA molecule The order of the bases provides the primary structure of DNA —phosphate—sugar—phosphate—sugar—phosphate—sugar— 21.2A The Secondary Structure of DNA Secondary structure of DNA proposed in 1953 by American molecular biologist James D. Watson and English biologist Francis H. C. Crick greatest discovery of modern biology Watson and Crick concluded that DNA is composed of two strands entwined around each other in a double helix In double helical DNA, wherever there is an adenine on one strand of the helix, there must be a thymine on the other strand, and similarly for guanine and cytosine. The two DNA strands with these matched sequences are said to be complementary to each other. 21.3 DNA Replication DNA responsible for one of the most essential functions of living organisms, the storage and transmission of hereditary information. Chromosomes a tightly packed bundle of DNA and protein that is involved in cell division A human cell normally contains 46 chromosomes each chromosome contains one molecule of DNA coiled tightly about a group of small basic proteins called histones Genes an individual sections of a chromosomal DNA molecule that is the fundamental unit of heredity Replication the process by which an exact copy of DNA is produced occurs when two strands of DNA separate and each serves as a template (pattern) for the construction of its own complement. Semiconservative replication - a replication process that produces DNA molecules containing one strand from the parent and a new strand that is complementary to the strand from the parent Replication fork a point where the double helix of a DNA molecule unwinds during replication Nicks the gaps or breaks between segments in the daughter strand Okazaki fragment DNA fragments separated by the nicks Produced during replication as a result of strand growth in a direction away from the replication fork Polymerase chain reaction (PCR) mimics the natural process of replication, in which the DNA double helix unwinds. a technique to make many copies of a specific DNA region in vitro (in a test tube rather than an organism) 21.4 Ribonucleic Acid (RNA) Ribonucleic Acid (RNA) long unbranched polymer consisting of nucleotides joined by 3’ —> 5’ phosphodiester bonds RNA molecules are single stranded, except in some viruses distributed throughout the cells; nucleus, cytoplasm & mitochondria cells contain three main kinds of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA) Messenger RNA (mRNA) RNA that carries genetic information from the DNA in the cell nucleus to the site of protein synthesis in the cytoplasm has a short lifetime—usually less than an hour Ribosomal RNA (rRNA) RNA that constitutes about 65% of the material in ribosomes Ribosome - a subcellular particle that serves as the site of protein synthesis in all organisms Transfer RNA (tRNA) RNA that delivers individual amino acid molecules to the site of protein synthesis smallest of all the nucleic acids, containing 73-93 nucleotides per chain Anticodon a three-base sequence in tRNA that is complementary to one of the codons in mRNA non-coding RNA (ncRNa) typically less than 200 nucleotides long and are not translated into protein junk RNA 21.5 The Flow of Genetic Information DNA the storehouse of genetic information in the cell and that the stored information can be passed on to new cells as it undergoes replication. Central Dogma of Molecular Biology well-established process by which genetic information stored in DNA molecules is expressed in the structure of synthesized proteins Two steps involved in the flow of information: transcription and translation Transcription the transfer of genetic information from a DNA molecule to a molecule of messenger RNA Translation the conversion of the code carried by messenger RNA into an amino acid sequence of a protein Genetic Code the communicative relationship between mRNA nucleotides and amino acids 21.6 Transcription: RNA Synthesis RNA polymerase an enzyme that catalyzes the synthesis of RNA Introns segment of a eukaryotic DNA molecule that carries no codes for amino acids Exons segment of a eukaryotic DNA molecule that is Coded for amino acids Heterogenous nuclear RNA RNA produced when both introns and exons of eukaryotic cellular DNA are transcribed 21.7 The Genetic Code Genetic code a series of three-letter words that represent the amino acids of proteins as well as start and stop signals for protein synthesis Codon a sequence of three nucleotide bases that represents a code word on mRNA molecules 21.8 Translation and Protein Synthesis 21.9 Mutations Mutations any change that results in an incorrect sequence of bases on DNA some occur naturally during DNA replication, whereas others are induced by environmental factors may be lethal or result in genetic diseases 21.10 Recombinant DNA Genetic engineering discovery and application of restriction enzymes and DNA ligases isolation of genes (DNA) that code for specific useful proteins and the introduction of these genes into the DNA of bacteria