Nucleic acids

• DNA and RNA are both types of nucleic acid found in all living cells
• Both DNA and RNA are needed to build proteins, essential for cell functioning
• DNA holds genetic information and contains instructions for growth and development of organisms
• RNA transfers genetic code from DNA to ribosomes in the cytoplasm for protein production
• Nucleotides in DNA and RNA are made up of a pentose sugar, a nitrogen-containing organic base, and a phosphate group
• RNA nucleotides have a ribose sugar, a phosphate group, and one of four nitrogenous bases: adenine, cytosine, guanine, or uracil
• Purines (adenine, guanine) have a double ring structure, while pyrimidines (cytosine, thymine, uracil) have a single ring structure
• DNA and RNA are polymers made of nucleotides joined by phosphodiester bonds, forming a sugar-phosphate backbone
• DNA is a double helix structure with two antiparallel polynucleotide strands held together by hydrogen bonds between complementary base pairs
• RNA, like DNA, is a polynucleotide made up of many nucleotides linked together in a chain
• RNA nucleotides contain adenine (A), guanine (G), cytosine (C), and uracil (U) instead of thymine (T)
• RNA nucleotides contain the pentose sugar ribose instead of deoxyribose
• RNA molecules are single-stranded, unlike DNA which is double-stranded
• RNA polynucleotide chains are relatively short compared to DNA
• Each RNA polynucleotide strand is made up of alternating ribose sugars and phosphate groups linked together, with the nitrogenous bases of each nucleotide projecting out sideways
• The sugar-phosphate bonds in RNA are covalent bonds known as phosphodiester bonds, forming the sugar-phosphate backbone
• Examples of RNA molecules include messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)
• Ribosomes are small organelles that are the site of protein synthesis, formed from RNA and proteins
• Ribosomes are composed of a small subunit and a large subunit, with eukaryotic cells having 80S ribosomes and prokaryotic cells having 70S ribosomes
• Ribosomes read RNA to make polypeptides in a process known as translation
• The RNA in ribosomes, ribosomal RNA (rRNA), has enzymatic properties that catalyze the formation of peptide bonds between amino acids
• During DNA replication, the enzyme helicase unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs on the two antiparallel polynucleotide DNA strands
• DNA replication involves the formation of two single polynucleotide DNA strands from the hydrogen bonds between the base pairs on the two antiparallel DNA strands
• New nucleotides are joined together by DNA polymerase through condensation reactions to form a new strand
• In semi-conservative replication, half of the original DNA molecule is conserved in each of the two new DNA molecules
• DNA polymerase synthesizes new DNA strands by catalyzing condensation reactions between adjacent nucleotides, creating the sugar-phosphate backbone
• DNA polymerase cleaves the two extra phosphates, using the released energy to create phosphodiester bonds between adjacent nucleotides
• Hydrogen bonds form between the complementary base pairs of the template and new DNA strands
• DNA polymerase synthesizes the leading DNA strand continuously in the 5' to 3' direction, while the lagging strand is synthesized in short segments called Okazaki fragments
• DNA ligase joins the lagging strand segments together to form a continuous complementary DNA strand by catalyzing the formation of phosphodiester bonds between the segments
• The Watson-Crick model proposed semi-conservative DNA replication, where the original DNA strands separate and each serves as a template for a new strand
• Watson and Crick's theory of semi-conservative DNA replication was confirmed by Meselson and Stahl's experiment using bacteria and nitrogen isotopes