nucleic acids

• Both DNA and RNA carry information, with DNA holding genetic information and RNA transferring this genetic information from DNA to ribosomes made of RNA and proteins
• Both deoxyribonucleic and ribonucleic acid are polymers of nucleotides
• Nucleotides consist of pentose (a 5 carbon sugar), a nitrogen-containing organic base, and a phosphate group
• In DNA nucleotides, components include deoxyribose, a phosphate group, and one of the organic bases adenine, cytosine, guanine, or thymine
• Adenine and guanine in DNA have a double ring structure and are classified as purine bases
• In RNA nucleotides, components include ribose, a phosphate group, and one of the organic bases adenine, cytosine, guanine, or uracil
• Thymine, uracil, and cytosine in RNA have a single ring structure and are classified as pyrimidines
• Nucleotides join together by phosphodiester bonds formed in condensation reactions
• DNA is a double helix composed of two polynucleotides joined by hydrogen bonds between complementary bases
• In DNA, the two strands lie antiparallel, and complementary base pairing takes place between the 5’ to 3’ strand and the 3’ to 5’ strand
• A purine always joins to a pyrimidine base in DNA
• Different numbers of hydrogen bonds are formed depending on the bases in DNA:

  • Adenine and Thymine join by 2 hydrogen bonds
  • Cytosine and guanine join by 3 hydrogen bonds
• Nucleotides in DNA are joined together by phosphodiester bonds
• RNA is a relatively short polynucleotide chain
• Semi-conservative replication of DNA ensures genetic continuity between generations of cells
• DNA replication occurs during the S phase of the cell cycle
• Steps of semi-conservative replication of DNA:

  • The double helix unwinds and the hydrogen bonds between the complementary bases break using DNA helicase
  • One strand is used as the template and complementary base pairing occurs with free nucleotides
  • Adjacent nucleotides are joined by phosphodiester bonds formed by DNA polymerase
• DNA polymerase works only in the 5’ to 3’ direction
• The leading strand is replicated continuously in the 3’ to 5’ direction
• The lagging strand is replicated discontinuously in the 5’ to 3’ direction, forming Okazaki fragments
• Okazaki fragments are joined together with DNA ligase
• Proteins are polypeptide chains coded for by a gene
• The genetic code is universal, and the sequence of bases determines which protein the gene is coding for
• The triplet code is the sequence of 3 nucleotides which code for either an amino acid, start codon, or stop codon
• There are two stages of protein synthesis: transcription and translation
• During transcription, a molecule of mRNA is made in the nucleus
• In eukaryotic cells, the RNA molecule formed from transcription is called the primary transcript
• During translation, amino acids join together to form a polypeptide chain
• Gene mutations occur when the base sequence of DNA is altered
• Effects of mutations include nonsense, missense, and silent mutations