DNA and RNA

DNA and RNA

DNA

  • DNA, or deoxyribonucleic acid, is a polymer made up of nucleotides consisting of a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base.

  • The four types of nitrogenous bases in DNA are adenine (A), guanine (G), cytosine (C), and thymine (T). Adenine pairs with thymine and guanine pairs with cytosine, known as complementary base pairing.

  • DNA is a double helix structure, which resembles a twisted ladder. The sugar-phosphate backbone forms the sides of the ladder while the bases, which pair up, form the rungs.

  • The specific sequence of bases in a DNA molecule forms the genetic code, which serves as the instructions for the construction and operation of living organisms.

RNA

  • RNA, or ribonucleic acid, differs from DNA in that it is single-stranded, uses the sugar ribose instead of deoxyribose, and uses uracil (U) in place of thymine.

  • The nucleotides in RNA consist of a 5-carbon sugar (ribose), a phosphate group, and one of the four nitrogenous bases: adenine, guanine, cytosine, and uracil.

  • RNA serves many functions, but its main role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins.

DNA Replication

  • DNA replication is the process by which DNA makes a duplicate of itself, which is fundamental to all life as it allows living organisms to grow and reproduce.

  • The process begins with the breaking of the hydrogen bonds between the base pairs in DNA by the enzyme Helicase. This splits the DNA molecule into two separate strands, each of which will act as a template for the new strand.

  • The synthesis of new DNA strands is facilitated by the enzyme DNA polymerase, which adds free nucleotides to the growing DNA strand in the 5’ to 3’ direction.

  • The replication is semi-conservative meaning each of the new DNA molecules consists of one original strand and one newly synthesized strand.

Transcription and Translation

  • The process by which DNA is copied into RNA is called transcription. It involves the synthesis of a complementary mRNA strand from a DNA template.

  • During transcription, the enzyme RNA polymerase binds to a specific portion of the DNA molecule that signals the start of a gene. RNA polymerase then adds complementary RNA nucleotides to synthesize the mRNA strand.

  • Translation is the process by which the genetic code on mRNA is read by the ribosome to synthesize a protein. Each set of three nucleotides on the mRNA, known as a codon, corresponds to a specific amino acid. The sequence of codons on the mRNA determines the sequence of amino acids in the protein.