Nucleic Acids and Their Components

Nucleic Acids: Components

• Nucleic acids transfer genetic information to new cells.
• Two main categories: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
• Both are long, linear polymers.

Ribonucleic Acid (RNA)

• Primarily found in the cytoplasm of living cells.
• Sugar component: D-ribose.

Deoxyribonucleic Acid (DNA)

• Primarily found in the nuclei of cells.
• Sugar component: D-deoxyribose.
• Lacks an oxygen atom at the second position of the heterocyclic ring.
• Both DNA and RNA sugars are in the β-configuration.

Nucleotides

• Monomers of nucleic acids.
• Composed of a heterocyclic base, sugar, and phosphate.
• Heterocyclic bases classified as pyrimidines or purines.
• Pyrimidines: Uracil, Thymine, Cytosine (U, T, C).
• Purines: Adenine, Guanine (A, G).
• Uracil and Thymine are only found in RNA and DNA, respectively.
• Adenine and Guanine are present in both DNA and RNA.

DNA Structure

• DNA is the largest known molecule.
• Contains millions of nucleotide units linked by phosphodiester bonds.
• Has a sugar-phosphate backbone, constant throughout the DNA molecule.
• The order of bases determines the primary DNA structure.

DNA Secondary Structure

• Proposed in 1953 by Watson and Crick.
• DNA is a double helix formed by two strands entwined around each other.
• Strands are complementary (A with T, G with C).

DNA Replication

• DNA replicates to produce identical copies.
• Semiconservative replication: each new DNA molecule contains one original strand.
• Replication occurs at a replication fork, where the double helix unwinds.

RNA Structure

• Long, unbranched polymer of nucleotides linked by 3' to 5' phosphodiester bonds.
• Usually single-stranded, except in some viruses.
• Found in the nucleus, cytoplasm, and mitochondria.
• Three main types: mRNA, rRNA, tRNA

mRNA

• Carries genetic information from DNA to the cytoplasm.
• Involved in protein synthesis.
• Short lifetime (usually less than an hour).

rRNA

• Major component of ribosomes (sites of protein synthesis)
• Constitutes about 65% of ribosome material.

tRNA

• Delivers amino acids to the ribosomes during protein synthesis.
• Smallest nucleic acid (73-93 nucleotides per chain).
• Contains an anticodon that aligns with corresponding mRNA codons.

Polymerase Chain Reaction (PCR)

• Mimics DNA replication in a test tube.
• Used to amplify specific DNA regions.

Genetic Code

• A series of three-letter words (codons) representing amino acids and start/stop signals.

Translation

• Converts mRNA codons into amino acid sequences.
• tRNA molecules bring amino acids to the ribosome.
• Complementary base pairing determines the amino acid order.
• Amino acids bond to form a protein with characteristic secondary/tertiary structures.

Mutations

• Changes in the DNA base sequence.
• Can be natural or induced.
• Can be lethal or cause genetic diseases.

Recombinant DNA

• Uses restriction enzymes and DNA ligases.
• Isolates genes and inserts them into bacteria to produce proteins.