Biology Nucleic Acids

Nucleic Acids

• Nucleic acids are composed of repeating units of nucleotides
• Nucleotides are the functional units of nucleic acids
• A nucleotide is composed of:
  • 5-carbon sugar
  • Phosphate group
  • Nitrogenous base

DNA and RNA

• DNA is double-stranded, while RNA is single-stranded
• DNA contains deoxyribose, while RNA contains ribose
• DNA and RNA have different sugar molecules, which distinguishes them

Nitrogenous Bases

• DNA has four nitrogenous bases:
  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)
• RNA has four nitrogenous bases:
  • Adenine (A)
  • Uracil (U)
  • Cytosine (C)
  • Guanine (G)
• Purine bases have a double carbon-nitrogen ring and include A and G
• Pyrimidine bases have a single carbon-nitrogen ring and include T and C

DNA Structure

• DNA has a double helix structure, allowing for faithful replication
• Complementary base pairing occurs between A-T and C-G
• A-T pairs have 2 hydrogen bonds, while C-G pairs have 3 hydrogen bonds
• DNA strands are antiparallel and complementary

DNA Replication

• DNA replication occurs in 2 steps:
  1. Separate DNA double helix into 2 strands via helicase
  2. DNA polymerase adds complementary nucleotides to each strand in the 5'-3' direction
• Replication occurs in the 5'-3' direction, creating 2 new DNA double helixes

The Genome

• The genome is the complete set of information of an organism's DNA
• Exons make up 2% of the genome, while introns make up 98%
• Exons are coding regions, while introns are non-coding regions

Packaging of Genome

• DNA is wrapped around histone proteins to condense it into the nucleus
• Chromatin is the combination of DNA and histones
• Chromosomes are condensed chromatin
• Centromere is the center of the chromosome
• Telomere is the end of the chromosome

Karyotype

• Karyotype is the complete set of chromosomes
• Can be used to identify chromosomal mutations (e.g. extra/missing chromosomes)

Central Dogma

• Describes the flow of genetic information during cell growth and replication
• DNA → RNA → Protein

Transcription

• Transcription occurs from DNA to RNA
• Unwinding of DNA double helix occurs, followed by RNA polymerase forming RNA
• Complementary base pairing occurs during transcription

Translation

• Translation occurs from RNA to Protein
• Requires mRNA, tRNA, and ribosome
• Amino acids are brought to the ribosome by tRNA
• Energy and enzymes are required for translation