Biology EOC Review - Section 3: DNA/RNA, DNA Replication, Protein Synthesis

DNA & RNA Basics

Nucleotides and Nucleic Acids

• Nucleic acids = Macromolecules made of nucleotides
• Monomer = Nucleotide
• Each nucleotide contains:
  • Phosphate group
  • Sugar molecule
  • Nitrogen base
• Examples: DNA (deoxyribonucleic acid) & RNA (ribonucleic acid)

Structure of DNA and RNA

• DNA:

  • Double helix shape
  • Sides: Pentose sugar
  • Center: Nitrogen bases with weak hydrogen bonds
  • Nitrogen Bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
  • Base Pairs: A-T, G-C
  • Never leaves the nucleus
  • Controls protein production

• RNA:

  • Single-stranded
  • Backbone: Alternating sugar (ribose) and phosphate
  • Nitrogen Bases: Adenine (A), Uracil (U), Guanine (G), Cytosine (C)
  • Base Pairs: A-U, G-C
  • Leaves the nucleus

DNA vs. RNA

• DNA: Double-stranded, contains Thymine
• RNA: Single-stranded, contains Uracil (no Thymine)

Genetic Code

• Universal to all life, indicating common ancestry
• Comprised of codons (triplets of nucleotides)
• Codons code for specific amino acids
• Mutations can alter protein sequences leading to species variation

Types of Mutations

• Gene Mutation: Changes in a single gene (point, substitution, insertion, deletion)

  • Causes: DNA replication errors, environmental factors, inheritance
  • Effects: Genetic disorders, changes in traits, disease risk

• Chromosomal Mutation: Changes in chromosome structure or number (deletion, duplication, inversion, translocation)

  • Can be spontaneous, environmentally induced, or inherited
  • Examples: Down syndrome, Turner syndrome

• Gene Mutations and Phenotypic Effects

  • Silent Mutations: No physical effect
  • Mutations can provide evolutionary advantages
  • Germline Mutations: Inherited, occur in gametes
  • Somatic Mutations: Non-inherited, occur in body cells

DNA Replication & Central Dogma

DNA Replication

• Process of copying DNA to produce two identical strands
• Occurs in eukaryotic cell nucleus
• Steps:
  1. Helicase unwinds DNA, breaking hydrogen bonds (forms replication fork)
  2. Each single strand serves as a template
  3. DNA polymerase adds nucleotides to form new strand
  4. Two identical DNA molecules result (semiconservative model)

Central Dogma

• Flow of genetic information: DNA -> RNA -> Protein
• Transcription: DNA -> mRNA
• Translation: mRNA -> Protein
• Proteins are essential for life functions

Protein Synthesis

Transcription (DNA -> RNA)

• Occurs in the nucleus
• mRNA synthesized from DNA template

Translation (RNA -> Protein)

• Occurs in the ribosome
• mRNA codons translated into amino acids
• Use codon chart for translation

Knowledge Check Questions

1. DNA Base Pairing: A pairs with T, G pairs with C
2. Number of Codons in Sequence: Count groups of three nucleotides
3. Importance of Proofreading: Prevents harmful mutations
4. DNA Replication Process: Uses complementary base pairing
5. Complementary DNA Strand: Formed using base pairing rules
6. DNA Sequence Comparison: High similarity suggests a common ancestor
7. Complementary Daughter Strand Formation: Use original DNA sequence for base pairing
8. Stopping Protein Production: Prevent transcription of DNA to mRNA
9. Transcription to RNA: DNA sequence used as template
10. Complementary DNA Strand: Formed during replication
11. MRNA Transcription: Corresponds to DNA template
12. Complementary DNA Strand During Replication: Formed using base pairing
13. Codon Chart Usage: Translates mRNA to amino acids
14. Transcription vs. Translation: Transcription in nucleus, Translation in cytoplasm