Exam Review and Key Biological Concepts

Exam Overview

• Exam Status:
  • Few students have yet to take the exam
• Exam Distribution:
  • Lecture Component: 70% of the overall grade
  • Based on 3 lecture exams and up to 9 online quizzes
  • Modal Grades:
  • Most common grade: B
  • Followed closely by: A, then C
• Office Hours:
  • Students can stop by for exam review

Gene Expression

• Definition: The process by which information from a gene is used to produce a functional product, typically a protein.

• Main Steps:

  1. Transcription:
  • Occurs in the nucleus
  • Produces RNA from DNA template
  • Enzyme involved: RNA polymerase
  1. Translation:
  • Occurs in the cytoplasm at ribosomes
  • mRNA is decoded to produce a polypeptide (protein)

• DNA Template Strand: Sequence of bases (e.g., Thymine (T), Adenine (A), Cytosine (C), Guanine (G))

  • Transcription example:
  • DNA: T - A - C - G
  • mRNA: A - U - G - C

• Codons:

  • Group of three nucleotides on mRNA
  • Examples:
  • Start codon: AUG (Methionine)
  • UCC and UCG (Serine)
  • Stop codon: UGA

Cell Division (Reproduction at the Cellular Level)

• Parent Cell: Divides to produce two daughter cells
• Types of Cell Division:
  • Mitotic Cell Division (M): Parent cell divides into daughter cells.
  • Cell Cycle: Sequence of stages a cell goes through, characterized by:
  1. Interphase (non-dividing phase)
  2. Mitotic Phase (dividing phase)
• Interphase Stages:
  • G1 Phase: First gap, cell grows and duplicates organelles.
  • S Phase: Synthesis - DNA is replicated.
    • Problematic terminology: "Synthesis" should instead reference DNA replication.
  • G2 Phase: Second gap, preparation for division (protein synthesis).
• Mitosis:
  • Involves 4 main stages:
  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
  • Cytokinesis: Physical division of the cytoplasm after mitosis.

DNA Replication

• Process:

  1. Hydrogen bonds break, DNA strands unwind.
  2. Complementary base pairing facilitated by DNA polymerase.
  3. Results in two identical DNA molecules (Semi-conservative replication)

• Enzymes:

  • RNA polymerase (for transcription) vs. DNA polymerase (for replication)

• Key Concepts:

  • Semi-Conservative Replication: Each new DNA molecule contains one original and one new strand.

Chromosome Concepts

• Chromatid Structure:
  • Duplicated chromosomes consist of two sister chromatids connected at a centromere.
• Chromosome Types:
  • Duplicated (homologous): Two sister chromatids; occurs during cell division.
  • Unduplicated: Single chromatid; occurs post-division.
• Chromosome Count:
  • Diploid Cells: 46 chromosomes (23 pairs) in humans.
  • Haploid Cells: 23 chromosomes (gametes: sperm and eggs).

Karyotypes

• Definition: Visual profile of the complete set of chromosomes in an individual
• Types of Chromosomes:
  • Autosomes: First 22 pairs, carry genes for traits.
  • Sex Chromosomes: 23rd pair, determine biological sex (XX is female, XY is male)
• Sex Determination:
  • Females inherit X from both parents, males inherit X from mother and Y from father.

Conclusion

• Importance of understanding gene expression and cell division processes should be emphasized for exams.