ch 9 BSC2010

Announcements

  • Today's lecture covers Chapter 9: Introduction to DNA and genetics.

  • Reminder about spring break next week, followed by another class to complete genetics.

  • Upcoming quiz will be available after the next class, with an exam scheduled the week of the 8th.

Exam Performance

  • Comparison of Exam 1 vs. Exam 2 showed a decline in grades, with more students receiving D's and F's.

  • Previous exam was easier, encourage students to review material daily.

  • Top three students acknowledged for their performance:

    • Elvin (only A), followed by Wilson and Melanie (B grades)

  • Class advised to participate in study groups for a better grasp of the material.

Nucleic Acids

  • Today's focus is on nucleic acids, an essential macromolecule.

  • Key objectives include:

    • Understanding nucleic acid structure.

    • Learning about bases, DNA replication, and chromosome structure.

Genetic Material Criteria

  • Genetic material must:

    • Contain information

    • Be replicable

    • Be transmissible to future generations

    • Allow for variation to produce diversity in species

Historical Context of DNA Understanding

  • Late 1800s: Initial theories about genetic inheritance via chromosomes.

  • 1920-1940: Misconceptions that proteins carried genetic information.

  • Recognized that DNA is the actual carrier of genetic information.

Composition of Nucleic Acids

  • Nucleotides are the building blocks of nucleic acids, composed of:

    • a phosphate group

    • a sugar (deoxyribose for DNA, ribose for RNA)

    • a nitrogenous base (A, T, G, C for DNA and A, U, G, C for RNA)

  • DNA is a double-stranded helix; RNA is a single-stranded molecule.

  • Complementary base pairing:

    • Adenine (A) pairs with Thymine (T) in DNA

    • Guanine (G) pairs with Cytosine (C)

Structure of DNA

  • DNA forms a double helix structure:

    • Composed of two strands running antiparallel (5' to 3' direction)

  • DNA wrapped around histone proteins forms chromosomes (46 chromosomes in total, 23 pairs in humans).

  • Chromosome shape: Visualized as an 'X' structure when condensed.

DNA Replication Process

  • Key steps in DNA replication:

    1. Unwinding of DNA by helicase, breaking hydrogen bonds.

    2. Stabilizing single strands by single-strand binding proteins.

    3. Synthesis of new strands by DNA polymerase, which requires a primer.

    4. RNA primers laid down by primase, later replaced with DNA nucleotides.

    5. Joining of Okazaki fragments by DNA ligase on the lagging strand.

Leading and Lagging Strands

  • Leading Strand:

    • Synthesized continuously in the same direction as the opening fork (5' to 3').

  • Lagging Strand:

    • Synthesized in segments (Okazaki fragments) due to the opposite direction of the replication fork.

Importance of Proteins in DNA Replication

  • Key proteins involved include:

    • Helicase: Unwinds DNA.

    • Topoisomerase: Prevents DNA from overwinding.

    • Single-strand binding proteins: Stabilize unwound strands.

    • DNA polymerase: Synthesizes new DNA strands.

    • Primase: Makes RNA primers.

    • DNA ligase: Joins Okazaki fragments on the lagging strand.

Aging related to DNA

  • Discussion about DNA replication leading to shorter DNA over time, causing aging.

  • Potential avenues for research towards immortality by fixing this problem with DNA.

Next Steps and Additional Resources

  • Video resources on DNA replication will be posted on Canvas for further review.

  • Encourage consistent study and engagement in materials discussed in class for better comprehension in upcoming exams.