Thank Me With TEA!

Biotech Lecture 3

Resources

Important

  • DNA – The primary macromolecule capable of storing and copying genetic information, composed of two anti-parallel strands held together by hydrogen bonds.
  • Chromosome – A packaged structure of DNA; diploid cells contain two copies of each chromosome (homologous chromosomes).
  • Mitosis – The process of somatic cell division resulting in two genetically identical diploid daughter cells.
  • Meiosis – The division of germ-line cells dedicated to gamete formation, resulting in haploid cells (sperm or egg).
  • Sister Chromatid – The identical copies formed by the DNA replication of a chromosome, which separate during cell division.
  • Homologous Chromosomes – A pair of chromosomes (one from each parent) that contain the same gene sequences.
  • Karyotype – A visual representation of an organism’s complete set of chromosomes, used to identify chromosomal abnormalities.
  • Mutation – An error or change in the DNA sequence; this can act as a “villain” by causing the loss of proteins that check for DNA errors, leading to a runaway cell cycle and cancer.
  • Nucleotide – The fundamental building block of DNA and RNA, consisting of three components: a phosphate group, a sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base.
  • Macromolecules – The massive molecules of living things; the primary classes include proteins, nucleic acids, carbohydrates, and lipids.
  • Polymers and Monomers – A polymer is a large molecule made of smaller, repeating subunit building blocks called monomers.
  • Enzyme nomenclature – Enzymes are typically designated with the suffix “-ase” (e.g., polymerase, helicase, ligase).
  • DNA Nitrogenous Bases – The four specific bases found in DNA are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
  • Complementary Strand Base Pairing – Adenine strictly pairs with Thymine (using 2 hydrogen bonds), and Guanine strictly pairs with Cytosine (using 3 hydrogen bonds).

Core concepts

  • Levels of Organization: The hierarchical structure of biological systems, progressing from atoms to molecules, macromolecules, organelles, cells, tissues, organs, organ systems, and finally whole organisms.
  • Mitosis Cell Cycle: The sequential phases of somatic cell division including Interphase, DNA replication, nuclear membrane dissolution, spindle formation, chromosome alignment, chromosome separation, cytokinesis (cell division), and nucleus reformation.
  • DNA Replication Requirements: The replication process requires a template strand, a primer with a free 3′-OH group, and multiple enzymes working together. Synthesis can only occur in the 5′ to 3′ direction.
  • DNA Replication Enzymes: DNA Polymerase adds new complementary nucleotides and has 5′ to 3′ exonuclease activity; Helicase unwinds the DNA; Topoisomerase (Gyrase) relieves tension; Primase makes RNA primers; and Ligase joins the DNA fragments together by sealing nicks.
  • Telomerase: An RNA-dependent enzyme that protects the ends of chromosomes from fusing or degrading. It controls replicative capacity and senescence, and its levels are notably high in cancer cells.
  • Prokaryotic vs. Eukaryotic Replication: Prokaryotes replicate DNA at a faster rate (~1000 nucleotides/sec) from a single origin of replication. Eukaryotes replicate at a slower rate (~50 nucleotides/sec) but utilize multiple sites of initiation.
  • Okazaki Fragments: Short segments of newly synthesized DNA formed on the lagging strand during replication. DNA polymerase removes the RNA primers between them, and DNA ligase connects the fragments.
  • Gene Structure: A sequence of nucleotides (minimum 1000 base pairs) containing an initiation/start site, a promoter control region, a coding region, and a termination site. Eukaryotic genes contain non-coding regions (introns) that are spliced out and coding regions (exons) that are expressed.
  • RNA Processing: A critical eukaryotic step between transcription and translation where introns are removed, exons are spliced together, a 5′ cap is added, and a 3′ poly(A) tail is added to create mature mRNA.
  • Nucleotide Words (Codons): The genetic code uses three-letter base sequences called codons. Because 64 unique codons code for only 20 amino acids (plus start/stop signals), the code features redundancy or “degeneracy,” meaning multiple codons can code for the same amino acid.
  • Transfer RNA (tRNA): Relatively small RNA molecules acting as “translators” that fold into complex 3D shapes to associate a specific amino acid on one end with its corresponding mRNA codon via an anticodon on the other end.
  • Protein Structure: Proteins are large chains of amino acids linked by peptide (amide) bonds. They possess primary structures (amino acid sequences), secondary structures (alpha-helices and beta-sheets), tertiary structures (3D folding), and quaternary structures (multiple interacting chains).
  • Control of Gene Expression: Cells conserve energy by regulating gene expression through various control points. The most logical and cost-effective point is prior to transcription, utilizing DNA packaging, promoters, enhancers, and transcription factors.

Theories and Frameworks

  • Central Dogma of Molecular Biology: The foundational biological framework describing the directional flow of genetic information: DNA is transcribed into RNA, and RNA is translated into proteins.
  • Semiconservative Replication Model: The proven model of DNA copying wherein the two strands of the parental double helix separate, and each functions as a template for synthesizing a new, complementary strand, resulting in two DNA molecules that each contain one old and one new strand.
  • Differential Gene Expression: The framework explaining how genetically identical cells within an organism can develop into specialized tissues (like heart or skin) by turning specific genes on or off in response to internal and environmental stimuli.

Notable Individuals

  • James Watson and Francis Crick: Proposed the foundational double-helical structure of DNA and specific base pairing rules in 1953, which immediately suggested a possible copying mechanism for genetic material.
  • Matthew Meselson and Franklin Stahl: Conducted the experiments proving that DNA replication follows the semiconservative model rather than conservative or dispersive models.
  • Fred Sanger: Made major contributions in 1953 to the sequencing of proteins, establishing that proteins have a unique, specific sequence of amino acids.
  • Francis Crick and George Gamow: Hypothesized in 1961 that a three-base nucleotide code (codons) translates to specific amino acids by studying mutated nucleotide sequences.