Genetics: DNA Structure and Protein Synthesis

• Genetics studies heredity and the variation of inherited characteristics.

DNA Structure

• DNA exists as a double-stranded helix.
• Nucleotides form the building blocks of DNA.
• A nucleotide comprises a deoxyribose sugar, a phosphate group, and a nitrogenous base.
• Four nitrogenous bases are present: adenine (A), guanine (G), cytosine (C), and thymine (T).
• Adenine pairs with thymine (A-T), and guanine pairs with cytosine (G-C) via hydrogen bonds, called complementary base pairing.

Protein Synthesis

• Proteins are created from DNA through protein synthesis.
• Transcription and translation are the two key stages.

Transcription

• Transcription occurs within the nucleus.
• RNA polymerase uses DNA as a template to produce messenger RNA (mRNA).
• The DNA sequence converts into a complementary mRNA sequence, with uracil (U) replacing thymine (T).

Translation

• Translation happens in the ribosomes.
• The mRNA sequence is read in codons, or sets of three nucleotides.
• Each codon specifies a particular amino acid or a stop signal.
• Transfer RNA (tRNA) molecules transport the appropriate amino acids to the ribosome, complementing the mRNA codons.
• Amino acids join to form a polypeptide chain that folds into a protein.

Cell Division: Mitosis

• PMAT refers to the four distinct stages of nuclear division in eukaryotic cells: Prophase, Metaphase, Anaphase, and Telophase.
• Mitosis yields two daughter cells with the same chromosome number and type as the parent nucleus, which is typical of ordinary tissue growth.
  • Prophase:
    • Chromosomes condense and become visible.
    • The nuclear envelope disintegrates.
    • Spindle fibers emerge.
    • Centrosomes move to opposite poles of the cell.
    • In animal cells, the nucleolus disappears.
  • Metaphase:
    • Chromosomes align along the metaphase plate in the cell's center.
    • Mitotic spindle is fully formed.
    • Each sister chromatid is attached to a spindle fiber originating from opposite poles.
    • Shorter than prophase generally.
    • The cell ensures all chromosomes are properly attached to the spindle before proceeding to anaphase via the metaphase checkpoint.
  • Anaphase:
    • Sister chromatids separate, moving to opposite cell poles.
    • The mitotic spindle shortens, pulling the sister chromatids apart.
    • Each sister chromatid is now considered an individual chromosome.
    • This is the shortest stage of mitosis.
    • By the end, the two poles of the cell have an equivalent and complete collection of chromosomes
  • Telophase:
    • Chromosomes reach the poles and begin to decondense.
    • The nuclear envelope reforms around each set of chromosomes.
    • Mitotic spindle breaks down
    • It is nearly the reverse of prophase.
  • Cytokinesis:
    • The cytoplasm divides, creating two identical daughter cells.
    • In animal cells, it occurs through cleavage furrow formation.
    • In plant cells, it occurs through cell plate formation.
    • Usually begins during anaphase or telophase and completes shortly after telophase.
    • While technically not part of PMAT, it follows PMAT so closely it is typically associated with it.

Cell Division: Meiosis

• Meiosis produces four daughter cells, each possessing half the number of chromosomes found in the parent cell, as seen in gamete and plant spore production.
• Meiosis involves two rounds of PMAT (PMAT I and PMAT II), producing four genetically different daughter cells.
• Meiosis I:
  • Prophase I:
    • Chromosomes condense.
    • Homologous chromosomes pair.
    • Genetic material is exchanged through crossing over.
  • Metaphase I: Homologous chromosome pairs align along the metaphase plate.
  • Anaphase I: Homologous chromosomes separate, moving to opposite poles.
  • Telophase I: Chromosomes arrive at the poles, and the cell divides, resulting in two cells with half the original chromosome number.
• Meiosis II:
  • Prophase II: Chromosomes condense again.
  • Metaphase II: Chromosomes line up along the metaphase plate.
  • Anaphase II: Sister chromatids separate and move to opposite poles.
  • Telophase II: Chromosomes reach the poles, and the cell divides, forming four haploid daughter cells.

Inheritance of Genetic Information

• Genes, segments of DNA, encode specific traits.
• Alleles are different versions of a gene.
• Individuals inherit one allele from each parent for every gene.
• Genotype refers to an individual’s genetic makeup (e.g., AA, Aa, aa).
• Phenotype describes an individual's observable characteristics (e.g., eye color, height).
• Dominant alleles mask the effects of recessive alleles.
• Homozygous: Having two identical alleles for a gene (e.g., AA or aa).
• Heterozygous: Having two different alleles for a gene (e.g., Aa).
• Genetic information is inherited

Punnett Squares

• Punnett squares predict the probability of offspring genotypes and phenotypes.
• The squares consider allele combinations from each parent.
• Monohybrid cross: A cross involving one gene.
• Dihybrid cross: A cross involving two genes.
• Punnett squares are used to make predictions about inheritance patterns.

Pedigree Charts

• Used with punnett squares to predict inheritance patterns
• Pedigree charts are used to make predictions about inheritance patterns.

Scientific Method

• A systematic approach to investigate and understand the natural world.
  • Observation: Notice and describe events or phenomena.
  • Ask a Question: Develop a question about the observation.
  • Hypothesis: Formulate a testable explanation or prediction.
  • Experiment: Design and conduct a controlled experiment to test the hypothesis.
  • Analysis: Analyze the data collected during the experiment.
  • Conclusion: Interpret the results and draw conclusions about whether the hypothesis is supported or not.
  • Communication: Share the findings with the scientific community.

Variations in PMAT

• Mitosis involves one round of PMAT, producing two identical daughter cells.
• Meiosis involves two rounds of PMAT (PMAT I and PMAT II), producing four genetically different daughter cells.
• The details of PMAT can vary slightly between different organisms and cell types.
• Errors in PMAT can lead to aneuploidy (an abnormal number of chromosomes) and other genetic abnormalities.

Significance of PMAT

• PMAT ensures that each daughter cell receives a complete and accurate set of chromosomes.
• PMAT is essential for growth, development, and repair in multicellular organisms.
• PMAT is a highly regulated process that is tightly controlled by a variety of signaling pathways and regulatory proteins.
• Malfunctions in PMAT can contribute to cancer and other diseases.
• An understanding of PMAT is fundamental to understanding cell biology and genetics.