Genetic Code and Protein Synthesis

Genetic Code

• The genetic code is a set of rules that dictates how the sequence of nucleotides in DNA or RNA is translated into the amino acid sequence of a protein.
• Each three-nucleotide sequence, called a codon, specifies a particular amino acid.
• The code is nearly universal across all known organisms.

Universality of Genetic Code

• The universality of the genetic code means that most organisms use the same codons to specify the same amino acids.
• This remarkable similarity highlights the shared evolutionary history of all life forms.
• The near-universal nature of the genetic code makes it possible to study genes from one organism in another.

Transcription

• Transcription is the process of synthesizing RNA from a DNA template.
• DNA's specific instructions for a protein are copied to a messenger RNA (mRNA) molecule.
• Enzymes, like RNA polymerase, catalyze this process.
• This process occurs in the nucleus of eukaryotic cells.

Translation

• Translation is the process of synthesizing proteins from an mRNA template.
• Transfer RNA (tRNA) molecules carry specific amino acids to the ribosomes.
• The ribosome reads the mRNA sequence and links the corresponding amino acids together.
• The resulting chain of amino acids folds into a functional protein.

Meiosis Phases

• Meiosis is a specialized type of cell division that produces gametes (sperm and egg cells) in sexually reproducing organisms.

• It involves two rounds of division (meiosis I and meiosis II).

• Meiosis I:

  • Prophase I: Homologous chromosomes pair up and exchange genetic material through crossing over, which is a significant source of genetic variation.
  • Metaphase I: Homologous chromosome pairs align at the metaphase plate.
  • Anaphase I: Homologous chromosomes separate and move to opposite poles.
  • Telophase I: Chromosomes arrive at the poles and the cell divides.

• Meiosis II:

  • Prophase II: Chromosomes condense again.
  • Metaphase II: Chromosomes align at the metaphase plate.
  • Anaphase II: Sister chromatids separate and move to opposite poles.
  • Telophase II: Chromosomes arrive at the poles and the cell divides again.

• The outcome of meiosis is four haploid daughter cells, each with half the number of chromosomes as the parent cell.

Meiosis' Role in Genetic Variation

• Meiosis introduces genetic variation through several mechanisms:

  • Crossing over during prophase I
  • Independent assortment of homologous chromosomes during metaphase I
  • Random fertilization of gametes

• These processes lead to diverse combinations of alleles in the offspring, increasing adaptability and resilience.

Dominant and Recessive Inheritance

• Inheritance patterns can be analyzed using Punnett squares, which predict the probability of offspring inheriting specific traits.
• Dominant trait: A trait expressed even when only one copy of the allele is present.
• Recessive trait: A trait expressed only when two copies of the recessive allele are present.
• Punnett squares visually depict possible genotypes and phenotypes of offspring based on the genotypes of parents.
• A monohybrid cross examines inheritance of one trait.