Genetic Code, Transcription, Translation, and Petrology

Posted on Feb 11, 2025 in Biology

Genetic Code

The genetic code is the manner in which nucleobases are arranged in DNA. Genetic information is stored as nucleobases. The information varies based on the bases and their order. To be utilized, the information must be translated.

Features:

  • It is universal; all living things are encoded in the same way.
  • The basic unit of information is a triplet of bases (e.g., AUG, UUA, AUU, ACC). This can have two meanings:
    • It may code for an amino acid.
    • It may indicate the start or end of the sequence.
  • It is a degenerate code; different triplets can have the same meaning, providing security in case of mutations.

Transcription

Transcription is the process of creating an mRNA copy of DNA. The fragment of DNA that is transcribed is called the transcription unit.

  1. Initiation: RNA polymerase (RNAP) reads the DNA until it finds the promoter sequence, from which it begins to synthesize RNA. It identifies the promoter when approximately 30 bases have been synthesized.
  2. Elongation: RNAP reads the DNA template strand from 3′ to 5′ and synthesizes the mRNA from 5′ to 3′. The DNA double helix then rejoins.
  3. Termination: The RNAP continues synthesizing until it finds a triplet that indicates the end.
  4. Maturation: The resulting RNA, consisting of exons and introns, undergoes processing. Enzymes remove the introns (which are not translated) and join the exons.

Translation

Translation takes place in ribosomes. Ribosomes translate each triplet into amino acids and manufacture proteins.

  1. Initiation: The ribosome starts reading the mRNA, searching for the start triplet (AUG). When located, it binds to a tRNA (anticodon) by complementary base pairing. It starts when the mRNA binds to the 30S subunit. Then, the large subunit (60S) joins the 30S subunit and mRNA.
  2. Elongation: Two reading sites are established. The first is occupied by the initial tRNA. The ribosome reads the next triplet and searches for a tRNA that has an anticodon complementary to that triplet. The amino acid located in the first tRNA is transferred to the amino acid on the second tRNA, forming a peptide bond. The first position is now empty, and translocation occurs: the triplet that was in the second position moves to the first. This process is repeated.
  3. Termination: This occurs when the ribosome reads a stop codon, indicating the end of synthesis. The completed protein is released, and the entire complex is dismantled.

Petrology

Rocks are classified into three groups according to their source: magmatic (or igneous), metamorphic, and sedimentary.

Igneous Rocks

  • Magmatic Assimilation: Where the walls of the magma chamber melt and contribute to the magma.

Three types:

  • Volcanic: With aphanitic and vitreous texture.
  • Plutonic: Phaneritic texture.
  • Intrusive: Porphyritic texture.

Bowen’s Reaction Series: Olivine, Pyroxene, Amphiboles, Biotite, Feldspars, Muscovite, and Quartz.

Process of Magmatic Differentiation: Minerals form as magma ascends and pressure and temperature decrease. Minerals with more silicon will continue rising, while heavier minerals with less silicon will tend to remain below.

Rocks that will be formed according to crystallization: Peridotites, Basalt, Andesite, Granite.

Metamorphic Rocks

  • Formed by changes in temperature or pressure.
  • Pressure:
    • Lithostatic: Due to the weight of overlying sediments.
    • Directed: Due to tectonic forces.

Metamorphic Processes:

  1. Brecciation: Caused by directed pressure.
  2. Reorientation of Minerals: Directed forces cause minerals to align in an orderly manner.
  3. Dehydration: Loss of water due to a temperature change.
  4. Metasomatism: Related to fluid activity; replacement of some chemical elements by others. When a fluid passes through a rock, it can change its composition.
  5. Recrystallization: Depending on pressure, minerals may crystallize in one way or another.

Types of Metamorphism:

  • Dynamometamorphism: Processes occurring on-site and resulting from directed forces.
  • Contact Metamorphism: Due to a change in temperature.
  • Regional Metamorphism: Due to a change in pressure or temperature, causing larger orogenic phenomena (e.g., Gneiss, Schist, Shale).

Sedimentary Rocks

  • Formed by the erosion of sediments.

Types:

  1. Detrital: Differentiated by granules and cement (e.g., limestone, clay, sandstone, conglomerates).
  2. Non-detrital: Evaporites and precipitates.