D

Nucleic Acids, Structures, and Function

  • Nucleic Acids

    • Large molecules formed from smaller subunits.
    • Polymers made of monomers called nucleotides.
    • Nuclear: Meaning one subunit.
    • Two main types: DNA and RNA.

  • Nucleotide Structure

    • Composed of three parts:
    • 5-Carbon sugar (pentose sugar).
    • Phosphate group.
    • Nitrogenous base (contains nitrogen atoms).
    • Example: ATP (adenosine triphosphate) has three phosphate groups.

  • Types of Nucleic Acids

    • DNA
    • Stands for deoxyribonucleic acid.
    • Stores genetic information necessary for the synthesis of RNA and proteins.
    • Inherited from parents and passed to offspring.
    • Contains regions called genes that direct traits (like hair color, height).
    • RNA
    • Stands for ribonucleic acid.
    • Synthesized from DNA but not inherited.
    • Helps turn the genetic instructions in DNA into proteins.

  • Nucleotide Composition

    • Sugars:
    • DNA: deoxyribose (lacks one oxygen compared to ribose).
    • RNA: ribose.
    • Bases:
    • Purines (bigger bases with two rings): adenine (A) and guanine (G).
    • Pyrimidines (smaller bases with one ring): cytosine (C), thymine (T - DNA exclusive), and uracil (U - RNA exclusive).
    • Abbreviations:
    • A, G, C, T (in DNA), and A, G, C, U (in RNA).

  • Nucleotide Linkage

    • Nucleotides connect by linking the phosphate of one to the sugar of another, forming a backbone of alternating sugars and phosphates.
    • In DNA: Two strands run next to each other, held by hydrogen bonds between complementary bases.
    • A pairs with T (two hydrogen bonds).
    • G pairs with C (three hydrogen bonds).
    • The structure resembles a twisted ladder known as a double helix.

  • RNA vs. DNA

    • RNA:
    • Single chain of nucleotides.
    • Sugar: ribose.
    • Bases are A, G, C, and U.
    • DNA:
    • Double helix (two nucleotide chains).
    • Sugar: deoxyribose.
    • Bases are A, G, C, and T.
    • Larger than RNA (45 million nucleotides).

  • Gene Expression (Transcription and Translation)

    • Transcription:
    • Occurs in the nucleus, where DNA is copied into RNA.
    • Involves RNA polymerase.
    • Translation:
    • Occurs in the cytoplasm at ribosomes, synthesizing proteins from RNA instructions.
    • Requires messenger RNA (mRNA) to carry instructions, ribosomal RNA (rRNA) to form ribosomes, and transfer RNA (tRNA) to deliver amino acids.

  • Protein Synthesis

    • Proteins are polymers made of amino acids.
    • Linked by peptide bonds forming polypeptides.
    • Genes provide instructions for making proteins, mediated through transcription (DNA to mRNA) and translation (mRNA to protein).

  • Summary of Steps in Gene Expression

    • The flow of information:

    • DNA (instructions) → Transcription (producing RNA in the nucleus) → RNA (mRNA, rRNA, tRNA) → Translation (amino acids assembling into proteins at ribosomes).

    • Together, transcription and translation constitute gene expression.

    • The concept of the central dogma describes the flow of genetic information: DNA → RNA → Proteins.