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.