DNA and RNA: Genetic Information and Protein Synthesis

Posted on Feb 26, 2025 in Biology

Nucleic Acids

Nucleotides are the building blocks of nucleic acids. They consist of:

  • A phosphate group (phosphorus and oxygen).
  • A five-carbon sugar (ribose or deoxyribose).
  • A nitrogenous base: adenine (A), guanine (G), cytosine (C), thymine (T), or uracil (U).

Nucleotides join to form long chains called polynucleotides.

Types of Nucleic Acids

There are two main types of nucleic acids:

  • Deoxyribonucleic acid (DNA)
  • Ribonucleic acid (RNA)

Deoxyribonucleic Acid (DNA)

DNA contains all the genetic information necessary for the development and function of a living being.

DNA Characteristics

  • Each DNA molecule is formed by two long polynucleotide chains.
  • These chains spiral around an imaginary axis, forming a double helix.
  • The two chains are antiparallel (parallel but running in opposite directions).
  • Chains are linked by hydrogen bonds between the nitrogenous bases:
    • Adenine (A) pairs with Thymine (T)
    • Guanine (G) pairs with Cytosine (C)

Expression of Genetic Information

Proteins are molecules resulting from the combination of monomers called amino acids. There are twenty different amino acids, and their number and order vary in each protein. The information in DNA is organized into triplets. A gene does not directly synthesize a polypeptide; the genetic information, encoded as triplets in DNA, must first be decoded.

Decoding Genetic Information

Decoding involves two main processes:

  1. Transcription: Copying the genetic information from DNA into a molecule of messenger RNA (mRNA). In eukaryotes, transcription occurs in the nucleus. The DNA double helix opens, and one strand serves as a template to synthesize mRNA.
  2. Translation: Converting the message in mRNA into the language of proteins. mRNA carries information from the nucleus to the cytoplasm, where ribosomes read the information in triplets called codons.

Ribonucleic Acid (RNA)

RNA is involved in expressing the information contained in DNA through protein synthesis. Proteins regulate most of an organism’s life processes. In eukaryotic cells, RNA is located in both the nucleus and the cytoplasm.

Types of RNA

  • Messenger RNA (mRNA): Copies DNA information and transports it to the ribosomes.
  • Ribosomal RNA (rRNA): Associates with proteins to form ribosomes.
  • Transfer RNA (tRNA): Carries amino acids to the ribosome to build proteins.

DNA Replication

DNA can replicate, creating copies of itself. Replication ensures that daughter cells receive the same genetic information as the parent cell. DNA replication occurs at the end of interphase.

Replication Process

  1. Replication begins with the breaking of hydrogen bonds between the nitrogenous bases, causing the two strands to separate and unwind.
  2. Each separated strand serves as a template for synthesizing a new complementary strand. Free nucleotides pair with their complementary bases on the template strand.
  3. As new strands form, hydrogen bonds are established between the bases, and the strands wind up. The result is two identical DNA molecules.

Genetic Code

During translation, the ribosome interprets the mRNA message. Each tRNA molecule carries a specific amino acid and has a triplet of nucleotides called an anticodon. tRNAs add amino acids to the growing polypeptide chain according to the order of codons in the mRNA. The correspondence between mRNA codons and amino acids is called the genetic code. The genetic code is universal, meaning it is the same for all living beings. There are 64 codons; some code for amino acids, and some are stop signals. The AUG codon signals the start of translation.