DNA Replication

Replication of DNAReplication is the biological process of making an identical copy of DNA. Each of the 46 chromosomes in a human cell is duplicated during this phase, which is crucial for cell division and reproduction.

Structure and Components

  • Sister chromatids: These are the identical copies of a chromosome connected by a region called the centromere, which plays a vital role during cell division.

Steps of DNA Replication

  1. Initiation:

    • The enzyme DNA helicase unwinds the double-stranded DNA helix. This occurs at specific locations known as origins of replication. The unwinding creates a structure termed the replication fork, where the two strands separate. The helicase breaks the hydrogen bonds that hold the two strands together.

  2. Elongation:

    • The enzyme DNA polymerase attaches to the separated strands. It adds free nucleotides from the nucleus to the growing new strand, adhering to the base-pairing rules (A pairs with T and C pairs with G). In addition to synthesizing new DNA strands, DNA polymerase also proofreads the newly formed strands to correct any errors that may occur during replication, ensuring fidelity in the genetic information passed to the daughter cells.

  3. Completion:

    • Upon reaching the end of the DNA strands, replication is completed. The two DNA strands then rewind into their double-helix structure. At this point, two new identical copies of the original DNA molecule have been generated, each containing one original strand and one newly synthesized strand, adhering to the semiconservative nature of DNA replication.

  4. Semiconservative Replication:

    • This means that during DNA replication, each daughter DNA molecule consists of one original strand and one newly synthesized strand, which is crucial for maintaining the integrity of genetic information across generations.

Types of Nucleic Acids

  • DNA (Deoxyribonucleic acid):

    • Structure: Double-stranded

    • Sugar: Deoxyribose

    • Nitrogenous Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

    • Function: Holds genetic information; cannot leave the nucleus due to its size.

  • RNA (Ribonucleic acid):

    • Structure: Single-stranded

    • Sugar: Ribose

    • Nitrogenous Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

    • Function: Plays a key role in protein synthesis and can leave the nucleus to carry genetic instructions to ribosomes for protein formation.