A1.2

DNA Replication

Production of identical copies of DNA

Semi-conservative Replication

New DNA molecules have one parent strand and one newly synthesized strand

Helicase

Enzyme that unwinds the DNA double helix by breaking hydrogen bonds

DNA Polymerase

Enzyme that links nucleotides to form a growing DNA strand using a template

Complementary Base Pairing

Adenine pairs with Thymine, Guanine pairs with Cytosine

Polymerase Chain Reaction (PCR)

Method for amplifying a DNA sequence from a small sample

Taq DNA Polymerase

Heat-stable DNA polymerase used in PCR

Electrophoresis

Technique used to separate charged molecules like DNA or proteins

DNA Profile

Pattern created from an individual's DNA fragments using gel electrophoresis

Leading Strand

Strand of DNA that is continuously replicated

Lagging Strand

Strand of DNA that is discontinuously replicated, forming Okazaki fragments

Okazaki Fragments

Short DNA fragments synthesized on the lagging strand

DNA Primase

Enzyme that inserts an RNA primer onto

Messenger RNA (mRNA)

mRNA carries genetic information from DNA to the ribosome.

Transfer RNA (tRNA)

tRNA transfers amino acids to the ribosome for protein synthesis.

Ribosomal RNA (rRNA)

rRNA is a component of ribosomes, catalyzing protein synthesis.

Hershey-Chase Experiment

A landmark experiment conducted in 1952 by Alfred Hershey and Martha Chase to confirm that DNA, not protein, is the genetic material.

Experimental Setup for Hershey-Chase

1. Bacteriophages: Used bacteriophages (viruses that infect bacteria), which consist of a DNA core and a protein coat.

2. Radioactive Labeling:

   • Labeled the DNA of one batch of phages with radioactive phosphorus (32P).

   • Labeled the protein coat of another batch of phages with radioactive sulfur (35S).

Infection and Blending for Hershey-Chase

1. Infection: Allowed the labeled phages to infect bacteria (E. coli).

2. Blending: After infection, the cultures were agitated in a blender to detach phage particles from the bacterial surface.

3. Centrifugation: The mixture was centrifuged to separate the heavier bacteria from the lighter phage particles and media.

Results and Conclusion from Hershey-Chase

The bacteria infected with phages containing 32P-labeled DNA were radioactive, indicating that DNA entered the bacterial cells.Convinced the scientific community that DNA is the genetic material