Topic 7: DNA and the Genetic Code; DNA replication

Frederick Griffith

found that heat-treatment didn’t destroy the “transforming” activityof living cells, which suggested that genetic material could be transferred between organisms

transformation

the process by which genetic material from one organism is taken up by another, leading to a change in phenotype

Alfred Hershey and Martha Chase

conducted experiments using bacteriophages that demonstrated DNA as the genetic material, confirming that DNA, not protein, carries genetic information (“Waring blender”)

James Watson and Francis Crick

determined DNA structure using X-ray crystallography

Semi-conservative

replication of DNA in which each strand serves as a template for the creation of a new complementary strand, resulting in two identical copies of the original DNA molecule

Origin of replication

specific location on a DNA molecule where replication begins

DNA helicase

unwinds the complementary DNA strands during DNA replication

Replication fork

Y-shaped region where the DNA splits into two strands

Single-stranded DNA-binding proteins

keeps helix from reforming during DNA replication

Topoisomerase

keeps DNA from getting tangled up as it is unwound

Primer

nucleic acid containing a 3’OH to which next nucleotide can be added

Template strand

strand of DNA that serves as the pattern for replication, guiding the synthesis of a complementary strand

Complementary strand

newly synthesized strand of DNA that is formed by base pairing with the template strand during DNA replication

Primase

makes a short RNA primer to start DNA synthesis

Leading strand

DNA strand that is synthesized continuously; only needs one RNA primer

Lagging strand

DNA strand that is synthesized discontinuously in short segments; needs multiple RNA primers

Okazaki fragments

short DNA segments synthesized on the lagging strand during DNA replication

DNA polymerase III

adds nucleotides to the 3’OH of RNA primer

DNA polymerase I

replaces the RNA primers with DNA

DNA ligase

enzyme that joins the Okazaki fragments to form a continuous DNA strand

Deoxynucleoside triphosphates

building blocks for DNA synthesis, consisting of a deoxyribose sugar, a nitrogenous base, and three phosphate groups

Mismatch repair

DNA polymerase “proofreads” its works and corrects errors as soon as they are made

transcription

the process of copying a segment of DNA into RNA by the enzyme RNA polymerase

RNA polymerase

enzyme that synthesizes RNA from a DNA template during the process of transcription

Translation/Protein synthesis

converts mRNA to proteins

Ribosome

facilitates the assembly of amino acids into protein chains during translation

Codon

three bases that specify an amino acid

Start (initiation) codon

specific codon that signals the beginning of protein synthesis (AUG)

Stop (termination) codon

specific codon that signals the end of protein synthesis (UAA, UAG, UGA)

Reading frame

the way in which nucleotides in mRNA are divided into codons for translation

Open-reading frame (ORF)

stretch of bases uninterrupted by termination codons

Coding sequence

portion of DNA or RNA that is translated into protein

Untranslated region (UTR)

segment of mRNA that is not translated into protein, located upstream or downstream of the coding sequence