DNA & the Genetic Code; DNA replication

module 2: topic 7

Frederick Griffith

 found that heat treatment didn't destroy the "transforming" activity, which was found when the genetic information for virulence was transferred from dead S cells to live R cells in rats!

Alfred Hershey & Martha Chase 

found that DNA carries genetic information through their "waring blender" experiment, which used a blender to separate the viral particles from the bacteria they infected, resulting in DNA carrying genetic information, NOT proteins. 

James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin 

discovered the structure of the DNA double helix through x-ray crystallography, which showed that a DNA double helix is made from two anti-parallel strands of DNA, the hydrophilic phosphate groups, and deoxyribose are exposed while the nitrogenous bases face inward; they interact via H-bonds (A with T; G with C)

DNA genetic blueprint

• Stores information in a sequence of bases so it mutates through a change sequence of bases

Prokaryotic replication

Complementary DNA strands pulled apart by DNA helicase

Two replication forks per bubble

Template strand

3’-5’ the top strand

Complementary strand

5’-3’ the bottom strand

Where does the DNA replication processes begins?

origin of replication

helicase

(1) Unzips at the origin site, via 2 strands of DNA by breaking through the H-bonds that hold DNA bases together. 

topoisomerase

(2) Keeps DNA from super colling

SSB proteins

(2) Single-stranded binding proteins bind to the DNA strands to keep them separated. 

Primase

(3) makes a primer (made of RNA), which allows DNA polymerase to know where to start working.

allows the synthesis of the leading strand of DNA. Primes ONCE for the leading strand; many times for the lagging strand.

DNA polymerase as a whole: 

(4) It can only build a new strand in the 5' to 3' direction. proofreads its work and corrects errors as soon as they’re made.

DNA polymerase I

replaces the RNA primers with DNA

DNA polymerase III

adds nucleotides to 3’OH of RNA primer

ligase

(5) joins the Okazaki fragments to form a continuous DNA strand (happens on the lagging strand due to not being able to fill the entire strand)

DNA synthesized by/ what is needed to initate DNA synthesis

DNA polymerase must have a “primer” to start DNA synthesis

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

What is a gene?

a unit of heredity that is passed from parent to offspring.

when is DNA accurately replicated

• before cell division due to the two DNA strands being Complementary, and the sequence of each strand contains the information needed to make a perfect copy of the other strand.

How is the other (lagging) strand of DNA synthesized?

The lagging strand is made in short pieces of DNA = Okazaki fragments.

Archilabld Garrod

published Inborn Errors of Metabolism, he propposed that defect in a “gene” is associated with defect in an enzyme.

george beadle & edward tatum

propsed the “one gene - one enzyme” hypothesis

How does a gene(DNA) direct the synthesis of a protein?

through mRNA( messenger RNA)

sequence of nucletiodes in a gene (DNA) is

transcribed into a sequence of nucleotides in an RNA molecule (hint think DNA = prokaryotic = no nucleus)

sequence of nucleotides in an RNA is translated…

into a sequence of amino acids in a polypeptide. (hint think RNA= eukaryotic = nucleus)

central dogma of molecular biology (process DNA RNA protein)

DNA transcription through RNA polymerase —> RNA —> translation through ribosomes —> protein

what is a codon?

three bases that specify an amino acid

important features of the genetic code

is redundant, not ambiguous, is universal

what is the STOP codon?

UAA,UAG,UGA

what is an open reading frame?

a stretch of bases uninterrupted by termination codons