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DNA Replication
Conservative replication – One new double helix that consisted of 100% new
material but still identical to original double helix is made
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DNA
polymerase collects free-floating nitrogen bases in the nucleoplasm of the nucleus
and aligns them opposite their complementary bases
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DNA ligase forms hydrogen bonds between the complementary bases (joining them
together) and then coils the DNA strands to form 2 identical double helix strands of
DNA
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Meselson and Stahl’s DNA replication using Nitrogen and Bacteria
1
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coli bacteria in a medium where their only source of Nitrogen
was the radioactive isotope of N15
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2
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coli
bacteria that were subject to N14
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3
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N14 is lighter then N15 and hence produced a
band high up the test tube
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4
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Why is DNA a triplet codon?
There are 20 amino acids that combine to make proteins in the body
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Due to this DNA is a triplet codon of bases to produce the
20 amino acids in the body
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Protein Synthesis
Transcription – DNA helicase uncoils the DNA double helix strand and breaks the
weak hydrogen bonds between the complementary bases
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The
RNA polymerase proofreads the mRNA opposite the DNA antisense strand and
checks to see whether the bases complement each other
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Phosphate groups and ribose sugars form between the RNA
bases
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Translation – The mRNA travels to the ribosome and attaches to a specific site on
the ribosome
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Only 2 triplet codon
bases of the mRNA are allowed on the ribosome specific site at any one time
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Each tRNA carries an amino acid
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The tRNA anti-codon aligns alongside the
mRNA strand pairing up the complementary bases
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Once this is done the mRNA is moved al

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