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DNA – the heredity material
Very early it was discovered chromosomes are composed of
proteins and DNA. But it took several experiments to
conclusively determine specifically which substance made up
Griffith Experiment
Documented movement of genes from one organism to another
(transformation 1928).
– Avery Experiment (1944)
„ Removed
almost all protein from bacteria, and found no
reduction in transforming activity.
– Hershey-Chase (1952)
„ U se d
radioactive isotopes to label DNA and protein. Found
genes used to specify new generations of viruses were made of
DNA - genetic material
– DNA located in the nucleus
membrane bound
– DNA located in the nucleoid. No membrane surrounded organelle
Discovering DNA Structure
DNA made up of nucleotides.
– Central sugar, phosphate group, and an organic base.
„ Purines
- Large bases
– Adenine and Guanine
„ Pyrimidines
- Small bases
– Cytosine and Thymine
Nucleotide Base
DNA – 4 nucleotide bases
4 base nucleotides
Chargaff’s Rule
A =T and G=C
Discovering DNA Structure
Watson and Crick 1953
&( Wilkins) deduced structure of DNA as a double helix.
Base pairs linked
Double Helix structure
two stands of nucleotides
Outer part of the ladder is the sugar-phosphate backbone
Anti-parallel allows for H-bonds between complementary base pairs
H- bonds between base pairs
3 H-bonds
Packaging DNA in the nucleus
DNA Replication
Weak hydrogen bonds between base pairs hold DNA strands
Each chain in the helix is a complimentary mirror image of
the other.
– Double helix unzips and undergoes semi-conservative replication.
„ Confirmed
by Meselson-Stahl Experiment.
Bi-directional replication
Proofreading by DNA polymerase III
Genes to Proteins
Producing proteins from genes is known as gene
– DNA -
„ Gene
Expression - Use of information in DNA to direct production
of particular proteins.
– Transcription - mRNA molecule is
synthesized from gene within DNA.
– Translation - mRNA used to direct protein
The RNA copy of a gene used to produce a protein is called
messenger RNA (mRNA).
Is all of the DNA expressed?
Codons – triplet code
Translation – mRNA >> polypeptide
Translation – the ribosome
Translation – the ribosome
Overview of translation