Molecular Genetics Unit
DNA Characteristics
-Double stranded
-Curves to the right
-Strands go in opposite directions
-Uniform diameter
Nucleic acids
Two types - DNA and RNA
Nucleic acids are polymers of nucleotides
Nucleotides have 3 parts
Parts of the nucleotide
Phosphate group
Pentose sugar (5-Carbon sugar)
Nitrogenous base
Nitrogenous bases
-Adenine, cytosine, uracil, guanine, thymine
Two famillies- Pyramidines (one ring), Purines (two rings)
Cytosine, Uracil and thymine, one ringed pyramidines
Adenine and guanine, two ringed purines
Pentose sugar
RNA - ribose pentose sugar
DNA - deoxyribose pentose sugar
Deoxyribose has one less oxygen molecule in it
Formation of Nucleic acids
Backbone: The phosphate of one nucleotide is attached
to the sugar of the next by phosphodiester linkages.
The “rungs of the ladder” are the nitrogenous bases, a
purine connected to a pyrimidine by hydrogen bonds.
Function of Nucleic acid
-storage and transmission of genetic information
-DNA stores information necessary to create mRNA (messanger RNA)
-mRNA takes protein building insturctions in nucleic acid to the cytoplasm, where the protiens are synthesized by the ribosomes
DNA Packaging
-Necessary for chromosomes to be properly distributed during Mitosis and Meiosis
-Eukaryotes wrap DNA up in a spool of proteins
Nucleosomes
-A length of DNA wraps 1.65 times around each histone octomer
-Nucleosomes are joined by linker DNA
-Held together either loosely or tightly
-Normal cell activites, held loosely (forming chromatin) during cell division they are pulled tightly (forming chromosomes)
-DNA is attracted to the histones, DNA negatively charged, histones positively charged
-Coiling of DNA occurs when the string of nucleosomes wraps up into higher order coils called supercoils
Histone octomer
-8 histone proteins
-2 of each four types
-A fifth histone H1, helps with coiling DNA
Complementary bases
Adenine with thymine
Guanine and Cytosine
Uracil is lonely
Apples in the tree, car in the garage
Chargaff's Rule
DNA contains equal amounts of adenine and thymine, and cytosine and guanine
Falsified the teranucleotide hypothesis (which would have had all four amounts of nucleotides be equal)
Falsification adresses the problem of induction
Hershey-Chase experiment
Established that DNA was the moluce of heredity
The origin of replication
in order for DNA to replicate, the strands must be unwounded and seperated from one and other
-Replication begins at the orgin of replication - there are many in each eukaryotic cell
-The enzyme helicase opens up the double helix and gyrase (a topoiseomerase) helps keep the double helix untwisted