The subunit of DNA is called the _nucleotide__. What are the 3 components of this subunit called?

The subunit of DNA is called the _nucleotide__.

• What are the 3 components of this subunit called?

3 Components:• Deoxyribose sugar• Nitrogen base• Phosphate

5 different types in genetic material:• Adenine – Purine– 2 rings, 2 bonds• Guanine – Purine– 2 rings, 3 bonds• Cytosine – Pyrimidine– 1 ring, 3 bonds• Thymine – Pyrimidine– 1 ring, 2 bonds• Uracil (found only in RNA)

A long sugar-phosphate backbone with a sequence of bases sticking off is formed.

This may go on for millions of nucleotides

The sugar may be one of two kinds (shown without the pesky hydrogens)

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4

5

With both DNA and RNA, • bases different from one nucleotide to the

next• Gives nucleic acids the appearance of

messages in some strange molecular language.

DNA has deoxyribose sugar; RNA ribose sugar.

DNA contains thymine; RNA contains uracil

Watson and Crick are credited with putting all the pieces together (pun intended) and coming up with this structure.

Each of the base pairs are nearly flat

Watson and Crick proposed stacking them up like stairsteps, with 2 sugar-phosphate strands around the outside

One complication:• The 2 strands wind in opposite directions• The sugars are “upside down” compared

with those of the other strand

The model clearly explains Chargaff’s observation that the number of T’s is equal to the number of A’s: T and A are always paired together!

Chromatin – uncondensed DNA (normal form) 4.6 X 107 bp DNA = shortest human

chromosome• 14,000 micrometers of DNA unpacked• 2 micrometers during mitosis• 7000 packing ratio

Nucleosomes – DNA wrapped around proteins called “histones”

Packing ratio of 6

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DNA replication

The discovery of DNA’s structure by Watson and Crick provided evidence that complementary base pairing was key to DNA’s ability to replicate.

New polynucleotide strands could then be synthesized using the originals as a template.

Several hypotheses were proposed as to the specific mechanism by which new strands are created.

Scientists proposed that DNA “unzipped” as hydrogen bonds between base pairs were broken.

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Mechanisms of DNA replication

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Meselson–Stahl DNA experiment

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DNA replication

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DNA replication enzymes

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DNA replication