Molecular
Genetics
DNA Review!
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Has shape of helix or corkscrew
Is about 2 nm in diameter
2m of it in a nucleus!!
Makes a complete helical turn ever (3.4 nm)
every 10 base pairs
DNA is Supercoiled:
• A strand of DNA in prokaryotic cells coils into a
closed loop, then twists on itself like a necklace
that is coiled into a series of small loops.
• HISTONES are base proteins that DNA wraps
around, that form the core of NUCLEOSOMES.
• Page: 230 textbook
https://www.youtube.com/watch?v=N5zFO
Scowqo
Three main components
• deoxyribose sugar
• a phosphate group
(same as RNA)
• nitrogenous base
▫ adenine
▫ guanine
▫ thymine
▫ cytosine
• DNA is composed of many
nucleotides held together by
phosphodiester bonds
(therefore it is a polymer)
• A phosphodiester bond is a
covalent bond that holds a
DNA strand together by
joining a phosphate group at
position 5 in the pentose
sugar of one nucleotide to
the hydroxyl group at
position 3 in the pentose
sugar of the next nucleotide
• Backbone of DNA is:
• Sugar – Phosphate – Sugar Phosphate
Structure of deoxyribose
• A sugar derived from ribose by replacing a
hydroxyl group with hydrogen.
The Double Helix
• DNA consists of two antiparallel strands of
nucleotides
• Bases of one strand are paired with bases in the
other strand
• Nitrogenous base pairs are arranged above each
other, perpendicular to the axis of the molecule
• A Purine always bonded to a Pyrimidine
▫ Adenine with Thymine
▫ Guanine with Cytosine
 Termed Complimentary Base Pairing
 Fundamental to the storage and transfer of
genetic information
Because I’m all about that Base….
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Purines – A & G
Pyrimidines – T & C (also U in RNA)
bases are bonded together by hydrogen bonds
right-handed helix (clockwise turn) makes
complete turn every 10 nucleotides
Two strands of DNA run antiparallel
• Directionality of DNA: refers the
end-to-end chemical orientation
of a single strand of nucleic acid.
• One strand runs in the 5’ to 3’
direction while the other strand
runs in the 3’ to 5’.
• The 3’ end terminates with the
hydroxyl group of the deoxyribose
sugar.
• The 5’ end terminates with a
phosphate group
• The 5′ is upstream; the 3′ is
downstream. DNA and RNA are
synthesized in the 5′ to 3′
direction
Finding the code...
• 5’ - ATGCCGTTA - 3’
• 3’ - TACGGCAAT - 5’
• By convention, only the 5’ to 3’ strand is written
since the complementary strand can easily be
deduced ...
• Try this one...
• 5’ - TGGACGCTT - 3’
Homework...
• Complete your worksheet
• https://www.youtube.com/watch?v=iMsJe3Ty
mqY
• What are your thoughts? Research some
controversial topics on bioengineering or GMO’s
and be ready to discuss Monday.