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DNA Structure and Replication
Reminder…what are the monomer units of a nucleic acid?
Nucleotides
A long chain of nucleotides strung together ‘phosphate to sugar’ make up one
strand of the DNA molecule…the nitrogen base sticks out on its own.
DNA is a “twisted
ladder”…alternating
sugar and
phosphate groups
make up the
uprights of the
ladder and the
rungs are nitrogen
bases hydrogen
bonded together
(recall hydrogen
bonds are weak
bonds and can
come apart easily).
The rungs are
always one purine
bonded to one
pyrimidine…A
always to T and C
always to G.
DNA structure in detail
Replication
Animation 1
Animation 3
Animation 2
DNA makes an exact copy of itself during the ‘S’ phase of Interphase
so that each new cell will get an identical copy of the genetic
instructions.
Replication is “semi-conservative” meaning that each new DNA
molecule is half old DNA and half new (one strand is from the original
molecule and one strand is newly synthesized using the old strand as
a template).
Building Proteins…turning the DNA sequence into
something the cell can use.
I. Transcription- turning the DNA sequence into a messenger RNA molecule
that can travel out of the nucleus and into the cytoplasm to the ribosomes
(site of protein synthesis).
(other animation)
II. Translation- turning the mRNA sequence into the proper sequence of
amino acids (monomers of proteins).
(other animation)
(another animation)