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DNA Biology
Lab 11
Nucleic Acids

DNA and RNA both built of nucleotides
containing



Sugar (deoxyribose or ribose)
Nitrogenous base (ATCG or AUCG)
Phosphate group
Nitrogenous Bases

Nitrogenous bases
can be double
ringed purines or
single ringed
pyrimidines.
Nitrogenous Bases

A purine will always pair with a
pyrimidine.
DNA

The phosphate
group and sugar
make up the
backbone of the
DNA molecule.
DNA

The DNA backbone



Phosphate groups and pentose sugars
The 5' end of each strand has a free
phosphate group attached to the 5'
carbon of the pentose sugar.
The 3' end has a free hydroxyl
group attached to the 3' carbon of
the pentose sugar.
DNA

DNA consists of
two
complementary
chains connected
by hydrogen
bonds.


A=T
C=G
DNA


DNA synthesis occurs in
the 5' to 3' direction in
both strands.
The DNA strands are
antiparallel


5' end of one is
associated with the 3'
end of the other.
The DNA ladder is
twisted into a double
helix

Ten base pairs occur
per turn.
RNA

RNA exists as a single
polynucleotide chain.


Ribose
Uracil
DNA Replication



DNA must replicate itself
prior to cell division.
Enzymes are responsible
for each step of
replication, including
proofreading.
The helix unwinds,
separates, and each half
acts as a template for the
formation of a new
complementary strand.

Reaction catalyzed by
DNA polymerase.
Gene Expression

Gene expression – the use of
information in DNA to direct the
production of particular proteins.


Transcription – first stage of gene
expression. A messenger RNA (mRNA)
is synthesized from a gene within DNA.
Translation – second stage – mRNA is
used to direct production of a protein.
DNA Coding


DNA codes for
the sequence
of amino acids
in a protein.
A codon is
three basepairs long and
is a segment
of mRNA that
codes for an
amino acid.
Transcription

Messenger RNA (mRNA) transcribes
the DNA and transports it out of the
nucleus.
Transcription

Before leaving the nucleus, segments of
mRNA called introns are removed and
the exons are spliced together.

Exons contain the information coding for the
protein that will be synthesized.
Translation


Translation occurs on ribosomes
outside the nucleus.
mRNA attaches to a ribosome and
protein synthesis begins.
Translation

Transfer RNA (tRNA)
collects free amino acids
from the cytoplasm and
delivers them to the
polysome (mRNAribosome complex)
where they are
assembled into a
polypeptide.

tRNA has a triplet – the
anticodon – that is
complementary to the
codon of mRNA.