The structure of nucleotides
• DNA is a polymer made of repeating subunits
called nucleotides.
Nitrogenous
base
Phosphate
group
Sugar (deoxyribose)
• Nucleotides have three parts: a simple sugar,
a phosphate group, and a nitrogenous base.
The structure of nucleotides
• The simple sugar in DNA, called deoxyribose
gives DNA its name—deoxyribonucleic acid.
• The phosphate group is composed of one atom
of phosphorus surrounded by four oxygen
atoms.
The structure of nucleotides
• A nitrogenous base is a carbon ring structure
that contains one or more atoms of nitrogen.
• In DNA, there are four possible nitrogenous
bases: adenine (A), guanine (G), cytosine (C),
and thymine (T).
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
The structure of nucleotides
• In DNA, the amount
of adenine is
always equal to the
amount of thymine,
and the amount of
guanine is always
equal to the
amount of cytosine.
• Adenine always
pairs with thymine
and cytosine
always pairs with
guanine!!!!
The structure of DNA
• In 1953, Watson and Crick proposed that
DNA is made of two chains of nucleotides
held together by nitrogenous bases.
• Watson and Crick also proposed that DNA is
shaped like a long zipper that is twisted into a
coil like a spring.
• Because DNA is composed of two strands
twisted together, its shape is called double
helix.
Rosalind Franklin
Rosalind Franklin's crucial contribution to science went largely
unrecognized at the time it was made. In 1952, while working as a
research associate at King's college in Cambridge, England, she
produced the first usable X-ray pictures of DNA ever taken. A
year later, Francis Crick and James Watson used her pictures to
determine that DNA spirals into a double helix.
Rosalind Franklin died in 1958 of ovarian cancer at the early age
of thirty-seven. Four years later, her coworker Maurice Wilkins,
along with Watson and Crick, were awarded the Nobel Prize for
Physiology or Medicine for the double-helix model of DNA.
Some of Franklin's contributions to the discovery of the
structure of DNA were posthumously acknowledged in Watson's
book The Double Helix. "Since my initial impressions of her, both
scientific and personal (as recorded in the early pages of this
book), were often wrong, I want to say something here about her
achievements. The X-ray work she did at King's is increasingly
regarded as superb," Watson writes in the epilogue in 1968.
The importance of nucleotide sequences
Chromosome
The sequence of
nucleotides forms the
unique genetic
information of an
organism. The closer
the relationship is
between two organisms,
the more similar their
DNA nucleotide
sequences will be.
The importance of nucleotide sequences
• Scientists use nucleotide sequences to
determine evolutionary relationships among
organisms, to determine whether two people
are related, and to identify bodies of crime
victims.
Replication of DNA
• Before a cell can divide by mitosis or
meiosis, it must first make a copy of its
chromosomes.
• The DNA in the chromosomes is copied in a
process called DNA replication.
• Without DNA replication, new cells would
have only half the DNA of their parents.
DNA
Replication
of DNA
Replication
Replication
DNA Replication
DNA contains the code that tells
the cell which proteins to make.
These proteins are responsible for
maintaining the health of an
organism.
Transcription and Translation are
the processes that direct the
making of the proteins !!!!
RNA—ribonucleic acid
•only 1 strand
•has ribose sugar
•contains the base uracil instead of
thymine
•3 types:
mRNA= messenger RNA
tRNA= transfer RNA
rRNA= ribosomal RNA
View Transcription Animation
http://plantandsoil.unl.edu/cropt
echnology2005/weed_science/ani
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ription.swfhttp://plantandsoil.unl.
edu/croptechnology2005/weed_s
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Transcription—from DNA to mRNA
•separation of DNA strands
•RNA nucleotides floating around and
move to the DNA
•reaches the STOP signal
•mRNA leaves nucleus through nuclear
pore to cytoplasm to ribosomes
View Translation Animation
http://plantandsoil.unl.edu/crop
technology2005/weed_science/
animationOut.cgi?anim_name=tr
anslation.swfhttp://plantandsoil.
unl.edu/croptechnology2005/we
ed_science/animationOut.cgi?an
im_name=translation.swf
Translation—from mRNA to protein
•mRNA and ribosome connect
•free amino acids in cytoplasm
•tRNA picks up specific amino acid
•codon on mRNA complements the
anti-codon on tRNA—this brings in
the correct a.a.