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MR. SURRETTE
VAN NUYS HIGH SCHOOL
CHAPTER 18: NUCLEIC ACIDS
CLASS NOTES
NUCLEIC ACIDS
Nucleic acids consist of DNA and RNA. They make up the genetic code and control the cell.
Chromosomes are long strands of nucleic acids wrapped and folded around proteins called histones.
DNA
The chromosomal DNA, deoxyribonucleic acid, consists of four nucleotides: adenine (A), thymine
(T), guanine (G), and cytosine (C).
DNA NUCLEOTIDES
Adenine, thymine, guanine, and cytosine are composed of a deoxyribose sugar, a phosphate group,
and a single or double- ringed base.
DNA STRUCTURE
The double helix structure of DNA was discovered by James Watson and Francis Crick in 1953. The
sugar and phosphate components join together by dehydration synthesis to form a strand of
nucleotides. The two strands line up looking like a two-dimensional ladder.
THE DNA DOUBLE-HELIX
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VAN NUYS HIGH SCHOOL
DNA STRUCTURE
Adenine on one strand always matches a thymine on the other. Guanine is always matched with
cytosine.
RNA
Another form of nucleic acid, ribonucleic acid (RNA) transcribes the code from sections of the
chromosomes, carries this copy to the cytoplasm of the cell, and constructs proteins. This allows the
nucleus to control the activities of the cell.
RNA
RNA is found in the nucleus and in the cytoplasm of cells. It conducts the synthesis of proteins.
RNA VERSUS DNA
The structure of RNA is similar to DNA, but there are three major differences:
1. RNA is single stranded.
2. The base sugar for RNA is ribose (not deoxyribose)
3. RNA has a uracil (U) nucleotide instead of thymine (T). The uracil pairs with adenine on the DNA
strand.
REPLICATION
During replication (the copying of the double helix) the two strands separate so that the matched bases
are unmatched. New complementary strands are made on each of the original strands, resulting in two
double strands.
DNA REPLICATION
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MR. SURRETTE
VAN NUYS HIGH SCHOOL
REPLICATION
The duplication of DNA is called semiconservative replication, because one new half is joined to each
old half to create two new DNA strands.
DNA CODE
The DNA code is a sequence of three nucleotides: ATA (adenine, thymine, adenine), CCG, TCA, and so
forth. This sequence of triplets in the DNA determines the sequence of amino acids in the protein that
is produced.
THE CENTRAL DOGMA
“DNA replicates itself and is able to transcribe and translate itself into proteins.”
CENTRAL DOGMA DIAGRAM
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MR. SURRETTE
VAN NUYS HIGH SCHOOL
TRANSCRIPTION
Transcription is similar to replication except that only one strand of DNA is copied. This single strand
of DNA is copied onto RNA nucleotides. This process begins with initiation as RNA polymerase
attaches to a section of DNA.
TRANSCRIPTION
RNA nucleotides find their complementary DNA bases and are joined in a long strand. The nucleotides
of the growing RNA strand peel away as messenger RNA (mRNA).
TRANSLATION
Translation is the process where a cell reads the mRNA and makes amino acid chains (proteins).
TRANSLATION
Genes (sequences of nucleotides on DNA molecules) express themselves by controlling the sequence of
amino acids in proteins that are manufactured in the cell. For example, the DNA sequence AGT will be
copied as UCA by the messenger RNA. This produces the amino acid serine. Nucleotide triplets are
called codons.
TRANSLATION
Transfer RNA (tRNA) are small and roughly “L” shaped. They do their work in the cytoplasm. The
most important feature of tRNA is a group of three nucleotides called the anticodon, at the bottom of
the “L.” Every anticodon is complementary to a particular mRNA codon.
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