Download THE NUCLEIC ACIDS

THE NUCLEIC ACIDS
t Are the Chemical Structures and Functions of Nucleic Acids?
Nucleic acids are polymers specialized for the
storage, transmission, and use of genetic
information.
DNA = deoxyribonucleic acid
RNA = ribonucleic acid
t Are the Chemical Structures and Functions of Nucleic Acids?
leotides Have Three Components
ucleotides are the monomers
at make up nucleic acids.
ucleotides consist of a pentose
gar, a phosphate group, and a
rogen-containing base.
nucleoside consists only of a
ntose sugar and a nitrogenous
se.
What Are the Chemical Structures and Functions of Nucleic Acids?
RNA contains the sugar ribose.
ribose
DNA contains deoxyribose.
deoxyribose
ng Nucleotides Together
leotides are linked
ether in condensation
ctions to form
sphodiester
ages.
phosphate groups link
bon 3′ in one sugar to
bon 5′ in another sugar.
leic acids are said to
w in the 5′-to-3′
ction.
What Are the Chemical Structures and Functions of Nucleic Acids?
Oligonucleotides (about 20 monomers): RNA
“primers” to start DNA duplication, RNA that
regulates gene expression, etc.
Polynucleotides, or nucleic acids (DNA and RNA):
can be very long—up
up to millions of monomers.
gen bases
A bases:
Adenine (A)
Cytosine (C)
Guanine (G)
Thymine (T)
A has uracil (U) instead of
ymine.
e 1.3
What Are the Chemical Structures and Functions of Nucleic Acids?
Complementary base pairing:
pairing purines pair with
pyrimidines by hydrogen bonds.
What Are the Chemical Structures and Functions of Nucleic Acids?
RNA is single-stranded,
stranded, but base pairing occurs
between different regions of the molecule.
Base pairing determines the three-dimensional
three
shape of some RNA molecules.
Complementary base pairing can also take place
between RNA and DNA.
re 1.25 RNA
What Are the Chemical Structures and Functions of Nucleic Acids?
The two strands of a DNA molecule form a double
helix.
All DNA molecules have the same structure; diversity
lies in the sequence of base pairs.
DNA is an informational molecule: information is
encoded in the sequences of bases.
re 1.26 DNA
• DNA is a double-stranded helix, with th
two strands connected by hydrogen
bonds.
• Most DNA double helices are righthanded;
• The DNA double helix is anti-parallel,
which means that the 5' end of one
strand is paired with the 3' end of its
complementary strand (and vice versa)
• Nucleotides are linked to each other by
their phosphate groups, which bind the
end of one sugar to the 5' end of the ne
sugar.
• Not only are the DNA base pairs
connected via hydrogen bonding, but th
outer edges of the nitrogen-containing
bases are exposed and available for
potential hydrogen bonding as well.
• These hydrogen bonds provide easy
access to the DNA for other molecules,
including the proteins that play vital role
in the replication and expression of DN
Base pairing in DNA.
Two hydrogen bonds
connect T to A;
three hydrogen bonds
connect G to C.
The sugar-phosphate
backbones (grey) run
anti-parallel to each
other, so that the 3’ an
5’ ends of the two
strands are aligned.
What Are the Chemical Structures and Functions of Nucleic Acids?
DNA transmits information in two ways:
• DNA can reproduce itself (replication).
(
• DNA sequences can be copied into RNA
(transcription).
). The RNA can specify a sequence
of amino acids in a polypeptide (translation).
(
What Are the Chemical Structures and Functions of Nucleic Acids?
Transcription plus translation = expression
What Are the Chemical Structures and Functions of Nucleic Acids?
DNA replication and transcription depend on base
pairing.
DNA replication involves the entire molecule, but
only relatively small sections of the DNA are
transcribed into RNA.
What Are the Chemical Structures and Functions of Nucleic Acids?
The complete set of DNA in a living organism is
called its genome.
Not all the information is needed at all times;
sequences of DNA that encode specific proteins are
called genes.
re 1.27 DNA Replication and Transcription
What Are the Chemical Structures and Functions of Nucleic Acids?
DNA carries hereditary information between
generations.
Determining the sequence of bases helps reveal
evolutionary relationships.
The closest living relative of humans is the
chimpanzee.
What Are the Chemical Structures and Functions of Nucleic Acids?
Other roles for nucleotides:
• ATP—energy
energy transducer in biochemical reactions
• GTP—energy
energy source in protein synthesis
• cAMP—essential
essential to the action of hormones and
transmission of information in the nervous system