Post on 16-Jul-2015
Malalay Institute Of Higher
Education
Madical Faculty
Author and computerized by: Noor
Sadat daughter of M. Essa
Semester: PCB 2
DNA structureNucleotide
- Nucleotides are organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA. The building blocks of nucleic acids, nucleotides are composed of a nitrogenous base, a five-carbon sugar (ribose or .deoxyribose), and at least one phosphate group
Deoxyribose, or more precisely 2-
deoxyribose, is a monosaccharide with
idealized formula H-(C=O)-(CH2)-
(CHOH)3-H.
Its name indicates that it is a deoxy
sugar, meaning that it is derived from
the sugar ribose by loss of an
oxygen atom.
Properties
Molecular formula C5H10O4
Molar mass 134.13 g·mol−1
Appearance White solid
Melting point 91 °C (196 °F; 364 K)
Solubility in water Very soluble
Nitrogenous Bases
A nitrogenous base is simply a nitrogen
containing molecule that has the same
chemical properties as a base. They are
particularly important since they make
up the building blocks of DNA and RNA:
adenine, guanine, cytosine, thymine and
uracil.
ONucleotide Base Definition: A nucleotide
base is a heterocyclic base
containing nitrogen that forms the base part
of nucleotide molecules.
OAlso Known As: nuclei base, nitrogenous
base
OExamples: Cytosine, guanine, and
adenine are all nucleotide bases.
Adenine
OAdenine, abbreviated 'A', has a two-ring
structure, so that makes it a purine. When
it's in DNA, it pairs up with Thymine. When
it's in RNA, it pairs up with Uracil. Adenine
also has other jobs in the cell - it makes up
part of the energy molecule ATP and
electron carriers FAD and NAD, which are
used in cellular respiration.
Thymine
OThymine is a pyrimidine (one
ring), and it's only present in DNA,
where it pairs with Adenine. Its
cousin Uracil does the same job
in RNA.
Guanine
OGuanine is part of both DNA and
RNA, where it bonds with
Cytosine. Guanine is a purine
(having two rings). Fun fact: it was
first discovered in bird feces,
known as guano ... hence the
name
Cytosine
OCytosine is part of DNA and RNA,
and bonds with Guanine. It has
one ring, so it's a pyrimidine.
Note
ONote :that adenine only bonds with thymine,
and cytosine only bonds with guanine.
The nitrogen bases are held together by
hydrogen bonds: adenine and
thymine form two hydrogen bonds; cytosine
and guanine form three hydrogen bonds.
To crack the genetic code found in DNA
we need to look at the sequence of bases.
The bases are arranged in triplets called
codons.
A G G - C T C - A A G - T C C - T A G
T C C - G A G - T T C - A G G - A T C
Phosphate group
Definition and Structure
OSurround a phosphorus atom with four
oxygen atoms and you get a phosphate.
Attach that cluster to one of the many carbon-
containing molecules in our bodies (or, really,
in any living thing) and we call that group of
phosphorus and oxygen atoms a phosphate
group.
Role in Nucleic Acids
O Nucleic acids, like DNA, are made of nucleotides.
Where do phosphates come in? Well, nucleotides
include a base, a sugar, and one or more
phosphates.
O When the nucleotide is off by itself, it may have three
phosphates. When it gets joined to the growing
strand of DNA (or RNA), two of its phosphates are
lost, and the remaining one attaches to another
nucleotide's sugar. This makes a sugar-phosphate
backbone with those important bases (like adenine,
thymine, and so on) hanging off
A. Basic Facts of DNA Replication
1. Complementary base pairing
makes replication possible
C – G
A - T
2. One side of
DNA
molecule is a
template for
making the
other side
(strand)
B. Process of DNA Replication
1. Uncoil & unzip
DNA molecule
2. Enzyme (-ase)
break
3. weak Hydrogen
Bond between
bases