1.
In this lecture we try to discuss
Definition of DNA and types .
 Explain The difference between DNA Replication and
gene expression .
Draw the central dogma of molecular biology in three
figures.
 Compare between Nucleotide and nucleoside and
between DNA  RNA and its types .
 Put pentose sugar , nitrogen base and phosphate group
in the correct order to pave the way for building of single
and double strand of DNA by base pairing process.
 Designing of Watson-Crick model for the structure of
DNA

2.
 DNA: the store house of genetic information, is present not
only in chromosomes in the nucleus of eukaryotic organisms,
but also in mitochondria of the cell. Nucleic acids are
required for the storage and expression of genetic
information. There are two chemically distinct types of
nucleic acids:
1. DNA.
2. RNA.
DNA

3.
Replication, Transcription and
Translation
 DNA must be replicate precisely each time a cell divides, each double strand
replicate itself in one step.
 While gene Expression occurs in 2 stages :
1. Transcription : ( RNA synthesis) is the first stage in the expression of genetic
information.
2. Translation : Next step, the code contained in the nucleotide sequence of
messenger RNA molecules is translated (protein synthesis), thus completing
gene expression.
 This flow of information from DNA to RNA to protein is termed the "central
dogma of molecular biology" and is descriptive of all organisms, with the
exception of some viruses that have RNA as the repository of their genetic
information.

4.
 Nucleotides: which consist of three components:
1. a nitrogenous base
2. a five-carbon sugar (pentose)
3. Phosphate group.
While: Nucleosides are similar to nucleotides but have no
phosphate groups.

5.
 Nucleic acids are polymers of nucleotides , usually present as
double stranded forming double helical structure.
 RNA is a Polynucleotide , usually present as single stranded
found in all cell types. There are three major classes of RNA :
 – mRNA (messenger RNA)
 – tRNA (transfer RNA)
 – rRNA (ribosomal RNA)

6.
Base Pairing

7.
 In the double helix, the two chains are coiled around a common
axis called the axis of symmetry. The chains are paired in an
antiparallel manner, that is, the 5'-end of one strand is paired with
the 3'-end of the other strand.
 The spatial relationship between the two strands in the helix
creates a major (wide) groove and a minor (narrow) groove.
These grooves provide access for the binding of regulatory
proteins to their specific recognition sequences along the DNA
chain.