Biomolecules
Nucleic acids
Nucleic acids
 Are
the genetic materials of all organisms
and determine inherited characteristics.
 The are two kinds of nucleic acids, DNA &
RNA.
 DNA is found in genes which are on
chromosomes and carries ‘instructions’ for
assembly of specific proteins. RNA is also
involved in this process (transcription and
translation). We will study this in UNIT4.
DNA
 All
life on Earth has a common thread at the
molecular level – DNA { deoxyribonucleic acid}
 DNA is a large (macro) molecule made up of a
series of chemical building blocks called
nucleotides.
 A nucleotide is composed of a phosphate group,
sugar and a nitrogen containing base.
 DNA is organised into segments called GENES
 In these genes are triplets called ‘codons’ that
translate the nucleotide sequences into amino
acids (protein)
Each NUCLEOTIDE is made of:
 A phosphate
group
 A 5 carbon sugar (deoxyribose),

[ in any nucleotide a phosphate is attached to the
5’ carbon and the base to the 1’ carbon]
 One
of the 4 bases (A,G,C,T)
Nucleotides join together to form a
polynucleotide chain. The two ends of the
chain are different and are referred to as
the 5’ & 3’. This makes the DNA
double helix ‘antiparallel’.
Complementary Base Pairs
 The
4 nitrogenous bases are:
 Adenine
(A) - Purine type double ring structure
 Guanine (G) - Purine type double ring structure
 Thymine (T) - Pyrimidine type single ring structure
 Cytosine (C) - Pyrimidine type single ring structure
 Of
these bases only A can bond to T and only
G can bond to C
DNA Structure
DNA may exist as a double-stranded helix.
Each strand is a polynucleotide.
Each nucleotide is made up of a deoxyribose sugar, a
purine or pyrimidine base and a phosphate group.
Structure of Nucleotides
The chemical structure of nucleotides:
Symbolic form
Phosphate: Links
neighboring
sugars
Base: Four types are possible
in DNA: adenine, guanine,
cytosine and thymine. RNA
has the same except uracil
replaces thymine.
Sugar: One of two types
possible: ribose in RNA
and deoxyribose in DNA
Nucleotides
The building blocks of nucleic acids (DNA and RNA) comprise the following
components:
a sugar (ribose or deoxyribose)
a phosphate group
a base (four types for each of DNA and RNA)
Adenine
Phosphate
Sugar
Base
DNA & RNA Compared
Structural differences between DNA and RNA include:
DNA
RNA
Strands
Double
Single
Sugar
Deoxyribose
Ribose
Bases
Guanine
Guanine
Cytosine
Cytosine
Thymine
Uracil
Adenine
Adenine
Purines
Nucleotide
Bases
The base
component of
nucleotides
which comprise
the genetic code.
Adenine
• Double-ringed
structures
• Always pair up
with pyrimidines
Guanine
Pyrimidines
Cytosine
• Singleringed
structures
•
Base
component of
a nucleotide
Always pair
up with
purines
Thymine
Uracil
Double strand formation
This occurs because of H-bonding between the base pairs
as follows:
H
O
N
H
N
H
7
N
N
H
CH3
O
7
N
N
H
N
N
3
N
Guanine
N
H
G
H
N
N
O
Cytosine
H
N
3
N
N
Adenine
O
Thymine
C
A
T
Note number of H-bonds between each base pair.
Watson and Crick double helix: B type
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Watson and Crick double helix: B type
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
The central DOGMA of Molecular Biology can be
summarised in the form:
RNA (ribonucleic acid)
 RNA is
a single nucleotide chain, similar to DNA
(double chain), but with the sugar ribose in place
of deoxyribose and uracil (U) rather than
thymine (T).
 The bases G, C, T and A in DNA are transcribed
respectively as C, G A and U in RNA.
 There
are three main forms of RNA:
ribosomal(rRNA), messenger (mRNA) and
transfer RNA (tRNA).
Synthesis of Proteins
How are such a diverse range of proteins possible? The code for making a protein is
found in your genes (on your DNA). This genetic code is copied onto a messenger
RNA molecule. The mRNA code is read in multiples of 3 (a codon) by ribosomes
which join amino acids together to form a polypeptide. This is known as gene
expression.
The protein folds
to form its
working shape
Gene Expression
Gene
DNA
G T
NUCLEUS
Chromosome
CELL
A C T A
The order of bases in
DNA is a code for
making proteins. The
code is read in groups of
three
Cell machinery
copies the code
making an mRNA
molecule. This
moves into the
cytoplasm.
Ribosomes read the
code and accurately
AUGAGUAAAGGAGAAGAACUUUUCACUGGAUA join Amino acids
together to make a
S
L F T
M
E
E
protein
K
Proteomics
 Proteomics
is the study of the proteome.
 The proteome is the entire complement of
proteins expressed by a genome, cell, tissue
or organism.
 More specifically, it is the expressed proteins
at a given time point under defined conditions.
 The term is a blend of proteins and genome.
 A cellular
proteome is the collection of
proteins found in a particular cell type under a
particular set of environmental conditions
such as exposure to hormone stimulation.
 It can also be useful to consider an
organism's complete proteome, which can
be conceptualized as the complete set of
proteins from all of the various cellular
proteomes. This is very roughly the protein
equivalent of the genome.
Proteome
 The
term "proteome" has also been used to
refer to the collection of proteins in certain
sub-cellular biological systems.
For example, all of the proteins in a virus can
be called a viral proteome.
 The proteome is larger than the genome,
especially in eukaryotes, in the sense that
there are more proteins than genes.