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Nucleic Acids
DNA and RNA
Hundreds of thousands of proteins exist inside each
one of us to help carry out our daily functions.
These proteins are produced locally, assembled
piece-by-piece to exact specifications
This information, detailing the specific structure of the
proteins inside of our bodies, is stored in a set of
molecules called nucleic acids.
Nucleic Acids DNA and RNA
DNA - deoxyribonucleic acid
RNA - ribonucleic acid
DNA- stores genetic information
RNA - use in protein synthesis
for putting genetic information
COMPOSITION OF NUCLEIC ACIDS
Nucleic Acids are POLYMERS
Proteins are polypeptides,
Carbohydrates are polysaccharides
Nucleic acid is polynucleotide- made of
NUCLEOTIDES
Structure of NUCLEOTIDE
The deoxyribonucleic acid, DNA, is a long chain of
nucleotides which consist of
– Deoxyribose (a pentose = sugar with 5
carbons)
– Phosphoric Acid
– Organic (nitrogenous) bases (Purines Adenine and Guanine, or Pyrimidines Cytosine and Thymine
The Structure of Nucleic Acid
Nucleic Acid is a polymer of
nucleotides
It is a very large molecule that have
two main parts. The backbone of a
nucleic acid is made of alternating
sugar and phosphate molecules
bonded together in a long chain
phosphodiester bonds.
Each of the sugar groups in the
backbone is attached (via the bond
shown in blue) to a third type of
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molecule called a nucleotide base.
The Structure of Nucleic Acids
The phosphodiester bonds link the 3' carbon in the
sugar ring of one nucleotide to the 5' carbon on the
next nucleotide
sequence of bases constitutes the genetic information
Different pentose sugars in RNA & DNA
RNA
DNA
Sugar carbons
have prime
numbers, to
distinguish them
from atoms in
bases
Nucleotides
Deoxyribonucleotides
Ribonucleotides
Heterocyclic Nitrogen Bases
RNA
DNA
DNA - POLYNUCLEOTIDE
NUCLEOTIDE
NUCLEOSIDE
PHOSPHATE
DEOXYRIBOSE
GETEROCYCLIC
NITROGEN BASE
ADENIN CYTOSIN GUANIN THYMINE
RNA - POLYNUCLEOTIDE
NUCLEOTIDE
NUCLEOSIDE
PHOSPHATE
RIBOSE
GETEROCYCLIC
NITROGEN BASE
ADENIN CYTOSIN GUANIN URACIL
Structure of Nucleic Acid
Only four different nucleotide bases can occur in a
nucleic acid, each nucleic acid contains millions of
bases bonded to it.
The order in which these nucleotide appear in the
nucleic is the coding for the information carried in
the molecule.
In other words, the nucleotide serve
as a sort of genetic alphabet on
which the structure of each protein
in our bodies is encoded.
DNA
• In the early 1950s, four scientists, James Watson and
Francis Crick at Cambridge University and Maurice
Wilkins and Rosalind Franklin at King's College,
determined the true structure of DNA from data and
X-ray pictures of the molecule that Franklin had taken.
In 1953, Watson and Crick published a paper in the
scientific journal Nature describing this research.
Watson, Crick, Wilkins and Franklin had shown that
not only is the DNA molecule double-stranded, but the
two strands wrap around each other forming a coil, or
helix.
WATSON-CRICK MODEL
Combination of two single strands
The Double Helix
Sugar-phosphate backbone
outside,
bases inside
1953
WATSON-CRICK MODEL
Bases form specific base pairs, held together by hydrogen bonds
Structure compatible with any sequence of bases
WATSON-CRICK MODEL
The nucleotide bases of the
DNA molecule form
complementary pairs:
adenine always bonds to thymine
(and vice versa)
and guanine always bonds to cytosine
(and vice versa).
This bonding occurs across
the molecule, leading to a
double-stranded system
As a trick for remembering how the
bases pair up (if symbols are arranged
in alphabetical order):
A
C
Adenine Cytosine
G
Guanine
T
Thymine
The base pairing is the key to understanding
how DNA functions
Watson-Crick base pairs
Hydrogen bonds are weaker than covalent bonds (eg. C-C or
C-N)
Covalent bonds determine structure,
Weak hydrogen bonds - Stabilize double helix
Base Pairing in DNA
DNA samples from different cells of the same species
have the same proportions of the four heterocyclic bases
DNA samples from different species have different
proportions of bases
Human DNA contains:
30% - Adenine
equal amounts
30% - Thymine
A=T
20% - Guanine
equal amounts
20% - Cytosine
G=C
The bases occur in pairs!!!
DNA replication
The double-stranded DNA molecule has
the unique ability that it can make exact
copies of itself, or self-replicate. When
more DNA is required by an organism
(such as during reproduction or cell
growth) the hydrogen bonds between the
nucleotide bases break and the two
single strands of DNA separate. New
complementary bases are brought in by
the cell and paired up with each of the
two separate strands, thus forming two
new, identical, double-stranded DNA
molecules.
DNA
The blueprint for the structure and functioning of our
bodies is contained in the genetic material found in the
nucleus.
The total number of base pairs in a human cell the
HUMAN GENOME is 3 billion base pairs
The genetic material (chromatin) is composed of DNA
(Deoxyribonucleic acid) and protein
When a cell is not actively dividing, its nucleus is occupied by
CROMATIN
CHROMATIN
DNA
HISTONE
Chromatin is DNA wound tightly around proteins called
histones.
During cell division, chromatin organizes itself into
CHROMOSOMES
Each chromosome contain a different DNA molecule!!!
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What is a chromosome?
It is a linear strand of DNA in combination with
nuclear proteins
We refer to this complex of DNA and proteins as
chromatin
It is a linear array
of genes
As a set - they are
our genome
CHROMOSOME
Organisms differ in their number of chromosomes
64 chromosomes - 32 pairs
38 chromosomes - 19 pairs
6 chromosomes - 3 pairs
46 chromosomes - 23 pairs
Heredity is encoded in DNA within the chromosomes
What is a GENE?
During cell division the DNA is duplicated so that each new
cell receives a complete copy
Each DNA molecule is made up of many GENES
GENE is individual segment of DNA that contains the
instructions that direct the synthesis of a single polypeptide
RNA
Ribonucleic acid, or RNA, gets its name from the
sugar group in the molecule's backbone - ribose.
Several important similarities and differences
exist between RNA and DNA.
DNA vs RNA
DNA consists of two associated
polynucleotide strands that
wind together in a helical
fashion. It is often described as
a double helix
Most RNA is single stranded
and does not form a double
helix
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DNA vs RNA
DNA Composition
RNA Composition
Deoxyribose (a pentose =
sugar with 5 carbons)
Ribose (a pentose = sugar
with 5 carbons)
Phosphoric Acid
Phosphoric Acid
Organic (nitrogenous) bases: Organic (nitrogenous) bases:
(Purines - Adenine and
Guanine, or Pyrimidines Cytosine and Thymine)
Purines (Adenine and
Guanine) and Pyrimidines
(Cytosine and Uracil)
DNA vs RNA
DNA Composition
RNA Composition
The base composition is
variable, but in all cases the
amount of adenine is equal
to the amount of thymine
(A=T).
The rule A+C=U+G CAN'T
BE APPLIED THERE
because most RNA is single
stranded and does not form a
double helix
In the same manner,
C=G.
Consequently
A+C = T+G
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RNA
RNA (ribonucleic acid) is the messenger of DNA within
the cell.
Forms of RNA direct the cell to manufacture specific
enzymes and other proteins
There are several different kinds of RNA made by the
cell:
• mRNA - messenger RNA
• tRNA - transfer RNA
• rRNA - ribosomal RNA
Central Dogma
How does the sequence of a strand of DNA correspond
to the amino acid sequence of a protein? This concept is
explained by the central dogma of molecular biology
that deals with the detailed residue-by-residue transfer
of sequential information, and states that:
• information cannot be transferred back from protein
to either protein or nucleic acid.
• In other words, 'once information gets into protein, it
can't flow back to nucleic acid.'
Central Dogma
Every time a cell divides, three fundamental
processes known as:
• Replication
• Transcription
• Translation
RNA take place in the duplication, transfer, and
use of genetic information
Replication
Process by which copies
of DNA are made when a
cell divides (each of two
daughter cells has the
same DNA)
Transcription
Process by which copies
the genetic information in
DNA is read and used to
synthesize RNA
• CODON - in the mRNA is
a series of three
ribonucleotides that is a
code for a specific amino
acid.
• Example: GGU on mRNA
- codon for GLYCINE
Translation
Process by which the genetic
message is decoded and
used to make proteins
Every cell contains 20 or
more different tRNAs, each
designed to carry a
specific amino acid.
A tRNA molecule is L-shaped
and it is a sequence of three
nucleotides called ANTICODON
• The Anticodon of each tRNA is complementary to mRNA codon
• Ex: mRNA CODON
CUG
•
tRNA ANTICODON
GAC
Points to remember
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Nucleic Acids and their structure
Nucleotide vs Nucleoside
DNA and RNA composition
Watson-Crick model of DNA
What is a chromosome?
What is a GENE?
DNA vs RNA
Replication, Transcription, Translation