nucleic acids (dna and rna)
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NUCLEIC ACIDS
(DNA and RNA)
They are large, complex molecules of high molecular weight.
They contain C, H, O, N and P.
Their monomers are nucleotides.
The Structure of a Nucleotide
PO4
5C Sugar
(ribose or deoxyribose)
Nitrogenous bases
(adenine, guanine, thymine,cytosine, uracil)
1
2
3
Nucleic acids are polymers of nucleotides.
Phosphoester bond Glycoside bond
Nitrogenous base
+5C
Sugar +Phosphate group
Nucleotides
Nucleic acidsNucleotide
Adenine =
Cytosine Guanine
Thymine
Number of H bonds between bases
Adenine
Guanine
Cytosine
Thymine
Purine bases
Pyrimidine bases
A
T= 1
G
C= 1
T+C
A+G = 1 Purines
Pyrimidines
= 1
Nucleoside
A+G T+C= =
Number of nucleotide in DNA
Number of nucleotide in DNA
1/2
A+G= =
T+C 1
Number of nucleotide in one strand
Number of nucleotide in one strand
Number of H bonds
= ( A X 2 ) + ( G X 3 )
Number of H bonds
= ( T X 2 ) + ( CX 3 )
Number of phosphodiester bonds
=Number of nucleotide in DNA - 2
Number of phosphodiester bonds
=Number of nucleotide in one strand - 1 X 2
• ratio is specific for species. If the ratio is smaller and it is resist to heating.
• In prokaryotes, DNA is found in cytoplasm and naked. In eukaryotes, histones are found in the structure of DNA. DNA is located in nucleus, mitochondrion, chloroplast.
• All kind of biological process are directed by DNA.
• DNA is replicated during interphase.• DNA undergoes mutations. If a mutation occurs
within the sex cell, it is inherited to next generation.
A+T
G+C
Nucleic Acids
DNA (Deoxyribonucleic acid)
RNA (Ribonucleic acid)
DNA: Found in nucleus, mitochondria and chloroplast in eukaryotes
Is the hereditary material that is transmitted from one generation to the next, during reproductionContains 5 C sugar(deoxyribose), phosphate group (PO4), nitrogenous bases adenine (A)
guanine (G)
cytosine (C)
thymine (T)
DNA is double stranded (double helix)
Crick and Watson walking along the Backs. 1953
RNA:
Found in nucleus and cytoplasm
Works with DNA, involved in protein synthesis
Contains 5 C sugar (ribose), phosphate group (PO4) and nitrogenous bases adenine (A)
guanine (G)
cytosine (C)
uracil (U)
RNA is single stranded.
DNA RNA
It is double stranded ( in some viruses, it is single)
It is single stranded ( but in some RNA viruses, it is double helix)
5C sugar is deoxyribose 5C sugar is ribose
Nitrogenous bases are A, G, C, T
Nitrogenous bases are A, G, C, U
Location:
prokaryotes: in cytoplasm
eukaryotes: nucleus, mitochondrion, chloroplast
Location:
prokaryotes: in cytoplasm
eukaryotes: nucleus, cytoplasm mitochondrion, chloroplast, ribosome
DNA RNA
Function: is the primary hereditary material, controls the structure of proteins synthesized and this way controls all cellular activities
Function: vital for protein synthesis
can replicate itself is transcribed by DNA
DNA RNA
Enzymes for replication:
DNA polymerase
DNA ligase
DNA nucleotide sentetase
Enzyme for production:
RNA polymerase
RNA nucleotide sentetase
Enzymes for depolymerization:
DNAse ( deoxyribonuclease)
Enzymes for depolymerization:
RNAse ( ribonuclease)
GRIFFITH’S EXPERIMENT
Griffith was trying to find out a vaccine against pneumonia
transformation
Blood analysis showed the presence of some live S- type bacteria
THE CHEMICAL BASES OF HEREDITY
HERSEY AND CHASE EXPERIMENT
Hersey and Chase worked with bacteriophage because it is analog of chromosome
The Hershey-Chase Experiment – Bacteriophage
1. Hershey and Chase forced one population of phages to synthesize DNA using radioactive phosphorous. 2. The radioactive phosphorous "labeled" the DNA.3. They forced another group of phages to synthesize protein using radioactive sulfur.4. The radioactive sulfur "labeled" the protein.5. Bacteria infected by phages containing radioactive protein did not show any radioactivity.6. Bacteria infected by phages containing radioactive DNA became radioactive.7. This showed that it was the DNA, not the protein, that was the molecule of heredity.
DNA REPLICATION
Three possible mechanisms of DNA replication
a) Semiconservative replication: The two parental strands seperate, each forms a template for new strand.
b) Conservative replication: Each of the two strands of parent DNA is replicated, without strand seperation.
c) Dispersive replication: During replication, parent chains break at intervals, and replicated segments are combined into strands with segments from parent chains. All daughter helixes are part old, part new.
DNA REPLICATION
DNA is labelled with 15 N isotope
Normal or 14 N compound medium
14 15 1514
F1 generation
100% hybrid DNA
15 15
Normal or 14 N compound medium 14 14 14 14 14 141515
50% hybrid DNA
15 N - 14 N
50% normal DNA
14 N - 14 N
F2 generation
If normal DNA is given;
2n
2 hybrid and 2 pure heavy DNA are formed
If hybrid DNA is given;
2n
one of the DNA is always hybrid the others are pure
DNA REPLICATION
Replication number
Replication number
DNA REPLICATION MECHANISM
DNA REPLICATION
Replication occurs in three stages:
1. UNWINDING: Helicase enzymes seperate the parental double helix by breaking down the H bonds, forming the replication fork.
Replication
fork
2. CONTINUOUS SYNTHESIS: The “leading strand” is assembled continuously in the 5' to 3' direction by DNA polymerase, using the single parental strand as a template, it adds nucleotides to the growing 3' end
DNA REPLICATION
C
A T
G 5'
5'
5'
3'
3'
Replication is continuous
DNA polymerase can work only in the 5' - 3' direction
3'
5'
5'
5'
3'
3'
3'
With okazaki fragments replication is discontinuous
DNA ligase links the okazaki fragments which are 1000- 2000 nucleotide long fragments in prokaryotes and 100-300 nucleotide long in eukaryotes
3. DISCONTINUOUS SYNTHESIS: The “lagging strand” is assembled discontinuously. It is produced as a series of short segments ( Okazaki fragments), each of which is synthesized in the 5' to 3' direction by DNA polymerase, using the single parental strand as a template
DNA REPLICATION
OKAZAKI FRAGMENTS
• In bacteria, the Okazaki fragments are each 1000-2000 nucleotides long
• In eukaryotes, they are 100 to 300 nucleotides length
• Finally, the fragments are joined to the 5' end of the growing chain by a DNA ligase enzyme
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