Download Molecular biology is the branch of biology that deals with the

3rd lecture
Principles of Biotechnology
 Nucleic acids (DNA & RNA) and Biotechnology
 Introduction:
1) Nucleic acids are organic molecules (biomolecules) that allow
organisms to transfer genetic information from one generation to the
next.
2) There are two types of nucleic acids: deoxyribonucleic acid, known
as DNA and ribonucleic acid, known as RNA.
 Why should study DNA and RNA in Biotechnology
1) One of the most important process in biotechnology is the ability to
manipulate the genetic material of an organism.
2) DNA represent as a genetic material in all organism except in some
viruses which have RNA as a genetic material.
3) So we need to study their structure, functions, replication,
transcription and translation in order to understand these molecules
and to know the mechanism that enable us to manipulate them.
 Why DNA is better than RNA as a genetic material
1) DNA is chemically more stable than RNA.
2) DNA has the ability to replicate itself.
3) DNA has the ability to evolve and change itself.
4) DNA is able to express the information when needed.
 Experiments to prove that DNA as genetic material
 Frederick Griffith’s Experiments (1928)
1) Griffith was studying two strains of the bacteria Streptococcus
pneumoniae, which causes pneumonia and other infections.
2) Smooth strain (S): Produced a polysaccharide capsule that gave its
colonies a smooth appearance.
3) Because of the capsule, the bacteria can evade the immune system and
cause disease (so called pathogenic strain)
1
Dr. Mohanad J.K. Al-Dawah
3rd lecture
Principles of Biotechnology
4) Rough strain (R): Does not produce a capsule, rough appearance, not
pathogenic and doesn’t cause disease (so called non-pathogenic strain)
5) Griffith treated his mice with the following bacterial preparations:
Treatment
Outcome
Live rough
Mice lives
Live smooth
Mice dies
Heat killed smooth (HKS)
Mice lives
HKS + live rough
Mice dies
 Griffith conclusions
1) Griffith concluded that the genetic instructions to make capsules
had been transferred to the rough bacteria, from the dead smooth
bacteria.
2) He called this phenomenon transformation.
3) However, he was unable to identify what type of molecule was
responsible for transformation.
Figure 1: Griffith experiment (Transformation experiment)
2
Dr. Mohanad J.K. Al-Dawah
3rd lecture
Principles of Biotechnology
 Oswald Avery’s Experiments (1944)
1) Avery repeated Griffith’s experiments using purified DNA, protein,
and other substances.
2) He showed that the chemical substance responsible for transformation
was DNA and not protein.
3) While many biologists were convinced, others remained doubtful.
 Hershey and Chase Experiments (1952):
1) They performed the definitive proof that DNA rather than protein
carries the hereditary information of life
2) E. Coli bacteriophage: A virus that infects bacteria.
3) Bacteriophages only contain a protein coat (capsid) and DNA.
4) They wanted to find out whether the protein or DNA carried the
genetic instructions to make more viruses.
5) They labeled either the viral proteins or DNA:
6) Protein capsid: Labeled with radioactive sulfur (35S)
7) DNA: Labeled with radioactive phosphorus (32P)
8) Radioactive labeled viruses were used to infect cells.
9) Bacterial cells that were infected with the two types of bacteriophage,
were then centrifuged and examined.
 Results:
1) Labeled viral proteins did not enter infected bacteria (found in
supernatant).
2) Labeled viral DNA did enter bacteria during viral infection (found
in cell pellet).
 Conclusion:
1) Protein is not necessary to make new viruses.
2) DNA is the molecule that carries the genetic information to make
new viruses.
3
Dr. Mohanad J.K. Al-Dawah
3rd lecture
Principles of Biotechnology
 Nucleic acids structure:
1) Both DNA and RNA structure composed of three parts:
a) Five carbon sugar
b) Nitrogen bases
c) Phosphate group
2) Five carbon sugar + nitrogen base is called nucleoside.
3) Nucleoside + phosphate group is called nucleotide.
4) Nucleotides are the building blocks of DNA and RNA.
5) Each nucleotide binds with another nucleotide by phosphodiester bond
and form the final structure of DNA and RNA.
6) Five carbon sugar is called pentose carbon sugar.
7) Nitrogen bases have two type
a) Purines which include Adenine (A) and Guanine (G).
b) Pyrimidines which include Thymine (T), Cytosine (C) and Uracil
(U).
8) Phosphate group gives the acidic property to DNA and RNA.
 DNA structure
1) The five carbon sugar that found in DNA is called deoxyribose
because the absence of oxygen in the position 2'.
2) The nitrogen bases that found in DNA are A, T, G and C.
3) binds with (T) by two hydrogen bonds (A=T), while (G) binds with
(C) by three hydrogen bonds (G≡C).
4) DNA usually found as a double strand.
5) DNA is found in the nucleus of the cell and in the mitochondria.
 RNA structure
1) The five carbon sugar that found in RNA is called ribose.
2) The nitrogen bases that found in RNA are A, U, G and C.
4
Dr. Mohanad J.K. Al-Dawah
3rd lecture
Principles of Biotechnology
3) binds with (U) by two hydrogen bonds (A=U), while (G) binds with
(C) by three hydrogen bonds (G≡C).
4) RNA usually found as single strand.
5) RNA found in cell nucleus, cytoplasm and ribosome depending on the
its type.
 Functions of DNA
1) DNA stores the heredity information of an individual.
2) DNA directs the machinery of a cell to make specific proteins
3) DNA indirectly controls all of the functioning of all living organisms.
4) DNA is responsible of the evolution of organisms.
5) DNA is responsible of transferring the genetic information from
parents to offspring.
 Functions of RNA
1) mRNA - messenger RNA, acts as a messenger that carries information
from DNA to ribosomes.
2) rRNA - ribosomal RNA, combines with proteins in the cytoplasm to
form the ribosomes.
3) tRNA - transfer RNA, reads the genetic code on the messenger RNA
in the cytoplasm to translate it into protein.
5
Dr. Mohanad J.K. Al-Dawah
3rd lecture
Principles of Biotechnology
Figure 2: Components of nucleic acids: bases, sugars, and phosphate.
Figure 3: The structure of DNA and RNA
6
Dr. Mohanad J.K. Al-Dawah