Biochemistry Department.Course Code :701Instructor : Dr/Omneya

DNA Denaturation

Outlines :-

A. Introduction.B. What's meant by DNA Denaturation.C. Causes of DNA Denaturation.D. Characters of Denatured DNA .E. Diseases caused by DNA Denaturation.F. DNA renaturation.G. Application on DNA denaturation and renaturation.H. References.I. Participants.

A. Introduction

-DNA is a double helix composed of 2 strands running in opposite directions . -Each strand composed of backbone of deoxy-ribose “sugar molecules linked together by phosphate linkage” .

•Each sugar molecule covalently linked to one of four bases Adenine, Guanine, Cytosine and Thymine.

•The two strands connected together by H-bond.

A.2. Function of DNA.

1. Stores an organism genetic material in the nuclei.

2. Replicates itself when dividing.

3. Provide code or template for particular sequencing of amino acid that bond together and make protein.

B.“DNA Denaturation” Definition

DNA Denaturation is the separation of a double strand into two single strands, which occurs when the hydrogen bonds between the strands are broken.

C.Causes of Denaturation.

Denaturation can occur when proteins and nucleic acids are subjected to :

1-elevated temperature. 2-extremes of pH. 3-nonphysiological concentrations of

salt, organic solvents, urea, or other chemical agents.

C.1-elevated temperature.

The most common type of denaturation is thermal denatuation.

Tm : temp at which DNA is half denatured.

*above Tm DNA is single strands.

*below tm DNA is double strands.

C.2-extremes of pH

At high PH the hydroxide ions (( negatively charged ions )) can pull hydrogen ions from base pairs – forming H bond between two strands – causing

them to separate.

C.3 non physiological salts

Low salt concentration could also denature DNA double-strands by removing ions that stabilize the negative charges on the two strands from each other.

D. Characters of Denatured DNA

1. Hyperchromic : increase the absorbance (A260) upon denaturation.

2. The rate of increase in absorbance is directly proportional to the rate of denaturation.

3. Viscosity decrease upon denaturation.

E.Diseases caused by DNA denaturation

DNA repair deficiency disorder is a medical condition due to reduce functionality of DNA repair .

DNA repair defects can cause both an accelerated aging disease and an increase risk of cancer.

Examples for DNA defects accelerated aging :1.Bloom syndrome.2.Fanconi`s anemia. 3.Xeroderma pigmentosum.

DNA repair defects and increased cancer risk : When a mutation is present in a DNA repair

gene, the repair gene will either not be expressed or expressed in an altered form so the repair function will likely be deficient .

DNA synthesis leading to mutations , some of which may give rise to cancer .

F.DNA Renaturation

Renaturation or annealing :I. is the formation of base repairs and complementary strands

of DNA come back together.

II. Renaturation occurs if double stranded DNA is heated above tm then the temperature is slowly decreased under appropriate conditions.

F.Applications on DNA denaturation and renaturation

1. Understanding the genome size and complexity.

2. Understanding genetic relatedness.

3. Understanding relative proportion of single copy and repetitive sequences.

G.References

1. Lecture notes “illustrated biochemistry I “ .

2. Harper`s illustrated Biochemistry.3. Lippincott's illustrated reviews.4. Oraby`s illustrated reviews of

biochemistry.