2013年11月28日 星期四

Topic 3.3: DNA structure

3.3.1 Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate.


DNA Nucleotide

Deoxyribose is linked to the phosphate group with the 5th carbon and the 3rd carbon

Phosphate group is a phosphate with a negative charge

Nitrogenous Base could include (Adenine, Thymine, Cytosine and Guanine)


3.3.2 State the names of the four bases in DNA

In order with respect to the photo:

Adenine, Guanine, Thymine and Cytosine

Adenine and Guanine are both double ring nitrogenous bases (Purines)
Cytosine and Thymine are both single ring nitrogenous bases (Pyrimidines)


3.3.3 Outline how DNA nucleotides are linked together by covalent bonds into a single strand.



Nucleotides are covalently bonded between the phosphate of one nucleotide to the C3 of the second nucleotide. The phosphate group creates a bridge connecting the C5 on one pentose and the C3 on the other. The bond is called the phosphodiester bond because it involves the phosphate group.


3.3.4 Explain how a DNA double helix is formed using complementary base pairing and hydrogen bonds.

Two polynucleotides of DNA are held together by hydrogen bonds between complementary bases.

Guanine and Cytocine bonds together with a triple hydrogen bond (C=3)

Adenine and Thymine bonds together with a double hydrogen bond.


In order for the nucleotides to face each other, one strand is reversed to the other.


3.3.5 Draw and label a simple diagram of molecular structure of DNA





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