DNA Structure

What does DNA stand for?

deoxyribonucleic acid

What is DNA composed of?

many nucleotides

What holds the two strands of DNA together? Where?

hydrogen bonds between the nitrogen base pairs

What are the three parts of a nucleotide in DNA?

deoxyribose (5C) sugar, phosphate, and one of four different nitrogenous bases

What are the different nitrogenous bases nucleotides can have in DNA?

adenine, thymine, guanine, cytosine

How many hydrogen bonds are between adenine and thymine?

two

How many hydrogen bonds are between guanine and cytosine?

three

Which bases are purines?

adenine and guanine (have double rings)

Which bases are pyrimidines?

thymine and cytosine (have a single ring)

What is the complementary base pair rule?

a purine will always pair with a pyrimidine!

adenine and thymine

guanine and cytosine

What is true about the percentages of the nitrogenous bases because of the complementary base pair rule?

in ANY DNA molecule...

%adenine=%thymine

%guanine=%cytosine

(purines=according pyrimidines)

Chargaff's Rule

%A=%T and %C=%G, so %A+%T+%C+%G=100

How are DNA strands arranged?

anti-parallel direction in a double helix, meaning the head of one strand (5' end) is OPPOSITE to the tail of the other strand (3' end) sticking upwards

How do you determine the 5' end vs. the 3'?

start counting the carbons on the 5C sugar from the point where the nitrogenous base attaches in a CLOCKWISE direction, the number sticking upwards determines the direction! (the fifth carbon is located on the phosphate)

What is the sugar-phosphate backbone? Why is it referred to in such way?

the repeating chain of sugar and phosphates on the sides of the DNA molecule; it serve as the framework sides of DNA's double helix and provides support and shaping (necessary for DNA's functions)

What bonds hold together the sugar-phosphate backbone?

covalent bonds