BIO MODULE 4:Set 2 — DNA Structure, Base Pairing & Polarity

What are the three components of a DNA nucleotide?

A deoxyribose sugar, a phosphate group, and a nitrogenous base.

What are the four nitrogenous bases in DNA?

Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).

What are purines?

Nitrogenous bases with two fused rings.

Which DNA bases are purines?

Adenine and Guanine.

What are pyrimidines?

Nitrogenous bases with one ring.

Which DNA bases are pyrimidines?

Thymine and Cytosine.

What are Chargaff's rules?

In double-stranded DNA, the amount of adenine equals thymine and the amount of guanine equals cytosine.

If DNA contains 30% adenine, what percentage is thymine?

30%.

If DNA contains 30% adenine, what percentage is guanine?

20%.

If DNA contains 20% cytosine, what percentage is guanine?

20%.

If DNA contains 20% cytosine, what percentage is adenine?

30%.

What is a polynucleotide chain?

A chain of nucleotides connected by phosphodiester bonds.

What forms the sugar-phosphate backbone of DNA?

Alternating deoxyribose sugars and phosphate groups.

What is a phosphodiester bond?

A covalent bond linking the 3′ carbon of one sugar to the 5′ carbon of the next through a phosphate group.

What does polarity mean in a DNA strand?

The strand has two chemically different ends, called the 5′ end and 3′ end.

What is found at the 5′ end of a DNA strand?

A phosphate group attached to the 5′ carbon of deoxyribose.

What is found at the 3′ end of a DNA strand?

A hydroxyl (-OH) group attached to the 3′ carbon of deoxyribose.

Who used X-ray diffraction to investigate DNA structure?

Rosalind Franklin and Maurice Wilkins.

What did Rosalind Franklin's X-ray diffraction results suggest?

DNA has a helical structure.

Who proposed the double-helix model of DNA in 1953?

James Watson and Francis Crick.

What is the double-helix structure of DNA?

Two polynucleotide strands twisted around each other with paired nitrogenous bases between them.

What does complementary base pairing mean?

Adenine pairs with thymine, and guanine pairs with cytosine.

How many hydrogen bonds form between adenine and thymine?

Two.

How many hydrogen bonds form between guanine and cytosine?

Three.

What does antiparallel mean in DNA?

The two strands run in opposite directions, with one oriented 5′ to 3′ and the other 3′ to 5′.

What type of bonds connect complementary nitrogenous bases?

Hydrogen bonds.

How is genetic information stored in DNA?

Through the linear sequence of nitrogenous bases along the DNA molecule.