Lecture 5 - DNA Structure and Properties 2

DNA is composed of many units called _________________.

nucleotides

DNA consists of ______________________________.

two complimentary polynucleotide chains

DNA is arranged in a _________________.

double helix

What components make up a nucleotide?

Nitrogenous Base + Deoxyribose Sugar + Phosphoric Acid

What type of deoxyribose sugar is seen in DNA?

A 5 ring Carbon sugar (C₅H₁₀O₄)

Purine

A two ringed heterocyclic nitrogenous base

Pyrimidine

A single ringed (monocyclic) nitrogenous base

How many atom rings does a purine have?

9

How many atom rings does a pyrimidine have?

6

What bases in DNA (or RNA) are considered purines?

1. Adenine (A)

2. Guanine (G)

What bases in DNA (or RNA) are considered pyrimidines?

1. Thymine (T) in DNA ONLY

2. Cytosine (C)

3. Uracil (U) in RNA ONLY

What type of sugar is pictured here?

Deoxyribose sugar

What type of sugar is pictured here?

Ribose sugar

What components make up a nucleoside?

Nitrogenous Base + Deoxyribose Sugar

What type of nucleoside is pictured here?

2’-deoxyadenosine

What type of nucleoside is pictured here?

2’-deoxycytosine

What type of nucleotide is pictured here?

2’-deoxyadenosine-5’-monophosphate

What type of nucleotide is pictured here?

2’-deoxycytosine-5’-monophosphate

N-glycosidic bond

A covalent bond linking a sugar to another molecule

What nitrogenous base type favors an anti configuaration?

Purines

Anti Configuration

A bond in a position that’s directed away from the sugar

Syn Configuration

A bond in a position that’s directed towards the sugar

Phosphodiester bond

A covalent bond that joins the 5' carbon atom of one sugar molecule to the 3' carbon atom of another sugar in DNA and RNA

Two strands of DNA are ____________ to each other.

Anti-parallel

What type of bonds are the bases in a DNA molecule linked by?

Hydrogen bonds

True or False: Purines pair with pyrimidines.

True

In a hydrogen bond, what two atoms are linked to each other?

Oxygen and Nitrogen

When Adenine (A) pairs with Thymine (T), how many hydrogen bonds do they have?

2 hydrogen bonds

When Guanine (G) pairs with Cytosine (C), how many hydrogen bonds do they have?

3 hydrogen bonds

The base pairs in a DNA molecule are _______________ to each other.

pseudosymmetrical

Hydrogen bonds are ___________ length/s.

the same

B-DNA twists in which direction?

Right-handed helix

What is the distance between the base pairs in a DNA molecule?

0.34nm

What is the distance between the major grooves of a DNA molecule?

3.4nm

What is the distance between the 5’ end and 3’ end of a DNA molecule?

2.0nm

Are DNA bases co-planar to each other? If or if not, why?

No, DNA bases are not co-planar to each other because successive pairs stack on top of each other with a twist

Even though this is a picture of a DNA molecule, why is it considered inaccurate?

The grooves are the same length and chemically, this would mean the hydrogen bonds between the base pairs would be different lengths, which isn’t true in a DNA molecule.

What type of DNA is pictured here?

B-DNA

What type of DNA is pictured here?

A-DNA

What type of DNA is pictured here?

Z-DNA

Select the characteristics that apply to B-DNA:

1. Double stranded

2. Contains water molecules

3. Chains are anti-parallel and complimentary

4. Bases are stacked and pointed inside the molecule

5. Bases are typically in the anti configuartion

Select the characteristics that apply to A-DNA:

1. Contains no water molecules

2. Bases are tilted (not stacked)

3. Molecule is wider and shorter

Select the characteristics that apply to Z-DNA:

1. Left-handed helical formation with zig-zag pattern

2. Has repeating purine-pyrimidine sequences

3. Bases are in the anti and syn configurations

4. Bases are in an alternate conformation

5. Molecule is more compact (narrower)

What’s important to remember about B, A, and Z-DNA?

1. A single chromosome can have all three types within it.

2. They can change back and forth.