Nucleic Acids

What are nucleic acids?

• Nucleic acids are information-carrying biological molecules.

What are the two types of nucleic acids?

The two types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

What do DNA and RNA carry?

They carry genetic information needed for making new cells and producing proteins.

What monomers are nucleic acids made from?

Nucleic acids are polymers made from many nucleotide monomers.

What is a mononucleotide and a polynucleotide?

• A mononucleotide is one nucleotide.

• A polynucleotide is a chain of many nucleotides.

What is the structure of a nucleotide?

• A pentose sugar — a sugar containing five carbon atoms.

• A phosphate group.

• A nitrogenous organic base.

What are the bases present in DNA?

• Adenine

• Guanine

• Cytosine

What are the bases present in RNA?

• Thymine

• Uracil

• 
  

What is the difference between DNA and RNA?

Feature	DNA	RNA
Full name	Deoxyribonucleic acid	Ribonucleic acid
Sugar	Deoxyribose	Ribose
Bases	A, T, C, G	A, U, C, G
Typical structure	Two polynucleotide strands	One polynucleotide strand
Main role	Stores genetic information	Helps use genetic information, including in protein synthesis

How are nucleotides joined together?

Nucleotides are joined by phosphodiester bonds.

How are the phosphodiester bonds formed?

through condensation reactions.

What bonds with what in a phosphodiester bond between two neighbouring nucleotides?

The bond links the phosphate group associated with one nucleotide to the sugar of the neighbouring nucleotide.

What does the repeated formation of phosphodiester bonds produce?

Repeated formation of phosphodiester bonds produces a long polynucleotide chain.

What is the sugar–phosphate backbone?

The sugar–phosphate backbone is the repeating chain of alternating sugar and phosphate groups along a polynucleotide strand.

What does the backbone form?

The backbone forms the outside of a DNA double helix.

What projects from the backbone?

the nitrogenous bases

what carries the genetic information?

the order of the bases

what are phosphodiester bonds?

Covalent bonds that hold together individual nucleotides in a polynucleotide strand together.

What do hydrogen bonds hold together?

Holds complementary bases between DNA strands together

What do 5′ and 3′ mean?

The pentose sugar has five carbon atoms, numbered 1′, 2′, 3′, 4′ and 5′. The prime symbol distinguishes these sugar carbon numbers from the numbering of atoms in a nitrogenous base.

What is attached to the 1’ carbon?

the nitrogenous base

What is attached to the 3’ carbon?

an OH- group which is important in extending the strand.

What is the structure of DNA?

DNA is a double helix consisting of two polynucleotide strands.

What is the detailed structure of DNA?

• Each strand has a sugar–phosphate backbone.

• The backbones are on the outside.

• The nitrogenous bases project inwards.

• The two strands run antiparallel to each other.

• Complementary bases pair through hydrogen bonds.

• The bases are arranged in a specific sequence.

What is complementary base pairing?

In DNA, the bases pair specifically:

• Adenine (A) pairs with thymine (T) through two hydrogen bonds.

• Cytosine (C) pairs with guanine (G) through three hydrogen bonds.

What holds the complimentary bases in the opposite strands of DNA?

Hydrogen bonds

What do the hydrogen bonds between the two DNA strands?

• They hold the two polynucleotide strands together.

• They stabilise the double helix.

Why is it crucial that the hydrogen bonds are weaker than the phosphodiester bonds within each back bone?

Because it allows the strands to separate when needed . , eg protein synthesis.

What are Purines?

a nitrogenous base containing two rings.

What are the two examples of purines?

Adenine (A)

Guanine (G)

What are pyrimidines?

a nitrogenous base consisting of one ring.

What are the 3 examples of pyrimidines?

Cytosine (C)

Thymine (T)

Uracil (U, in RNA)

Why does DNA pair one purine with one pyrimidine?

Purines have two fused rings, whereas pyrimidines have one ring. Pairing one of each maintains a consistent distance between the two sugar–phosphate backbones and therefore a consistent width of the DNA double helix.

Why are purines and pyrimidines paired together rather than two of each?

Two purines would make the pair too wide, while two pyrimidines would make it too narrow.