DNA and RNA: Nucleotides and the Double Helix (Lecture Notes)

A set of 30 question-and-answer flashcards covering DNA, RNA, nucleotides, base pairing, the double helix, and related concepts from the lecture notes.

What does DNA stand for and what is its role as genetic material?

Deoxyribonucleic acid; stores hereditary information and can be copied and passed to daughter cells and offspring.

What is RNA and do some viruses use RNA as their genetic material?

Ribonucleic acid; some viruses (e.g., coronaviruses and HIV) use RNA as their genetic material.

Where were nucleic acids first discovered?

In the cell nucleus.

What subunits make up nucleic acids?

Nucleotides.

What are the three components of a nucleotide?

A sugar (pentose), a phosphate group, and a nitrogenous base.

What sugar is found in DNA?

Deoxyribose.

What sugar is found in RNA?

Ribose.

Name the four bases in DNA.

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

Name the four bases in RNA.

Adenine (A), Cytosine (C), Guanine (G), Uracil (U).

How are nucleotides linked to form a nucleic acid chain?

By covalent phosphodiester bonds between the phosphate of one nucleotide and the sugar of the next, creating a sugar–phosphate backbone.

What direction do nucleic acids polymerize in?

From the 5' end to the 3' end (5' to 3' direction).

What forms the backbone of DNA and RNA?

The sugar–phosphate backbone formed by linking sugar and phosphate groups.

How many strands are in DNA and in RNA?

DNA is typically double-stranded; RNA is single-stranded.

Which bases are complementary in DNA base pairing?

Adenine pairs with Thymine; Guanine pairs with Cytosine.

Which base is present in DNA but not in RNA?

Thymine is present in DNA; RNA uses Uracil instead.

What is the overall shape of DNA?

A double helix with antiparallel strands and a diameter of about 2 nanometres.

What does antiparallel mean in the context of DNA?

The two strands run in opposite directions (one 5' to 3' and the other 3' to 5').

Why are the two DNA strands twisted into a helix and antiparallel?

To enable hydrogen bonding between complementary bases while maintaining a stable, uniform diameter.

What is stored in the sequence of bases of DNA?

Genetic information encoded in a coded form—the universal genetic code.

How is RNA formed as a polymer?

As a polymer formed by condensation of nucleotide monomers; it is a single, unbranched chain.

What happens during a condensation reaction that links nucleotides?

Water is eliminated; a hydroxyl from one phosphate and a hydrogen from another sugar form a covalent bond, linking nucleotides.

What is the sugar–phosphate backbone’s role in nucleic acids?

It provides the structural support and maintains the sequence of bases.

Do all viruses disprove the DNA-for-all-living-organisms claim?

Some viruses use RNA as their genetic material, but viruses are not considered living organisms, so it does not falsify the claim that DNA is the genetic material of living organisms.

Do viruses reproduce independently?

No; they rely on a host cell for reproduction and are not considered living organisms.

How many types of bases exist in DNA and RNA, and how many nucleotides does this imply?

There are four types of bases; there are four types of nucleotides in DNA and RNA (A, C, G, plus T or U).

What are nitrogenous bases?

Bases that contain nitrogen and are the informational components of DNA and RNA.

What does the term 'universal genetic code' refer to?

The concept that the base sequence encodes information used by all organisms.

What is the key difference in sugar between DNA and RNA?

DNA contains deoxyribose (lacks an oxygen at the 2' carbon) while RNA contains ribose.

What does the full name 'deoxyribonucleic acid' indicate about its sugar?

'Deoxy' refers to the absence of an oxygen atom in the sugar (deoxyribose) compared to ribose.

How are hydrogen bonds involved in DNA structure?

Hydrogen bonds form between complementary bases (A–T and G–C) to hold the two strands together.

What is meant by the term 'complementary base pairing' in DNA?

A pairs with T and G pairs with C, aligning the two strands for proper replication and function.

Where are nucleotides added during nucleotide synthesis in RNA and DNA?

To the growing chain via the sugar–phosphate backbone through phosphodiester bonds in the 5' to 3' direction.

Why is RNA considered a single-stranded molecule unlike DNA?

RNA is typically single-stranded, while DNA is normally double-stranded, forming a double helix.

What is the role of uracil in RNA?

Uracil (U) replaces thymine (T) in RNA and pairs with adenine.

What is the significance of the 2 nm diameter in DNA?

It is the characteristic width of the DNA double helix due to the arrangement of the two antiparallel strands and base pairs.

What is meant by the ‘pentose sugar’ in nucleotides, and what are its two key forms?

The five-carbon sugar in nucleotides; ribose in RNA and deoxyribose in DNA.

How do nucleotides relate to genes?

Nucleotides form the sequence that encodes genetic information; genes are segments of DNA defined by this sequence.