A1.2 Nucleic Acid HL

What is the directionality of a DNA strand?

• 5' to 3'
• 3' to 5'
• 2' to 4'
• 1' to 3'

Answer explanation

DNA strands have directionality, running from 5' to 3' or from 3' to 5'. The direction is important for processes like replication and transcription.

Which bases pair together in DNA?

• Adenine and Thymine
• Cytosine and Guanine
• Adenine and Uracil
• Thymine and Guanine

Answer explanation

In DNA, adenine pairs with thymine, and cytosine pairs with guanine. Uracil pairs with adenine in RNA, and thymine does not pair with guanine.

Fill in the blank: The process of copying the base sequence of DNA into RNA is called _____.

Answer explanation

Transcription is the process of copying the base sequence of DNA into RNA. Translation is the process of synthesizing proteins from RNA.

What type of bond links nucleotides together in a single strand of DNA or RNA?

• Covalent bond
• Hydrogen bond
• Ionic bond
• Peptide bond

Answer explanation

Nucleotides are linked together by covalent bonds in the sugar-phosphate backbone of DNA and RNA. Hydrogen bonds form between complementary bases.

What is the role of complementary base pairing in DNA replication?

• Ensures accurate replication
• Provides energy for replication
• Protects DNA from damage
• Inhibits replication

Answer explanation

Complementary base pairing ensures accurate replication by guiding the pairing of bases. It does not provide energy, protect DNA, or inhibit replication.

Which scientist(s) are credited with developing the double helix model of DNA?

• Watson and Crick
• Franklin and Wilkins
• Hershey and Chase
• Meselson and Stahl

Answer explanation

Watson and Crick are credited with developing the double helix model of DNA. Franklin and Wilkins contributed to the discovery with their X-ray diffraction images.

What is the main advantage of chromosomes being 'supercoiled' during cell division?

• Efficient packaging of DNA
• Protection from mutations
• Increased stability of RNA
• Enhanced transcription rates

Answer explanation

Supercoiling allows efficient packaging of DNA into the confined space of the nucleus during cell division, ensuring proper segregation of chromosomes.

Which experiment provided evidence that DNA is the genetic material?

• Hershey-Chase experiment
• Meselson-Stahl experiment
• Griffith's experiment
• Watson-Crick model

Answer explanation

The Hershey-Chase experiment provided evidence that DNA is the genetic material. The Meselson-Stahl experiment provided evidence for the semi-conservative model of DNA replication.

How many hydrogen bonds are formed between adenine and thymine?

• Two
• Three
• Four
• One

Answer explanation

Two hydrogen bonds are formed between adenine and thymine. Three hydrogen bonds are formed between cytosine and guanine.

Fill in the blank: The genetic code is described as _____.

Answer explanation

The genetic code is described as universal because it is the same in almost all organisms.