IB Bio HL - Nucleic

What are the monomers of nucleic acids?

Nucleotides

What sugar is found in DNA?

Deoxyribose

What sugar is found in RNA?

Ribose

Which nitrogenous base is unique to DNA?

Thymine is the nitrogenous base unique to DNA, replacing uracil found in RNA.

State the role of RNA polymerase in transcription.

RNA polymerase unzips the DNA and catalyzes it, adding RNA nucleotides to form a complementary strand of RNA. To make a mRNA transcript that will later translate into the proteinduring protein synthesis, thus playing a critical role in gene expression.

Explain why transcription occurs in the nucleus in eukaryotes.

Transcription occurs in the nucleus in eukaryotes because it allows the DNA, which is housed in the nucleus, to be transcribed into mRNA before the mRNA is transported to the cytoplasm for translation. This separation ensures that the delicate DNA remains protected while the RNA synthesis takes place.

Identify the direction in which RNA polymerase synthesizes mRNA.

RNA polymerase synthesizes mRNA in the 5' to 3' direction.

Outline how introns and exons are processed before translation.

Introns are removed from the pre-mRNA by spliceosomes, while exons are joined together to form a continuous coding sequence, creating a mature mRNA transcript ready for translation.

A DNA sequence is TAC GGA CTT. What is the mRNA produced?

The mRNA produced is AUG CCU GAA.

State the function of the ribosome during translation.

The ribosome facilitates the assembly of amino acids into a polypeptide chain by reading the mRNA sequence and providing the site for tRNA molecules to bring the corresponding amino acids.

Which nitrogenous bases are purines?

Adenine and Guanine

Which nitrogenous bases are pyrimidines?

Cytosine, Thymine, Uracil.

What type of bond holds complementary base pairs together in DNA?

Hydrogen bonds

Which base replaces thymine in RNA?

Uracil

Who discovered the double helix structure of DNA?

Watson and Crick, using Rosalind Franklin’s X-ray diffraction data.

What enzyme unwinds the DNA double helix?

Helicase, separates the two strands of DNA during replication, allowing them to be copied.

What is the role of DNA polymerase?

DNA polymerase synthesizes new DNA strands by adding nucleotides complementary to the template strand during DNA replication.

Which strand is synthesized continuously?

Leading Strand

Which strand is synthesized in fragments?

Lagging Strand is synthesized in Okazaki Fragments

What experiment demonstrated DNA replication is semi-conservative?

Meselson–Stahl experiment using heavy nitrogen (¹⁵N).

What enzyme joins Okazaki fragments?

DNA ligase.

What experiment showed DNA is the genetic material?

The Hershey–Chase experiment with bacteriophages.

What experiment demonstrated bacterial transformation?

Griffith’s experiment.

What is the central dogma of molecular biology?

Information flows from DNA → RNA → Protein.

Where does translation occur?

At ribosomes in the cytoplasm or rough ER.

What molecule carries amino acids to the ribosome?

tRNA.

What is the start codon in translation?

AUG (codes for methionine).

What are the stop codons?

UAA, UAG, UGA.

In which direction is mRNA read?

5′ to 3′ direction.

What type of bond forms between amino acids?

Peptide bonds.

What is the role of the ribosome?

Aligns mRNA and tRNA, catalyzes peptide bond formation.

What is the role of tRNA?

Carries a specific amino acid and pairs its anticodon with the mRNA codon

What is a missense mutation?

A mutation that changes one amino acid.

What is a nonsense mutation?

A mutation that changes a codon to a stop codon, ending translation early.

What is a silent mutation?

A mutation that does not change the amino acid sequence.

What is a frameshift mutation?

A mutation caused by insertion or deletion that shifts the reading frame.

What is the effect of changing UAU (tyrosine) to UAA?

A nonsense mutation, introducing a premature stop codon.

What is the role of helicase in DNA replication?

Helicase unwinds and separates the DNA double helix by breaking hydrogen bonds between complementary base pairs at the origin of replication, creating the replication fork.

What is the function of DNA ligase in replication?

DNA ligase joins Okazaki fragments by sealing the sugar-phosphate backbone with phosphodiester bonds, forming a continuous strand.

How does DNA gyrase assist DNA replication?

DNA gyrase relieves torsional strain caused by unwinding by helicase. It does this by relaxing positive supercoils through negative supercoiling.

What is the function of single-stranded binding (SSB) proteins?

SSB proteins bind to separated DNA strands to prevent them from re-annealing or being degraded by nucleases. They are later displaced when DNA polymerase synthesizes the new strand.

What role does DNA primase play in replication?

DNA primase synthesizes short RNA primers (~10–15 nucleotides) that provide a starting point for DNA polymerase III, which cannot initiate synthesis on its own.

In what direction does DNA polymerase III synthesize DNA?

DNA polymerase III synthesizes DNA in the 5’ → 3’ direction, extending from the 3’-end of the RNA primer.

Why is replication continuous on the leading strand but discontinuous on the lagging strand?

On the leading strand, DNA polymerase III moves toward the replication fork and synthesizes continuously. On the lagging strand, it moves away from the fork and synthesizes discontinuously in short segments called Okazaki fragments.

What are Okazaki fragments?

Okazaki fragments are short DNA segments synthesized on the lagging strand, later joined to form a continuous DNA molecule.What is the function of DNA polymerase I in replication?

What is the function of DNA polymerase I in replication?

DNA polymerase I removes RNA primers from the lagging strand and replaces them with DNA nucleotides.