DP IB Biology HL – Nucleic Acids Review

Forty question-and-answer flashcards covering nucleotide structure, DNA/RNA differences, base pairing, nucleosomes, experimental evidence, directionality, and key concepts required for DP IB Biology HL nucleic acids.

What three components make up a nucleotide?

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

Which pentose sugar is present in DNA molecules?

Deoxyribose.

Which nitrogenous base found in RNA replaces thymine?

Uracil.

What strong covalent bond joins one nucleotide to the next in a strand of DNA or RNA?

A phosphodiester bond.

What word describes the fact that the two DNA strands run in opposite directions?

Antiparallel.

How many hydrogen bonds form between adenine and thymine?

Two.

How many hydrogen bonds form between guanine and cytosine?

Three.

Which two nitrogenous bases are purines?

Adenine and guanine.

Name the pyrimidine bases found in DNA.

Cytosine and thymine.

What name is given to the repeating chain of sugars and phosphates in nucleic acids?

The sugar-phosphate backbone.

What is a codon?

A sequence of three mRNA bases that specifies one amino acid.

Approximately how many base pairs of DNA wrap around one histone octamer in a nucleosome?

About 147 base pairs (two loops).

Which classic 1952 experiment confirmed DNA is the hereditary material?

The Hershey & Chase bacteriophage experiment.

In the Hershey & Chase experiment, which radioisotope was used to label DNA?

Radioactive phosphorus-32 (³²P).

When DNA was radio-labelled in the Hershey & Chase experiment, where was radioactivity detected after centrifugation?

In the pellet containing the infected bacteria.

According to Chargaff’s data, what is always true about the amounts of adenine and thymine in DNA?

They are equal in quantity (A = T).

According to Chargaff’s rule, what is always true about the amounts of guanine and cytosine in DNA?

They are equal in quantity (G = C).

What does it mean when we say the genetic code is universal?

Nearly all organisms use the same mRNA codons to specify the same amino acids.

In which direction does DNA polymerase synthesize a new strand?

5′ to 3′ direction.

During replication, which DNA strand is synthesized continuously?

The leading strand.

Which enzyme unwinds the DNA double helix ahead of the replication fork?

Helicase.

What is the primary role of messenger RNA (mRNA)?

To carry the genetic code from DNA to the ribosome.

What is the main function of transfer RNA (tRNA)?

To deliver specific amino acids to the ribosome during translation.

Which ribosomal component catalyzes peptide-bond formation during translation?

The rRNA peptidyl transferase centre (making the ribosome a ribozyme).

What chemical group characterizes the 5′ end of a nucleic acid strand?

A free phosphate group attached to carbon-5 of the sugar.

Which carbon in ribose bears an –OH group that is missing in deoxyribose?

Carbon-2′.

What is chromatin?

The complex of DNA and associated proteins (mainly histones) found in eukaryotic nuclei.

In which type of cells is DNA "naked" and not wrapped around histones?

Prokaryotic cells.

Why must a purine always pair with a pyrimidine in DNA?

To keep the width of the double helix constant.

Define a nucleosome.

DNA wrapped twice around an octamer of eight histone proteins, plus linker DNA.

What is meant by DNA having an "almost limitless capacity" for information storage?

Four bases can be arranged in countless sequences along very long molecules, encoding vast amounts of data.

Approximately how many protein-coding genes are found in the human genome?

Around 20,000–21,000 genes.

What is the simplest definition of a gene?

A sequence of DNA that encodes the information to produce a specific polypeptide or RNA molecule.

What is complementary base pairing?

Specific hydrogen bonding of A with T (or U) and G with C between nucleic acid strands.

What name is given to the short DNA fragments synthesized on the lagging strand?

Okazaki fragments.

Which nitrogenous base is unique to RNA and absent from DNA?

Uracil.

State one structural difference between ribose and deoxyribose.

Ribose has an –OH on carbon-2′, whereas deoxyribose has only –H at that position.

What is meant by the primary sequence of a protein?

The specific linear order of amino acids in the polypeptide chain.

What is alternative splicing?

The process by which different combinations of exons are joined to produce multiple mRNA variants from one gene.

Which philosophical problem did Karl Popper address with the concept of falsification in science?

The problem of induction—the idea that no number of confirming observations can prove a hypothesis absolutely true.