DNA and RNA structure

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What chemical property of the 3' carbon on deoxyribose is essential for DNA strand elongation?

Its carboxyl group acts as a catalyst for nucleotide polymerization.
Its hydroxyl group allows for phosphodiester bond formation with the 5' phosphate group of the next nucleotide. (correct)
Its aldehyde group prevents unwanted binding of nucleotides.
Its methyl group provides stability to the growing DNA strand.

Which of the following best describes the arrangement of the two DNA strands in a double helix?

Anti-parallel, but only during DNA replication.
Anti-parallel, with one strand running 5' to 3' and the other running 3' to 5'. (correct)
Parallel, with both strands oriented in the same direction from 3' to 5'.
Parallel, with both strands oriented in the same direction from 5' to 3'.

In a lab experiment, a researcher identified a nucleic acid containing uracil. What can they conclude about this nucleic acid?

It is definitely DNA.
It could be either DNA or RNA.
It is definitely RNA. (correct)
It is neither DNA nor RNA, but a modified nucleotide.

How do the nitrogenous bases contribute to the structure of a DNA molecule?

They form hydrogen bonds that hold the two DNA strands together. (B) Signup and view all the answers

If a DNA strand contains the sequence 5'-GATTACA-3', what is the sequence of the complementary strand?

3'-CTAATGT-5' (A) Signup and view all the answers

Which of the following structural features distinguishes a DNA nucleotide from an RNA nucleotide?

The sugar component attached to the 2' carbon. (C) Signup and view all the answers

If a segment of DNA has 20% adenine, what percentage of guanine would be expected?

30% (D) Signup and view all the answers

What type of bond connects two nucleotides in a DNA or RNA polymer?

Phosphodiester bond (A) Signup and view all the answers

Which of the following is NOT a component of a nucleotide?

A double helix (C) Signup and view all the answers

Why is the packaging of DNA into chromosomes important for the cell?

It allows a large amount of DNA to fit within the nucleus. (D) Signup and view all the answers

Which of the following describes the orientation of the two strands in a DNA double helix?

Antiparallel, with one strand running 5' to 3' and the other 3' to 5'. (A) Signup and view all the answers

Which of the following is a pyrimidine?

Cytosine (C) Signup and view all the answers

What is the primary reason RNA is less stable than DNA?

RNA has a hydroxyl group on the 2' carbon of its sugar. (C) Signup and view all the answers

Which of the following is a key structural difference between DNA and RNA?

DNA contains deoxyribose sugar, while RNA contains ribose sugar. (A) Signup and view all the answers

During cell division, what structural change occurs to eukaryotic chromosomes to make them visible under a microscope?

Chromatin condenses into a thicker structure through repeated folding into loops. (A) Signup and view all the answers

Which of the following describes the relationship between genes, mRNA, and protein synthesis according to the central dogma?

Genes are transcribed into mRNA, which is then translated by ribosomes to produce specific proteins. (C) Signup and view all the answers

What is the significance of the antiparallel arrangement of DNA strands in the double helix?

It allows for stronger hydrogen bonding between complementary base pairs. (B) Signup and view all the answers

If a segment of DNA has the sequence 5'-GCTAG-3' on one strand, what would be the sequence of the complementary strand?

5'-CTAGC-3' (A) Signup and view all the answers

How does the packaging of DNA into chromatin affect gene expression?

Unpacked chromatin allows easier access for transcription factors and RNA polymerase, facilitating gene expression. (A) Signup and view all the answers

During what process is mRNA directly involved in protein synthesis?

Translation (D) Signup and view all the answers

Which of the following base pairs requires more energy to disrupt, and why?

G/C, because it has more hydrogen bonds. (C) Signup and view all the answers

Pyrimidines

Small, single-ring nitrogenous bases. Includes Cytosine (C), Uracil (U - RNA only), and Thymine (T - DNA only).

Purines

Large, double-ring nitrogenous bases. Includes Adenine (A) and Guanine (G).