Biology Chapter on Nucleic Acids

Questions and Answers

Nucleic acids are polymers made up of which of the following monomers? (Select all that apply)

Amino acids

Nitrogenous bases

Nucleotides (correct)

Ribose sugars

Phosphates

What is the difference between a ribonucleotide and a deoxyribonucleotide?

Ribonucleotides have a hydroxyl group on the 2 carbon of their sugar subunit.

What is/are the variable structure(s) of a nucleotide?

The sugar

The sugar and the base (correct)

The base

The phosphate group

Which of the following includes all of the pyrimidines found in RNA and DNA?

Cytosine, uracil, and thymine Signup and view all the answers

When nucleotides polymerize to form a nucleic acid, what occurs?

A covalent bond forms between the sugar of one nucleotide and the phosphate of a second Signup and view all the answers

If you wanted to radioactively label the nucleic acids separately from the protein, you would use radioactive?

Phosphorus Signup and view all the answers

What feature of single nucleotides provides the energy needed for polymerization when nucleic acids are formed?

Their phosphate groups Signup and view all the answers

Which of the following descriptions best fits the class of molecules known as nucleotides?

A nitrogenous base, a phosphate group, and a sugar Signup and view all the answers

Which of the following are pyrimidine nitrogenous bases?

Cytosine and uracil Signup and view all the answers

Which of the following are purine nitrogenous bases?

Guanine and adenine Signup and view all the answers

The difference between the sugar in DNA and the sugar in RNA is that the sugar in DNA?

Contains one less oxygen atom Signup and view all the answers

If cells are grown in a medium containing radioactive 32P-labeled phosphate, which of these molecules will be labeled?

Nucleic acids Signup and view all the answers

What is the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in RNA?

There is no difference. Signup and view all the answers

Nucleic acids have a definite polarity, or directionality. How are these ends described?

One end has an unlinked 3' carbon; the other end has an unlinked 5' carbon. Signup and view all the answers

If a double-stranded DNA sample were composed of 10 percent thymine, what would be the percentage of guanine?

40 Signup and view all the answers

DNA double helices are soluble in water but insoluble in alcohol. How do these physical properties reflect the chemical structure of the DNA molecule?

The charged phosphate groups and sugars of DNA are hydrophilic. Signup and view all the answers

You have a polymer of DNA with 10 adenine bases followed by 10 cytosine bases. If that strand bonded to a strand of 20 thymine bases, how would the double helix shape vary from a typical DNA double helix?

The width of the double helix would vary along the length of the strand. Signup and view all the answers

Which of the following best describes DNA's secondary structure?

Double antiparallel helical strands Signup and view all the answers

Which of the following did Watson and Crick already know when they were trying to determine the structure of DNA? The number of?

Purines is always the same as pyrimidines Signup and view all the answers

Franklin and Wilkins analyzed DNA by bombarding DNA crystals with X-rays. Their analysis yielded two numbers that sparked interest, 3.4 nm and 0.34 nm. What is the significance of these numbers?

These numbers demonstrate there are 10 rungs, or steps, on the DNA 'ladder' for every turn of the helix. Signup and view all the answers

A double-stranded DNA molecule contains a total of 120 purines and 120 pyrimidines. This DNA molecule could be composed of?

120 thymine and 120 adenine molecules Signup and view all the answers

What is the structural feature that allows DNA to replicate?

Complementary pairing of the nitrogenous bases Signup and view all the answers

Enzymes that break down DNA catalyze the hydrolysis of the covalent bonds that join nucleotides together. What would happen to DNA molecules treated with these enzymes?

The phosphodiester linkages of the polynucleotide backbone would be broken. Signup and view all the answers

Which of the following pairs of base sequences could form a short stretch of a normal double helix of DNA?

5'-ATGC-3' with 5'-GCAT-3' Signup and view all the answers

Compare proteins to nucleic acids. Which of the following is TRUE?

Both have primary and secondary structure. Signup and view all the answers

Which of the following statements best summarizes the differences between DNA and RNA?

DNA nucleotides contain a different sugar than RNA nucleotides. Signup and view all the answers

Why is it that RNA can catalyze reactions but DNA cannot?

The sugar of RNA is much more reactive than the sugar of DNA. Signup and view all the answers

Both DNA and RNA?

Are information-containing molecules Signup and view all the answers

RNA and proteins combine in cells to form structures called ribosomes. Based on their chemical structures, do you think protein or RNA molecules actually form the active site within the ribosome?

It could be either, because both molecules have catalytic properties. Signup and view all the answers

Which of the following statements about the 5' end of a polynucleotide strand of RNA is correct?

The 5' end has a phosphate group attached to the number 5 carbon of ribose. Signup and view all the answers

One of the primary functions of RNA molecules is to?

Function in the synthesis of proteins Signup and view all the answers

If 14C-labeled uracil is added to the growth medium of cells, what macromolecules will be labeled?

RNA Signup and view all the answers

In the context of chemical evolution, DNA's structure is interesting because it suggests a possible copying mechanism. What about DNA's structure facilitates copying?

The strands of the double helix are complementary. Signup and view all the answers

DNA is the main hereditary material of all life. However, DNA lacks one important characteristic for the first forms of life. Why have researchers rejected the idea that DNA was found in the first life-form?

It does not function as a catalyst. Signup and view all the answers

Why do researchers think the first self-replicating molecule was RNA?

RNA can carry information and catalyze chemical reactions. Signup and view all the answers

Recall the Bartel lab group experiment to create a ribozyme from scratch. If they had created exact copies of each ribozyme (rather than creating copies with a few differences), the ribozymes would have?

Stayed the same with each round of selection Signup and view all the answers

Bartel's research group showed that an RNA replicase ribozyme could be created by?

Starting with random components and allowing selection to result in molecules that were better and better at replicating Signup and view all the answers

The work of Bartel's group on the ribozyme RNA replicase supports which conclusion?

An RNA world could produce molecules that could self-replicate. Signup and view all the answers

Study Notes

Nucleic Acids and Nucleotide Structure

Nucleic acids are polymers composed of nucleotides, consisting of a nitrogenous base, sugar, and phosphate group.
Ribonucleotides differ from deoxyribonucleotides by the presence of a hydroxyl group on the 2' carbon of their sugar subunit.
The variable structures of nucleotides are found in the sugar and base components.
Pyrimidines in RNA and DNA include cytosine, uracil, and thymine.
Nucleotides polymerize via covalent bonds between the sugar of one nucleotide and the phosphate of another.

Molecular Labels and Energy Sources

Radioactive phosphorus is used to label nucleic acids due to the presence of phosphate groups.
The energy required for nucleotide polymerization comes from phosphate groups.

DNA and RNA Characteristics

DNA is structured as double antiparallel helical strands with a defined 5' and 3' polarity.
The sugar in RNA contains one more oxygen atom than the sugar in DNA.
The complementary pairing of nitrogenous bases enables DNA replication.
The structural feature that allows DNA to replicate is its complementary base pairing.

Structural Features and Base Pairing

The nucleotide composition of DNA maintains equal numbers of purines (adenine and guanine) and pyrimidines (cytosine and thymine).
In DNA, a double-stranded arrangement results in consistent base pairing, leading to a helical structure.
For a given DNA sample with known thymine content, guanine levels can be deduced based on base pairing rules (A=T and G≡C).

Experimental Findings and Molecular Functions

Ribosomes, composed of RNA and proteins, serve as sites for protein synthesis, with both molecules potentially facilitating catalytic activity.
RNA molecules can serve multiple functions, including the synthesis of proteins and self-replication capabilities in the context of early life forms.

Evolutionary Perspectives

The hypothesis that RNA was the first self-replicating molecule stems from its ability to carry genetic information and catalyze reactions.
Bartel's experiments suggest an RNA world capable of producing self-replicating molecules through random selection and optimization of ribozymes.

Key Distinctions

Enzymatic breakdown of DNA involves hydrolysis of phosphodiester linkages, leading to the separation of strands.
Unlike DNA, which does not catalyze reactions, RNA can function enzymatically due to its more reactive sugar and diverse roles in cellular processes.

Conclusion

DNA encodes genetic information; however, it lacks the catalytic function seen in RNA, suggesting early life forms may have relied on RNA for self-replication and functioning.

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Description

Test your knowledge on nucleic acids and their building blocks with this quiz. Focus on the differences between ribonucleotides and deoxyribonucleotides, and reinforce your understanding of nucleotides. Ideal for biology students!