Chatper 4 Nucleic Acids

If a DNA sample were composed of 10% thymine, what would be the percentage of guanine?

40

Starting at the 5' end, what is the base sequence of the RNA strand shown in Figure 4.3?

UAGC

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

their phosphate groups

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

What determines the primary structure of an RNA molecule?

the sequence of ribonucleotides

By convention, nucleotide sequences are always written from the _____.

5' end to the 3' end All nucleic acids have a 5' end with a free phosphate and a 3' end with a free hydroxyl. Because nucleic acid synthesis proceeds by adding nucleotides onto the 3' end, primary sequence is given from the 5' end to the 3' end.

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'

If one strand of a DNA molecule has the sequence of bases 5'ATTGCA3', the other complementary strand would have the sequence _____.

5'TGCAAT3'

What are the complementary base pairs that form in RNA?

A-U and G-C

Which statement concerning the DNA double helix is correct?

Complementary base pairing is the chemical interaction that underlies the replication of genetic information stored in DNA.

How are nucleotides linked together to form a polynucleotide chain?

In DNA and RNA, a phosphodiester linkage connects the 3' carbon of one nucleotide and the 5' carbon of another.

Complementary base pairing is possible only if two DNA strands align in antiparallel—instead of parallel—fashion. Which statement best explains why?

Only antiparallel strands create the geometry that allows complementary base pairs to form via hydrogen bonding. Given the bond angles and distances in nucleotides, a DNA double helix anchored by complementary base pairing is possible only with antiparallel polynucleotide strands.

Which statement accurately summarizes a difference between ribonucleotides and deoxyribonucleotides?

Ribonucleotides have a hydroxyl group bonded to their 2' carbon; deoxyribonucleotides have an H at the same location.

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 tell us there are ten rungs, or steps, on the DNA "ladder" for every turn of the helix.

In a DNA double helix, what kind of chemical bonds form between the complementary nitrogenous bases?

Three hydrogen bonds form between GC base pairs and two hydrogen bonds form between AT base pairs.

When nucleotides polymerize to form a nucleic acid _____.

a covalent bond forms between the sugar of one nucleotide and the phosphate of a second

What are the components of a nucleotide?

a sugar, a phosphate group and a nitrogenous base All nucleotides contain these three components. In ribonucleotides the sugar is ribose and in deoxyribonucleotides the sugar is deoxyribose.

What is the structural feature that allows DNA to replicate?

complementary pairing of the nitrogenous bases

Which of the following are pyrimidine nitrogenous bases?

cytosine and uracil

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

double antiparallel helical strands

One of the primary functions of RNA molecules is to _____.

function in the synthesis of proteins

Which of the following are purine nitrogenous bases?

guanine and adenine

In a nucleic acid polymer, the bonds that help to hold regions of double-strandedness together occur between what parts of the nucleotide monomers?

nitrogenous bases Three hydrogen bonds form between GC base pairs and two hydrogen bonds form between AT base pairs.

The condensation reaction that forms nucleic acid polymers occurs between a _____ group on one nucleotide and a _____ group on a second nucleotide.

phosphate, hydroxyl A phosphate group on the 5' carbon of the sugar forms a phosphodiester bond with a hydroxyl on the 3' carbon of a second sugar, forming a sugar-phosphate backbone.

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

the sugar and the base