High School Biology : Understanding Differences with DNA

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #1 : Understanding Differences With Dna

How are RNA and DNA similar?

Possible Answers:

They both have a deoxygenated 2' carbon

They are both double stranded

They both have nucleotides linked by phosphodiester bonds

They both use the exact same bases

Correct answer:

They both have nucleotides linked by phosphodiester bonds

Explanation:

Although RNA and DNA have some key differences that result in different functions, they also have some key similarities. Both are composed of nucleotide monomers linked together by phosphodiester bonds. They are also both read in the 5'-3' direction. It is important to know that the backbone of both DNA and RNA is made by phosphodiester bonds, but it is hydrogen bonds that bind two strands to DNA together to form the double-helix.

DNA and RNA both use adenine, cytosine, and guanine, but only DNA uses thymine and only RNA uses uracil. Only DNA is double-stranded; RNA is single-stranded. Deoxyribose, in DNA, is deoxygenated at the 2' carbon, but ribose in RNA is oxygenated.

Example Question #101 : Dna, Rna, And Proteins

Which of the following bases is replaced by uracil during transcription?

Possible Answers:

Guanine

Thymine

None of these

Adenine

Cytosine

Correct answer:

Thymine

Explanation:

DNA uses four nitrogenous bases: adenine, thymine, cytosine, and guanine. Adenine residues bond to thymine residues, and cytosine binds to guanine.

During transcription, DNA is used as a template to generate mRNA. During this process, bases are matched to the DNA template and used to build a single strand of RNA. In RNA, there are also four nitrogenous bases: adenine, cytosine, guanine, and uracil. Thymine is not found in RNA.

Example Question #2 : Understanding Differences With Dna

Which nucleotide is present in RNA sequences, but not DNA sequences?

Possible Answers:

Guanine

Thymine

Adenine

Uracil

Correct answer:

Uracil

Explanation:

DNA sequences contain the following nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G). Guanine and cytosine bases pair together, while adenine and thymine bases pair together. In RNA, thymine is replaced by uracil (U).

Example Question #3 : Understanding Differences With Dna

The following RNA sequence is reverse transcribed to generate cDNA (complementary DNA). What is the corresponding DNA sequence?

3'-AUCGGAUGCACA-5'

Possible Answers:

5'-ATCGGATGCACA-3'

5'-AUCGGAUGCACA-3'

5'-TAGCCTACGTGT-3'

5'-UAGCCUACGUGU-3'

Correct answer:

5'-TAGCCTACGTGT-3'

Explanation:

cDNA (and all DNA) sequences contain thymine (T) rather than uracil (U), which will form base pairs with adenine. Additionally, complementary DNA contains the "complement" of each RNA nucleotide. The resultant DNA will be oriented anti-parallel to the template RNA, and use complementary pairs of adenine-to-thymine and cytosine-to-guanine.

RNA: 3'-AUCGGAUGCACA-5'

DNA: 5'-TAGCCTACGTGT-3'

Example Question #4 : Understanding Differences With Dna

Where is mature mRNA found in the cell?

Possible Answers:

In vesicles that are exocytosed by the cell

In the nucleus

In the mitochondria

In the cytoplasm or in the endoplasmic reticulum

In the nucleolus 

Correct answer:

In the cytoplasm or in the endoplasmic reticulum

Explanation:

RNA goes through modifications known as "post-transcriptional modification" before it becomes a mature mRNA molecule. By the time that it is mature, it is allowed to leave the nucleus to interact with the ribosomes for translation. Ribosomes are free-floating in the cytoplasm of a cell and also on the rough endoplasmic reticulum. These are the targets of the mature mRNA.

The nucleus contains heteronuclear RNA (htRNA) before it becomes mature mRNA. The nucleolus accepts rRNA and helps form ribosomes subunits.

Example Question #5 : Understanding Differences With Dna

There are several different types of RNA with different general structures and functions. What is common to all RNA molecules?

Possible Answers:

Thymine

A hairpin loop

Nitrogenous bases

A globular structure

Correct answer:

Nitrogenous bases

Explanation:

Each type of RNA is designed to complete a different function in the cell. Messenger RNA (mRNA) has a linear structure and provides the codon template for translation. Transfer RNA (tRNA) has a hairpin loop structure and carries amino acid residues to ribosomes for elongation of the polypeptide created from translation. Ribosomal RNA (rRNA) has a globular structure and forms an integral component of the ribosome subunits.

Despite their differences, all RNA molecules have the same backbone structure, which contains ribose sugars and phosphate groups, and the same nitrogenous bases: adenine, cytosine, guanine, and uracil.

Example Question #6 : Understanding Differences With Dna

How does RNA differ from DNA in eukaryotes?

I. RNA contains ribose 
II. RNA is found only in the cytoplasm
III. RNA uses bases A, C, U, G
IV. RNA is predominantly single-stranded 

Possible Answers:

I and III

I and III

I, III, and IV

I, II, III, and IV

I and IV

Correct answer:

I, III, and IV

Explanation:

RNA differs from DNA in that it contains a ribose instead of deoxyribose, uses uracil instead of thymine, and is not only found in the nucleus like DNA. In eukaryotes, RNA is transcribed in the nucleus, then it is exported into the cytoplasm where it binds to ribosomes during translation. RNA is indeed predominantly single-stranded.

Example Question #7 : Understanding Differences With Dna

Which of the following statements are true?

Possible Answers:

DNA contains phosphates, while RNA does not.

RNA contains uracil, while DNA contains thymine.

RNA and DNA have no structural differences whatsoever.

RNA is double stranded, while DNA is single stranded.

The 5-C sugar is exactly the same in both RNA and DNA.

Correct answer:

RNA contains uracil, while DNA contains thymine.

Explanation:

RNA is different than DNA in that it 1) is single stranded (DNA is double stranded), 2) contains uracil (DNA contains thymine instead), and 3) contains a ribose sugar (DNA contains a deoxyribose sugar). And since both DNA and RNA are made up of nucleotides, they will both contain phosphates.

Example Question #8 : Understanding Differences With Dna

Which of the following characteristics best describe RNA?  

I. It contains base pairs C, G, U, and A

II. It is double stranded

III. It stores hereditary information

IV. It is responsible for transcription of proteins

V. It is synthesized from DNA

Possible Answers:

II, IV, and V

V only

I, II, and III

III and IV

I, IV, and V

Correct answer:

I, IV, and V

Explanation:

RNA is composed of the sugar ribose and contains the nitrogenous bases C, G, U, and A.  RNA is single stranded and is essential for gene expression, transcription and translation of proteins.  RNA is synthesized by DNA; only DNA contains hereditary information.

Example Question #28 : Rna

Which DNA base is replaced by uracil in RNA? 

Possible Answers:

Cytosine 

Adenine 

Guanine 

Thymine 

Correct answer:

Thymine 

Explanation:

DNA is made up of Adenine, Thymine, Guanine, and Cytosine. RNA has these same bases, except in RNA, there is no Thymine. Instead, Uracil is found.  

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