Understanding Differences with DNA

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Questions 1 - 10
1

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

Thymine

Adenine

Guanine

Cytosine

None of these

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.

2

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

Nitrogenous bases

Thymine

A globular structure

A hairpin loop

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.

3

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

I and III

I, III, and IV

I, II, III, and IV

I and IV

I and III

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.

4

Which DNA base is replaced by uracil in RNA?

Thymine

Adenine

Guanine

Cytosine

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.

5

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

I, IV, and V

I, II, and III

II, IV, and V

III and IV

V only

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.

6

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

Uracil

Thymine

Adenine

Guanine

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).

7

Which of the following statements are true?

RNA contains uracil, while DNA contains thymine.

RNA is double stranded, while DNA is single stranded.

RNA and DNA have no structural differences whatsoever.

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

DNA contains phosphates, while RNA does not.

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.

8

DNA contains the following nitrogenous bases: adenine, guanine, thymine, and cytosine. RNA contains which of the following sets of nitrogenous bases?

Adenine, guanine, cytosine, and uracil

Adenosine, guanine, cystine, and uracil

Adenine, guanine, cystine, and thymine

Adenine, guanine, cytosine, and uracil

Explanation

Thymine is exclusively present in DNA. Uracil replaces thymine in RNA; thus, RNA contains the following four nitrogenous bases: adenine, guanine, cytosine, and uracil.

9

Where is mature mRNA found in the cell?

In the cytoplasm or in the endoplasmic reticulum

In the nucleus

In the nucleolus

In the mitochondria

In vesicles that are exocytosed by the cell

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.

10

How are RNA and DNA similar?

They both have nucleotides linked by phosphodiester bonds

They both use the exact same bases

They are both double stranded

They both have a deoxygenated 2' carbon

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.

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