AP Biology : AP Biology

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #25 : Dna, Rna, And Proteins

In the messenger RNA, with which base on DNA does uracil pair?

Possible Answers:

Guanine

Adenine

Thymine

Cytosine

Correct answer:

Adenine

Explanation:

Uracil in RNA bonds to adenine on the DNA template during transcription. These two nitrogenous bases form two hydrogen bonds.

Example Question #14 : Understanding Differences Between Dna And Rna

What would be the sequence of mRNA translated from the DNA segment 5' - ACGTCA - 3' ?

Possible Answers:

5' UGCAGU 3'

5' TACTTU 3'

5' TGCAGT 3'

5' UGACGU 3'

5' UCGAGU 3'

Correct answer:

5' UGACGU 3'

Explanation:

mRNA contains uracil instead of thymine, therefore your answer should not contain the base thymine. Remember, DNA is read in the 3' to 5' direction and the corresponding strand is created in the 5' to 3' direction. It is important to pay attention to polarity of the strands. Adenine pairs with thymine, and/or uracil. Guanine pairs with cytosine.

Example Question #22 : Dna, Rna, And Proteins

Which of the following RNA molecules transports amino acids to ribosomes to be used to assemble the protein molecule?

Possible Answers:

snRNA

rRNA

mRNA

tRNA

pre-mRNA

Correct answer:

tRNA

Explanation:

mRNA is messenger RNA, it carries the genetic code that determines the protein. snRNA directs splicing of pre-mRNA. tRNA transports the amino acids used for assembling proteins. rRNA is a component of ribosomes (the other component is protein). pre-mRNA- single strand of RNA processed to form mRNA.

Example Question #1 : Understanding The Sugar Phosphate Backbone

The most prevalent negative charge on DNA can be found on which of the following molecular components?

Possible Answers:

Hydroxyl residues

Hydrogen bonds between base pairs

Phosphate backbone

Phosphodiester linkage

Ribose sugar ring

Correct answer:

Phosphate backbone

Explanation:

The phosphate backbone of DNA is negatively charged due to the bonds created between the phosphorous atoms and the oxygen atoms. Each phosphate group contains one negatively charged oxygen atom, therefore the entire strand of DNA is negatively charged due to repeated phosphate groups. 

Example Question #22 : Dna, Rna, And Proteins

Please complete the analogy.

Nitrogen : Nucleic Acids :: Phosphorous : ______________.

Possible Answers:

Phospholipids

DNA

ATP

All answer choices

ADP

Correct answer:

All answer choices

Explanation:

Nitrogen is essential to create all the nucleic acids, and phosphorous is essential to create phospholipids (an obvious choice), ATP and ADP (they are the same class of molecule, and the P stands for phosphate), and DNA (for the phosphate-sugar backbone).

Example Question #23 : Dna, Rna, And Proteins

Which of the following is not true of a DNA molecule?

Possible Answers:

Adenine and thymine are held together by phosphodiester bonds

A purine or pyrimidine is bound to each sugar-phosphate group

Uracil is not a component of the molecule

Complementary strands are held together by hydrogen bonds

Correct answer:

Adenine and thymine are held together by phosphodiester bonds

Explanation:

DNA is a polymer composed of nucleotide monomers. Each nucleotide is formed from a deoxyribose sugar, a phosphate, and a nitrogenous base. There are two types of nitrogenous bases: purines and pyrimidines. The purines are adenine and guanine, while the pyrimidines are thymine and cytosine (and uracil). Adenine will always bind thymine and cytosine will always bind guanine. Uracil is only found in RNA, and is absent from DNA.

During DNA replication and synthesis, nucleotides align so that the nitrogenous bases are correctly paired. The bases bind to one other via hydrogen bonding to secure the nucleotide to the template strand. The protein DNA ligase then fuses the sugar-phosphate groups of adjacent nucleotides to create the DNA backbone. These bonds are known as phosphodiester bonds.

The only false statement concerns the identity of bonding between nitrogenous bases. Bases are held together by hydrogen bonds, and the DNA backbone is held together by phosphodiester bonds.

Example Question #1 : Understanding The Sugar Phosphate Backbone

A __________ bond between the sugar of one nucleotide and the phosphate of an adjacent nucleotide stabilizes the backbone of the DNA. 

Possible Answers:

weak

covalent

ionic

metallic

hydrogen

Correct answer:

covalent

Explanation:

The bond formed between the sugar of one nucleotide and the phosphate of an adjacent nucleotide is a covalent bond. A covalent bond is the sharing of electrons between atoms. A covalent bond is stronger than a hydrogen bond (hydrogen bonds hold pairs of nucleotides together on opposite strands in DNA). Thus, the covalent bond is crucial to the backbone of the DNA. 

Example Question #22 : Dna And Rna Structure

Which of the following nitrogenous bases is used to produce RNA, but not DNA?

Possible Answers:

Adenine

Uracil

Thymine

Guanine

Correct answer:

Uracil

Explanation:

Uracil is bound to adenine in the production of RNA, while thymine is used in its place in the production of DNA. Adenine, guanine, and cytosine are all used in the production of both RNA and DNA.

Example Question #21 : Dna And Rna Structure

How many total hydrogen bonds would there be between base pairs of a piece of DNA if the sequence of one side was CGTTTGAC?

Possible Answers:

Correct answer:

Explanation:

Cytosine and guanine form three hydrogen bonds between each other, while tyrosine and adenine form two hydrogen bonds. We simply need to count how many of each base we have and multiple cytosine and guanine by three, and thymine and adenine by two.

CGTTTGAC has 2 cytosine, 2 guanine, 3 thymine, and 1 adenine.

Example Question #1 : Understanding Nucleotides And Base Pairs

What element would you NOT find in either DNA, or RNA?

Possible Answers:

Carbon

Hydrogen

Nitrogen

Potassium

Phosphorus

Correct answer:

Potassium

Explanation:

DNA and RNA are made of nucleotides, which contain oxygen, hydrogen, nitrogen, carbon, and phosphorus. The nucleic acid backbone is comprised of sugars, made of carbon, hydrogen, and oxygen, and phosphate groups, made of phosphorus, hydrogen, and oxygen. The backbone binds to bases, which contain a nitrogen element.

Potassium is not found in nucleic acid structure, and is used in other parts of the body like muscles and nerves for signal propagation.

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