AP Biology : Understanding Protein Folding and Structure

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #131 : Dna, Rna, And Proteins

Which of the following choices best identifies the method(s) used by scientists to study protein folding?

Possible Answers:

Mutation studies

X-ray cyrstallography

All of these

Spectroscopy

Correct answer:

All of these

Explanation:

There are a number of ways that scientists study protein folding and structure. They include the following processes: mutation studies, x-ray crystallography, and spectroscopy. Mutation studies compare the folding patterns of wild type proteins and those with targeted point mutations. X-ray crystallography is a form of high-resolution microscopy that uses x-rays to study the atomic structure of protein crystals through diffraction patterns. Last, a number of spectroscopy methods are employed to study protein folding by comparing unfolded, folded, and partially folded proteins.

Example Question #132 : Dna, Rna, And Proteins

In a cell membrane-bound protein, the majority of hydrophobic amino acids residues are found where?

Possible Answers:

In the portion of the protein that sticks out of the membrane

In the portion of the protein that is buried in the membrane

In the cytosol

On the outside of the protein

On the portion of the protein that faces inside the cell

Correct answer:

In the portion of the protein that is buried in the membrane

Explanation:

Since the interior of cell membranes are made up of the hydrophobic tails of the phospholipids, proteins that are bound in membranes need region that contains high amounts of hydrophobic amino acids residues that can contact the hydrophobic tails molecules and keep it stable. Therefore, in a membrane-bound protein, one would expect the majority hydrophobic amino acid residues to be in the portion of the protein that is buried within the cell membrane.

Example Question #133 : Dna, Rna, And Proteins

The formation of alpha helices and beta-pleated sheets occurs at which level of protein structure?

Possible Answers:

All of these

Primary

Secondary

Quaternary

Tertiary

Correct answer:

Secondary

Explanation:

The formation of beta pleated sheets and alpha helices occur in the secondary structure of a protein immediate after the sequence of the polypeptide has been formed. These two structures, alpha helices and beta-pleated sheets, are formed by the hydrogen bonds that occur among the amino acids of the polypeptide.

Example Question #134 : Dna, Rna, And Proteins

Which of the following explains why the folding of proteins is important in their functions in reactions?

Possible Answers:

The folding of proteins determines the primary protein structure

The folding of proteins determines its shape, which influences how it binds to substrates and catalyzes reactions

The folding of proteins determines how long it will last in the cell

The folding of proteins is only determined by the sequence of amino acids

Correct answer:

The folding of proteins determines its shape, which influences how it binds to substrates and catalyzes reactions

Explanation:

The folding of proteins is the second and third level of organization in a protein and determines the protein's shape and how it bonds to substrates. The sequence of amino acids does not determine the shape as much as the folding in the second and third levels. The folding does not determine how long the protein will last in a cell. It does, however, influence the shape of the enzyme, which dictates the types of interactions between the enzyme and substrate, which ultimately determines the rate of the reaction that it catalyzes.

Example Question #135 : Dna, Rna, And Proteins

When cooking an egg, opening the egg over a hot pan causes the non-yolk part of the egg to go from clear and viscous to white and solid. Adding heat to the egg white protein part of the egg is part of a process called what?

Possible Answers:

Thermodynamics

Denaturation

Naturalization

Hybridization

Thermosolidification

Correct answer:

Denaturation

Explanation:

Denaturation is the correct answer here. The denaturation of a protein occurs when a catalyst causes the disruption and/or destruction of the bonds in a protein structure. Heat is one of the ways to denature a protein because the heat causes the molecules to vibrate quickly and coagulate into the white substance we eat.

Example Question #136 : Dna, Rna, And Proteins

Which of the following is a characteristic of secondary structure of proteins?

Possible Answers:

Beta pleated sheets

Two or more polypeptide chains joined by non covalent bonds

3D folding protein

Gamma helix

Linear sequence of amino acids

Correct answer:

Beta pleated sheets

Explanation:

Secondary structure is made up of alpha helix and beta pleated sheets. Linear sequence of amino acids is found in primary structure, 3D folding is found in tertiary structure, and two peptide chains joined by non covalent bonds are found in quaternary.

Example Question #141 : Dna, Rna, And Proteins

A point mutation in DNA can produce a premature stop codon in mRNA. This in turn can result in a protein that is truncated, incomplete, and nonfunctional. This is referred to as a __________ mutation.

Possible Answers:

nonsense

frameshift

silent

missense

negative

Correct answer:

nonsense

Explanation:

When a point mutation results in an inadvertent stop codon, it results in a truncated, and often, nonfunctional protein. This is referred to as a nonsense mutation. A point mutation is caused by a switch of a single base pair in the DNA, which may or may not result in the substitution of an amino acid for another since the genetic code is redundant. 

Example Question #142 : Dna, Rna, And Proteins

Which of the following proteins is responsible for packaging the DNA into these compact structures?

Possible Answers:

Microtubules

Myosin

Integrins

Actin 

Histones

Correct answer:

Histones

Explanation:

Histone proteins are highly basic proteins found in the eukaryotic cell nuclei that are integral proteins needed to package DNA tightly inside. They are the chief protein components of chromatin, acting as spools around which the DNA winds and plays an important role in gene regulation. Without histones, the unwound DNA in chromosomes would be very long and difficult to control. 

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