High School Biology : Understanding Protein Folding

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #1 : Understanding Protein Folding

Ribosomes are involved in what level of protein folding?

Possible Answers:

Secondary structure

None of these

Quaternary structure

Tertiary structure

Primary structure

Correct answer:

Primary structure

Explanation:

Ribosomes are responsible for translating mRNA into protein. tRNA molecules transport amino acids to the ribosome, where they are joined by peptide bonds to form a chain. This chain of amino acids is known as the protein primary structure.

Secondary structure, tertiary structure, and quaternary structure form in the cytoplasm or endoplasmic reticulum after the ribosome has released the polypeptide.

Example Question #2 : Protein Structure

In which level of protein structure will you find alpha-helices and beta-sheets?

Possible Answers:

Primary

Tertiary

Quaternary

Alpha-helices and beta-sheets are only found in the DNA double-helix

Secondary

Correct answer:

Secondary

Explanation:

Proteins have four levels of structure. Secondary structure involves the formation of alpha-helices and beta-sheets via hydrogen bonding between the amino acid backbone in the protein chain.

Primary protein structure simply refers to the linear sequence of amino acid residues in the polypeptide chain. After initial folding of the backbone in secondary structure, functional groups of the amino acids interact to generate tertiary structure. Tertiary structure contains hydrogen bonding, hydrophobic interactions, and disulfide bridges. Some proteins then develop quaternary structure, when multiple polypeptide chains are joined as subunits to build a large protein complex.

Example Question #2 : Understanding Protein Folding

Which of the following correctly describes the tertiary stucture of a protein?

Possible Answers:

Hydrogen bonding between the polypeptide backbone

Formation of alpha-helices and beta-pleated sheets 

Hydrogen bonding and hydrophobic interaction between amino acid side chains

Interaction between multiple polypeptide subunits to form a functional protein structure

Polypeptide sequence formed by individual amino acids

Correct answer:

Hydrogen bonding and hydrophobic interaction between amino acid side chains

Explanation:

Formation of a protein involves four distinct levels of structure. The tertiary structure is the third level of protein formation, and occurs when the side chains of the individual amino acids interact. These side chains can attract one another to form hydrogen bonds or disulfide bonds, or they can repel each other and contribute ot hydrophobic interactions. The result is a three-dimensional shape. This is the final level of structure to create a function protein subunit.

The primary structure of the protein is derived from the chain of amino acids synthesized during translation; this amino acid sequence is the primary structure. Secondary structure is generated from the interactions between amino and carboxyl groups in the polypeptide backbone. These groups can form hydrogen bonds to generate alpha-helices and beat-pleated sheets. Tertiary structure, as described above, results in a functional protein subunit. For some protiens, tertiary structure is the final step in folding. For other proetins, multiple subunits can be bound together to generate a quaternary structure.

Example Question #4 : Protein Structure

Hemoglobin is a oxygen-carrying protein present in red blood cells. Its structure is that of four subunits—two alpha units and two beta units. What level of structure is implicated in this description?

Possible Answers:

Quaternary structure

Secondary structure

Tertiary structure

Quintary structure

Primary structure

Correct answer:

Quaternary structure

Explanation:

There are four essential levels of protein structure. The fourth and final level is called quaternary structure. This level of structure is only present in proteins with multiple subunits. Since hemoglobin has four subunits, we know that the question is talking about the quaternary structure of the protein.

Primary structure is simply the amino acid sequence generated during translation. Soon after translation, the carboxyl and amino groups present in the polypeptide backbone begin to form hydrogen bonds. The result is the protein's secondary structure, frequently made of alpha-helices and beta-pleated sheets. Tertiary structure is the three-dimensional shape of the final polypeptide, and is derived from hydrophobic interactions, hydrogen bonds, and disulfide bonds related to the amino acid side chains (R groups). When multiple polypeptides (subunits) join together, they generate a quaternary structure.

Example Question #3 : Protein Structure

What must be true for a protein to have quaternary structure?

Possible Answers:

The protein must contain at least two polypeptide chains

The protein must contain at least four polypeptide chains

The protein must be found in the cytoplasm

The protein must only have one polypeptide chain

The protein must be an enzyme

Correct answer:

The protein must contain at least two polypeptide chains

Explanation:

Protein quaternary structure involves interactions between different subunits. Each subunit will be created by folding an independent polypeptide chain into a 3-dimensional tertiary structure. The joining of these independent subunits results in quaternary structure. In order for a protein to have quaterary structure, it must have multiple subunits; this means it must consists of at least two polypeptide chains.

Example Question #3 : Understanding Protein Folding

You closely analyze the disulfide bridges in a protein molecule.  In which phase of protein synthesis/structure would you first find these disulfide bridges? 

Possible Answers:

Tertiary structure

Quaternary structure

Secondary structure

RNA transcription

Primary structure

Correct answer:

Tertiary structure

Explanation:

The primary structure of a protein is the sequence of amino acids, which determines the unique shape of the protein.  The secondary structure consists of the coiled and folded patterns that contribute to the protein’s overall shape (alpha helix or beta pleated sheet respectively).  The tertiary structure is the overall shape of the polypeptide that results from interactions and hydrogen bonding between the side chains, or R groups, of the various amino acids present. It is during this stage of protein formation that disulfide bridges and hydrophobic interactions are first seen.  Last,the quaternary structure is the overall protein structure resulting from the aggregation of at least two polypeptide units. 

Example Question #4 : Understanding Protein Folding

Bob, a biologist who was researching a new eukaryotic unicellular species, wanted to study a particular protein Y. After obtaining and purifying the sample, Bob discovered that this protein had 3 subunits: A, B, and C. Through substantive scientific analysis, Bob discovered that protein Y operated in a membrane; however, he could not deduce which particular membrane. Nonetheless, Bob found that only subunit B was traversed through the interior of the membrane. With Bob’s findings, please answer the following questions.

What is the highest order of protein structure exhibited by Bob’s protein?

Possible Answers:

Secondary

Quaternary

Primary

Tertiary

Pentane

Correct answer:

Quaternary

Explanation:

The protein does possess primary, secondary, and tertiary structure but since the protein has three distinct subunits, the entire molecule is exhibiting a higher order quaternary structure. 

Example Question #7 : Protein Structure

Val-Gly-Ser-Leu is an example of which level of protein structure? 

Possible Answers:

Tertiary structure

Primary structure

Auxiliary

Secondary structure 

Quatenary structure

Correct answer:

Primary structure

Explanation:

Primary structure refers to a linear sequence of amino acids in the polypeptide chain, such as the example in the question stem. Secondary structure has two main types, the alpha helix and the beta strand (or beta sheets). The alpha helix or beta sheets are folded into a compact globular structure to form the tertiary structure. Quaternary structure is a three-dimensional structure of a multi-subunit protein and how the subunits fit together. There is no such thing as auxiliary protein structure.

Example Question #8 : Protein Structure

A peptide bond represents a connection between two __________.

Possible Answers:

amino acids

triglycerides

carbohydrates

nucleotides

Correct answer:

amino acids

Explanation:

A peptide bond is a covalent chemical bond formed between two amino acids. The process is known as a dehydration synthesis reaction (or a condensation reaction). It is named so because the synthesis of the peptide bond occurs when the carboxyl group of one amino acid reacts with the amino group of another amino acid, which releases one molecule of water.

Example Question #5 : Understanding Protein Folding

The primary structure of a protein is created by which type of bonds?

Possible Answers:

Van der Waals forces

Hydrogen bonds

Peptide bonds

Ionic interactions

Correct answer:

Peptide bonds

Explanation:

Peptide bonds are responsible for the primary structure of a protein (The primary structure of a protein is the linear sequence of its amino acids.) Further folding through hydrogen bonds and other forces are responsible for secondary, tertiary, and if applicable, quaternary structure.

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