Proteins and Protein Structure

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Questions and Answers

What is the reason why glutamate, aspartate, histidine, lysine, or arginine disrupt the helix?

They are hydrophobic amino acids and interfere with the formation of the beta sheet.

They are large amino acids and interfere with the formation of the alpha helix.

They are non-polar amino acids and cannot form hydrogen bonds.

They are charged amino acids and form ionic bonds, or repel each other electrostatically. (correct)

What is the characteristic of the backbone of the polypeptide chain in the beta conformation?

It is a coiled structure.

It is a folded structure.

It is a helical structure.

It is an extended zigzag structure. (correct)

How are hydrogen bonds formed in the beta sheet?

Between non-adjacent amino acids.

Between adjacent segments of polypeptide chain. (correct)

Between adjacent amino acids.

Between non-adjacent segments of polypeptide chain.

What is the key difference between alpha helix and beta sheet?

The number of polypeptide chains. Signup and view all the answers

What is the orientation of the N-termini and C-termini in an antiparallel beta sheet?

The N-termini and C-termini are alternating. Signup and view all the answers

What is the function of beta turns in globular proteins?

They link successive runs of alpha helix or beta conformation. Signup and view all the answers

What is the percentage of proteins that contain beta turns or loops?

Nearly 2/3rds of the proteins. Signup and view all the answers

What is the role of beta turns in relation to beta sheets?

They connect the ends of two adjacent segments of an antiparallel beta sheet. Signup and view all the answers

What is the primary structure of proteins?

The sequence of amino acids in a protein Signup and view all the answers

What is an example of a protein that contains α-helices?

Keratin Signup and view all the answers

What is the quaternary structure of proteins?

The association of two or more polypeptide chains Signup and view all the answers

What is the significance of the primary structure of proteins?

It is required for an understanding of a protein's structure and function Signup and view all the answers

What is the role of hydrogen bonds in α-helices?

They stabilize the helix structure Signup and view all the answers

What is the effect of proline on α-helix stability?

It disrupts the helix structure Signup and view all the answers

What is the significance of the secondary structure of proteins?

It is involved in the formation of α-helices and β-sheets Signup and view all the answers

What is the difference between human and animal insulin?

The primary structure of human insulin is different from animal insulin Signup and view all the answers

What is the significance of the tertiary structure of proteins?

It is involved in the folding of the polypeptide by R-group interactions Signup and view all the answers

What is the result of protein misfolding?

It leads to the loss of normal function Signup and view all the answers

What determines the three-dimensional shape of a functional protein?

Interactions between the side chains of amino acids Signup and view all the answers

What is the role of cis-trans prolyl isomerases in protein folding?

To increase the rate of folding by catalyzing inter-conversion of cis and trans peptide bonds of proline residues Signup and view all the answers

What is the result of positively and negatively charged side chains interacting with each other?

Attraction Signup and view all the answers

What is the role of protein disulfide isomerases in protein folding?

To catalyze the breakage and formation of disulfide cystine linkages Signup and view all the answers

What type of interactions do similarly charged side chains exhibit during protein folding?

Repulsion Signup and view all the answers

What type of proteins facilitate the folding process in cells?

Chaperone proteins Signup and view all the answers

What determines the tertiary structure of a polypeptide chain?

The primary structure of the polypeptide chain Signup and view all the answers

What is a characteristic of the core of globular proteins in aqueous solutions?

High-density packing of atoms Signup and view all the answers

Where are hydrophobic side chains typically found in globular proteins in aqueous solutions?

In the interior of the molecule Signup and view all the answers

Why do alpha-helix and beta-sheet structures provide stability to protein folding?

They provide maximal hydrogen bonding for peptide bond components Signup and view all the answers

What is the result of maximal hydrogen bonding within the interior of polypeptides?

The possibility of water molecules binding to hydrophilic groups is eliminated Signup and view all the answers

Where are hydrophilic groups generally found in globular proteins in aqueous solutions?

On the surface of the molecule Signup and view all the answers

What type of protein is associated with transmissible spongiform encephalopathies (TSEs)?

Prion protein Signup and view all the answers

What is the result of misfolding of transthyretin protein produced by the liver?

Formation of amyloid fibrils Signup and view all the answers

What is the percentage of African Americans who are carriers of the most common variant of transthyretin amyloidosis?

3-4% Signup and view all the answers

What is the name of the condition caused by the accumulation of transthyretin fibrils in the myocardium?

Transthyretin Amyloidosis cardiomyopathy (ATTR-CM) Signup and view all the answers

What is the percentage of patients with heart failure who have Transthyretin Amyloidosis cardiomyopathy (ATTR-CM)?

14% Signup and view all the answers

What is the primary cause of Transthyretin Amyloidosis (ATTR)?

Mutation in gene coding for TTR Signup and view all the answers

What is the characteristic of wild-type ATTR?

Common in 25% of patients over 80 years Signup and view all the answers

What is the primary characteristic of wATTR-CM?

More common in older patients and has male predominance Signup and view all the answers

Study Notes

Protein Structure

Proteins have a linear sequence of linked amino acids, which contains the information necessary to generate a protein molecule with a unique three-dimensional shape.
The complexity of protein structure is best analyzed by considering the molecule in terms of four organizational levels: primary, secondary, tertiary, and quaternary.

Primary Structure

The primary structure of a protein is the sequence of amino acids in a protein.
It is required for understanding a protein's structure, its mechanism of action at a molecular level, and its relationship to other proteins with similar physiological roles.
Many genetic diseases result in proteins with abnormal amino acid sequences, which cause improper folding and loss or impairment of normal function.

Secondary Structure

The secondary structure of a protein is the regular arrangement of amino acids that are located near to each other in the linear sequence.
Examples of secondary structures frequently encountered in proteins include:
- α-helix (a spiral structure, tightly packed, coiled polypeptide backbone core, and side chains extending outward from the central axis)
- β-sheet (a zigzag structure, hydrogen bonds formed between adjacent segments of polypeptide chain)
- β-bend (a connecting element that links successive runs of α-helix or β-conformation)

Tertiary Structure

The tertiary structure of a protein is the overall 3D shape of the protein molecule.
It is determined by the primary structure of a polypeptide chain.
Globular proteins have a compact, high-density core with hydrophobic side chains buried in the interior and hydrophilic groups on the surface.

Protein Folding

Protein folding occurs within the cell in seconds to minutes and employs a shortcut through the maze of all folding possibilities.
Interactions between the side chains of amino acids determine how a long polypeptide chain folds into the intricate three-dimensional shape of the functional protein.
Cells contain enzymes that facilitate the folding process, including cis-trans prolyl isomerases, protein disulfide isomerases, and chaperone proteins.

Protein Misfolding

Deposits of misfolded proteins are associated with a number of diseases, including amyloidoses.
Examples of protein misfolding diseases include:
- Alzheimer disease
- Transthyretin amyloidosis cardiomyopathy (ATTR)
- Transmissible spongiform encephalopathies (TSEs), including Creutzfeldt-Jakob disease, scrapie, and bovine spongiform encephalopathy (mad cow disease)

Transthyretin Amyloidosis (ATTR)

ATTR occurs as a result of misfolding of transthyretin protein produced by the liver.
It produces amyloid fibrils that can deposit in various tissues, causing irreversible damage.
Mutation in the gene coding for TTR can cause structural changes leading to misfolding (hATTR).
The wild-type ATTR is common in 25% of patients over 80 years.
Transthyretin Amyloidosis cardiomyopathy (ATTR-CM) is a systemic amyloidosis caused by accumulation of tranthyretin fibril in the myocardium.

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Description

Quiz on proteins and protein structure, covering topics from Lehninger's Principles of Biochemistry, Harper's Illustrated Biochemistry, and Biochemistry by Berg et al.