Protein Structures and Functions

Questions and Answers

Which structure represents the secondary structure of a protein?

β-pleated sheet

Tertiary structure

Primary structure

α-helix (correct)

What is an important tool for predicting protein structure and function?

Determining sequence homology

Protein function is directly related to the protein's tertiary structure.

True

The tertiary structure of a protein is less conserved than the primary structure.

False Signup and view all the answers

What holds the β-pleated sheet together?

Hydrogen bonds Signup and view all the answers

Where are the side chains located in an α-helix?

On the outside of the helix Signup and view all the answers

What amino acid residue's backbone forms a hydrogen bond with the backbone of the sixth residue?

2 Signup and view all the answers

Which peptide segment is most likely to be part of a stable α-helix at physiological pH?

−Glu−Leu−Ala−Lys−Phe− Signup and view all the answers

How many residues are in a segment of a single chain in an antiparallel β sheet that has a length of 305 Å?

87 Signup and view all the answers

Match the following descriptions to the correct structure (α Helices, β Sheets, β Turns, or All):

First residue hydrogen-bonded to fifth residue = α Helices Successive R groups point in opposite directions = β Sheets First residue hydrogen-bonded to fourth residue = β Turns Contains --NH hydrogen-bonded to C=O = All Signup and view all the answers

What is the length of a 35.0 kDa single-stranded α-helical protein segment?

477 Å Signup and view all the answers

What characterizes an amphipathic α helix?

One side with mainly hydrophobic side chains and the other side with hydrophilic side chains Signup and view all the answers

Which two synthetic polypeptides can form an α-helix at the indicated pH values?

Polylysine at pH 13 and polyglutamate at pH 2 Signup and view all the answers

Study Notes

Protein Structures

The secondary structure of a protein includes configurations like the α-helix and β-pleated sheet.
An α-helix exhibits side chains on its exterior, while β-pleated sheets are stabilized by hydrogen bonds between adjacent segments.

Tertiary and Evolutionary Relationships

Sequence homology is crucial for predicting protein structure and function.
Tertiary structures are more conserved evolutionarily than primary structures.

α-Helices

The α-helix structure involves hydrogen bonding between the first and fifth residues (H-bonding occurs between residue n and n+4).
Length of a 35.0 kDa single-stranded α-helix segment is approximately 477 Å, based on 318 residues, with each residue contributing 1.5 Å.

β-Sheets

In β-sheets, successive R groups alternate directions, allowing for unique structural integrity.
An antiparallel β-sheet segment measuring 305 Å comprises approximately 87 residues, calculated using the 3.5 Å distance between residues.

β-Turns

β-turns involve hydrogen bonding between the first and fourth residues (H-bonding occurs between residue n and n+3).

Classification of Structures

All protein structural types (α-helices, β-sheets, β-turns) feature –NH groups that form hydrogen bonds with C=O groups.
Amphipathic α-helices have one side of predominantly hydrophobic residues and another of hydrophilic residues, while amphipathic β-sheets alternate between polar and nonpolar residues.

Synthetic Polypeptides

Polylysine can form an α-helix at pH 13, while polyglutamate does so at pH 2, illustrating the impact of chemical environment on protein structure.

Description

Explore the intricate details of protein structures including secondary, tertiary, and evolutionary relationships. This quiz covers key configurations such as α-helix and β-pleated sheets, and emphasizes the significance of sequence homology in predicting protein function.