23 Questions
What is the primary structure of a protein?
The sequence of amino acids
What is the consequence of a defect in the primary structure of a protein?
It can lead to diseases
What is the significance of the N-terminal and C-terminal in a polypeptide chain?
They determine the direction of the sequence
What type of amino acid residues are rarely found in the alpha helix due to their structural properties?
Proline and glycine
Which type of protein structure involves the 3-D arrangement of all atoms in a protein and contains the active site where reactions occur?
Tertiary structure
What gives strength and hardness to α-keratin in structures like rhinoceros horn?
Disulphide bonds between coiled coils
Which chemical sequencing process labels and removes the amino-terminal residue from a peptide, leaving all other peptides intact?
Edman's degradation
What technique is used to determine protein sequences and elucidate the history of life on earth?
Tandem MS or MS/MS
How is protein concentration commonly determined using UV spectrophotometry?
Using the Beer-Lambert equation
What is the primary structure of collagen?
Left-handed triple helix with Gly-X-Y repeating tripeptide unit
What causes denaturation of proteins?
Heat affecting H bonds
What is the structure of myoglobin?
Backbone of 8 α helices with β turns
What is the predominant conformation of silk fibroin?
Antiparallel β conformation rich in Ala and Gly residues
What is the function of vitamin C in relation to collagen?
Stabilizes collagen structure
What is the structure of hemoglobin?
4 polypeptide chains – 2α and 2β
Collagen is a globular protein with a recognizable folding pattern involving two or more elements of secondary structure.
False
Silk fibroin is predominantly in the β conformation, rich in Ala and Gly residues.
True
Denaturation of proteins is caused by disruption of the hydrophobic aggregation of nonpolar amino acid side chains and hydrogen bonds.
True
Myoglobin has a predominant antiparallel β conformation.
False
Collagen fibrils are made up of collagen in a parallel fashion and cross-linked for strength.
False
Explain the structure and composition of collagen fibrils at a molecular level, including the role of specific amino acid residues.
Collagen fibrils are supramolecular structures composed of a triple helix of collagen, with each collagen molecule consisting of three left-handed α chains. These α chains are rich in glycine (Gly), proline (Pro), and 4-hydroxyproline (4-Hyp), with a repeating tripeptide unit of Gly–X–Y, where X is often Pro and Y is often hydroxyproline (Hyp). The collagen fibrils are cross-linked by lysine (Lys) or histidine (His) residues, contributing to their strength and stability.
Discuss the significance of ascorbic acid (vitamin C) in maintaining the stability of collagen and the implications of vitamin C deficiency.
Ascorbic acid (vitamin C) plays a crucial role in maintaining the stability of collagen by facilitating the post-translational modification of proline and lysine residues, which are essential for collagen maturation and cross-linking. A deficiency in vitamin C leads to the instability of collagen, resulting in the deterioration of connective tissues and diseases such as scurvy.
Provide an overview of the tertiary and quaternary structure of myoglobin, emphasizing its unique features and functional significance.
Myoglobin is a globular protein with a tertiary structure consisting of a heme group coordinated within a hydrophobic pocket formed by a single polypeptide chain. This structure allows myoglobin to efficiently bind and store oxygen in muscle tissues. Additionally, myoglobin contains a backbone of eight α helices with β turns, and its quaternary structure involves a single polypeptide chain of 153 amino acid residues, contributing to its role in oxygen storage and muscle function.
Study Notes
Protein Structure and Analysis Techniques
- Fredrick Sanger determined the amino acid sequence in bovine insulin in 1953.
- Edman's degradation is a two-step chemical sequencing process that labels and removes the amino-terminal residue from a peptide, leaving all other peptides intact.
- For larger proteins, disulfide bonds must be eliminated by performic acid or dithiothreitol (DTT).
- Mass spectrometry provides an alternative method to determine amino acid sequences, offering accurate molecular weight and short sequence determination in a short time.
- Two techniques developed to solve the problem of mass spectrometry not working for large macromolecules are MALDI MS and ESI MS.
- Tandem MS or MS/MS is used to determine protein sequences and elucidate the history of life on earth.
- Tracing evolution involves identifying suitable families of homologous proteins and using them to reconstruct evolutionary paths.
- Aromatic R groups in amino acids have various properties, including UV light absorption at 280 nm for protein characterization.
- Protein concentration can be determined using UV spectrophotometry and the Beer-Lambert equation.
- The Bradford assay uses a standard calibration curve of bovine serum albumin (BSA) to determine protein concentration.
- M1V1 = M2V2 equation is used to prepare stock solutions of protein standards.
- The common protein secondary structures include α-helix, β conformations, β-turn, and random coil, with the α-helix being observed in hair and porcupine quills.
Test your knowledge of protein structure and analysis techniques with this quiz. Explore topics such as amino acid sequencing, mass spectrometry, evolution tracing, protein characterization, and concentration determination.
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