Torsion Angles in Biochemistry

Questions and Answers

What is the primary consequence of nonenzymatic oxidation on collagen and glycosylated proteins?

Formation of carbon-carbon double bonds

Development of advanced glycosylation end-products (AGEs) (correct)

Increased solubility in water

Creation of stable peptide bonds

How does a low pH affect protein structure?

It increases hydrophobic interactions

It disrupts ionic and hydrogen bonds formed by carboxylate groups (correct)

It enhances ionic bond stability

It solidifies the protein's tertiary structure

What effect does temperature have on protein denaturation?

It increases vibrational and rotational energies in bonds (correct)

It only affects the hydrophobic interactions

It decreases vibrational energy of bonds

It stabilizes the three-dimensional conformation

What is a significant role of gastric juice in protein digestion?

It denatures proteins to improve substrate accessibility for enzymes Signup and view all the answers

How do hydrophobic molecules influence protein structure?

They disturb hydrophobic interactions and denature proteins Signup and view all the answers

What is the outcome of thermal denaturation as illustrated by the cooking of an egg?

The protein converts to a denatured white precipitate Signup and view all the answers

What structural feature allows the β2-Adrenergic Receptor to span the membrane?

Membrane-spanning domains with α-helices Signup and view all the answers

What role do the extracellular loops of the β2-Adrenergic Receptor serve?

They form a binding site for adrenaline. Signup and view all the answers

Which of the following statements accurately describes the interaction of adrenaline with the β2-Adrenergic Receptor?

Adrenaline induces a conformational change in helical structures. Signup and view all the answers

What type of protein interacts with the β2-Adrenergic Receptor upon adrenaline binding?

Heterotrimeric G protein Signup and view all the answers

Which posttranslational modifications are important for the β2-Adrenergic Receptor's structure?

All of the above Signup and view all the answers

What prevents the β2-Adrenergic Receptor from being static within the membrane?

Flexible helical structures Signup and view all the answers

What initiates the signaling cascade triggered by the β2-Adrenergic Receptor?

Conformational change in helical structure Signup and view all the answers

In terms of chemical groups, what is significant for the structure of transmembrane proteins like the β2-Adrenergic Receptor?

They incorporate diverse posttranslational modifications. Signup and view all the answers

Why are the domains of the β2-Adrenergic Receptor crucial for its function?

They enable specific binding reactions and signal transduction. Signup and view all the answers

Which correctly describes the composition of a heterotrimeric G protein involved in signaling from the β2-Adrenergic Receptor?

Three different subunits Signup and view all the answers

Which of the following statements about torsion angles is correct?

Torsion angles are limited by the specific amino acids present. Signup and view all the answers

What is the main consequence of steric constraints in torsion angles?

They limit the secondary and tertiary structures that can be formed. Signup and view all the answers

Which configuration is preferred due to steric interference of R groups?

Trans configuration Signup and view all the answers

How do the -C=O and -NH groups behave over a pH range of 2.0 to 12.0?

They neither accept nor give off protons. Signup and view all the answers

Which terminal group of a polypeptide is typically charged?

N-terminal alpha-carboxyl group Signup and view all the answers

What role do side chains play in relation to torsion angles?

They help maximize the distance between atoms. Signup and view all the answers

Whose properties determine the steric constraints on torsion angles?

The specific amino acids present Signup and view all the answers

Which of the following groups is NOT considered an ionized group in polypeptides?

C-alpha methyl group Signup and view all the answers

What best describes the nature of torsion angles in amino acids?

They are restricted and depend on side chain configurations. Signup and view all the answers

What is the role of the palmitoyl group in the amino terminus?

It anchors the terminus to the lipid plasma membrane. Signup and view all the answers

What is the primary structural composition of adult hemoglobin (HbA)?

2 α and 2 β chains Signup and view all the answers

What distinguishes embryonic hemoglobin from adult hemoglobin in terms of chain composition?

It includes ε and ζ chains. Signup and view all the answers

Which amino acids are primarily involved in the phosphorylation sites at the COOH terminus?

Serine and threonine Signup and view all the answers

What characteristics do the membrane-spanning segments of certain ion channel proteins possess?

They consist of α-helices with exposed hydrophobic residues. Signup and view all the answers

What advantage does embryonic hemoglobin provide in low oxygen tensions?

Much higher affinity for O2. Signup and view all the answers

What defines the quaternary structure of proteins?

The arrangement of polypeptide subunits in a specific geometrical manner. Signup and view all the answers

What term refers to proteins that differ in primary structure but retain the same function across different tissues?

Isoforms Signup and view all the answers

How much sequence homology do Creatine Kinase isoforms share?

60 to 72% Signup and view all the answers

What types of noncovalent interactions contribute to the stability of quaternary structures in proteins?

Hydrophobic interactions, hydrogen bonds, and ionic bonds. Signup and view all the answers

Which form of Creatine Kinase is produced in skeletal muscle?

MM creatine kinase Signup and view all the answers

Which group of proteins typically shares a common structural feature related to membrane spanning?

Ion channel proteins, transport proteins, and receptor proteins. Signup and view all the answers

How many subunits are typically involved in a dimer?

Two Signup and view all the answers

Which of the following statements about cardiac isoforms of Creatine Kinase is true?

The most common form is the heterodimer MB. Signup and view all the answers

What is the primary role of Creatine Kinase isoforms?

Catalyzing the phosphorylation of creatine. Signup and view all the answers

What is the significance of loops connecting membrane-spanning segments?

They contain hydrophilic amino acid side chains that extend into the aqueous medium. Signup and view all the answers

Which residues are primarily linked to oligosaccharides in the amino terminus?

Asparagine Signup and view all the answers

What evolutionary change is believed to lead to the formation of the ζ chain in embryonic hemoglobin?

Mutation of a duplicated α gene. Signup and view all the answers

Which type of Creatine Kinase isoform is referred to as the cardiac isoform?

MB heterodimer Signup and view all the answers

What is a characteristic feature of oligomers in protein quaternary structures?

They can create a functional protein by combining multiple different polypeptide subunits. Signup and view all the answers

Study Notes

Torsion Angles

Rotation around the bond between α-carbon and α-amino group or carbonyl group can occur.
Steric constraints limit rotation to maximize distance between amino acid side chains.
Close proximity of side chain atoms is forbidden to maintain structural integrity.
Torsion angles vary based on specific amino acid composition, influencing polypeptide secondary and tertiary structures.
Trans configuration preferred due to steric hindrance in the cis configuration.

Uncharged but Polar Groups

Peptide bonds feature -C=O and -NH groups, remaining neutral across a pH range of 2.0 - 12.0.
Charged groups in polypeptides include N-terminal α-amino group and C-terminal α-carboxyl group, alongside ionized side chain groups.

Determination of Amino Acid Composition

Adult HbA consists of two α and two β chains.
Embryonic hemoglobin is composed of ε and ζ chains, evolving from mutations in duplicated α genes, providing higher O2 affinity for the fetus.
Tissue-specific isoforms, or isozymes, differ in primary structure but retain similar functions across tissues.

Creatine Kinase Isoforms

Composed of two subunits, showing 60-72% sequence homology, and bind to muscle sarcomeres.
M Form (MM creatine kinase) is expressed in skeletal muscle.
B Form (BB creatine kinase) is produced in the brain.
Cardiac isoforms include heterodimer MB and MM dimer; additional forms include heart mitochondrial creatine kinase.

Posttranslational Modifications

Proteins often undergo modifications post-translation, influencing three-dimensional structure and function.
Example: β2-Adrenergic Receptor features membrane-spanning domains made of α-helices with hydrophobic residues.
Conformational changes in helices upon ligand binding (e.g., adrenaline) activate intracellular domains that recruit signaling proteins.

Ion Channel and Transport Proteins

Share similar membrane-spanning segments with hydrophobic residues exposed to the lipid bilayer, maintaining structural integrity.
Rigid helices connected by loops of hydrophilic amino acids interact with the aqueous environment.

Quaternary Structure of Proteins

Defined by the specific arrangement and association of polypeptide subunits (dimers, tetramers, or oligomers).
Functional proteins arise from the combination of subunits in a defined geometrical pattern.

Noncovalent Interactions

Integral to protein structure stability: hydrophobic interactions, hydrogen bonds, and ionic bonds contribute to maintaining quaternary structure.

Nonenzymatic Oxidation

Modifies proteins like collagen, forming advanced glycosylation end-products (AGEs) that aggregate into larger proteins.

Protein Denaturation

Occurs due to environmental factors such as temperature, pH, and solvent composition, disrupting crucial ionic, hydrogen, and hydrophobic bonds.
Low pH (e.g., gastric juice pH 1-2) disrupts ionic and hydrogen bonds without cleaving peptide bonds, aiding protein digestion.
Elevated temperatures increase molecular vibrations, exemplified by the denaturation of albumin in cooking.
Hydrophobic molecules, such as long-chain fatty acids, can disrupt protein structure by interfering with hydrophobic interactions, inhibiting enzyme function.

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Description

This quiz explores the concept of torsion angles related to amino acids, focusing on the allowed rotational angles around the bonds connected to the alpha carbon. Learn about steric constraints and how they affect the spatial arrangement of atoms in amino acid side chains.