15 Aug, 2024
· Biology

Which of the following is true of integral membrane proteins

  • They are loosely bound to the surface of the bilayer.
  • They are usually transmembrane proteins.
  • They are not mobile within the bilayer.
  • They serve only a structural role in membranes.
Short Answer
Some answer Some answer Some answer
Long Explanation

Explanation

Integral membrane proteins exhibit a distinct set of characteristics that differentiate them from peripheral membrane proteins.

Key Characteristics

  1. They are usually transmembrane proteins

    • Integral membrane proteins often span the entire lipid bilayer. They typically possess one or more helical segments that traverse the membrane, establishing their position within it.

  2. They possess tertiary structure

    • Unlike peripheral proteins that may lack tertiary structure, integral membrane proteins generally have complex secondary and tertiary structures. These structural features are vital for their function and stability within the bilayer environment.

Incorrect Statements

  • They lack tertiary structure

    • This is incorrect as integral membrane proteins commonly have well-defined tertiary structures.

  • They are loosely bound to the surface of the bilayer

    • Unlike peripheral proteins, integral membrane proteins are not loosely bound to the surface but are embedded within the bilayer.

  • They are not mobile within the bilayer

    • Some integral membrane proteins can exhibit lateral movement within the membrane. Hence, saying they are not mobile is not universally true.

  • They serve only a structural role in membranes

    • Integral membrane proteins have diverse roles, including acting as channels, receptors, and enzymes. Their functions go beyond mere structural support.

Important Formulas

For illustration, the typical structure of an integral membrane protein can be described by the equation:

Proteinintegral=∑i=1nHydrophobicSegmenti+\text{Protein}_{\text{integral}} = \sum_{i=1}^{n} \text{HydrophobicSegment}_i + +∑j=1mHydrophilicSegmentj+ \sum_{j=1}^{m} \text{HydrophilicSegment}_j

Where nn and mm denote the number of hydrophobic and hydrophilic segments, respectively. Usually, the hydrophobic segments interact with the lipid bilayer, while hydrophilic segments may interact with the aqueous environments on either side of the membrane.

In conclusion, the most accurate statement about integral membrane proteins is:

They are usually transmembrane proteins.

Verified By
RG
Rebecca Green

Biology and Health Content Writer at Math AI

Rebecca Green, who recently completed her Master's in Biology from the University of Cape Town, works as a university lab teaching assistant and a part-time contract writer. She enjoys making biology fun and accessible through engaging content.

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Concept

Transmembrane Proteins

Role of Transmembrane Proteins

Transmembrane proteins are integral membrane proteins that span across the cell membrane, often multiple times. These proteins play crucial roles in various cellular processes and have a hydrophobic region that traverses the lipid bilayer and hydrophilic regions that interact with the aqueous environment on either side of the membrane.

Structure of Transmembrane Proteins

Transmembrane proteins typically have one or more alpha-helical or beta-barrel regions that span the lipid bilayer. The hydrophobic alpha-helices anchor the protein within the hydrophobic core of the membrane.

Hydrophobic region→(CH2)ngroups\text{Hydrophobic region} \rightarrow \left( \text{CH}_2\right)_{n} \text{groups}

Functions of Transmembrane Proteins

  1. Transport: Many transmembrane proteins function as transporters or channelsthat control the movement of ions and molecules across the cell membrane. This can be exemplified by the action of ion channels and aquaporins.
Ion channel transportAout→→[Channel]→→Ain\begin{aligned} &\text{Ion channel transport} \\ &\text{A}_{\text{out}} \rightarrow\rightarrow [\text{Channel}] \rightarrow\rightarrow \text{A}_{\text{in}} \end{aligned}
  1. Signal Transduction: They are involved in signal transduction pathways, acting as receptors for extracellular signals such as hormones, growth factors, and neurotransmitters. Binding of a ligand to a receptor triggers a conformational change that initiates a cellular response.
Receptor + Ligand→Conformational Change→\text{Receptor + Ligand} \rightarrow \text{Conformational Change} \rightarrow →Signal Cascade\rightarrow \text{Signal Cascade}
  1. Cell Adhesion: Transmembrane proteins also contribute to cell adhesion, interacting with extracellular matrix components and other cells, crucial for tissue structure and integrity.
CellA↔CAM↔CellB\text{Cell}_A \leftrightarrow \text{CAM} \leftrightarrow \text{Cell}_B
  1. Enzymatic Activity: Some transmembrane proteins have enzymatic activities. For instance, the production of ATP in mitochondria involves ATP synthase, a transmembrane protein.
ADP+Pi→ATP SynthaseATP\text{ADP} + \text{P}_\text{i} \xrightarrow{\text{ATP Synthase}} \text{ATP}
  1. Tethering and Structural Roles: Scaffolding proteins stabilize cell shape and anchor other proteins in specific cellular locations.

Importance in Medicine

Given their roles, transmembrane proteins are critical in medicine. They are targets for many drugs acting as inhibitors or activators of these proteins. For example, antihypertensive drugs often target ion channels or transporters.

Understanding these multifaceted proteins provides insight into cellular functionality and has profound implications in disease treatment and pharmaceutical development.

Concept

Tertiary Structure

Understanding Tertiary Structure

Tertiary structure refers to the overall 3D shape of a protein molecule. It is formed by the folding and interactions of the secondary structural elements (like alpha-helices and beta-sheets) into a compact, globular shape.

Key Forces in Tertiary Structure:

  • Hydrophobic Interactions: Nonpolar side chains of amino acids tend to cluster in the interior of the protein, avoiding water. This helps stabilize the protein's structure.
  • Hydrogen Bonds: These form between polar side chains and main-chain atoms, contributing to the stability of the structure.
  • Ionic Bonds (Salt Bridges): Electrostatic interactions between oppositely charged side chains can stabilize the structure.
  • Disulfide Bridges: Covalent bonds formed between the sulfur atoms of cysteine residues, providing significant stability.
  • Van der Waals Forces: Weak attractions between all atoms when they are very close together.

Example of Tertiary Structure Representation:

Protein tertiary structure can be represented as:Ptertiary=∑Hydrophobic interactions+∑Hydrogen bonds+∑Ionic bonds+∑Disulfide bridges+∑Van der Waals\begin{aligned} &\text{Protein tertiary structure can be represented as:} \\ &P_{\text{tertiary}} = \sum_{\text{Hydrophobic interactions}} + \sum_{\text{Hydrogen bonds}} + \sum_{\text{Ionic bonds}} + \\ &\quad \sum_{\text{Disulfide bridges}} + \sum_{\text{Van der Waals}} \end{aligned}

Importance of Tertiary Structure

  • Functionality: The shape of the protein, determined by its tertiary structure, is critical for its function. For example, enzymes have an active site perfectly shaped to bind to their substrates.
  • Specificity: Tertiary structure allows proteins to interact specifically with other molecules. The precise 3D conformation dictates interaction specificity and affinity.
  • Stability: The folded tertiary structure is usually the most energetically favorable arrangement, giving the protein stability under physiological conditions.

By understanding the tertiary structure, one can gain deep insights into the functional and interaction capabilities of proteins.