Cell Membrane Structure

Questions and Answers

What function do channel proteins serve in the membrane?

They act as receptors for signaling molecules.

They decrease the membrane's permeability.

They form a hydrophobic barrier.

They provide a hydrophilic channel for specific substances. (correct)

What role do aquaporins play in cellular transport?

They create a hydrophobic environment for molecules.

They inhibit the movement of water across the membrane.

They facilitate the rapid passage of water molecules. (correct)

They transport glucose into the cells.

How do carrier proteins differ from channel proteins?

Carrier proteins can transport water, while channel proteins cannot.

Carrier proteins allow multiple substances to pass simultaneously.

Carrier proteins change shape to shuttle substances across the membrane. (correct)

Carrier proteins do not shape shift to transport substances.

Why is the glucose transporter in red blood cells so selective?

It rejects fructose, which is a structural isomer of glucose. Signup and view all the answers

What characteristic of transport proteins enhances their specificity?

Their design to translocate only certain substances. Signup and view all the answers

What happens to the rate of glucose transport when using its specific carrier protein?

It increases dramatically. Signup and view all the answers

What is the main advantage of channel proteins over passive diffusion for hydrophilic substances?

They enable a much faster transport rate. Signup and view all the answers

What type of molecules primarily utilize channel proteins to cross the membrane?

Small polar molecules and ions. Signup and view all the answers

What structural feature characterizes carrier proteins in transport?

They have flexible structures that change shape. Signup and view all the answers

Which of the following correctly describes transport proteins?

Transport proteins are selective for certain substances. Signup and view all the answers

Study Notes

Cell Membrane Structure

The plasma membrane separates living cells from their surroundings and is responsible for regulating the passage of substances in and out of the cell.
Exhibits selective permeability, allowing the cell to control chemical exchanges crucial for life.

Composition of Cellular Membranes

Membranes are fluid mosaics composed primarily of lipids and proteins, with carbohydrates playing an important role.
Phospholipids are the most abundant lipids, characterized as amphipathic molecules with hydrophilic heads and hydrophobic tails.
The phospholipid bilayer forms a stable boundary, protecting hydrophobic tails from water while exposing hydrophilic heads.

Membrane Characteristics

Described as a fluid mosaic due to the lateral drifting motion of its molecular components.
Cholesterol maintains membrane fluidity by impacting how phospholipids behave under varying temperatures.

Types of Membrane Proteins

Integral membrane proteins penetrate the bilayer, while peripheral proteins are attached to extracellular or cytoplasmic surfaces.
Membrane proteins perform various functions, including transport, enzymatic activity, cell adhesion, and signal reception.

Functional Roles of Membrane Proteins

Transport proteins create pathways for ions and polar substances.
Enzymes catalyze essential chemical reactions.
Recognition proteins identify self versus foreign cells, aiding the immune response.
Adhesion proteins foster cell adhesion.
Receptor proteins bind external molecules and trigger internal responses.

Importance of Membrane Proteins in Medicine

Many pharmaceuticals target membrane proteins; examples include omeprazole (Prilosec) for heartburn and fluoxetine (Prozac), an antidepressant affecting serotonin reuptake.

Fluidity of Membranes

Membrane fluidity decreases when temperature drops, but phospholipids rich in unsaturated tails remain fluid to lower temperatures due to their structural configuration.
Cholesterol acts as a “fluidity buffer,” making membranes less fluid at high temperatures and preventing them from stiffening at low temperatures.

Evolutionary Adaptations in Membrane Lipids

Variations in lipid composition among species help maintain appropriate fluidity in various environments.
Cold-adapted organisms, such as certain fishes and plants, have higher levels of unsaturated phospholipids to retain membrane fluidity in extreme cold.

Role of Membrane Carbohydrates

Cell-cell recognition is essential for tissue formation and immune response.
Recognition involves carbohydrates attached to membrane proteins, which serve as identifiers for the immune system.

Transport Proteins

Channel proteins facilitate the passage of hydrophilic substances, such as water through aquaporins, increasing transport rates markedly.
Carrier proteins bind specific molecules, altering their shape to transport substances across the membrane selectively, exemplified by glucose transporters in red blood cells that expedite glucose uptake.

Description

Explore the intricacies of cell membrane structure in this quiz designed for General Cell and Developmental Biology (BIO 102). Understand how the plasma membrane serves as a protective barrier, controlling the movement of substances in and out of living cells. Test your knowledge on critical concepts related to cellular boundaries and their functions.