Cell Membrane Structure and Function

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Questions and Answers

What is the primary function of channel proteins in the cell membrane?

Catalyze specific biochemical reactions

Provide structural support to the membrane

Selective interaction with specific molecules

Allow substances to move across the membrane (correct)

Which type of membrane protein is primarily involved in the immune system's recognition of cells?

Carrier proteins

Cell recognition proteins (glycoproteins) (correct)

Receptor proteins

Enzymatic proteins

What effect does solidification of the membrane have on its functionality?

Enhances fluidity and transport efficiency

Increases enzyme activation and permeability

Decreases permeability and deactivates enzymes (correct)

Allows for easier lateral drift of proteins

How are peripheral proteins primarily associated with the cell membrane?

By weak electrostatic interactions with membrane proteins Signup and view all the answers

Which of the following is NOT a function of membrane proteins?

Energy storage Signup and view all the answers

What role do unsaturated hydrocarbon tails play in the membrane structure?

They increase membrane fluidity by hindering close packing Signup and view all the answers

Which statement correctly describes the movement of membrane lipids and proteins?

They mostly drift laterally within the membrane. Signup and view all the answers

What is the main function of carbohydrates attached to the cell membrane?

They act as receptors and attach cells to each other. Signup and view all the answers

What is the primary structural feature of the plasma membrane that allows it to function as a barrier?

A double layer of phospholipids Signup and view all the answers

Which component is primarily responsible for the selective permeability of the plasma membrane?

Proteins spanning the membrane Signup and view all the answers

What percentage of the plasma membrane composition is made up of carbohydrates?

3% Signup and view all the answers

How does cholesterol affect the fluidity of the cell membrane?

It stabilizes membrane structure by making it more rigid Signup and view all the answers

What type of substances can easily penetrate the lipid bilayer of the plasma membrane?

Fat-soluble substances Signup and view all the answers

Which of the following statements about the phospholipids in the cell membrane is correct?

They form a lipid bilayer with hydrophobic and hydrophilic parts Signup and view all the answers

What role do negatively charged carbohydrates play on the surface of the plasma membrane?

Participating in intracellular communication Signup and view all the answers

What characteristic of the membrane lipids contributes to their stability as a low energy structure?

Amphipathic nature of phospholipids Signup and view all the answers

Study Notes

Membrane Structure and Function

Membranes act as a barrier, receive information, move and expand.
Membranes are dynamic and active.

Plasma Membrane

It is an elastic structure, approximately 7.5 to 10 nanometers thick.
The plasma membrane surrounds the cell and separates its internal structures from the extracellular environment.
It is selectively permeable, controlling the passage of materials into and out of the cell.
It participates in intracellular communication.

Structure of the cell membrane

Composed of a double layer of phospholipids (hydrophobic/hydrophilic parts), proteins that span or partially span the membrane, and negatively charged carbohydrates attached to the outer surface.

Fluid Mosaic Model

This describes the structure of cell membranes.
The membrane is composed of approximately 55% proteins, 42% lipids (including 25% phospholipids, 13% cholesterol, and 4% glycolipids) and 3% carbohydrates.

Cell Membrane Lipids

The lipid bilayer is a stable, low energy structure.
Lipids are amphipathic, meaning they have both hydrophobic and hydrophilic parts.
Hydrophobic compounds can reach equilibrium quickly.
Lipids are effective barriers to some compounds.

Cell Membrane Phospholipids

Phospholipids consist of a glycerol head that contains a phosphate group (polar and hydrophilic) and two fatty acid 'tails' (nonpolar and hydrophobic).

Cholesterol

The steroid nucleus of cholesterol molecules is highly fat-soluble.
Cholesterol helps determine the permeability of the membrane to water-soluble substances.
It also controls the fluidity of the membrane.
The lipid layer in the middle of the membrane is impermeable to water-soluble substances like ions and glucose.
Fat-soluble substances like oxygen, carbon dioxide, and alcohol can easily penetrate the membrane.

Cell Membrane Proteins

Integral proteins span the membrane.
- They provide structural channels or pores.
- They can act as enzymes or receptors (for peptide hormones).
Peripheral proteins are embedded on one side of the membrane.
- They are associated with membrane proteins or lipids by weak electrostatic bonds.

Functions of Plasma Membrane Proteins

Transporters: Facilitate movement of molecules across the membrane.
Enzymes: Catalyze specific reactions.
Cell surface receptors: Bind specific molecules, triggering cellular responses.
Cell surface identity markers: Identify cells to the immune system.
Cell-to-cell adhesion proteins: Help cells adhere to each other.
Attachments to the cytoskeleton: Provide structural support.

Functions of Integral Proteins

Channel protein: Allows specific substances to move across the membrane.
Carrier protein: Selectively interacts with specific molecules or ions, aiding their transport across the membrane.
Cell recognition protein: Called glycoproteins, these allow cells to be recognized by the body's immune system.
Receptor protein: Specifically shaped to bind to a specific molecule.
Enzymatic protein: Catalyzes specific reactions.

Cell Membrane Carbohydrates

Primarily attached to the outer surface of the membrane as glycoproteins (majority) and glycolipids (smaller proportion).

General Functions of Cell Membrane Carbohydrates

Cell to cell attachments: They help attach cells to each other.
Receptor substances: Act as receptors for specific molecules.
Basis for rejection of foreign cells: Basis for immune system recognition of foreign cells.
Overall negative surface charge: Give most cells a negative surface charge, influencing their interaction with regulatory molecules.

Why is fluidity important?

Membrane fluidity is essential for proper functioning.
Solidification can lead to changes in permeability and enzyme deactivation.
Unsaturated hydrocarbon tails enhance membrane fluidity by preventing close packing of phospholipids.

How does the membrane move?

The membrane is held together by weak hydrophobic interactions.
Most membrane lipids and some proteins can move laterally within the membrane.
Molecules rarely flip transversely (flip-flop) across the membrane because hydrophilic parts would have to cross the membrane's hydrophobic core.

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Description

Explore the complex structure and functionality of cell membranes in this quiz. Understand the components of the plasma membrane, including its selectively permeable nature and the fluid mosaic model. Test your knowledge on how membranes serve as barriers and facilitate communication within cells.