Biological Membranes Overview

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Questions and Answers

Which function is NOT associated with lipid rafts?

Signal transduction

Cell division (correct)

Protein trafficking

Membrane fluidity

What characterizes integral proteins in the membrane?

They are partially or totally immersed in the lipid bilayer. (correct)

They are immobile and cannot move within the membrane.

They only interact with the hydrophilic heads of phospholipids.

They are temporarily attached to the membrane surface.

Which of the following statements about membrane carbohydrates is accurate?

They compose a majority of the membrane composition.

They are solely responsible for the membrane's fluid nature.

Carbohydrates can exist freely in the membrane.

They always attach as glycoproteins or glycolipids. (correct)

What does the fluid mosaic model emphasize about the structure of plasma membranes?

Phospholipids and proteins can move freely within the membrane. Signup and view all the answers

What ensures the membrane remains fluid at normal cellular temperatures?

A correct mixture of saturated and unsaturated fatty acids. Signup and view all the answers

What is the movement of phospholipids within a bilayer called?

Lateral diffusion Signup and view all the answers

What is one of the primary functions of biological membranes?

Serve as a location for some chemical reactions Signup and view all the answers

How often does a phospholipid molecule typically undergo flip-flop movement?

Once in several hours Signup and view all the answers

What effect does cholesterol have on phospholipid bilayers?

Reduces side movement of phospholipids Signup and view all the answers

Which component of the cell membrane is primarily responsible for its selectively permeable nature?

Phospholipids forming a bilayer Signup and view all the answers

What is the primary function of glycolipids in cell membranes?

Facilitate cellular recognition Signup and view all the answers

How does the protein-to-lipid ratio in cell membranes vary?

It varies depending on the specific functions and types of cells Signup and view all the answers

Which protein marker is specific to the plasma membrane?

Na,K-ATPase Signup and view all the answers

What defines lipid rafts in cell membranes?

Microdomains enriched with cholesterol and sphingolipids Signup and view all the answers

What is the nature of phospholipids in biological membranes?

They are amphipathic, with hydrophilic and hydrophobic regions Signup and view all the answers

What role does the OH group of cholesterol play in the phospholipid bilayer?

It is near the polar head group of phospholipids Signup and view all the answers

Which of the following statements about carbohydrates in cell membranes is true?

They are attached to proteins or lipids but never exist independently Signup and view all the answers

What percentage of cell membrane content is typically cholesterol?

5-25% Signup and view all the answers

Which of the following describes the hydrophobic and hydrophilic regions of a phospholipid?

The phosphate group is hydrophilic, and the fatty acid chains are hydrophobic Signup and view all the answers

Which statement about protein mobility in membranes is correct?

Protein mobility varies from 10-4 to 0.4 mm/sec Signup and view all the answers

Which of the following components contributes to the diverse functions of cell membranes?

The variety of proteins and lipids present Signup and view all the answers

What effect does an increase in temperature have on membrane fluidity?

It increases fluidity by causing hydrophobic side chains to become disordered. Signup and view all the answers

How does the chain length of fatty acids impact the fluidity of a membrane?

Shorter chain fatty acids increase membrane fluidity. Signup and view all the answers

What is the role of double bonds in fatty acids concerning membrane fluidity?

More double bonds increase the membrane fluidity. Signup and view all the answers

How does cholesterol influence membrane fluidity at high temperatures?

It stabilizes the membrane, reducing its fluidity. Signup and view all the answers

Which type of fatty acids increases membrane fluidity due to their configuration?

Unsaturated fatty acids in cis configuration Signup and view all the answers

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

Glycosylated proteins Signup and view all the answers

What is the effect of low temperature on membrane fluidity?

It decreases fluidity, making the membrane less flexible. Signup and view all the answers

What is one function of membrane proteins classified as receptors?

Detect and transmit signals. Signup and view all the answers

Study Notes

Functions of Biological Membranes

Selectively permeable, allowing specific substances to cross.
Creates a concentration gradient between extracellular fluid (ECF) and intracellular fluid (ICF).
Facilitates cell-to-cell communication.
Identifiable by specific protein markers, e.g., Na,K-ATPase for plasma membranes and succinate dehydrogenase for mitochondria.
Serves as a site for various chemical reactions.

Major Components of Cell Membranes

Comprised of lipids, proteins, and carbohydrates linked either to lipids or proteins; carbohydrates are never free.
Different membranes exhibit varying protein-to-lipid ratios, affecting the composition.

Phospholipids

Types include phosphatidylcholine, ethanolamine, phosphatidylserine, cardiolipin, and sphingomyelin.
Amphipathic nature: hydrophilic head and hydrophobic fatty acid tails.
Phospholipids exhibit lateral movement within the bilayer, allowing dynamic changes in cell shape (2 mm/sec).
Transverse diffusion (flip-flop) occurs infrequently (every several hours).
Proteins mostly do not rotate within the membrane.

Lipid Bilayers

Composed of phospholipids arranged in a bilayer.
Asymmetric structure where lipid composition differs between leaflets.

Cholesterol

Comprising 5-25% of membrane content, it is a key structural component.
Cholesterol molecules exist between phospholipids, affecting membrane fluidity by reducing lateral movement.
Its arrangement (OH group near polar heads) contributes to overall membrane stability.

Glycolipids

Combinations of carbohydrates and lipids; less abundant (<5%).
Carbohydrates are attached to phospholipids and oriented outward, facilitating cellular recognition and tissue formation.

Lipid Rafts

Thicker membrane microdomains enriched with cholesterol and sphingolipids.
Facilitate signal transduction, protein trafficking, and influence membrane fluidity.

Membrane Proteins

Classified into integral (spanning the bilayer) and peripheral (temporarily attached) proteins.
Integral proteins can be transmembrane, while peripheral proteins associate with the membrane surface.

Carbohydrates in Cell Membranes

Minor component (5-8%); always attached to proteins (glycoproteins) or lipids (glycolipids).
Form the glycocalyx, which protrudes from the outer surface of the membrane and plays a role in cell recognition.

Fluid Mosaic Model

Describes membrane structure as a fluid dynamic bilayer with dispersed proteins, creating a mosaic effect.
Fluidity is affected by temperature and lipid composition: short, unsaturated fatty acids increase fluidity, while saturated fatty acids decrease it.
Cholesterol acts as a fluidity buffer, maintaining membrane integrity across varying temperatures:
- At high temperatures, it limits movement, reducing fluidity.
- At low temperatures, it decreases rigidity, enhancing fluidity.

Membrane Protein Functions

Proteins serve as receptors, transporters, ion channels, and structural components.
Many membrane proteins are glycosylated, affecting their function and interactions.

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Description

Explore the essential functions and components of biological membranes. Learn about the selective permeability, concentration gradients, and the role of various lipids and proteins in membrane structure and function. Discover key concepts essential for understanding cellular processes.