Cell Membrane Structure and Composition

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Questions and Answers

What is the primary component that constitutes the mass of the cell membrane?

Nucleic acids

Lipids (correct)

Carbohydrates

Proteins

What function does the cell membrane serve in biological systems?

It acts as a barrier to proteins.

It serves as a physical and electrical barrier. (correct)

It stores genetic information.

It facilitates enzymatic reactions.

Which of the following statements about the cell membrane is not true?

It plays a crucial role in cellular communication.

It contributes to the cell's structural integrity.

It is composed of a variety of lipids.

It is solely made of phospholipids. (correct)

Which authors provided an integrated approach to human physiology relevant to cell membranes?

Silverthorn et al. Signup and view all the answers

In which year was 'Cell Biology by the Numbers' published?

2016 Signup and view all the answers

What characterizes the head of a phospholipid?

It is made of phosphate esterified with alcohol hydroxyl groups. Signup and view all the answers

What is the primary role of the hydrophobic tail in phospholipids?

To align in the middle of the lipid bilayer. Signup and view all the answers

How many types of phospholipids are typically found in biological membranes?

Over 100 types Signup and view all the answers

What characteristic do more than 50% of fatty acids in membranes have?

They contain one or more double bonds. Signup and view all the answers

What was significant about the use of RBCs in Gorter and Grendel's 1925 study?

Their membrane composition makes them ideal for measurement. Signup and view all the answers

What is the primary function of the cell membrane?

To control the exchange of ions and nutrients with the environment Signup and view all the answers

Which of the following describes passive simple diffusion?

Always occurs from high to low concentration Signup and view all the answers

Which mechanism of membrane transport does not require energy?

Facilitated diffusion Signup and view all the answers

What role do lipid bilayers play in cellular function?

They maintain concentrations of solutes that differ from those in extracellular fluid Signup and view all the answers

What is one of the key functions of membrane transport mechanisms?

Excrete metabolic waste products and regulate ion concentrations Signup and view all the answers

Which of the following is NOT a basic mechanism of crossing membranes?

Endocytosis Signup and view all the answers

How do cells regulate the concentrations of ions inside them?

By using channels and pumps that require energy Signup and view all the answers

What is the typical direction of solute movement in passive transport mechanisms?

From an area of high concentration to low concentration Signup and view all the answers

What effect does a double bond between carbon atoms have on a hydrocarbon chain?

It produces a kink in the hydrocarbon chain. Signup and view all the answers

How does the length of hydrocarbon chains in the lipid bilayer affect its characteristics?

Longer chains are stiffer and less permeable. Signup and view all the answers

What would be the expected effect of having shorter hydrocarbon tails in a lipid bilayer?

The lipid bilayer would become more fluid. Signup and view all the answers

What is the impact of having all hydrocarbon tails in a lipid bilayer be unsaturated?

The lipid bilayer becomes less stable. Signup and view all the answers

Which factor contributes to the permeability of the lipid bilayer?

Both the length of hydrocarbon tails and the number of double bonds. Signup and view all the answers

What occurs to membrane fluidity with longer hydrocarbon tails?

Fluidity decreases as the tails become stiffer. Signup and view all the answers

What is the primary effect of unsaturation in hydrocarbon chains on lipid bilayers?

Increases fluidity by preventing tight packing. Signup and view all the answers

How do the characteristics of lipid molecules influence the overall structure of the lipid bilayer?

They determine fluidity and permeability of the bilayer. Signup and view all the answers

Which phospholipid is characterized by having a smaller polar head and a conical shape?

Phosphatidylethanolamine Signup and view all the answers

What is a characteristic of phosphoglycerides in mammalian membranes?

Their composition can affect the membrane's physical state. Signup and view all the answers

Which one of the following phospholipids contributes to a flat monolayer structure?

Phosphatidylserine Signup and view all the answers

Which lipid would likely be found in the membranes of organisms adapted to cold environments?

Unsaturated phospholipids Signup and view all the answers

What role does the lipid distribution in eukaryotic membranes play?

It can affect both the physical state and protein activity of the membrane. Signup and view all the answers

Which of the following statements is true about sphingomyelin?

It is classified as a sphingolipid. Signup and view all the answers

Which phospholipid is not part of the phosphoglyceride class?

Sphingomyelin Signup and view all the answers

What characteristic primarily differentiates cardiolipin from other phospholipids?

Presence of two glycerol backbones. Signup and view all the answers

The term 'lipid bilayer' primarily refers to which aspect of membrane structure?

The two layers of phospholipids forming a semipermeable barrier. Signup and view all the answers

Which type of lipid is primarily responsible for cell signaling in animal membranes?

Phosphatidylinositol Signup and view all the answers

Study Notes

Cell Membrane Composition

Cell membranes are primarily composed of lipids, with phospholipids being the most abundant.
Phospholipids contain a hydrophilic head and a hydrophobic tail.
The hydrophilic head faces the water-side of the lipid bilayer, while the hydrophobic tail aligns in the middle of the bilayer.
More than 50% of fatty acids in membranes have one or more double bonds.
Membranes contain over 100 types of phospholipids.

Lipid Bilayer Structure

Gorter and Grendel (1925) determined the structure of the lipid bilayer, showing that it is a double layer of phospholipids.
The structure of the lipid bilayer is determined by the properties of its lipid molecules:
- The number of double bonds in hydrocarbon tails impacts fluidity, with double bonds creating "kinks" and increasing fluidity.
- The length of hydrocarbon tails affects fluidity and permeability, shorter chains leading to increased fluidity and permeability.

Major Phospholipids in Mammalian Plasma Membranes

The predominant phospholipids in mammalian cell membranes include Phosphatidyl-inositol (PI), Phosphatidyl-ethanolamine (PE), Phosphatidyl-serine (PS), Phosphatidyl-choline (PC), and Sphingomyelin (SM).
Phospholipids are classified based on their head group - the molecule attached to the phosphate group.
Each phospholipid has a different shape:
- PI has an inverted conical shape.
- PE has a smaller polar head and a conical shape.
- PS and PC have cylindrical shapes, forming a flat monolayer.

Lipids Distribution in Eukaryote Membranes

Eukaryote membranes have a diverse lipid composition, with varying ratios of different phospholipids.
The distribution of lipids can affect the physical state of the membrane and influence the activity of membrane proteins.
- PC: Phosphatidylcholine
- PS: Phosphatidylserine
- PE: Phosphatidylethanolamine
- PI: Phosphatydilinositol
- SM: Sphingomyelin
- ISL: Inositol sphingolipid
- CL: Cardiolipin
- MBP: Bis monoacylglycerol phosphate

Cell Membrane as a Barrier

The cell membrane acts as a barrier that regulates the movement of substances across the membrane.
It controls the entry of ions and nutrients into the cell, the elimination of cellular wastes, and the release of products from the cell.

Membrane Transport

The lipid bilayer of the cell membrane maintains concentration gradients for solutes, creating differences between the cytosol and extracellular fluid.
Cells have evolved to transfer specific water-soluble molecules and ions across their membranes, facilitating nutrient uptake, waste excretion, and ion regulation.

Mechanisms of Crossing the Membrane

Solutes can cross the cell membrane through four main mechanisms:
- Passive-Simple diffusion: Always from high to low concentration.
- Facilitated diffusion
- Active transport
- Vesicular transport
Each mechanism handles different molecules and contributes to maintaining cellular homeostasis.

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Description

This quiz explores the composition and structure of cell membranes, focusing on the role of phospholipids in forming the lipid bilayer. Understand how the properties of lipid molecules, including double bonds and tail length, affect membrane fluidity and permeability.