Cell membrane Flashcards
What are the structural and protective functions of the cell membrane?
Selective permeability: regulates the entry and exit of substances, maintaining the internal environment of the cell.
Anchoring: provides structural support by anchoring the cytoskeleton to the membrane, maintaining cell shape.
Adhesion: Contains adhesion molecules that help cells bind to each other and to the extracellular matrix.
Compartmentalization: Divides the cell into distinct regions, enabling specialized functions in organelles.
Protection: Acts as a barrier against mechanical damage ad harmful substances.
What are the interactive and functional roles of the cell membrane?
Transport: Facilitates the movement of ions and molecules through protein channels, carriers and pumps.
Energy Transduction: Supports processes like ATP synthesis in mitochondria by forming gradients.
Signal transduction: Contains receptor proteins that detect and transmit chemical signals to the cells interior.
Cell recognition: Supports cell-cell recognition through glycolipids and glycoproteins that act as molecular tags.
Intercellular communication: Includes proteins involved in forming gap junctions or plasmodesmata for cell-to-cell communication.
What is the general structure of the cell membrane?
A lipid bilayer that contains two sheets of lipids interspersed with proteins.
What is the structure of a phospholipid?
- Hydrophilic head
-Hydrophobic tails
They are amphipathic molecules (contain both hydrophobic and hydrophilic parts)
-Their bilayer is crucial for membrane formation and repair
When a bilayer is formed the lipids form structures in water, what do these depend on?
-The type of lipid
-concentration
What are the functional properties of the lipid bilayer?
Selective permeability- The bilayer is permeable to small, nonpolar molecules and some small polar molecules but is impermeable to ions and large polar molecules, requiring transport proteins for their movement.
Assymetry- The two leaflets of the bilayer have different lipid compositions which is critical for functions like cell signalling and membrane trafficking.
What are the physical properties of the lipid bilayer?
-Self assembly- form spontaneously in aqueous environments
-Fluidity- dynamic nature, capable of lateral movement within the plane of the membrane. (influenced by temperature, degree of saturation and cholesterol content)
How does hydrocarbon length influence membrane thickness?
Longer hydrocarbon chains increase the thickness of the lipid bilayer.
Shorter chains result in a thinner and more flexible membrane
How does hydrocarbon length influence fluidity?
Longer chains lead to increased van der waals interactions, reducing membrane fluidity. Shorter chains allow greater fluidity due to weaker tail interactions.
How does hydrocarbon length influence permeability?
Longer chains create a denser hydrophobic core, reducing permeability to polar and small molecules. shorter chains increase permeability by reducing packing density.
How does Hydrocarbon length influence stability?
-Membranes with longer hydrocarbon tails are more thermally stable, as
they have higher melting points.
* Shorter tails lower the melting temperature, making the membrane less
stable at higher temperatures
How does hydrocarbon length influence packing density?
- Longer hydrocarbon chains promote tighter lipid packing in the bilayer.
- Shorter chains result in looser packing, increasing flexibility.
How does unsaturation influence membrane fluidity?
Unsaturated hydrocarbon tails contain double bonds that introduce kinks, preventing tight packing and increasing membrane fluidity.
How does unsaturation influence the phase transition temperature of layer?
Membranes with a higher proportion of unsaturated fatty acids have
lower melting points, remaining fluid at lower temperatures.
* Saturated tails increase the melting point, making the membrane more
rigid at higher temperatures
How does the level of unsaturation influence the adaptation of environmental conditions?
*Organisms in colder environments tend to have more unsaturated fatty
acids to maintain membrane fluidity.
*Saturated fatty acids dominate in organisms in warmer environments to
maintain stability.
How does unsaturation influence the membrane thickness?
Unsaturated tails with kinks reduce the effective thickness of the
bilayer.
* Saturated tails contribute to a thicker, more uniform bilayer
How does unsaturation influence properties of layer?
Unsaturated tails create more spaces in the bilayer, increasing
permeability to small molecules.
Why is cholesterol present in the membrane?
Cholesterol is added to areas
that have lots of unsaturated
lipids to help fill in the gaps
between the tails.
* Helps to stiffen and stabilize the bilayer
– Less fluid
– Less permeable
What is endocytosis?
Endocytosis is a cellular process in which
the plasma membrane invaginates to engulf
extracellular materials, forming vesicles that
transport these substances into the cell. This mechanism allows cells to internalize
nutrients, regulate signaling, and remove
membrane components.
What is pinocytosis?
Non-specific uptake of extracellular fluid and small molecules.
*The plasma membrane invaginates to form small vesicles containing fluid and dissolved substances.
What is exocytosis?
Involves small vesicles, such as exosomes or
microvesicles, that fuse with the plasma
membrane to release their contents.
What is a trans-membrane protein?
Proteins that cross both layers of
the phospholipid bilayer. Cross-membrane with alpha-helices or beta-sheets
What are peripheral proteins?
Proteins that are only on the top half or bottom half of the phospholipid bilayer. Linked by lipids – on either surface of the membrane
What are the functions of transmembrane proteins?
-Transporters
-Linkers
-Receptors
-Enzymes
