BIO 1140 - Cell Membrane Flashcards
What are Cell Membranes?
Cell membranes act as selective barriers
- A living cell is a self-reproducing system of molecules held inside a container
- That container is the plasma membrane
What is the Plasma Membrane?
Plasma membrane is a thin fatty film studded with proteins and coated with carbohydrates
- only membrane for SOME bacteria
- eukaryotes have internal membranes
What is the Function of the Plasma Membrane?
- Receiving information through receptor proteins
- import and export of small molecules through transport proteins
- capacity for movement and expansion
What is the Plasma Membrane involved in?
- cell communication
- import and export of molecules
- cell growth
- motility
What are all Cell Membranes composed of?
All cell membranes is composed of lipids and proteins
- The lipids are arranged in two closely apposed sheets, forming a lipid bilayer
- A type of lipid molecule called phospholipids are the major lipid components of all biological membranes
- Phospholipids have a hydrophilic head and two hydrophobic tails
What is the Major Lipid component of all Biological Membranes?
A type of lipid molecule called phospholipids are the major lipid components of all biological membranes
- Phospholipids have a hydrophilic head and two hydrophobic tails
What is the most common Phospholipid in Biological Membranes?
Phosphatidylcholineis themost commonphospholipid in biological membranes
- The hydrophilic head of phosphatidylcholine is composed of a choline molecule and a phosphate group
- The hydrophobic tails are composed of two fatty acids (14 and 24 carbon atoms)
- Glycerol links the hydrophilic head to the hydrophobic tail
What are Saturated and Unsaturated Hydrocarbons?
The hydrocarbon tail with no double bonds is calledsaturated
The hydrocarbon tail with double bond(s) is calledunsaturated.
What are Amphipathic Molecules?
Molecules with both hydrophilic and hydrophobic parts aretermedamphipathic.
- All membrane lipids are amphipathic
What is a Triacylglycerol?
Triacylglycerol is the main constituents of animal fats and plant oils
- is entirely hydrophobic
What do Phospholipid Bilayers form?
Phospholipidbilayersspontaneously close in on themselves to form sealed compartments
The closed structure is stable because it avoids the exposure of the hydrophobic hydrocarbon tails to water (energetically favourable)
What is the Fluid Mosaic Model?
- Cell membrane is made up of many discrete components.
- membrane structure is mosaic.
- The components can move freely.
- membrane structure is fluid.
What does the Fluidity of a Lipid Bilayer depend on?
The fluidity of a lipid bilayer depends on its lipid composition
- Fluidity decreases at reduced temperatures
- Cholesterol tends to stiffen cell membranes
- Lipid bilayers with unsaturated hydrocarbon tails are more fluid
- Lipid bilayers with shorter fatty acid chains are more fluid
Where is new Membrane synthesized?
New membrane is synthesized in the ER
Where is new Membrane motified?
New membrane is modified in the Golgi membrane
- Certain phospholipids are confined to one side of the membrane
- This asymmetry is preserved during membrane transfer
How are Membranes transported?
Membranes are transported by aprocess of vesicle budding andfusing
- Membranes retain their orientation during transfer between cell compartments
How are Phospholipids and Glycolipids distributed?
Phospholipids and glycolipids are distributed asymmetrically
- Glycolipids are located mainly in the plasma membrane.
- At the plasma membrane they are at the non-cytosolic half of the bilayer
What are Most Membrane Functions carried out by?
Most membrane functions are carried out by membrane proteins
- Plasma membrane proteins have a variety of functions.
What are some functions of Plasma Membrane Proteins?
- Transporter
- Ion Channels
- Anchor
- Receptors
- Enzyme
What are the Two Types of Membrane Proteins?
- Integral Protein: extend through the lipid bilayer (transmembrane, associated with the lipid monolayer, or lipid-linked)
- Peripheral Protein: interact with integral membrane proteins or phospholipids
How can Integral Proteins be removed?
Integral proteins can be removed only by disrupting the bilayer withdetergents
What is the distribution of Membrane Proteins?
The distribution of membrane proteins is asymmetrical
What is a Transmembrane Protein?
An integral protein that extends all the way through the phospholipid bilayer is called a transmembrane protein.
How do Cells confine particular proteins to localized areas?
Cells can confine particular proteins to localized areas by:
- binding the meshwork of proteins inside the cell (cell cortex)
- binding extracellular matrix molecules
- binding proteins on the surface of another cell
- restricted by diffusion barriers.
What are Membrane Domains?
They can create functionally specialized regions called membrane domains.
What is the Plasma Membrane reinforced by?
The plasma membrane Is reinforced by the underlying cell cortex
- Cell membrane by itself is extremely thin and fragile.
- Cell membranes are supported by a framework of proteins called the Cell Cortex
What is the Glycocalyx?
All of the carbohydrate on the glycoproteins, proteoglycans, and glycolipids is located on the outside of the plasma membrane
- This sugar coating is called the carbohydrate layer or glycocalyx
What is the Function of Glycoproteins & Proteoglycans?
The carbohydrates of glycoproteins and proteoglycans often function in cell recognition and adhesion.
What do Cell Surface Carbohydrates allow?
Cell surface carbohydrates allow:
- cell adhesion
- neutrophils migration at sites of infection
What are the Three Types of Cell Junction?
- Tight Junction
- Desmosomal Adhesion
- Gap Juncrion
What is Tight Junction?
Protein complex between two cells that creates a seal to prevent substances from moving through the spaces between cells
- cells lining the bladder have tight junctions so urine cannot leak out into the body cavity
What are Desmosomes?
Desmosomes hold neighboring cells firmly together, acting like spot welds or rivets
- Localized spot-like adhesions
- Materials can still move around in the extracellular matrix
- This provides mechanical stability for tissues such as skin that receive physical stress
- Randomly arranged on the lateral sides of the cell
What are Gap Junctions?
Gap junctions are channels that run between membrane pores in adjacent cells, allowing substances to pass
between cells
- allow the rapid spread of electric current (mediated by ions) so the heart muscle cells beat in unison
