Plasma Membrane: Composition & Functions Flashcards
What are the main functions of the cell membrane?
- boundary that separates the living cell from its surroundings
-Essential for all cells
-A barrier to prevent the contents of the cell from escaping and mixing with molecules in the surrounding environment (e.g. nutrients must pass inward, waste products must move out)
-exhibits selective permeability, allowing some substances to cross it more easily that others
- protection/support to the cell, regulating its shape
In Eukaryotic cells, inner membranes allow what?
-the compartmentalisation of individual organelles (specific composition for specific reactions)
Diagram of Bacterial and Eukaryotic cell membrane?
Cell membranes are composed of what?
different kinds of lipids and proteins (different functions) and share a common general structure
What is a lipid bilayer?
-lipids are arranged in two closely apposed sheets, forming a lipid bilayer, in which proteins are embedded and some carbohydrates
What are Phospholipids?
-(phosphoglycerides) are the most abundant lipids in the plasma membrane arranged in two-layer sheets (phosphatidycholine is the most abundant)
-Phospholipids are amphipathic, containing hydrophobic and hydrophilic regions
What does amphipathic mean?
What does hydrophobic mean?
-Their hydrophobic (’water repellent’) tails are arranged inwards, to shield water and form a sealed comportment
What does hydrophilic mean?
-The Phosphate group or other hydrophilic (’waterloving’) heads are arranged to face outwards, exposed to the aqueous solutions
Hydrophillic and Hydrophobic diagram?
What is the Fluid Mosaic?
- dynamic and complex structure of the plasma membrane
What are the components of the mosaic ?
-phospholipids, Glycolipids, sterols (cholesterol in mammalian cells) and various proteins and glycoproteins are contained.
Fluidity of a lipid bilayer depends on what?
-its composition
What can a lipid molecule do?
-2-dimensionally move along the plane of the bilayer
What is a Glycoprotein?
-A protein with a carbohydrate attached
What is a Glycolipid?
-A lipid with a carbohydrate attached
Phospholipids movements can lead to what?
-Rapid lateral diffusion of lipid molecules within the plane of each monolayer
- Spin in place (rotation -up to 500 revolutions per second)
- Flexion: contraction movement
- Flip-flop from a side to the other (very rarely)
-Proteins (usually do not move and they are anchored to the cytoskeleton)
- Only some proteins can slightly and slowly move driven by the motor proteins
Diagram of Phospholipids movements?
Other lipids of the plasma membrane ?
-Cholesterol (only in animal cell membranes), and glycolipids are also amphipathic
- Cholesterol (20% of the membrane lipids) modulates the membrane fluidity and improving its stability
- Stiffen the membrane (less flexible and less permeable). Reducing molecules passage
Other lipids of the plasma membrane diagram?
What are Glycolipids?
-lipids containing sugars representing their hydrophilic head. Sugar groups always facing the cell exterior (The bilayer is asymmetrical)
What are membrane Proteins?
–synthesised in the rough ER, (secretory pathway)
- Most are trans-membrane / integral membrane proteins, crossing the membrane
-They are amphipathic
-Hydrophobic regions (non-polar amino acids), often coiled into alpha helices, lie in the interior of the bilayer
-Hydrophilic regions of amino acids are exposed to the external aqueous environment.
- Other proteins are embedded in the membrane, exclusively on the cytosolic
- Or peripheral membrane proteins, on either side of the membrane and covalently attached to membrane lipids or other integral membrane proteins.
Extracellular Space diagram?
What are the functions of membrane proteins?
- Transport of molecules
-Protect the cell surface from mechanical damage and involved in cell-to-cell communication
- Enzymatic activity
- Signal transduction/cell communication
- Structural support/Attachment to the extracellular matrix (ECM)
Most membrane proteins are what?
-Glycoproteins
Glycoproteins/ membrane proteins are what?
-short chains of sugars linked to amino acids (facing extracellular space)
What is Protein glycosylation?
-post-translational modification in Rough ER and Golgi apparatus