Biological Membranes Flashcards
What are the 5 roles of membranes?
-Compartmentalisation
-Site of chemical reactions
-Allows exchange of molecules
-Cell signalling
-Vesicle formation
Why is the fluid mosaic model used to describe plasma membranes?
-FLUID - phospholipid molecules are constantly moving relative to each other
-MOSAIC - there are multiple proteins embedded within the bilayer in pattern
What is the role of carrier proteins?
They are usually involved in active transport, and occasionally facilitated diffusion. They change shape to allow specific molecules through.
What is the role of channel proteins?
They allow molecules to pass through the membrane in facilitated diffusion. They do not change shape (don’t use ATP)
What are integral proteins?
Chanel proteins and carrier proteins are both examples. They span the width of the bilayer and allow the passage of large / hydrophilic / charged particles.
What are extrinsic proteins?
Proteins that do not span the bilayer. They are involved in chemical reactions.
What are glycoproteins?
They act as receptors for specific molecules, have a role in cell signalling, act as surface antigens
What effect does temperature have on membranes?
-At low temperatures the phospholipids have little KE so they move slowly meaning the bilayer is not very fluid
-As the temperature increases, the phospholipids gain KE so more faster so they fluidity of the bilayer increases.
-If the temperature gets too high, the proteins in the bilayer denature and large gaps will appear.
What effect do solvents have on membranes?
-Solvents such as ethanol can diffuse directly across the phospholipid bilayer as it is non-polar.
-It can also insert its self in between phospholipids which creates large gaps in the bilayer.
-This means water can flood into cells and burst them
What is the definition for diffusion?
Diffusion is the passive movement of small molecules or lipid soluble molecules across a phospholipid bilayer down a concentration gradient
What is the definition for facilitated diffusion?
Facilitated diffusion is the transport of ions and large polar molecules across the phospholipid bilayer from an area of higher concentration to an area of lower concentration that pass through proteins not phospholipids.
What is the definition for active transport?
The movement of molecules across the cell membrane up the concentration gradient, requiring energy and carrier proteins
What are endocytosis and exocytosis both examples of?
Bulk transport
What is exocytosis and how does it happen?
Movement of molecules out of the cell.
A vesicle fuses with the plasma membrane and releases its contents. The vesicle then becomes part of the cell membrane
What is endocytosis?
Movement of molecules into the cell
