Biological Membranes Flashcards
What is a partially permeable membrane?
selectively permeable
A membrane where some substances pass freely in and out of the cell while others are controlled selectively.
What is compartmentalisation?
The formation of separate membrane-bound areas.
What are some of the roles of membranes? (9)
Isolate harmful enzymes in lysosomes.
Form vesicles to transport molecules around the cell.
Provide a large SA for enzymes to occupy.
Permit cell recognition by the immune system.
Allow cell signalling (hormones).
Form microvilli for absorption.
Help cells to attach forming tissues.
Protect cells from external environment.
Compartmentalise the cytoplasm of cells.
Allow formation of concentration gradients.
How is the phospholipid bilayer formed?
Phospholipids have polar hydrophilic heads and 2 non-polar hydrophobic tails. This causes them to form membrane structures as a bilayer with the hydrophobic tails facing inwards.
What is the fluid mosaic model?
Membranes can be described as a fluid mosaic of different molecules that perform different functions and are constantly moving.
What are the roles of phospholipids in the membrane?
Allow lipid-soluble substances to enter/leave cell.
Prevent water-soluble substances passing through.
Give the membrane fluidity.
What is the role of cholesterol in the membrane?
Reduces lateral movement of phospholipids, making the membrane less fluid at high temperatures. This helps prevent the leakage of water and dissolved ions from the cell.
(Maintains fluidity).
What are the roles of proteins in the membrane?
Provide structural support.
Intrinsic proteins can be carrier or channel proteins, transporting water-soluble substances and large molecules.
Function as enzymes.
Form ion channels.
What is the role of glycolipids in the membrane?
(Antigens)
Act as recognition sites allowing self-recognition.
What is the role of glycoproteins in the membrane?
Act as recognition sites for hormones and neurotransmitters.
Act as binding sites for drugs.
Help cells attach to one another, forming tissues.
How can a membrane be interrupted?
A solvent or heat causing the phospholipid bilayer to lose its structure.
How can a solvent cause interruption of a membrane?
Phospholipids are soluble in solvents less polar than water (organic solvents) such as alcohol or detergent. This disrupts the structure of the bilayer, affecting permeability.
How can temperature cause a membrane to be interrupted?
Molecules have greater kinetic energy, so the membrane becomes more fluid. At high temperatures, the bilayer loses its structure becoming more permeable. Also, intrinsic proteins denature, disrupting the membrane.
What are factors that increase the rate of diffusion through a membrane? (7)
Steeper concentration gradient. Shorter diffusion pathway. More pores (channel/carrier proteins). Smaller molecules diffuse faster. Fat soluble (non-polar molecules) diffuse faster. Higher temperatures. Greater surface area.
Which molecules cannot pass through a phospholipid bilayer via diffusion?
Large/Hydrophillic molecules.
Which molecules can pass through a phospholipid bilayer via diffusion?
Small/Hydrophobic molecules.
