Cell boundaries (membranes and walls) Flashcards
What do cell boundaries allow?
Formation of a suitable semi-fluid matrix
Formation of specialized microenvironments
Segregation of harmful activities
Boundary to the outside environment
What is the structure of the membrane?
Sheet-like structures of a phospholipid bilayer and proteins/carbohydrates/sugars in varying quantities
What is one of the most common phospholipids in eukaryotes?
Phosphatidyl choline
What is the structure of phospholipids?
Amphipathic as they contain hydrophilic heads (water-loving) and hydrophobic tails (water-hating)
Hydrophilic heads orientate themselves next to the external environment, with the hydrophilic tails tucked inside.
What is the role of cholesterol in the cell membrane?
Stiffens it and reduces fluidity
RBC have lots of cholesterol as they are not protected by cells in the blood
Replaced by ergosterol in fungi
What is the fluid-mosaic model of the membrane?
Contains integral proteins penetrating the lipid bilayer and peripheral proteins outside linked by non-covalent bonds
Sometimes there are lipid-anchored membrane proteins used as kinases, G-proteins and cell adhesion.
Asymmetrical as scramblase/flippase flip lipids from one layer to the other
How is the membrane linked to its function?
Semi-permeable barrier of solutes and gases allowing small, non-polar and lipid-soluble molecules to pass
Water moves quickly across by osmosis, aided by aquaporins (mainly in root hair cells)
Integral proteins allow for larger, polar and water-soluble molecules to pass across the membrane in active processes (channel/carrier)
Sugar and carbohydrate side chains needed for cell recognition
Flexibility for cell movement and division
What are the different types of cell walls?
BACTERIA - peptidoglycan cell walls
FUNGI - chitin cell walls
PLANTS - cellulose cell walls
What do erythrocytes have instead of a cell wall?
Spectrin - forms a meshwork for support and cell shape connected to the plasma membrane
Others contain collagen to form strong fibres to protect the cell surface from mechanical and chemical damage
