Plasma Membranes Flashcards
What is the purpose of plasma membranes at the surface of cells?
Separation of cell contents from the environment
Cell recognition & signalling
Regulating the transport of materials in and out of cells
What is the purpose of plasma membranes within cells?
Isolate the contents and therefore metabolic pathways of the cell
Provides a site for the attachment of enzymes
Provide selective permeability
Creation of concentration gradients
Explain the term cell signalling
The process that leads to coordination and communication between cells
example:
hormones binding to their receptors on cell surface membranes to trigger a response inside the cell
Role of membrane bound receptors in terms of hormones and drugs
Hormones: Target cells have receptors that are complimentary to the hormone = bind
Drugs: Bind to receptors
such as antipsychotics
What is meant by the fluid-mosaic model
A bilayer of phospholipids forms the main layer
Various proteins are embedded in the bilayer - some are partially embedded (extrinsic) where some span the membrane (intrinsic)
Role of phospholipids in plasma membranes
Hydrophobic head & hydrophilic fatty acid tail
From the bilayer separating the inside and outside of the cell
Fluid - components can move around with ease
Act as a barrier (partially permeable) - select what goes in and out (small, non polar molecules)
Role of cholesterol in plasma membranes
Stability - sits between phospholipids’ fatty acids
Prevent molecules like water and ions passing through
Role of glycolipids in plasma membranes
Phospholipids that have a carbohydrate part attached
Cell signalling
Cell surface antigens
Cell adhesion
Role of proteins in plasma membranes
Channel proteins = small polar molecules can move in and out
Carrier proteins = actively move substances across the cell surface membrane
Role of glycoproteins in plasma membranes
Protein molecules with a carbohydrate part attached
Act as antigens
Cell signalling
Receptors for hormones
Receptors on transport proteins to trigger movement
All cell adhesion (hold tissues together)
Attach to water molecules to stabilise the membrane
How does increasing temperature effect plasma membranes
more kinetic energy,
membrane becomes leaky,
molecules that would not normally be able to can move in and out of cell,
membrane structure is disrupted,
proteins are denatured,
membrane more permeable.
What is diffusion & link to plasma membranes
net movement of molecules from a region of high concentration to an area of lower concentration down a concentration gradient
small, non polar molecules can diffuse through the phospholipid bilayer.
What is facilitated diffusion in terms of plasma membranes
Large, polar molecules need to be transported across the phospholipid bilayer but cannot just diffuse across.
Channel proteins only allow certain ions through
example: aquaporins only allow water through.
Carrier proteins are complimentary, once a molecules enters the proteins changes shape to allow the molecule to the other side
What is active transport & link to plasma membranes
The movement of molecules across membranes using ATP against a concentration gradient
Mineral ions moving into root hair cells
Hydrogen ions moving out of companion cells
Mineral ions moving across the endodermis
Movement of sucrose out of sieve tube at the sink
Endocytosis
Active transport of large quantities of a substance into a cell, using ATP
