B2.1 Membranes and membrane transport Flashcards
lipid bilayers structure
phospholipids - 2 layers
hydrophobic tail
hydrophobic head
what are phospholipids known as
having both hydrophilic and hydrophobic parts - amphipathic
phosphate head of phospholipid
polar and therefore soluble in water (hydrophilic)
fatty acid tail of a phospholipid
nonpolar and therefore insoluble in water (hydrophobic)
phospholipid monolayer formation
phospholipids are placed in water
hydrophilic phosphate heads go towards the water
hydrophobic hydrocarbon tails go away from the water
monolayer
1 layer
bilayer
2 layers of phospholipids
lipid bilayer barriers - large molecules
Large molecules cannot pass through the barrier as the hydrophobic region is tightly packed and has low permeability to larger molecules
lipid bilayer barriers - polar molecules and ions
Polar molecules and ions cannot pass through the hydrophobic tails of the phospholipid structure
The hydrophilic nature of these molecules and ions means that they will not interact with the hydrophobic fatty acid tails of the phospholipids
lipid bilayer barriers - in general
The bilayer forms an effective barrier so that it is able to control which molecules pass through and out of the cell
Integral protiens
- partially hydrophobic
- embedded in the phospholipid bilayer
- can be embedded across both layers or just one layer
peripheral proteins
- attached to the surface of the bilayer
- hydrophilic
- inside or outside
increasing of diffusion rate
- increase in temp
- increase in surface area
- increase in distance
simple diffusion
- random continuous net movement of a molecule from a region of higher concentration to a region of lower concentration
Membrane protein function
transport, receptors, cell adhesion, cell-to-cell recognition and immobilized enzymes
transport protein
function
Transport proteins allow ions and polar molecules to travel across the membrane
Channel proteins
form holes, or pores, through which molecules can travel
Carrier proteins
change shape to transport a substance across the membrane, e.g. protein pumps and electron carriers
Receptors
- binding of peptide hormones, e.g. insulin
- The binding generates a signal that triggers a series of reactions inside the cell
Immobilised enzymes
integral proteins with the active site exposed on the surface of the membrane
Cell adhesion
Cell adhesion allows cells to attach to neighbouring cells within a tissue
Cell-to-cell recognition
cell’s ability to distinguish one type of neighboring cell from another.
occurs when complementary molecules on opposing cell surfaces meet.
Glycocalyz (protein + lipid) act as cell markers, or antigens, for cell-to-cell recognition
molecules that move by simple diffusion
oxygen
co2
Osmosis
net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane
Facilitated Diffusion
movement of water down concentration gradient - movement assisted by protiens and is passive
examples of substances that use Facilitated Diffusion
Large molecules
Polar molecules
Ions
Active Transport
The movement of molecules and ions across a cell membrane, from a region of lower concentration to a region of higher concentration, using energy from respiration
requires carrier proteins
active transport helps to
- take up essential nutrients
- remove waste materials from the cell
- maintain right concentration of ions in cells
2 types of active transport
direct and indirect
direct active transport
energy released by an exergonic reaction like the breakdown of atp
indirect active transport
movement of one solute down its concentration gradient drives the movement of the second solute against its concentration gradient
ATP
adenosine triphosphate
ADP
adenosine diphosphate
Selective Permeability
ability of the membrane to differentiate between different types of molecules, only allowing some molecules through while blocking others
achieved through diffusion and active transport
Glycoproteins
are cell membrane proteins that have a carbohydrate chain attached on the extracellular side
Extracellular = outside cells
Glycolipids
lipids with carbohydrate chains attached, also located on the outer surface of cell membranes
The function of glycoproteins and glycolipids
The carbohydrate chain enables them to act as receptor molecules
This allows them to bind with substances at the cell surface
Membranes
Membranes form partially permeable barriers between the cell and its environment, between cytoplasm and organelles and also within organelles
Membranes play a role in cell signalling by acting as an interface for communication between cells
Fluid mosaic model components
Phospholipids
Cholesterol
Glycoproteins and glycolipids
Integral and peripheral proteins
fluid mosaic model explains
- how biological molecules are arranged to form cell membranes
- Passive and active movement between cells and their surroundings
- Cell-to-cell interactions
- Cell signalling
Why is the mosaic model fluid
No bonds
Attraction to eachother but not strictly tied in place
what do carbohydrates do in membranes
help with cell recognition and cell adhesion
highly hydrophilic and attracts large amounts of water
what are aquaporins
a water channel pore in a membrane that allow water to diffuse through the plasma membrane
is a protein
what is facilitated diffusion detailed
particles of a substance that cannot diffuse across the plasma membrane are helped across the membrane by integral proteins that span the membrane
functions of peripheral proteins
shuttles between integral proteins
scaffold proteins that hold shape
receptors for extra cellular signals
