2.3 Transport Across Membranes Flashcards
Role of membrane in rough ER?
Holds ribosomes in place
Forms vesicles to separate protein products from cytoplasm
Role of membrane in mitochondria?
Holds protein/ enzymes in place required for aerobic respiration
Organelle - inner membranes folded into cristae
Role of membrane in lysosome?
Separates hydrolytic enzymes from the cytoplasm (preventing autolysis)
Organelle - vesicle containing hydrolytic enzymes
Role of membrane in nucleus?
Organelle - nuclear pores & nuclear envelope
Control the movement of molecules into and out the nucleus
What are membranes needed for?
Control entry and exit of substances
Contain cell contents and organelles
Compartmentalise individual metabolic processes
Communication with external environment
Site of chemical reactions
Allows cell to change shape
Transport and packaging within a cell
Isolate enzyme that might damage the cell (lysosomes)
What is a phospholipid made up of?
2 fatty acids + glycerol + phosphate
Hydrophilic head + hydrophobic tail
Function of phospholipid?
Allow lipid soluble substances to cross the membrane
Prevent water soluble substances crossing
Fluid layer that allows flexibility
Phospholipid properties?
1) micelles - phospholipids in water, hydrophilic heads attracted, hydrophobic tails repelled so sphere with head pointing out and tails inside
2) liposome - water inside and outside structure, spherical belayer, forms with hydrophilic heads facing outwards and hydrophobic tails inwards
3) bilayer sheet - cytoplasm contains lots of water, tissue fluid surrounding the cell is also mostly water, hydrophilic heads attracted to both and hydrophobic tails repelled by both so bilayer forms
Cholesterol?
Fatty substance
Hydrophobic so pulls together phospholipid tails
Reduces fluidity of membrane (particularly at high temperatures)
Prevents leakage of molecules
Adds strength and some rigidity to membrane (increases stability)
Intrinsic proteins?
Span the membrane and act as a channel and carrier proteins
Extrinsic ?
On the surface of the membrane
Acts as receptor or enzymes
May have carbohydrate bound to them
Glycoproteins?
Carbohydrates bonded to protein
Recognition
Attach to other cells to form tissues
Cell surface receptor (hormones + neurotransmitters)
Glycolipids?
Carbohydrates bonded to lipids
Carbohydrate part extends into extra cellular fluid
Cell surface receptor (i.e. blood group)
Maintains stability of membrane
Attach to other cells to form tissues
Define diffusion
The net movement of molecules or ions from an area of high concentration to an area of low concentration, down its concentration gradient
Does diffusion require energy? What type of process is it?
Does not require energy (other than heat)
Passive process
What is diffusion caused by?
Random movement of particles due to kinetic energy
What are the 4 factors that affect diffusion?
Temperature
Concentration gradient
Surface area
Distance
What is Fick’s law? What do we assume?
Rate of diffusion is proportional to surface area x conc gradient / distance
Assuming temp remains constant
What molecules are affected by facilitated diffusion?
Larger hydrophilic molecules e.g. glucose, amino acids, ions
Repelled by hydrophobic tails of phospholipids
Pass through intrinsic proteins instead
Protein channels?
Water filled hydrophilic channels, allow water soluble ions to pass through
Carrier proteins?
Specific molecules (i.e. glucose) bind to protein, change shape, no external energy required
What type of molecules does simple diffusion diffuse?
Small, lipid soluble, unchanged molecule
E.g. O2, CO2
What type of molecules does facilitated diffusion diffuse?
Channel proteins: small, polar molecules + ions
E.g. Na+, H+
Carrier proteins: larger, lipid insoluble molecules (water soluble)
E.g. glucose, amino acids
How does bilayer formed by phospholipid affect entry of substances in and out of a cell?
Allows movement of lipid soluble/ non polar molecules
Prevents movements of water soluble/ polar
Pass through partially permeable membrane
