Lecture 15: Membranes Flashcards
Functions of the biological membranes are? (6)
- Define cell boundary - PM specific
- Define enclose compartments
- Control movement of material into and out of cell/organelles - PM specific
- Allow response to external stimuli. - PM specific
- Enable interactions between cells - PM specific
- Provide scaffold for biochemical activities
Biological membranes are _______ structures
Semi-permeable
(Control what goes in and out)
Energy production is done by which two organelles?
Mitochondria and chloroplast (photosynthesis)
Biological membranes are ________ structures
Trilaminar (3 layers)
Membranes are _____
Lipid bilayers
The lipid bilayer is made up of?
Phospholipids
In the phospholipid bilayer, there are many ____ embedded
Proteins
Fluid mosaic model is?
Fluid - components are mobile
Mosaic - diverse proteins, carbs, cholesterol, components can interact
Outer leaflet faces?
Exterior of the cell
Inner leaflet faces?
Cytosol, or inside of the structure
Biological membranes consist of ?
Outer leaflet and Inner leaflet
Phospholipid structure consists of?
Glycerol backbone bound by two non-polar fatty acrylic molecules (FA chains) and a polar head group linked by phosphate residue
Phospholipids are amphipathic..?
Hydrophilic - attracted to water
Hydrophobic - repelled by water
Hydrophilic part of phospholipid is?
Polar head
Hydrophobic part of phospholipid is?
FA tails
Types of phospholipids with different heads (4)
Ethanolamine
Choline
Serine
Inositol
If thrown in water, phospholipids will…?
Spontaneously aggregate to bury their hydrophobic tails in the interior and expose their hydrophilic heads to the water
Where do phospholipids come from?
Synthesis occurs in multistep process at cytosol and outer endoplasmic reticulum membrane - ER membrane contains all enzymes for synthesis and distribution
What are the three classes of membrane proteins?
- Integral
- Peripheral
- Lipid-anchored
Membrane protein - Integral
Span the lipid bilayer, parts of proteins exposed to one side of membrane and another part that is also on the other side, (sticks out of both side), can be transport proteins
Membrane proteins - Peripheral
Associate with surfaces of the lipid bilayer, do not interact with the membrane itself but interact with other proteins or other objects integrated in the membrane itself
Membrane proteins - Lipid anchored
Attach to a lipid in the lipid bilayer, integrate into one of the leaflets
Functions of membrane proteins (3)
- Transport of nutrients and ions
- Cell-cell communication (gap junction) (pores)
- Attachment
Dynamic of plasma membrane
(Lateral shift) Lipids move laterally, easily, within leaflet
(Transverse diffusion) Lipids movement between leaflets is difficult and slow
Dynamics of proteins in the biological membranes
Diffuse within the bilayers, movement is restricted, diffusion is slow, rapid movement is spatially limited
Modifications to allow proteins to move
Structure of biological membranes (4)
- 6nm thick
- Stable
- Flexibke
- Capable of self assembly
Biological membrane - mitochondria
- inner membrane of mitochondria have very high concentration of proteins to make ETC and ATP synthesis
Biological membrane - neuronal cells
- myelin sheath - consists of layers of plasma membrane wrapped around neurons axon, provides insulation and increases speed
- myelin sheaths have ow amounts of protein
Symmetry of biological membranes is _______
Asymmetrical
The two leaflets of a membrane are _____
Distinct
Leaflet distinction
- Distinct lipid composition
- Outer leaflet contains glycolipids and glycoproteins (sugar molecules)- attach to proteins and phospholipids
- Glycolipids and glycoproteins - tells cell where to move to, glycosylation event, allows proteins to binds and perform certain functions
How does temperature affect the fluidity of biological membranes? (2)
- warming increases fluidity - fluid like
- cooling decreases fluidity - gel
Membrane fluidity is determined by nature of _____ in membrane
Lipids
(Double bonds - Kinks) Unsaturated lipids ____ _____
Increase fluidity
(Single bonds) Saturated lipids _____ ______
Reduce fluidity
Balance between rigid and disordered structure allows (3)
- mechanical support and flexibility
- membrane assembly and modification
- dynamic interactions between membrane components
What modulate membrane fluidity?
Cholesterol
How does cholesterol regulate membrane fluidity?
- bidirectional
- at high temp, stabilizes membrane and raises melting point
- at low temp, intercalates between phospholipids and prevents from clustering together and stiffening
Cholesterol impacts (3)
- alter packing and flexibility of lipids
- if added to a liquid crystal membrane, fluidity will decrease
- if added to crystalline gel membrane, fluidity will increase
