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Biology - Cell Membranes and Transport
Terms in this set (77)
artificially prepared membrane-bound compartments (vesicles)
How are liposomes prepared?
break up biological membranes into pieces; these re-seal themselves into balls resembling empty cells (smaller); surrounded by phospholipid bilayer, with aqueous interior
What are liposomes used for?
artificial models of cells, medical application, deliver drugs, provide safe way of delivering staurosporine, deliver skin care products (aloe vera, collagen, elastin) when rubbed on skin, delivery of food supplements by mouth (high absorption rates)
How are liposomes used to deliver drugs?
1. liposomes is made while in a solution of the drug (drug is inside liposome)
2. liposome introduced into the body
3. reaches target cell (cancer cell or other diseased cell)
4. fuses with the cell surface membrane and delivers the drug inside the cell
How can precise targeting be achieved with drug delivering?
insert a correct recognition molecule (antigen or antibody) into liposome membrane
What is staurosporine?
powerful anti-cancer drug that kills any cells that it comes into contact with because it interferes with several cell signaling pathways
How can liposomes provide a safe way of delivering staurosporine?
disguising agents are added to the outer surfaces of liposomes carrying the drug which hide the drug from the immune system and allows it to target cancer cells only
What is the cell surface membrane?
thin membrane that controls the exchange of materials such as nutrients and waste products between the cell and its environment
What are some functions of membranes?
regulation of transport,
enable cells to receive hormone messages
What do phospholipids form?
cells and organelles
What are cells and organelles?
little bags that can be formed by phospholipids inside which chemicals can be isolated from the external environment
What happens if phospholipid molecules are spread over the surface of water?
form a single layer with their hydrophilic heads in the water, and their hydrophobic tails projecting out of the water
What parts of a phospholipid are hydrophobic/hydrophilic?
The head is hydrophilic (polar), tails are hydrophobic (nonpolar)
What does polar mean?
uneven distribution of charge that occurs in some molecules
What are micelles?
stable ball-like structures of phospholipids where the hydrophilic heads face outwards into the water, shielding the hydrophobic tails that point in towards each other
How are micelles formed?
when phospholipids are shaken up with water
What are bilayers?
two-layered structures that can form in sheets when phospholipids are shaken up with water
What happens when phospholipids are shaken up with water?
they can form micelles of bilayers
What is the basic structure of membranes?
What does the double black line of the phospholipid bilayer visible during electromicrographs show?
the hydrophilic heads of the two phospholipid layers
What is the pale zone of the phospholipid bilayer?
hydrophobic interior of the membrane
How wide is the phospholipid bilayer?(thickness of membrane)
Do membranes contain proteins?
What is the origin of the fluid mosaic model?
created by Singer and Nicolson in 1972. model that describes membrane structure; Fluid = phospholipids and proteins can move about by diffusion; mosaic = pattern produced by the scattered protein molecules when the membrane surface is viewed from above
How do phospholipids move?
move sideways in their own layers
What kind of fluidity does the phospholipid bilayer?
that of olive oil
How do protein molecules move about within the phospholipid layer?
like icebergs in the sea (others remain fixed to structures inside or outside the cell)
What are the features of the fluid mosaic model?
membrane is a bilayer of phospholipid molecules; tails point inwards creating a nonpolar hydrophobic interior, heads face the aqueous medium surrounding the membrane
How do the phospholipid molecules move in the bilayer?
move about by diffusion within their own monolayers
Are phospholipid tails saturated or unsaturated?
The more unsaturated the phospholipid tails are --
the more fluid the membrane because the unsaturated fatty acid tails are bent and therefore fit together more loosely
What determines the fluidity of the membrane?
saturation and tail length
The longer the phospholipid tail --
the les fluid the membrane
What happens to the membrane as temperature decreases?
membranes become less fluid, some organisms that cannot regulate their own temperature increase the proportion of unsaturated fatty acids in membranes
What are intrinsic proteins/integral proteins?
proteins found embedded within the membrane; found in the inner layer, the other layer
What are transmembrane proteins?
integral proteins that span the whole membrane; hydrophobic regions that cross membrane are made up of 1+ alpha-helical chains
What is the structure of intrinsic proteins?
hydrophobic and hydrophilic regions
Why do intrinsic proteins stay in the membrane?
1. the hydrophobic regions (made of hydrophobic amino acids) are next to the hydrophobic fatty acid tails and are repelled by the watery environment either side of the membrane
2. the hydrophilic regions (made from hydrophilic amino acids) are repelled by the hydrophobic interior of the membrane and face into the aqueous environment inside or outside the cell, or line hydrophilic pores which pass through the membrane
What is the location of intrinsic protein molecules?
- some float like mobile icebergs in the phospholipid layers
- some fixed like islands to structures inside or outside the cell and do not move about
What are extrinsic proteins/peripheral protein?
protein found on the inner or outer surface of the membrane;
What is the location of extrinsic proteins?
many bound to intrinsic proteins, some are held by binding to molecules inside or outside the cell, or to phospholipids
What are glycoproteins?
proteins that have short, branching carbohydrate chains attached to that side of the molecule which faces the outside of the membrane
What are glycolipids?
lipids that have short, branching carbohydrate chains attached to that side of the molecule which faces the outside of the membrane
What is found in the cell surface membrane?
phospholipids, intrinsic and extrinsic proteins, glycoproteins, glycolipids, and cholesterol
What are the three types of lipid called?
phospholipids, cholesterol, glycolipids
Why is it hard for polar molecules or ions to pass through membranes?
the non polar tails of phospholipids act as a barrier to most water soluble substances
(sugar, amino acids, proteins cannot leak out of cell, unwanted water-soluble molecules cannot enter)
What happens when phospholipids are modified chemically to act as signaling molecules?
1. may move about in bilayer, activating other molecules such as enzymes
2. can be hydrolyzed to release small, water-soluble, glycerol-related molecules that diffuse through the cytoplasm and bind to specific receptors
How do phospholipids bring about exocytosis of digestive enzymes from pancreatic cells?
it causes the release of calcium ions from storage in the ER which causes exocytosis
What is cholesterol?
relatively small molecule that has a hydrophilic head and a hydrophobic tail so that they can fit neatly between phospholipids with their heads at the membrane surface
Cell surface membranes in animal cells contain _____________cholesterol as phospholipid.
almost as much
How common is cholesterol in plant cell membranes and prokaryotes?
less common, absent respectively
What does cholesterol do at low temperatures?
increases the fluidity of the membrane and prevents it from becoming too rigid; caused because it prevents close packing of phospholipid tails
What does increased fluidity (from cholesterol) do for the cell?
cells can survive colder temperature
At high temperatures, what do cholesterol and phospholipids interact for?
their interaction helps stabilize cells at higher temperatures when the membrane could otherwise become too fluid
What is cholesterol's function?
- increase fluidity of membrane at low temperature to help cells survive colder temperatures
- stabilize cells at higher temperatures
- mechanical stability of membranes (otherwise it would quickly break and cell would burst open)
- hydrophobic regions of cholesterol prevent ions or polar molecules from passing through membrane
Why is cholesterol important in the myelin sheath?
because the hydrophobic regions of cholesterol molecules help prevent ions and polar molecules passing through the many layers of cell surface membranes of the sheath, where leakage of ions would slow down nerve impulses
What is the significance of the carbohydrate chains of glycolipids and glycoproteins?
they project into the watery fluids surrounding the cell where they form hydrogen bonds with water molecules which helps stabilize the membrane structure; they help the glycoproteins/glycolipids act as receptor molecules that bind with particular substances at the cell surface
What is the glycocalyx?
a sugary coating to the cell formed by carbohydrate chains
What is the glycocalyx formed by in animals?
What is the glycocalyx formed by in plants?
What receptors are on cells?
different cells have different receptors depending on their function
How many major groups of receptor are there?
signaling receptors, receptors involved in endocytosis, receptors involved in cell adhesion
What are signaling receptors?
group of receptors that are part of a signaling system that coordinates the activities of cells and recognize messenger molecules
What are messenger molecules?
What are neurotransmitters?
chemicals that cross synapses which allow nerve impulses to pass form one cell to another
What happens when a messenger molecule binds to a receptor?
a series of chemical reactions are triggered inside a cell
Example of signaling receptor
glucagon receptor in liver cells (cells that do not have glucagon receptors are not affected by glucagon)
What do the receptors involved in endocytosis do?
bind to molecules that are parts of the structures to be engulfed by the cell surface membrane
What do the receptors involved in cell adhesion do?
bind cells to other cells in tissues and organs of animals
How do glycolipids and glycoproteins act as cell markers or antigens?
each type of cell has it own type of antigen (ABO blood group antigens are glycolipids and glycoproteins that have a small difference in their carbohydrate portions)
What are transport proteins?
provide hydrophilic channels or passageways for ions and polar molecules to pass through the membrane
What are the two types of transport protein?
channel proteins and carrier proteins
Each transport protein is ______ for a particular kind of ion or molecule.
specific (so the types of substances that enter or leave the cell can be controlled)
Membrane proteins can be
enzymes, transport proteins, receptor molecules, cytoskeleton attachments
What do the digestive enzymes in the cell surface membranes in the small intestine do?
catalyze the hydrolysis of molecules like disaccharides
What do the proteins attached to the cytoskeleton do?
help maintain and decide the shape of the cell and be involved in changes of shape when cells move
What roles do proteins play in membranes of organelles?
involved in the processes of respiration and photosynthesis in the membranes of mitochondria and chloroplasts
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