B2.1 Membrane and Membranes Transport Flashcards
what are amphipathic membranes
Molecules that have both hydrophilic and hydrophobic parts
examples of other amphipathic molecules
Other amphipathic molecules besides phospholipids are some of the proteins like integral proteins
example of simple diffusion across membranes
movement of oxygen and carbon dioxide molecules between phospholipids
Both oxygen and carbon dioxide are small and uncharged molecules
Diffusion of these gases move from a high concentration area to a low concentration area
Oxygen and carbon dioxide can diffuse across the plasma membrane to carry out gas exchange in between the cell and the surrounding environment. This can also be carried out in the alveoli of the lungs and gill filament of different animals. Plant cells can also have diffusion of these gases for photosynthesis and respiration
integral proteins
a kind of membrane protein that is anchored in the plasma membrane with amphipathic nature. It has both a hydrophilic (interacting with the phosphate groups of the membrane) and a hydrophobic (interacting with the hydrophobic tails of the membrane)
Structure of Phospholipids
Consist of a polar hydrophilic head composed of a glycerol and a phosphate molecule
Consist of two non-polar hydrophobic tails composed of fatty acid (hydrocarbon) chains
Because phospholipids contain both _hydrophilic (water-loving) and lipophilic (fat-loving) regions, they are classed as amphipathic.
Arrangement of the Phospholipid Bilayer
Phospholipids spontaneously arrange into a bilayer
The hydrophobic tail regions face inwards and are shielded from the surrounding aqueous fluids, while the two hydrophilic head regions associate with the cytoplasm and extracellular fluids respectively
types of proteins
hormone-binding
enzymatic
cell adhesion
cell-to-cell communication
channel forming
pumps for active transport
hormone-binding
these proteins have specific shapes exposed to the exterior that fits the shape of specific hormones. the attachment between the protein and the hormone causes a change in the shape of the protein, which results in a message being relayed to the interior of the cell
enzymatic
these proteins occur on either the interior or the exterior membrane surface. they are often grouped together so that a sequence of metabolic reactions, called. metabolic pathway, is catalyzed
cell adhesion
this protein type allows temporary or permanent connections called junctions between cells. there are two types of junctions, gap junctions and tight junctions
cell-to-cell communication
most of these proteins have carbohydrate molecules attached. They provide an identification label so that organisms can distinguish between self and non-self material
channel forming
some proteins span the membrane, providing passageways for substances to be transported through
pumps for active transport
in active transport, proteins shuttle a substance from one side of the membrane to another by changing shape. This process requires the expenditure of energy in the form of adenosine triphosphate (ATP)
channel proteins
channel proteins exist to transfer large or polar substances, e.g. water
aquaporin
A type of integral proteins to allow water molecules to pass through the plasma membrane
The middle part of this protein allows water to go through but not for charged ions or solutes
cell junctions
tight junctions
desmosomes
gap junctions
tight junctions
impermeable junctions
prevent molecules from passing through intercellular space
e.g. lining of the digestive tract
desmosomes
anchoring junctions bind to adjacent cells like Velcro
form internal tension-reducing network of fibers; plaques on surface of membrane attach to protein filaments
e.g. found in tissues subject to stress like skin; heart muscle
gap junctions
allow for intercellular communication
allow ions and small molecules to pass through channels formed by connexon protein cylinders
e.g. found in electrically excitable tissue (heart; smooth muscle) to synchronize
simple diffusion
substances moving from a high concentration gradient to a low concentration gradient
hypertonic
net flow of water out of the cell, the cell loses volume
isotonic
no net water movement
hypotonic
lower concentration of solute than another solution
plasmolyzed
plasma membrane and cell wall separate
cytosol
fluid part of cytoplasm
cytoplasm
consists of all the organelles
cholesterol
Cholesterol is a component of animal cell membranes.
Cholesterol functions to immobilise the outer surface of the membrane, reducing fluidity.
It makes the membrane less permeable to very small water-soluble molecules.
active transport
Active transport
Exocytosis
Endocytosis
passive transport
Diffusion
Facilitated diffusion
Osmosis
Facilitated diffusion
the net movement of charged particles from a region of high concentration to a region of low concentration through protein channels
Osmosis
net movement of water molecules from a region of high water potential to a region of low water potential through a semipermeable membrane.
Water potential (trident w)
a measure of potential energy per unit volume in water
Active Transport
the movement of particles from a region of low concentration to a region of high concentration using protein pump and ATP
Indirect active transport
uses the energy produced by the movement of one molecule down a concentration gradient to transport another molecule against a gradient.
E.g. Sodium-dependent glucose transporter / Sodium-glucose linked transporter (SGLT)
Sodium-glucose linked transporter (SGLT)
- There are more Na+ ions outside the intestinal cells
- Na+ and glucose bind to the transport protein
- Na+ pass through the carrier to the inside of the cell down a concentration gradient, with the carrier capturing the energy released by this movement
- Using the energy from the transportation of the Na+, glucose is pumped as well.
- The captured energy is used to transport the glucose through the same protein into the cell.
Exocytosis
The export of substances using vesicles and energy
Furthermore, as the vesicles are made of phospholipids, it can fuse with the membrane when carrying out exocytosis.
E.g. Exporting extracellular protein(the protein is first made in the rER, then using vesicle to transported to the golgi apparatus to be modified and packaged, then the vesicles will fuse with the membrane to release its content.)
Endocytosis
The import of substances using vesicles and energy
Vesicles is made of phospholipid, which is important to transport substance in cell.
The fluidity of the plasma membrane allows the membrane to change shape and helps to bud off to form vesicles when carrying out endocytosis.
Glycolipid
carbohydrate chain attached on the phosphate group of the phospholipid
Membrane fluidity
Membrane fluidity allows vesicles to form and carry out endocytosis or exocytosis at different locations of the plasma membrane
Different types of endocytosis
phagocytosis
pinocytosis
phagocytosis
“cell eating”
Plasma membrane forms a pseudopodium
pinocytosis
“cell drinking”
Plasma membrane wraps around and pull in to form vesicles
Receptor-mediated endocytosis
Looking for a specific item to pull in
It has to fit the receptors to go into the cell
How Extracellular Proteins Move Through the Golgi Apparatus
- Protein produced by the ribosomes of the rough ER enters the lumen of the ER. The protein is packed into a vesicle.
- The vesicle fuses with the cis of the Golgi apparatus.
- As the protein moves through the Golgi apparatus, it is modified on the trans side inside another vesicle.
- The vesicle moves towards and fuses with the plasma membrane, secreting the contents from the cell (exocytosis)
Voltage-gated ion channels in neurons
Voltage-gated ion channel is a kind of integral protein in the plasma membrane of neuron
The channel will open and close depending on a certain rage of membrane potential due to electrical stimuli (nerve impulse)
example of voltage-gated ion channels
Sodium voltage-gated channel proteins
Potassium voltage-gated channel proteins
Calcium voltage-gated channel proteins
