Membranes, Energy, and Cell Communication

each phospholipid has a specific phase transition temperature; above this temperature, the lipid is in liquid crystalline phase and fluid; below this temperature, the lipid is in a gel phase and is rigid

unsaturated fatty acids provide a bend in the structure of the phospholipid bilayer, allowing for more fluidity; the presence of unsaturated fatty acids also helps the membrane withstand low temperatures

the presence of cholesterol regulates the movement of phospholipids in membranes; at moderate temperatures it helps to reduce movement while in low temperatures, it prevents packing between phospholipids

Peripheral proteins are anchored to the membrane

Integral proteins are partially or fully inserted into the membrane. If they are fully inserted than they are called transmembrane proteins.

A cell has to regulate transport of substances across the cellular membrane. This is important because it helps manage and separate different materials traveling throughout the cell. Small nonpolar molecules and small uncharged polar molecules have higher permeability and can travel through the bilayer. Large uncharged polar molecules and ions have low permeability and cannot pass through the membrane on its own.

Aquaporin are types of proteins that aid in the transport of water across membranes.

Passive transport is a movement across a membrane that does not require any energy. It is moving down the concentration gradient, from an area of high concentration to low concentration.

Facilitated diffusion is passive transport aided by proteins. They help move hydrophilic substances across membranes as they cannot diffuse on their own.

Channel proteins provide channels that allow a specific molecule or ion to cross the membrane.

Carrier proteins undergo subtle changes that help transport proteins from on side to another. Sort of like an elevator, it takes in a few molecules at a time, closes, and opens up on the other side.

Diffusion is the tendency for molecules to spread out evenly into available space. They always move from areas of high concentration to low concentration.

Osmosis is the diffusion of water across a selectively permeable membrane. Water diffuses from an area of lower solute concentration to an area of higher solute concentration until the concentrations are equal on both sides.

tonicity is the ability of a surrounding solution to cause a cell to gain or lose water

solute concentration is the same as inside the cell; no net water movement

solute concentration is greater than inside the cell with respect to the cell/solute concentration is greater than that outside of the cell with respect to the environment

solute concentration is less than that inside the cell with respect to the cell/ solute concentration is less than that outside of the cell with respect to the environment

Active transport moves substances from low to high concentration, against concentration gradients, requiring energy (ATP).

The sodium potassium pump aids in the transport of sodium and potassium ions in a cell. There is usually in abundance of sodium outside the cell and abundance of potassium inside the cell. 3 Na+ are transported out of the cell for every 2 K+ ions transported in.

Electrogenic pumps are proteins that generate voltage across a membrane. These also help store energy used for cellular work.

A positive charge leaves the cell, and a slight negative charge develops inside the cell and a positive charge outside the membrane.

Cotransport occurs when active transport of a solute indirectly drives transport of other substances. For example, plant cells use the H+ generated from proton pumps to drive active transport of nutrients into the cell.

Large molecules cross the membrane in bulk in vesicles.

Transport vesicles move towards the membrane, fuse with it and release their contents. Exocytosis is used to export products.

Endocytosis takes in molecules. There are three types: phagocytosis, pinocytosis, receptor-mediated endocytosisphagocytosis takes in large food particles/ other cells by extending its membrane outpinocytosis takes in extracellular fluid from outside in vesiclesreceptor mediated endocytosis is a specialized type of pinocytosis that allows for the cell to acquire bulk quantities of specific substances even if they may not be concentrated in the extracellular fluid

Membrane potential is the amount of voltage in the cell. When there is no net movement of certain ions across the membrane then equilibrium potential is reached.

Ion channels are membrane proteins that allow for transport of ions across membranes. They are always open but can be closed at times. This would depend on the voltages within the membrane.

Ion channels are always open and allow for ions to move through.

Ion channels are able to open and close in response to stimuli.stretch gated - open when membrane is deformedligand gated - open and close when a neurotransmitter binds to channelvoltage gated - open and close in response to changes in membrane potential

solute concentration is less than that inside the cell with respect to the cell/ solute concentration is less than that outside of the cell with respect to the environment

Depolarization occurs when ion channels cause the inside of the cell to become less negative. It is a reduction in the magnitude of the membrane potential. This also triggers an action potential.

The K+ channels have to close up again and before this happens there is a slight overly negative charge in the cell before it is able to reach its resting state once again.

Most voltage gated Na+ and K+ channels are closed.

The voltage begins to increase until it reaches action potential.

The inside of the cell becomes negative again.

hypotonic - lysedisotonic - normalhypertonic - shriveled

hypotonic - turgid/ normal (plants need a lot of water to survive)hypertonic - plasmolyzed (loss of water/ cell can die)isotonic - flaccid (not net movement of water and can cause plant to wilt)