AP BIO- Unit 4-8: Plasma Membranes and Permeability

Amphipathic

Composed of both Hydrophilic and Hydrophobic

Glycolipids

Carbohydrates bonded to lipids

• A membrane carbohydrate.. important for cell-to-cell recognition

Glycoproteins

Carbohydrates bonded to proteins.

• most abundant

• A membrane carbohydrate.. important for cell-to-cell recognition

Fluid Mosaic Model

A model used to describe the structure of cell membranes

• fluid: membrane held together by weak hydrophilic interactions and can therefore move and shift

Integral proteins

Located in the membrane. Proteins embodied into the lipid bilayer

• Amphipathic

• aka transmembrane proteins

• MAJOR CATEGORY

Peripheral proteins

Proteins that are not embodied into lipid bilayer.

• loosely bonded to surface

• major membrane protein

Hydrophilic

“Water loving” - head of phospholipid

Hydrophobic

“Water-fearing” - tails of phospholipids

Purpose of Plasma Membrane?

To regulate the cell by managing the temp, and controlling what goes in and out of the cell by delegating external environment from internal

How is membrane fluidity maintained in varying temps?

Cholesterol located and embedded in the membrane maintains the fluidity.

• Cold→ Reduce tightly packed phospholipids

• Hot→ Reduce movement

Selective permeability

Property of cell membranes that allow certain molecules and ions to pass through while blocking others

Polar

Uneven distribution of electron charge.

• Asymmetrical

• Creates partial - and +

• EX: H20 and NH3 and Glucose

Nonpolar

Share electrons equally

• Symmetrical

• EX: CO2 and CH4 and oxygen

Nonpolar molecules are…

Hydrophobic! They can easily pass through the plasma membrane because they can easily mix and dissolve

• “Like dissolves like”

Polar molecules are…?

Hydrophilic! They face a chemical barrier because the interior of the lipid bilayer is hydrophobic and Nonpolar

Passive transport

Transport of a molecule that does not require energy from the cell because a solute is moving with its concentration or electromagnetic gradient

• happens at different rates

• EXAMPLES: Facilitated/ Diffusion, osmosis

Active transport

Requires energy because it moves a solute against its concentration gradient

• EXAMPLE: pumps, cotransport, exocytosis, endocytosis

Active Transport: Endocytosis

The uptake of molecules from vesicles fused from the plasma membrane

• pinocytosis, phagocytosis, receptor mediated

Active Transport: Exocytosis

The secretion of molecules via vesicles that fuse to the plasma membrane

• vesicles form a bilayer to membrane

Pinocytosis

Non-specific uptake of fluid containing dissolved molecules

• protein coat helps mediate transportation

Diffusion

Spontaneous process resulting from the constant motion of molecules

• high to low concentration

Molecules move from __ to _ concentration

High to low

Passive Transport: Facilitated Diffusion

Diffusion of molecules through its membrane via transport molecules

• INCREASES the rate of diffusion

• passive because the proteins are helping move down their concentration gradient and no energy is required

Passive Transport: Carrier Proteins

Used to undergo conformational changes for substances to pass

• Transport molecule

Passive Transport: Channel Proteins

Provides a channel for molecules and ions to pass

• transport molecule

Passive Transport: Aquaporins

Specific channel protein for water

Active Transport: Pumps

Maintain membrane potential

• Membrane potential: unequal concentrations of ions across the membrane results in an electrical charge (electrochemical gradient)

• thank you to ATP!

ATP

Energy source used by cells that can transfer the terminal phosphate group to the transport protein → changes the shape of the transport protein to better move a protein

• Adenosine Triphosphate

If there was a mutation that changed the amino acid sequence of the proteins that make up aquaporins?

It would disrupt the cell's ability to regulate water balance (osmoregulation), potentially leading to cell death or severe dysfunction.

Concentration gradient

The gradual difference in the concentration of a substance (such as solutes, ions, or gas molecules) between two regions, space, or across a cell membrane

How can a chemical gradient be a source of energy for the cell?

It can act as potential energy because ions and molecules naturally want to move from an area of high concentration to an area of low concentration

Chemical gradient

The difference in the concentration of a chemical substance (solute or ion) between two regions, such as across a cellular membrane or within a fluid

Concentration gradient vs Chemical gradient?

Concentration gradient is the general difference in the amount of a substance (solute or gas) between two areas. A chemical gradient is simply a concentration gradient specifically applied across a biological membrane (like a cell wall)

Osmosis

Diffusion of water down it’s concentration gradient across a selectively permeable membrane

• low to high solute concentration

Tonicity

The ability of an extracellular solution to cause a cell to gain or lose water

• depends on concentration of solutes

Hypertonic

Mixture with higher concentration of solutes and higher osmotic pressure compared to another solute

• concentration is higher outside the cell

• cells immersed in this lose water to their extracellular surroundings

Plasmolysis

Vacuole shrinks and the plasma membrane pulls from the cell wall

Isotonic

“Same”— A fluid that has the same concentration of dissolved substances (solutes) and water as the inside of a cell. Flaccid

• concentrations outside the cell is equal to the inside

• Cells immersed in this have NO NET MOVEMENT OF WATER

Flaccid

A cell that is soft, limp, or lacking rigidity because water has left the cell or is in equal movement

• typically isotonic

Hypotonic

Liquid that has lower concentration of solutes and higher concentration of water.Turgid

• Cells immersed in this gain water

• concentration is lower outside the cell

Turgid

A cell that is swollen, distended, and firm because it has absorbed water

• typically hypotonic

Osmoregulation

Cells must be able to regulate their solute concentrations and maintain water balance

• animal cells react differently then cells with walls

Hypertonic, Isotonic, and Hypotonic in terms of solute concentration, movement of water, and cell size

Hypertonic →High concentration, water outwards, size shrink

Isotonic → Equal concentration, water equal flow, same size

Hypotonic → Low concentration, water inwards, size swell

Ѱs = -iCRT

Solute= -(1)(mol/L)(0.0831)(273+C^o)