Bio test 5

Cell Membranes

Complex, dynamic structures made of lipid/carb and protein molecules

Functions of cell membranes

Define cell as a compartment. Regulate passage of materials. Help organisms maintain homeostasis, by the movement of substances across the membrane known as passive transport.

Cell membranes can…

Physically separate cell interior from extra cellular environment.

Small molecules

Like water can move in and out freely.

Large molecules

Like proteins and carbohydrates cannot move easily across the membrane.

The membrane

Is semipermeable or selectively permeable

Phospholipid

Molecules are a phi Patric and contain hydrophobic and hydrophilic regions.

Membrane properties

Orderly arrangement of phospholipid molecules make the cell membrane a liquid crystal. Allow molecules to move rapidly. Proteins move within membrane.

Lipid bilayers are

Flexible, self-sealing, can fuse with other membranes

Integral membrane proteins

Embedded in the bilayer

Transmembrane proteins

Integral proteins that extend completely through the membrane

Peripheral membrane proteins

Associated with the surface of the bilayer

Membrane proteins, lipids, and carbohydrates

Asymmetrically positioned to bilayer. Sides have different composition and structure.

Function of membrane proteins

Transport of materials, Acting as enzymes or receptors, Cell recognition, Structurally linking cells.

Diffusion

Net movement of a substance from a region of greater to lower concentration

Kinetic energy

Keeps molecules in constant motion causing the molecules to move randomly away from each other in a liquid or a gas

Rate of diffusion

Depends of temperature and size of molecules. Diffuse faster at higher temps. Smaller molecules diffuse faster than larger molecules

Solutions

Contain 2 parts. The solute which is being dissolved in the solvent. Water serves as the main solvent in living things

Equilibrium

When a concentration gradient no longer exists, Diffusion continues until the concentration of the molecules is the same on both sides of the membrane

Osmosis

Water passes through selectively permeable membrane from region of higher concentration to lower

Hypertonic Solution

Solute concentration outside the cell is higher. Water diffuses out of the cell until equilibrium is reached. Cells will shrink and die if too much water is lost. RBC shrink. Plasmolysis in plant cells. Solute concentration greater inside the cell. Animal cells swell and burst if they take in too much water. Turgid pressure in plant cells..

Isotonic Solution

Concentration of solutes same inside and outside of cell.

How cells deal with osmosis

The cells of animals on land are usually in isotonic environments. Freshwater organisms live in hypotonic environments so water constantly moves into their cells. Some marine organisms can pump out excess salt.

Facilitated diffusion high→low

No ATP needed. Occurs down a concentrated gradient. Faster than simple diffusion.

Active Transport

Moves materials against their concentration gradient from an area of lower to higher concentration. Roll up a hail. Need ATP

Bulk transport

Moves large, complex molecules such as proteins across the cell membrane.