Cell Membrane & Passive Transport

Plasma/Cell Membrane definition:

-Gatekeeper of the cell’s interior

-Separates the cell’s interior from its surrounding environment

-Controls passage of organic molecules, ions, water, oxygen, and wastes in and out of the cell

Hydrophilic outer layers and hydrophobic inner layer

Separates fluid within the cell from fluid outside the cell

Fluid Mosaic Model

Describe the structure and function of the plasma membrane

Plasma membrane is a _

Mosaic of components

Plasma membrane components:

-Phospholipids

-Cholesterol

-Proteins

-Carbohydrates

Phospholipids

Made of a glycerol, two fatty acids, and a phosphate group

Cholesterol

-Type of lipid

-Made of four fused carbon rings

Cell membrane proteins

Peripheral & Integral membrane proteins

Carbohydrates

Found on the exterior of plasma membrane and consist of:

-Glycoprotein

-Glycolipid

Glycoprotein

Protein with an attached carb

Glycolipid

Lipid with an attached carb

Mosaic gives membrane a ____ character

Fluid

Integral proteins

Proteins that integrate completely into the membrane structure

Integral proteins have ___ _____

Hydrophobic & hydrophilic parts

Peripheral proteins may serve as:

-Enzymes
-Structural attachments for the cytoskeleton’s fibers

-Part of the cell’s recognition sites (how tissues form from similar cells)

Peripheral proteins

Proteins that are either on the membrane’s exterior or interior surfaces (does not span entire membrane)

Glycocalyx definition

Collective term for glycoproteins + glycolipids

Glycocalyx function

Highly hydrophilic and attracts large amounts of water to the cell’s surface

Cell recognition allows your immune system to _

differentiate between your cells and foreign cells or tissues

Glycoproteins and glycolipids aid in

Cell recognition

Purpose of plasma membrane carbohydrates

-Form specialized sites with unique patterns on the cell surface that allow cells to recognize each other

-Important for things like your immune system

Phospholipid location

Main membrane fabric

Cholesterol location

Attached between phospholipids and between the two phospholipid layers

Integral proteins location

Embedded within the phospholipid layer; may or may not penetrate through both layers

Peripheral proteins

On the phospholipid bilayer’s inner or outer surface; not embedded within the phospholipids

Carbohydrates (glycoproteins/glycolipids)

Generally attached to proteins on the outside membrane layer

Plasma membranes are selective permeable

They allow some substances to pass through, but not others

Passive transport definition

Naturally occurring movement of substances across plasma membrane; does not require any energy to accomplish movement

Passive transport movement

Always moves substances from areas of high concentration to areas of lower concentration

Concentration gradient

Difference in concentration of a substance between two areas

Diffusion

Movement of substances from areas of higher concentration to areas of lower concentration without assistance

Diffusion continues until _

The concentration is equal across a space and there is no concentration gradient left

When diffusion is completed

Molecules will still be around but there will be no net movement

Dynamic equilibrium:

When concentrations of a substance are equal and there is no longer a concentration gradient and no net movement

7 factors that affect how fast diffusion will happen:

Extent of concentration gradient
Mass of the molecules diffusing

Temperature

Solvent density

Solubility

Surface area and plasma membrane thickness

Distance traveled

Extent of the concentration gradient

Bigger difference in concentration= faster diffusion; slows down as it approaches dynamic equilibrium

Mass of the molecules diffusing

Heavier molecules = move slower

Lighter molecules = move faster

Temperature

High temperature = fast movement of molecules

Solvent density

Increased solvent density= decreased diffusion rate (high density slows you down)

Solubility

Nonpolar or lipid-soluble materials pass through more easily compared to polar materials

Surface area and plasma membrane thickness

Increased surface area= increased diffusion rate; thicker membrane= slower diffusion

Distance traveled

Greater the distance the substances must travel, the slower the diffusion rate (too much surface area = molecules can’t move around)

Facilitated transport:

Materials diffused across the plasma membrane with the help of membrane proteins

2 types of proteins that are used in facilitated transport:

Channel proteins

Carrier proteins

Transmembrane proteins (span the entire phospholipid bilayer)

Channel & carrier proteins

Channel proteins

Have hydrophobic parts that are exposed to the interior and exterior of cell and a hydrophilic channel through their core that allows passage of polar compounds

Carrier proteins

Binds with substance and then changes shape to move bound molecule from one side of the membrane to the other

Osmosis

-The movement of water across the plasma membrane

-Water moves towards areas with high solute concentration

Tonicity:

Water balance across the plasma membrane

Hypotonic

Solute concentration is lower outside the cell, so water enters the cell

Isotonic

Equal water and solute concentrations on ether side of the membrane

Hypertonic

Solute concentration is higher outside the cell, so water leaves the cell

Solute

A substance that gets dissolved in a solvent to form a solution

Hypertonic cell shape

Shrinks

Hypotonic cell shape

Swells (may burst)

Isotonic cell shape

Normal

Solvent

Liquid substance that dissolves solutes to form a solution

Types of passive transport

Facilitated, diffusion, osmosis