Unit 5

Membranes components

Phospholipids, Proteins, and Carbohydrates

Phospholipids

Forms basic matrix

Proteins

Embedded into or around membrane, aids in transport

Carbohydrates

May be attached to lipid or protein

Phospholipid Bilayer

Framework of membrane made of two layers of phospholipids

Proteins in membrane

Transmembrane Proteins, Lipid-anchored proteins, and Peripheral membrane proteins

Transmembrane Proteins

Embedded inside phospholipid bilayer

Lipid-anchored proteins

Lipid tail embedded inside phospholipid bilayer

Peripheral membrane proteins

Non-covalently bound to proteins near or on the surface of membrane

Membranes

Semifluid and allows movements in two dimensions, need the right level of fluidity, and selectively permeable

Lateral/Rotational Movement

Keeps nonpolar tails within hydrophobic interior; energetically favorable

Flip-Flop Movement

Polar head travels through hydrophobic region, requires flippase and ATP; energetically unfavorable

Length of nonpolar tails

Longer tail lengths can create van der Waal forces, decreasing fluidity

Presence of double bonds

Doubles bonds create a bend in the structure, makes it more fluid (think unsaturated fats)

Presence of Cholesterol

Cholesterol stabilizes membrane, temp can control how fluid it is

High temperature

More fluid

Low temperature

More rigid

Transmembrane proteins

Limited in movement because of their large size

Membrane Transport

Movement of ions and molecules across membranes

Phospholipid bilayer

Bans simple diffusion of hydrophilic solutes

Hydrophobic interior

Doesn’t allow for diffusion of ions and hydrophobic molecules

Size

Smaller is faster diffusion

Polarity

Non-polar substance is faster diffusion

Charge

Non-charged substance is faster diffusion

Concentration

Rate of movement is higher if concentration is higher

Transmembrane gradient

Concentration of solutes is higher on one side and lower on the other

Electrochemical Gradient

A gradient with electrical & chemical components (ions)

Isotonic

When concentrations of solutes on both sides are equal

Hypertonic

Concentration of solutes is higher outside than interior

Hypotonic

Concentration of solutes is lower outside than interior

Osmosis

The movement of water from lower concentration to higher concentration

Channels and Passageways

Open passageways facilitate diffusion, molecules freely move through to inside of cell when open, and most are gated to control flow of solutes

Transporters

Transmembrane proteins bind to one or more solutes, bring it to the inside of the cell, and provides pathway for cellular uptake of organic molecules

Active Transport

Movement of a solute against a gradient from lower concentration to higher; requires ATP

Primary Active Transport

Involves a pump, pumps one solute across membrane

Secondary Active Transport

Uses pre-existing pump to transfer two solutes across membrane

ATP-Driven pumps

Generate electrochemical gradients

Na+/K+ ATPase pumps

In animal cells Na+ concentration is lower inside cell, while K+ concentration is higher inside cell

Multicellular organisms

Have intercellular channels and allows for direct movement of substances between adjacent cells

Gap Junctions

Small gaps between the plasma membrane, found in tissues & organs where cells need to communicate with each other, allows for passage of ions and small molecules

Plasmodesmata

Intercellular channels in plant cells

Exocytosis and Endocytosis

Ways to transport larger molecules

Exocytosis

Materials are packed inside vesicles & vacuoles and are excreted into extracellular environment

Endocytosis

When the plasma membrane folds inward to bring in material three types

Mediated Endocytosis

Receptor is specific for a specific molecule

Pinocytosis

When cells bring in fluids

Phagocytosis

When cells bring in solids

Junctions

How cells physically adhere to each other and/or extracellular matrix (ECM)

Anchoring Junctions

Junctions between adjacent cells, link cells, and ECM

Adheren Junctions

Connects cells to each other via cadherins; helps binds to actin filaments

Desmosomes

Connects cells to each other via cadherins; binds to intermediate fibers

Hemidesmosomes

Connects cells to ECM via integrins; binds to intermediate fibers

Focal Adhesions

Connects cells to ECM via integrins; binds to actin fibers

Tight Junctions

Creates a tight seal that prevents materials from leaking or coming in