Cell Transport

Notes

•All cells have a cell membrane made of proteins and lipids

Cell Membrane

lipid bilayer

protein channel

protein pump

Layer 1

Layer 2

Cell Membrane

Function of Cell Membrane• Cell membrane separates the components of a cell from its

environment—surrounds the cell

• “Gatekeeper” of the cell—regulates the flow of materials into and out of cell—selectively permeable

• Cell membrane helps cells maintain homeostasis—stable internal balance

Cell Membrane Structure

Phospholipids• Lipids (fatty acid) with a phosphate group attached. • Polar head and non-polar tails• Hydrophilic (likes water) head and hydrophobic

(afraid of water) tail

Tail

Hydrophilic and Hydrophobic

Hydrophilic: “likes water”

Hydrophobic: “fears water” - repels water

Transport Proteins• Found in plasma membrane (also known as

transport proteins)• Allows larger substances to move through the

plasma membrane.

Cholesterol molecule

• Helps stabilize the phospholipids

• Prevents the fatty acid chains of the phospholipids from sticking together

Passive TransportMovement of material down the

concentration gradient, requires NO energy from the cell

Diffusion…going with the flowDiffusion: The random movement of

molecules from an area of high concentration to an area of low concentration.

Osmosis

Osmosis: The movement of water across a semipermeable membrane due to differences in the solute on each side.

Facilitated DiffusionPassive Transport by Proteins

(NO energy required)

• Channel proteins – form channels to allow specific molecules to flow through

• Carrier proteins – change shape to allow a substance to pass through the membrane.

outside of cell

inside of cell

Glucose molecules

Active TransportMovement of material through a membrane

against a concentration gradient, requires energy from the cell

outside of cell

inside of cell

Carbon Dioxide molecules

Transport of Large Particles

1. Endocytosis – the process by which a cell surrounds and takes in material from its environment. (engulfed)

2. Exocytosis – the expulsion or secretion of materials from a cell.

Same Conc. Lower Conc. Higher Conc.

Effect of concentration

Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel.

Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.

Isotonic Solutions: contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.

http://upload.wikimedia.org/wikipedia/commons/7/76/Osmotic_pressure_on_blood_cells_diagram.svg

HYPOTONIC HYPERTONIC

ISOTONIC