Cell Transport

The Need For Security The cell membrane controls what may enter or exit the cell. It is semi-permeable – only certain substances may pass into, or out of, the cell. Not just anyone gets to hang with us McLovin!

Passive vs. Active Transport Passive transport does not require the use of ATP. Active transport does require the energy of ATP. What factors decide which method of cell transport will be employed? –Size of molecules – big or little? –The concentration gradient – with or against it? –Charge on molecules?

Passive Transport - DIFFUSION Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. The movement continues in this high to low manner until the concentration in both areas is the same – this is equilibrium. Temperature and pressure can also affect the rate of diffsuion.

Passive – SIMPLE DIFFUSION

PASSIVE - OSMOSIS Osmosis is the movement of water from an area of higher concentration to an area of lower concentration across a semi-permeable membrane. Water moves because a solute within the cell is imbalanced with what is in the etracellular fluid. The water moves in order to push out or bring together the internal solute particles in an effort to match the concentration of the external solute particles.

OSMOSIS – Isotonic Conditions If the solute concentration in the cell and its external solution is the same – the conditions are said to be isotonic. Water still moves into and out of the cell but does so in a way that there is no net change in the concentration One water molecule moves in while another water molecule exits the cell.

OSMOSIS – Isotonic Conditions

OSMOSIS – Hypertonic Conditions

OSMOSIS – Hypotonic Conditions

PASSIVE – Facilitated Diffusion Facilitated diffusion uses transmembrane proteins as channels to transport ions or polar molecules across the membrane from high to low. The proteins used here are called transport proteins and there are two types: Channel Proteins – A hydrophilic pathway that allows water and ions to pass through it. Carrier Proteins – A protein that binds to a molecule and transports it across the phospholipid bilayer.

PASSIVE – FACILITATED DIFFUSION

PASSIVE TRANSPORT

ACTIVE TRANSPORT Active transport invovles the use of ATP. There are several methods of active transport including: Protein Pumps Primary & Secondary Transport Phagocytosis Pinocytosis Receptor-Mediated Endocytosis Exocytosis with Vesicles

ACTIVE – PROTEIN PUMPS Primary Transport – The protein pumps substances against the concentration gradient with the use of ATP. Energy (ATP) is consumed in the process. Secondary Transport – The protein pumps substances against the concentration gradient using the energy of an electrostatic gradient created by a method of primary transport.

PRIMARY TRANSPORT

SECONDARY TRANSPORT

ACTIVE – PROTEIN PUMPS

ACTIVE - PHAGOCYTOSIS Phagocytosis means “process of cell eating”. The cell recignizes the vital molecule or foreign invader. Then, extensions of the cell memebrane called pseudopods reach out and engulf the nutrient or neighbouring cell and place it in a (phagocytic) vesicle. We see this in unicellular protists and white blood cells.

ACTIVE – PHAGOCYTOSIS

ACTIVE - PINOCYTOSIS Pinocytosis means “process of cell drinking”. This process used to take in smaller dissolved nutrients. The cell invaginates (indents) and takes in a small portion of the extracellular fluid and the dissolved molecules within it. This fluid and solute is placed in a (pinocytic) vesicle.

ACTIVE - PINOCYTOSIS

ACTIVE - RECEPTOR-MEDIATED ENDOCYTOSIS The cell membrane has proteins on its outer surface that can be used to identify cell surface proteins on a nearby cell or protien based hormones. The shape of receptor protein and target protein are like a key and lock. When several receptor proteins have their target proteins attached, they move along the fluid membrane of the cell to a common point. Now the cell will carry out a process much like pinocytosis and encapsulate the target protein molecules and receptors in a vesicle.

ACTIVE - RECEPTOR-MEDIATED ENDOCYTOSIS

ENDOCYTOSIS METHODS

ACTIVE - EXOCYTOSIS Exocytosis is the process of materials being moved from the cytoplasm, inside the cell, to the extracellular fluid, outside of the cell. We often see this process undertaken with proteins made by the Rough ER. They are sent to the Golgi, packaged in a secretory vesicle and sent to the cell membrane where they are released into the extracellular fluid or blood.

ACTIVE - EXOCYTOSIS & VESICLES

ENDOCYTOSIS & EXOCYTOSIS

FIN