Cell Transport

Cell Membrane: Function: Maintain homeostasis. This is also called equilibrium. Allow passage of some molecules while preventing the passage of others This is called being “Selectively permeable” or “semi-permeable”

Semipermeable Membrane The Plasma Membrane 4/20/2017 Semipermeable Membrane Small molecules and larger hydrophobic molecules move through easily. e.g. O2, CO2, H2O G. Podgorski, Biol. 1010

Semipermeable Membrane The Plasma Membrane 4/20/2017 Semipermeable Membrane Ions-hydrophilic molecules larger than water, and large molecules such as proteins do not cannot pass through the membrane without help. G. Podgorski, Biol. 1010

Membrane structure: Composed of a phospholipid bilayer Have a phosphate head which is polar- does react with water Have a fatty acid (lipid) tail that is non-polar- does not react with water Together these make up the membrane

The outside of the membrane is hydrophobic- which means it does react with water The inside of the membrane is hydrophilic- which means it does not react with water

Contains proteins within its structure Integral proteins (transport proteins)- which allow the passage of molecules to large too pass through the membrane without help Peripheral proteins- aid in signaling for the cell to communicate with other cells

Cell Structure: Make up a metaphor for the phosphate heads of the membrane and the lipid tails of the membrane. The cell’s structure allows it to maintain homeostasis in different situations.

Concentration Gradient Concentration gradients occur when there is a higher amount of solutes in one area of solution then in another. Molecules will tend to travel from areas of high concentration to areas of lower concentrations

Passive transport Molecules flow with or down a concentration gradient No energy required Two types: Diffusion Ex. Osmosis Facilitated Diffusion

Diffusion  

Facilitated Diffusion Diffusion for molecules that are not lipid soluble or are too large to pass through the membrane. Carrier proteins change shape to aid these molecules across the membrane No Energy Required. Example: Glucose, Fructose

Osmosis Diffusion involving water moving from high solute concentrations to low solute concentration. Water can move freely across the membrane No energy required.

Osmosis There are three different types of osmotic solutions: Hypotonic isotonic Hypertonic

Hypotonic Solution Higher concentration of solutes within the cell More free water outside the cell Water moves into the cell The cell becomes swells or gets larger Hypo Hippo- it gets big and swells.

Hypertonic Solution Higher concentration of solute outside the cell More free water in the cell Water moves out of the cell Cell shrinks

Isotonic solution Solutions are equal between the two areas Water moves both directions to keep the solutions at an equilibrium.

What will happen to water in the cell?

Three different Osmotic Solutions Hypotonic- higher concentration of solutes in the cell Hypertonic- higher amount of water inside the cell Isotonic – equal amount of solutes inside and outside the cell

Example- Plants: In a hypotonic solution plant cell’s membrane is pushed against the cell wall Turgor Pressure In a hypertonic solution a plant cell’s membrane will shrink within the cell wall Plasmolysis Causes wilting when plants dehydrate

Turgor Pressure Plant cell become engorged with water Gives plant the stiffness in their stem

Plasmolysis Plant cell membrane shrinks from the cell wall Causes plant to wilt.

Active Transport Molecules are transported against the concentration gradient by proteins Requires energy (ATP) Example: Sodium-Potassium Pump A protein that transfer Na+ and K+ ions up the gradient Cell has a high Na+ concentration outside the cell and a high K+ concentration inside the cell http://www.youtube.com/watch?v=GTHWig1vOnY

Active transport Enodcytosis: Exocytosis: cells engulf substances that are too large to enter the cell by passing through the cell membrane cellular wastes are removed from sacs at the cell’s surface

Exocytosis- moving things out. The Plasma Membrane 4/20/2017 Exocytosis- moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another. copyright cmassengale G. Podgorski, Biol. 1010

The Plasma Membrane Exocytosis 4/20/2017 Exocytic vesicle immediately after fusion with plasma membrane. copyright cmassengale G. Podgorski, Biol. 1010

The Plasma Membrane 4/20/2017 Large molecules move materials into the cell by one of three forms of endocytosis. copyright cmassengale G. Podgorski, Biol. 1010

Pinocytosis- Most common form of endocytosis. The Plasma Membrane 4/20/2017 Pinocytosis- Most common form of endocytosis. Takes in dissolved molecules as a vesicle. G. Podgorski, Biol. 1010

Pinocytosis- Cell forms an invagination The Plasma Membrane 4/20/2017 Pinocytosis- Cell forms an invagination Materials dissolve in water to be brought into cell Called “Cell Drinking” copyright cmassengale G. Podgorski, Biol. 1010

Example of Pinocytosis The Plasma Membrane 4/20/2017 Example of Pinocytosis Transport across a capillary cell (blue). mature transport vesicle pinocytic vesicles forming copyright cmassengale G. Podgorski, Biol. 1010

Receptor-Mediated Endocytosis The Plasma Membrane 4/20/2017 Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc. copyright cmassengale G. Podgorski, Biol. 1010

copyright cmassengale

Endocytosis – Phagocytosis The Plasma Membrane 4/20/2017 Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria, etc. into vesicles Called “Cell Eating” copyright cmassengale G. Podgorski, Biol. 1010

The Plasma Membrane 4/20/2017 Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) copyright cmassengale G. Podgorski, Biol. 1010

So to review the three types of Endocytosis are: Phagocytosis Pinocytosis Receptor mediated Endocytosis.

The Plasma Membrane 4/20/2017 Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane. copyright cmassengale Inside Cell Cell environment G. Podgorski, Biol. 1010

What are the three different types of active transport? Protein pumps Endocytosis Exocytosis

Cell Transport Passive transport: molecules travel along the concentration gradient No energy required Active Transport: molecules are transported against the concentration gradient energy required