CELLULAR ORGANIZATION

Organisms Are Made of Cells Some organisms are single-celled (unicellular) – Ex. Bacteria, Protists (euglena, paramecium, algae), certain types of fungus Some are made of many cells (multicellular) Everything that an organism does is ultimately happening at the cellular level.

Some Types of Cells

A. Cells – the smallest functional unit of life 1. Eukaryote – organism with a nucleus, membrane-bound organelles, and more than one chromosome. Usually either a plant or an animal. Ex. – anything BUT bacteria 2. Prokaryote – unicellular organism with NO nucleus, NO membrane- bound organelles, and circular-stranded DNA. Ex. – bacteria

Differences Between a Plant Cell & Animal Cell Plant Cell Has both a cell membrane AND a cell wall Has a giant vacuole for water storage and structure Usually a rectangular shape Contains chloroplasts for photosynthesis Animal Cell Has only a cell membrane Has several smaller vacuoles for water, food, or waste storage Can come in any shape No chloroplasts, only mitochondria.

Why are most cells so small? Because if they were any bigger, they wouldn’t be able to take in enough food or get rid of enough wastes fast enough. (i.e., they would either starve to death or drown in their own waste)!

Cell Membrane Located around the cell Protects the cell and controls what enters or leaves the cell Is selectively permeable - lets some things in but keeps others out; essential for maintaining homeostasis.

II. Cell Membranes

How does a substance enter a cell? If it’s small enough, like O 2 and H 2 O, it can pass directly through the phospholipid bilayer. – This is a type of passive transport called simple diffusion (O 2 ) or osmosis (H 2 O). More about this later! If the substance is too big, like C 6 H 12 O 6, it needs the help of a special protein embedded in the phospholipid bilayer. – This is a type of passive transport called facilitated diffusion. More about this later!

The indirect route : The indirect route : Thru cell membrane proteins Channel protein Receptor protein Marker protein Carrier Protein

4 types of proteins: 1.Channel Proteins 2.Receptor Proteins 3.Carrier Proteins 4.Marker Proteins

Channel Proteins Doughnut shaped Allows needed molecules and ions to pass into cell Type of passive transport because it requires no energy expenditure (moves down the concentration gradient). Facilitated Diffusion

Channel Proteins Polar Non-polar Polar > > * ** * * * * *** * * * * * * * * * * *

Channel Proteins in Action! Large molecules like glucose (macromolecule).

Receptor Proteins When a messenger molecule binds to the receptor protein, the protein induces the pseudopodia to engulf the two and pull them both into the cell forming a vesicle. If the messenger molecule doesn’t bind with the receptor protein, it won’t let it inside of the cell. Receptor Mediated Endocytosis * * * We have a match! “messenger” usually a hormone

Receptor Proteins in Action! Induces pseudopodia Forms a vesicle Lysosomes will dissolve the unwanted material (the green dots).

Carrier Proteins in Action

Carrier Proteins Shaped like a puzzle piece. Work like a lock and key. The incoming substance (key) has to fit into the carrier protein (lock) perfectly. If it does, it induces the protein to change shape and allow the substance into the cell. If the incoming substance doesn’t fit into the carrier protein, it won’t be let into the cell. Allows needed molecules and ions to pass into cell Type of passive transport because it requires no energy expenditure (moves down the concentration gradient). Facilitated Diffusion

Marker Proteins Elongated with short chains of carbohydrates attached “name tags” of the cell Every cell has markers that ‘say’ they belong to you and what type of cell it is I’m a heart cell.

Marker Proteins Polar Polar Non-polar CarbohydrateChain

Diffusion The movement of substances from a high concentration to a low concentration. A solution reaches equilibrium when the solute is the same on both sides of the membrane, and moves back and forth at a constant rate.

III. Movement Across Membranes – Passive Transport A. Simple Diffusion – molecules that are SMALL ENOUGH to fit through the phospholipid bilayer move from areas of high concentration to low concentration. Requires no energy input. B. Facilitated Diffusion – a molecule diffuses through a channel protein or carrier protein. Still moving from a high to low concentration gradient, requiring no energy input.

Movement Across Membranes – Active Transport C. Active Transport – uses a membrane protein to act as a pump to move molecules AGAINST the concentration gradient from LOW to HIGH; requires ATP (energy). Your body often does this with potassium & sodium while you are physically active.

Movement of H 2 O Across the Cell Membrane - Osmosis Osmosis – movement of water, from a high concentration to a low concentration; requires no energy input; this is how a cell maintains homeostasis! – 1. isotonic – the solute (salt, sugar, etc) concentration is the same both inside and outside the cell; a state of equilibrium. Water moves in and out of the cell at a constant rate. – 2. hypertonic (more H 2 O) – higher concentration of water inside the cell, so it moves to a lower concentration OUT of the cell; causes the cell to shrink. If this happens in a plant, it is called plasmolysis. – 3. hypotonic (less H 2 O) – low concentration of water inside the cell, so water moves INTO the cell to even it out; causes the cell to swell up, if it’s an animal cell, maybe even burst! This is called cytolysis. If it’s a plant cell, the cell wall is strong enough to keep it from bursting. This called turgor pressure!

Movement Across Membranes Cont’d F. Endocytosis – involves the movement of large or multiple substances into the cell; often used by white blood cells to engulf bacteria and viruses. – 1. phagocytosis – the intake of solids, “cell eating”; arms of the cell engulf the material and bring it in. – 2. pinocytosis – the intake of fluid, “cell drinking”; arms of the cell engulf the liquid and pull it in. – 3. receptor-mediated endocytosis – involves a specific receptor protein on the cell membrane that recognizes the molecule and binds with it, allowing it access into the cell. Then, the arms of the cell surround the material and bring it in.

Movement Across Membranes Cont’d Exocytosis – the movement of materials out of the cell