Membranes and Transport First, the Phospholipid Challenge

Membrane Structure made of many different pieces that move around; “FLUID MOSAIC” Main piece = phospholipid Helper pieces = proteins and carbs for special jobs (such as tunnels, ID badges, etc) The membrane is selectively permeable, meaning controls what comes in/out

Phospholipids consist of a hydrophilic phosphate head and hydrophobic lipid tails. Since the heads love water and the tails hate water, they automatically form a double layer with the heads facing out towards the water and the tails facing in away from the water.

Membrane Proteins act as doors/filters, allowing good things to cross, but keeping bad things out. Some are always open, but others open/close. These proteins help the membrane control transport. Other proteins/carbs/lipids perform other jobs like identification and communication

WHY? Examples of maintaining homeostasis Membranes maintain homeostasis (a constant internal balance). If a cell does not maintain homeostasis, then it will die. Examples of maintaining homeostasis Constant body temperature Right amount of food/water Keeping out diseases

Transport Two types Passive Transport: No cell energy needed Only moves from HIGH concentration to LOW concentration Active Transport: Requires cell energy (ATP) Only used from LOW concentration to HIGH concentration

Types of Passive Transport Diffusion = movement of ANY molecule from high concentration to low (down the gradient)

Types of Passive Transport Osmosis = diffusion of WATER (still from high to low) through proteins called Aquaporins Depends on the concentration of water inside and outside of cell. Since water is ALWAYS allowed in or out of the cell, having a lot of stuff (solvent) dissolved INTO the water will affect how the water moves. To determine whether water will enter or leave a cell, we look at the tonicity (or concentration) of the cell’s surroundings which are called hyper/hypo/isotonic conditions

HYPOTONIC: More dissolved “stuff” inside than outside, meaning MORE WATER outside the stuff can’t move to equalize the gradient, so the water has to move instead. Water will move IN causing the cell to swell Animal cells could burst Plant cells are protected by their cell wall (called Turgor Pressure) “Hypo, Oh No! There’s too much H2O outside my cell, I’m going to swell.”

HYPERTONIC: More dissolved stuff outside, meaning LESS water outside the cell. Water leaves the cell to try and even things out. Cell will shrink or shrivel (like a raisin) Plants wilt because they lose the turgor pressure (called plasmolysis) “Hyper Sucks”

ISOTONIC: Concentration of water/solutes is the SAME in and out Cell does not gain or lose water (no change) Dynamic Equilibrium “iso means same”

Red Blood Cells in hypo/hyper/isotonic conditions Red Blood Cells in hypo/hyper/isotonic conditions. (Note that the isotonic cells look “normal”) Hypo/hyper/isotonic concentrations always refer to what is OUTSIDE the cell, never the inside.

Osmosis Practice – Identify the following as hypo, hyper, or iso (Hint: find the WATER)

More Types of Passive Transport Facilitated Diffusion = diffusion through protein tunnels to help larger molecules (like sugar) cross the membrane. Facilitated means “assisted”. Still passive. No energy/ATP.

What if the cell wants to move things against the concentration gradient? ACTIVE TRANSPORT

Types of Active Transport Anytime a molecule wants to move against the concentration gradient (from low to high), it must be moved through ACTIVE transport. Reminder: This requires the cell to use its own energy with ATP “batteries”. Protein pumps use ATP energy to move individual molecules against the gradient - low to high (like a vacuum) Example - Sodium-Potassium Pump: Protein that actively transports sodium and potassium ions into or out of the cell. Necessary for your nervous system.

Protein Pumps

Types of Active Transport The Golgi uses active transport/ATP to move material through endo/exocytosis Endocytosis = moving particles into the cell using vesicles; opposite of exocytosis Pinocytosis = drinking action, used for small particles or water Phagocytosis = devouring action, used for large particles like food Exocytosis = removing particles from the cell using vesicles; opposite of endocytosis

Endo/Exocytosis

Transport Video Demos Passive transport (high to low, no cell energy) Diffusion Facilitated Diffusion Osmosis Active transport (low to high, needs cell energy) Protein Pumps Endo/Exocytosis Amoeba using endocytosis to eat

So why are cells so small? Cells are small because it makes transport easier. Larger cells have difficulty bringing in materials through diffusion. It takes too long. Easier transport is due to having a large surface area to volume ratio. As any object gets larger, the volume (inside) gets bigger faster than the surface area (outside). The more surface area you have AS COMPARED TO your volume, the easier transport becomes. SA to V ratio is indirectly proportional to size. Smaller Cells have a LARGER SA to V ratio Cells can also be slightly larger than other cells, but they need to be flat to increase their surface area as much as possible.

Surface Area to Volume Ratio Note: As the cubes get larger, the ratio gets smaller.

Multicellular Organisms To be larger than microscopic, cells form multicellular groups. This means they can be a large organism together, but individually they are all still small. Many small cells have easier transport than one giant cell.

Multicellular Organisms Multicellular organisms also have specialization/differentiation to work together as a team Cell specialization: every cell in the organism focuses on completing one job Cell differentiation: every cell type looks/performs differently to do its job