Cell Boundaries

Regulating Cell Environment The cell has to be able to regulate its internal environment. Its internal environment is very different than the external environments that it is bathed in. Cells use cell walls and cell membrane to control its environment. Most cells except for animal cells have cell walls. They are composed of carbohydrates depending on the kingdom. Cell walls are dead and are used to prevent the cells from bursting and give them structures.

Some Cell Wall Carbohydrates Bacteria-Muramic acid (modified sugars held with peptide cross linkages) Plants-Cellulose Fungi-Chitin

Cell walls are porous and allow most anything to cross-the cell membrane is a barrier that regulates what gets “into or out of” the cell. In plant cells, the first cell wall that is laid down is the primary cell wall and is elastic. The middle lamella is the layer holding adjacent cells together.

Plant cells with soft tissue have only one cell wall Plant cells with soft tissue have only one cell wall. Harder cells lay down a secondary cell wall. This is laid inside the primary cell wall and is thicker.

Summary Cell walls- found in all cells except animal cells. Gives cell shapes and prevents it from bursting. Porous most everything crosses wall. Plants made of cellulose Prokaryotes made of maramic acid Fungi made of chitin Plants may have 2 cell walls- primary wall elastic. Secondary cell wall hardened with lignin. Middle lamella hold cells together.

All cells have cell membranes All cells have cell membranes. The basic structure is a bilayer of phospholipids with proteins and cholesterol inserted in the layer. This model is the fluid mosaic layer of cell membranes.

Phospholipids are modified triglycerides Phospholipid with atoms illustrated: Phospholipids usually illustrated such as:

Summary: All cells have cell membranes And it regulates what gets into and out of the cell. Structure is a bilayer of phospholipids with proteins and cholesterol in the layer. Called fluid mosaic model

Basic Cell membrane Has two layers of phospholipids as seen below The phosphate heads are facing water-inside and outside the cell, keeping the hydrocarbons away from it

Summary: Cell membrane Phosphate heads face the water-inside and outside, the hydrocarbon tails face one another Proteins are “stuck” in the membrane like a mosaic (intrinsic) or can be on the surface (extrinsic) Functions of membrane proteins 1.Used as transport 2.Used as receptors or as enzymes 3.Used as attachment for cytoskeleton

Glycolipid

Summary: Cell membranes Cell membranes are semi permeable or (selectively permeable) because some molecules can pass the membrane and others can not Permeable are molecules that can pass the membrane usually small molecules (O2 and CO2) and lipids like steroids Impermeable are molecules that can not cross the membrane usually large molecules, polar molecules and ions

Passive Diffusion The molecules (CO2, O2, etc) involved are permeable to the membrane. Predicting the net movement as if there was no membrane at all. The molecules move from high to low concentration. In the first system, A is more concentrated on side 2 than side 1. A is permeable Net movement Side 2 to 1 Equilibrium is reached Equal movement on both sides

Summary: Passive diffusion- is the movement of permeable material across the membrane. The net movement of material is from high concentration to low concentration until equilibrium is reached. Then the movement of material across the membrane will be equal in both directions

Summary: Facilitated Diffusion Smaller, charged or polar molecules (glucose, amino acids, etc.) are impermeable to the membrane. A transport protein is needed. The net movement is like passive diffusion moving from high to low concentration.

Active Transport Active transport-molecules are impermeable to the membrane The molecules are moving against the concentration gradient (from low to high). A transport protein and ATP are needed.

Osmosis Is a special case of movement of water. When things are impermeable to the membrane, and not in equilibrium, water will move across the membrane to help reach equilibrium. “Water likes to dilute”

Terms Hypertonic-higher concentration of solutes. Lower concentration of water Hypotonic-lower concentration of solutes. Higher concentration of water Isotonic-Two solutions that have equal solutes on both sides of the membrane

What is happening and Why?

Think pair share! What is happening? Why ? Animal cell? Plant cell? Name the process Net movement

Movement of Molecules Using the Cell Membrane Endocytosis- is movement of larger particles into the cell by use of membrane vesicles. Two Types: Phagocytosis-cell eating Pinocytosis-cell drinking Exocytosis-is the movement of larger particles out of the cell by use of membrane vesicles.

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