Cell Membrane

Cell Membrane and Homeostasis Homeostasis is maintaining a stable internal environment within the cell The cell membrane helps to do this by controlling what can cross into and out of the cell

Selectively Permeable The cell membrane is selectively permeable, meaning that not everything can go across it. Only certain things can get into the cell and only certain things can leave the cell

Structure Cell membrane structure helps it regulate what can pass through and what can’t

Structure continued… Phospholipids: special lipid (fat) molecule that has a phosphate head and two fatty acid tails Phosphate head is polar (has a charge) and likes water Hydrophilic Fatty acid tails are nonpolar (doesn’t have a charge) and don’t like water Hydrophobic

Structure continued… These phospholipids form a double layer called a phospholipids bilayer with the phosphate groups on the outside and the fatty acid tails in the middle This happens because there is water inside and outside of the cell, so the water loving phosphate end is always by the water

What can pass through the membrane? This allows small, nonpolar substances to pass through because all other substances are repelled by the nonpolar fatty acids

The cell needs to let other things inside and out of the cell at certain times to its uses membrane proteins to allow specific things across the membrane at specific times.

Types of Membrane Proteins

Cell-Surface Proteins Similar to a nametag A chain of carbohydrates attached to the cell membrane to identify each type of cell Ex: Heart cells have one type of sugar chain, while lung cells have another type of sugar chain Attached to the cell membrane using glycoproteins Glycoproteins can help cells work together

Receptor Proteins Similar to you smelling, hearing, or touching your surroundings Enable a cell to sense its surroundings by binding certain substances outside the cell Allows the cell to react to its surroundings

Enzymes Help with important chemical reactions inside the cell

Transport Proteins Allows certain necessary substances that cannot pass through the cell membrane into and out of the cell