Cell Membrane

Homeostasis Cells must maintain homeostasis in order to live One way is by controlling the movement of water through the cell membrane

Cell Membrane A fluid sea of lipids in which proteins float Allows only some materials to enter the cell

Phospholipid Specialized lipid made of a phosphate head and two fatty acid tails

Lipid Bilayer Phospholipids form a lipid bilayer One polar head faces the cytoplasm Other polar head faces outside

Lipid Bilayer

Barrier The phospholipids form a barrier through which only small, nonpolar substances can pass.

Proteins Nonpolar parts are attracted to inside of lipid bilayer Polar parts are attracted to outside

Types of Proteins Cell-surface markers – identify each type of cell by the kind of sugars Attached to the surface by glycoproteins

Types of Proteins cont. Receptor Proteins – enable the cell to sense its surroundings by binding to certain substances outside the cell Causes changes in cell

Types of Proteins cont. Enzymes – Proteins in the cell membrane help with important biochemical reactions in the cell

Types of Proteins cont. Transport Proteins – Many substances the cell needs cannot pass through the lipid bilayer Proteins aid the movement of these substances in and out of the cell