Download Biology Chapter 5, Lesson 1 Notes

Chapter 5, Lesson 1 Notes
What are Cell Membranes?
Cell Membrane Structure
 The plasma membrane separates the cell’s contents from the
external environment.
 Cell membranes are made up of two layers of phospholipids.
 Phospholipids are lipid molecules that have a head and a tail.
 The tail or fatty acid end of a phospholipid molecule is
hydrophobic (water hating) and carries a neutral charge and is
nonpolar. The tails keep water from rushing into the cell, that
could cause the cell to burst.
 The head of a phospholipid molecule is hydrophilic (water
loving) and interacts with the watery external environment so
the cell can get the nutrients it needs.
 The phospholipids form a bilayer (2 layers) that has
hydrophobic tails on the inside and hydrophilic heads on the
outside.
Cell Membrane Function
 The function of the cell membrane is to serve as a divider
between the cell and its outside environment (plasma
membrane).
 The membrane allows some proteins and molecules to pass
through its walls and others not to pass (selectively
permeable).
 There are transport proteins in the plasma membrane that
help molecules cross through the membrane.
 The fluid mosaic model of a cell membrane has
phospholipids and proteins that move around together.
Extracellular Matrix
 The extracellular matrix is a sticky extra layer outside of the
plasma membrane.
 This extra layer is found only in animal cells.
 The function of the extracellular matrix is to keep cells joined
together. This helps similar cells in similar tissues to act
together.
Inside the Plasma Membrane
 Organelles float in an area called the cytoplasm.
 Cytoplasm is made of organelles and a fluid called cytosol.
 Cytosol suspends the organelles and carries the molecules
needed by the cell and its organelles.