Cell Structures Part: 2 September 18th, 2012

Cell (Plasma) Membrane The cell membrane forms a barrier between the inside of the cell and the outside, so that the chemical environments on the two sides can be different Allows for food molecules (ex: glucose) to come in and it allows for waste products to go out (ex: carbon dioxide) The cell membrane is made of phospholipids and protein Cell membrane is basically like a plastic bag with tiny holes! The phospholipids form the plastic bag and the proteins form the tiny holes

What is the Cell Membrane Made of? The cell membrane is made of a double layer of phospholipid molecules, called the phospholipid bilayer Scientists describe the organization of the phospholipids and proteins as the fluid mosaic model It is called fluid because, the phospholipid molecules and proteins are free to drift around in fluid motion. Fluid consistency of olive oil It is called mosaic because the position of the protein molecules are random

The Phospholipid Bilayer Bi = two  two layers of phospholipid molecules Hydrophilic heads are on the outside, while the Hydrophobic tails are on the inside The proteins are embedded at random locations

Proteins in the Cell Membrane! Two kinds of proteins: intrinsic (integral) and peripheral proteins Intrinsic proteins are permanently attached to the cell membrane Peripheral proteins are not bonded as strongly to the cell membrane. They usually sit on the surface of the cell membrane Other kinds of proteins even cross the cell membrane

What are the Functions of Proteins in the Cell Membrane Structural Support: Part of the cell’s cytoskeleton. Maintain cell shape. Recognition: Binding sites on some proteins can serve to identify the cell to other cells, such as those of the immune system Communication: Used for cell to cell communication Transport: Proteins form transporters or channels, allowing substances to pass into and out of the cell

Glycoproteins Glycoproteins are a type of integral (intrinsic) protein Have a carbohydrate component as well Play an important role in cell-to-cell interaction Attachment sites for molecules that need to enter or carry a message to the cell Important for immune system recognition!

What can go into and out of the cell membrane? Hydrophobic molecules can pass through freely Hydrophilic molecules cannot pass through freely, and usually need to go through channels or need a transport protein for assistance

What is the role of cholesterol within the Cell Membrane? Role: Cholesterol helps keep the cell membrane fluid At low temperatures, the cell membrane keeps the phospholipids apart. If it did not do this, then the phospholipids would come together and crystallize Keeps the fluidity of the cell membrane not too mushy and not too firm - keeps it just perfect for the cell membrane to perform its functions

The Cell Wall The cell wall is a protective structure made primarily of cellulose (polysaccharide). Much stronger and thicker than the cell membrane Only found in plants, bacteria, some protists and fungi Provides structural support – rigid and strong

The Nucleus: The Brain of the Cell The largest organelle in the cell Regulates all cell activity Contains the cell’s DNA Separated from the rest of the cell through the nuclear envelope Nuclear envelope: double lipid bilayer that separates the DNA within the nucleus from the rest of the cell Nuclear Pores: surround the nuclear envelope. Nuclear pores allow for exchange of materials between the nucleus and the rest of the cell

The Nucleus, continued … Within the nucleus is the Nucleolus, whose role is to manufacture ribosomes The nucleolus does not have a membrane around it Ribosomes (protein construction teams): protein builders

DNA in the Nucleus The nucleus contains the cell’s DNA (genetic information) In eukaryotic cells, the DNA is combined with proteins and called chromatin Before cell division (mitosis), the chromatin changes to chromosomes Chromosomes are organized structures of DNA and protein that contain information for how cells operate

Cytoplasm The cytoplasm helps to hold the cell’s organelles in place Jelly-like substance Gives the cell shape: balloon analogy Fills the space between the nuclear envelope and the cell membrane Cytoplasm consists of cytosol – liquid that contains ions and various molecules like ATP, enzymes, amino acids and carbohydrates