1. Cell Structures Part: 2
September 18th, 2012

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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!

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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