Plasma Membrane - the "fence"
The plasma membrane surrounds the entire cell and is often described as the phospholipid bilayer. The plasma membrane is called a bilayer due to the two layers of phospholipids, that are situated with their tails facing eachother and their heads facing outwards.
This structure is found in all living organisms, and often surrounds organelles within the cell. The diagram to the left is called a fluid mosaic model and is used to clearly illustrate all the parts of the plasma membrane.
The plamsa membrane is selectively permeable, and therefore controls what enters and exits the cell. Objects that are large, charged, or polar must enter the cell through one of the many proteins that cover the plasma membrane.
One of the great features of the plasma membrane is it's ability to move and bend, while still maintaining it's job as a protective barrier. The phospholipids are constantly shifting sideways, allowing for small particles, such as oxygen and alcohol to slip through.
This structure is found in all living organisms, and often surrounds organelles within the cell. The diagram to the left is called a fluid mosaic model and is used to clearly illustrate all the parts of the plasma membrane.
The plamsa membrane is selectively permeable, and therefore controls what enters and exits the cell. Objects that are large, charged, or polar must enter the cell through one of the many proteins that cover the plasma membrane.
One of the great features of the plasma membrane is it's ability to move and bend, while still maintaining it's job as a protective barrier. The phospholipids are constantly shifting sideways, allowing for small particles, such as oxygen and alcohol to slip through.
Polysomes (Polyribosomes)
Polysomes are long chains of ribosomes floating freely in the cytoplasm of the cell. Every ribosome in these long chains processes the same stands of mRNA and makes bulk proteins for the inside of the cell.
Cell Organelle Interrelationships
1. Nucleolus→Nucleus→Nuclear Membrane→Rough ER→Ribosomes
First the nucleolus makes the ribosomes, then sends the ribosomes out through the nuclear membrane, through a nuclear pore, to the rough ER. Inside the nucleus, a single gene is copied into the form of mRNA, and sent out through the nuclear membrane, through a nuclear pore, to the rough ER. The mRNA then attaches to a ribosome, and the ribosome "reads" the mRNA, and from that information, makes a protein. The rough ER then will sometimes modify the protein, and then enclose the protein in a vesicle and send it to the golgi body.
2. Rough ER →Smooth ER→Golgi Body→Vesicle→ Plasma Membrane (a.k.a The Secretory Pathway)
First, inside the nucleus, a single gene is copied into the form of RNA. The RNA is then sent out through the nuclear membrane, through a nuclear pore, to the rough ER. The RNA then attaches to a ribosome, and the ribosome "reads" the mRNA, and from that information, makes a protein. The rough ER then will sometimes modify the protein, and then enclose the protein in a vesicle and send it to the golgi body. Once at the golgi body, the proteins will be modified, stored, and then sent out of the golgi body in a vesicle. The vesicle goes to the plasma membrane, where it dumps its contents outside the cell through a process called exocytosis, and the protein is released into the body. The smooth ER makes hormones and lipids, puts them in a vesicle and then sends them to the golgi body. Once at the golgi body, the hormones and lipids will be modified, stored, and then sent out of the golgi body in a vesicle. The vesicle goes to the plasma membrane, where it dumps its contents outside the cell through a process called exocytosis, and the hormones are released into the body.
3. Plasma Membrane→Vacoule→Lysosome
Outside the plasma membrane a food particle approaches and is brought into the cell through process called endocytosis. Through endocytosis, a vesicle forms around the food particle. The golgi body then makes a lysosome, to digest the contents of the vesicle.The lysosome then attaches to the vesicle and will digest the contents with the hydrolytic enzymes that it contains. Once the food is digested into its simplest molecules, the cell then is able to use those molecules for whatever purpose is needed. The lysosomes will also attach to old cell parts to digest the useless organelles that are being sent out of the cell.
First the nucleolus makes the ribosomes, then sends the ribosomes out through the nuclear membrane, through a nuclear pore, to the rough ER. Inside the nucleus, a single gene is copied into the form of mRNA, and sent out through the nuclear membrane, through a nuclear pore, to the rough ER. The mRNA then attaches to a ribosome, and the ribosome "reads" the mRNA, and from that information, makes a protein. The rough ER then will sometimes modify the protein, and then enclose the protein in a vesicle and send it to the golgi body.
2. Rough ER →Smooth ER→Golgi Body→Vesicle→ Plasma Membrane (a.k.a The Secretory Pathway)
First, inside the nucleus, a single gene is copied into the form of RNA. The RNA is then sent out through the nuclear membrane, through a nuclear pore, to the rough ER. The RNA then attaches to a ribosome, and the ribosome "reads" the mRNA, and from that information, makes a protein. The rough ER then will sometimes modify the protein, and then enclose the protein in a vesicle and send it to the golgi body. Once at the golgi body, the proteins will be modified, stored, and then sent out of the golgi body in a vesicle. The vesicle goes to the plasma membrane, where it dumps its contents outside the cell through a process called exocytosis, and the protein is released into the body. The smooth ER makes hormones and lipids, puts them in a vesicle and then sends them to the golgi body. Once at the golgi body, the hormones and lipids will be modified, stored, and then sent out of the golgi body in a vesicle. The vesicle goes to the plasma membrane, where it dumps its contents outside the cell through a process called exocytosis, and the hormones are released into the body.
3. Plasma Membrane→Vacoule→Lysosome
Outside the plasma membrane a food particle approaches and is brought into the cell through process called endocytosis. Through endocytosis, a vesicle forms around the food particle. The golgi body then makes a lysosome, to digest the contents of the vesicle.The lysosome then attaches to the vesicle and will digest the contents with the hydrolytic enzymes that it contains. Once the food is digested into its simplest molecules, the cell then is able to use those molecules for whatever purpose is needed. The lysosomes will also attach to old cell parts to digest the useless organelles that are being sent out of the cell.