6 Orgenels Project
Ribosomes
What's most important?
· Ribosomes are small dot-like structures in cells.
· Ribosomes are often associated closely with endoplasmic reticulum(ER), forming rough ER.
· Ribosomes are the site of protein synthesis in cells.
Structure
Ribosomes are made up of proteins and ribonucleic acid(RNA). These molecules are arranged into two subunits called the large and small subunits. These subunits are attached to each other and together form the entire ribosome. When viewed through a light microscope the ribosomes appear as dots, they are very small and the subunits can not be seen.
Function
The only function of ribosomes is to build proteins. The plan for the protein in the form of mRNA passes through a groove in the ribosome. The ribosome "reads" the plan and assembles the proper sequence of amino acids to build the protein.
There are two kinds of ribosomes, those attached to the endoplasmic reticulum and those floating in the cell cytoplasm. Attached ribosomes make proteins that are used in the ER or transported within the ER. Free ribosomes make proteins that are used in the cytoplasm.
The details of how ribosomes make proteins are presented in the "Protein Synthesis" section of your biology book. This is a complicated process beyond the scope of this document.
Details
Ribosomes are made in the nucleus of the cell.
Ribosomes are about 60% rRNA by weight.
A ribosome can make the average protein in about one minute.
Ribosomes often line up in clusters called polyribosomes, these are connected by the mRNA and all make the same protein. In this way the cell can make many copies of a protein very fast.
The cell or plasma membrane was once thought to be a simple barrier that kept the contents of the cell, the cytoplasm, contained. It serves as a gateway which helps to control materials going in and out of the cell. With more research, it turns out the cell membrane is very important in a wide range of cell activities including functions related to cancer and AIDS.
Structurally, the membrane is a lipid bilayer. What this means is that, under the electron microscope two separate layers can be seen. The layers are composed of a two part molecule called a phospholipid. The lipids (fatty acids) are "water fearing" (hydrophobic) molecules. Just try to mix oil and water to see what that means. The phosphate end is water loving (hydrophilic). The membrane forms...