Meaghan Malcolm Madi THE NUCLEUS/NUCLEOLUS

THE NUCLEUS So what is the nucleus? The nucleus is essentially the brain of the cell. It’s job is to control the cells actions as well as to store and replicate genetic information. It’s almost like a big hard drive for the cell. That’s the basic, now we’ll look more in depth into the nucleus.

The nucleus is the largest organelle of the eukaryotic cell. The nucleus contains the DNA that gives the cell it’s characteristics, this cellular information is floating inside a substance called “nucleoplasm”. Separating all of this valuable information from the rest of the cell is something called a nuclear envelope. The nuclear envelope is a double membrane. The outer layer of the membrane is like the rough ER, it is dotted with ribosomes. The inner side of the double membrane is a sheet like structure of protein filaments called the “nuclear lamina” All throughout the nuclear envelope are holes, these holes are called “nuclear pores”. The pores job is to allow proteins and mRNA of a certain variety to pass through as well as select molecules that need to access the stored information the nucleus contains. These nuclear pores exist because the information within the nucleus is too valuable to be released into the cell where it could potentially be destroyed or otherwise changed. Therefor the pores make the nuclear envelope a semi-permeable membrane. Video.

DNA is how everything in your body is controlled. It works like an instruction manual for every part of the body with different parts of the genome being activated depending on what part of the body the cell is in. The nucleus dishes out the instructions and the other organelles follow them, in turn causing effects on the organism on a much larger scale. The DNA within the nucleus is usually in the form of chromatin, only during a very brief time in the cells cycle is it in the form of chromosomes. Chromatin is made up of tightly coiled DNA double helixes. Chromatin itself is usually found floating inside the nucleus coiled around proteins. Also found inside the nucleus is a fluid like substance called “nucleoplasm”. It can also be called “nuclear sap”, or “karyoplasm”. Nucleoplasm is primarily composed of water but also contains dissolved ions and complex molecules. The nucleoplasm serves as a suspension tool for everything contained inside the nucleus. Another function of the nucleoplasm is to maintain the shape and structure of the nucleus, as well as the transport of ions and other important substances important to the cells metabolism and function.

CHROMATIN VS. CHROMOSOMES Chromatin is the form groups of DNA take while in it’s normal state. Chromatin is tightly wound groups of DNA surrounded by protein. Chromosomes are the state that DNA takes during cell replication. This is the only time that DNA is in this state.

The Nucleus is highlighted in pink

The Nucleolus Scientists have known about the nucleus and what it does for quite awhile now, but more recently discovered is the nucleolus. Although discovered in the 18 th century the function of the nucleolus was not known until the 1960’s. The purpose of the nucleolus is to manufacture the parts required to create ribosomes, which then produce proteins. The more proteins produced by a cell the larger the nucleolus will be. It also the site of rRNA transcription. Once the rRNA has been transcribed within the nucleolus, it is combined with proteins. It then they are assembled into two subunits, one large and one small. These subunits leave the nucleolus and the nucleus through the nuclear pores all around the nucleus. When the subunits enter the cytoplasm of the cell, they come together to create a ribosomes. The ribosomes then go off to construct amino acids. Normally eukaryotic cells contain only one nucleolus, however it is possible for more than one to be present. In recent years scientists have begun to think that the nucleolus might be related to cell aging, although exact reasons remain unknown.

WHERE IS IT?

Because that was a lot to take in, here’s a summary. Nucleus is the largest organelle in the cell. Contains DNA, the instruction manual for everything. The DNA is in the form of chromatin (Tightly wound in groups of double helix DNA) When the cell is replicating the chromatin changes to chromosomes (Condensed chromatin) Nuclear envelope is a double membrane, it surrounds the nucleus and separates it from the rest of the cell. Nuclear Pores allow for the transport of mRNA and other molecules. (Semi-permeable membrane) Inside the nucleus is nucleoplasm, things are suspended inside it, it also transports important molecules. Nucleolus makes rRNA and ribosomes, located within the nucleus.