Nucleus
we're going to take a tour through this cell, talking about what all the structures of the cell are and then what they do, so the first thing we got to talk about is the cell's brain. It is the center of the cell where everything that a cell is a really begins in all centers around, and that is the nucleus; this is the big mama. The nucleus now what we have to talk about with the nucleus is a couple of different components of the nucleus. The presence of cells was reported in 1831 by Robert Brown. Its early discovery was due to its prominence in many cells. In animal cells, it generally occupies the central space, while in plant cells, it is pushed toward the periphery due to a large vacuole. The nucleus may be irregular or spherical. The cells have one nucleus and are called mononucleate. On the other, hand the cell having two nuclei are binucleate while with more than two nuclei as Multinucleate.
1) Nuclear envelope
well, the first part of the nucleus is, as you can see, a membrane that's double-layered here, so you have an outer layer, and then you have an inner layer on this side right, so this is our inner layer; these two components make up what's called the nuclear envelope. So, you have an outer layer, and then you have an inner layer. I know that sounds pretty obvious, but there's a difference; there are different functions for the outer and the inner layers. In the nuclear envelope, you have two layers, the outer layer,, and the inner layer. What is the purpose of these layers? So the first thing that you need to remember is that the outer layer is where you have lots of ribosomes.
Ribosomes are going to be found outside on that outer layer. In the actual nucleus you make, you take DNA and convert it into a structure called mRNA, and mRNA has to move out via the nuclear pores and bind onto ribosomes on these outer membranes,, which then get moved to the rough er. We'll talk about that a little bit later. But that's the big thing I want you to remember about the outer membrane; the inner membrane has a important protein structure that binds to the DNA and histone proteins and controls a lot of cell division. It's this green protein here that the green protein that lines the inner membrane is called lamins, and lamins are important structures that control the structure of the nuclear envelope. They're also important for cell division and interacting a lot with the chromatin. There's a disorder whenever there's a mutation in this lamins it causes progerias, so it's important that we know these two components of the nuclear envelope.
2) Nuclear pores
The nuclear pores allow the exchange of material between the nucleus and cytoplasm.
The next thing is in the nuclear envelope; you see these red proteins dispersed throughout it. Those red proteins that are dispersed throughout it are called nuclear pores. So what are these called nuclear pores?
if we want to move things in ions, proteins, nucleotides, different things in and out of the nucleus. That's the function of the nuclear pores, and there are special types of transporters associated with those nuclear pores. Another important thing is that it's a part of the nuclear envelope. If you will, that actually kind of uh kind of separates different portions, where there are little pores is called these nuclear pores,, and again the whole purpose of this is to allow for transport and what kind of transport between the cytoplasm to the nucleus or nucleus to the cytoplasm that's all it is pretty straightforward. The number of nuclear pores is highly variable. Each pore has a definite structure.
3) Nucleolus
The next one is this red diced-up structure here called the nucleolus is very important, and the reason why is this is the site of a particular type of RNA synthesis. It is a darkly stained body within the nucleus without any membranous boundary to separate it from the rest of the nuclear material. There may be one or more nucleoli in the nucleus. You know there is a particular type of RNA, what we call rRNA. So we're going to denote this as rRNA synthesis; this occurs in what structure this occurs within the nucleolus. When you take rRNA, you synthesize it within the nucleolus, and you combine this with proteins so then combine with other types of small proteins; guess what you make, you make ribosomes, so really what we can say is that the nucleolus, which is a component in the nucleus is important for making ribosomes which are made up of rRNA and small protein. The nucleolus comprises two regions, the peripheral granular area composed of precursors of the ribosomal subunit and the central fibrils area, consisting of large molecular weight RNA and rDNA.
4) Chromatin
The last part is small proteins the last part of the nucleus is all of these blue structures; you see all these blue structures that are dispersed throughout; I kind of made circles around them; this is called chromatin. The nucleus is often deeply stained with basic dyes because of chromatin material. Chromatin is very important because this is what makes up who we are as humans,,, and we need to know the different components of chromatin. Within the nucleus, you have this structure called chromatin. Chromatin comprises two primary things DNA and proteins,, but the main protein is histone proteins. These two things make up our actual genetic material. Chromatin can come in two important forms: Euchromatin and Heterochromatin.
Euchromatin is the loose chromatin,, and it's the one that's going to be more for expression of the DNA to transcribe the DNA and make different types of mRNA or undergo replication,, so euchromatin should be more in the center of the actual nucleus.
Heterochromatin: The next one here will be hetero the,, and the heterochromatin will be the tight chromatin; this will be the chromatin that you're going to see closer towards the inner membrane of that nuclear envelope.
We can take DNA,, and we can make more DNA,, which is called DNA replication. I can take DNA and make RNA,, which is called transcription,, and also,, you need to know that there are different types of RNA. What are the different types of RNA? There is tRNA, there is
mRNA and rRNA.We need to understand this kind of thing that is happening inside the nucleus.
5) Chromosomes
During cell division, chromatin material is converted into darkly stained thread-like structures known as chromosomes. A chromosome is composed of DNA and proteins. Information necessary to control the cell's activities is located on the chromosomes in the form of genes, which are transferred from one generation to the other. The number of chromosomes in all individuals of the same species remains constant,, generation after generation. For example, in man, each cell contains 46 chromosomes. Etc...
Under a compound microscope, chromosomes appear to be made of arms and centromeres. The centromere is the place on the chromosome where spindle fibers are attached during cell division. Each chromosome consists of two identical chromatids at the beginning of cell division held together at the centromere.
You must be logged in to post a comment.