The Cell
Organelles
- Cell Membrane
- Cell Wall
- Nucleus
- Nucleolus
- Endoplasmic Reticulum
- Golgi Apparatus
- Vacuole
- Lysosome
- Peroxisome
- Secretory Vesicle
- Mitochondrion
- Cytoskeleton
- Centrosome
- Centrioles
Other Cell Sites
CELLS alive!
Parts of the Cell
Introduction to Cytology
A cell is the smallest structural unit of an organism that is capable of independent functioning, consisting of one or more nuclei, cytoplasm, and various organelles, all surrounded by a semipermeable cell membrane. Cells are divided into two types: Prokaryotic and Eukaryotic. The way cells are classified into either of these two types depends on how complex the cell is. All living things are made of atleast one cell, ranging from tiny bacteria to even the divine mightyness that is Mr. T.
Types of Cells
Prokaryotic cells, such as bacteria, are very simple, with little or no organelles, and no, not Redneck simple, simple as in inelaborate. Prokaryotic cells have a cell wall to give them structure, underneath which is a cell membrane. They have a nucleoid, which isn't distinctly shaped, but it's where the DNA of the cell generally is. Prokaryotic cells also have ribosomes, which articulate RNA messages into the production of proteins. These cells also have storage granules, which are used to store anything from lipids to sulfer in the cell. Some prokaryotiic cells make endospores, which are resistant to harsh conditions. Once the conditions cease, the endospores will germinate and create a new population.
Eukaryotic cells, such as plant and animal cells, are much more complex than prokaryotic cells. They are also generally larger than prokaryotic cells, and, as such, have developed ways to support their larger size.
Organelles
Cell Membrane: The membrane of the cell is the thin layer around the outside of the cell that allows molecules to pass in or out. It is comprised of phospholipids, which have a hydrophilic head and a hydrophobic tail, and are grouped together through self-assembly. There are also cholesterol in membranes, which are used to pack the phospholipids together, and can be converted to Vitamin D. The membrane is believed to be fluid, so that osmosis can occur and proteins can flow in and out.
Cell Wall: The cell wall is a rigid wall of polysaccharides, is found only in plant cells and prokaryotic cells, and provides structure and shape for the cell, as well as protection.
Nucleus: The nucleus is surrounded by two cell membranes, and has multiple pores through which to communicate with the surrounding cell. Inside the nucleus is DNA, which is similar throughout an organism. During mitosis, or cell division, the DNA condense into chromosomes that we can see with a microscope.
Nucleolus: Inside of the nucleus is the nucleolus, which produces rhibosomes. It will sometimes move to the rough endoplasmic reticulum, where is is necesary for protein synthesis.
Endoplasmic Reticulum (ER): An extention of the outer membrane of the nucleus, the ER takes up a large amount of space in the cell. There are smooth sections of the ER, and there are rough sections. This section appears rough due to the ribosomes present there, which are important for protein synthesis. The smooth ER is used for lipid synthesis, as well as membrane protein synthesis. The ER has transport vesicles, which it uses to transport RNA-rich ribosomes from the ER to the Golgi Apparatus.
Golgi Apparatus: A network of stacked membranous vesicles present in most living cells that functions in the formation of different secretions within the cell, including lysosomes, peroxisomes and secretory vesicles.
Vacuole: Vacuoles are membrane-bound sacks that help in cell digestion and cellular waste release. Vacuoles are generally small in animal cells, though they are huge in some plant cells. When plants are watered, the water is stored in the vacuole, and the cell and plant remains rigid. When the vacuole loses that water, the cells become less rigid and the plant begins to wilt.
Lysosome: Contains hydrolytic enzymes that are needed for cellular digestion. When a cell is digesting another cell, the lysosomes release their enzymes into the vacuole of the cell to digest the other cell. If lysosomes uncontrollibly release enzymes into the cytoplasm, then cell death can occur.
Peroxisomes: These cells break down the hydrogen peroxide of the lysosomes into water and oxygen so that cell death doesn't occur.
Secretory Vesicles: Cell secretions are packed into these at the golgi apparatus, then these organelles are transported to the cell's surface to release the secretions, such as hormones and neurotransmitters.
Mitochondrion: These are about the size of prokaryotic cells, and they provide the energy for the cells. Mitochondria have a double membrane, like the nucleus, but the inner membrane, the cristae, is folded. On these, sugar is combined with oxygen to make ATP, the energy source for the cells.
Cytoskeleton: This organelle helps maintain the cell's shape, as well as giving the cell mobility. The cytoskeleton is a network of three protein filaments: microtubules, actin filaments, and intermediate fibers.
Centrosome: The place where microtubules are produced. Within the centrosome of animal cells there are two centrioles, each made up of nine microtubules, and are arranged perpendicular to each other. During mitosis, the centrosome splits into two, each with two centrioles, and microtubules from each side stretch out into a spindle, which hook onto the chromosomes which to to the corresponding cell.
