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Cell structure

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kitchasorn soontornnapaluk

on 15 October 2012

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Transcript of Cell structure

dee grade 10 Cell structure Prokaryotes - have a nucleus
- have organelles (compartments that enable a cell to function by making and releasing energy, helping the cell to maintain homeostasis, and enabling a cell to reproduce)
- all other cells (other than bacteria)
- found in the Protista, Fungi, Plant, and Animal kingdoms
- have 1000 times more DNA than prokaryotic cells Eukaryotic cell Animal cell What's the difference between prokaryotic and eukaryotic cells? Plant cell Animal cells do not have rigid cell walls like plant cells. This allows animal cells to form and adopt various shapes. A type of animal cell called the phagocytic cell can even absorb other structures. This ability is not inherent in plant cells.

Further, unlike animal cells, plant cells have chloroplasts for the utilization of sunlight and this is what also gives plant cells their green color. It is with the help of chloroplasts that contain chlorophyll, the plant cells perform the function of photosynthesis which is a process absent in animal cells.

Plant cells also contain a larger central vacuole (enclosed by a membrane) as compared to animal cells. Also, while animal cells depend on an analogous system of gap-junctions that allows communication between cells, the plant cells use linking pores in their cell wall to connect to each other and pass information.
What's the difference between plant and animal cells? Capsule - Found in some bacterial cells, this additional outer covering protects the cell when it is engulfed by other organisms, assists in retaining moisture, and helps the cell adhere to surfaces and nutrients. Cell Wall - Outer covering of most cells that protects the bacterial cell and gives it shape. Cell Membrane or Plasma Membrane - This is a lipid bilayer similar to the plasma membrane of other cells. There are numerous proteins moving in or on this layer that transport waste, ions, and nutrients across the membrane. Pili – These are hollow, hair-like extensions made of protein allow prokaryotes to attach to other cells. One particular type, the sex pilus, allows the transfer of DNA from one prokaryote to another. Pili are also called fimbriae. Flagella - Flagella located just under the cytoplasmic membrane. They are used to move the cell around. Prokaryotes may have one, a few, or many flagella in different places on the cell. Ribosomes – Ribosomes make the cytoplasm of prokaryotes look granular appearance in electron micrographs. They are smaller than ribosomes in eukaryotic cells, but they do the same job of translating the genetic message in messenger RNA so as to produce proteins. Periplasmic space – This is found only in prokaryotes with both an outer membrane and plasma membrane. In the space between the two membranes are enzymes and other proteins that help digest and move nutrients into the cell. - have no nucleus
- have no membrane-bound organelles
- make up the kingdoms Monera (bacteria) and Archaea
- prokaryotes are more primitive than eukaryotes
- cells have a single circular chromosome - have ribosomes surrounded by a cell membrane and a cell wall
- may have photosynthetic pigments - some prokaryotes have an external flagellum for locomotion or pili for adhesion - shapes: baccilli (rods), cocci (round), spirilla (helical) nucleus - controls the cell’s activities; contains the DNA cell membrane - the thin layer of protein and fat that surrounds the cell. The cell membrane is semipermeable, allowing some substances to pass into the cell and blocking others. Ribosomes - Ribosomes made of protein and RNA molecules. ribosome assembly begins in the nucleolus and is completed in the cytoplasm. Mitochondria - the mitochondria that the sugar is finally burnt during cellular respiration. The energy thus released is stored as high-energy chemicals called ATP (adenosine triphosphate). Hence, mitochondria are termed as the “power house” or the “power plant” of the cell. The body cells use the energy stored in ATP for synthesis of new chemical compounds. Nucleolus - The prominent structure in the nucleus is the nucleolus. The nucleolus produces ribosomes, which move out of the nucleus and take positions on the rough endoplasmic reticulum where they are critical in protein synthesis. cytoplasm - the region of the cell that is within all of the organelles. The rough endoplasmic reticulum - manufactures membranes and secretory proteins. In leukocytes the rough ER produces antibodies. In pancreatic cells the rough ER produces insulin. The rough and smooth ER are usually interconnected and the proteins and membranes made by the rough ER move into the smooth ER to be transferred to other locations.
the smooth endoplasmic reticulum - The smooth ER has a wide range of functions including carbohydrate and lipid synthesis. It serves as a transitional area for vesicles that transport ER products to various destinations. In liver cells the smooth ER produces enzymes that help to detoxify certain compounds. In muscles the smooth ER assists in the contraction of muscle cells, and in brain cells it synthesizes male and female hormones. The Golgi apparatus - is integral in modifying, sorting, and packaging these macromolecules for cell secretion (exocytosis) or use within the cell. It primarily modifies proteins delivered from the rough endoplasmic reticulum but is also involved in the transport of lipids around the cell, and the creation of lysosomes. In this respect it can be thought of as similar to a post office; it packages and labels items which it then sends to different parts of the cell. Chloroplasts - The most important characteristic of plants is their ability to photosynthesize, in effect, to make their own food by converting light energy into chemical energy. This process is carried out in specialized organelles called chloroplasts. vocuole - A vacuole is a membrane-bound sac that plays roles in intracellular digestion and the release of cellular waste products. In animal cells, vacuoles are generally small.
Vacuoles tend to be large in plant cells and play a role in turgor pressure. When a plant is well-watered, water collects in cell vacuoles producing rigidity in the plant. Without sufficient water, pressure in the vacuole is reduced and the plant wilts.
The cell wall is composed of cellulose fiber, polysaccharides, and proteins. In new cells the cell wall is thin and not very rigid. This allows the young cell to grow. This first cell wall of these growing cells is called the primary cell wall. When the cell is fully grown, it may retain its primary wall, sometimes thickening it, or it may deposit new layers of a different material, called the secondary cell wall.
Cell wall - the cell wall is a rigid layer that lies outside the cell's plasma membrane. plant cell wall contain a carbohydrate called cellulose. cellulose is embedded in a matrix of proteins and other carbohydrates that form a stiff box around each cell. pores in the cell wall allow water, ions, and some molecules to enter and exit the cell. Eukaryotic cells have a true nucleus, bound by a double membrane. Prokaryotic cells have no nucleus. The purpose of the nucleus is to sequester the DNA-related functions of the big eukaryotic cell into a smaller chamber, for the purpose of increased efficiency. This function is unnecessary for the prokaryotic cell, because its much smaller size means that all materials within the cell are relatively close together. prokaryotic cells do have DNA and DNA functions. Eukaryotic DNA is linear; prokaryotic DNA is circular Eukaryotic DNA is complexed with proteins called "histones," and is organized into chromosomes; prokaryotic DNA is "naked," meaning that it has no histones associated with it, and it is not formed into chromosomes. Though many are sloppy about it, the term "chromosome" does not technically apply to anything in a prokaryotic cell. A eukaryotic cell contains a number of chromosomes; a prokaryotic cell contains only one circular DNA molecule and a varied assortment of much smaller circlets of DNA called "plasmids." The smaller, simpler prokaryotic cell requires far fewer genes to operate than the eukaryotic cell. Both cell types have many, many ribosomes, but the ribosomes of the eukaryotic cells are larger and more complex than those of the prokaryotic cell. Ribosomes are made out of a special class of RNA molecules and a specific collection of different proteins.
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