- List the organelles of the cell and their functions.
- Distinguish between plant and animal cells.
Do brain cells (pictured above) have the same internal structures as your other cells?
Yes. Although brain cells look quite different from your other cells, they have the same internal structures as other cells. They need the same structures because they need to perform the same tasks, such as making proteins and obtaining energy.
In some ways, a cell is like a factory. A factory has many machines and people, and each has a specific role. Just like a factory, the cell is made up of many different parts. Each part has a special role. The different parts of the cell are called organelles, which means "small organs." Organelles are found in eukaryotic cells. Prokaryotic cells are "simpler" than eukaryotic cells. Though prokaryotic cells still have many functions, they are not as specialized as eukaryotic cells. Thus, prokaryotic cells do NOT have most types of organelles.
Below are the main organelles found in eukaryotic cells (Figure 2.1):
- The nucleus of a cell is like a safe containing the factory's trade secrets. The nucleus contains the genetic material-the information about how to build thousands of proteins.
- The mitochondria are the powerhouses of the cell; they provide the energy needed to power chemical reactions. This energy is in the form of ATP (adenosine triphosphate). Cells that use a lot of energy may have thousands of mitochondria.
- Vesicles are small membrane bound sacs that transport materials around the cell and to the cell membrane.
- The vacuoles are like storage centers. Plants store water and nutrients in their large central vacuoles.
- Lysosomes are like the recycling trucks that carry waste away from the factory. Lysosomes have digestive enzymes that break down old molecules into parts that can be recycled.
- In both eukaryotes and prokaryotes, ribosomes are the non-membrane bound organelles where proteins are made. Ribosomes are like the machines in the factory that produce the factory's main product. Proteins are the main product of most cells.
- Some ribosomes can be found on folded membranes called the endoplasmic reticulum (ER), others float freely in the cytoplasm. If the ER is covered with ribosomes, it looks bumpy like sandpaper, and is called the rough endoplasmic reticulum. Many proteins are made on the ribosomes on the rough ER. These proteins immediately enter the ER, where they are modified, packaged into vesicles and sent to the Golgi apparatus. If the ER does not contain ribosomes, it is smooth and called the smooth endoplasmic reticulum. Lipids are made in the smooth ER, which also detoxifies poisons.
- The Golgi apparatus works like a mail room. The Golgi apparatus receives proteins from the rough ER and puts "shipping addresses" on them. The Golgi then packages the proteins into vesicles and sends them to the right place in the cell or to the cell membrane. Some of these proteins are secreted from the cell (they exit the cell); others are placed into the cell membrane.
- The cytoskeleton gives the cell its shape, and the flagella helps the cell to move. Prokaryotic cells may also have flagella.
Figure 2.1 Eukaryotic cells contain special compartments surrounded by membranes, called organelles. For example, notice in this image the mitochondria, lysosomes, and Golgi apparatus.
Do plants have cells like yours?
Yes, your cells are actually very similar to a plant's cells. For example, they are both eukaryotic cells, both contain DNA in a nucleus, and both make proteins in ribosomes. However, plant cells also differ in some crucial ways from your own cells.
But even though plants and animals are both eukaryotes, plant cells differ in some ways from animal cells (Figure2.2)
Figure 2.2 The Plant Cell
(1) Plant cells have a large central vacuole that holds a mixture of water, nutrients, and wastes. A plant cell's vacuole can make up 90% of the cell’s volume. The large central vacuole essentially stores water. What happens when a plant does not get enough water? Many animal cells do not have vacuoles; if they do, the vacuoles are much smaller.
(2) Plant cells have a cell wall, while animal cells do not (Figure 2.3). The cell wall surrounds the plasma membrane but does not keep substances from entering or leaving the cell. The cell wall also makes plant cells look like blocks as compared to animal cells.
Figure 2.3 A cell wall gives the plant cell strength and protection.
(3) Plant cells have chloroplasts which are needed for photosynthesis. Chloroplasts contain chlorophyll, which gives them their green color. Chloroplasts convert the sun's energy into the energy usable energy for the cell.
Be able to:
Instead of questions this time, complete the chart at the end of your Notes Packet as directed below regarding the organelles or cell parts listed in the first column
(a) Describe each organelle's function in the second column.
(b) Write the "factory metaphor" (if given in the list earlier in this reading)
(c) For the fourth column, go to http://www.cellsalive.com/cells/cell_model_js.htm
•Select "Animal Cell" and click on the organelles listed. Record a short summary phrase based on what you read.
•Select "Plant Cell" and clock on the organelles specific to plants. Record a short summary phrase.
Cell Part Review
- The nucleus stores the genetic information.
- The vacuoles are needed for storage.
- The lysosomes recycle waste.
- The cytoskeleton provides the shape of the cell.
- The ribosomes produce proteins.
- The rough ER is covered with ribosomes and makes proteins, while the smooth ER makes lipids.
- The Golgi apparatus packages proteins.
- Plant and animal cells differ in that plants have a large central vacuole, while animals have smaller vacuoles.
- Plant cells also have cell walls and chloroplasts, while animal cells do not.