Cells Chapter 3
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- Also call the plasma membrane. The cell membrane separates intracellular (inside the cell) maerial from extracellular (outside the cell) materials. It allows the selection of substances allowed to enter or leave the cell.
A semipermeable membrane, also termed a selectively-permeable membrane, a partially-permeable membrane or a differentially-permeable membrane, is a membrane that will allow certain molecules or ions to pass through it by diffusion and occasionally specialized "facilitated diffusion".
- The nucleus is the most obvious organelle in any eukaryotic cell. It is a membrane-bound organelle and is surrounded by a double membrane. It
- communicates with the surrounding cytosol via numerous nuclear pores. Within the nucleus is the DNA responsible for providing the cell with its
- unique characteristics. The DNA is similar in every cell of the body, but depending on the specific cell type, some genes may be turned on
- or off - that's why a liver cell is different from a muscle cell, and a muscle cell is different from a fat cell. When a cell is dividing, the DNA and surrounding protein condense into chromosomes (see photo) that are visible by microscopy. The prominent structure in the nucleus is the nucleolus. The nucleolus produces ribosomes, which move out of the nucleus to positions on the rough endoplasmic reticulum where they are critical in protein synthesis.
The nucleus contains genetic information and controls all protein synthesis. Is covered by a double layer Nuclear membrane.
Contain large pores that allow free movement of certain substances between the nucleus and cytoplasm.
a substance filled in the nucleus.
Is a gel-like substance found inside the cell but outside the nucleus (Like the white of a raw egg). The gel of the cell is composed primarily of water, electrolytes, and nutrients. The cutoplasm contains numberous organelles and inclusion bodies.
- In cell biology, an organelle (pronounced /ɔrɡəˈnɛl/) is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer.
- The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name organelle, the suffix -elle being a diminutive). Organelles are identified by microscopy, and can also be purified by cell fractionation. There are many types of organelles, particularly in eukaryotic cells. Prokaryotes were once thought not to have organelles, but some examples have now been identified.
Are tiny, slipper-shaped organelles. Number per cel varies, depending on the metabolic activity of the cell. The more it's active, the more mitochondria per cell.
Mitochondria provide the energy a cell needs to move, divide, produce secretory products, contract - in short, they are the power centers of the cell. They are about the size of bacteria but may have different shapes depending on the cell type.Mitochondria are membrane-bound organelles, and like the nucleus have a double membrane. The outer membrane is fairly smooth. But the inner membrane is highly convoluted, forming folds called cristae. The cristae greatly increase the inner membrane's surface area. It is on these cristae that food (sugar) is combined with oxygen to produce ATP - the primary energy source for the cell.
The inner layer of the mitochondria.
Cristae (singular crista) are the internal compartments formed by the inner membrane of a mitochondrion. They are studded with proteins, including ATP synthase and a variety of cytochromes. The maximum surface for chemical reactions to occur is within the mitochondria. This allows cellular respiration (aerobic respiration since the mitochondria requires oxygen) to occur.
- Cells need to make proteins. Those proteins might be
- used as enzymes or as support for other cell functions. When you need to
- make proteins, you look for ribosomes. Ribosomes are the protein builders or the protein synthesizers of the cell. They are like construction guys who connect one amino acid at a time and build long chains.
- Ribosomes are found in many places around the cell. You might find them floating in the cytoplasm (cytosol). Those floating ribosomes make proteins that will be used inside of the cell. Other ribosomes are found on the endoplasmic reticulum. Endoplasmic reticulum with attached ribosomes is called rough. It looks bumpy under a microscope. Those attached ribosomes make proteins that will be used inside the cell and proteins made for export out of the cell.
Another organelle in the cell is the endoplasmic reticulum (ER). While the function of the nucleus is to act as the cell brain, the ER functions as a packaging system. It does not work alone. The ER works closely with the Golgi apparatus, ribososmes, RNA, mRNA, and tRNA. It creates a network of membranes found through the whole cell. The ER may also look different from cell to cell, depending on the cell's function.
- Rough and Smooth
- As you learn more about cells you will discover two types of ER. There are rough ER and smooth ER. They both have the same types of membranes but they have different shapes and rough ER has ribosomes attached. Rough ER looks like sheets of bumpy membranes while smooth ER looks more like tubes. Sometimes the ER looks like a flat balloon. Sacs of the ER called cisternae store the complex molecules.
Smooth endoplasmic reticulum
- Smooth ER has its purpose in the cell. It acts as a storage organelle. It is important in the creation and storage of steroids. It also stores ions
- in solution that the cell may need at a later time. Steroids are a type of ringed organic molecule used for many purposes in an organism. They
- are not always about building muscle mass like a weight lifter. The ion storage is important because sometimes a cell needs ions fast. It might
- not want to search the environment for ions, so it is easier to have them stored in a pack for easy use.
Rough endoplasmic reticulum
Rough ER was mentioned in the section on ribosomes. They are very important in the synthesis and packaging of proteins. Some of those proteins might be used in the cell and some are sent out. The ribosomes are attached to the membrane of the ER. As the ribosome builds the amino acid chain, the chain is pushed into the ER. When the protein is complete, the rough ER pinches off a vesicle. That vesicle, a small membrane bubble, can move to the cell membrane or the Golgi apparatus.
- lysosomes are in nearly every animal-like eukaryotic cell. Lysosomes hold enzymes that were created by the cell. The purpose of the lysosome is to digest things. They might be used to digest food or break down the cell when it dies. What creates a lysosome? You'll have to visit the Golgi complex for that answer.
- A lysosome is basically a specialized vesicle that holds a variety of enzymes. The enzyme proteins are first created in the rough endoplasmic reticulum. Those proteins are packaged in a vesicle and sent to the Golgi apparatus. The Golgi then does its final work to create the digestive
- enzymes and pinches off a small, very specific vesicle. That vesicle is a lysosome. From there the lysosomes float in the cytoplasm until they
- are needed. Lysosomes are single-membrane organelles.
- Since lysosomes are little digestion machines, they go to work when the cell absorbs or eats some food. Once the material is inside the cell,
- the lysosomes attach and release their enzymes. The enzymes break down complex molecules that can include complex sugars and proteins. But what if food is scarce and the cell is starving? The lysosomes go to work even if there is no food for the cell. When the signal is sent out,
- lysosomes will actually digest the cell organelles for nutrients.
Are paired, rod-shaped microtubular structures that play a key role in cellular reproduction.
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.
Are short, hairlike projections on the outer surface of the cell.
Are similar to cilia in that both are hairlike projections; however, it is thicker, longer and fewer in number.
- Flagella are long, thread-like appendages which provide some live single cells with the ability to move, motility. Bacteria which have flagella are either rod or spiral-shaped and are known as bacilli and spirochetes, respectively. Cocci, or round bacteria, are almost all nonmotile. Animal
- sperm cells also have flagella. However, prokaryotic cells (such as bacteria) have flagella made up of the protein flagellin. Whereas,
- eukaryotic cells (such as sperm) which have a nucleus have flagella composed of tubulin proteins.
Passive transport means moving biochemicals and atomic or molecular substances across the cell membrane. Unlike active transport, this process does not involve chemical energy. The four main kinds of passive transport are diffusion, facilitated diffusion, filtration and osmosis.
- Active transport is the movement of a substance against its concentration gradient using energy. In cells this is usually concerned
- with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, amino acids. If the process uses chemical energy,
- such as from adenosine triphosphate (ATP), it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient. Active transport uses energy, unlike passive transport, which does not use any energy. Active transport is a good example of a process for which cells require energy. Examples of active transport include the uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of plants.
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