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Transcript
MAJOR PARTS OF THE CELL A cell wall is a tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing over-expansion when water enters the cell. They are found in plants, bacteria, fungi, algae, and some archaea. Animals and protozoa do not have cell walls. Plasma Membrane. This is the outer boundary of the cell. It is made of phospholipids (fats) and cholesterol. Proteins are embedded with in the membrane. These proteins allow certain molecules to enter and exit the cell. The proteins and phospholipids block many harmful molecules from entering the cell, but they will allow important molecules such as oxygen and food molecules to enter. Each cell must “breathe and eat”. If nothing could enter the cell, then the cell would suffocate and starve. Just like you the cell must be able to get rid of waste products such as carbon dioxide and food waste. The proteins embedded in the plasma membrane allow these waste products to exit without letting out nutrients the cell needs to survive. The CARBOHYDRATES on the outside of the cell are tags that identify the cell to other cells. They can also hold out signs that tell the immune system that they have been invaded by a disease and need to be destroyed by the immune system. Nucleus:This is the largest organelle in the cell. It is separated from the cytoplasm by a double phospholipid membrane (similar to the plasma membrane) called the nuclear membrane. The cell’s DNA is inside the nucleus. The DNA is packaged into 46 chromosomes. The nuclear envelope is an extra layer of protection for the DNA from anything harmful that might enter the cell. Since the DNA has all the instructions for the cell to follow, the DNA must communicate with the rest of the cell. Large pores within the nuclear membrane allow messenger molecules to enter and exit the nucleus. These pores are guarded by proteins. The proteins will not allow the DNA to exit and prevent many harmful molecules from entering. The nucleolus is a large factory that builds ribosomes. The ribosomes exit the nuclear pores. DNA:DNA stands for deoxyribonucleic acid. DNA controls all of the cells activities. The DNA sends out messenger proteins that tell the cell what to do. Messenger proteins also report to the DNA about the cells activities. The cell would not know what to do without the DNA. Every cell within an organism contains an identical set of DNA. Endoplasmic Reticulum (ER):The ER looks like flattened sheets, sacs and tubes of membrane. The ER surrounds the nucleus and extends into the cytoplasm of the cell. The ER BUILDS lipids (fats) and membrane proteins. The ER will also TRANSPORT these molecules to the place in the cell they need to go next. The ER is divided into two parts. The ROUGH ER and the SMOOTH ER. The Rough ER has RIBOSOMES studded on the outer membranes of the ER. The ribosomes are what build large protein molecules. The Smooth ER is smooth because it has no ribosomes on the surface. This part of the ER builds large lipid molecules. When the lipids and proteins are ready for transport they will be packaged into small membrane bound vesicles that break off of the ER. Many times these vesicles are headed to the GOLGI APPARATUS. (Look at next picture.) Golgi Apparatus:The golgi apparatus is a system of stacked, membrane-bounded, flattened sacs. The golgi apparatus modifies macromolecules (large molecules) by adding or removing pieces to make the final product. It will also sort macromolecules into groups so they can be packaged and sent to different places. Some of these packages are sent out of the cell. Some are sent to other organelles. Membrane bound vesicles transport these macromolecules between the flattened sacs of the golgi apparatus and to other parts of the cell. These vesicles are formed by the golgi’s membrane. Lysosomes: These are membrane-bounded vesicles that contain acid and enzymes that digest or break down intracellular macromolecules. The macromolecules are broken down into their smaller molecular components. They are then secreted (released) by the lysosome to be used by the cell or sent out of the cell as waste. A few examples of enzymes found inside the lysosome are protease, lipase, and nuclease. The enzyme protease breaks down protein macromolecules. The enzyme nuclease breaks down nucleotides found in DNA. The enzyme lipase breaks down lipids or fats. Mitochondria: These organelles create all the energy for the cell. There are many of these within each cell. Since an organism is a composition of cells, all the energy needed for the organism comes from the mitochondria. Chloroplasts – are plastids containing the pigment chlorophyll. Chlorophyll is used during photosynthesis to capture light energy. That light energy is used to break apart the chemical bonds of Carbon dioxide and water so the atoms can be used to build sugar molecules. A group of plastids is called a thylakoid.