Cells / Human Bio 160

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ORGANELLES

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little organs.

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ALL CELLS HAVE:

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Lysosomes,Ribosomes,Nucleus, Cytoplasm, Nucleolus, Cell Membrane, Mitochondria, Endoplasmic Reticulum, Golgi Apparatus

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PLANT CELLS HAVE:

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Cell Wall, Vacuoles, Chloroplasts

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LYSOSOMES

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hold chemicals that break down food molecules, old cell parts, and harmful bacteria. They are surrounded by a lipid bilayer membrane that keeps their strong digestive chemicals contained inside. Thus, the lysosomes have similar functions to the digestive system of the body.

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RIBOSOMES

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are little grains of RNA and proteins. Their job is to assemble amino acids into proteins under the direction of the cell's DNA. Some ribosomes are associated with the rough endoplasmic reticulum and assist with its protein synthesis

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MITOCHONDRIA

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are the organelles that make the molecules that provide cell energy (ATP). One of these organelles is a mitochondrion which means thread-like granule. Mitochondria are small spherical or elliptical organelles surrounded by a special lipid bilayer membrane. The membranes of mitochondria both separate them from the cytoplasm and divide the inside into leaflets. Mitochondria are where the cell's energy is made. Thus mitochondria are sometimes called the cell's powerhouse

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cell membrane

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1. Functionally the cell membrane serves as both a gateway and a barrier for the cell.
2. The cell membrane is composed of phospholipids and proteins.
3. The heads of the phospholipids are polar so they like to be with water, which is inside and outside of the cell.
4. The tails of the phospholipids are not polar.
5. The tails do not like to be with water and thus a lipid bi-layer may be formed when phospholipids are exposed to water.

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cell membrane Location:

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The cell membrane surrounds the cell.

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cell membrane Structure:

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Cell membranes are made up of phospholipid molecules (fats) with various large globular protein molecules suspended in them. The lipid bi-layer (two layers of phospholipids) is formed because of the chemical structure of a phospholipid. Since cells are constantly in water, the phospholipids form a double layer, with the heads towards the water and the tails inside so that they can stay away from the water. These bi-layers have proteins scattered about in them. Sometimes carbohydrates (sugars) are attached to cell membrane phospholipids and to cell membrane proteins. A selectively permeable (sometimes called semi-permeable) membrane allows some molecules across but not others.

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cell membrane JOB:

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The cell membrane controls what enters and exits the cell and thus protects the cell.

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The heads of PHOSPHOLIPIDS

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The heads of the PHOSPHOLIPIDS are composed of glycerol and a phosphate group and like to dissolve in water. Water is a polar molecule (it acts like it has two poles) and other molecules that are polar easily dissolve in water. These molecules that easily dissolve in water are called water-loving (or hydrophilic) molecules.

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The tails of PHOSPHOLIPIDS

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The tails of the PHOSPHOLIPIDS are mostly fatty acids made up of long carbon and hydrogen chains. Carbon and hydrogen chains are not polar and do not like to dissolve in water. Molecules that do not easily dissolve in water are called water-hating (or hydrophobic) molecules.

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Diffusion vs. Active Transport:

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molecules move across cell membranes by two major processes diffusion or active transport. Diffusion is the movement from a high concentration of molecules to a low concentration of molecules. Molecules can diffuse across membranes through the phospholipid bilayer or using a special protein. Either kind of diffusion does not need energy from the cell. Some special proteins move certain molecules across cell membranes only with the help of cell energy (either directly or indirectly). Moving molecules with cell energy is called active transport. The cell energy is the ATP made in the mitochondria.

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osmosis

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When water diffuses the process is called osmosis. Water moves from a high concentration of water (less salt or sugar dissolved in it) to a low concentration of water (more salt or sugar dissolved in it). This means that water would cross a selectively permeable membrane from a dilute solution (less dissolved in it) to a concentrated solution (more dissolved in it).

Water can cross the cell membrane through the lipid bi-layer and with special proteins. If enough water enters the cell by osmosis, the cell can swell enough to burst open and die. in a glass of distilled water (all water with no salt or sugar in it). Because there is a higher concentration of water outside the cell, water enters the cell by OSMOSIS. In this case too much water enters and the cell swells to the point of bursting open. In the end pieces of cell membrane are left in the water. Pieces of red blood cell membranes are known as red blood cell ghosts.

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NUCLEUS

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A NUCLEUS acts as the control center for the cell. It contains DNA that directs all functions of the cell. The nucleus has its own lipid bilayer membrane with large pores. Thus the nuclear membrane is also a selectively permeable membrane that regulates what can enter or leave the nucleus. The nucleus has a similar function to the brain of the body.