Kristelle Dae B. Pagunsan 11 HUMSS - SOCRATES Cell Theory The study of cell started about 300 years ago with the help of one powerful instrument called the ‘microscope’ invented by Hans and Zacharias Janssen, the cell has begun to be known to humans. The development and refinement of magnifying lenses and light microscopes made the observation and description of microscopic organisms and living cells possible. Revised Cell Theory 1. Cells are the basic units of structure and function in an organism. 2. All living things are made up of cells. 3. Cells came from pre-existing cells by division. Continued advances in microscopy allowed observation of cell organelles and structure. Proponents and Contributors of the Cell Theory Robert Hooke – An English Scientist who coined the term ‘cell’. He observed that a cork has small regular boxes in it that he called “cells.” He is the inventor of the compound microscope. Anton van Leeuwenhoek “Father of Ancient Microbiology” - He’s a Dutch business man and scientist who was the first to see bacteria and protists. He described cells in a drop of pond water that he called “animalcules”. Matthias Schleiden – A German botanist who concluded that all plant tissues are composed of cells. Theodor Schwann – A German Zoologist. He concluded that all animal tissues are composed of cells. He is one the proponents of the Cell Theory. Rudolph Virchow – A German Scientist who discovered that all cells came from pre-existing cells. He completed the cell theory by expounding his famous “omnis cellula e cellula” which means “cells develop from pre-existing cells.” According to Schwann, 1.) The cell is the unit of structure, physiology, and organization in living things. 2.) The cell retains a dual existence as a distinct entity and a building block in the construction of organisms. 3.) Cells form by free-cell formation, similar to the formation of crystals (Spontaneous Generation). Robert Brown – English botanist who discovered the nucleus in plant cells (orchid). Hans and Zacharias Janssen – Credited for the production of lenses. Differences of Plant and Animal Cell Plant Cell Animal Cell 1. Rectangular/Box-like shape 1. Spherical/Round shape 2. Relatively larger in size 2. Relatively smaller in size 3. Covered by a thick cell wall 3. No Cell wall. Only covered by a thin cell membrane. 4. Vacuole is big, prominent, and permanent 4. Vacuole is small, not so prominent, and temporary 5. Plastids are only present in plant cell 5. Plastids are absent 6. Absence of Centrosome 6. Centrosome is present in Animal cell 7. Number of Mitochondria is less in plant cell than animal cell 8. Cell division occurs by cell plate 9. Have 9 parts composed of; Cell membrane, cell wall, chloroplasts, chromosomes, cytoplasm, mitochondria, nuclear membrane, nucleus, and vacuoles 7. Number of Mitochondria is approximately more in animal cell 8. Cell division occurs by furrow in spite of cell plate 9. Only have 7 parts which are; Cell membrane, chromosomes, cytoplasm, mitochondria, nuclear membrane, nucleus, and vacuoles Prokaryotic and Eukaryotic Cells Prokaryotic Cells - have no nucleus or organelles enclosed within membranes a single cell organism that does not have a nucleus do not have nucleus, and their genetic material is not stored in the nucleus less complicated than eukaryotes all bacteria are prokaryotes Eukaryotic Cells - a more complex cell with a nucleus and many organelles they all have a nucleus where the genetic material of the cell is stored have many organelles that work together to help the cell function can be just one cell or can make up more complex multi-cellular organisms all plants, animals, fungi, and protists are eukaryotic cells Parts of a Cell and their Functions 1. Cell Membrane – holds the cell together and lets substances pass in and out of the cell; separates the cell from other cells ; allows molecules to pass through 2. Nucleus – controls the cell’s activities 3. Cell Wall – gives a stiff and rigid shape to the cell; gives protection and support 4. Cytoskeleton – structural support; cell movement 5. Flagella – motility or moving fluids over surfaces 6. Plasma Membrane – regulates what passes into and out of the cell 7. Endoplasmic Reticulum (ER) – connects the nuclear membrane to the cell membrane; passageway for material moving through the cell; participates in protein and lipid synthesis 8. Golgi – packages proteins for export from cell; forms secretory vesicles 9. Lysosomes – contain enzymes which are used in digestion; play role in cell death 10. Micro bodies – isolate particular chemical activities from the rest of the cell 11. Mitochondria – “power house”/ “power plants” of the cell; releases energy for cell function 12. Chloroplasts - sites of photosynthesis; they contain chlorophyll, a chemical that allows plants to store solar energy 13. Chromosomes – contain hereditary information; made up of genes 14. Nucleolus – assembles ribosomes 15. Nuclear Membrane – allows substances to pass in and out of the nucleus 16. Ribosomes – sites of protein synthesis; help make proteins 17. Vacuoles – store food and chemicals Cytoplasmic Organelles By definition, organelles are the membrane-bound structures in a cell. The nucleus is an example. Other organelles are located in the cytoplasm such as mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, peroxisomes, lysosomes, vacuoles and glyoxisomes. - - Mitochondria An eukaryotic cell contains many mitochondria, occupying up to a quarter of the cytoplasmic volume. The size of a mitochondrion is about 1.5-2 μm in length, 0.5-1 μm in diameter, approximately the same as E. coli. It has two membranes: outer membrane and inner membrane. Mitochondria also have their own DNA (represented as mtDNA), which encodes some of the proteins and RNAs in mitochondria. However, most proteins operating in mitochondria still originate from nuclear DNA. The major role of mitochondria is to produce ATP (adenosine triphosphate), which carries high energy to power most cellular processes. Such energy is stored in the phosphoanhydride bonds of ATP. During ATP hydrolysis, the bond is broken, releasing 7.3 kcal/mole of energy. Many cellular processes can utilize the released energy by coupling with the ATP hydrolysis. Chloroplasts Like mitochondria, a chloroplast also contains both outer and inner membranes on its surface. Inside the chloroplast, there are many thylakoids, each is enclosed by a membrane. Chlorophylls are located on the thylakoid membrane to absorb light for photosynthesis. - - - - - - Endoplasmic reticulum Endoplasmic reticulum (ER) can be divided into rough ER and smooth ER. The major role of rough ER is to process the newly synthesized peptides from ribosomes. Therefore, the surface of rough ER is usually associated with ribosomes and thus appears "rough". Smooth ER is involved in the synthesis and metabolism of lipids. Hepatocytes are abundant in smooth ER. Golgi apparatus Golgi apparatus is a major site for sorting and modifications of proteins and lipids. After proteins are sorted at rough ER, they are enclosed in transport vesicles and carried to the Golgi apparatus. Some proteins could be modified into glycoproteins and then transported to other destinations. Peroxisomes Peroxisomes contain enzymes for degrading amino acids and fatty acids. These reactions produce harmful hydrogen peroxide. Hence, peroxisomes also contain catalase to convert hydrogen peroxide into water and oxygen Lysosomes The major function of lysosomes is to degrade various macromolecules in the cell. They contain nuclease for degrading DNA and RNA, protease for degrading proteins and other enzymes for degrading polysacchrides and lipids. Lysosomes exist only in animal cells. Although plant cells do not have lysosomes, their vacuoles are also capable of degrading macromolecules. Vacuoles Vacuoles store small molecules such as water, ions, sucrose and amino acids. They can also hold waste products which will be slowly degraded. They typically occupy more than 30% of the cell volume, but may expand up to 90%. Glyoxisomes Glyoxisomes are found mainly in plant seeds. Their major function is to convert fatty acids into acetyl CoA for the glyoxylate cycle where two acetyl-CoA molecules are converted to a 4-carbon dicarboxylic acid. Peroxisomes and glyoxisomes are also called microbodies.
