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The Cell - Types of Cells - Cell Organelles -- Cellular Organization and Function
- 1. The Cell Types ofCells Cell Organelles Cellular Organization and Function Dr. Ali Azzawri
- 2. The concept ofthe cell )its structure and functions( The cell It is the structural and functional unit of the body of a living organism and consists of a living protoplasmic mass containing a nucleus and cytoplasm, each surrounded by a membrane . The cell is complex in structure and this allows it to undergo hundreds of chemical reactions in the narrow space of the cell and this is done in a way that does not affect one another for the benefit of the cell's work. When there is a lack of harmony and interconnection between the activities of the cell, it is destroyed and dies. Cell shapes and sizes The functions of cells and the way they are assembled together differ, so their shapes and sizes differ. Cell sizes are often very small and cannot be seen with the naked eye except under a microscope, such as nerve and muscle cells in the human body. They may be small in size but can be seen with the naked eye, such as fish eggs. Cells take multiple shapes, star-shaped as in nerve cells, spindle-shaped as in muscles, spherical as in animal eggs, or variable in shape as in white blood cells. Despite the diversity of cell shapes and sizes and the difference in their functions, they have the same structural basics. The cell consists of a protoplasmic mass that represents the natural basis of life surrounded by a membrane and contains a network of channels that permeate the cytoplasm.
- 3. Cellstructureandcontents Protoplasm isa colorless, transparent substance that is denser than water. It contains 70-80% of the protein, carbohydrates, fats, and salts. The fluidity of protoplasm changes due to the effect of temperature and other factors. The cell's protoplasm consists of two main parts: the cytoplasm and the nucleus. The cytoplasm is surrounded by a thin membrane called the plasma membrane. These membranes separate the different parts of the cell. Some reactions occur on the surfaces of these membranes, where the enzymes involved in the reactions adhere to them. The many cellular structures perform specific, specialized, and complex functions and are called organelles. The Cell Theory: In 1838, the German botanist Matthias Schleiden concluded that all plants were composed of cells. In 1839, Theodor Schwann concluded the same thing for animals. In 1855, Rudolf Virchow noted that all cells come from other cells. The cell theory states that: 1) All organisms are composed of one or more cells. 2) The cell is the basic unit of structure and function of organisms. 3) All cells come from pre-existing cells. A cell is the smallest unit that can carry on all of the processes of life
- 4. The Organism’s BasicUnit of Structure and Function Prokaryotic Eukaryotic Micro-organisms All other forms of life with true nucleus before nucleus Do not contain membrane-bound organelles Contain membrane-bound organelles How many different types of cells are there? There are many different types of cells. For example, in you, there are blood cells, skin cells, bone cells, and even bacteria. Here we have drawings of bacteria and animal cells. Can you tell which depicts various types of bacteria? However, all cells - whether from bacteria, humans, or any other organism - will be one of two general types: prokaryotic or eukaryotic. In fact, all cells other than bacteria will be one type, and bacterial cells will be the other. And it all depends on how the cell stores its DNA. Two Types of Cells There are two cell types : prokaryotes and eukaryotes. Prokaryotic cells are usually single-celled and smaller than eukaryotic cells. Eukaryotic cells are usually found in multicellular organisms, but there are some single-celled eukaryotes.
- 5. Prokaryotic and eukaryoticcells differ in size and complexity All cells are surrounded by a plasma membrane. The semi-fluid substance within the cell is called “cytosol”, containing the cell organelles. All cells contain chromosomes which have genes in the form of DNA. All cells have tiny organelles called “Ribosomes” that make proteins. Similarities
- 6. 1). Prokaryotic andeukaryotic cells differ in size and complexity A major difference between prokaryotic and eukaryotic cells is the location of DNA. In an eukaryotic cell, DNA are contained in a true nucleus which is bounded by a double membranes. In a prokaryotic cell, the DNA is concentrated in the nucleoid without a membrane separating it from the rest of the cell. In prokaryotic cell, DNA is a single strand or double strand DNA. But in eukaryotic cell, DNA is double strand. Eukaryotic cells are about 10 times the size of a typical prokaryote; they range between 10 and 100 µm in diameter while prokaryotes range between 1 and 10 µm in diameter, as shown in the Figure. Differences
- 7. Prokaryotes Bacteria Archaea - Existin extreme environments (hot and salty) - Exist in most environments They are differing in some other structural, biochemical and physiological characteristics Types of Prokaryotes Prokaryotes are microscopic organisms that have neither a membrane-bound nucleus nor membrane-bound organelles. All metabolic functions carried out by a prokaryote take place in the plasma membrane or the cytosol. Prokaryotes are the smallest types of cells, averaging 2-5μm in diameter. Despite their small size, inside each cell there is chemical and biochemical machinery necessary for growth, reproduction, and the acquisition and utilization of energy. Reproduction in prokaryotic cells is by binary fission; a process of growth, enlargement and division. This will be discussed in the Cell Division: Prokaryotic (Advanced) concept. A- Prokaryotes
- 8. The common featuresof prokaryotic cells are: Cell wall, plasma membrane, ribosomes, genetic material, capsule (most, but not all), flagella (most, but not all), pili (most, but not all), lack of compartmentalization, plasmid (most, but not all) All prokaryotes have a cell wall that adds structural support, acts as a barrier against outside forces, and anchors the whip-like flagella. Diagram of a typical prokaryotic cell
- 9. Some prokaryoteshave an extra layer outside their cell wall called a capsule, which protects the cell when it is engulfed by other organisms, assists in retaining moisture, and helps the cell adhere to surfaces and nutrients. Pili are hair-like structures on the surface of the cell that attach to other bacterial cells or surfaces. Within the plasma membrane, the cytoplasm is not subdivided by membranes into organelles, a lack of compartmentalization that is most evident in the organization of the genetic material. Prokaryotic cells contain only a single circular piece of chromosomal DNA stored in an area called the nucleoid. Some prokaryotes also carry smaller circles of DNA called plasmids. Plasmids are physically separate from and can replicate independently of the chromosomal DNA. The genetic information on the plasmids is transferable between cells, allowing prokaryotes to share abilities, such as antibiotic resistance.
- 10. A eukaryoteis an organism whose cells are organized into complex structures by internal membranes and a cytoskeleton, as shown in the Figure above. The most characteristic membrane-bound structure of eukaryotes is the nucleus. This feature gives them their name, which comes from Greek and means "true nucleus. The nucleus is the membrane-enclosed organelle that contains DNA. Eukaryotic DNA is organized in one or more linear molecules, called chromosomes. Some eukaryotes are single-celled, but many are multicellular. Eukaryotes include all protists, fungi, plants and animals. Because of their complex level of organization, eukaryotic cells can carry out many more functions than prokaryotic cells. In addition to having a plasma membrane, cytoplasm, nucleus, and ribosomes, eukaryotic cells also contain membrane-bound organelles. Each organelle in a eukaryote has a distinct function. Keep in mind that some eukaryotic cells may have characteristics or features that other eukaryotic cells lack, such as the cell wall. B- Eukaryotic Cell
- 11. Eu: True Karyon: Nucleus AnimalCell Plant Cell Compare between Animal and Plant cell? What are the functions of cell organelles ?
- 13. Description of cellstructure Cell Wall The cell is surrounded by a wall that separates it from the external environment and maintains its morphological shape and functional entity, as it keeps the protoplasmic substance maintaining its composition, and the cell wall is solid and is often composed of cellulose (as in plant cells). Cell Membrane It is a very thin membrane, about 0.07 micrometers thick, consisting of phospholipid substances and small amounts of cholesterol, as well as protein substances in a high percentage (50-70%), most of which are enzymes related to the passage of materials through the membrane, then some sugars, and the membrane has permeable properties as it contains very small holes through which water molecules and ions pass, and the plasma membrane surrounds the contents of the cell and regulates the passage of chemical solutions and water to and from the cell, and the cell membrane represents the outer borders of the cell.
- 14. Basic functions ofcell membrane The surfaces of the cell membrane may carry microvilli which help increase the surface area of the tissue concerned with absorption or transport processes. Or cilia which help move materials on the surfaces of cells as in the lining of the respiratory tract or flagellum which contribute to cell movement as in sperm. Determining the shape of the cell and separating its components Contacting with the surfaces of other cells Providing cells with receptors for chemical substances (hormones, enzymes and antibodies) Controlling the entry and exit of materials to and from the cell. The cell membrane is selectively permeable.
- 15. The nucleus Contains thecell’s genetic library Small, round and membrane bound structure near center of a cell. Plays a central role in cellular activities/reproduction. Contains most of the genes in an eukaryotic cell. The nucleus is separated from the cytoplasm by a double membrane called the “nuclear envelope” made up of two phospholipid bilayers. The nuclear membrane contains pores that allow RNA and other materials to enter and leave the nucleus. The nuclear envelope maintains the shape of the nucleus. The nucleus contains “chromatin fibers” which is the DNA associated with proteins. When the cell prepares to divide, the chromatin fibers coil up to be seen as “chromosomes”. Each eukaryotic species has a characteristic number of chromosomes - A typical body (somatic) cell has 46 chromosomes, but sex cells (eggs andsperm) have only 23 chromosomes.
- 16. The nucleus Contains thecell’s genetic library The nucleus directs protein synthesis by synthesizing messenger RNA (mRNA). The mRNA travels to the cytoplasm and combines with ribosomes to translate its genetic message into the primary structure of a specific protein Nucleolus is a dark region involved in production of ribosomal RNA which makes ribosomes. Functions: The nuclear membrane has many pores that control what enters and exits the nucleus, allowing selective transport of regulatory factors and energy molecules. The nucleolus, located inside the nucleus, produces ribosomes and stores proteins and RNA, playing a vital role in protein synthesis. Chromosomes contain the cell’s genetic information (DNA), which is stored in the form of long, thin strands called chromatin; during cell division, chromatin is organized into chromosomes within the nucleus. The nucleus is the site of transcription, where messenger RNA (mRNA) is produced to guide protein synthesis outside the nucleus. There is a continuous exchange of hereditary molecules (DNA and RNA) between the nucleus and the rest of the cell through the nuclear pores. Overall, the main function of the nucleus is to control gene expression and mediate DNA replication during the cell cycle
- 17. It is thepart enclosed between the cell membrane and the nucleus and contains the living and non-living contents of the cell: Living contents include the following: Endoplasmic reticulum It appears in the cytoplasm in the form of a network of double-membrane channels that connect the plasma membrane to the nucleus and the interconnected vacuoles. Their diameters vary according to the functional state and type of cells. Cytoplasm They are often parallel to each other, forming a semi-circular network around the nucleus. These channels are surrounded by a membrane that has the same basic structure as the plasma membrane. These membranes divide the cytoplasm into a substance enclosed within the channels and vacuoles and a substance outside them called hyloplasm. The endoplasmic membranes contain enzymes that build glycogen and make cholesterol and lipids.
- 18. Endoplasmic reticulum functions: oProviding surfaces for the attachment of enzymes involved in cell activities o Participating in the manufacture and representation of various materials such as fats o Transporting materials from the depths of the cell to the surface and vice versa o Forming the surfaces of its membranes as a site for the attachment of ribosomes o Some of its parts transmit electrical changes from the plasma membrane to the depths of the muscle fiber where the fibers that perform the process of muscle contraction are located. There are two types of endoplasmic reticulum: 1) Rough Endoplasmic Reticulum (RER) It is the one that has ribosomes attached to its outer surface. 2) Smooth Endoplasmic Reticulum (SER) It is the one that does not have ribosomes attached to its outer surface.
- 19. They areextensions of the cell membrane and are not common in all cells, but some cells contain them, such as the mucous cells lining the respiratory tract, the inner ear canals, and the bile ducts. They have a similar structure, as they contain nine double fibers on the outside in addition to one pair in the middle. There is also a light-colored body called (basal grounnule) at the base of each cilium or flagellum. Microvilli or Flagella They are fine structures that are mostly found on some membranes of the endoplasmic reticulum, and are a center for building protein materials inside the cell and are in the form of many spherical particles that adhere to the outer surface of the endoplasmic reticulum, and give a rough appearance to the membranes of this reticulum and some of them in the hyloplasm, their numbers vary from one type to another in the cells and the degree of cell activity and are abundant in secretory cells. Ribosomes are rich in ribonucleic acid as they contain (50-60%) of the total amount of this material in the cell, while this constitutes (15-20%) of the cell mass. Ribosomes are alkaline-loving because they contain RNA and also contain protein and fatty materials and are the site of protein manufacture in the cell. Ribosomes
- 20. They are spherical,oval or thread-like bodies that vary greatly in diameter and length, depending on the functional state of the cell. Their length is (1-5) micrometers and their thickness is (5.0) micrometers. Their number in a single cell may reach a few hundred. There is a positive relationship between the number of mitochondria and the effectiveness of the cell because they contain respiratory enzymes that oxidize nutrients to release energy (therefore called power houses of the cells). Mitochondria are composed of: 65-70% proteins, 25-30% lipids (fats), 0.5% RNA and small amount of DNA. Most of its proteins are enzymes involved in the process of aerobic respiration Their main task is to supply the cell with energy (ATP) extracted from the cell's sugars. More than 90% of the energy used by cells comes from aerobic respiration. They are found immersed in the cytoplasm in the form of small structures resembling wheat grains or rods and sometimes gather around the nucleus. They contain the enzymes necessary to release the energy that is important in the occurrence of vital activities. Mitochondria (cell powerhouses)
- 21. Golgi apparatus It isa secretory apparatus that varies in shape and size from one cell to another. It is located near the nucleus and is in the form of layers of sacs surrounded by smooth membranes stacked on top of each other. It is common in secretory cells (salivary glands and pancreas). It has a ductal structure with sacs of different sizes and smooth membranes because it does not contain ribosomal membranes. The Golgi apparatus is different in composition. It is small in size in muscle fibers and large in cells with secretory activity. . It contains a high percentage of lipids and protein lipids and a small number of enzymes, but it lacks nucleic acids. Their most important functions are the formation of enzymes and hormones and help in the secretion and synthesis of sugars, especially those that combine with cell proteins
- 22. The centrosome,derived from the Latin “centrum” (center) and Greek “sōma” (body), is an organelle that serves as the main microtubule- organizing center (MTOC) in animal cells and plays a key role in regulating cell-cycle progression. It is the primary site where microtubules are organized and controls the stages leading to cell division. During the prophase stage of the cell cycle, centrosomes associate with the nuclear membrane. When mitosis begins, the nuclear membrane breaks down, allowing microtubules nucleated by the centrosome to interact with chromosomes and form the mitotic spindle. Contained within the centrosome are centrioles—short cylindrical structures approximately 2.0 micrometers in diameter that appear during cell division. Each centriole consists of nine pairs of microtubule doublets arranged in a structure similar to that of cilia. During division, centrioles duplicate and move toward opposite poles of the cell, helping to organize the spindle fibers that steer chromosome movement. Under the microscope, centrioles appear as small spherical bodies near the nucleus. Unlike animal cells, most plant cells lack centrioles. Centrosome
- 23. Lysosomes areresponsible for intracellular digestion of both internal and external substances. They have a single membrane and maintain an acidic pH of about 5. They contain enzymes called hydrolases for digesting materials. The enzyme content varies depending on tissue needs and metabolic activity. LYSOSOMES Biomedical importance The lysosomal membrane is impermeable and requires specific transporters for material movement. Vesicles containing external material fuse with lysosomes to form digestive vesicles. Lysosomes are involved in autophagy (self-digestion). Digestion products are released and reused by the cell. Indigestible materials accumulate in structures called residual bodies, which are expelled by exocytosis. In non-dividing cells, residual bodies may contain a pigmented substance called lipofuscin, known as the aging or wear-and-tear pigment. In some genetic diseases, lysosomal enzymes are missing, leading to accumulation of specific substances, enlargement of lysosomes, and interference with normal cell function. These are called lysosomal storage diseases, with I-cell disease being the most important example.
- 24. Cell inclusions :These include the materials that are formed in the cytoplasm as a result of the vital activities of the cell. They are different materials and may be in the form of granules or crystals, and non-living materials that are found in the form of solid, semi-solid or fatty bodies. These materials include the following: Glycogen: They are carbohydrate materials stored in plants. There are other carbohydrate materials stored in animal cells called animal starch (glycogen). They are also stored in the liver and muscle cells. Melanin: They are granular structures that are responsible for the coloration of the skin, hair and eyes in vertebrates. They are also found in plant cells. Oil droplets: They are found in fat cells in the form of volatile or fixed fatty oils used as an energy reserve. Volatile oils are responsible for the fragrant smells of roses, lemons, and others, such as mucus, which is found in the cells lining the digestive and respiratory systems and works to protect and lubricate the passages of these two systems. Crystals: Some salts of inorganic materials are deposited in the cytoplasm of some cells in the form of crystals, and some of them take fixed geometric shapes such as rod and star crystals. Vacuoles: They are small vacuoles containing cell juice, which is composed of mineral salts, sugars, some organic acids, dissolved fatty and protein materials, and pigments. Therefore, cell vacuoles can be considered temporary stores for collecting cellular waste. non-living inclusions found in cytoplasm