Cell Part 1_undergraduate cell biology.pptx

Cell Part 1_undergraduate cell biology

1. All About Cell

2. Cell Cell is the structural and functional unit of life. The term “Cell” was coined by Robert Hooke in 1665. Cell is the smallest unit of life. Life is not possible without cells. Each cell has a definite life span. Cells contain genetic information and are the means to use it. Cells are capable of self-division and self-regulation. Each cell has its own metabolism. In the human body, there are 260 types of cells. Humans have 100 trillion cells.

3. There are two main types of cells, prokaryotic and eukaryotic. Prokaryotes are cells that do not have membrane bound nuclei, whereas eukaryotes do. The rest of our discussion will strictly be on eukaryotes. Think about what a factory needs in order to function effectively. At its most basic, a factory needs a building, a product, and a way to make that product. All cells have membranes (the building), DNA (the various blueprints), and ribosomes (the production line), and so are able to make proteins (the product - let’s say we’re making toys). This article will focus on eukaryotes, since they are the cell type that contains organelles.

4. An organelle (think of it as a cell’s internal organ) is a membrane bound structure found within a cell. Just like cells have membranes to hold everything in, these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells. You can think of organelles as smaller rooms within the factory, with specialized conditions to help these rooms carry out their specific task (like a break room stocked with goodies or a research room with cool gadgets and a special air filter). These organelles are found in the cytoplasm, a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell. 

5. Types of cells

6. Cell Organelles

7. Protoplasm Protoplasm is the living substance of which a cell is made. It includes all parts of a cell. It is a transparent and jelly-like material. Huxley has defined protoplasm as the physical basis of life. O Hertwig (1892) proposed protoplasmic theory which states that living matter of plants and animals is the protoplasm. Protoplasm is divided into cytoplasm and nucleoplasm. Carbon, hydrogen, nitrogen and oxygen are the main constituents of protoplasm. Protoplasm contains both inorganic and organic substances. Inorganic substances include water that forms 90 per cent of the protoplasm and mineral salts like sodium chloride and gases like oxygen and carbon dioxide.

8. Protoplasm (contd.) Organic substances include proteins, carbohydrates, lipids, nucleic acid and enzymes. It has ability of nutrition, respiration, excretion, reproduction, metabolism and growth. It shows irritability and conductivity. It is heavier than water. Its viscosity is more than water. It contains positively (+) and negatively (-) charged particles. Protoplasm is colloidal in nature. The colloidal particles of protoplasm may exist both as sol and gel states. The movement of molecules of protoplasm is known as the Brownian movement. The substances formed by protoplasm are known as ‘ Deutoplasm ’.

9. Cell wall Cell wall is a rigid or semirigid envelope lying outside the cell membrane of plants, fungal and most of the prokaryotic cell. It is the cell wall that provides the most remarkable difference between plant cells and other eukaryotic cells. The cell wall is outside the protoplast and is thus part of the apoplast. It provides structural support, protection and also acts as a filtering device. Most of the carbon in the terrestrial ecosystem is located in the cell walls of plants. In plants, it is made up of cellulose and often lignin; in fungi, it is composed mainly of polysaccharides; in bacteria, it is composed of peptidoglycan.

10. Cell Membrane Every cell is surrounded by a thin and elastic membrane which isolates cytoplasm from the external environment. This membrane is known as cell membrane. This membrane is selectively permeable and is also known as plasma membrane or plasmalemma. This membrane is not visible under light microscope. Cell membrane is responsible for controlled entry and exit of ions like sodium, potassium and calcium. This membrane is found both in prokaryotes and eukaryotes. In bacteria, yeast and plants, this membrane is bounded by the cell wall. Generally, thickness of this membrane is approximately 70–75Å. Chemically, this membrane is made up of lipid, protein and a little amount of carbohydrate.

11. Cell Membrane Plasma membrane provides shape to the cell as well as protection to cytoplasmic organelles. It permits movements of certain substances in and out of the cell. The transportation of molecules across the membrane takes place by active or passive transport. The plasma membrane contains specific sites which help in the recognition of specific hormones. It regulates fusion of the membrane with other membranes in the cell via specialised junctions. It provides special site for binding and catalysis of enzymes. It helps in the release of secretary products of the cell.

12. Cytoplasm It is the part of the cell between the cell membrane and the nuclear membrane. It consists of cytosol (matrix) and organelles. The cytosol is a transparent semifluid substance that is not held within organelles. Organelles are membrane-bound structures in a cell. Organelles are found embedded in the cytoplasm. Cell organelles have characteristic shape, specific chemical composition and functions. Cell organelles may be extra cytoplasmic (nucleus) or cytoplasmic (mitochondria, plastids, Golgi complex, lysosomes, ribosomes, endoplasmic reticulum, centrosomes, cytoskeleton, cilia, flagella, etc.) structures. Cytoplasm is the medium for chemical reactions.

13. Plastids Plastids are large cell organelles found only in autotrophic cells. The term ‘plastid’ was coined by Schimper (1885). They are generally spherical or ovoid in shape. All plastids are derived from proplastids . They can be easily seen through a light microscope. Once formed, one type of plastids can be converted into other types. There are three types of plastids: Leucoplasts Chromoplasts Chloroplasts

14. Leucoplasts Leucoplasts are colourless plastids They a re abundantly found in the cells of fruits, seeds, tubers and rhizomes They store nutrients (a) Amyloplasts: Store starch (b) Elaioplasts : Store fat (c) Aleuroplasts : Store protein Chromoplasts Chromoplasts are red, yellow or orange in colour . Their colour is due to the presence of two pigments, viz., carotene and xanthophylls. They are found in petals of flowers and fruits. Chloroplasts Chloroplasts are the second largest and semi-autonomous cell organelle found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts converts light energy (from the sun) to chemical energy via the process of photosynthesis. The shape, size and volume of chloroplasts are altered by sunlight. The main pigment located in chloroplasts is chlorophyll. In green plants, there are two types of chlorophylls, viz. chlorophyll a and chlorophyll b.

15. Mitochondria Mitochondria are known as the powerhouse of the cell because it is responsible for the extracting energy from food through cellular respiration. The energy is released in the form of the cell’s primary energy molecule ATP (adenosine triphosphate). ATPs are the energy currencies of the cell. Mitochondria are the most important cell organelle present in the cytoplasm of all eukaryotic cells. They are descendents of a free-living bacterium and occupy 20 percent volume of the cytoplasm. Mitochondria are the chief site of cellular respiration and oxidative phosphorylation. Mitochondria were first observed by Kolliker (1850). Flemming (1882) named them as fila, whereas Altmann (1892) called them bioblasts . Benda (1897) gave the term mitochondria (Mito-thread; chondrion -granule). Michaelis (1905) stained them with Janus Green B.

16. Kingsburry (1912) pointed out that mitochondria are the site of cellular respiration. Palade and Sjastrand (1940–1950) studied the fine structure of mitochondria. In animal cells, mitochondria are the second largest organelle, whereas in plant cells it is the third largest organelle. Mitochondria are semi-autonomous cell organelle. Mitochondria are the cell organelle containing electron transport chain. The lifespan of mitochondria is 5–10 days. Mitochondria are absent in prokaryotes and mature mammalian erythrocytes. The number of mitochondria varies from individual to individual and even in different cells of the same individual. There are more mitochondria in the cell where metabolic activities take place. The number of mitochondria in a cell can increase by fission (following mitosis) and decrease by their fusing together. Defect in either process can produce serious, even fatal illnesses.

17. The shape of mitochondria is variable. Generally, the shape of mitochondria is sausage-like. The size is also variable. Generally, the length of mitochondria is approximately 1.5–10µm, whereas diameter is approximately 0.25–1 µm. Mitochondria are covered by a double membrane called outer membrane and inner membrane. A mitochondrion contains outer and inner membranes composed of phospholipid bilayers and proteins. The two membranes have different properties. Because of this double-membraned organization, there are five distinct parts to a mitochondrion: The outer mitochondrial membrane, The intermembrane space (the space between the outer and inner membranes), The inner mitochondrial membrane, The cristae space (formed by infoldings of the inner membrane/ finger-like projections ), and The matrix (space within the inner membrane), which is a fluid. Mitochondria have folding to increase surface area, which in turn increases ATP (Adenosine Tri Phosphate) production. The shape of cristae is variable, and the number of cristae is directly associated with the efficiency of mitochondria.

18. Outer membrane is permeable to many metabolites. Outer membrane contains a protein called porins. The inner membrane contains five complexes of integral membrane proteins NADH dehydrogenase (Complex I) Succinate dehydrogenase (Complex II) Cytochrome c reductase (Complex III) Cytochrome c oxidase (Complex IV) ATP synthase (Complex V) The most prominent roles of mitochondria are to produce the energy currency of the cell, ATP (i.e., phosphorylation of ADP), through respiration and to regulate cellular metabolism. The central set of reactions involved in ATP production are collectively known as the citric acid cycle, or the Krebs cycle. However, the mitochondrion has many other functions in addition to the production of ATP.

19. Endoplasmic Reticulum Branching off and continuous with the outer membrane of the nucleus, there is a double-walled space which is zigzag throughout in the cytoplasm. This is called endoplasmic reticulum. The term ‘endoplasmic reticulum’ was coined by Porter (1953). Endoplasmic reticulum is found in all eukaryotic cells except mature mammalian erythrocytes. It forms 30–60 per cent of the total endomembrane system. Endoplasmic reticulum is of two types, viz., rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The ER is continuous with the nuclear envelope. Rough ER has ribosomes attached to it, giving it a rough appearance, whereas smooth ER does not.

20. 1   Nucleus     2   Nuclear pore    3  Rough endoplasmic reticulum (RER)    4  Smooth endoplasmic reticulum (SER)    5   Ribosome  on the rough ER    6   Proteins  that are transported    7  Transport  vesicle     8   Golgi apparatus     9  Cis face of the Golgi apparatus    10  Trans face of the Golgi apparatus    11  Cisternae of the Golgi apparatus

21. Ribosomes bound to rough ER synthesize proteins to be secreted by the cell or to be localized in the plasma membrane or particular organelles within the cell. The synthesis of proteins other than those distributed via the ER is performed by ribosomes that are free in the cytoplasm. The endoplasmic reticulum is found in most eukaryotic cells and forms an interconnected network of flattened, membrane-enclosed sacs known as cisternae (in the RER), and tubular structures in the SER. Structurally endoplasmic reticulum consists of cisternae, vesicles and tubules. Cisternae are flattened, tubular structures arranged parallel to each other. They are connected with each other and are more abundant in rough endoplasmic reticulum. Vesicles are oval to rounded structures and abundant in secretary cells. Tubules are unbranched or branched structures and abundant in cells synthesising lipids.