STI-Gen. Biology - Cell Theory PDF

CELL THEORY HISTORICAL BACKGROUND Robert Hooke (1665), British scientist observed mass of tiny cavities from thin slices of cork with his self-made microscope, he named these structures “cells” since these structures reminded him of the small rooms in a monastery. Anton van Leeu...

CELL THEORY HISTORICAL BACKGROUND Robert Hooke (1665), British scientist observed mass of tiny cavities from thin slices of cork with his self-made microscope, he named these structures “cells” since these structures reminded him of the small rooms in a monastery. Anton van Leeuwenhoek (1674) Dutch scientist- made pioneering discoveries concerning protozoa, red blood cells, capillary system & the life cycles of insects. He also perfected the construction of the compound microscope. Robert Brown (1831) British botanist- observed plant cells with a distinct central part (nucleus); described the streaming movement of the cytoplasm. (Brownian movement) Felix Dujardin (1835) French biologist- observed that cells were not empty but filled with thick, jelly- like fluids (protoplasm). Matthias Schleiden (1838) German botanist- concluded that plants are composed of cells and formulated the plant cell theory. Theodore Schwann (1839) German zoologist- concluded that animals are composed of cells and formulated the animal cell theory. Rudolf Virchow (1858) German pathologist- concluded that all cells must come only from pre- existing cells. Max Knoll & Ernst Ruska (1932) German engineers- built the first transmission electron microscope James Watson American biochemist & Francis Crick British biophysicist (1953)- discovered the structure of DNA that ushered in the era of molecular biology.  The microscopes we use today are far more complex than those used in 1600’s by Anton van Leeuwenhoek, a Dutch naturalist who had great skills in crafting lenses. Despite the limitations of his now- ancient lenses, he observed the movements of Protista (a type of unicellular organism) and sperm, which he collectively termed as animalcules. The observations & conclusions of Matthias Schleiden (1838), Theodore Schwann (1839) & Rudolph Virchow (1858) established the cell theory 1. All organisms are made up of cells and a cell is the structural & functional unit of organisms. 2. Cells are capable of self-modification and cells come only from pre-existing cells. TYPES OF CELLS Prokaryotic Cells (Greek pro, before & karyon, nucleus) -cells without a true nucleus -characteristic of bacteria with a size ranging from 1 to 10 μm -outer boundary is composed of cell wall & plasma membrane-cytoplasm contains ribosomes, thylakoids & innumerable enzymes -nucleoid contains single chromosome (DNA only) CELL SIZE & SHAPE -smallest cell, a bacterium known as a mycoplasma, is 0.0001mm in diameter; largest cell are the nerve cells in a giraffe’s neck, 3.0m in length -in human, variety of sizes, from small red blood cells that measure 0.00076mm to liver cells that may be ten times larger, about 10,000 averaged-sized human cells can fit on the head of a pin -common unit of measure in the study of cell is micrometer (μm) =1 X 10-6 meter or 1/1,000,000 meter.  -smaller cell has more surface area per volume a larger cell -ideal shape of an isolated cell is spherical -the shape of the cell is related to its function; long for contraction (muscle cells), with protoplasmic process, conduction of impulses (nerve cell), concave disc for distribution of oxygen (blood cell)  -factors affecting variations in cell shapes: elasticity or rigidity of the membrane, surface tension, viscosity of the cytoplasm, exerted by neighbouring cell and functional adaptation. Eukaryotic Cell (Greek eu, true & karyon, nucleus) -cells with true nucleus -characteristics of protist (unicellular), fungi, plants & animals (multicellular) -consists of a plasma membrane, cytoplasm and a distinct nucleus -outer membrane is composed of plasma membrane made up of phospholipid layer with embedded proteins -nucleus is membrane-bounded containing multiple chromatin -cytoplasm contains compartmentalized organelles  Characteristics Prokaryotic Cell Eukaryotic Cell Ribosomes Small Large Microtubules Usually absent Present Flagella Lack 9 + 2 tubular Have 9 + 2 tubular structure structure Cytoplasmic streaming Does not occur May occur Cell wall Contains murein Does not contain murein  Characteristics Prokaryotic Cell Eukaryotic Cell Nuclear Membrane Absent Present Chromosomes Single, composed only Multiple, composed of of nucleic acid nucleic acid + protein Golgi Apparatus, ER, Absent Present Lysosomes Mitochondria Absent, but same Present function performed by plasma membrane Photosynthetic May contain chlorophyll Chlorophyll, when apparatus but not it chloroplasts present contained in chloroplast PLASMA MEMBRANE -molecular bilayer of phospholipids with proteins arranged at random outer half, inner half of the lipid or extend entirely through the bilayer -called as the fluid-mosaic model as proposed by Singer and Nicholson in 1972 -semi-fluid in nature allowing motility of the lipids and proteins within the membrane FUNCTIONS OF PLASMA MEMBRANE -gives strength, shape & protection to the cell -regulates traffic flow of materials between the interior of the cell and its environment MODIFICATION OF THE PLASMA MEMBRANE -with microvilli at the apical surface to increase surface area for absorption -with glycocalyx, a carbohydrate-protein or a carbohydrate-lipid complex acted as a cell coat for cell interactions -in plant cells, with thick cell wall outside of the plasma membrane that provides strength & rigidity of the cell Apoplast Pathway- water moves through the spaces between the cells and in the cells walls themselves. Symplast Pathway- water passes from cytoplasm to cytoplasm through plasmodesmata Sap Vacuole- are enormous vacuoles that are found in plant cells. Its function is to store resources and sustain the cell mechanically. It also keeps the cell's Turgor pressure constant. Cell sap is the fluid that exists inside the vacuole. Contractile Vacuole- to collect and remove excess water from a cell (usually in single-celled organisms in the kingdom Protista). The excess water contains various solutes, usually waste products. The contractile vacuole expands as it collects the water and contracts to expel the water and waste outside of the cell. Food Vacuole- a membrane-enclosed sac, which has a digestive function. It is present in unicellular protozoans such as amoeba, plasmodium, etc. They work as an intracellular stomach, digesting the ingested food. PROTOPLASM -substance that exhibits the properties and activities of life -the living material of the cell PHYSICAL PROPERTIES OF THE PROTOPLASM -colloidal/heterogeneous solution, particles not affected by gravity due to small -viscous, resistance to flow; may be in form of a sol (liquid) or a gel (semi-solid); it can change from sol to gel (gelation) or from gel to sol (solation) Continuation… -translucent and grayish in color -reticular (net-like), granular (powdered), alveolar (cup- shaped) or fibrillar (linear/rod-like) in nature Cytoplasm -the cell content outside the nucleus -the ground substance of the cell composed of protein, carbohydrates and lipids dispersed in a watery medium resulting in a colloidal solution -the most active region of the cell due to numerous biochemical reactions of the organelles and the inclusions Cytoplasm -the cell content outside the nucleus -the ground substance of the cell composed of protein, carbohydrates and lipids dispersed in a watery medium resulting in a colloidal solution -the most active region of the cell due to numerous biochemical reactions of the organelles and the inclusions  Structures Composition/ Functions Description Cell Wall Contains cellulose fibrils Support & protection (plant cell only) Plasma Membrane Phospholipids bilayer Passage of molecules in with embedded proteins and out of the cell Nucleus Nuclear envelope Cellular reproduction & surrounding control of protein nucleoplasm, synthesis chromosomes and nucleoli Nucleolus Concentrated area of Ribosome formation chromatin, RNA and proteins Ribosome Protein and RNA in 2 sub- Protein synthesis units Protein Channels- proteins that can generate hydrophilic holes in cell membrane allowing molecules to go up down a concentration gradient. Carrier Proteins- are essential proteins that carry chemical across membrane in both direction, down & up the concentration gradient.  Structures Composition/ Functions Description Endoplasmic Membranous flattened Synthesis of protein Reticulum channels and tubular and other substances canals and transport by vesicles formation Rough ER Studded with ribosomes Transport and protein synthesis Smooth ER No ribosomes Transport by vesicles formation and lipid synthesis in some cells Golgi Apparatus Stack of membranous Cellular secretion & saccules protein synthesis  Structures Composition/ Functions Description Lysosomes Membranous vesicles Intracellular digestion containing digestive enzymes Mitochondrion Inner membrane (cristae) Cellular respiration within outer membrane Chloroplast Grana with inner and Photosynthesis (plant cell only) outer membrane Centriole Arrangement of Cell division & (animal cell only) microtubules formation of basal bodies  Structures Composition/ Functions Description Cilia and Flagella Arrangement of Movement of cell microtubules Vacuole and vesicles membranous sacs Storage of substances Cytoskeleton Microtubules & Shape of the cell and microfilaments movement of its parts THYLAKOID- TRAPS LIGHT ENERGY & THE TRANS- DUCTION OF THIS ENERGY INTO THE CHEMICAL ENERGY FORMS, ATP & NADPH. GRANA- SITE WHERE LIGHT REACTIONS OF PHOTOSYNTHESIS OCCUR CONDUCTS THE PHOTOSYNTHESIS PROCESS. GRANA (STACKS OF THYLAKOID). LUMEN- IT PLAYS AN IMPORTANT ROLE IN THE ATP SYNTHESIS OR PHOSPHORYLATION DRIVEN BY CHEMIOSMOSIS. STROMA- PROVIDES VOLUME AROUND THE DIFFERENT STRUCTURES INSIDE THE CHLOROPLAST FOR PROTECTION. IT IS WHERE THE LIGHT- INDEPENDENT REACTION PROCESS OF PHOTOSYNTHESIS (CARBON CYCLE) TAKES PLACE. OUTER MEMBRANE- SIGNAL TRANSDUCTION, PROTEIN IMPORT, LIPID BIOSYNTHESIS AND REMODELING, EXCHANGE OF IONS AND NUMEROUS METABOLITES, PLASTID DIVISION MOVEMENT, AND HOST DEFENSE. INNER MEMBRANE- REGULATES PASSAGE OF MATERIALS IN AND OUT OF THE CHLOROPLAST. IN ADDITION OF REGULATION ACTIVITY, THE FATTY ACIDS, LIPIDS AND CAROTENOIDS ARE SYNTHESIZED IN THE INNER CHLOROPLAST MEMBRANE. INTERMEMBRANE SPACE- FUNCTION OF THE INTER-MEMBRANE SPACE IS NUCLEOTIDE PHOSPHORYLATION.