Biology Chapter 3 INTRODUCTION TO CELLS History of

Biology Chapter 3 INTRODUCTION TO CELLS

History of Cells Cytology – the study of cells � 1665 Robert Hooke � �wrote Micrographia … cork cells � 1674 Anton van Leeuwenhoek �observe living organisms under microscope � 1833 Robert Brown �described the nucleus � 1838 Matthias Schleiden �All plants are made of cells.

History of Cells � 1839 Theodor Schwann �All animals are made of cells. � 1840 J. E. Purkinje �protoplasm � 1855 Rudolf Virchow �Cells come only from preexisting cells.

Cell Theory �The cell is the basic unit of all living things �Cells perform all the functions of living things �Cells come from the reproduction of existing cells

Cell as a Basic Unit � All organisms are made of cells. �Cells are similar in size. �Size of organisms depends on number of cells not size of cells. � The total organism is not all cells, but is made of materials that cells manufacture �i. e. . The exoskeleton of an insect is a cell secretion.

Functional Unit �Nutrition �Absorption - Transport of water- soluble substances into cells �Digestion - Breakdown of substances by enzymes

Functional Unit � Internal Functions �Synthesis - Putting together of organic compounds: growth, secretion, or repair �Respiration - Breakdown of food to release energy for the cell �Movement – Locomotion; Internal movement �Irritability - The ability of a cell to respond to its environment

Functional Unit � Materials Release �Excretion - Removal of soluble waste materials �Egestion - Elimination of nonsoluble, nondigestible wastes �Secretion - Release of synthesized materials from the cell

Functional Unit � Continuation of Existence �Homeostasis - Maintaining a steady state or balance �Reproduction - Formation of new cells by cellular division

Functional Unit � Cells are responsible for all the functions of any living thing. � Not all cells perform every function, but for an organism to be alive all functions must occur. � In complex organisms, like humans, some cells perform a few functions exclusively.

Reproductive Unit � Once a cell reaches a particular size it slows its growth, secretes materials or divides. �Cellular division is essential for most cells. � Cells reproduce by dividing and produce: �New organism (if unicellular) �More cells in same organism �Sex cell – egg or sperm

Levels of Cellular Organization � Unicellular – composed of one cell �i. e. . Bacteria, many protozoans, algae, and fungi � Multicellular – composed of many cells �i. e. . Some algae and fungi; animals, humans and plants �Colonial Organism – a collection of similar cells living together; if one were separated it could sustain life

Levels of Cellular Organization � Cell – the building blocks of organisms �Tissue – a group of similar cells that work together to carry out a specific function �Organ – several types of tissues working together to perform a specific function �System – a group of organs that work together to accomplish life functions

Cell Junctions – hold cells together � Three types: � �Tight junction – found predominantly in tissues that form the linings of organs where a tight, sealed barrier is needed; stomach �Anchoring junction – mechanically attach the cytoskeleton of one cell to the cytoskeleton of another cell �Gap junction – provides a narrow passageway between cells that allows small molecules and ions to move directly from the cytoplasm of one cell to the other

Cells � Two Types: �Prokaryotic – lacks a membrane around the nucleus and contains only non-membrane bound organelles ○ i. e. bacteria, blue-green algae �Eukaryotic – have a membrane-bound nucleus and membrane-bound organelles ○ i. e. humans, plants, animals ○ Organelle – a cytoplasmic structure that performs special functions in the cell

Cellular Anatomy � Three basic categories: �Boundary that encloses the cell �Cytoplasm containing structures and molecules �Nucleus containing DNA and other material

Boundary � Plasma membrane – controls movement of substances in and out of cell; �A. k. a. cell membrane �Outermost boundary of the cell itself �Protects the boundary from the environment yet must allow the cell to have access to the environment; i. e. nutrients absorbed, wastes excreted, material secretion �Phospholipid bilayer

Boundary � Cell wall – provides structural support �Outside the plasma membrane �Two layers form at different times in development �Primarily made of cellulose

Cytoplasm � Includes all structures and materials inside the plasma membrane except the nucleus � a. k. a cytosol � Mitochondria – transfers energy in sugars to usable cellular energy �“powerhouse of the cell” �Bean shaped �Mitochondria number may vary depending on type of cell and its function

Cytoplasm �Two membranes: smooth outer and folded inner (cristae) which increases surface area tremendously �Cristae also contain enzymes and other proteins that help with cellular respiration �Chemical processes used during cellular respiration occur at the cristae �Cristae fold number may vary depending on type of cell �Mitochondria contain their own DNA

Cytoplasm � Ribosome – non-membrane-bound in both cell types �Composed of proteins and multiple strands of RNA �Primary function is protein synthesis �Free floating or attached to ER

Cytoplasm � Endoplasmic Reticulum – synthesizes proteins and sterols and transports materials within cell �Interconnected folded membranes �Some cells have continuous ER with the membranes around nucleus �Provides transportation network for compounds �Helps maintain cells shape

Cytoplasm �Rough – studded with ribosomes ○ Found in cells that produce proteins to be secreted by the cell �Smooth – no attached ribosomes ○ Found in cells that secrete sterols � Golgi Apparatus – prepares substances to be secreted by the cell �Flattened, curved membrane-covered sacs �Final processing and packaging of many complex polysaccharides, proteins, and lipids

Cytoplasm � Lysosomes – breaks down ingested substances, old organelles, and cytoplasmic molecules �Small irregularly shaped membrane-bound �Filled with digestive enzymes �Digests invading bacteria and viruses �Digests food substances ingested by the cell �Breaks down old or nonfunctional cellular structures ○ i. e. absorption of a tadpole’s tail once it is no longer needed

Cytoplasm � Cytoskeleton – provides structure of cell, necessary for movement and reproduction �Microscopic system of fibers crisscrossing the inside of the cell �Controls the cells shape �Give it strength �Move structures around inside the cell �Cellular locomotion �Centrosome – a region near the nucleus that is important in the production of microtubules

Cytoplasm � Flagella and Cilia – provide locomotion of cell; propel substances over cell surface �Flagellum – long tubular extension of the plasma membrane surrounding a special arrangement of microtubules; longer that the cell and usually single but could be 2, 3, 4, or 5’s �Cilium – similar to flagellum in internal structure; shorter and more numerous

Cytoplasm � Plastid – houses pigments and stores starches �Found in plants, algae, and a few other organisms �NOT in animals or humans �Leucoplast – colorless; used as storehouses �Chromoplast – contain pigments and usually function in synthesis processes ○ Chloroplast – green organelle in which light energy is converted into organic compounds ○ Contain their own DNA

Cytoplasm �Vacuoles and Vesicles ○ Multipurpose membrane-bound organelles ○ Vacuoles – similar to household containers – holds variety of items � Contains: - Food, water, wastes, or other materials Tend to be stationary in the cell or move VERY slowly Central Vacuole – in plants; can be 90% of cell volume Large central vacuole creates turgor pressure; plant wiltiness ○ Vesicles – similar to vacuoles; usually smaller and more mobile

Nucleus �The control center of the cell �Most prominent structure when observing �Where DNA replication and RNA transcription occurs � Nuclear Envelope �Double membrane that completely surrounds nucleus

Nucleus � Nuclear Pores �Openings in the nuclear envelope that allows substances to exit and enter the nucleus � Nuclear Sap �Protein-rich fluid inside the nucleus � Chromatin material �DNA and other materials that make up the nuclear sap

Nucleus � Nucleolus �Dark-staining spherical structure found in most cells �Contains large concentrations of RNA �The site where ribosomes are partially assembled before going into the cytoplasm

Cells and Their Environment � Homeostasis – “steady state”; actually dynamic equilibrium �Organisms are always reacting to the external environment; must maintain homeostasis � Optimal Point – the point at which something functions at its best

Homeostasis � Overheated – body will send blood to the limbs to help cool; sweat � Underheated – body will not send blood; body shivers; hair on limbs stands up

Cellular Solutions � Isotonic – same concentration of solutes on the inside and outside of the cell � Hypotonic – lower concentration of solutes � Hypertonic – higher concentration of solutes

Cellular Destruction Cytolysis – the cell takes up enough water to make it burst; the cell is in a hypotonic solution therefore the inside of the cell has more “stuff” and water goes into the cell to try to equalize the “stuff” � Crenate – the cell collapses due to secreted water from the cell; The cell is in a hypertonic solution therefore the water from inside the cell moves to the solution to try to equalize the “stuff” �

Cellular Reactions � Cells are better equipped to withstand the hypotonic solution than the hypertonic solution. � Contractile vacuoles will absorb extra water inside the cell and secrete it to the outside before cytolysis occurs.

Cellular Reactions � Plasmolysis – when the cell releases enough water to the outside that the cell dies �Gardeners – think that the more fertilizer the better…. but actually too much will cause a hypertonic soil and the cells will go through plasmolysis

Cellular Transport � Passive – spontaneous; goes with the concentration gradient �Simple diffusion – uses only concentration gradient �Facilitated diffusion – uses mechanisms within the plasma membrane but NOT cellular energy �Osmosis – spontaneous - net movement of water molecules � Active – requires cellular energy; goes against the concentration gradient

Facilitated Diffusion � aka – passive mediated transport �Uses membrane proteins with channels to help molecules cross the plasma membrane ○ Protein channel – has small pores that go directly through the membrane ○ Carrier protein – has a specific binding site for a specific molecule; designed to transport only one molecule

Endocytosis and Exocytosis � Endocytosis – process a cell uses to transport substances in bulk across the membrane �Gathers substances into a bunch on the outside of the cell next to the plasma membrane then the membrane begins to engulf the substance and surround it until it is contained within a vacuole within the membrane; then it pinches off on the inside of the cell

Endocytosis � Two types of endocytosis – depends on what is contained in the vacuole �Phagocytosis – the substance is another cell; phagocytic vacuole – cellular eating �Pinocytosis – the substance is generally fluid or solutes – pinocytic vacuole – cellular drinking

Exocytosis � The reverse process of endocytosis – the vacuole is formed from the inside of the cell and pinched off on the outside of the cell