Cell Theory and Structure Biology Corsicana High School

Development of the Cell Theory Robert Hooke (1665)---first to observe cells. Looked at thin slices of cork. Saw “little boxes.” Named them cells. Anton von Leeuenhoek (1675)---first to observe living cells: “wee beasties” in drop of pond water

Definitions cell---the smallest unit that can carry on all the processes of life unicellular---a complete living thing that consists of only one cell multicellular---a living thing consisting of more than one cell

Development of the Cell Theory (continued) Matthias Schleiden (1838)--- concluded that all plants are composed of cells Theodor Schwann (1839)---concluded that all animals are composed of cells Rudolph Virchow (1855)--- determined that cells come only from other cells

The Cell Theory All living things are composed of one or more cells. Cells are organisms’ basic units of structure and function. Cells come only from existing cells.

Two Main Types of Cells eukaryotes---contain a definite nucleus and membrane-bound organelles –examples: animal cells, plant cells –“eu” = true; “karyo” = nucleus prokaryotes---cells that do not have a definite nucleus or organelles –example: bacteria –“pro” = before

Parts of the Cell organelles---cell components that perform specific functions in the cell (“little organs”)

Three Main Components of Cells cell membrane---forms the outer boundary of the cell cytoplasm---inside the membrane. Contains water, salts, organelles nucleus---contains DNA and directs the activities of the cell

Cytoplasmic Organelles ribosome---tiny granules, site of protein synthesis endoplasmic reticulum---system of membranes throughout the cytoplasm. Acts as a transportation system –smooth ER---does not have ribosomes attached to it –rough ER---has ribosomes attached

Cytoplasmic Organelles Golgi apparatus---stack of fluid- filled membranes or sacs near the nucleus. The cell’s processing, packaging and secreting organelle mitochondrion---respiration centers of the cell –release energy from molecules –produce ATP –have their own DNA

Cytoplasmic Organelles lysosomes---organelles that contain digestive enzymes –only in animal cells –“suicide sacs” microtubules---long, slender protein tubes which shape and support the cells –spindle fibers---specialized microtubules that aid in movement of chromosomes during cell division

Cytoplasmic Organelles microfilaments---fine protein threads which contract to move cellular materials –cytoskeleton---microfilaments and microtubules collectively forming the framework of the cell

Organelles for Movement cilia---large numbers of short, hairlike extensions out from the surface of the cell; for movement flagellum---long, whiplike structure for movement. Occur singly or in pairs “9 + 2” construction of cilia and flagella---composed of 9 pairs of microtubules around the circumference and 2 in the center

Plant Cell Organelles cell wall---surrounds the cell membrane. Supports and protects the plant cell –structure is long chains of cellulose embedded in pectin and lignin vacuole---large, fluid-filled cavity which stores enzymes, wastes, etc. In a mature plant cell, the vacuole may take up 90% of the volume of the cell.

Plastids make and/or store food or pigments chloroplast---contains chlorophyll; the site of photosynthesis chromoplast---synthesizes and stores other pigments leucoplast---stores food such as starches, proteins, lipids

Nucleus contains DNA and directs the activities of the cell nuclear membrane (nuclear envelope)---double membrane that surrounds the nucleus. Has pores for substances to enter and leave nucleolus---spherical body in nucleus; stains dark; synthesizes ribosomes

Nucleus (continued) chromatin---fine strands in nucleus made of DNA and protein –chromosome----when the cell gets ready to divide, the chromatin coils and condenses and can be seen with a microscope as these rod-shaped bodies in the nucleus nucleoplasm---dense, protein-rich substance inside the nuclear membrane

Cell Membrane selectively permeable---allows some molecules to pass through, but not others

Composition of Cell Membrane 2 layers of lipid molecules –carboxyl group (hydrophilic) is turned to outside of membrane –hydrocarbon end (hydrophobic) is turned to inside of membrane protein molecules embedded in the lipid layer

Outside the cell Inside the cell

Fluid Mosaic Model the lipid molecules in the membrane can move around (flow---->fluid) proteins also move the pattern (“mosaic”) of proteins and lipids is constantly changing

Cell Types size ranges from 2 meters long (nerve cell in giraffe’s leg) down to 0.2 micrometers (bacteria) –usually micrometers –size is limited by ratio of surface area to volume shape is mostly cube- or sphere- shaped. The shape of a cell depends on its functions

Differences Between Plant Cells and Animal Cells lysosomes found only in animal cells vacuoles are large, central structures in plant cells. If present in animal cells, they are small and scattered cell wall found only in plant cells plastids (chloroplasts, chromoplasts, leucoplasts) found only in plant cells

Multicellular Organization In true multicellular organisms: –cell specialization---each cell does only one particular job for the organisms –division of labor---each cell depends on other cells to perform one or more functions to keep the entire organism alive colonial organism---a group of more or less similar cells that live together in closely-connected groups, but in which there is no cell specialization

Levels of Structure cell---the basic unit of life tissue---a group of similar cells that carry out a common function organ---several types of tissues that interact to perform a specific function organ system---a group of organs that work together to perform a set of related tasks