Cell Structure

Cell Theory All living organisms are made of one or more cells. The cell is the basic organizational unit of life. All cells come from pre-existing cells. Why study cells? Haven’t we already learned about them? Most diseases/disorders can be explained due to a default at the cellular level.

Cell Characteristics Genetic material single circular molecule of DNA in prokaryotes double helix located in nucleus in eukaryotes – nuclear envelope (double membrane Cytoplasm fills cell interior – sugars, amino acids, proteins – organelles Plasma membrane encloses the cell – phospholipid bilayer Phospholipid Membrane proteins

Generalized Eukaryotic Cell

Cell Size Most cells are relatively small because as size increases, volume increases much more rapidly. longer diffusion time

Visualizing Cells

Found in plants, as well as some bacteria, protists, and fungi Cell Wall Found in plants, as well as some bacteria, protists, and fungi Structure Thicker, stronger, and more rigid than cell membranes Capable of supporting large plants (e.g., tall trees) Made up of tiny fibres of cellulose Perforated with many pores Function Protects cell from rupturing Allows cell to exchange material with environment and to communicate with other cells

Cell Wall

Nucleus Contains genetic material (DNA) Directs activities of the cell Usually single, some cells several, RBC none Nuclear membrane surrounds nucleus Nuclear pores – controls the movement of molecules in and out of the nucleus Nucleolus found inside nucleus makes ribosomes

Nucleus

Endoplasmic Reticulum Transports molecules throughout the cell Made of membranes that act as channels or passageways

Golgi Apparatus (also called Golgi “body” or “complex”) Packages proteins and other molecules for transport out of the cell Does this by surrounding the protein with membranes and puts the proteins in a “vesicle” (tiny vacuole)

Cisternae cis face Proteins trans face Protein Ribosome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cisternae cis face Proteins trans face Transport vesicle Golgi apparatus Protein Vesicle budding from rough endoplasmic reticulum Migrating transport vesicle Fusion of vesicle with Golgi apparatus Ribosome

Organelles made of just a membrane Vesicles – transport materials out of the cell or transports and stores materials inside the cell Lysosomes - membrane-bound vesicles containing digestive enzymes Vacuoles - contain water and other materials; used for storage plant cells have usually 1 large vacuole animal cells have several small vacuoles

Cytoplasm Extracellular fluid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasm Endoplasmic reticulum Phagocytosis Food vesicle Golgi apparatus Lysosomes Transport vesicle Old or damaged organelle Plasma membrane Digestion of phagocytized food particles or cells Breakdown of old organelle Extracellular fluid

Ribosomes Make proteins Some ribosomes float around in the cytoplasm while others are attached to the endoplasmic reticulum

glucose + oxygen  carbon dioxide + water + energy Mitochondria Releases energy from glucose (cellular respiration) glucose + oxygen  carbon dioxide + water + energy Structure - outer and inner membranes, (folds called cristae) Have their own DNA

carbon dioxide + water  glucose + oxygen Chloroplasts Traps energy from the sun to make glucose in photosynthesis: carbon dioxide + water  glucose + oxygen Grana – closed compartments of stacked membranes Thylakoids – disc shaped structure – light capturing pigment Stroma – fluid matrix

Cytoskeleton Network of protein fibers supporting cell shape and anchoring organelles Actin filaments cell movement Microtubules Hollow tubes Facilitate cell movement Centrioles – barrel shaped organelles occur in pairs – help assemble animal cell’s microtubules Intermediate filaments Stable - don’t break down Actin Microtubules Intermediate filaments

Cytoskeleton

Cytoplasm Includes the cytosol (liquid), organelles and dissolved sugars, etc. within the cell membrane Every chemical reaction takes place within the cytoplasm