Organization of the Cell

Cell Theory Cells are the basic living units of organization and function All cells come from other cells Work of Schleiden, Schwann, and Virchow contributed to this theory Each cell is a microcosm of life

Biological Size and Cell Diversity

Cell surface area-to-volume ratio Plasma membrane must be large enough relative to cell volume to regulate passage of materials Volume increases faster than surface area so cells must divide Cell size and shape related to function

Cell Surface Area-to-Volume Ratio

Microscopes Light microscope, referred to as compound microscope, used by most students Two features determine how clearly an object is viewed Magnification Resolution Light microscope has 500 times more resolution than human eye

Electron microscope Developed in the 1950s Allows study of the ultrastructure of cells 10,000 times more resolution than human eye

Types of electron microscope Transmission electron microscope TEM Used to view internal cell structures Scanning electron microscope SEM Produces 3-D picture of cell surface Can’t be used to view living cells

Comparing light and electron microscopy

Cell fractionation Used to determine isolate & tell function of organelles Cells broken apart and the resulting cell extract spun in a centrifuge Centrifugal force separates extract Pellet – heavier cell organelles Supernatant – liquid poured off

Cell fractionation

Prokaryotic Bacteria and Archaea (ancient bacteria) DNA not enclosed in a nucleus Eukaryotic All other known organisms Highly organized membrane-enclosed organelles Cytoplasm Nucleoplasm

Functions of cell or plasma membranes Divide cell into compartments, allowing for specialized activities Interacting membranes form endomembrane system Vesicles transport materials between compartments (ER  Golgi, Golgi  plasma membrane…)

Diagram of a plant cell

Diagram of an animal cell

The cell nucleus Contains DNA Bounded by Nuclear envelope Double membrane perforated with nuclear pores DNA forms chromatin, which is organized into chromosomes Nucleolus RNA synthesis and ribosome assembly

The cell nucleus

Endoplasmic reticulum (ER) Network of folded internal membranes in the cytosol Connected to Nuclear envelope Smooth ER Site of lipid synthesis Site of detoxifying enzymes Detoxifies drugs & alcohol Stores Ca++ in muscle cells Rough ER Ribosomes on surface manufacture secretory proteins Proteins may be moved into the ER lumen (interior)

Endoplasmic reticulum (ER)

Golgi complex Glycoproteins Cisternae that process, sort, and modify proteins In animal cells, Golgi complex also manufactures lysosomes Glycoproteins Transported to the cis face (receiving side) Golgi modifies carbohydrates and lipids and packages into vesicles that pinch off the trans face (shipping side)

Golgi complex

Lysosomes break down worn-out cell structures, bacteria, and other substances Responsible for cell death & recycling Peroxisomes Involved in lipid metabolism and detoxification Contain enzymes (catalase) that produce and degrade hydrogen peroxide H2O2  H2O + O2

Lysosomes

Mitochondria Sites of aerobic respiration Organelles enclosed by a double membrane Has its own genome Place important role in apoptosis Cristae (internal folds) and matrix (innermost space) contain enzymes for aerobic respiration Nutrients broken down and energy packaged in ATP Carbon dioxide and water by-products

Mitochondria

Chloroplasts Plastids that carry out photosynthesis Inner membrane of chloroplast encloses the stroma gel-like liquid) Contains stacks of interconnected sacs called thylakoids Stack of thylakoids called grana During photosynthesis, chlorophyll traps light energy (sunlight) Energy converted to chemical energy in ATP

Chloroplast

Cellular respiration and photosynthesis

Cytoskeleton Internal framework made of Microtubules - tubulin Microfilaments - actin Intermediate filaments - keratin Provides structural support Involved with transport of materials in the cell Make up cilia, flagella, and centrioles

The Cytoskeleton

Cilia and flagella Thin, movable structures that project from cell surface Function in movement Microtubles anchored in cell by basal body

Structure of cilia

Many animal cells also surrounded by an extracellular matrix (ECM) Glycocalyx Cell coat formed by polysaccarides extending from plasma membrane Many animal cells also surrounded by an extracellular matrix (ECM) Most bacteria, fungi, and plant cell walls made of carbohydrates

Extracellular matrix

Plant cell walls