A tour of the cell Chapter 4

Most Cells Are Microscopic

Effect of Cell Size on Surface Area

Scanning & Transmission Electron Microscopes

Prokaryotic cells are structurally simpler than eukaryotic cells

Eukaryotic cells are partitioned into functional compartments Human cells have three basic parts: Plasma membrane—flexible outer boundary Cytoplasm—intracellular fluid containing organelles Nucleus—control center

NUCLEUS: Nuclear envelope Chromosomes Smooth endoplasmic reticulum Nucleolus Rough endoplasmic reticulum Lysosome Centriole Ribosomes Figure 4.4A An animal cell. Peroxisome Golgi apparatus CYTOSKELETON: Microtubule Plasma membrane Intermediate filament Mitochondrion Microfilament

NUCLEUS: Rough endoplasmic reticulum Nuclear envelope Chromosome Ribosomes Nucleolus Smooth endoplasmic reticulum Golgi apparatus CYTOSKELETON: Central vacuole Microtubule Chloroplast Intermediate filament Cell wall Plasmodesmata Microfilament Figure 4.4B A plant cell. Mitochondrion Peroxisome Plasma membrane Cell wall of adjacent cell

Plasma Membrane Bimolecular layer of lipids and proteins Constantly changing Dynamic role in cellular activity Separates intracellular fluid (ICF) from extracellular fluid (ECF) Outside cell Inside cell

The nucleus is the cell’s genetic control center Contains chromatin, a complex of proteins and DNA Genetic library with blueprints for nearly all cellular proteins Bound by a nuclear envelope with pores Contains a nucleolus, dark-staining spherical bodies w/in nucleus (ribosome assembly)

The endoplasmic reticulum is a biosynthetic factory Interconnected tubes & parallel membranes (cisternae) Continuous with nuclear membrane Two varieties: Rough ER-external surface studded with ribosomes Ribosomes are the platform for protein synthesis Smooth ER-lacks ribosomes; functions in lipid synthesis and detoxification of drugs, synthesis of steroid sex hormones

Lysosomes are digestive compartments within a cell Spherical membranous bags containing digestive enzymes (acid hydrolases) Digest unwanted material for the cell Membranous sacs containing powerful oxidases and catalases Peroxisomes Detoxify harmful or toxic substances, neutralize dangerous free radicals

Mitochondria harvest chemical energy from food Double-membrane structure with shelflike cristae and its own DNA Provide most of cell’s ATP

Chloroplasts convert solar energy to chemical energy Chloroplasts: plant organelles ; site of photosynthesis Found in: All green parts of a plant; leaves are main site of photosynthesis Contain: green pigment chlorophyll involved in photosynthesis

Chloroplasts convert solar energy to chemical energy Stroma Inner and outer membranes Figure 4.15 The chloroplast. Granum Intermembrane space

The Golgi apparatus finishes, sorts, and ships cell products Stacked and flattened membranous sacs (cisternae) Protein processing Rough ER ER membrane Phagosome Plasma mem- brane Vesicle becomes lysosome Secretory vesicle Golgi apparatus Secretion by exocytosis Extracellular fluid

The cell’s internal skeleton helps organize its structure and activities Elaborate series of rods throughout cytosol Microtubules (hollow) Microfilaments (solid) Intermediate filaments (solid)

Intermediate filament Microtubule Nucleus Nucleus Actin subunit Fibrous subunits Tubulin subunit Figure 4.17 Fibers of the cytoskeleton: microfilaments are stained red (left), intermediate filaments are stained yellow-green (center), and microtubules are stained green (right). 7 nm 10 nm 25 nm Microfilament Intermediate filament Microtubule

Cilia and flagella move when microtubules bend Flagella - whiplike, tails that move entire cell Cilia -short, hairlike structures that move substances across cell surfaces

Membrane Junctions Three types: Tight junctions- Prevent fluids and most molecules from moving between cells Desmosomes- Rivets” or “spot-welds” that anchor cells together Gap junctions-Transmembrane proteins form pores that allow small molecules to pass from cell to cell For spread of ions between cardiac or smooth muscle cells

Tight junctions Anchoring junction Gap junctions Plasma membranes Figure 4.21 Three types of cell junctions in animal tissues. Plasma membranes of adjacent cells Extracellular matrix