A Tour of The Cell Chapter 4

Effect of Cell Size on Surface Area Same total volume, but greater surface area to volume in smaller cells

Most Cells Are Microscopic Small things have a greater SA to volume ratio, allowing cells to maximize exchange across the plasma membrane Larger cells have less SA relative to their volume which is not efficient for maximizing exchange Why are cells so small: https://www.youtube.com/watch?v=wuXSEOKNxN8 https://www.youtube.com/watch?v=nw_EybrVJ-M

Scanning & Transmission Electron Microscopes

Prokaryotic cells are Structurally Simpler than Eukaryotic Cells

NUCLEUS: Nuclear envelope Chromosomes Smooth endoplasmic reticulum Nucleolus Rough endoplasmic reticulum Lysosome Centriole Ribosomes Figure 4.4A An animal cell. The harvard cell: https://www.youtube.com/watch?v=wJyUtbn0O5Y 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

Eukaryotic Cells are Partitioned into Functional Compartments A eukaryotic cell has: A nucleus- DNA surrounded by a nuclear membrane Cytoplasm - intracellular fluid outside of nucleus containing organelles A plasma membrane—flexible outer boundary of cell

Plasma Membrane Bimolecular layer of lipids and proteins Plays a 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 = threadlike complex of DNA & proteins Is surrounded by a nuclear envelope with nucleopores Contains a nucleolus, where ribosomes are assembled

The Endoplasmic Reticulum is a Biosynthetic Factory Interconnected tubes & parallel membranes (cisternae) Continuous with the 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 shelf-like cristae and its own DNA Provides most of cell’s ATP

Chloroplasts convert solar energy to chemical energy Chloroplasts are plant organelles ; site of photosynthesis Found in all green parts of a plant Chloroplast Stroma Inner and outer membranes Figure 4.15 The chloroplast. Granum Intermembrane space

The Golgi Apparatus Stacked and flattened membranous sacs (cisternae) Processing, packaging and shipping proteins Rough ER ER membrane Phagosome Plasma mem- brane Vesicle becomes lysosome Secretory vesicle Golgi apparatus Secretion by exocytosis Extracellular fluid

The Cytoskeleton Helps Organize the Cell’s 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 - whip like, tails that move an entire cell Cilia -short, hair-like 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- proteins form pores that allow small molecules to pass from cell to cell For spread of ions between cardiac or smooth muscle cells https://www.youtube.com/watch?v=gJ9WTD0XEnc

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

The Inner Life of The Cell