Cells The smallest unit of life Discovering the Cell 1665 - Robert Hooke Anton van Leeuwenhoek late 17th, early 18th centuries • 1839 – Cell Theory is proposed independently by Theodore Schwann and Matthias Jakob Schleiden. • Cell Theory: • The cell is the fundamental structure of all living things. • All living things are made of cells. • Cells arise from pre-existing cells through cell division. Ernst Ruska - 1938 Light micrograph Paramecium Scanning electron micrograph Transmission electron micrograph Cell Membrane Scanning electron micrograph Prokaryotic Cells Prokaryotic Features • No membrane-bound organelles, such as a nucleus. • DNA in one large ring-shaped chromosome • An enormous variety of metabolic pathways. • Highly successful and adaptable. External structure Coccus (spherical) Spirillus (spiral) Bacillus (rod-shaped) Internal Structure chromosome (nucleoid region) pili ribosomes food granule prokaryotic flagellum capsule or slime layer cell wall plasma membrane cytosol plasmid (DNA) Viruses • A virus is usually not considered living. • A virus consists only of a protein coat (sometimes with a lipid outer layer) and a piece of genetic material (DNA or RNA). Bacteria vs. Virus Features Reproduces independently? Has genetic material? Has cell membrane? Has metabolism? Living? Bacteria Virus Eukaryotic Cells Eukaryotic Features • Cells contain membrane-bound organelles. • Nucleus holds multiple strands of DNA, which condense into chromosomes during cell division. • May be single-celled or multi-cellular organisms. Animal cell nuclear pore chromatin (DNA) nucleolus nuclear envelope cytosol nucleus centriole rough endoplasmic reticulum plasma membrane lysosome ribosomes on rough ER smooth endoplasmic reticulum free ribosome mitochondrion Figure 4-3 Biology: Life on Earth 8/e ©2008 Pearson Prentice Hall, Inc. Golgi apparatus vesicle Plant Cell - same organelles as an animal cell, plus a few more plastid mitochondrion choloroplast cytosol Golgi apparatus smooth endoplasmic reticulum central vacuole vesicle plasmodesma rough endoplasmic reticulum cell wall plasma membrane nuclear pore nucleus chromatin (DNA) nucleolus nuclear envelope ribosomes free ribosome Things we will see in cells • First let’s focus on things we can see using a light microscope and ordinary stains: • Cell nucleus • Cell membrane • Cell wall • Plastids (Chloroplast, amyloplast, chromoplast) • Plant cell vacuole Nucleus nuclear envelope nucleolus nuclear pores chromatin Cell Wall secondary cell wall primary cell wall plasma membrane middle lamella Chloroplast outer membrane inner membrane stroma thylakoid channel interconnecting thylakoids granum (stack of thylakoids) 1 micrometer Amyloplasts and other plastids plastid starch globules 0.5 micrometer Protein-making Machinery • Information for making proteins is in DNA, stored in the nucleus. • An RNA copy is made in the nucleus and sent out to the rough Endoplasmic Reticulum (ER). • Proteins leave the ER and are finished and packaged in the Golgi apparatus. Endoplasmic Reticulum ribosomes rough ER vesicles smooth ER Golgi Apparatus Protein-carrying vesicles from ER merge with Golgi apparatus Golgi apparatus Vesicles carrying modified protein leave Golgi apparatus ER and Golgi function 5 Vesicles merge with the plasma membrane and release protein by exocytosis. 4 Completed protein is packaged into vesicles. 3 Vesicles fuse with Golgi. The protein may be altered and finished. 2 Protein is packaged into vesicles and travels to Golgi apparatus. 1 A protein is synthesized in the rough ER. Organelles in Cell Energy • Chloroplasts capture energy from the sun and use that energy to manufacture sugars (chemical energy storage). • Mitochondria break the bonds in sugars and release the energy that was stored there. Mitochondrion outer membrane inner membrane matrix cristae intermembrane compartment 0.2 micrometer Chloroplast outer membrane inner membrane stroma thylakoid channel interconnecting thylakoids granum (stack of thylakoids) 1 micrometer Single-Celled Organisms • Single-celled organisms carry out the same functions that our multicellular bodies do, but all within a single cell. How do they do it? One-celled Eukaryotic organisms have unique challenges. A Paramecium must: ingest food excrete waste sense and respond to the environment (a) Cilium propulsion of fluid power stroke plasma membrane return stroke (b) Flagellum direction of locomotion propulsion of fluid continuous propulsion protein "arms" central pair of microtubules section of cilium (transmission EM) Paramecium plasma membrane basal body 0.1 micrometer cilium contractile vacuole full reservoir contracted reservoir Water enters collecting ducts, fills central reservoir. collecting ducts central reservoir pore Reservoir contracts, expelling water through pore. Recap • Prokaryotic cells have no membranebound organelles. • Eukaryotic cells have membrane-bound organelles, which compartmentalize processes for better efficiency. • ALL cells have a cell membrane and DNA.