Cells & Organelles A Dr. Production
Two Basic Types of Cells • Prokaryotes: • prounounced: pro-carry-oats • Eu karyotes • Proun: you-carry-oats
A. Prokaryotes Small, simple cells (relative to eukaryotes) Size: about 1 µm (1 micron) No internal membrane-bounded organelles No nucleus Simple cell division Single linear chromosome Contain the domains; 1. True (Eu)bacteria & 2. Archaebacteria
1. True Bacteria = Eubacteria • Majority of bacteria • Examples include: E. coli, Lactobacillus (yogurt), Lyme disease
Eubacteria • Peptidoglycan cell walls (carbos & AA) • Separated into Gram + and - forms
Gram positive Gram negative
Bacteria in the Environment example: Iron utilizing Baceria B A A) An acid hot spring in Yellowstone is rich in iron and sulfur. B) A black smoker chimney in the deep sea emits iron sulfides at very high temperatures (270 to 380 degrees C).
2. Archaebacteria • Live in extreme environments: high salt, high temps • Different cell wall • Very different membrane lipids • Unusual nucleic acid sequence
Archaea types: Based on their physiology, Archae can be organized into three types: • Methanogens (prokaryotes that produce methane); • Extreme halophiles (prokaryotes that live at very high concentrations of salt (NaCl); • Extreme (hyper) thermophiles (prokaryotes that live at very high temperatures). All archaea have features that distinguish them from Bacteria (i.e., no murein in cell wall, ether-linked membrane lipids, etc.). And, these prokaryotes exhibit unique structural or biochemical attributes which adapt them to their particular habitats.
B. Eukaryotes • Bigger cells: 10-100 µm • True nucleus • Membrane-bounded structures inside. Called organelles • Divide by a complex, well-organized mitotic process Liver Cell 9,400x
Eukaryotes • Larger more complex cells that make up most familiar life forms: plants, animals, fungi, protists • Surrounded by a cell membrane made of lipids
The Cell Theory • Cells first observed by R. Hooke 1665 • Named for the Monk prayer cells • Cell Theory states that; 1. All life is composed of cells 2. Cells are the basic units of life 3. Cells arise from already existing cells
Cells are typically Small Typical cell size
Why are Cells Small? • Cells must exchange gases & other molecules with environment… • Nutrients in, Wastes out • As size increases, the rate of diffusion exchange slows down…. • This is due to the ratio of surface area to volume
Surface Area to Volume • Cell surface area is important in taking in nutrients • Surface area increases as the square of cell diameter • But… entire cell volume needs to be fed • And, cell volume increases as the cube of cell diameter
Consider 2 Cells... 100 µm diameter 10 µm diameter
The Eukaryotic Cell: Components • Outer cell membrane composed of lipids and proteins • Cytosol: interior region. Composed of water & dissolved chemicals…a gel • Numerous organelles….
Organelles • Specialized structures within eukaryotic cells that perform different functions... • Analogous to small plastic bags within a larger plastic bag. • Perform functions such as : • protein production (insulin, lactase…) • Carbohydrates, lipids…
Organelles of Note:The Nucleus • Contains the genetic material (DNA), controls protein synthesis. DNA --> RNA --> Protein • Surrounded by a double membrane with pores • Contains the chromosomes = fibers of coiled DNA & proteinin the form of chromatin
Chromosomes All Chromosomes from a single cell One chromosome Pulled apart A single chromosome Showing the amount of DNA within
Mitochondria • Generate cellular energy in the form of ATP molecules • ATP is generated by the systematic breakdown of glucose = cell respiration • Also, surrounded by 2 membrane layers • Contain their own DNA! • A typical liver cell may have 1,700 mitoch. • All your mitoch. come from your mother..
Plastids Synthesize carbohydrates • Leucoplasts: white in roots and tubers • Chromoplasts: rainbow accessory pigments • Chloroplasts: green in leaves and stems
Chloroplasts • Found in plants and some protists. Responsible for capturing sunlight and converting it to food = photosynthesis. • Surrounded by 2 membranes • And…contain DNA
Ribosomes • Size ~20nm • Made of two subunits (large and small) • Composed of RNA and over 30 proteins • Come in two sizes…80S (40s + 60s) and 70S (30s + 50s) • S units = Sedimentation speed
Ribosomes • DNA --> RNA --> Protein • The RNA to Protein step (termed translation) is done on cytoplasmic protein/RNA particles termed ribosomes. • Contain the protein synthesis machinery • Ribosomes bind to RNA and produce protein.
Endoplasmic Reticulum = ER • Cytoplasm is packed w. membrane system which move molecules about the cell and to outside • Outer surface of ER may be smooth (SER): synthesizes secretes, stores, carbs, lipids and non pps • Or Rough (RER): synthesizes pp for excretion • ER functions in lipid and protein synthesis and transport
Golgi Complex • Stacks of membranes… • Involved in modifying proteins and lipids into final form… • Adds the sugars to make glyco-proteins and glyco-lipids • Also, makes vesicles to release stuff from cell
Lysosomes • important in breaking down bacteria and old cell components • contains many digestive enzymes • The ‘garbage disposal’ or ‘recycling unit’ of a cell • Malfunctioning lysosomes result in some diseases (Tay-Sachs disease) • Or may self-destruct cell such as in apoptosis
Vacuoles • Formed by the pinching of the cell membrane • Very little or no inner structure • Stores various items
Peroxisomes/Microbodies • Large vesicles containing oxidative enzymes which transfer H from substrates to O • Contains catalase that changes H2O2 to H2O • In plants responsible for photorespiration and converting fat to sugar during germination
Cytoskeleton • Composed of 3 filamentous proteins: Microtubules Microfilaments Intermediate filaments • All produce a complex network of structural fibers within cell The specimen is human lung cell double-stained to expose microtubules and actin microfilaments using a mixture of FITC and rhodamine-phalloidin. Photo taken with an Olympus microscope.
Microtubules Function in: - division of cells (formation of spindle fibers) - some aspects of shape - many cell movements (flagella and cilia) - “transport” system within cell
Microtubules • Universal in eukaryotes • Involved in cell shape, mitosis, flagellar movement, organelle movement • Long, rigid, hollow tubes ~25nm wide • Composed of a and ß tubulin (small globular proteins) • 9+2 vs 9x3 arrangement Protist Movement
Microfilaments • Thin filaments (7nm diam.) made of the globular protein actin. • Actin filaments form a helical structure • Involved in cell movement (contraction, crawling, cell extensions)
Intermediate filaments • Fibers ~10nm diam. • Very stable, heterogeneous group • Examples: Lamins: hold nucleus shape Keratin: in epithelial cells Vimentin: gives structure to connective tissue Neurofilaments: in nerve cells Image of Lamins which reside in the nucleus just under the nuclear envelope
Cell Motility:Flagella & Cilia • Both cilia & flagella are constructed the same • In cross section: 9+2 arrangement of microtubules (MT) • MTs slide against each other to produce movement
Flagella (flagellum) • Motile structure of many eukaryotic cells; long, hair-like projection - e.g., tail of sperm • Core composed of 9 + 2 array of microtubules that arise from a basal body apparatus • Flagellated E. coli
Cilia (cilium) • Motile or sensory structure in eukaryotes composed of 9 + 2 array of microtubules • Usually numerous short, hair-like projections along outside of cell • Found in many Protista and in lining of lungs • Stentor feeding • Paramecium rotating
Endosymbiosis • Theory that eukaryotic cells arose from an early prokaryote (1) engulfing a second, smaller prokaryote (2) • The internalized #2 was not digested but became a symbiote. • Today’s mitochondria & chloroplasts may have arisen this way
Support for this Theory: • Eg. of this type of symbiosis are found today. Sponges harbor photosyn. algae within their tissues, allowing them to photosynthesize. • The organelles (chloroplasts and mitochondria) resemble bacteria in size and structure. • These organelles each contain a small amount of DNA but lack a nuclear membrane. • Each has the capability of self-replication. They reproduce by binary fission. • They make their own proteins. • During protein synthesis, these organelles use the same control codes and initial amino acid as prokaryotes. • They contain and make their own ribosomes, which resemble prokaryote’s. • The enzymes that replicate DNA and RNA (polymerases) of the organelles are similar to those in prokaryotes but different from those of eukaryotes. • The organelles have a double membrane that might be derived from a prokaryote’s plasma membrane and the membrane of a vesicle.
Resources • Rediscovering Biology Animation Guide • Cell Signaling and Cell Cycle Animations