Overview of Cells Prokaryotes vs Eukaryotes The Cell Organelles The Endosymbiotic Theory
Prokaryotic Cells Archaea Bacteria Come in many different shapes and sizes.5 µm 2 µm, up to 60 µm long Have large surface to volume ration nutrients from outside can easily reach all parts of the cell
Eukaryotic Cells Protists Fungi Animal Cells Plant Cells Like prokaryotic cells, eukaryotic cells come in many different shapes and sizes, but have the same basic set of organelles Multicellular organisms (fungi, plants and animals) have specialized eukaryotic cells that each perform a particular job and all work together for the benefit of the organism
Eukaryotic Cells Common Organelles Plasma membrane Nucleus Chromatin (DNA) Nucleolus Nuclear Envelope Ribosomes Rough Endoplasmic Reticulum (rough ER) Smooth Endoplasmic Reticulum (smooth ER) Golgi Apparatus Centrioles Mitochondria Cytoskeleton Vesicles, Peroxisomes, Lysosomes, Small Vacuoles
Eukaryotic Cells Organelles only found in Plants All those in animal cells except Centrioles plus Cell Wall Chloroplasts Large Vacuoles The cell wall and vacuoles help plant cells maintain a rigid shape (keep plant from drooping)
Organelles Organelles are the parts within a cell that have specific functions Prokaryotic cells (e.g. bacteria) are smaller and less complex (fewer organelles) than eukaryotic cells. Prokaryotic Cells Plasma Membrane Cytoplasm Cell Wall DNA (no nucleus) Ribosomes Eukaryotic Cells Plasma Membrane Plant Cells Cytoplasm (eukaryotic) Nucleus Cell Wall Chromatin (DNA) Chloroplasts Nucleolus Vacuole Nuclear Envelope Ribosomes Vesicles, Peroxisomes, Lysosomes Rough Endoplasmic Reticulum Smooth Endoplasmic Reticulum Golgi Apparatus Centrioles Mitochondria Cytoskeleton
Organelles Organelles are made of: Proteins made of amino acids Lipids made of fatty acids Carbohydrates - polysaccharides made of sacharides (sugars) Nucleic Acids (DNA and RNA) made of nucleotides Polysaccharides Nucleic Acids Proteins (Polypeptides) Lipids
Components found in all cells Plasma Membrane Made of a Phospholipid Bilayer Various proteins, lipids, and sugars float in membrane Semipermeable Small hydrophobic molecules pass easily through Contains pores that enable water and very small ions to pass through large molecules must pass through channel proteins
Components found in all cells Plasma Membrane Eukaryotic cells also membrane-bound internal organelles composed of lipid bilayer membranes Nuclear Envelope Golgi Apparatus Endoplasmic Reticulum (rough and smooth) Mitochondria Chloroplasts (in plants) Vesicles, Lysosomes, Peroxisomes & Vacuoles
Components found in all cells Cytoplasm The fluid that fills cells and surrounds the organelles Consists of: Water (mostly) Proteins (e.g. hormones and enzymes) Small Molecules (e.g. ions)
Components found in all cells DNA Prokaryotic Cells May be linear or circular Contained in the nuclear region (nucleoid) May also include short, circular plasmids Eukaryotic Cells Longer (approx. 9 feet per cell in humans), coiled around histone proteins to help pack it into the cell Always linear Contained in the nucleus Known as chromatin when relaxed and chromosomes when condensed (supercoiled)
Components found in all cells Ribosomes Float freely in the cytoplasm of prokaryotic and eukaryotic cells Also coat the rough ER of eukaryotic cells
Components found in all cells Ribosomes Build proteins using instructions encoded in DNA
Components found in all cells Ribosomes Build proteins using instructions encoded in DNA Complex of protein and rrna forming two subunits Purple = Proteins Blue = rrna of small subunit Grey = rrna of large subunit
Components found only in Eukaryotic Cells Nucleus Nuclear Envelope double membrane nuclear pores allow RNA to exit Chromatin relaxed DNA Nucleolus where ribosomes are assembled
Components found only in Eukaryotic Cells Rough Endoplasmic Reticulum (ER) Folded membrane that forms compartments where newly synthesized proteins are processed (cut, joined, folded into their final shape) Ribosomes bind to rough ER when they start to synthesize proteins that are intended to be exported from the cell the proteins enter the ER directly from the ribosome
Components found only in Eukaryotic Cells Smooth Endoplasmic Reticulum (ER) Synthesis of lipids and steroids Metabolism of carbohydrates and steroids Regulation of calcium concentration Drug/toxin detoxification Attachment of receptors on cell membrane
Components found only in Eukaryotic Cells Golgi Apparatus Folded membranes form compartments that each contain different enzymes which selectively modify the contents depending on where they are destined to end up Processes and packages macromolecules produced by the cell (e.g. proteins and lipids) sent out as excretory vesicles labeled for their destination
Components found only in Eukaryotic Cells Cytoskeleton Network of long protein fibers (microtubules, actin filaments, and intermediate filaments) Helps support cell shape and movement transport organelles and vesicles throughout the cytoplasm to other areas within the cell The cytoskeleton is stained green in this image (the nucleus is stained blue and the cell membrane is stained red)
Components found only in Eukaryotic Cells Membranous Sacs Excretory Vesicles Carry products of protein synthesis to parts of the cell or to membrane to be excreted via exocytosis Vacuoles Store nutrients such as starch, glycogen, or fat Take up most of space in many plant cells, full of water Peroxisomes In animal cells full of enzymes that oxidize amino acids In plant cells full of enzymes that oxidize fat In plant and animal cells convert hydrogen peroxide to water Lysosomes Contain digestive enzymes Fuse with vesicles and vacuoles containing food, cell refuse, captured bacteria, etc
Components found only in Eukaryotic Cells Centrioles Form centrosome and initiate formation of the mitotic spindle during cellular replication Found in animal cells and some plant cells not in higher plants or fungi Composed of microtubules (like those in the cytoskeleton)
Components found only in Eukaryotic Cells Mitochondrion (plural Mitochondria) Brakes down glucose (sugar) using oxygen to produce energy for the cell = cellular respiration Many cells have only a single mitochondrion, whereas others can contain several thousand Have own DNA and ribosomes
Photosynthetic Organelles Chloroplasts (plant cells and photosynthetic protists) Use light energy to convert atoms in water and CO 2 (from air) into sugars and starches Have double membrane (inner and outer) Have own DNA and ribosomes Grana (stacks of thylakoids) where light energy is captured by chlorophyll and converted into chemical energy = photosynthesis Stroma fluid inside chloroplasts Chlorophyll light-absorbing pigment in thylakoids
Endosymbiotic Theory Concept that mitochondria and chloroplasts are the result of years of evolution initiated by the endocytosis of bacteria and blue-green algae which, instead of becoming digested, became symbiotic
Endosymbiotic Theory Concept that mitochondria and chloroplasts are the result of years of evolution initiated by the endocytosis of bacteria and blue-green algae which, instead of becoming digested, became symbiotic Have their own DNA which resembles bacterial DNA Have their own 70s ribosomes and produce their own proteins Double membrane indicates they entered cell via endocytosis Membrane composition strongly resembles Gram-negative bacteria Divide within eukaryotic cell via binary fission (the way of bacteria) Similar symbiotic relationships exist between organisms that are still distinct species from one another Some evidence indicates that eukaryotic flagella and cilia may have originated as symbiotic bacteria as well
Evolution of Eukaryotes Some protists lack mitonchondria which indicates that the eukaryote lineage evolved before the ancestral bacterial of mitochondria established a symbiotic relationship with early protists
Cell Walls Tough, rigid wall around cell membrane Most prokaryotes Eukaryotes: plants, algae and fungi only Functions: Prevents over-expansion when water enters the cell via osmosis Structural support (otherwise cells would be spherical) Protection
Cell Walls Composed of cellulose and/or chitin in eukaryotes (only plant and fungi cells have cell walls in eukaryotes)
Other External Structures Flagella Creates movement in prokaryotes by rotating like a propeller Whip-like movement in eukaryotes Larger and more complex in eukaryotes - common in protozoa, found in some algae - only spermatozoa cells in humans Positive chemotaxis cell moves up concentration gradient Negative chemotaxis cell moves down concentration gradient Phototaxis cell moves towards (positive) or away from (negative) light
Other External Structures Cilia (eukaryotes only) Numerous on surface of cell Beat in a coordinated pattern creating a wave of movement Mostly occur in protozoa, but some human cells too (like those lining the respiratory tract) Pili (prokaryotes only) also known as fimbria Hair-like appendage on bacteria that help the bacteria connect to other cells in order to exchange plasmids (DNA)