Components found only in Eukaryotic Cells

1. 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

2. 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

3. 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

4. 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)

5. 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

6. 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)

7. 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

8. Photosynthetic Organelles Chloroplasts (plant cells and photosynthetic protists) • Use light energy to convert atoms in water and CO2 (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

9. 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

10. 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

11. 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

12. 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

13. Cell Walls • Composed of cellulose and/or chitin in eukaryotes (only plant and fungi cells have cell walls in eukaryotes)

14. 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

15. 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 thathelp the bacteria connect to other cells in order to exchange plasmids (DNA)