Unit 2.3: Cells and Organelles

1. Unit 2.3: Cells and Organelles

2. Complexity of Cells Next time: Include prokaryote = primitive and highlight “pr” • Prokaryotic cells: “pro-” = before; “karyo-” = nucleus; before nucleus • Very small: 0.2-2.0 μm in diameter • **No nucleus: instead they have a nucleoid region where DNA is found • DNA is circular/loop • **No membrane-bound organelles • Small ribosomes (70S) • for making proteins • Asexual reproduction/binary fission • Daughter cells are genetically identical to parent cells • 1 cell splits to become 2 cells

3. Eukaryotic cells: “eu” = true; “karyo-” = nucleus; true nucleus • Larger: 10-100 μm in diameter • **True nucleus: membrane-bound • DNA is “linear”, not circular • **Membrane-bound organelles: compartmentalize cellular functions • Larger ribosomes (80S) • 70S ribosome in some organelles • Sexual reproduction (usually) • Offspring are genetically different from parent cells • 2 gametes join to become 1 cell

4. Viruses: • Smaller than prokaryotic cells: 5-300nm • Has DNA or RNA, but not both • Capsid: a protein coat surrounding nucleic acid • Does not have: • Nucleus • Cytoplasm • Organelles • Cell membrane • Cannot reproduce without a host • Cannot metabolize/use energy

5. Comparison of Cell Types:

6. So which is which?

7. Function: provides structure, controls what enters cell Structure: a bilayer of phospholipids Two layers of lipid tails “sandwiched” between phosphate heads Lipid tails are hydrophobic; no water in the middle of the “sandwich” so they are “protected” Phosphate heads are hydrophilic; can interact with water The Cell Membrane

8. Selectively permeable: Lets some things in, keeps others out Like a chain-link fence: golf balls get thru but not footballs Or a security guard: lets Brad Pitt through, but not me :o( Materials that need to get into or out of the cell pass through protein channels: Peripheral: on one side or the other; for cell recognition Integral: go all the way thru; like “tunnels”, but specific to certain molecules

9. Cytoplasm, also called cytosol: Function: to maintain shape of the cell, provide suspension of organelles Structure: contains water, dissolved salts, minerals, organic molecules… All cells contain cytoplasm. Some prokaryotic cells push cytoplasm into “pseudopods” to help them move Cell Organelles

10. Cytoskeleton: • Function: to provide structure, movement • Structure: made of “microfilaments” • ‘micro-’ = small; ‘filum’ = thread • “Small threads” made of actin and tubulin proteins • All cells have a cytoskeleton.

11. Cilia: many and short • Function: move materialsover cell surface • Structure: many, short hair-like projections made of tubulin proteins • Ex: cilia line bronchioles in your throat, helps to filter dust that you breathe in • Common in prokaryotes and animal cells, not plants • Flagella: few and long • Function: movement of cell • Structure: few, long whip-like “tails” near one end of cell, made of tubulin • Common in prokaryotes and animal cells, not plants; why?

12. The Nucleus: • Three functions: • Stores DNA: • DNA is the “master plan” for making a copy of a cell, so must be well-protected, like money in bank vault. • Directs transcription: • Transcription: a “blueprint” of the master copy, contains instructions for making proteins • Contains nucleolus: • Function of the nucleolus is to make ribosomes • Structure: nucleolus is made of RNA/proteins

13. Structure of the nucleus: • Also made of a phospholipid bilayer, like the cell membrane • Has “nuclear pores” for materials to move into and out of nucleus, like the “protein channels” in the cell membrane • Only found in eukaryotes: • “true nucleus”

14. Ribosome • Ribosome: • Function: to make proteins • Structure: two subunits made of RNA and protein • Found in all cells: • Smaller ribosome (70S) in prokaryotes • Larger ribosome (80S) in eukaryotes • Can be free-floating in cytoplasm, or attached to ER • If protein stays inside cell, then made on “free” ribosome • If protein is meant to leave the cell, then made on a ribosome attached to the ER • Like a sewing machine…

15. Endoplasmic Reticulum (ER) • Function: to transport proteins • Structure: interconnected “cisterns/sacs” • Can be rough or smooth • Rough if ribosomes are attached: common in cells that export many proteins • Smooth if no ribosomes attached: common in cells that detoxify substances • Like a conveyor belt or highway system • Found in all eukaryotic cells

16. Golgi Apparatus: • Function: to modify proteins for export • “tags” them with molecules to direct where they will be “delivered” • Structure: flattened sacs of ER • like a portion of ER that has “budded off” • Found in all eukaryotic cells • Lysosome: • “lyse-” = break apart; “soma-” = “body • Function: Stores enzymes that “break down” foods, old organelles, viruses/bacteria • Structure: phospholipid bilayer surrounding hydrolytic enzymes • In animal cells, but not plant cells

17. Mitochondria • Function: converts food into energy – respiration • C6H12O6 + O2CO2 + H2O + ATP • Structure:rod-shaped, has a “double” membrane • Inner membrane (cristae) is highly folded, increases surface area for more reactions. • Found in all eukaryotic cells: • Cells that need lots of energy have more mitochondria • Ex: muscle cells

18. Was once a free-living organism that was ingested by a larger organism • Evidence of endosymbiosis: • Has double membrane: inner membrane was original cell; outer membrane from the larger cell • Same size as bacteria • Divide like bacteria • Has own DNA

19. Plant Organelles: • Chloroplast: • Function: converts energy into food – photosynthesis • CO2 + H2O + solar energy  C6H12O6 + O2 • Structure: pod-shaped with double membrane • Contains chlorophyll – pigment that captures light energy • Was once a free-living organism (like mitochondria) • Same evidence of endosymbiosis: • Has double membrane: inner membrane was original cell; outer membrane from the larger cell • Same size as bacteria • Divide like bacteria • Has own DNA

20. Central Vacuole: • Functions: • Helps plant to maintain stable water concentration • Filled with fluid: if “full,” plant is erect (turgid), but if “empty” then plant wilts (flaccid) • Stores hydrolytic (digestive) enzymes and metabolic waste • Like lysosome in animal cells • Keeps toxins (poisons) away from rest of cell • Those toxins can provide defense against herbivores

21. Cell Wall: • Function: to support and protect plant • Structure: Made of cellulose • Plants have cell membrane (like all other cells) that lies just inside the cell wall

22. Plants only, but… • Some prokaryotes have cell wall made of “peptidoglycan” • “peptido-” = protein; “glyc-” = sweet • So, made of protein and carbohydrates • And some fungi have a cell wall made of “chitin” • Cross-linked proteins and sugars

23. Which came first: the plant cell or the animal cell? Animal, then plant b/c plant has both mitochondria and chloroplast

24. Warm-up answers for this unit: