A Tour of the Cell

1. A Tour of the Cell Chapter 6

2. Objectives • Distinguish between a prokaryotic and eukaryotic cell • Describe the unique structures of a prokaryotic cell • Describe the structural differences between plant and animal cells • Describe the complex structural and functional interconnections among the organelles of the endomembrane system • Describe the structure of the eukaryotic nucleus, mitochondrion and chloroplast • Describe the surface structures of the cell that provide support, protection, and movement in, and communication with, the extracellular environment

4. Introduction • Cell is smallest functional unit of life • cell theory: • all organisms composed of cells • all existing cells arise from pre-existing cells • Common characteristics of all cells: • cell contents surrounded by plasma membrane • cytoplasm consists of semifluid matrix • organelles are embedded in cytoplasm • contain genes in the form of DNA

5. Fundamental features of life • Cells are highly structured • Structure and function are related • Membranes separate the cell from the external environment • Each cell had DNA as the genetic material • Each cell carries out metabolism

6. Cell Organization • Two types of cells-prokaryotic and eukaryotic • Prokaryotic: • small • lacks nucleus; DNA in nucleoid region • cytoplasm (also know as cytosol) surrounded by plasma membrane and outer cell wall • flagella and pili may be present

7. Eukaryotic Cells • Larger than prokaryotic cells • complex internal structure with membranous and non-membranous organelles • Membranous components: nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes and peroxisomes • Non-membranous components: ribosomes, microtubules, centrioles, flagella and cytoskeleton

8. Prokaryotes vs. Eukaryotes Both have… • DNA as their genetic material (it’s DNA that tells cells what kind of cells they should be). • Covered by a cell membrane. • RNA • The same basic chemicals: carbohydrates, proteins, nucleic acid, minerals, fats and vitamins. • Ribosomes • Regulate the flow of the nutrients/wastes • Similar basic metabolism like photosynthesis and reproduction. • Require a supply of energy. • Highly regulated by elaborate sensing systems ("chemical noses”) that make them aware of the reactions within them and the environment around them. Differences • Prokaryotic “older” then eukaryotic • 3.5 billion years-Pro • 1.5 billion years-Euk • Pro usually smaller then Euk • Pro no nucleus for DNA • Euk has the following while Pro doesn’t • Nucleus • Endoplasmic Reticulum (ER) • Golgi Apparatus • Mitochondria/Chloroplasts

9. Plant vs. Animal Cells • Animal cells surrounded by plasma membrane only • Plant cells surrounded by plasma membrane and rigid cell wall; also have central vacuole and chloroplasts

10. Eukaryotic Cell Organization • Eukaryotic organelles form four functional groups: • manufacture • breakdown • energy processing • support, movement and communication (SMC)

11. Manufacturing • Nucleus • Ribosomes • Endoplasmic reticulum : rough and smooth • Golgi apparatus

12. Nucleus • Nucleus is cell’s genetic control center • surrounded by double membrane • contains pores to allow passage of material between nucleus and cytoplasm • DNA normally present as strands of chromatin • During cell division, chromatin coils up to form chromosomes • Nucleolus-organelle within nucleus-responsible for ribosomal RNA synthesis

13. Ribosomes • Made up of RNA and proteins • Synthesis proteins • Free ribosomes in the cytosol • Bound ribosomes • Nucleus • Endoplasmic Reticulum

14. Endomembrane system • Collection of membranes either inside or surrounding the eukaryotic cell, related through direct physical contact or by transfer of vesicles • Endomembrane system: RER and SER • Rough endoplasmic reticulum contains ribosomes; protein synthesis ( RER) • Smooth endoplasmic reticulum synthesizes lipids, processes materials, acts as storage and detoxifies substances (SER)

16. Golgi • Golgi apparatus receives products from ER • Chemically modifies the products sent to it • Puts “Zip Codes” on products so they know where to go in the cell • Puts these modified products in vesicles and sends them out • The Golgi Apparatus is the “UPS” of the cell • Its receives, warehouses, sorts, modifies, packs and reships substances

18. Breakdown • Lysosomes • Vacuoles

19. Lysosomes • Lysosomes contain enzymes to digest substances and wastes; defective lysosomes cause fatal diseases • Lysosomes help your cells recycle materials: Each Liver cell recycles half of its synthesized macromolecules per week

21. Vacuoles • Vacuoles function in general cell maintenance • In plants they can hold organic substances • In protists vacuoles can hold food or water, or act as pumps

22. Energy Processing • Mitochondria • Chloroplasts • Peroxisomes

23. Mitochondria • found in all eukaryotic cells, except anaerobic protozoans • surrounded by double membrane • site of cellular respiration • Prokaryotes don’t have them… What do they do?? • Inner and outer membrane • Matrix and Cristae

24. Chloroplasts • found in plants and algae • convert solar energy to chemical energy • Surrounded by double membrane • site of photosynthesis

25. Evolutionary origins of Mito and Chloroplasts • Both similar to bacteria • Double membrane • Contain free ribosomes and circular DNA molecules • Grow and reproduce somewhat independently in cells • Endysombiont theory • Early eukaryote ancestors engulfed a nonphotosynthetic prokaryotic cell which formed a symbiotic relationship • Both evolved together • Over time a photosynthetic prokaryote consumed which evolved into chloroplasts

27. Peroxisomes • Single membrane compartment • Removes H atoms form substrates • Breaks down fatty acids and amino acids • Product is H2O2 which is toxic • Contains enzyme that converts hydrogen peroxide into water (catalase) • Detoxify blood toxins in the liver and kidney

28. Support, Movement, and Communication • Internal cell skeleton-cytoskeleton • composed of 3D meshwork of proteins • rods of globular proteins-microfilaments • ropelike strands of fibrous proteins-intermediate filaments • hollow tubes of globular proteins-microtubules • microtubules provide anchors for organelles, act as conveyor belts and form cilia and flagella

30. Mircotubeles • Provide anchors for organelles • Act as conveyor belts • Form cilia and flagella

31. Cilia and flagella • function to move whole cell • structure consists of 9 microtubule doublets arranged around central pair (9+2)

32. Movement of cilia and flagella occurs when arms consisting of the protein dynein move the microtubule doublets past each other

34. Microfilaments cause contraction of muscle cells • They also function in ameboid movement, cytoplasmic streaming and support for cellular projections

35. Centrioles, located adjacent to the nucleus, anchor and organize the microtubules that form the spindle during cell division

36. Intermediate Filaments • Support cell shape • Fix organelles in place

37. Eukaryotic Cell Organization • Cell surfaces • protect, support and join cells • in plants, neighboring cells joined to form interconnected and coordinated group • cell walls multi-layered, composed of mixtures of polysaccharides and proteins • plasmodesmata-channels through cell walls connecting cytoplasm of adjacent cells- plants

38. Extracellular Matrix • in multi-cellular animals cells often surrounded by sticky mixture of polysaccharides and proteins • Extends outward from the cell membrane • Lots of collagen is found there • Function • Support • Adhesion • Movement • regulation

40. Eukaryotic Cell Organization • Several type of junctions between cells: • tight junctions: leak proof; block movement of substances • anchoring junctions- join cells and provide structural support; like the rivets in your blue jeans • communicating junctions ( gap junctions)-provide channels between cells; allow rapid transport of materials

42. Checklist • Differences between prokaryotic and eukaryotic? • Characteristics of each? • Differences between plants of animals • 4 functional groups of eukaryotes? Organelles in these groups? • What is the function of each organelle? • What are the functions of microtubules, cilia, flagella, intermediate filaments, microfilaments? • What are the types of junctions and what do they do?