Biology I for Non-Majors

1. Biology I for Non-Majors Prokaryotes and Eukaryotes

2. Unified Cell Theory • Botanist Matthias Schleiden and zoologist Theodor Schwann proposed the unified cell theory • All living things are composed of one or more cells • The cell is the basic (and smallest) unit of life • New cells arise from existing cells • Rudolf Virchow later made important contributions to this theory. • Microscopes are used to study forms and parts of life • Light microscopes: study living cells • Electron microscopes: higher magnification and higher resolution, but sample preparation kills the specimen

3. All Cells Share Four Features • A plasma membrane, an outer covering that separates the cell’s interior from its surrounding environment • Cytoplasm, consisting of a jelly-like region within the cell in which other cellular components are found • DNA, the genetic material of the cell • Ribosomes, particles that synthesize proteins

4. Prokaryotic Cells • A simple, single-celled (unicellular) organism that lacks a nucleus, or any other membrane-bound organelle Concepts of Biology.  • Bacteria and Archaea • Bacteria have a cell wall made of peptidoglycan and many have a polysaccharide capsule • Some prokaryotes have flagella, pili, or fimbriae

5. Eukaryotic Cells • A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments or sacs, called organelles, which have specialized functions • Eukaryotic = true nucleus • Organelle = little organ • Typically larger than prokaryotic cells • May be single-cells organisms or may be part of a multicellular organism

6. Individual Cell Size is Limited • Cell size is limited because volume increases much more quickly than does cell surface area • This limits the size of prokaryotes to allow ions and organic material to enter and spread throughout them quickly • Eukaryotic cells have structural adaptations to enhance cellular transport

7. Shared Characteristics of Eukaryotes • Nucleus surrounded by a nuclear envelope with nuclear pores • Mitochondria • A cytoskeleton containing the structural and motility components • Flagella and cilia, organelles associated with cell motility • Chromosomes • Mitosis, a process of nuclear division • Sex, a process of genetic recombination unique to eukaryotes • Cell walls in all major lineages

8. Endosymbiosis and the Evolution of Eukaryotes • All living eukaryotes are descendants of a chimeric organism that was a composite of a host cell and the cell(s) of an alpha-proteobacterium that “took up residence” inside it • Endosymbiosis = one cell engulfing another such that the engulfed cell survives and both cells benefit • Evidence for endosymbiotic origins can be seen in mitochondria and in plastids

10. Cytoplasm: Found in all Cells • Cytoplasm: the matrix inside cells • Slightly different in eukaryotes and prokaryotes • In eukaryotic cells, which have a nucleus, the cytoplasm is everything between the plasma membrane and the nuclear envelope • In prokaryotes, which lack a nucleus, cytoplasm simply means everything found inside the plasma membrane • One major component of the cytoplasm in both prokaryotes and eukaryotes is the gel-like cytosol • A water-based solution that contains ions, small molecules, and macromolecules

11. Eukaryotic Organelles: The Nucleus • The nucleus is the most prominent organelle in a cell • Houses the cell’s DNA in the form of chromatin and directs the synthesis of ribosomes and proteins • Surrounded by a double-membrane structure punctuated by pores • Connects to the endomembrane system

12. Eukaryotic Organelles: The Endomembrane System • The endoplasmic reticulum (ER) is a series of interconnected membranous tubules • Collectively modify proteins and synthesize lipids • Rough and Smooth ER have specialized functions • The Golgi apparatus • Responsible for sorting, tagging, packaging, and distribution of lipids and proteins 

13. Ribosomes: Found in all Cells • Ribosomes are the cellular structures responsible for protein synthesis • Free ribosomes appear as either clusters or single tiny dots floating freely in the cytoplasm • May be attached to plasma membrane or ER • Found in practically every cell, although they are smaller in prokaryotic cells

14. Eukaryotic Organelles: Mitochondria • Mitochondria (singular = mitochondrion) are often called the “powerhouses” or “energy factories” of a cell because they are responsible for making adenosine triphosphate (ATP), the cell’s main energy-carrying molecule • Oval-shaped, double-membrane organelles • Have their own ribosomes and DNA

15. Eukaryotic Organelles: Vesicles and Peroxisomes • Vesicles are membrane-bound sacs that function in storage and transport • Can fuse with the membranes of other cellular components • Perform a variety of functions • Metabolism • Transport • Buoyancy control • Enzyme storage • Peroxisomes are small, round organelles enclosed by single membranes • Carry out oxidation reactions that break down fatty acids and amino acids • Detoxify many poisons that may enter the body

16. Eukaryotic Structures: The Cytoskeleton • Microfilaments are the thinnest of the cytoskeletal fibers and function in moving cellular components • Intermediate filaments are of intermediate diameter and have structural functions • Microtubules are the thickest of the cytoskeletal fibers and guide organelle movement and are the structures that pull chromosomes to their poles during cell division

17. Microtubules also form Flagella and Cilia • Flagella (singular = flagellum) are long, hair-like structures that extend from the plasma membrane and are used to move an entire cell • Flagella are found in both prokaryotes and eukaryotes • When cilia (singular = cilium) are present, however, they are many in number and extend along the entire surface of the plasma membrane

18. The Plasma Membrane Holds it all Together • Eukaryotes and prokaryotes both have a phospholipid bilayer plasma membrane

19. Plant Cell Specific Organelles • The cell wall is a rigid covering that protects the cell, provides structural support, and gives shape to the cell • Found in plants • Fungal and protist cells also have cell walls • Prokaryotes also have cell walls • Each type is made of different macromolecules • Chloroplasts function in photosynthesis and can be found in photoautotrophic eukaryotic cells such as plants and algae • Plasmodesmata are numerous channels that pass between the cell walls of adjacent plant cells, connecting their cytoplasm and enabling signal molecules and nutrients to be transported from cell to cell

20. Animal Cell Specific Organelles • Lysosomes are the cell’s “garbage disposal • The extracellular matrix hold cells together to form a tissue, and it also allows the cells within the tissue to communicate with each other • Cells can also communicate with each other by direct contact, referred to as intercellular junctions • A tight junction is a watertight seal between two adjacent animal cells • Desmosomes act like spot welds between adjacent epithelial cells • Gap junctions in animal cells are like plasmodesmata in plant cells in that they are channels between adjacent cells that allow for the transport of ions, nutrients, and other substances that enable cells to communicate

21. Cell Connections

22. Quick Review • What is the unified cell theory? • When would different types of microscopes be used? • List the features common to all cells • What are the two groups of prokaryotes? • List the key features that define eukaryotic cells. • What is the main limit on cell size? • Describe the endosymbiotic theory and eukaryotic origins • Can you label all the organelles in a eukaryotic cell? • Match each organelle with its function • What organelles are unique to animals? To plants?