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Chapter 4. The Cell: Basic Unit of Life

Chapter 4. The Cell: Basic Unit of Life. Why do we study cells?. Cell Theory. All organisms are made up of cells The cell is the basic living unit of organization for all organisms All cells come from pre-existing cells. Biological diversity & unity.

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Chapter 4. The Cell: Basic Unit of Life

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  1. Chapter 4.The Cell: Basic Unit of Life BIOLOGY 114

  2. Why do we study cells?

  3. Cell Theory • All organisms are made up of cells • The cell is the basic living unit of organization for all organisms • All cells come from pre-existing cells

  4. Biological diversity & unity • Underlying the diversity of life is a striking unity • DNA is universal genetic language • Cells are the basic units of structure & function • lowest level of structure capable of performing all activities of life

  5. Activities of life • Most everything you think of a whole organism needing to do, must be done at the cellular level… • reproduction • growth & development • energy utilization • response to the environment • homeostasis

  6. How do we study cells? • Microscopes opened up the world of cells • Robert Hooke (1665) • the 1st cytologist Drawings by Hooke cork flea

  7. How do we study cells? • Microscopes • light microscopes • electron microscope • transmission electron microscopes (TEM) • scanning electron microscopes (SEM) Technology advancing science

  8. Light microscopes • 0.2µm resolution • ~size of a bacterium • visible light passes through specimen • can be used to study live cells

  9. Electron microscope • 1950s • 2.0nm resolution • 100 times > light microscope • reveals organelles • but can only be used on dead cells

  10. Transmission electron microscopes • TEM • used mainly to study internal structure of cells • aims an electron beam through thin section of specimen rabbit trachea cucumber seed leaf

  11. Scanning electron microscopes • SEM • studying surface structures • sample surface covered with thin film of gold • beam excites electrons on surface • great depth of field = an image that seems 3-D rabbit trachea

  12. SEM images grasshopper

  13. SEM images spider head

  14. Isolating organelles • Cell fractionation • separate organelles from cell • variable density of organelles • ultracentrifuge What organelle would be heaviest? What organelle would be lightest?

  15. Ultracentrifuge • spins up to 130,000 rpm • forces > 1 million X gravity (1,000,000g) Why is it in a BIG thick lead-lined housing?

  16. Microcentrifuge • Biotechnology research • study cells at protein & genetic level

  17. Tour of the Cell BIOLOGY 114

  18. Cell characteristics • All cells: • surrounded by a plasma membrane • have cytosol • semi-fluid substance within the membrane • cytoplasm = cytosol + organelles • contain chromosomes which have genes in the form of DNA • have ribosomes • tiny “organelles” that make proteins using instructions contained in genes

  19. Prokaryotic cell DNA in nucleoid region, without a membrane separating it from rest of cell Eukaryotic cell chromosomes in nucleus, membrane-enclosed organelle Types of cells • Prokaryotic vs. eukaryotic cells • Location of chromosomes

  20. Prokaryote Eukaryote Cell types internal membranes “Let’s go to the video tape!” (play movie here)

  21. “Let’s go to the video tape!” (play movie here) The prokaryotic cell is much simpler in structure, lacking a nucleus and the other membrane-enclosed organelles of the eukaryotic cell.

  22. Eukaryotic cells • Eukaryotic cells are more complex than prokaryotic cells • within cytoplasm is a variety of membrane-bounded organelles • specialized structures in form & function • Eukaryotic cells are generally bigger than prokaryotic cells

  23. “Let’s go to the video tape!” (play movie here)

  24. Limits to cell size • Lower limit • smallest bacteria, mycoplasmas • 0.1 to 1.0 micron (µm = micrometer) • most bacteria • 1-10 microns • Upper limit • eukaryotic cells • 10-100 microns • micron = micrometer = 1/1,000,000 meter • diameter of human hair = ~20 microns

  25. What limits cell size? • Surface to volume ratio • as cell gets bigger its volume increases faster than its surface area • smaller objects have greaterratio of surface area to volume What cell organelle governs this? Why is a huge single-cellcreature not possible? 6:1 ~1:1 6:1 s:v

  26. Limits to cell size • Metabolic requirements set upper limit • in large cell, cannot move material in & out of cell fast enough to support life aa aa What process is this? CH NH3 aa CHO O2 CH CHO CO2 CHO CO2 CO2 aa NH3 O2 NH3 O2 NH3 CHO aa CO2 CH aa CH O2 aa O2 What’s the solution?

  27. How to get bigger? • Become multi-cellular (cell divides) But what challenges do you have to solve now? CO2 CO2 O2 NH3 aa NH3 aa CO2 NH3 O2 CO2 CO2 CH CHO CO2 NH3 aa O2 NH3 NH3 CO2 CO2 CO2 CHO aa NH3 NH3 NH3 CH CHO CO2 CO2 O2 aa aa CH

  28. Cell membrane • Exchange organelle • plasma membrane functions as selective barrier • allows passage of O2, nutrients & wastes

  29. Organelles & Internal membranes • Eukaryotic cell • internal membranes • partition cell into compartments • create different local environments • compartmentalize functions • membranes for different compartments are specialized for their function • different structures for specific functions • unique combination of lipids & proteins

  30. Any Questions?? BIOLOGY 114

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