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Cell Structure and Function

Cell Structure and Function. Chapter Outline. Cell theory Properties common to all cells Cell size and shape – why are cells so small? Prokaryotic cells Eukaryotic cells Organelles and structure in all eukaryotic cell Organelles in plant cells but not animal Cell junctions. Cell Theory.

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Cell Structure and Function

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  1. Cell Structure and Function

  2. Chapter Outline • Cell theory • Properties common to all cells • Cell size and shape – why are cells so small? • Prokaryotic cells • Eukaryotic cells • Organelles and structure in all eukaryotic cell • Organelles in plant cells but not animal • Cell junctions

  3. Cell Theory • All organisms consist of 1 or more cells. • Cell is the smallest unit of life. • All cells come from pre-existing cells.

  4. Observing Cells (4.1) • Light microscope • Can observe living cells in true color • Magnification of up to ~1000x • Resolution ~ 0.2 microns – 0.5 microns

  5. Observing Cells (4.1) • Electron Microscopes • Preparation kills the cells • Images are black and white – may be colorized • Magnification up to ~100,000 • Transmission electron microscope (TEM) • 2-D image • Scanning electron microscope (SEM) • 3-D image

  6. SEM TEM

  7. Cell Structure • All Cells have: • an outermost plasma membrane • genetic material in the form of DNA • cytoplasm with ribosomes

  8. Plasma Membrane • The outer plasma membrane • isolates cell contents • controls what gets in and out of the cell • receives signals • Membranes are phospholipidbilayers with embedded proteins

  9. All Cells have DNA • DNA is the genetic material for all cells. • In eukaryotes the DNA is linear and in the nucleus. • In prokaryotes the DNA is circular and not isolated in a nucleus.

  10. Cytoplasm with Ribosomes • The fluid portion of the cell is called the cytoplasm. • All cells have ribosomes in the cytoplasm. • The function of ribosomes is to make proteins

  11. Review Cell Structure • All Cells have: • an outermost plasma membrane • genetic material in the form of DNA • cytoplasm with ribosomes

  12. Why Are Cells So Small? (4.2) • As cell volume increases, so does the need for the transporting of nutrients in and wastes out. • Nutrients and wastes enter/exit the cell at the plasma membrane. • Cells need sufficient surface area to allow adequate transport of nutrients in and wastes out.

  13. Why Are Cells So Small? • However, as cell volume increases the surface area of the cell does not expand as quickly. • If the cell’s volume gets too large it cannot transport enough wastes out or nutrients in. • Thus, surface area limits cell volume/size.

  14. Why Are Cells So Small? • Cells have several strategies for increasing surface area and thus size: • Some have “frilly” edges • Others are long, narrow, and/or thin. • Plant cells have inner vacuoles to store nutrients and wastes. • Round cells will always be small.

  15. Prokaryotic Cell Structure (4.3) • Prokaryotic Cells are smaller and simpler in structure than eukaryotic cells. • Typical prokaryotic cell is ~ 0.5 -10 microns • Prokaryotic cells do NOT have: • Nucleus • Membrane bound organelles

  16. Prokaryotic Cell Structure • Structures • Plasma membrane • Cell wall • Cytoplasm with ribosomes • Nucleoid (and plasmid*) • Capsule* • Appendages • Flagella* • Pili* and fimbriae* *present in some, but not all prokaryotic cells

  17. Prokaryotic Cell

  18. Prokaryotic Cell TEM or SEM? PLASMA MEMBRANE

  19. Pili Vibriocholerae – single flagellum

  20. Eukaryotic Cells (4.4 – 4.16) • Structures in all eukaryotic cells • Nucleus • Ribosomes • Endomembrane System • Endoplasmic reticulum – smooth and rough • Golgi apparatus • Vesicles • Mitochondria • Cytoskeleton

  21. NUCLEUS CYTOSKELETON RIBOSOMES ROUGH ER MITOCHONDRION CYTOPLASM SMOOTH ER CENTRIOLES GOLGI BODY LYSOSOME PLASMA MEMBRANE VESICLE

  22. Nucleus (4.5) • Function – isolates the cell’s genetic material, DNA • DNA directs/controls the activities of the cell • DNA determines which types of RNA are made • The RNA leaves the nucleus and directs the synthesis of proteins in the cytoplasm at a ______________

  23. Structure of the Nucleus • The outer layer of the nucleus is called the nuclear envelope • The nuclear envelope is two Phospholipidbilayers with protein lined pores • Each pore is a ring of 8 proteins with an opening in the center of the ring

  24. Structure Nuclear Envelope Nuclear pore layer facing cytoplasm Nuclearenvelope Proteins Layer facing nucleoplasm The fluid of the nucleus is called the nucleoplasm.

  25. Nucleus • The nucleus protects the cell’s DNA • DNA is arranged in eukaryotic cells is arranged in linear chromosomes • Chromosome – fiber of DNA with proteins attached • Chromatin – all of the cell’s DNA and the associated proteins

  26. Nucleus • Nucleolus • Where ribosomal RNA (rRNA) and ribosomal subunits are made • rRNA made ion the nucleus joins with proteins to make the ribosomal subunits • Proteins are made in the cytoplasm and enter the nucleus through nuclear pores • Subunits exit the nucleus via nuclear pores • The nucleolus is visible under the light microscope.

  27. ADD THE LABELS

  28. Ribosomes • Function - Ribosomes use instructions from the nucleus to synthesize proteins. • Structure - Ribosomes are composed of rRNA and protein • Each ribosome has 2 subunits • They can be free floating in the cytoplasm or attached to the endoplasmic reticulum (RER) or the outside of the nuclear envelope

  29. Endomembrane System (4.7 – 4.9) • Series of organelles responsible for: • Modifying protein chains into their final form • Synthesizing of lipids • Packaging of fully modified proteins and lipids into vesicles for export or use in the cell • And more that we will not cover!

  30. Structures of theEndomembrane System • Endoplasmic Reticulum (ER) • Continuous with the outer membrane of the nuclear envelope • Two forms - Smooth (SER) and Rough (RER) • Transport vesicles • Golgi apparatus

  31. Endoplasmic Reticulum (ER) • The ER is continuous with the outer membrane of the nuclear envelope • There are 2 types of ER: • Rough ER – has ribosomes attached • Smooth ER – no ribosomes attached • Tubular in structure Turn to Page 60

  32. Rough Endoplasmic Reticulum RER - Network of flattened membrane sacs create a “maze” • Ribosomes attached to the outside of the RER and make it appear rough • Proteins are made in the cytoplasm and if they have the correct code (aa sequence) they enter the RER

  33. Rough Endoplasmic Reticulum • In the RER the proteins are modified as needed by enzymes, e.g. • Segments removed • Oligosaccharides attached • Multiple chains joined to form a 40 structure • Once modified, the proteins are packaged in transport vesicles for transport to the Golgi body Figure 4.8B

  34. Smooth Endoplasmic Reticulum • The SER is a tubular membrane structure • Continuous with RER • No ribosomes attached • Functions of the SER • Lipids are made inside the SER • fatty acids, phospholipids, sterols.. • Lipids are packaged in transport vesicles and sent to the Golgi • Detoxification of drugs brought in to the cell • Storage and secretion of Calcium ions

  35. Transport Vesicles • Transport Vesicles • Vesicle = small membrane bound sac • Transport modified proteins and lipids from the ER to the Golgi apparatus (and from Golgi to final destination)

  36. Golgi Apparatus • Golgi Apparatus /Body • Stack of flattened membrane sacs • The Golgi apparatus sorts, tags and packages fully processed proteins and lipids in vesicles Page 61

  37. Golgi Apparatus • In the Golgi molecular tags are added to the fully modified proteins and lipids • These tags allow the substances to be sorted and packaged appropriately. • Tags also indicate where the substance is to be shipped.

  38. Golgi Apparatus • Transport vesicles from the ER merge with the receiving side of the Golgi • Vesicle contents enter the Golgi • Substances pass through the layers of the Golgi by way of vesicles • Substances are modified, sorted, tagged and placed in vesicles for release at the shipping side of the Golgi

  39. Golgi Apparatus

  40. Endomembrane System • Putting it all together • DNA directs RNA synthesis  RNA exits nucleus through a nuclear pore  ribosome  protein is made  proteins with proper code enter RER  proteins are modified in RER and lipids are made in SER  vesicles containing the proteins and lipids bud off from the ER

  41. Endomembrane System • Putting it all together ER vesicles merge with Golgi body  proteins and lipids enter Golgi  each is fully modified as it passes through layers of Golgi  modified products are tagged, sorted and bud off in Golgi vesicles  …

  42. Endomembrane System • Putting it all together • Golgi vesicles either merge with the plasma membrane and release their contents OR remain in the cell and serve a purpose • Another animation

  43. Lysosomes (4.10) • The lysosome is an example of an organelle made at the Golgi apparatus. • Golgi packages digestive enzymes in a vesicle. The vesicle remains in the cell and: • Digests unwanted or damaged cell parts • Merges with food vacuoles and digest the contents • Figure 4.10A and B

  44. Lysosomes (4.11) • Tay-Sachs disease occurs when the lysosome is missing the enzyme needed to digest a lipid found in nerve cells. • As a result the lipid accumulates and nerve cells are damaged as the lysosome swells with undigested lipid.

  45. Peroxisomes • Peroxisome– not made at the Golgi • Where fatty acids are metabolized • Also play a role in detoxifying alcohol in liver cells • Reactions in the peroxisome make hydrogen peroxide (toxic) • Enzymes in the peroxisome catalyze the breakdown of hydrogen peroxide to water and oxygen (study this enzyme in lab)

  46. Mitochondria (4.13) • Function – synthesis of ATP • Structure: • ~1-5 microns • Two membranes • Outer membrane and highly folded inner membrane • Folds called cristae • Intermembrane space (or outer compartment) • Matrix – contains DNA and ribosomes

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