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BIO 105

BIO 105. The Cell. Overview of Cell Structure. All organisms are comprised of cells. Many different types of cells but all have similar features: A plasma membrane surrounds each cell. Central portion of cell contains its genetic material. Cytoplasm fills the rest of a cell’s interior.

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BIO 105

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  1. BIO 105 The Cell

  2. Overview of Cell Structure • All organisms are comprised of cells. • Many different types of cells but all have similar features: • A plasma membrane surrounds each cell. • Central portion of cell contains its genetic material. • Cytoplasm fills the rest of a cell’s interior.

  3. Size of Cells • The smallest is about 1 m (1 x 10-6M) • The largest is about 100m (1 x 10-4M)

  4. The Smallest Human Cell

  5. The Largest Human Cell

  6. Why Are Cells So Small? • Bigger the better????….not really • Surface area = 4r2 • Volume = 4/3r3 • As radius increases, surface area increases in a squared function. • As radius increases, volume increases in a cubed function. • Therefore, volume increases much more rapidly than surface area. • Small cell size keeps surface-to-volume ratio high.

  7. SA to V Ratio

  8. Why Are Cells So Small? • Better communication within the cell • Adequate communication between cell and environment

  9. History of the Cell Theory • Until the 1600’s we didn’t have any idea what comprised organisms • Invention of the microscope led to the discovery of the cell. • Robert Hooke, 1665, observed cork bark • Comprised of small compartments • Called them cellulae – small rooms • Coined the term cell

  10. History of the Cell Theory • Antonie van Leeuwenhoek – first person to see living cells….drop of pond water. • Mathias Schleiden, 1838, -- “all plants are comprised of cells” • Theodor Schwann, 1839, -- “all animals are comprised of cells”

  11. The Cell Theory • All organisms are comprised of one or more cells. • Metabolism and heredity occur within these cells. • The cell is the smallest living thing. • Cells arise only by division of a previously existing cell.

  12. The Most Simple Cells • Bacteria are the simplest cells and organisms. • About 2500 species • Has a plasma membrane • Has a central located region of hereditary material called the nucleoid • DNA is double-stranded and circular • Cell filled with cytoplasm

  13. Bacterium

  14. Structure of Bacteria • Come in many shapes COME IN SEVERAL SHAPES RODS COCCI SPHERICAL

  15. Strong Cell Wall • Most bacteria are surrounded by a cell wall • Located outside of plasma membrane • Comprised of carbohydrate matrix (sugars) linked by short proteins • Provides external strength (support) for the cell • Bacteria can also be classified according to their type of cell wall

  16. 2 Types of Cell Wall • Hans Christian Gram invented a stain for the bacterial cell wall – the Gram stain • Gram-positive bacteria – single thick wall that retains stain….appear purple. • Gram-negative bacteria – wall is thinner and does not retain stain

  17. Simple Internal Organization • Lacks compartmentalization • Biochemical pools and reactions are not separated from each other. • No nucleus

  18. Prokaryotes • Cells that lack a nucleus -- bacteria no compartments

  19. Eukaryotes • Cells that possess a nucleus – not bacteria

  20. Rotating Flagella • Some bacteria possess flagella

  21. Rotating Flagella • Used in locomotion and feeding • Bacteria can move 20 cell diameters/sec.

  22. Eukaryotic Cells: An Overview • Complex in structure vs. prokaryotes • Hallmark is compartmentalization • Cytoplasm contains membrane-bound organelles • Biochemical pools and reactions are separated into compartments (organelles) • Have a nucleus – membrane-bound organelle containing DNA • Internal support -- cytoskeleton

  23. Cell Review • Eukaryotic cells possess: • Plasma membrane – next lecture • Cytoplasm – liquid within the cell • Organelles – reside in the cytoplasm

  24. Organelles • Nucleus • Largest and most easily observable organelle within the cell • Usually located in the central part of the cell • Supported in place by proteins of the cytoskeleton which are also attached to the plasma membrane • Repository of all of the cell’s genetic (hereditary) information

  25. 1. Nucleus (cont.) • Most cells possess a single nucleus • Fungi and skeletal muscle cells are multi-nucleated • Mature red blood cells (rbc or erythrocytes) do not possess a nucleus

  26. The Nucleus • nuclear envelope • DNA • nucleolus

  27. A. Nuclear Envelope • Surface of nucleus bounded by 2 membranes – inner and outer • Both membranes form the nuclear envelope • Nuclear envelope has nuclear pores where inner and outer membranes fuse to form “holes” • Pores are 50-80 nm (50-80 x 10-9M) in diameter.

  28. A. Nuclear Envelope (cont.)

  29. A. Nuclear Envelope (cont.) nuclear pores regulate what gets into and out of nucleus

  30. B. DNA • Unlike prokaryotes, DNA is wound into structures called chromosomes just before the cell divides

  31. B. DNA • When the cell prepares to divide, the long strands of DNA coils around organizing proteins called histones. • Histones organize the DNA into chromosomes.

  32. Histones and DNA

  33. Nucleosome • A nucleosome consists of the following 3 components: • A region of DNA • A central histone • A spacer histone

  34. C. Nucleolus

  35. C. Nucleolus • Function is to produce ribosomal RNA • YIKES – What is ribosomal RNA? • There are 3 types of RNA. • Ribosomal RNA (rRNA) • Messenger RNA (mRNA) • Transfer RNA (tRNA)

  36. 2. Ribosomes • Organelle that synthesizes proteins • Consists of two subunits large & small

  37. Composition of Ribosomes • One of the most complex molecular structures in a cell • Found in prokaryotic and eukaryotic cells • Both subunits comprised of: • rRNA • proteins • Subunits are larger in eukaryotic cells than prokaryotic cells • mRNA and tRNA associate with ribosomes to synthesize proteins within the cell. • Can be “free” or attached to membranes

  38. 3. Endoplasmic Reticulum (ER) • Membrane-bound tunnels within the cytoplasm • Membranes similar to plasma membrane • Two types of ER A. Rough ER (rER) B. Smooth ER (sER) • Names based on microscopic appearance

  39. Two Types of ER

  40. A. rER • ER that has ribosomes attached to outside of membrane • Ribosomes synthesize proteins therefore--- • rER is associated with protein synthesis • Proteins are inserted into the tunnels of the ER

  41. rER and Protein Synthesis • Ribosomes attached to outside of rER insert synthesized proteins into the tunnels of the ER

  42. B. sER • ER without ribosomes • Functions: • Synthesis of lipids • Synthesis of carbohydrates • Detoxification of drugs

  43. Structure and Function • The structure of a cell can often allow you to guess its function. • Cell that has lots of rER is probably a muscle cell • Cell that has lots of sER is probably making lipids….testes and ovaries…. making lots of testosterone and estrogen.

  44. 4. Golgi Apparatus • The delivery system of the cell • Especially abundant in cells that synthesize and secrete substances • Collects, modifies, packages and distributes proteins and lipids within the cell • Consists of membrane-bound pancake-like structures….flattened

  45. Golgi Glycosylation – addition of sugars to proteins and lipids – a mailing address within the cell

  46. Golgi (Overview)

  47. Golgi • Accepts products from ER (protein, CHO and lipids) via transport vesicles

  48. Transport Vesicles • Products of ER pinched off into membrane bound transport vesicles ER

  49. Transport Vesicles • Membrane bound transport vesicles fuse with membranes of Golgi

  50. Golgi • Products get modified within the Golgi and passed on to outer stacks of membranes

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