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Lecture 9

Lecture 9 - Vesicular Transport - Feb 5.docx

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Department
Biology
Course
BIOL 2021
Professor
Patricia Lakin- Thomas
Semester
Winter

Description
Lecture 9: February 5th, 2013 Chapter 13: Vesicular Transport  Figure 13-37  Lysosomes: o Marker: acid phosphatase o Function: Digestion of macromolecules by hydrolytic enzymes (acid hydrolyses)  Require acid pH  V-type ATPases o Creates protein gradient and acidifies the contents  Transport proteins used to carry digestion products away to the cytosol  Figure 13-36  How does the low pH of lysosomes protect the rest of the cell from lysosomal enzymes in case the lysosome breaks? o Lysosomal enzymes are acid hydrolyses with optimal pH of 5.0 and therefore will be inactive at pH 7 in the cytosol  Figure 13-39  Plant and fungal vacuoles are a kind of lysosome o Used for storage o Ex. Proteins in peas and bean seeds, flower pigment, garlic flavor--> all stored in vacuoles that are like lysosomes o Degradation o Important for maintaining osmotic pressure and size regulation (plant will take water into is vacuole and expand to grow)  Formation of Lysosomes: o Digestive enzymes delivered from Golgi to endosomes o Figure 13-42a o 1) Starts out as endosome from endocytosis pathway (piece of plasma membrane wraps around something the cell wants to digest)  Early endosome receives enzymes from golgi and thus becomes a lysosome  Or 2) Phagocytosis= cell eating o Phagosome then fuses with endosome or lysosome-->becomes lysosome  Or 3) Autophagy: self eating o Used to degrade old cell components or faulty components o Autophagosome fuses with lysosome-->lysosome o Figure 13-42a  Lysosomes have a marker- Mannose-6-phosphate: M6P o Recognized by M6P receptor  Trans golgi faces OUTWARDS , cis Golgi faces nucleus  Figure 13-43  Figure 13-44  1. N-linked oligosaccharide added in ER  2. Transported in golgi  3. Enzymes in golgi recognize the signal patch in the protein  4. Mannose phosphorylated in Golgi  5. M6P receptor in trans-golgi binds to M6P and adaptor proteins  6. Clathrin coated vesicles bind then immediately fall off --- coat lost  7. Vesicles fuse with endosomes and deliver the hydrolytic enzyme to endosome  8. M6P released from receptor at low pH (endosome)  Reason receptor can pick up at one place and let go of it at endosome= pH gradient  9. M6P dephosphorylated  10. Receptors recycled back to trans-Golgi Endocytosis  Taking up large particles from exterior of cell o End up in lysosomes for digestion  2 kinds: o phagocytosis= cell eating o Pinocytosis= cell drinking  Phagocytosis: o Ingesting microorganisms or dead cells (sometimes cells die on purpose for their neighbors to eat them) o Protozoa use this as a means for eating o Animal cells: only occurs in specialized cells  Scavenging dead cells, or defend against invaders  Cells of the immune system: macrophages, neutrophils  Figure 13-47 o This process requires a trigger  Receptors on phagocyte bind on particle to be eaten  Activates signals inside the cell  Cause actin polymerization (will push pseudopods outwards and form hyaline cap)  Pinocytosis: o
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