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2011 National Academies Northstar Institute for Undergraduate Education in Biology
Endocytosis: the Dynamic Nature
of the Endomembrane System
Notes to Instructors are italicized on slides
and in notes
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Context1 class session in Introductory Biology for majors
Taught in a large lecture hall
Pre-existing information (from previous lectures)
Cell parts (including cytoskeleton)
Membrane structure
Exocytosis
Reading before class:Textbook section on endocytosis
How Viruses HijackEndocyticMachinery
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Goal: Understand the role of endocytosis incell physiology
Outcomes Explain steps in endocytosis using the concepts of
molecular recognition and sorting
Explain the function of endocytosis in cell metabolism Predict how perturbations of endocytic processes
affects cells Explain how the endocytic process may be hijacked by
pathogens Analyze and interpret experimental data Connect graphical data with visual representations
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Assessments
Identify and order the steps of endocytosis Use concepts of molecular recognition and sorting to
explain specificity in the process Interpret data about how a perturbation affects
endocytosis and predict consequences for cells Given information about how a drug affects endocytosis,
analyze experimental data to determine how a pathogenenters a cell
Predict how drug treatment might prevent a pathogenfrom reaching the cytosol
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7/14/11
New material is presented in multiple waysincluding extensive use of animations.
Interactions include everyone in the class.
The unit incorporates a variety of learningactivities and student interactions.
Material incorporates diverse examples that willreach different audiences.
Diversity
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Class plan (single class session)
Before class: Students complete assigned reading
1. Think-pair-share activity (10 min)
Use a diagram to identify and order steps
in the endocytic pathway
2. Lecture (20 min)
Key concepts: molecular recognition and sorting
3. Data analysis and predictions (20 min)Brainstorming and clicker questions
Homework assignment
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How do cells eat?
Membrane transporters & channels
Endocytosis
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Pathogens use the endocytic pathway to get into cells
e.g.: flu virus
Salmonella ?
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Think-Pair-Share: Endocytosis
A) THINK INDIVIDUALLY (4 minutes)Read the terms on next slideChoose endocytosis termsDraw a labeled diagram using those terms
B) PAIR (2 minutes)Discuss your diagram with your neighborModify your diagram as needed
C) SHARE (2 minutes)We will use one stellar example in lectureModify your diagram as we discuss
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Choose appropriate terms andcreate your own labeled diagram
CargoClathrinCoated pit
Coated vesicleEndosomeERGolgi
LysosomeMitochondriaNaked vesiclePlasma membraneReceptor
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Lecture starts
Mini-lecture + student input to cover theconcepts on the next few slides and videos
Remind students to add to their diagram:
Phagocytosis, pinocytosis
differences and similarities
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Types of Endocytosis
1. Multiple pathways ofendocytosis
2. Molecular recognition between cell (receptor)
and cargo (internalized object)
Biology (2002) Campbell et al.
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Receptor-mediated Endocytosis
Animated Video: Key Points
1. Recognition of SPECIFIC cargo
2. Multiple steps + compartments
3. Consequences for cargo
http://www.youtube.com/watch?v=lNKKg6hIBcM
Molecular Biology of the Cell (2002) Alberts et al.
http://www.youtube.com/watch?v=lNKKg6hIBcMhttp://www.youtube.com/watch?v=lNKKg6hIBcMhttp://www.youtube.com/watch?v=lNKKg6hIBcM7/27/2019 Endocytosis, Midwest 2011
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Lecture continues
Coverstepsclathrin
acidification-2 steps
Concepts:Molecular recognition
Sorting
cargo-receptor
vesicle-vesicle
Why do we need this? Molecular Biology of the Cell (2002) Alberts et al.
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Phagocytosis
Animated Video: Key Points
1. Similarities to receptor-mediated endocytosis
Molecular recognition
Sorting
2. Differences
No clathrin
http://www.youtube.com/watch?v=7VQU28itVVw
Animation: McGraw-Hill
http://www.youtube.com/watch?v=7VQU28itVVwhttp://www.youtube.com/watch?v=7VQU28itVVw7/27/2019 Endocytosis, Midwest 2011
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Phagocytosis
Molecular recognition between cell and bacterium
Lysosomes fuse with phagosome:
Sorting: vesicles specific places
Molecular recognition: lysosomes phagosomes
What would happen if lysosomes fused withany (all) cellular membranes?
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Exercise:Assess understanding of endocytosis by interpretingreal data
A study used a drug that blocks endocytosis to determinehow viruses enter/infect cells.
Viruses:
Ebola virusVesicular stomatitis virus (VSV)Human Immunodeficiency Virus (HIV)
Drug: Chlorpromazine (Drug C)
Adapted from: Bhattacharyya et al (2010)
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Drug C: effect on normal cell endocytosis
Images show clathrin localization inside cells.
nucleus
nucleus
Clathrin coated
pits or vesicles
Clathrin clumps
C
Adapted from: Bhattacharyya et al (2010)
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Brainstorm in pairs (2 min):
What steps of endocytosis might be affected by Drug C?
Drug C: effect on normal cell endocytosis
nucleus
nucleus
Clathrin coated
pits or vesicles
Clathrin clumps
C
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Drug C
Clathrin clumps= non-functional
?
?
Adapted from Genes & Dev. 1998. 12: 3663-3674
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%o
fcellsi
nfected
Drug C
Ebola
Drug C: effect on viral entry into cells
Test cells received Drug C + virus. Untreated cells received only virus. Control cells received no virus. 3 viruses: Ebola, VSV and HIV.
Infection is when virus reached cytosol
Adapted from: Bhattacharyya et al (2010)
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%o
fcellsi
nfected
Drug C
Ebola
Drug C: effect on viral entry into cells
Test cells received Drug C + virus. Untreated cells received only virus. Control cells received no virus. 3 viruses: Ebola, VSV and HIV.
Infection is when virus reached cytosol
Clicker Q1 (1 min): Whichvirus(es) enter the cell byclathrin-mediated endocytosis?
A. Ebola onlyB. VSV onlyC. HIV only
D. VSV and HIV
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%o
fcellsinfected
Drug C
Ebola
Drug C: effect on viral entry into cells
Test cells received Drug C + virus. Untreated cells received only virus. Control cells received no virus. 3 viruses: Ebola, VSV and HIV.
Infection is when virus reached cytosol
Clicker Q2 (1 min): Whichvirus(es) require receptors to
enter the cell?
A. Ebola onlyB. VSV onlyC. HIV onlyD. Not enough information
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Clicker Q3 (1 min.): Bafilomycin blocks endosomeacidification. Which cell diagram represents whereEbola will be located after treatment with this drug?(Small spots = virus.)
A B C D
V C
VC
PREDICT THE OUTCOME
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Drug C
Clathrin clumps= non-functional
BafilomycinBlocks endosome
acidification?
?
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Q1: What is the most likely method by which VSVgenters the cell?A. Clathrin-mediated endocytosisB. phagocytosisC. pinocytosisD. not enough information
Q2: Justify your answer to Q1
Q3: Based on experiments with Chlorpromazine(discussed in class) and Bafilomycin, whatmethod do you think HIV uses to enter the cell?
Q4: What would happen to a normal cell treated
with Bafilomycin, i.e. what are the side effectsof this drug?
%o
fcellsinfected
Bafilomycin
This experiment is like the one in class, except
cells were treated with Bafilomycin, whichinhibits endosome acidification.
HomeworkBafilomycin: effect on viral entry into cells
Ebola
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