4 - cell i
TRANSCRIPT
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The Cell and Cell Functions I
Chapter 3
http://www.cnas.missouristate.edu/labimages/Biology/Bio122/week8.htm
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About how many cells are in the human body (approx) ?
1. 1 million
2. 10 million
3. 100 million
4. 1 billion
5. 10 billion
6. 100 billion
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Outline for Today
I. Introduction
II. Major RegionsA. Plasma Membrane
1. Structure
2. Functions of membrane components
3. Structural modifications for adhesion/communication
4. Extensions of the plasma membrane
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Introduction
Fig. 3.5
Lateral S
urface
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Introduction
• Three basic regions
• Plasma Membrane• Cytoplasm
– Organelles in watery fluid
• Nucleus
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Representative Animal Cell
Limiting border:separates cell from
extracellular materialNucleus
CytoplasmPlasma membrane
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Introduction
• “Edges of the Cell” Apical Edge
Lateral Edge
Basal Edge(rests on anothercell or the basement membrane)
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http://www.funhousefilms.com/sciencpg.htm
Plasma (Cell) Membranes
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Plasma Membrane Composition
• Phospholipids• Proteins• Cholesterol
Fig. 3.6
Plasma membrane comp
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Proteinsintegral to bilayer
Proteins
peripheral to bilayer
water
water
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Phospholipids
• Phospholipid bilayer• Hydrophobic region is
inside; hydrophilic region faces the extracellular fluid and the intracellular fluid– Therefore the
hydrophobic tails are sandwiched between the hydrophilic heads
• Some of these have sugars associated with them– Form the glycocalyx
Fig. 3.7
Plasma membrane structure
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Plasma Membrane Structure Cholesterol
• Stiffens the membrane, making it less fluid – Up to a point
• Integrates with the lipid portion of the phospholipid– A lot in the typical cell
membrane Fig. 3.6
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Proteins
• Transmembrane (integral) proteins go all the way through the membrane– Most are glycoproteins
• Peripheral proteins– At least partially
embedded in the membrane
– Usually associated with transmembrane proteins
Fig. 3.7
Plasma membrane structure
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Functions of Membrane Proteins
1. Determines permeability
2. Transport across bilayer
3. Identification
4. Reception
5. Enzymatic Activity
6. Adhesion
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Glycocalyx
• The outer component of a cell surface,
• usually contains strongly acidic sugars
• it carries a negative electric charge.
• Unique in everyone
Plasma membrane structure
Fig. 3.10a
www.answers.com
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Adhesion
• Cells need to stick to each other along the lateral border and the basal border (to basement membrane)
• Specialized structures– Tight junctions– Desmosomes– Gap junctions
Plasma Membranes Adhesion
Fig. 5.28
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Tight Junctions
• On the lateral surface• Want the cell fixed in
place• Tight binding between
integral proteins of one cell and another
• Space between the cells is stitched together so the space is occluded
• Compartmentalizes the space so nothing can pass between the apical and basal regions
• E.g. digestive tract
Plasma Membranes Adhesion
Fig. 5.28
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Desmosomes
• Cell to cell (desmosome) or cell to matrix/basement membrane (hemidesmosome)
• Usually deep to tight junctions
• Button like area formed by thickening of membrane
• Sugar chains of glycoproteins hold cells together
• “spot welds”• e.g. in cardiac muscle and
skin
Plasma Membranes Adhesion
Fig. 5.28
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Gap Junctions
• Function in communication– Sometimes called
communicating junctions
• Proteins in each cell align to form a pore– Direct cytoplasmic
communication results
• Only small stuff goes through– Monosaccharides and ions
• e.g. : heart
Plasma Membranes Adhesion
Fig. 5.28
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Plasma Membrane: Extensions of the cell membrane
• Not all cells have them
• Epithelial cells have the most because they have a free edge
• Cilia, microvilli, and flagella
Fig. 3.10a
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Extensions of the Plasma Membrane
i. Microvilli – “small fingers”
in epithelial cells on the free edge (apical border)
surface area of the membrane
High number in absorptive cells
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Microvilli
• “little finger”• Increase surface area
by 15x to 40 x• Best in cells designed
for absorption– Kidney– Small intestines
• Anchored with actin
Fig. 3.10a
Extensions of cell membrane
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Cilia• Hairlike structures 7-
10 µm long• Motile examples
include– In the inner ear for
balance– Trachea and Uterine
(Fallopian) tube have motile cilia• 50-200 on one cell
Fig. 3.11
Extensions of cell membrane
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Cilia
Fig. 3.12
Movement is unidirectional
Extensions of cell membrane
Saline layer
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Cilia
Photo: T. Chubb
Extensions of cell membrane
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Flagella
• Structure is same as cilia but the flagellum is longer
• Only flagellum in humans in tail of sperm cell
Photo: T. Chubb
Extensions of cell membrane
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We shall return
• We will return to the cell membrane when we talk about permeability and transport
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=656