Transcript Biol 178 Lecture 10

Bio 178 Lecture 10
Cell Structure (Cntd.)
Copyright: E.G. Platzer
Reading
•
Chapters 5 & 6
Quiz Material
•
Questions on P 104 & 124
•
Chapters 5 & 6 Quiz on Text Website
(www.mhhe.com/raven7)
Outline
• Eukaryotic Cells (Cntd):
1. Cell Movement
2. Extracellular matrix
3. Specialized Plant Cell Features
•
Biological Membranes
Myosin and Actin Video
Alberts et al.: Molecular Biology of the Cell, 16.8
Cell Movement
Involves actin filaments and microtubules.
Crawling
Mechanism
• Actin polymerizes to form protrusions that attach to
substratum & pull cytoplasm forward.
• Involves myosin motors.
http://www.bio.umass.edu/vidali/web/cell_motil/sept_26_long.htm
Cell Crawling (Cntd.)
Functions
• Embryo formation
• Immune system
• Cancer
Cell Movement
Mouse
Fibroblasts
Mouse
Melanoma
Chick
Fibroblasts
Fish
Epidermis
http://cellix.imolbio.oeaw.ac.at/Videotour/video_tour_2.html
Video: 15-3, Alberts: Molecular Biology of the Cell. Also at:
http://www.biochemweb.org/fenteany/research/cell_migration/neutrophil.html
Cell Movement (Cntd.)
Swimming
Mechanism
• Cilia - Short projections that beat with a whip-like
motion, eg. Vertebrate respiratory tract, Paramecium.
• Flagella - Longer than cilia. Undulating motion, eg.
Sperm.
Structure
• Microtubules in 9 + 2 arrangement.
• Use dynein for motion.
• Anchored by a basal body.
Cilia and Flagella
http://ic.ucsc.edu/~wx
cheng/envs161/Lectur
e8/
http://www.tmd.ac.jp/artsci/biol/textbo
ok/cellmove.htm
http://www.vetanatomists.org/LIBRARY/tn
mrepro3.htm
Structure of the ECM of Animals
Extracellular Matrix (ECM)
Description
• Acellular part of a tissue.
• Composed mainly of fibrous proteins and glycoproteins
in animals.
Attachment to Cell
• Integrins (transmembrane proteins) anchor
intracellularly to the cytoskeleton and extracellularly to
fibronectin.
• Fibronectin connects to the ECM.
ECM (Cntd.)
Functions
• Scaffold for tissue stabilization
• Regulation of cell behavior (eg. migration, development,
survival, proliferation, shape, function)
Examples
Cartilage, bone, cornea…
Extracellular Matrix Tissue Repair
ECM: Recruits cells for tissue remodeling without scarring.
http://www.vanaqua.org/aquanew/archive.php?show=month&mont
h=October&year=2004
Specialized Structures of Plant Cells
Vacuoles
Structure
Membrane bound compartment that contains water,
organic compounds, inorganic ions, and pigments.
Functions
Many, including storage, increased cell surface area, and
growth.
Plant Cell Vacuole
Plant Cell Walls
Specialized Structures of Plant Cells
Cell Wall
Structure
• Cellulose
• Primary cell walls produced first, followed by middle
lamella between the cells.
• Secondary cell walls laid down on the cellular side of the
primary cell wall in some plant cells.
The Fluid Mosaic model
Davson-Danielli Model (1935)
“Phospholipid bilayer sandwiched between 2 globular
protein layers”.
But…membrane proteins were known to have large hydrophobic
regions…
Singer and Nicholson (1972)
“The proteins span the membrane with the polar regions
on the outside and the non-polar regions on the inside”.
The Fluid Mosaic Model
The Fluid Mosaic Model
Description
• Membrane is a mosaic of protein and lipid.
• Membrane is fluid - proteins and lipids move within it.
Fundamental Components of All Cell Membranes
• Lipid:
Mainly phospholipid and cholesterol.
• Protein
• Carbohydrate
Effect of Cholesterol on Membrane Fluidity
High Temperatures
Reduces membrane fluidity by interfering with
phospholipid mobility.
Low Temperatures
Increases membrane fluidity by preventing fatty acid tail
interactions.
Membrane Proteins
Functions
• Transportation
• Enzymes
• Receptors
• Recognition
• Adhesion
• Anchoring
Functions of Membrane Proteins
Membrane Proteins
2 types of membrane protein:
Peripheral
• Do not extend through the membrane
• Attached via non-covalent interactions with anchoring
molecules. Easily removed.
Integral
• Protein held tightly in membrane. Can only be removed
by disrupting the bilayer.
• Includes transmembrane proteins and proteins anchored
in the bilayer by lipid groups.
Transmembrane Proteins
Transmembrane Proteins
1. Single-Pass Transmembrane Proteins
Protein passes through membrane once - one non-polar
region.
2. Multiple-Pass Transmembrane Proteins
Protein passes through membrane several times using 
helices  Channel
Example
• Bacteriorhodopsin - 7 pass protein  Channel for
protons to pass during photosynthesis.