Transcript Lecture 4 - Harford Community College

Chapter 3
How Cells Are Put
Together
The Plasma Membrane
• “Sheet” of molecules that encases all living cells
• Fluid mosaic model
– A model for the plasma membrane
– The PM is composed of proteins, lipids and
carbohydrates all of which are embedded in the
phosholipid bilayer and may be exposed to the cell
exterior/interior
– The PM is fluid; lipids that make up the plasma
membrane can move laterally
Phospholipid
Phospholipid Bilayer
Proteins Embedded in Lipid Bilayer
Fig. 4.7
Nonpolar
regions of
the lipid
bilayer lock
proteins into
membranes
Eukaryotic Cell
Plant Cell
The Nucleus
• Spherical structure ensheathed in the
nuclear envelope (a double-layered
membrane)
• Fx = Command center of the cell!!
– 1. Directs protein synthesis
– 2. Directs cell reproduction
– 3. Stores genetic information (DNA)
– 4. Site where DNA is converted to RNA
Nuclear Envelope
• Membrane that surrounds the nucleus
• Contains “openings” through which RNA
(once it’s converted from DNA) exits
The Nucleus
Animal
Plant
The Endomembrane System
• Route through which material is passed
within the cell
• Main components include:
– Nuclear envelope
– Endoplasmic Reticulum
– Golgi Complex
– Vesicles
– Cell membrane
Endoplasmic Reticulum
• An extensive system of internal membranes
that form channels and interconnections; also
vesicles
• ER surface: cell makes proteins to be exported
here
• 2 types:
Rough ER
Smooth ER
•Heavily studded with ribosomes
•Fx = sites of protein synthesis
•RNA is converted to a
polypeptide chain
•Surface ribosomes are
scarce
•Rather, surface is embedded
w/ enzymes that aid in
manufacturing carbs and
lipids
Animal
Plant
Endoplasmic Reticulum
Golgi Complex
• Sacs of flattened vesicles (“pancake-like”)
• Receives polypeptide chain from ER
where it is modified (i.e. carb addition) and
packaged into secretory vesicles
• Fx = packages protein for export from the
cell
Animal
Plant
Golgi Complex
Lysosomes
• Spherical organelles that arise from Golgi
• Contain digestive enzymes that break
down macromolecules
• “Recycling centers” of the cell: they digest
intracellular matter
The Endomembrane System
Fig. 4.15
Additional Organelles
• Mitochondria
• Chloroplasts
Mitochondria
• Rod-shaped organelles that derived from a bacterium
that invaded a host cell
• The powerhouse of the cell!
• Only organelle other than the nucleus to house DNA
– Mitochondrial DNA (mtDNA) has unique genes in their DNA that
are lacking in nuclear DNA
• Place where oxidative phosphorylation occurs
– Energy (ATP) is extracted from food through a series of chemical
reactions
• Two-membrane structure:
– Outer
– Inner: forms folds (cristae) which encompass the matrix
Mitochondria
Animal
Plant
Chloroplast
•
•
•
•
Unique to plants
Organelle in which photosynthesis occurs
Plant cells can contain one to several hundred
Two-membrane structure (outer and inner
membranes)
• Larger size than mitochondria and more
complex inner membrane organization
– Thylakoids: fused inner membranes that form stacks
in which photosynthesis occurs
Chloroplast
Plant
The Cytoskeleton
• Dense fiber structure
• Fx:
1. Provide support to cellular structure
2. Anchors organelles to fixed locations
• Composed of dynamic protein fibers that are embedded
to membrane proteins embedded in the PM
– Microfilaments
– Microtubules
– Intermediate Filaments
Cytoskeletal Proteins
The Cytoskeleton, continued
Microfilaments
• Fine, thread-like protein fibers
• Composed of the contractile
protein actin, the most
abundant cellular protein!!!
• Prevent excessive stretching of
cells
• Form and dissolve readily ≡
major role in determining cell
shape
• Roles in cellular movement
include gliding and contraction
(when in combination with
myosin)
http://www.biology.arizona.edu/cell_bio/tutorials/cytoskeleton/page1.html
The Cytoskeleton, continued
Microtubules
• Composed of tubulin protein
• Assembled by centrioles
– Located near the nuclear
envelope in the cytoplasm at
right angles to each other
• “Conveyor belts” of the cell
• They move vesicles and
organelles (i.e. mitochondria) as
well as chromosomes
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Microtubule.gif
Centrioles
The Cytoskeleton, continued
Intermediate Filaments
•
•
•
•
Filamentous fibers
‘Intermediate’ in size
Ubiquitous throughout the body
Bundles of IFs are found in
characteristic ‘plaques’ that form
in AD in brain
• Includes keratin
http://www.cytoskeleton.com/aif.htm
Fig. 4.23
Central
Vacuole
Plant
Central Vacuole
• Storage center
• Contains large amounts of water, ions,
sugars and pigments
• Increases surface-to-volume ratio outside
the vacuole
– Applies pressure to plasma membrane
– Plasma membrane expands → ↑ surface area
• ↑ surface area → MORE EFFICIENCY!!
Is there anything outside the
plasma membrane??
Cell Wall
Plants
Cell Wall
•
•
•
•
•
Present in plants and fungi – NOT ANIMAL CELLS
Composed of cellulose (polysaccharide)
Primary walls are laid while plant is growing
Individual cells are held together by the middle lamella
Secondary walls are present in some plants
– Inside the Primary walls of fully expanded, grown cells
•
•
Located OUTSIDE the plasma membrane
Fx: maintain cell shape
protection
prevents excessive water uptake
Fig. 4.25
Extracellular
Matrix
Animal cell
Extracellular Matrix
• Present in ANIMAL cells
• Mixture of glycoproteins, collagen, elastin, proteoglycans
• Fx: serves as a protective layer for the cell
helps coordinate cell behavior
• Attached to the plasma membrane by fibronectin
– Glycoprotein
– Bind to integrins in the plasma membrane
Everyday Science
• Forensic Science uses mitochondrial DNA testing
• mtDNA is maternally inherited
• Why use mtDNA vs. nuclear DNA?
– mtDNA is more abundant – in every mitochondria in
the cell
– nuclear DNA may degrade more easily as there is
only one copy
•
What is the drawback of mtDNA testing?
• Relatives from the same mother can’t be excluded