Transcript Nerve activates contraction

CHAPTER 7
A TOUR OF THE CELL
The Cell
Theory
• The basic unit of life
• Cells come from cells
Microscopes provide windows to
the world of the cell
• 17th century – cells observed through microscope
(CYTOLOGY)
Microscopy: History
Simple
Compound
Microscopy: History
Microscopy: History
Goals of Microscopy
Produce a magnified image of
the specimen (Magnification)
Separate the details in the
image (Resolving Power)
Render the details visible to
the human eye or camera.
Magnification
• Magnification - ratio of an object’s image to its
real size
Onion – 40X
Onion – 1000X
Resolving power
Resolving power is a
measure of image clarity.
–It is the minimum
distance two points can be
separated and still viewed
as two separate points.
– It is determined by the
wavelength of light
used
0.2mm
0.1nm
Enhancing Light Microscope Images
• Electron
microscope (EM)
-focuses a beam
of electrons
through the
specimen or onto
its surface
• Can study only
DEAD CELLS!
• Transmission electron microscopes (TEM)
are used mainly to study the internal
ultrastructure of cells (2D).
Fig. 7.2a (Rabbit Trachea)
• Scanning electron microscopes (SEM) are
useful for studying surface structures (3D).
Fig. 7.2b
Gravitational Biology Facility (GBF)
Cell biologists can isolate organelles
to study their functions
• Cell fractionation - separate the major organelles
of the cells so that their individual functions can
be studied.
Fig. 7.3
• Ultracentrifuge- a machine that can spin at up to
130,000 revolutions per minute and apply forces
more than 1 million times gravity (1,000,000 g).
1) Homogenization- disrupt the cell and release its
contents.
2) Spin homogenate in a centrifuge.
3) Heavier pieces will separate into the pellet while
lighter particles remain in the supernatant.
4) Repeat at higher speeds and longer durationssmaller and smaller organelles can be collected in
subsequent pellets.
Prokaryotic and Eukaryotic cells
All cells have:
• Plasma membrane.
• Cytoplasm
• Chromosomes
• Genes, DNA
• Ribosomes, (make proteins using the instructions
contained in genes)
The prokaryotic cell
The Eukaryotic cell
Prokaryotes
•
•
•
•
No nucleus, ‘naked’ DNA
No membrane bound organelles
Cell wall has peptidoglycan
Smaller in size (1-10um)
Eukaryotes
• Nucleus bound by a
membrane
• Membrane Bound Organelles
• No peptidolycan in cell wall
of plants
• Upto 10 times larger (10100um)
• More complex
Similarities:
-Both have Ribosomes
-Are both covered by plasma membrane!
-Both have DNA
-DNA-> mRNA -> Protein (universal genetic code)
Fig. 7.7
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 7.8
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The plasma membrane functions as a selective
barrier that allows passage of oxygen, nutrients,
and wastes
• Made up of phospholipids and proteins
Nucleus (5 microns)
Contains most of the
genes
Nuclear Membrane
(double) covers it
Pores in Nuclear
Membrane (why?)
Nucleolus – rRNA is
sythesized here
Chromatin is inside
nucleus (DNA+protein)
Chromosomes (46)
Nucleus
Function: Stores genes
(DNA)
Makes mRNA and other
types of RNA
Ribosomes
Made up of rRNA and Protein
 Located ‘free’ in cytoplasm or in association with ER/ nuclear
membrane (‘bound’)
Function – Protein synthesis ‘benches’
Proteins made on Free ribosomes – these proteins stay in cytoplasm
Proteins made on Bound ribosomes – proteins are located in the
Plasma Membrane or exported out of the cell
Endomembrane System
Nuclear Envelope
 Endoplasmic Reticulum
Golgi apparatus (or body)
Lysosomes
Vacoules
Plasma Membrane
Endoplasmic Reticulum
What cell has a lot of RER?
 Made
of sacs - cisternae
-Cells involved in synthesis of enzymes for digestion ex: pancreas
cellSmooth
has a lot ER
of SER?
2What
types:
and Rough
ER-Cells involved in detoxification - in a alcoholic!
-Cells making steroid hormones!
 Smooth ER functions: Lipid
synthesis, glucose metabolism,
detoxification of drugs (alcohol),
muscle contraction
Rough ER functions: Proteins fold
in cisternae, some proteins are
modified; plasma membrane
proteins and phospholipids are
synthesized
Transport Vesicles
 Pinch off from the ER
and contain the
macromolecules being
transported to the Golgi
apparatus
Golgi Apparatus
 Made of sacs – cisternae; cis side- receiving, trans side –
news vesicles bud off
Functions: Tags (attaches chemical groups), sorts, and
packages macromolecules (warehouse)
Lysosomes
 membrane-bounded sac of
hydrolytic enzymes that digests
macromolecules; low pH (5) inside
lysosome protects the cell - how?
Functions:
Phagocytosis-In Amoeba –
digestion of food vacoules
Autophagy - recycling of cells own
macromolecules (suicide bags)
Destroy bacteria, viruses – in WBC
Vacuoles
 Vesicles and vacuoles (larger
versions) are membrane-bound
sacs with different functions.
Food vacuoles, fuse with
lysosomes during phagocytosis
Contractile vacuoles, pump excess
water out of the cell (amoeba)
Central vacuoles are found in
many mature plant cells – stores
water, salts, proteins, defensive
compounds, pigments, metabolic
byproducts
Mitochondria and chloroplasts are
What cell has a lot of Mitochondria?
the
main
transformers
of cells
-Cells
needing aenergy
lot of ATP - heart
muscle cell (for pumping),
and
liver cell (synthesis)
Chloroplast
• Found only in
photosynthetic organisms
(plants, some primitive
eukaryotes)
• Site for photosynthesis
(makes glucose)
• Has its own DNA
• Has its own ribosomes
• Has a double outer
membrane
Mitochondria
• Found in plants and animals
• Converts macromolecules
into usable energy – ATP
(site for cellular respiration)
• Has its own DNA
• Has its own ribosomes
• Has a double outer
membrane
• Is semi-autonomous
Peroxisomes generate and degrade
H2O2
– Peroxisome has catalase that converts H2O2 to water;
detoxify alcohol and other harmful compounds
Cytoskeleton
• Network of fibers
extending throughout the
cytoplasm
• Provides mechanical
support and maintains
shape
• Provides anchorage for
many organelles and
enzymes
• Is dynamic - dismantling
in one part and
reassembling in another to
Movement of
organelles
Movement of
cilia, flagella,
muscles
• 3 main types of fibers in the cytoskeleton:
Microtubules, Microfilaments, and
Intermediate filaments.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
1) Microtubules – made of tubulin (protein)
• They grow or shrink as more tubulin molecules
are added or removed.
• Move chromosomes during cell division
• Guide organelles
• Are part of centrioles – (important to cell
division)
• Make up cilia and flagella
2) Microfilaments (Actin)
Fig. 7.26 The shape of the
microvilli in this intestinal cell
are supported by microfilaments,
anchored to a network of
intermediate filaments.
-Support
-Muscle contraction
-Amoeboid movement
-Cytoplasmic streaming
3) Intermediary filaments
- cell shape, organelle location
Plant cells are encased by cell walls
• Microfibrils of cellulose embedded in a matrix of
proteins and other polysaccharides.
Extracellular matrix (ECM) of
animal cells
COLLAGENglycoprotein
Intracellular junctions help
integrate cells
• Neighboring cells in tissues, organs, or organ
systems often adhere, interact, and communicate
through direct physical contact.
• Plant cells are perforated with plasmodesmata,
channels allowing cysotol to pass between cells.
• Animal Cells:
Fig. 7.30
A cell is a living unit greater than
the sum of its parts
– Macrophages use actin filaments to move and extend
pseudopodia, capturing their prey, bacteria.
– Food vacuoles are digested by lysosomes, a product
of the endomembrane system of ER and Golgi.
• The enzymes of the lysosomes and proteins of
the cytoskeleton are synthesized at the
ribosomes.
• The information for these proteins comes from
genetic messages sent by DNA in the nucleus.
• All of these processes require energy in the
form of ATP, most of which is supplied by the
mitochondria.
• A cell is a living unit greater
than the sum of its parts.
Fig. 7.31