The ultrastructure and molecular organization (right)
of the cell membrane. The dark linesat left represent the two dense
layers observed in the electron microscope; these are caused by the
deposit of osmium in the hydrophilic portions of the phospholipid
molecules.
68 trang |
Chia sẻ: lylyngoc | Lượt xem: 1750 | Lượt tải: 0
Bạn đang xem trước 20 trang tài liệu Basic Cell Biology, để xem tài liệu hoàn chỉnh bạn click vào nút DOWNLOAD ở trên
Basic Cell Biology
I. Cytoplasm
A. Plasma membrane
B. Mitochondria
C. Ribosomes
D. Endoplasmic reticulum
1. Rough
2. Smooth
E. Golgi apparatus
F. Lysosomes
G. Cytoskeleton
II. Nucleus
A. Nuclear Envelope
B. Chromatin
C. Nucleolus
D. Nuclear matrix
III. Cell division
© 2002 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.
Asymmetrical arrangement of
phospholipids in plasma membrane
ATP-dependent phospholipid translocase
Molecular Cell Biology, Lodish et al., 4th edition.
Figure 2—1. The ultrastructure and molecular organization (right)
of the cell membrane. The dark lines at left represent the two dense
layers observed in the electron microscope; these are caused by the
deposit of osmium in the hydrophilic portions of the phospholipid
molecules.
© 2002 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.
Figure 11—14. Electron micrograph of a transverse section of a continuous capillary.
Note the nucleus (N) and the junctions between neighboring cells (arrowheads).
Numerous pinocytotic vesicles are evident (small arrows).
C. Ribosomes
Structure- 2 subunits, composed of 4 types of
RNA and 80 different proteins.
RNA is synthesized in the nucleolus
Protein is synthesized in the cytoplasm.
Characteristics
Ribosomes are very basophilic, stain with
hematoxylin , toluidine blue
Found in clusters called polyribosomes that are held
together by a strand of RNA.
mRNA
Ribosome
Polyribosomes
Ribosome function
Translation of mRNA into protein
Free polyribosomes- synthesize proteins
used in the cytoplasm
Polyribosomes attached to the ER- used
to synthesize
Secreted proteins
Integral membrane proteins
Lysosomal proteins
Three dimensional ribosome structure, L1 is a ribosomal protein
© 2002 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.
•Ribosome-two thirds RNA, one third protein
•Each ribosome has three binding sites for tRNA, and a binding site for mRNA
© 2002 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.
Endoplasmic Reticulum
Segregation of newly synthesized proteins
from the cytoplasm
Glycosylation of certain proteins
Lipid synthesis
RER structure
RER
Contains polyribosomes, very basophilic
Prominent in protein synthesizing cells
Functions
Synthesize proteins with the following destinations:
Storage in lysosomes
Storage in secretory granules
Use as integral proteins
SRP- 6 non-identical
proteins, 7 S RNA
© 2002 by Bruce Alberts, Alexander
Johnson, Julian Lewis, Martin Raff, Keith
Roberts, and Peter Walter.
Figure 2—19. The ultrastructure
of a cell that synthesizes (but
does not secrete) proteins on
free polyribosomes (A); a cell
that synthesizes, segregates, and
stores proteins in organelles (B);
a cell that synthesizes,
segregates, and directly exports
proteins (C); and a cell that
synthesizes, segregates, stores in
supranuclear granules, and
exports proteins (D).
SER
Structure
Lacks polyribosomes, hard to see at light
microscope level
Function
Detoxification (liver)
Steroid synthesis (gonad, adrenal)
Ca2+ reservoir in skeletal muscle
Golgi apparatus
Posttranslational processing including
glycosylation, phosphorylation, proteolysis
Packing and concentration of secretory
granules
Apical
Basal
Lysosomes
Membrane bound vesicles that contain
hydrolytic enzymes for digestion
Heterophagy
Digestion of extracellular material
Autophagy digestion of intracellular organelles
Review Table 2-3 for clinical correlations
Eg. Tay-Sachs disease- accumulation of glycolipid in
nerves
Figure 2—27. Current concepts of
the functions of lysosomes.
Synthesis occurs in the rough
endoplasmic reticulum (RER), and
the enzymes are packaged in the
Golgi complex. Note the
heterophagosomes, in which
bacteria are being destroyed, and
the autophagosomes, with RER
and mitochondria in the process of
digestion. Heterophagosomes and
autophagosomes are secondary
lysosomes. The result of their
digestion can be excreted, but
sometimes the secondary
lysosome creates a residual body,
containing remnants of undigested
molecules. In some cells, such as
osteoclasts, the lysosomal
enzymes are secreted to the
extracellular environment. Nu,
nucleolus.
Cytoskeleton
Microtubules
Microfilaments
Intermediate filaments
Function
Maintain cell shape
Cell movement (diapedesis)
Cytoplasm movement (ie. transport of secretory
granules)
Microtubules
Polymers of the protein tubulin
Intracellular movement
Form centrioles
9 microtubules triplets
Form cilia and flagella
9 microtubules pairs called axonemes surrounding
two central microtubules
Immotile cilia syndrome of Kartagener
Microfilaments
Eg. Actin, @ 6-8 nm thick
Most cells have actin to some extent
Intermediate filaments
Table 2-4
@ 10 nm diameter
Lamin, nuclear envelope protein
GFAP, glial fibrillary acidic protein, glial
cells (astrocytes)
10 nm
© 2002 by Bruce Alberts, Alexander
Johnson, Julian Lewis, Martin Raff, Keith
Roberts, and Peter Walter.
Nuclear envelope
Invisible with light microscope
Nuclear pores- areas of fusion between
two sheaths of nuclear envelope
< 10 nm pass freely through
Selective barrier between nuclear contents
and cytoplasm
RER
Nuclear
pore
Nuclear
envelope
Perinuclear space
Figure 3—5. Illustration to
show the structure, the
localization, and the
relationship of the nuclear
lamina with chromosomes.
The drawing also shows
that the nuclear pore
complex is made of 2
protein rings in an
octagonal organization.
From the cytoplasmic ring,
long filaments penetrate the
cytosol, and from the
intranuclear ring arise
filaments that constitute a
basketlike structure. The
presence of the central
cylindrical granule in the
nuclear pore is not
universally accepted.
Figure 3—6. Electron
micrographs of nuclei showing
their envelopes composed of 2
membranes and the nuclear pores
(arrows). The two upper pictures
are of transverse sections; the
bottom is of a tangential section.
Chromatin, frequently condensed
below the nuclear envelope, is
not usually seen in the pore
regions. x80,000.
Figure 3—7. Electron
micrograph obtained
by cryofracture of a
rat intestine cell,
showing the two
components of the
nuclear envelope and
the nuclear pores.
(Courtesy of P Pinto
da Silva.)
© 2002 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.
Nuclear lamina
Fibrous, between nuclear envelope and
chromatin
Composed of intermediate filaments-
lamins
Pulls nucleus back together during
telophase
© 2000 by Geoffrey M. Cooper
Phosphorylation of lamins causes dissolution
Chromatin
Heterochromatin- very e- dense,
basophilic
Euchromatin- very light staining
Can be used to determine cell activity
Light staining- active
Dark staining- not active
Figure 3—9. Schematic
representation of a nucleosome. This
structure consists of a core of 4
types of histones (2 copies of each)–
H2A, H2B, H3, and H4–and one
molecule of H1 or H5 located
outside the DNA filament.
Figure 3—10. The orders of
chromatin packing believed to
exist in the metaphase
chromosome. Starting at the top,
the 2-nm DNA double helix is
shown; next is the association of
DNA with histones to form
filaments of nucleosomes of 11 nm
and 30 nm. Through further
condensation, filaments with
diameters of 300 nm and 700 nm
are formed. Finally, the bottom
drawing shows a metaphase
chromosome, which exhibits the
maximum packing of DNA.
Nucleolus
Spherical, lots of RNA and protein
Very basophilic
Site of ribosome synthesis
Cell division (mitosis)
© 2002 by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter.
Figure 3—12. Human karyotype preparation made by means of a banding technique. Each
chromosome has a particular pattern of banding that facilitates its identification and also the
relationship of the banding pattern to genetic anomalies. The chromosomes are grouped in numbered
pairs according to their morphologic characteristics.
Figure 3—16.
Photomicrograph of cultured
cells to show cell division.
Picrosirius-hematoxylin stain.
Medium magnification. A:
Interphase nuclei. Note the
chromatin and nucleoli inside
each nucleus. B: Prophase.
No distinct nuclear envelope,
no nucleoli. Condensed
chromosomes. C: Metaphase.
The chromosomes are located
in a plate at the cell equator.
D: Late anaphase. The
chromosomes are located in
both cell poles, to distribute
the DNA equally between the
daughter cells.
Figure 3—18. Electron
micrograph of a section of a
rooster spermatocyte in
metaphase. The figure
shows the two centrioles in
each pole, the mitotic
spindle formed by
microtubules, and the
chromosomes in the
equatorial plane. The
arrows show the insertion of
microtubules in the
centromeres. Reduced from
x19,000. (Courtesy of R
McIntosh.)
Interphase
G1- RNA, protein synthesis
S- DNA synthesis
G2-cell growth, synthesis of tubulin,
energy substrates
Figure 3—21. The 4 phases of
the cell cycle. In G1 the cell
either continues the cycle or
enters a quiescent phase called
G0. From this phase, most
cells can return to the cycle,
but some stay in G0 for a long
time or even for their entire
lifetime. The checking or
restriction point (R) in G1
stops the cycle under
conditions unfavorable to the
cell. When the cell passes this
restriction point, it continues
the cycle through the synthetic
phase (S) and the G2 phase,
originating 2 daughter cells in
mitosis (M) except when
interrupted by another
restriction point (not shown)
in G2.
Figure 3—20. Phases of the cell cycle in bone tissue. The G1 phase (presynthesis)
varies in duration, which depends on many factors, including the rate of cell
division in the tissue. In bone tissue, G1 lasts 25 h. The S phase (DNA synthesis)
lasts about 8 h. The G2-plus-mitosis phase lasts 2.5—3 h. (The times indicated are
courtesy of RW Young.)