Download Chapter 7. Intracellular Sorting and the maintenance of cellular

Teaching plan of Cell Biology
Chapter 7. Intracellular Sorting and the
maintenance of cellular compartments
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
Lesson plans
roll number：_______7________
Course Title
Medical Cell
Biology
Major
clinic
Class
Teacher
Xiamixinuer.Yilike
Plan hours
8hours
Professional
level
Professional
Title
Biology Professor
The time of
writing
Name of the
Lecture
Chapter 7. Intracellular Sorting and the
maintenance of cellular compartments
Using time
undergraduate
course
Teaching Purposes: To learn the structural and functional relationship between
the ER, Golgi complexes, lysosomes and plasma membranes of eukaryotic cells.
Teaching
Purposes
and
Requiremen
t
Teaching Requirements:
1. Mastering: definition of endomembrane system; ultrastructure and functions of
Endoplasmic Reticulum and Golgi complex; signal hypothesis; formation process
of lysosomes.
2. Comprehending: structural form, types and chemical composition of the
lysosome; Palade Model.
3. Understanding: morphology and chemical composition of Endoplasmic
R ti l
dG l i
l
lt t t l f
df
ti
f th
Important points ：Types ultrastructure and function of endoplasmic
Important reticulum.ultrastructure Golgi complexes.Types ultrastructure and function of of
and Difficult lysosomes
Difficult points:：signal hypothesis,transport protein sorting of Golgi complex
points
；The formation of the lysosomes by Golgi complex .
Update
teaching
content
Teaching
methods
and
organization
al
arrangemen
Teaching
tools
Textbook
and
reference
books
collective
preparation
of
instruction
Opinion of
thedepartm
ent
Add animation to demonstrate the signal hypothesis and sorting and transporting
protein by Golgi complex.2 new cases increased.
Teaching methods ：Multimedia lectures given . Heuristic teaching methods will
be used.
Organizational arrangements ：Endoplasmic Reticulum 4 hours,Golgi
complex 2hours,Lysosomes and peroxisome 2 hours,
multiedia will be used.
Text book ：Cell Biology , China Medical University（6th edition）
Reference ：1.Essential Cell Biology.Bruce Albert’s；2.Cell and Molecular
Biology，Gerald Karp；3. Molecular Biology Disc；4. Lysosomes in biology and
pathology J. T. Dingle5.The cytoskeleton: an introductory survey/ Q28/C74,M.
Schliwa;6.Essentials of cell biology/2d ed. Q28/C71=2,Dyson, Robert D. Allyn
Mainly Teaching the definition of endomembrane system; ultrastructure and
functions of Endoplasmic Reticulum and Golgi complex; signal hypothesis;
formation process of lysosomes.Simple teach the reliationship these organelles
between clinical diseases.
Agreed to prepared the lessons content. Give attention to use appopirate
teaching
methods
.
signature of the dean：
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
Review:
1. Describe ultrastructure of Mt detailed.
2. Describe briefly the functions of Mt.
3. Describe the main opinions briefly about Mitchell’s Chemiosmotic theory.
4. Membrane –bounded organelles include which organelles in the eukaryotic cell?
Teaching Purposes: To learn the structural and functional relationship between the
ER, Golgi complexes, lysosomes and plasma membranes of eukaryotic cells.
Learning objective:
1. Mastering: definition of endomembrane system; ultrastructure and functions of
Endoplasmic Reticulum and Golgi complex; signal hypothesis; formation
process of lysosomes.
2. Comprehending: structural form, types and chemical composition of the
lysosome; Palade Model.
3. Understanding: morphology and chemical composition of Endoplasmic
Reticulum and Golgi complex; ultrastructural form and function of the
peroxisome.
Textbook
<Cell Biology> Abridgen by department of Cell Biology China Medical
University,sixth edition,2000.
Reference
(1) Arberts, B. et al. Molecular Biology of the Cell, Garland Publishing, Inc.
2002, 2004, 2008.
(2) Arberts, B. et al. Essential Cell Biology, An Introduction to the Molecular
Biology of the cell, Garland Publishing, Inc. 1997, 2004.
(3) Karp, G. Cell and Molecular Biology--Concepts and Experiments, John &
Whley Sons, Inc. 2002, 2005, 2007.
(4) Lodish H. et al. Molecular Cell Biology, W.H.Freeman, Inc. 1999, 2007.
(5) Becker W.M. The World of the Cell, The Benjamin/Cummings Publishing
Company. 2000 .
(6) Kleinsmith L.J and Kish V.M. Principles of Cell and Molecular Biology,
Harper Collins College Publishers. 1995.
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
Teaching Outline
1, the morphology, chemical component and types of ER.
2, the ultra structure and functions of RER.
4, Signal Hypothesis.
5, the glycosilation of RER.
6, the ultrastructure and function of SER.
7, the morphology, chemical component and functions of Golgi complex.
8, the morphology, types and functions of lysosome.
9, the morphology, chemical component, ultra structure and functions of peroxisome.
attention： master point※※※；comprehending point※※；understand※
Human cell (eukaryotic cell) has a nucleus and many other organelles with
specialized functions. As you know under electronic microscope we can see
developed membrane bounded organelles. Membrane-bound structures (organelles)
are found in all eukaryotic cells, such as plasma membrane, the nucleus, peroxisome,
the endoplasmic reticulum, the Golgi apparatus, lysosome. all kinds of vesicles，
Non-membrane-bound organelles: chromatin, nucleolus, ribosome, cell skeleton,
cytoplasm, nuclear sap.
Now we learn one group of membrane bound organelles in the cytoplasm called
<The Endomembrane System >. Now let us define it.
1§The Endomembrane System※※※:
A system of membranes through which materials are sequestered from the cytoplasm
and transported throughout the cell. Include endoplasmic reticulum, Golgi apparatus,
lysosomes, vacuoles, and vesicles.
The membrane connected to nuclear envelope & extends throughout cell accounts for
50% membranes.
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
Let us see an example.
Relative volumes occupied by the major intracellular compartments in Liver Cell
Intracellular compartment
% of total cell volume
Cytosol
54
Mittchondria
22
Rough ER cisternae
9
Smooth ER cisternae plus Golgi cisternae
6
Nucleus
6
Peroxisome
1
Lysosomes
1
Endosomes
1
A. The Dynamic Nature of the Endomembrane System※: Most organelles are
part of a dynamic system in which vesicles
move between compartments. The dynamic
activities of endomembrane systems are
highly conserved despite the structural
diversity of different cell types.
Biosynthetic pathways move proteins,
carbohydrates and lipids within the cell.
Secretory pathways discharge proteins from
cells. Endocytic pathways move materials into cells. Sorting signals are recognized by
receptors and target proteins to specific sites.
B. The Chemical Component of Endomembrane System※: Protein and Lipid are
the main chemical components of it. ER includes more than 30 types of enzymes,
among them glucose-6-phosphate （G-6-Pase）is the symbolic enzyme of it.
C.The Functions of Endomembrane System※: Assembly of polypeptides on
ribosome; Modification of polypeptides into functions proteins; Transportation of
proteins out of the cell; Also involved in assembly and
transportation of lipids; Manufactures membranes &
performs, many bio-synthesis functions;
detoxifications etc. Now we began to study them
detailed.
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
1. Endoplasmic Reticulum: Endoplasmic means within the “plasm”, Reticulum
means network.
Types of ER: Divide into Rough Endoplasmic Reticulum (RER) and Smooth
Endoplasmic Reticulum (SER).
Microsomes are heterogeneous mixtures of similar-sized vesicles, formed from
membranes of the ER and Golgi complex.
Morphology o ER※※※:
Includes flattened sacs, network of tubular and globular.
Among them RER has ribosome on the cytosolic side of
continuous, flattened sacs (cisternae) studded with ribosome;
SER is an interconnecting network of tubular and globular
membrane elements.
- Proteins made on RER ribosomes are
segregated away from the cytoplasm and can be
chemically modified Membranes of the RER are
continuous with the nuclear membrane(In
pancreatic cell, all is RER)
Functions of the RER※※※:
(1) Protein Synthesis. Proteins synthesized on
ribosome of RER and include secretary proteins,
integral membrane proteins and soluble proteins
of organelles.
Ribosomes divide into free ribosome and membrane
bounded ribosomes. Structural protein synthesis on
free ribosomes while secreted protein synthesis on
attached ribosomes and have three ways to go. As
picture shows below right side.
The Biology Department of Xinjiang Medical University
Road map of protein sorting in cytosol
Teaching plan of Cell Biology
(2)Modification, folding and processing of newly synthesized
proteins:Glycosylation. A Glycosylation type in the RER is N-linked glycosylation.
N-linked glycosylation: Oligosaccharide side chains linked to the amide nitrogen of
asparagine –NH2 group in a protein(Asp-X-Ser or Asp-x-Thr) are said to be Nlinked oligosaccharide, common on glycoprotein. This occurs in RER, but futher
modification hold on in Gol.
(3)Quality control of newly synthesized proteins. ensuring that misfolded proteins do
not leave ER.Assembly coated proteins on the vesicles (Clathrin, COPII and COPI);
Only Properly folded and assembled proteins are allowed secreted out even
sometimes wrong protein secreted then catch it back and after corrected secreted
again ; The orientation of transported proteins is not changed during transporting.
(4) Protein sorting within the cell: Protein sorting: Protein molecules move from the
cytosol to their target organelles or cell surface directed by the sorting signals in the
proteins. (see the table below).
It is
belongs to vesicular transport (see below left side picture). The process of vesicular
transport includes budding, transporting, docking and at last fusion with target
membrane. Assembly coated proteins on the vesicles (Clathrin, COPII and COPI);
Proteins are imported into organelles by three mechanisms※:
(1)Gated Transport: Transport through nuclear pores; (2)
Transmembrane transport: ER, Mit, Chl, Per ;(3)Vesicular transport:
ER-Golgi-PM-Lys, Endosome
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
Only Properly folded and assembled proteins; The orientation of transported proteins
and lipids is not changed during transporting.
Now let us study Proteins synthesized on ribosome of RER.
Signal Hypothesis: - Discovered by G.Blobel &Sabatini, in 1971. Explain the
process how the free ribosome becomes membrane-bound ribosome.It is a model for
the signal mechanism of cotranslational export of a secretory protein on a membranebound ribosome of the RER, also is the evidence that protein synthesized on
ribosomes attached to ER membranes pass directly into the ER Lumen.
Signal hypothesis refer: signal peptide, signal-recognition particle (SRP) and SRP
receptor.
Signal-recognition particle, SRP: Six different polypeptides complexed with a 300nucleotide (7S) molecule of RNA.
ER signal sequence: Typically 15-30 amino acids: Consist
of three domains: a positively charged N-terminal region, a
central hydrophobic region, and a polar region adjoining the site where cleavage from
the mature protein will take place. A signal sequence on nascent seretory proteins
targets them to the ER and is then cleaved off.
SRP has three main active sites: One that recognizes and binds to ER signal
sequence; one that interacts with the ribosome to block further translation; the other
that binds to the ER membrane (docking protein).The whole processes of Signal
Hypothesis
(1)Once the ER signal sequence emerges from the ribosome, it is bound by a signalrecognition particle (SRP) and causes a pause in translation (as shown below picture).
(2)The SRP delivers the ribosome/nascent
polypeptide complex to the SRP receptor in
the ER membrane (as shown picture).
(3) Transfer of the ribosome/nascent
polypeptide to the translocon (protein
translocator) leads to opening of this
translocation channel and insertion of the signal sequence and adjacent segment of the
growing polypeptide into the central pore.
(4)Both the SRP and SRP receptor once
dissociated from the translocon and then are
ready to initiate the insertion of another
polypeptide chain(see picture left).
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
(5)Translation start again.
(6)As the polypeptide chain elongates, it passes through the translocon channel into
the ER lumen, where the signal sequence is cleaved by signal peptidase and is rapidly
degraded.
(7)The peptide chain continues to elongate as
the mRNA is translated toward the 3’ end.
(8)Once translation is complete, the ribosome
is released, the remainder of the protein is
drawn into the ER lumen, the translocon closes,
and the protein assumes its native folded
conformation. See the complete process at
below picture
2. Smooth Endoplasmic Reticulum (SER)
Structure※※※
- Smooth appearance is due to the
absence of ribosomes (In muscle cell,
all are SER)
Functions of the SER※※※:
1. Lipid metabolism:Factory processing operations many metabolic processes
synthesis & hydrolysis enzymes of smooth ER…synthesize lipids, oils, phospholipids,
steroids & sex hormones . Most membrane lipids are synthesized entirely within the
SER,so it is a membrane factory: Synthesize membrane Phospholipids build new
membrane as ER membrane expands, bud off & transfer to other parts of cell that
need membranes synthesize membrane proteins membrane bound proteins
synthesized directly into membrane processing to make glycoprotein.There are two
exceptions:sphingomyelin and glycolipids, (begins in ER; completed in Golgi) and
some of the unique lipids of the Mit and Chl membranes (themself).The membranes
of different organelles have markedly different lipids composition.They transport by
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
budding：ER→GC、Ly、PM and transport by phospholipid exchange
proteins(PEP)：ER→other organelles（including Mit and Chl）
2.Detoxification :hydrolysis (breakdown) of glycogen (in liver) into glucose detoxify
drugs & poisons (in liver) w ex. alcohol 3.Muscle contraction;4.Sequestration of
Ca2+.
Golgi Apparatus (complex): Golgi apparatus is a flattened
membranous sacs called cisternae , it has 2 sides with 2
functions.cis: receives material by fusing with vesicles
“receiving” trans buds off vesicles that travel to other sites
“shipping” (transport)(see the picture). It
finishes, sorts, & ships cell products:“receiving
shipping department” center of manufacturing,
warehousing, sorting &shipping extensive in
cells specialized for secretion
Golgi processing: During path from cis to trans,
products from ER are modified into final form tags, sorts, & packages materials into
transport vesicles Golgi = “UPS headquarters” Transport vesicles = “UPS trucks”
delivering packages that have been tagged with
their own barcodes. Two views about the transport
from one cisterna to the next: cisternal maturation
model and vesicular transport model.
The Golgi networks are
processing and sorting stations
where proteins are modified,
segregated and then shipped in
different directions.
The structure of Golgi
apparatus※:
Cisterna of Golgi apparatus
divides into Cis, medial, Tran’s
three parts.
Cis Golgi network (CGN) named Cis face while Trans Golgi network (TGN) called
Trans face shortly.
Golgi complex plays a key role in the assembly of the carbohydrate component of
glycoproteins and glycolipids.
The Functions of Golgi complex※※※:
The Biology Department of Xinjiang Medical University
&
Teaching plan of Cell Biology
(1)Glycosylation. O-linked oligosaccharide takes place in Golgi complex.
(2)Protein sorting (3) Cell secretion: Cell’s secretion involve in: RER, Golgi
complex, secretory vesicle and plasma membrane.
Two pathways for cell’s secretion: constitutive secretory pathway and regulated
secretory pathway.(see picture below)
(4) Biogenesis of Lysosomes.
Lysosomes: Lysosomes discovery in 1960s by Christian de Duve, He received Nobel
Prize in 1974 for this important discovery. lyso– means breaking things apart –some
means body, it is also the “clean up crew” of the cell.
Lysosome is a heterogenous organelle: divide into primary lysosome and second
lysosomes (heterophagic, autophagic); Residual body
Structure※※: Membrane-bounded sac of hydrolytic enzymes that digests
macromolecules. Enzymes & membrane of lysosomes are synthesized by rough ER &
transferred to the Golgi complex for modification then budding off into cytosol to
form lysosome.
Lysosomal enzymes: Lysosomal enzymes work best at pH 5 it means lysosomes
contain plenty acid hydrolases that can digest every kind of biological molecule---the
principal sites of intracellular digestion. Marker enzyme of lysosome: acid
phosphatase.Organelle how creates custom pH? proteins in lysosomal membrane
pump H+ ions from the cytosol into lysosome .enzymes are very sensitive to pH
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
Enzymes are proteins — pH affects structure. Digestive enzymes won’t function well
if leak into cytosol . don’t want to digest yourself!
Lysosome membrane:
(1)H+-pumps: internal proton concentration is kept high
by H+-ATPase
(2)Glycosylated proteins: may protect the lysosome from
self-digestion.
(3)Transport proteins: transporting digested
materials.
The mannose 6-phosphate (M6P) pathway,
the major route for targeting lysosomal
enzymes to lysosomes:
(1)Precursors of lysosomal enzymes migrate
from the rER to the cis-Golgi where mannose residues
are phosphorylated.
(2)In the TGN, the phosphorylated enzymes bind to
M6P receptors, which direct the enzymes into vesicles
coated with the clathrin.
(3)The clathrin lattice surrounding these vesicles is
rapidly depolymerized to its subunits, and the uncoated
transport vesicles fuse with late endosomes.
(4)Within this low-pH compartment, the phosphorylated
enzymes dissociate from the M6P receptors and then are
dephosphorylated.
(5)The receptors recycle back to the Golgi.
(6)The enzymes are incorporated into a different transport vesicle that buds from the
Function※※※: Lysosome is it is a little “stomach” for the cell. Cellular
digestion:Lysosomes fuse with food vacuoles polymers
are digested into monomers pass to cytosol to become
nutrients of cell. see picture.
The Recycler: Where old proteins go to die!
Fuse with organelles or macromolecules in cytosol to
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
recycle materials
Lysosomes are involved in three major cell functions:
① phagocytosis; ② autophagy; ③ endocytosis.
Lysosome take part in the process of fertilization: acrosome is a special lysosome.
What if a lysomome digestive enzyme doesn’t function? When things go wrong don’t
digest a biomolecule instead biomolecule collects in lysosomes lysosomes fill up
with undigested material lysosomes grow larger &larger eventually disrupt cell &
organ function.
Autolysis: A break or leak in the membrane of lys releases digestive enzymes into the
cell which damages the surrounding tissues (Silicosis)
Lysosomal storage diseases※ are due to the absence of one or more lysosomal
enzymes, and resulting in accumulation of material in lysosomes
as large inclusions. are usually fatal
Tay-Sachs disease※: lipids build up in brain cells hild dies
before age 5 Sometimes it supposed to work that way…
Apoptosis = cell death:u critical role in programmed destruction
of cells in multicellular organisms auto-destruct mechanism
“cell suicide” some cells have to die in an organized fashion,
especially during development w ex: development of space
between your fingers during embryonic development if cell
grows improperly this self-destruct mechanism is triggered
to remove damaged cell n cancer over-rides this to enable
tumorgrowth Fetal development
Palade Model ※※: Membrane flow among ER, Golgi
complex, vesicle, endosome, lysosome and plasma
membrane.
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
Peroxisomes
Structure※: belongs to a microsomal body, is other digestive enzyme sac in both
animals & plants, one membrane bound organelle. Mostly round or oval with
diameter range is 200～1700nm. Only exist in kidney and liver cells of the body. It
has more than 40 types of enzymes.The paraxrystalline electron-dense
inclusions (crystalloid core) （nucleoid）exist in peroxisome are the
enzyme urate oxidase. It can distinguish the peroxisome from
lysosome. But human and birds have no the enzymes.
The function of peroxisomes※:
(1)Detoxify various toxic molecules. All half of the ethanol we drink is oxidized to
acetaldehyde in this way.
(2)Convert excess H2O2 accumulates in the cell to water.
Reaction steps:
oxidases
RH2+O2
R+H2O2
urate oxidase
2H2O2
2H2O +O2
Vacuoles & vesicles※
Function: a little “transfer ships”, its types include:
a. Food vacuoles: phagocytosis, fuse with lysosomes ;
b. Contractile vacuoles in freshwater protists, pump excess H2Oout of cell;
c. Central vacuoles: in many mature plant cells
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
Another division types:
A.clathrin-coated vesicle; B.COPI（coatmer-protein subunits）; C.COPII
(A)
Summary of the chapter
a. Definition and members of the endomembrane system, membrane-bound
structures ,non-membrane-bound organelle and microsomes
b. Functions of RER and SER
c. Proteins types which synthesized on ribosomes of RER
d. Signal hypothesis
The Biology Department of Xinjiang Medical University
Teaching plan of Cell Biology
e. N-linked and O-linked glycosalation
f. The structure and functions of Golgi complex
g. Marker enzyme of lysosome
h. Functions of lysosome
i. Palade modelThe function of peroxisomesTypes of vesicle transport and their
functions
Home work:
a. Define the endomembrane system and It include which organelles?
b. Describe briefly the functions of RER and SER.
c.
Describe the main contents of Signal hypothesis
d. Describe Palade model detailed.
Any Questions??
Reference of Major Journals
Cell
Nature
Science
EMBO
Annual Review of Cell Biology
Trends in Cell Biology
Cell Research
Biology Website
http://www.ebiotrade.com/
http://www.bioon.com/
http://www.bbioo.com/
http://bbs.bioon.com/bbs/index.php
http://www.dxy.cn/
http://bbs.biooo.com/
NCBI-American http://www.ncbi.nlm.nih.gov
The Biology Department of Xinjiang Medical University