CELL STRUCTURES INVOLVED IN
MANUFACTURING AND BREAKDOWN
The Endomembrane System
This term refers to the organelles that are
connected
together
by
phospholipid
membranes.
Prokaryotes don’t have an endomembrane
system
The endomembrane system includes
the nuclear envelope, endoplasmic
reticulum (ER), Golgi apparatus,
lysosomes, vesicles, vacuoles, and the
plasma membrane
Transport system for moving molecules through interior of the
cell.
 Lipid bi-layer Composition with proteins attached to either side
or transversing them.
 Divides cell into organelles.
S E PA R AT E S L I V I N G C E L L F R O M N O N L I V I N G
SURROUNDINGS
o thin barrier = 8nm thick
 CONTROLS TRAFFIC IN & OUT OF THE CELL
o selectively permeable
o allows some substances to cross more easily than others hydrophobic
vs hydrophilic
M A D E O F P H O S P H O L I P I D S , P R O T E I N S & O T H E R
MACROMOLECULES



Fatty acid tails
o hydrophobic
Phosphate group head
o hydrophilic
Arranged as a bi layer
Phosphate
Fatty acid
Polar
hydrophilic
heads
Nonpolar
hydrophobic
tails
Polar
hydrophilic
heads
Membrane is a collage of proteins &
other molecules embedded in the fluid
matrix of the lipid bilayer
Glycoprotein
Extracellular fluid
Glycolipid
Phospholipids
Cholesterol
Peripheral
protein
Cytoplasm
Trans membrane
proteins
Filaments of
cytoskeleton

Fat composition affects flexibility
o membrane must be fluid & flexible
o % unsaturated fatty acids in phospholipids keep
membrane less viscous
o cold-adapted organisms, like winter wheat increase %
in autumn
o Cholesterol in membrane

Proteins determine membrane’s specific functions
 Peripheral
proteins
o loosely bound to surface of membrane
o cell surface identity marker (antigens)
 Integral
proteins
o penetrate lipid bi layer, usually across whole
membrane
o Trans membrane protein
o Transport proteins
oChannels, Permeases (pumps)
H+
Retinal
chromophore
NH2
Water Channels in Bacteria
Porin monomer
b-pleated sheets
Bacterial
outer
membrane
Nonpolar
(hydrophobic)
a-helices in the
cell membrane
COOH
H+
Cytoplasm
Proton pump channel in photosynthetic
acteria
Function through conformational change
Outside
Plasma
membrane
Inside
Transporter
Cell surface Identity
marker
Enzyme Activity
Cell surface
Receptor
Cell Adhesion
Attachment to
Cytoskeleton

Play a key role in cell-cell recognition
o important in organ & tissue development
o basis for rejection of foreign cells by
immune system
Getting through cell membrane

Passive Transport

Simple diffusion
 diffusion of non polar, hydrophobic molecules
 lipids
 high  low concentration gradient

Facilitated transport
 diffusion of polar, hydrophilic molecules
 through a protein channel
 high  low concentration gradient

Active transport

diffusion against concentration gradient
 low  high


uses a protein pump
requires ATP
ATP
Getting through cell membrane
ATP
Why an Endomembrane System?
•Membranes provide compartmentalization,
which allows different places in the cell to have
different environments.
•With this arrangement, the cell can “build” in
some areas, “break down” in others, and reserve
other areas for storage or other functions.
Let’s Follow a Protein…
From the start of its existence through a
few possible paths in the endomembrane
system.
Protein structure is determined in the cell’s DNA,
which is in the NUCLEUS.
The nucleus controls the cell’s activities and is
responsible for inheritance
–Inside is a complex of proteins and DNA called
chromatin, which makes up the cell’s chromosomes
–When it’s time to make a protein, the appropriate
DNA is read and converted into RNA (transctiption)
within the nucleus.
Once a chain of RNA gets made, it exits the nucleus via
pores in the nuclear envelope.
The nuclear envelope is a
double membrane with
pores that allow material to
flow in and out of the
nucleus
–It is attached to a
network of cellular
membranes called the
endoplasmic reticulum.
Two membranes of
nuclear envelope
Nucleus
Nucleolus
Chromatin
Pore
Endoplasmic
reticulum
Ribosomes
See where the pores are? See how the
nuclear envelope hooks up to the ER
like a big maze?
Ribosomes make proteins for use in the cell and
export
Ribosomes are involved in the cell’s protein
synthesis
–Ribosomes are synthesized in the
nucleolus, which is found in the nucleus
–Cells that must synthesize large
amounts of protein have a large
number of ribosomes
Can you name a few cells that
would have a lot of ribosomes?
Some ribosomes are free ;
others are bound
–Free ribosomes are
hanging out in the
cytoplasm
–Bound ribosomes are
attached to the
endoplasmic reticulum
(ER) which is connected
with the nuclear
envelope
Ribosomes are
NOT made of
membranes!
–They are made of
protein and RNA.
–They are
associated with
the endomembrane
system.
Cytoplasm
Ribosomes
ER
Endoplasmic reticulum
(ER)
Free
ribosomes
Bound
ribosomes
Large
subunit
TEM showing ER
and ribosomes
Diagram of
a ribosome
Diagram of
a ribosome
Small
subunit
Many cell organelles are connected through the
Endomembrane system
Some components of the endomembrane system
communicate with others via the formation and
transfer of small membrane “balloons” called
vesicles
–One important result of communication is the
synthesis, storage, and export of molecules
Proteins get created in The endoplasmic reticulum – A
biosynthetic factory
There are two kinds of endoplasmic reticulum
smooth and rough
Smooth ER has no attached ribosomes
Rough ER is “studded” with attached ribosomes
–They differ in structure and function, but they
are connected
Nuclear
envelope
Ribosomes
Smooth ER
Rough ER
The endoplasmic reticulum is a Bio-factory
Smooth ER is involved in a bunch of diverse metabolic processes
–For example, enzymes produced by the smooth ER are
involved in synthesizing lipids, oils, phospholipids, and
steroids.
ROUGH ER USES LIPIDS FROM THE SMOOTH ER TO BUILD MEMBRANES.
Rough ER makes additional membrane for itself
It also makes all proteins destined for secretion (export)
–Once proteins are synthesized, they are transported
in vesicles to other parts of the Endomembrane
system.
4
Transport vesicle
buds off
Ribosome making protein
3
Transport
vesicle
With secretory
Protein inside
Sugar chain added
to a protein
(glycosylation)
1
2 Glycoprotein
Polypeptide
Rough ER
Next Stop for our vesicle with protein
inside: THE GOLGI.
The Golgi apparatus finishes, sorts, and ships cell
products
The Golgi apparatus alongside the ER by
modifying products of the ER
–Products travel in transport vesicles from the
ER to the Golgi apparatus
–One side of the Golgi apparatus functions as a
receiving dock for the product and the other as
a shipping dock
–Products are modified as they go from one
side of the Golgi apparatus to the other.
–After going through the Golgi, the proteins
(or other stuff) is shipped out in a new set of
vesicles.
Golgi apparatus
“Receiving” side of
Golgi apparatus
Golgi
apparatus
Transport
vesicle
from ER
New vesicle
forming
“Shipping” side
of Golgi apparatus
Transport
vesicle from
the Golgi
Where are the Proteins going?
If the proteins are digestive enzymes, they may go
to LYSOSOMES.
A lysosome is a membranous sac containing digestive
enzymes
–The enzymes and membrane are produced by the ER
and transferred to the Golgi apparatus for processing
–The membrane serves to safely isolate these potent
enzymes from the rest of the cell
–If it weren’t there, the cell would digest itself.
Lysosomes are digestive compartments within
a cell
One of the several functions of lysosomes is
to remove or recycle damaged parts of a cell
–The damaged organelle is first enclosed
in a membrane vesicle
–Then a lysosome fuses with the vesicle,
dismantling its contents and breaking
down the damaged organelle
Digestive
enzymes
Lysosome
Plasma
membrane
Digestive
enzymes
Lysosome
Plasma
membrane
Food vacuole
Digestive
enzymes
Lysosome
Plasma
membrane
Food vacuole
Digestive
enzymes
Lysosome
Plasma
membrane
Digestion
Food vacuole
Lysosome
Vesicle containing
damaged mitochondrion
Lysosome
Vesicle containing
damaged mitochondrion
Lysosome
Digestion
Vesicle containing
damaged mitochondrion
Some proteins go to assist in the function of
VACUOLES, which do maintenance jobs in the cell
Vacuoles are membranous sacs that are
found in a variety of cells and possess an
assortment of functions
–Examples: central vacuole in plants with
hydrolytic (water-breaking) functions,
–pigment vacuoles in plants to provide
color to flowers, and
–contractile vacuoles in some protists to
expel water from the cell
Nucleus
Contractile
vacuoles
Chloroplast
Nucleus
Nucleus
Nuclear
membrane
Rough ER
Transport
vesicle
Smooth
ER
Transport
vesicle
Golgi
apparatus
Lysosome
Vacuole
Plasma
membrane
Proteins can be exported out of the cell by
EXOCYTOSIS
A cell uses two mechanisms for moving large
molecules across membranes
–Exocytosis is used to export bulky molecules,
such as proteins or polysaccharides
–Endocytosis is used to import substances useful
to the livelihood of the cell
In both cases, material to be transported is packaged
within a vesicle that fuses with the plasma
membrane
Exocytosis and endocytosis transport large
molecules across membranes
There are three kinds of endocytosis
–Phagocytosis is engulfment of a particle by
wrapping cell membrane around it, forming a
vacuole
–Pinocytosis is the same thing except that
fluids are taken into small vesicles
–Receptor-mediated endocytosis is where
receptors in a receptor-coated pit interact with
a specific protein, initiating formation of a
vesicle
Phagocytosis
Phagocytosis
EXTRACELLULAR
FLUID
CYTOPLASM
Pseudopodium
“Food” or
other particle
Food
vacuole
Food
being
ingested
Pinocytosis
Pinocytosis
Plasma
membrane
Vesicle
Plasma membrane
Receptor-mediated endocytosis
Plasma membrane
Coat protein
Receptors
Coated
vesicle
Coated
pit
Coated
pit
Specific
molecule
Material bound
to receptor proteins
Coated
pit