1. CYTOLOGY & HISTOLOGY Lecture Four
DR. ASHRAF SAID

2. Review
Of the third lecture

3. Concept 3
The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes

4. Start
Of this lecture

5. Objectives of lecture three
The Endoplasmic Reticulum: Biosynthetic Factory
Lysosomes: Digestive Compartments

6. The endomembrane system
Concept 4
The endomembrane system regulates protein traffic and performs metabolic functions in the cell
The endomembrane system
Includes many different structures

7. The Endoplasmic Reticulum: Biosynthetic Factory
The endoplasmic reticulum (ER)
Accounts for more than half the total membrane in many eukaryotic cells

8. The ER membrane Is continuous with the nuclear envelope Figure 1.12
Smooth ER
Rough ER
ER lumen
Cisternae
Ribosomes
Transport vesicle
Transitional ER
200 µm
Nuclear
envelope
Figure 1.12

9. There are two distinct regions of ER
The ER membrane
There are two distinct regions of ER
Smooth ER, which lacks ribosomes
Rough ER, which contains ribosomes

10. Functions of ER The rough ER The smooth ER Rough Smooth
Has bound ribosomes
Produces proteins and membranes, which are distributed by transport vesicles
The smooth ER
Synthesizes lipids
Metabolizes carbohydrates
Stores calcium
Detoxifies poison

11. The Golgi Apparatus: Shipping and Receiving Center
Receives many of the transport vesicles produced in the rough ER
Consists of flattened membranous sacs called cisternae

12. Functions of the Golgi apparatus include
Modification of the products of the rough ER
Manufacture of certain macromolecules

13. Functions of the Golgi apparatus
cis face
(“receiving” side of
Golgi apparatus)
Vesicles move
from ER to Golgi
Vesicles also
transport certain
proteins back to ER
Vesicles coalesce to
form new cis Golgi cisternae
Cisternal
maturation:
Golgi cisternae
move in a cis-
to-trans
direction
Vesicles form and
leave Golgi, carrying
specific proteins to
other locations or to
the plasma mem-
brane for secretion
Vesicles transport specific
proteins backward to newer
Cisternae
trans face
(“shipping” side of
0.1 0 µm 1 6 5 2 3 4
Golgi
apparatus
Figure 1.13
TEM of Golgi apparatus

14. Membrane proteins and lipids
Are synthesized in the ER and Golgi apparatus
Figure 7.10
Transmembrane
glycoproteins
Secretory
protein
Glycolipid
Golgi
apparatus
Vesicle
glycoprotein
Membrane glycolipid
Plasma membrane:
Cytoplasmic face
Extracellular face
Secreted 4 1 2 3 ER

15. Concept 7.5:
Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
Large proteins
Cross the membrane by different mechanisms

16. Exocytosis In exocytosis
Transport vesicles migrate to the plasma membrane, fuse with it, and release their contents

17. Endocytosis In endocytosis
The cell takes in macromolecules by forming new vesicles from the plasma membrane

18. Three types of endocytosis
In phagocytosis, a cell
engulfs a particle by
Wrapping pseudopodia
around it and packaging
it within a membrane-
enclosed sac large
enough to be classified
as a vacuole. The
particle is digested after
the vacuole fuses with a
lysosome containing
hydrolytic enzymes.
EXTRACELLULAR
FLUID
Pseudopodium
CYTOPLASM
“Food” or
other particle
Food
vacuole
1 µm
of amoeba
Bacterium
Food vacuole
An amoeba engulfing a bacterium via
phagocytosis (TEM).
PINOCYTOSIS
Pinocytosis vesicles
forming (arrows) in
a cell lining a small
blood vessel (TEM).
0.5 µm
In pinocytosis, the cell
“gulps” droplets of
extracellular fluid into tiny
vesicles. It is not the fluid
itself that is needed by the
cell, but the molecules
dissolved in the droplet.
Because any and all
included solutes are taken
into the cell, pinocytosis is nonspecific in the substances it transports.
Plasma
membrane
Vesicle
PHAGOCYTOSIS
Figure 7.20

19. RECEPTOR-MEDIATED ENDOCYTOSIS
Ligand
Coat protein
Coated
pit
vesicle
A coated pit
and a coated
vesicle formed
during
receptor-
mediated
endocytosis
(TEMs).
Plasma
membrane
Coat
protein
Receptor-mediated endocytosis enables the
cell to acquire bulk quantities of specific
substances, even though those substances
may not be very concentrated in the
extracellular fluid. Embedded in the
membrane are proteins with
specific receptor sites exposed to
the extracellular fluid. The receptor
proteins are usually already clustered
in regions of the membrane called coated
pits, which are lined on their cytoplasmic
side by a fuzzy layer of coat proteins.
Extracellular substances (ligands) bind
to these receptors. When binding occurs,
the coated pit forms a vesicle containing the
ligand molecules. Notice that there are
relatively more bound molecules (purple)
inside the vesicle, other molecules
(green) are also present. After this ingested
material is liberated from the vesicle, the
receptors are recycled to the plasma
membrane by the same vesicle.

20. Lysosomes: Digestive Compartments
A lysosome
Is a membranous sac of hydrolytic enzymes
Can digest all kinds of macromolecules

21. Lysosomes carry out intracellular digestion by phagocytosis
(a) Phagocytosis: lysosome digesting food
1 µm
Lysosome contains
active hydrolytic
enzymes
Food vacuole fuses with lysosome
Hydrolytic
enzymes digest
food particles
Digestion
Food vacuole
Plasma membrane
Lysosome
Digestive
Nucleus
Figure 1.14 A

22. (b) Autophagy: lysosome breaking down damaged organelle
Lysosome containing
two damaged organelles
1 µ m
Mitochondrion
fragment
Peroxisome
Lysosome fuses with
vesicle containing
damaged organelle
Hydrolytic enzymes
digest organelle
components
Vesicle containing
damaged mitochondrion
Digestion
Lysosome
Figure 1.14 B
Autophagy

23. Intercellular Junctions

24. Animals: Tight Junctions, Desmosomes, and Gap Junctions
In animals, there are three types of intercellular junctions
Tight junctions
Desmosomes
Gap junctions

25. Types of intercellular junctions in animals
Tight junctions prevent
fluid from moving
across a layer of cells
Tight junction
0.5 µm
1 µm
Space
between
cells
Plasma membranes
of adjacent cells
Extracellular
matrix
Gap junction
Tight junctions
0.1 µm
Intermediate
filaments
Desmosome
Gap
junctions
At tight junctions, the membranes of
neighboring cells are very tightly pressed
against each other, bound together by
specific proteins (purple). Forming continu-
ous seals around the cells, tight junctions
prevent leakage of extracellular fluid across
A layer of epithelial cells.
Desmosomes (also called anchoring
junctions) function like rivets, fastening cells
Together into strong sheets. Intermediate
Filaments made of sturdy keratin proteins
Anchor desmosomes in the cytoplasm.
Gap junctions (also called communicating
junctions) provide cytoplasmic channels from
one cell to an adjacent cell. Gap junctions
consist of special membrane proteins that
surround a pore through which ions, sugars,
amino acids, and other small molecules may
pass. Gap junctions are necessary for commu-
nication between cells in many types of tissues,
including heart muscle and animal embryos.
TIGHT JUNCTIONS
DESMOSOMES
GAP JUNCTIONS
Figure 1.31

26. Tank you
End of first Lecture