Paula Ingram Darasaw
pmid2@aol.com
1
 Be


Principles of cell theory
General cellular anatomy



able to discuss the:
Lipid bilayer membrane and function
Overview of organelles
Cellular physiology


Overview of cell transport and diffusion
Vesicular transport
2

The cell is the smallest structural and functional unit capable of carrying
out life processes.

The functional activities of each cell depend on the specific structural
properties of the cell.

Cells are the living building blocks of all plant and animal organisms.

All organism’s structure and function ultimately depend on the individual
and collective structural characteristics and functional capabilities of its
cells.

All new cells and new life arise only from pre-existing cells.

Because of this continuity of life, the cells of all organisms are
fundamentally similar in structure and function.
3
 All
cells have some common structures and
functions

Human cells have three basic parts:



Plasma membrane—flexible outer boundary
Cytoplasm—intracellular fluid containing
organelles
Nucleus—control center
4
Chromatin
Nucleolus
Nuclear envelope
Nucleus
Smooth endoplasmic
reticulum
Mitochondrion
Cytosol
Lysosome
Centrioles
Centrosome
matrix
Cytoskeletal
elements
• Microtubule
• Intermediate
filaments
Plasma
membrane
Rough
endoplasmic
reticulum
Ribosomes
Golgi apparatus
Secretion being
released from cell
by exocytosis
Peroxisome
5
 Bimolecular
layer of lipids and proteins in
a constantly changing fluid mosaic
 Plays
a dynamic role in cellular activity
 Separates
intracellular fluid (ICF) from
extracellular fluid (ECF)
 Interstitial fluid (IF) = ECF that
surrounds cells
6
7

Integral proteins
Firmly inserted into the membrane (most are
transmembrane)
 Functions:



Transport proteins (channels and carriers), enzymes, or
receptors
Peripheral proteins
Loosely attached to integral proteins
 Include filaments on intracellular surface and
glycoproteins on extracellular surface
 Functions:


Enzymes, motor proteins, cell-to-cell links, provide
support on intracellular surface, and form part of
glycocalyx
8
1.
2.
3.
Transport
Receptors for
signal
transduction
Attachment to
cytoskeleton and
extracellular
matrix
4.
5.
6.
Enzymatic
activity
Intercellular
joining
Cell-cell
recognition
9
 Three
types:

Tight junction - Prevent fluids and most
molecules from moving between cells

Desmosome - “Rivets” or “spot-welds” that
anchor cells together

Gap junction - Transmembrane proteins form
pores that allow small molecules to pass from
cell to cell
10
 Passive
processes
 No cellular energy (ATP) required
 Substance moves down its concentration
gradient
 Active processes
 Energy (ATP) required
 Occurs only in living cell membranes
11
12
Simple
diffusion
Carrier-mediated facilitated
diffusion
Channel-mediated facilitated
diffusion
Osmosis
13
14
15

16





Movement of solvent (water) across a selectively
permeable membrane
Water diffuses through plasma membranes:
 Through the lipid bilayer
 Through water channels called aquaporins (AQPs)
Water concentration is determined by solute
concentration because solute particles displace water
molecules
Osmolarity: The measure of total concentration of
solute particles
When solutions of different osmolarity are separated
by a membrane, osmosis occurs until equilibrium is
reached
17
18
(a)
Membrane permeable to both solutes and water
Solute and water molecules move down their concentration gradients
in opposite directions. Fluid volume remains the same in both compartments.
Left
compartment:
Solution with
lower osmolarity
Right
compartment:
Solution with
greater osmolarity
Both solutions have the
same osmolarity: volume
unchanged
H2O
Solute
Membrane
Solute
molecules
(sugar)
19
Figure 3.8a
(b)
Membrane permeable to water, impermeable to solutes
Solute molecules are prevented from moving but water moves by osmosis.
Volume increases in the compartment with the higher osmolarity.
Left
compartment
Right
compartment
Both solutions have identical
osmolarity, but volume of the
solution on the right is greater
because only water is
free to move
H2O
Membrane
Solute
molecules
(sugar)
20
Figure 3.8b
21
Two
types of active processes:
 Active transport
 Vesicular transport
Both use ATP to move solutes
across a living plasma membrane
22
 Requires
carrier proteins (solute pumps)
 Moves solutes against a concentration
gradient
 Types of active transport:


Primary active transport
Secondary active transport
23
24
Extracellular fluid
Na+
Na+-K+ pump
K+
ATP-binding site
Cytoplasm
11Cytoplasmic
Na+ binds
to pump protein.
Cytoplasmic Na+ binds to pump protein.
25
Na+ bound
P
ATP
ADP
2 Binding of Na+ promotes
phosphorylation of the protein by ATP.
26
Figure 3.10 step 2
Na+ released
P
3 Phosphorylation causes the protein to
change shape, expelling Na+ to the outside.
27
K+
P
4 Extracellular K+ binds to pump protein.
28
K+ bound
Pi
5 K+ binding triggers release of the
phosphate. Pump protein returns to its
original conformation.
29
K+ released
6 K+ is released from the pump protein
and Na+ sites are ready to bind Na+ again.
The cycle repeats.
30
31
 Functions:

Exocytosis—transport out of cell

Endocytosis—transport into cell

Transcytosis—transport into, across, and then out
of cell

Substance (vesicular) trafficking—transport from
one area or organelle in cell to another
32
1 Coated pit ingests
Extracellular fluid
substance.
Protein coat
(typically
clathrin)
Plasma
membrane
Cytoplasm
2 Protein-
coated
vesicle
detaches.
3 Coat proteins detach
and are recycled to
plasma membrane.
Transport
vesicle
Endosome
Uncoated
endocytic vesicle
4 Uncoated vesicle fuses
with a sorting vesicle
called an endosome.
5
Transport
vesicle containing
membrane components
moves to the plasma
membrane for recycling.
Lysosome
6 Fused vesicle may (a) fuse
(a)
with lysosome for digestion
of its contents, or (b) deliver
its contents to the plasma
membrane on the
opposite side of the cell
(transcytosis).
(b)
33
Plasma membrane
Extracellular
SNARE (t-SNARE)
fluid
Secretory
vesicle
Vesicle
SNARE
(v-SNARE)
Molecule to
be secreted
The process
of exocytosis
Fusion pore formed
1 The membrane-
3 The vesicle
bound vesicle
migrates to the
plasma membrane.
and plasma
membrane fuse
and a pore
opens up.
Cytoplasm
2 There, proteins
4 Vesicle
at the vesicle
surface (v-SNAREs)
Fused
v- and bind with t-SNAREs
t-SNAREs (plasma membrane
proteins).
contents are
released to the
cell exterior.
34
35
 Located
between plasma membrane and
nucleus
 Cytosol

Water with solutes (protein, salts, sugars, etc.)
 Cytoplasmic

organelles
Metabolic machinery of cell
 Inclusions

Granules of glycogen or pigments, lipid droplets,
vacuoles, and crystals
36
 Membranous
Mitochondria
 Peroxisomes
 Lysosomes
 Endoplasmic
reticulum
 Golgi apparatus

 Nonmembranous



Cytoskeleton
Centrioles
Ribosomes
37
 Double-membrane
structure with shelflike
cristae
 Provide most of cell’s ATP via aerobic cellular
respiration
 Contain their own DNA and RNA
38
 Granules
containing protein and rRNA
 Site of protein synthesis
 Free ribosomes synthesize soluble proteins
 Membrane-bound ribosomes (on rough ER)
synthesize proteins to be incorporated into
membranes or exported from the cell
39
 Interconnected
tubes and parallel
membranes enclosing cisternae
 Continuous with nuclear membrane
 Two varieties:


Rough ER
Smooth ER
40
Smooth ER
Nuclear
envelope
Rough ER
Ribosomes
(a) Diagrammatic view of smooth and rough ER
41
Figure 3.18a
 External
surface studded with ribosomes
 Manufactures all secreted proteins
 Synthesizes membrane integral proteins and
phospholipids
42
 Tubules
arranged in a looping network
 Enzyme (integral protein) functions:
In the liver—lipid and cholesterol metabolism,
breakdown of glycogen, and, along with
kidneys, detoxification of drugs, pesticides,
and carcinogens
 Synthesis of steroid-based hormones
 In intestinal cells—absorption, synthesis, and
transport of fats
 In skeletal and cardiac muscle—storage and
release of calcium

43
 Stacked
and flattened membranous sacs
 Modifies, concentrates, and packages
proteins and lipids
 Transport vessels from ER fuse with convex
cis face of Golgi apparatus
 Proteins then pass through Golgi apparatus to
trans face
 Secretory vesicles leave trans face of Golgi
stack and move to designated parts of cell
44
1 Protein-
containing
vesicles pinch
off rough ER
and migrate to
fuse with
membranes of
Golgi
apparatus.
Rough ER
Phagosome
ER
membrane
Proteins in
cisterna
Pathway C:
Lysosome containing
acid hydrolase
enzymes
Vesicle becomes
lysosome
2 Proteins are
modified within
the Golgi
compartments.
3 Proteins are
then packaged
within different
vesicle types,
depending on
their ultimate
destination.
Plasma
membrane
Golgi
apparatus
Pathway A:
Vesicle contents
destined for exocytosis
Secretory
vesicle
Pathway B:
Vesicle membrane
to be incorporated
into plasma
membrane
Secretion by
exocytosis
Extracellular fluid
45
Figure 3.20
 Spherical
membranous bags containing
digestive enzymes (acid hydrolases)
 Digest ingested bacteria, viruses, and toxins
 Degrade nonfunctional organelles
 Break down and release glycogen
 Break down bone to release Ca2+
 Destroy cells in injured or nonuseful tissue
(autolysis)
46
 Overall


function
Produce, store, and export biological molecules
Degrade potentially harmful substances
The Endomembrane System includes the
Endoplasmic Reticulum, Golgi Apparatus,
Secretory Vesicles and Lysosomes as well as the
Nuclear Envelope
47
 Membranous
sacs containing powerful
oxidases and catalases
 Detoxify harmful or toxic substances
 Neutralize dangerous free radicals (highly
reactive chemicals with unpaired electrons)
 Oxidases convert free radicals to hydrogen
peroxide, which is also reactive and
dangerous but is quickly converted to water
by catalase enzymes
48
 Elaborate
series of rods throughout cytosol
that support cellular structures and provide
the machinery to generate various cell
movements. There are three types of rods in
the cytoskeleton, in order of increasing size:



Microfilaments
Intermediate Filaments
Microtubules
49
 Dynamic
actin strands attached to
cytoplasmic side of plasma membrane
 Involved in cell motility, change in shape,
endocytosis and exocytosis
50
(a) Microfilaments
Strands made of spherical
protein subunits called actins
Actin subunit
7 nm
Microfilaments form the blue network
surrounding the pink nucleus in this
photo.
51
Figure 3.23a
 Tough,
insoluble ropelike protein fibers
 Resist pulling forces on the cell and attach to
desmosomes
 Because the protein composition of
intermediate filaments varies in different
cell types, these cytoskeleton elements have
a variety of names depending on the type of
cell, e.g., they are called neurofilaments in
nerve cells and keratin filaments in epithelial
cells
52
(b) Intermediate filaments
Tough, insoluble protein fibers
constructed like woven ropes
Fibrous subunits
10 nm
Intermediate filaments form the purple
batlike network in this photo.
53
Figure 3.23b
 Dynamic
hollow tubes
 Most radiate from centrosome
 Determine overall shape of cell and
distribution of organelles
54
(c) Microtubules
Hollow tubes of spherical protein
subunits called tubulins
Tubulin subunits
25 nm
Microtubules appear as gold networks
surrounding the cells’ pink nuclei in
this photo.
55
Figure 3.23c
 Protein
complexes that function in motility
(e.g., movement of organelles and
contraction)
 Powered by ATP
56
Vesicle
ATP
Receptor for motor molecule
Motor molecule (ATP powered)
Microtubule of cytoskeleton
(a) Motor molecules can attach to receptors on
vesicles or organelles, and “walk” the organelles
along the microtubules of the cytoskeleton.
ATP
Motor molecule (ATP powered)
Cytoskeletal elements
(microtubules or microfilaments)
(b) In some types of cell motility, motor molecules attached to one
element of the cytoskeleton can cause it to slide over another
element, as in muscle contraction and cilia movement.
57
Figure 3.24
 “Cell
center” near nucleus
 Generates microtubules; organizes mitotic
spindle
 Contains centrioles: Small tube formed by
microtubules
58
Centrosome matrix
Centrioles
(a)
Microtubules
59
Figure 3.25a
 Cilia




and flagella
Whiplike, motile extensions on surfaces of
certain cells
Contain microtubules and motor molecules
Cilia move substances across cell surfaces
Longer flagella propel whole cells (tail of sperm)
60
Outer microtubule
doublet
Dynein arms
The doublets
also have
attached motor
proteins, the
dynein arms.
Central
microtubule
Cross-linking
proteins inside
outer doublets
The outer
microtubule
doublets and
the two central
microtubules
are held
together by
cross-linking
proteins and
radial spokes.
Radial spoke
TEM
A cross section through the
Microtubules cilium shows the “9 + 2”
arrangement of microtubules.
Cross-linking
proteins inside
outer doublets
Radial spoke
Plasma
membrane
Plasma
membrane
Triplet
Basal body
TEM
A longitudinal section of a
cilium shows microtubules
running the length of the
structure.
Cilium
TEM
Basal body
(centriole)
A cross section through the
basal body. The nine outer
doublets of a cilium extend into
a basal body where each doublet
joins another microtubule to
form a ring of nine triplets.
61
Figure 3.26
Power, or
propulsive,
stroke
1
2
3
4
Recovery stroke, when
cilium is returning to its
initial position
5
6
7
(a) Phases of ciliary motion.
Layer of mucus
Cell surface
(b) Traveling wave created by the activity of
many cilia acting together propels mucus
across cell surfaces.
62
Figure 3.27
 Microvilli



Fingerlike extensions of plasma membrane
Increase surface area for absorption
Core of actin filaments for stiffening
63
 Genetic
library with blueprints for nearly all
cellular proteins
 Responds to signals and dictates kinds and
amounts of proteins to be synthesized
 Most cells are uninucleate
 Red blood cells are anucleate
 Skeletal muscle cells, bone destruction cells,
and some liver cells are multinucleate
64
Nuclear pores
Nuclear envelope
Nucleus
Chromatin (condensed)
Nucleolus
Cisternae of rough ER
(a)
65
Figure 3.29a
 Double-membrane
barrier containing pores
 Outer layer is continuous with rough ER and
bears ribosomes
 Inner lining (nuclear lamina) maintains shape
of nucleus
 Pore complex regulates transport of large
molecules into and out of nucleus
66
Surface of nuclear envelope.
Fracture
line of outer
membrane
Nuclear
pores
Nucleus
Nuclear lamina. The netlike
lamina composed of intermediate filaments formed by
lamins lines the inner surface
of the nuclear envelope.
(b)
Nuclear pore complexes.
Each pore is ringed by
protein particles.
67
Figure 3.29b
 Dark-staining
spherical bodies within nucleus
 Involved in rRNA synthesis and ribosome
subunit assembly
68
 Threadlike
strands of DNA (30%), histone
proteins (60%), and RNA (10%)
 Arranged in fundamental units called
nucleosomes
 Condense into barlike bodies called
chromosomes when the cell starts to divide
69
1 DNA double
helix (2-nm diameter)
Histones
2 Chromatin
(“beads on a
string”) structure
with nucleosomes
Linker DNA
Nucleosome (10-nm diameter; eight
histone proteins wrapped by two
winds of the DNA double helix)
(a)
3 Tight helical fiber
4 Looped domain
(30-nm diameter)
5 Chromatid
structure (300-nm
diameter)
(700-nm diameter)
(b)
Metaphase
chromosome
(at midpoint
of cell division)
70
Figure 3.30