2. Learning Objectives
Define a cell, and discuss modern cell theory.
Discuss structure and function of plasma membrane.
Discuss transport of substances across plasma membrane.
Describe cytoplasm and its components.
Cytosol and organelles: cytoskeleton, centrosome, cilia and flagella, ribosomes,
endoplasmic reticulum, golgi complex, lysosomes, peroxisomes, proteasomes,
mitochondria.
Define a nucleus and discuss its parts: nuclear membrane, nucleoplasm, nucleolus,
chromosomes.
Discuss structure of chromosomes, and processes of transcription and translation.
Describe cell division
Discuss cellular diversity.
Discuss medical terminology related to changes in normal structure, shape and function
of the cells
3. A cell is the basic unit of all living things.
Prokaryotic cells
Eukaryotic cells
The Cell
4. All eukaryotic cells are composed of three main
parts:
1. Plasma membrane or “plasmalemma”
2. Cytoplasm - a gelatin-like substance, plus
structural fibers and organelles (but not the
nucleus)
3. Nucleus - contains the genetic library of the
cell
A Generalized Cell
5. 1. The plasma membrane forms the cell’s
outer boundary and separates the cell’s
internal environment from the outside
environment.
A Generalized Cell
6. 2. The cytoplasm contains all the cellular
contents between the plasma membrane
and the nucleus.
A Generalized Cell
7. 3. The nucleus is a large organelle that contains DNA
in molecules called chromosomes.
Each chromosome consists
of a single molecule of DNA
and associated packaging
proteins.
A chromosome contains
thousands of hereditary
units called genes.
A Generalized Cell
8. A Generalized Cell
Figure shows a generalized body cell labeled with the
plasma membrane, cytoplasm (and organelles) and nucleus.
9. The plasma membrane is much more than just a “fence” – it
is a flexible yet sturdy, “intelligent” semipermeable regulator
that:
Covers and protects the cell
Controls what goes in and
comes out
Links to other cells
The Plasma Membrane
10. The Plasma Membrane
The Fluid Mosaic Model describes the
arrangement of molecules within the
membrane: They resemble a sea of
phospholipids with protein “icebergs”
floating in it.
11. The Plasma Membrane
The structure of the membrane
Phospholipids form a lipid bilayer - cholesterol
and glycolipids (sugar-lipids) also contribute.
Integral proteins - extend into or through the
bilayer.
• Transmembrane proteins
• Peripheral proteins
12.
13. The Plasma Membrane
Glycoproteins are membrane proteins with
a carbohydrate group attached that protrude
into the extracellular fluid.
The Glycocalyx
14. The Plasma Membrane
The Functions of the membrane proteins
Transporters - selectively move substances
through the membrane.
Receptors - for cellular recognition; a ligand is a
molecule that binds with a receptor.
Enzymes - catalyze chemical reactions
Others act as cell-identity markers.
15. Functions of Membrane Proteins
1. Transport
2. Receptors for signal transduction
3. Attachment to cytoskeleton and extracellular matrix
(1) Transport (2) Receptors (3) Attachment
17. The Plasma Membrane
Examples of different membrane proteins
include
Ion channels
Carriers
Receptors
18. The Plasma Membrane
Examples of different
membrane proteins
include
Enzymes
Linkers
Cell identity markers
19. Because of the distribution of lipids and the
proteins embedded in it, the membrane
allows some substances across but not
others; this is called Selective permeability
The Plasma Membrane
courtesy of Dr. Jim Hutchins
20. Membrane Permeability
For those substances that are needed by the cell but
for which the membrane is impenetrable (impermeable),
transmembrane proteins act as channels and
transporters.
21. Transport Processes
Passive processes involve substances
moving across the cell membranes without
the input of any energy - they are said to
move “with” or “down” their concentration
gradient ([gradient] , where [ ] indicates
“concentration”).
Active processes involve the use of energy,
primarily from the breakdown of ATP, to
move a substance against its [gradient].
22. Transport Processes
Passive processes
Diffusion of solutes
Diffusion of water (called osmosis)
Facilitated diffusion (requires a specific channel
or a carrier molecule, but no energy is used)
Active processes
Various types of transporters are used, and
energy is required.
23. Concentration gradients
Concentrations of some key ions are very
different on the inside versus the outside
of cells creating a gradient
IN:
[Na+] = low
[K+] = high
[Ca2+] = very
low
[Cl-] = low
OUT:
[Na+] = high
[K+] = low
[Ca2+] = low
[Cl-] = high
(blood,
interstitial fluid)
24. Passive Transport Processes
Diffusion is the passive spread of particles
through random motion, from areas of high
concentration to areas of low concentration.
Amount of substance and the steepness of the
concentration gradient.
Temperature
Surface area
Diffusion distance
27. Passive Transport Processes An example of Channel-Mediated Facilitated Diffusion is
the passage of potassium ions through a gated K+
Channel
An example of Carrier-Mediated Facilitated Diffusion is the
passage of glucose across the cell membrane.
28. Diffusion Through the Plasma Membrane
Figure 3.7
Extracellular fluid
Cytoplasm
Lipid-
soluble
solutes
Lipid
bilayer
Lipid-insoluble
solutes
Water
molecules
Small lipid-
insoluble
solutes
(a) Simple diffusion
directly through the
phospholipid bilayer
(c) Channel-mediated
facilitated diffusion
through a channel
protein; mostly ions
selected on basis of
size and charge
(b) Carrier-mediated facilitated
diffusion via protein carrier
specific for one chemical; binding
of substrate causes shape change
in transport protein
(d) Osmosis, diffusion
through a specific
channel protein
(aquaporin) or
through the lipid
bilayer
29. Passive Transport Processes
Osmosis is the net movement of water
through a selectively permeable membrane
from an area of high water concentration to
one of lower water concentration.
Water can pass through plasma membrane
in 2 ways:
through lipid bilayer by simple diffusion
through aquaporins (integral membrane
proteins)
33. KEY CONCEPT
Concentration gradients tend to even out due
to random motion of particles
In the absence of a membrane, diffusion
eliminates concentration gradients
When different solute concentrations exist on
either side of a selectively permeable
membrane, either:
1. diffusion of permeable molecules equalizes
concentrations OR
2. osmosis moves water through the
membrane to equalize the concentration
gradients
34. Active Transport Processes
Cytoplasm
Extracellular fluidK+ is released and
Na+ sites are ready to
bind Na+ again; the
cycle repeats.
Cell
ADP
Phosphorylation
causes the
protein to
change its shape.
Concentration gradients
of K+ and Na+
The shape change
expels Na+ to the
outside, and
extracellular K+ binds.
Loss of phosphate
restores the original
conformation of the
pump protein.
K+ binding triggers
release of the
Binding of cytoplasmic
Na+ to the pump protein
stimulates phosphorylation
by ATP.Na+
Na+
Na+
Na+Na+
K+K+
K+
K+
Na+
Na+
Na+
ATP
P
P
Na+
Na+
Na+
K+
K+
P
Pi
K+
K+
36. Transport in Vesicles
Vesicle - a small spherical sac formed by budding off
from a membrane
Endocytosis - materials move into a cell in a vesicle
formed from the plasma membrane three types:
receptor-mediated endocytosis
phagocytosis
bulk-phase endocytosis (pinocytosis)
Exocytosis - vesicles fuse with the plasma membrane,
releasing their contents into the extracellular fluid
Transcytosis - a combination of endocytosis and
exocytosis
40. Cytoplasm - 2 Components
1. Cytosol - intracellular fluid, surrounding the
organelles
- The site of many chemical reactions
- Energy is usually released by these reactions.
- Reactions provide the building blocks for cell
maintenance, structure, function and growth.
2. Organelles
- Specialized structures within the cell
41. Network of protein
filaments
throughout the
cytosol
Provides structural
support for the cell
The Cytoskeleton
43. Organelles
Centrosome - located near the nucleus, consists of two
centrioles and pericentriolar material
44. Organelles
Cilia - short, hair-
like projections
from the cell
surface, move
fluids along a cell
surface
Flagella - longer
than cilia, move
an entire cell; only
example is the
sperm cell’s tail
47. Organelles
Endoplasmic
reticulum - network of
membranes in the
shape of flattened sacs
or tubules
- Rough ER - connected
to the nuclear envelope,
a series of flattened
sacs, surface is studded
with ribosomes,
produces various
proteins
50. Organelles
Lysosomes - vesicles that form from the Golgi
complex and contain powerful digestive enzymes
51. Organelles
Peroxisomes
Smaller than lysosomes
Detoxify several toxic substances such as alcohol
Abundant in the liver
Proteasomes
Continuously destroy unneeded, damaged, or
faulty proteins
Found in the cytosol and the nucleus
52. Organelles
Mitochondria - the “powerhouses” of the cell
Generate ATP
Have inner and outer mitochondrial membranes similar in
structure to the plasma membrane
Cristae - the series of folds of the inner membrane
Matrix - the large central fluid-filled cavity
Self-replicate during times of increased cellular demand or
before cell division
Contain own DNA
• Inherited only from your mother
65. Somatic Cell Division - Mitosis
The cell cycle is a sequence of events in which a body
cell duplicates its contents and divides in two
Human somatic cells contain 23 pairs of chromosomes
(total = 46)
The two chromosomes that make up each pair are called
homologous chromosomes (homologs)
Somatic cells contain two sets of chromosomes and are
called diploid cells
66. Cell Division
Interphase - the cell is not dividing
- The cell replicates its DNA
- Consists of three phases, G1, S, and G2,
replication of DNA occurs in the S phase
Mitotic phase - consists of a nuclear
division (mitosis) and a cytoplasmic
division (cytokinesis) to form two identical
cells
69. Nuclear Division: Mitosis
Prophase - the chromatin fibers change into chromosomes.
Metaphase - microtubules align the centromeres of the chromatid
pairs at the metaphase plate.
Anaphase - the chromatid pairs split at the centromere and move
to opposite poles of the cell; the chromatids are now called
chromosomes.
Telophase - two identical nuclei are formed around the identical
sets of chromosomes now in their chromatin form.
70. Cytoplasmic Division: Cytokinesis
Division of a cell’s cytoplasm to form two
identical cells
Usually begins in late anaphase
The plasma membrane constricts at its
middle, forming a cleavage furrow
The cell eventually splits into two daughter
cells.
77. 1
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
all at 700xLM
1
LateEarly
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Chromosome
(two chromatids
joined at
centromere
(a) INTERPHASE
(b) PROPHASE
Centrioles
Centrosome:
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
2
all at 700xLM
Centromere
1
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Metaphase plate
(a) INTERPHASE
Centrioles
Centrosome:
(c) METAPHASE
2
3
LateEarly (b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
all at 700xLM
Chromosome
(two chromatids
joined at
centromere
Centromere
1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Chromosome
(a) INTERPHASE
Centrioles
Centrosome:
(c) METAPHASE
2
3
4
Cleavage
furrow
LateEarly (b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
all at 700xLM
Chromosome
(two chromatids
joined at
centromere
Centromere
1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
Cleavage furrow
(e) TELOPHASE
(c) METAPHASE
2
3
4
5
Cleavage
furrow
LateEarly (b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
Chromosome
all at 700xLM
Chromosome
(two chromatids
joined at
centromere
Centromere
1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
(f) IDENTICAL CELLS IN INTERPHASE
Cleavage furrow
(e) TELOPHASE
(c) METAPHASE
Cleavage
furrow
2
3
4
5
6
LateEarly (b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
Chromosome
all at 700xLM
Centromere
Chromosome
(two chromatids
joined at
centromere
Mitosis
78. Reproductive Cell Division
During sexual reproduction, each new
organism is the result of the union of two
gametes (fertilization), one from each
parent.
Meiosis - reproductive cell division that
occurs in the gonads (ovaries and testes) that
produces gametes with half the number of
chromosomes.
Haploid cells - gametes contain a single set
of 23 chromosomes.
Fertilization restores the diploid number of
chromosomes (46).
79. Reproductive Cell Division
Meiosis occurs in two successive stages: meiosis I and
meiosis II .
Each of these two stages has 4 phases: prophase,
metaphase, anaphase, and telophase.
Summary - Meiosis I begins with a diploid cell and ends
with two cells having the haploid number of
chromosomes; in Meiosis II, each of the two haploid cells
divides, and the net result is four haploid gametes that are
genetically different from the original diploid starting cell.
82. Cellular Diversity
The average adult has
nearly 100 trillion cells.
There are about 200
different types of cells.
Cells come in a variety of
shapes and sizes.
Cellular diversity permits
organization of cells into
more complex tissues and
organs.