Unit 2
The Cellular Basis of Life
2A. Basic Cell Structure and Function
2B. Viruses
2C.
2C Membranes and Cell Transport
2D. Energy and Metabolism
2E. How Cells Harvest Energy
2F. Photosynthesis
2G. Cell Communication
Module 2A
Basic Cell Structure and Function
„ Cells
are the basic units of life.
Therefore, an understanding of cells is
essential for an understandingg of livingg
organisms.
„ In this module, we will take an
introductory look at the structure and
function of living cells.
1
2
Objective # 1
Objective 1
„ In
1655, the English scientist Robert
Hooke coined the term “cellulae” for
the small box
box--like structures he saw
while examining a thin slice of cork
under a microscope.
„ A few years later, a Dutchman named
Anton van Leeuwenhoek observed
and described numerous living cells.
Describe the general plan
of cellular organization
common to all cells.
3
4
Onion Cells
Objective 1
„ Further
5
study has shown that all cells
have the following basic structure :
¾ A thin, flexible plasma membrane
surrounds the entire cell.
¾ The interior is filled with a semisemi-fluid
material called the cytoplasm.
cytoplasm.
¾ Also inside are specialized structures
called organelles and the cell’s genetic
material..
material
6
1
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Objective # 2
Plasma membrane
Cytoplasm
List and explain the 3
principles
i i l off the
h cellll theory.
h
O
Organelles
ll
Genetic material
Identify the
Basic
Components
of a cell
8
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Objective 2
Objective 2
„ In
1838 – 1839, the German scientists
Schleiden and Schwann
Schwann,, proposed the
first 2 principles of the cell theory:
„ About
15 years later, the German
physician Rudolf Virchow proposed
the third and final principle of the cell
theory:
¾ All cells arise from prepre-existing cells.
¾ All
organisms are composed of one or
more cells.
¾ Cells are the basic units of life.
„ This
is now qualified with “under the
current conditions on earth”.
9
10
Objective # 3
Objective 3
„ Why
are cells so small?
¾ Because a cell usually has only 1 or 2
sets of genetic instructions, there is a
limit to the volume of cytoplasm that
can be effectively controlled.
controlled
¾ Methods used to transport materials
and information inside the cell are
efficient over short distances only.
¾ Problem with surfacesurface-toto-volume ratio.
Describe some factors that
act to limit cell size.
size
11
12
2
Objective 3
„ Assuming
constant shape, as an object
gets bigger what happens to its surface
area?
„ What happens to its volume?
„ What happens to its surfacesurface-toto-volume
ratio?
¾ The S/V ratio decreases because
volume increases at a faster rate than
surface area.
The ratio of
Surface Area
to Volume
gets smaller
as this cell
gets larger
1 unit
10 unit
Surface area (4πr2)
12.57 unit2
1257 unit2
Volume ( 43 πr3)
4.189 unit3
4189 unit3
3
0.3
Cell radius (r)
Surface Area- /Volume
13
14
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Objective 3
Objective 3
„ Why
is decreasing S/V ratio a problem?
„ In order to survive , a cell must exchange
materials with its environment. Cell
volume determines the amount of
materials that must be exchanged, while
surface area limits how fast exchange can
occur. In other words, as cells get larger
the need for materials increases faster
than the ability to absorb them.
„ How
have organisms become larger in
spite of these problems?
„ At
first, single
g cells simply
p got
g larger.
g
Average eukaryotic cell is 1,000 X
larger in volume than average
prokaryotic cell. Eventually, limits to
size of individual cells were reached.
15
16
Objective 3
Objective 3
„ Colonial
„ Coenocytic
organisms – sac of
cytoplasm continued to increase in size
but became multinucleate and evolved
thin, flat shapes or long, narrow shapes
to increase S/V ratio. e.g. some
protists, fungi
17
organisms – instead of one
large mass of cytoplasm, body was
divided into many small, similar cells,
each with its own nucleus. e.g. some
protists
„ Multicellular organisms – similar to
colonial except cells became
specialized to carry out specific
functions. e.g. plants, animals
18
3
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Objective # 4
Objective 4
Be able to
describe the
structure and
function all cell
parts shown on
this diagram of
a typical
prokaryotic cell
Describe the structure of a
typical
i l prokaryotic
k
i cell.
ll
19
Cytoplasm
Ribosomes
Nucleoid (DNA)
Pl
Plasma
membrane
b
Cell wall
Capsule
Pili
Flagellum
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Copyright © The McGraw‐Hill Companies, Inc. Permission required for reproduction or display.
Fig. 4.4
Electron
micrograph of a
photosynthetic
prokaryotic cell
Nucleoid
Cytoplasm
Cell wall
Plasma
membrane
0.6 µm
22
Photosynthetic membranes
Courtesy of E.H. Newcomb & T.D. Pugh, University of Wisconsin
Objective # 5
Nucleus
Nuclear envelope
Nucleolus
Nuclear pore
Ribosomes
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Microvilli
Cytoskeleton
Actin filament
Microtubule
Ribosomes
Intermediate
filament
Describe the structure of a
typical
i l eukaryotic
k
i cell.
ll
C ti l
Centriole
Cytoplasm
Lysosome
Be able to describe
the structure and
function of all cell
parts shown on
this diagram of a
typical animal cell
23
Exocytosis
Vesicle
Golgi apparatus
Plasma membrane
Peroxisome
Mitochondrion
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4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Ribosome
Nucleus
Nucleus
Nuclear envelope
Nuclear pore
Nucleolus
Intermediate filament
„
Central vacuole
Cytoskeleton
„
Intermediate
filament
Microtubule
Actin filament
(microfilament)
„
Peroxisome
Mitochondrion
Golgi
apparatus
Vesicle
Chloroplast
„
y p
Cytoplasm
Repository of the genetic information
Most eukaryotic cells possess a single nucleus
Nucleolus – region where ribosomal RNA synthesis
takes place
Nuclear envelope
¾
¾
Be able to describe
the structure and
function of all cell
parts shown on
this diagram of a
typical plant cell
„
In eukaryotes, the DNA is divided into multiple linear
chromosomes
¾
Adjacent cell
wall
Cell wall
Plasma membrane
2 phospholipid bilayers
b
Nuclear pores – control passage in and out
Chromatin is chromosomes plus protein
Plasmodesmata
26
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Ribosomes
„ Cell’s
Be able to
describe the
structure and
function of the
eukaryotic
nucleus
27
protein synthesis machinery
„ Found in all cell types in all 3 domains
„ Ribosomal RNA (rRNA)
(rRNA)--protein
complex
co
pe
„ Protein synthesis also requires
messenger RNA (mRNA) and transfer
RNA (tRNA)
„ Ribosomes may be free in cytoplasm
or associated with internal membranes
28
Endomembrane System
Fig. 4.9
A system of membranes that run through
the cytoplasm and divide the cell into
compartments where different cellular
functions occur
„ Present in e
eukaryotic
kar otic cells onl
only
„ Components of the endomembrane system
include: the endoplasmic reticulum, the
Golgi, lysosomes,
lysosomes, microbodies,
microbodies, vacuoles,
and vesicles
„
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Large subunit
Ribosome
Small subunit
Be able to describe the structure and
function of ribosomes
30
5
Endoplasmic reticulum
„
„
„
Be able to describe the structure and
function of the rough and smooth
endoplasmic reticulum:
Rough endoplasmic reticulum (RER)
¾ Attachment of ribosomes to the membrane gives a
rough appearance
¾ Synthesis of proteins to be secreted, sent to
lysosomes or plasma membrane
S
Smooth
h endoplasmic
d l
i reticulum
i l
(SER)
¾ Relatively few bound ribosomes
¾ Variety of functions – synthesis, store Ca2+ ,
detoxification
Ratio of RER to SER depends on cell’s function
32
31
Golgi apparatus
„ Flattened
stacks of interconnected
membranes (Golgi bodies)
„ Functions in packaging and
distribution of molecules synthesized
at one location and used at another
within the cell or even outside of it
„ Cis and trans faces
„ Vesicles transport molecules to
destination
Be able to
describe the
structure and
function of
the Golgi
apparatus:
34
33
Lysosomes
„ Membrane
Membrane--bound
sacs that contain
digestive enzymes
„ Arise from the Golgi apparatus
„E
Enzymes
y es catalyze
cata y e the
t e breakdown
b ea dow of
o
macromolecules
„ Destroy cells or foreign matter that the
cell has engulfed by phagocytosis
35
36
6
Vacuoles
Microbodies
„ Membrane
Membrane--bounded
sacs that carry
out various functions depending on
the cell type
• Variety of enzyme‐
bearing, membrane‐
enclosed vesicles • One type are peroxisomes
„ There
– Contain enzymes involved in the oxidation of fatty acids
– H2O2 produced as by‐
product – rendered harmless by catalase
are different types of vacuoles:
¾ Central
vacuole in plant cells
vacuole of some protists
¾ Storage vacuoles
¾ Contractile
37
38
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Nucleus
Nuclear pore
Ribosome
Be able to
describe the
movement of
proteins
through the
endomembrane
system of a
eukaryotic cell:
Electron
micrograph
showing the
large central
vacuole of a
plant cell
Rough
endoplasmic
reticulum
Membrane
protein
Newly
synthesized
protein
1. Vesicle containing
proteins buds from
the rough endoplasmic reticulum,
diffuses through the
cell and ffuses
cell,
ses to
the cis face of the
Golgi apparatus.
Transport
vesicle
Smooth
endoplasmic
reticulum
cis face
Golgi membrane protein
Cisternae
Golgi
Apparatus
trans face
2. The proteins are
modified and
packaged into
vesicles for
transport.
Secretory vesicle
Secreted
protein
Cell membrane
39
Mitochondria
„
„
Found in all types of eukaryotic cells
Bound by membranes
¾
¾
¾
¾
„
„
3. The vesicle may
travel to the plasma
membrane,
releasing its
contents to the
extracellular
environment.
Extracellular fluid
Be able to describe the structure and
function of a mitochondrium:
Outer membrane
Intermembrane space
Inner membrane has cristae
Matrix
On the surface of the inner membrane, and also
embedded within it, are proteins that carry out
oxidative metabolism
Have their own DNA
41
42
7
Chloroplasts
Be able to describe the structure and
function of a chloroplast:
Organelles present in cells of plants and
some other eukaryotes
„ Contain chlorophyll for photosynthesis
„ Surrounded by
y 2 membranes
„ Thylakoids are membranous sacs within
the inner membrane
¾ Grana are stacks of thylakoids
„ Have their own DNA
„
44
43
Endosymbiosis
This theory proposes that some eukaryotic
organelles evolved by a symbiosis between
two cells that were each freefree-living
„ One cell, a prokaryote, was engulfed by
and became part of a larger cell
cell, which
hich was
as
the precursor of modern eukaryotes
„ Organelles that probably arose by
endosymbiosis include mitochondria and
chloroplasts
„
Some
eukaryotic
organelles
evolved
through the
process of
endosymbiosis:
46
45
Cytoskeleton
„A
network of protein fibers and tubes
found in all eukaryotic cells
¾ Supports
the shape of the cell
¾ Keeps organelles in fixed locations
system – constantly forming
and disassembling
3 Components of the Cytoskeleton
„
Microfilaments ((actin
actin filaments)
¾
¾
„
Microtubules
¾
¾
„ Dynamic
¾
„
Largest of the cytoskeletal elements
Dimers of αα- and ββ-tubulin subunits
Facilitate movement of cell and materials within cell
Intermediate filaments
¾
¾
47
Two protein chains loosely twined together
Movements like contraction, crawling, “pinching”
Between the size of actin filaments and microtubules
Very stable – usually not broken down
48
8
Centrosome
Be able to describe the structure and
function of the 3 components of the
cytoskeleton:
„ Region
containing a pair of centrioles
„ Centrioles function as microtubulemicrotubuleorganizing centers. They can initiate
the assembly of new microtubules.
„ Animal cells and most protists have
centrioles
„ Plants and fungi usually lack centrioles
49
50
Cell Movement
A pair of centrioles. Each centriole is
composed of 9 triplets of microtubules:
„ Essentially
all cell motion is tied to the
movement of actin filaments,
microtubules, or both
„ Some cells crawl using
g actin
microfilaments
„ Eukaryotic flagella and cilia have 9 + 2
arrangement of microtubules
Microtubule triplet
¾ Not
like prokaryotic flagella
Copyright © The McGraw‐Hill Companies, Inc. Permission required for reproduction or display.
Be able to describe the structure and function of a
eukaryotic flagellum. Cilia have a similar structure,
except they are shorter and more numerous.
52
A green algal
cell with
numerous
flagella and a
paramecium
covered with
cilia
53
9
„
Extracellular matrix (ECM)
Eukaryotic cell walls
„ Animal
Plants, fungi, and
many protists
¾ Different from
prokaryote
¾ Prokaryotes
y
peptidoglycan
¾ Plants and protists –
cellulose
¾ Fungi – chitin
¾ Plants – primary and
secondary cell walls
¾
55
Extracellular matrix surrounding an
animal cell
cells lack cell walls
„ Secrete an elaborate mixture of
glycoproteins into the space around
them
„ Collagen may be abundant
„ Form a protective layer over the cell
surface
„ Integrins link ECM to cell’s
cytoskeleton
56
Table 4.2
57
Objective # 6
Describe the similarities and
differences between
prokaryotic and eukaryotic
cells.
59
60
10
Objective 6
Prokaryotes
organisms monera
(bacteria)
Objective 6
Eukaryotes
all other
organisms
Prokaryotes
Eukaryotes
always present always present
size
very small
much larger
(1 – 5 μm)
(10 – 100 μm)
complexity relatively simple more complex
cell wall
membranemembranebound
organelles
ribosomes
cytoskeleton
flagella
usually present sometimes
(contains
present (lacks
peptidoglycan) peptidoglycan)
61
Objective 6
Prokaryotes Eukaryotes
absent
present
smaller and
free in the
cytoplasm
absent
solid flagellin;
rotate
larger and
may be bound
to ER
present
microtubules;
bend
plasma
membrane
internal
may contain
membranes
b
i f ldi
infoldings
off
the plasma
membrane but
usually lack
internal
membranes
complex system
off internal
i
l
membranes
divides cell into
specialized
compartments
62
Objective 6
63
Prokaryotes
Eukaryotes
structure single, naked, many linear
of genetic circular DNA chromosomes,
material molecule
each made of 1
DNA molecule
joined with protein
location in an area of inside a
of genetic the cytoplasm membrane
membrane--bound
material called the
nucleus
nucleoid
Objective # 7
64
Objective 7
„ Cell
surface markers allow the cells of
a multicellular organism to recognize
each other and to distinguish “self”
from “non“non-self.”
„ In this section, we will examine 2 types
of cell surface markers:
Name and describe the types
of surface markers that ggive
cells identity.
¾ Glycolipids
¾ MHC
65
proteins
66
11
Objective 7
Objective 7
„ Glycolipids:
„ MHC
proteins:
¾ Are proteins embedded in the surface
of the plasma membrane.
¾ Allow
ow ce
cellss of
o the
t e immune
u e system
syste to
distinguish foreign cells from the
body’s own cells so they can mount an
attack against any foreign cells.
¾ Are
lipids embedded in the plasma
membrane with cabohydrate groups
attached
¾ Allow cells that are part of the same
tissue to recognize each other and
form intimate connections to better
coordinate their functions.
67
68
Objective # 8
Objective 8
Explain what cell junctions are, and
discuss the following types of cell
junctions:
g junction
j
a) tight
b) anchoring junction
c) communicating junction
„ Cell
junctions refer to long
long--lasting
or permanent connections between
adjacent cells.
„ We
will examine 3 types of cell
junctions:
69
70
Objective 8a
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Tight junction
Adjacent plasma
membranes
a) Tight junctions connect cells into
sheets. Because these junctions
form a tight seal between cells, in
order to cross the sheet,,
substances must pass through the
cells, they cannot pass between
the cells.
Tight junction
proteins
Intercellular
space
a.
2.5 µm
Microvilli
Tight Junction
Tight
junction
Anchoring
junction
(desmosome)
Intermediate
filament
Communicating
junction
Basal lamina
71
Courtesy of Daniel Goodenough
12
Objective 8b
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Anchoring
Junction
b) Anchoring junctions attach the
cytoskeleton of a cell to the
matrix surrounding the cell, or to
the cytoskeleton of an adjacent
cell.
Microvilli
Anchoring junction (desmosome)
Intercellular space
Adjacent plasma
membranes
Tight
junction
C dh in
Cadherin
Cytoplasmic
protein plaque
Anchoring
junction
(desmosome)
Cytoskeletal filaments
anchored to plaque
b.
Intermediate
filament
0.1 µm
Communicating
junction
Basal lamina
73
© Dr. Donald Fawcett/Visuals Unlimited.
Objective 8c
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
c) Communicating junctions link
the cytoplasms of 2 cells
together, permitting the
controlled p
passage
g of small
molecules or ions between them.
In animals, these junctions are
called gap junctions
junctions;; in plants
they are called plasmodesmata
plasmodesmata..
Communicating
Junction
Microvilli
Tight
junction
Anchoring
junction
(desmosome)
Intermediate
filament
Communicating junction
Communicating
junction
Intercellular space
Connexon
Two adjacent connexons
forming an open channel
between cells
Channel (diameter 1.5 nm)
Adjacent plasma
membranes
75
Plasmodesmata connect plant cells
c.
Basal lamina
1.4 µm
© Dr. Donald Fawcett/Visuals Unlimited.
Table 4.4
77
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