All Organisms Consist of Cells
Cell Structure and Function
Basic types of cells
„
Basic cell functions
The nucleus
Then endomembrane system
Prokaryotic and eukaryotic cells are similar in that they
all are enclosed by a cell membrane, are filled with an
aqueous cytoplasm and carry their genetic information
in chromosomes. Prokaryotic and eukaryotic cells differ in that
eukaryotic
cells have membrane bound organelles and a defined
nucleus and prokaryotic cells lack these structures.
The cytoskeleton
A prokaryotic cell
A prokaryotic cell
Ribosome
Flagella
Ribosomes
Cell wall
Cytoplasm
Chromosome
Cell membrane
Flagella
Cytoplasm
Chromosome
3.5 µm
Cell wall
Cell membrane
1
Animal and Plant cells
Plant and Animal Cells Are Eukaryotic
Nuclear
envelope
Nucleolus
Generalized animal cell
„
„
Several vital organelles such as a nucleus, the endomembrane
system, the cytoskeleton and mitochondria are found in all
eukaryotic cells.
Chromatin
Rough
endoplasmic
reticulum
Centrioles
Ribosomes
Lysosome
Smooth
endoplasmic
reticulum
Other organelles such as a cell wall, chloroplasts
and lysosomes are specialized to plant or animal
cells.
Gogli
apparatus
Peroxisome
Mitochondrion
Cytoskeletal
element
Cell membrane
(Plasma
membrane)
Generalized plant cell
The organelles within eukaryotic cells subdivide
the cell into functional compartments
Nuclear
envelope
Nucleolus
„
The nucleus is the site of information storage and retrieval
Chromatin
Central vacuole
Cell wall
Chloroplast
Rough
endoplasmic
reticulum
Cross-sectional view of nuclear envelope
DNA in nucleus
Inner membrane
Ribosomes
Outer membrane
Smooth
endoplasmic
reticulum
Cytoplasm
Gogli
apparatus
Peroxisome
DNA in nucleus
Mitochondrion
Inner membrane
Nucleus
Cytoskeletal
element
Cell membrane
(Plasma
membrane)
Nuclear envelope
Outer membrane
Cytoplasm
Nuclear pore complex
2
Molecules move in and out of nucleus
Where does the chemical energy used to power cell activities come from?
DNA
DNA archives
instructions
mRNA
RNA is a copy of the
instructions
ATP
Adenosine
triphosphate
Hydrolysis
ADP
Pi
Adenosine
diphosphate
Inorganic
phosphate
group
Energy
Ribosome
mRNA
Protein
RNA instructions are
used to make
proteins
Surface view of nuclear envelope
Proteins are shipped to
specific locations in the
cell
Some proteins enter
nucleus and assist with
copying DNA or making
RNAs
Figure 5.5
„
Molecules enter the nucleus through the nuclear pores
The endomembrane system is the site of biomolecule synthesis.
Rough ER (with ribosomes attached)
Smooth ER (no ribosomes attached)
Nucleus
Nucleus
Cytoplasm
Golgi apparatus
Cytoplasm
3
How do proteins destined for secretion enter
the endomembrane system?
Secreted proteins follow a pathway
THE SECRETORY PATHWAY: A MODEL
RNA
Rough ER
THE SIGNAL HYPOTHESIS
1. Secreted
proteins enter ER
as they are being
synthesized by
ribosome.
RNA
Signal sequence
2. Protein exits
ER in vesicle.
cis face of Golgi
apparatus
Ribosome
Receptor
Golgi apparatus
3. Protein travels
through the
cisternae of the
Golgi apparatus.
Interior of rough
ER
4. Protein enters
a secretory
vesicle that fuses
with cell membrane.
trans face of
Golgi apparatus
1. Signal sequence is
synthesized by
ribosome.
Plasma membrane
5. Protein is
secreted from cell.
Glycosylation adds carbohydrate groups to proteins
H2N
3. Protein enters ER.
Signal sequence is
removed.
How are proteins sorted into vesicles?
How are these vesicles targeted to a destination?
PROTEIN SORTING AND VESICLE TARGETING
COOH
Protein
2. Signal sequence
interacts with receptor
protein in ER
membrane.
Interior of Golgi
apparatus
1. In the endomembrane
system, proteins bound for
different destinations are
given different carbohydrate
"tags."
2. Proteins are sorted in the
Golgi apparatus.
Carbohydrate group
Asn
3. Transport vesicles bud
from the Golgi apparatus and
travel to their destinations.
N-acetylglucosamine
Return to the ER
Mannose
Lysome
Glucose
To plasma membrane for
secretion
4. Proteins on vesicle surface
interact with receptors at
destination.
5. Vesicle delivers contents.
4
The organelles within eukaryotic cells subdivide the
cell into functional compartments
„
The cytoskeleton is the infrastructure on which most intracellular transport
occurs.
Protein subunits
Structure
Microfilaments
Actin
Two intertwined strands
7 nm
Actin subunit
Functions
• maintain cell shape
by resisting tension (pull)
• motility via pseudopodia
(see Chapter 27)
• muscle contraction
(see Chapter 43)
• cell division in animals
(see Chapter 8)
Intermediate filaments
Keratin, vimentin,
lamin, others
Fibers wound into thicker
cables
Keratin subunits
Fluorescence micrograph of
microfilaments in mammalian cells
Microtubules
α-tubulin and βtubulin dimers
Hollow tube
10 nm
• maintain cell shape by
resisting tension (pull)
• anchor nucleus and
some other organelles
How are cytoskeletal elements distributed in the cells?
Fluorescence micrograph of
intermediate filaments in mammalian cells
25 nm
Tubulin dimer
• maintain cell shape
by resisting
compression (push)
• motility via flagella
or cilia
• move chromosomes
during cell division
(see Chapter 9)
• move organelles
A motor protein moves vesicles along microtubules
Structure of kinesin
Tail
Kinesin "walks" along a microtubule track
Transport
vesicle
ATP
Stalk
Kinesin
ADP+Pi
ATP
ADP+Pi
Microtubule
Head
5
The structure of cilia and flagella
TEM of axoneme
Cilia
Flagella
75 nm
Microtubule doublet
Diagram of axoneme
Cell membrane
Central pair
Outer doublet
Dynein
Bridge
Spoke
Be
nd
How do flagella bend?
6
7