Biology 1011
General Biology I
Inside the Cell:
Cell Structure and Function
October 3, 2011
Cell theory states that all organisms are made up of cells. Like
whole organisms, each cell must be able to perform certain vital
functions for survival.
Requirements include:
Maintenance of integrity
Energy generation
Metabolism (including anabolism and catabolism)
Reproduction
Recycle or dispose of waste
Communication
Transport / movement
In organisms these functions are performed or shared among
various tissues and organs.
In cells they are performed by individual organelles.
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Organisms can be classified in many ways; one of the most basic
is whether they have a nucleus.
Prokaryote - no nucleus; DNA is not confined
Includes:
- Bacteria
- Archaea
Eukaryote - membrane-bound nucleus containing DNA
Includes:
- Algae
- Fungi
- Plants
- Animals
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Prokaryotic cells (including domains Bacteria and Archaea) are
characterized by the lack of a membrane-bound nucleus.
Ribosomes
DNA
Plasmids
Cytoplasm
20 nm
Chromosome
Flagella
Supercoiled DNA
in chromosome
Plasma
membrane
Cell wall
Plasma
membrane
Cell wall
1 m
Cytoplasm
100 nm
The interior of a prokaryotic cell is complex and highly organized.
Chromosome
Ribosome
Flagellum
Glycolipids
Cytoskeleton
Plasma
membrane
Cell wall
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Certain bacteria are able to carry out photosynthesis; this process
uses light energy to produce organic (carbon) compounds.
Photosynthetic
membranes
0.5 m
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Eukaryotes and prokaryotes have several fundamental differences.
Eukaryotes compared to prokaryotes:
- larger size (usually)
prokaryote - 1-10 μm
eukaryote - 5-100 μm
- extensive internal membranes and compartments
- chromosomes located in nucleus
- diverse and dynamic cytoskeleton
- options for single or multicellularity
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Eukaryotic cells differ in many respects from prokaryotic cells,
including size; typical animal and plant cells have 1000-fold
greater volume than typical prokaryotic cells.
Cut-away views showing organelles.
Animal cell
Bacterial cell
Plant cell
Eukaryotes v. prokaryotes: ~ 10X size, ~ 1000X volume
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Eukaryotic cells physically and functionally compartmentalized;
many cellular functions are performed by organelles.
Generalized animal cell
Centrioles
Nuclear envelope
Nucleus
Nucleolus
Chromosomes
Rough endoplasmic
reticulum
Peroxisome
Ribosomes
Cytoskeletal
element
Smooth endoplasmic
reticulum
Golgi apparatus
Lysosome
Mitochondrion
Plasma membrane
Eukaryotes v. prokaryotes: ~ 10X size, ~ 1000X volume
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Eukaryotic cells physically and functionally compartmentalized;
many cellular functions are performed by organelles.
Generalized plant cell
Nuclear envelope
Ribosomes
Nucleolus
Chromosomes
Nucleus
Cell wall
Rough endoplasmic
reticulum
Vacuole
(lysosome)
Smooth endoplasmic
reticulum
Golgi apparatus
Peroxisome
Chloroplast
Mitochondrion
Plasma membrane
Cytoskeletal element
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Cell components:
•
•
•
•
•
•
•
•
•
•
•
•
Plasma membrane
Nucleus
Ribosomes
Smooth Endoplasmic Reticulum (ER)
Rough Endoplasmic Reticulum (ER)
Golgi Apparatus
Peroxisomes
Lysosomes
Mitochondria
Chloroplasts
Cytoskeleton
Cell Wall (plant and fungi only)
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Nucleus
Nuclear pores
Loosely
packed sections
of chromosomes
Densely
packed sections
of chromosomes
Nuclear
lamina
Nucleolus
- rRNA production
Nuclear envelope
2 m
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Rough endoplasmic reticulum
Ribosomes
Lumen of
rough ER
Ribosomes
on outside
of rough ER
Free
ribosomes
in cytoplasm
200 nm
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Ribosomes
Contains RNA & proteins
- large & small subunits
- eukaryotic/prokayrotic
ribosomes similar but
different sizes
100 nm
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Golgi Apparatus cis
trans
Vesicle
Lumen
Cisternae
Vesicles
100 nm
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Smooth endoplasmic reticulum
Lumen of
smooth ER
200 nm
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Peroxisome
Peroxisome
membrane
Enzyme
core
Peroxisome
lumen
100 nm
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Lysosome
Material being
digested within
lysosomes
500 nm
Process - Phagocytosis
Phagosome
Lysosome
Transport &
recycling
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Phagocytosis of C. albicans
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Process - Autophagy
Lysosome
Damaged
organelle
Transport &
recycling
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Process - Receptor-Mediated Endocytosis
Recycling
of membrane
proteins
Early
endosome
Early
endosome
Vesicle
from Golgi
apparatus
Transport &
recycling
Late
endosome
Lysosome
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Process – Pinocytosis
Non-specific transport
of liquids or small
particles via
endocytosis
- material not
transported to
lysosomes
Wikimedia Commons; Nicolle Rager Fuller, National Science Foundation
http://www.nsf.gov/news/mmg/media/images/myosin_nucleus_h.jpg
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Mitochondrion (plural – mitochondria)
Outer
and inner
membranes
Matrix
Cristae
0.1 m
Note – double membranes
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Cytoskeleton
Plasma
membrane
Cytoskeletal
elements
Cell structure,
movement,
flexibility
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Vacuole
Note – in plants
and fungi,
not animal cells
Vacuole
1 m
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Chloroplast
Note – plants and
algae only
Stroma
Thylakoids
Granum
Outer and inner
membranes
1 m
Note – double outer membranes plus third inner membrane - thylakoid
Cell wall
Note – plants, fungi,
and algae only
Plasma
membrane
of cell 1
Plasma
membrane
of cell 2
50 nm
Cytoplasm Cell wall Cell wall Cytoplasm
of cell 1
of cell 1 of cell 2 of cell 2
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Cell components: You should be able to fill in this chart.
Structure/organelle
Membrane
structure
Components
and/or structure
Function
Plasma membrane
Nucleus
Ribosomes
Smooth ER
Rough ER
Golgi Apparatus
Peroxisomes
Lysosomes
Mitochondria
Chloroplasts
Cytoskeleton
Cell Wall
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Cell structure correlates with function.
0.5 m
Animal pancreatic
cell
Lysosomes
Golgi
rER
Animal testis cell
sER
0.5 m
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Cell structure correlates with function.
Chloroplasts
Plant leaf cell
1 m
Plant root cell
Starch
vacuoles
1 m
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Cells are dynamic, with constant movement of molecules into and
out of the cell, plasma membrane components, organelles,
cytoskeletal elements, and enzymes.
e.g.
1) Molecular diffusion and osmosis of water.
2) Plasma membrane channels and transporters; e.g.
porins, Na+/K+ ATPase.
3) Nuclear envelope: Transport of materials in and out
of the nucleus.
4) Endomembrane system: manufacturing and
shipping proteins.
5) Cytoskeleton: Energy-dependent movement of materials.
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The nucleus is highly organized; the nuclear envelope consists
of two lipid bilayers and is punctuated by numerous pores.
Cross-sectional view of nuclear envelope
0.1 m
Ribosomes,
mRNA
Nuclear lamina
Nuclear
envelope
Nuclear
pore
complex
Nuclear
matrix
DNA in
nucleus
Inner membrane
Outer membrane
Cytosol
Building blocks of DNA
and RNA, enzymes
Secreted proteins are processed by the rER and Golgi apparatus.
RNA
Ribosome
cis face of
Golgi apparatus
Rough ER
Protein
trans face of
Golgi apparatus
Plasma membrane
Proteins intended for secretion have an amino acid ‘tag’ (signal
sequence) that allows receptors on the rER to identify them.
Ribosome RNA
SRP (signal recognition particle)
Cytosol
Lumen of
rough ER
Signal
sequence
SRP receptor
Protein
(note folding)
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Many proteins are enzymatically glycosylated in the lumen of
the rough endoplasmic reticulum.
Carbohydrate
group
Protein
NH2
COOH
N-acetylglucosamine
Asparagine (often)
Mannose
= Glycoprotein
Glucose
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Nascent proteins are labeled with different carbohydrates in the
Golgi, then shipped to their destinations in corresponding vesicles.
Lumen of
Golgi apparatus
„Tags‟
To plasma
membrane
for secretion
Lysosome
Receptors
Transport vesicles
Return to
the ER
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The cytoskeleton provides support, but it is also a dynamic,
interactive network, constantly altering in content and orientation.
Major components:
Microfilaments
Plasma
membrane
Cytoskeletal
elements
Intermediate filaments
Microtubules
Also: various motor
proteins
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Microfilaments are polymers made up of actin monomers.
Monomer:
Actin
Polymer structure:
Strands in double helix
7 nm
- end
+ end
Maintains cell shape - resists tension (pull)
Note - polarized
Moves cells (cell crawling & muscle contraction)
Provides the power for cell division (animals)
Provides tracks to move organelles and
cytoplasm (plants, fungi, animals)
Microfilament
cytoskeleton
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The enzyme myosin (a motor protein) uses the energy from ATP
to move actin filaments. This is the basis of muscle movement, as
well as cytokinesis (cell division) and cytoplasmic streaming.
Myosin
“Head”
region
Actin
Note – polarized
(plus (+) and minus (-) ends)
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Intermediate filaments are static polymers made up from a large
variety of proteins; they are defined by size and composition.
Monomer:
Polymer structure:
Keratin, vimentin,
lamin, etc.
Fibers wound into
thicker cables
10 nm
Maintain cell shape
Note - non-polarized
Anchors nucleus and organelles
Intermediate
filament
cytoskeleton
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Microtubules are polymers made up from tubulin dimers.
Monomer:
Polymer structure:
α- and β-tubulin
dimers
Hollow tube
25 nm
- end
+ end
Maintain cell shape - resists compression (push)
Note - polarized
Provide power for flagella and cilia
Move chromosomes during cell division
Move proteins and organelles
Provides tracks for intracellular transport
Microtubule cytoskeleton
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Microtubules originate from microtubule organizing centers;
in animals this is found in the centrosome.
Centrosome
Centrioles (oriented
at 90° to each other)
Centrioles
200 m
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Microtubules provide the tracks for organelles, vesicles, and
chromosomes to follow.
Vesicle
Alain Viel & Robert A. Lue
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Microtubules provide the tracks for organelles, vesicles, and
chromosomes to follow. Kinesin and dynein are two enzymatic
motor proteins that provide motive force.
Vesicle
Transport
vesicle
Kinesin
Microtubule
 end
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 end
The polarity of microtubules is used by the motor protein to move
vesicles in different directions.
Kinesin
Dynein
(+)
(-)
(+)
(-)
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Microtubules also make up the axonemes that form the structure
of eukaryote cilia and flagella.
Cilia
Flagellum
50 m
10 m
75 nm
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Axonemes are constructed of microtubules, dynein ATPase,
and several additional structural elements.
Plasma membrane
Dynein ATPase
Spoke
Central microtubules
Outer doublet of
microtubules
75 nm
Link
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Dynein ATPase ‘walks’ on one side of the microtubule doublet,
forcing neighboring doublets to bend.
Link
Slide
Microtubule
doublet
Dynein arms
Microtubule
doublets
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No energy input
 ATP: Sliding causes bending