Cell Structure and Function
Chapter 4
Principles of Modern Cell Theory
• Every living organism is made up of one
or more cells.
• The smallest living organisms are single
cells.
– Cells are the functional units of multicellular
organisms.
• All cells arise from preexisting cells.
The Microscope: Viewing Cells
Relative Sizes
in Biology
•Most cells are 1-100 µm.
•Larger cells would be
too slow at exchanging
nutrients.
• Light Microscope
– Uses lenses of glass to focus visible light rays on the specimen.
– Cells first described by Robert Hooke
and refined by Anton van Leeuwenhoek
in the late 1600s.
The Microscope: Viewing Cells
• Electron Microscope
– Uses beams of electrons focused by magnetic fields.
– Transmission Electron Microscopy (TEM)
• Visualize internal features of a cell.
– Scanning Electron Microscopy (SEM)
• Visualize surface structures of a cell.
Cells Share Common Features
• Plasma Membrane
– Encloses the cell.
– Mediates interactions between the cell and its
environment.
• Cytoplasm
– The materials and structures within the plasma
membrane.
• DNA and RNA
– DNA used as a hereditary blueprint
– RNA used to copy the blueprint and implement its
construction.
• Obtain energy and nutrients from the environment.
The Plasma Membrane
• Composed of phospholipids
and proteins.
• Isolates the cells contents
from the external
environment.
• Regulates the flow of
materials into and out fo the
cell.
• Allows for interaction with
other cells and the
extracellular environment.
The Cytoplasm
• Includes all of the material between the plasma
membrane, outside the region of DNA.
• The fluid that makes up the cytoplasm is called
the cytosol.
– It consists of water,
salts, and organic
molecules.
• Location of most
metabolic activity in
the cell.
The cytoplasm is a very crowded place.
Two Types of Cells
Prokaryotic Cells
• Prokaryotic: “before the nucleus”
– Bacteria and Archaea
– “Simpler” life forms
• Eukaryotic: “true nucleus”
– Bodies of animals, plants, fungi, and protists.
– Possess many more organelles which contribute to
complexity
• membrane bound structures that perform specific
functions.
The Prokaryotic Cell
Unique Properties of Prokaryotes
• Nucleoid
– Regional location of non-membrane bound
circular chromosomal DNA.
• Plasmids
– Small rings of DNA that are located outside
the nucleoid.
• Novel Propulsion and Attachment
– Prokaryotic flagella (movement)
– Pili (attachment and sharing)
Prokaryotic Flagella Assembly
Prokaryotic Flagella Assembly
• The Prokaryotic flagella is a long helical filament
made of many protein subunits.
- The motor is assembled inside the cell in concentric rings
that use H+ for power to rotate at 20,000rpm.
- The filament pushes through the membrane and assembles
20-30,000 protein subunits folding on the outside of the cell.
Animated video from Dr. Keiichi Namba.
http://www.nanonet.go.jp/english/mailmag/2004/011a.html
Thiocapsa sp.
The Eukaryotic Animal Cell
Prochlorococcus Nitrosococcus
Helicobacter pylori
Anabaena
Planctomyces Desulfovibrio desulfuricans
Beggiatoa
Prokaryotic
Diversity
Leptospira
http://www.nanonet.go.jp/english/mailmag/2004/011a.html
Agrobacterium
The Eukaryotic Plant Cell
Cytoskeleton
Made up of thin
microfilaments,
medium-sized
intermediate filaments,
and thick microtubules.
Cytoskeleton
Functions of the Cytoskeleton
• Intermediate filaments determine cell shape.
• Microtubules and microfilaments assemble
and disassemble, causing cell movement.
• Microtubules and microfilaments move
organelles within the cell.
• Microfilaments form centrioles, the spindle
that apportions the genetic material during
cell division.
Movement in Eukaryotes
• Cilia are shorter and more
numerous.
– Rowing motion.
• Flagella are longer and
fewer in number.
– Provide force perpendicular
to the cell membrane.
• Both are composed
of microtubules.
The Nucleus
• Organelle that houses
genomic DNA.
• The nuclear envelope
is a double membrane
dotted with nuclear
pores.
Nuclear pores keep nuclear
material in, while allowing water,
ions, and small molecules to pass.
Chromatin
• The interior of the nucleus is filled with
chromatin, DNA associated with proteins,
which form chromosomes for cell division.
Chromosomes are long
strands of DNA and its
associated proteins that
become “condensed”
(thicker and shorter) for
cell division.
Nucleolus
• “Little Nuclei”
• Site of ribosome
synthesis.
• Consists of ribosomal
RNA (rRNA), proteins,
ribosomes in stages of
synthesis, and DNA.
– DNA contains the
genes for rRNA.
Ribosomes
• Two subunit complex of RNA
and proteins.
• Synthesize proteins from
messenger RNA (mRNA).
• Located freely throughout the
cytoplasm or associated with
the nuclear envelope and
endoplasmic reticulum.
Protein structures from the RCSB Protein Databank
The Cytoplasm Contains a
System of Membranes
• A set of membrane bound organelles that
connect the nucleus with the outside.
• Three major components:
– The endoplasmic reticulum
• Contacts the nucleus directly.
– Vesicles
• Membrane bound sacs that act as shuttles between to
an from the organelles.
– The golgi apparatus
• Final modifications to the exported product.
The Endoplasmic Reticulum (ER)
• “Network within the cytoplasm”
• Interconnected membrane-enclosed
tubes and channels through the
cytoplasm.
•Composed of two parts:
•Smooth ER
•Without ribosomes.
•Rough ER
•With ribosomes.
• Smooth Endoplasmic Reticulum:
• Without ribosomes.
• Manufacture of lipids.
• Detoxification in the liver.
• Creates vesicles through budding.
• Rough Endoplasmic Reticulum:
• With ribosomes.
• Site of protein synthesis.
• Manufacture of membrane proteins,
digestive enzymes and protein hormones
• Synthesis of new ER membrane.
• Aide in tertiary structure folding.
Protein Synthesis
and Export
5
4
3
2
1
1. The protein is synthesized on
ribosomes and transported into
channels of the rough ER.
2. Protein is packaged into vesicles.
3. Vesicles fuse with Golgi and
carbohydrates (or other
modification) are added.
4. Completed protein is packaged
in vesicles.
5. Vesicles merge with the plasma
membrane to release the protein.
The Golgi Apparatus
• Set of membranes
derived from the ER.
• Modify, sort, and
package proteins:
– Modifies some molecules
• Example: adding carbohydrates
make glycoproteins.
– Synthesizes polysaccharides
• Example: Cellulose and pectin.
– Sorts proteins and lipids from the ER to their
destination.
– Packages molecules into vesicles for transport.
Lysosomes
• The cell’s digestive system.
• Enclosed vesicles housing digestive
enzymes (to break apart “food” subunits)
• Merge with food vacuoles to digest “food”
into amino acids, fatty acids, and
monosaccharides.
• Recycle by breaking down defective
organelles and membrane sections.
Food Vesicles
Recycling
Formation of
Lysosomes and
Food Vacuoles
4
3
1.
2.
3.
4.
2
1
Enzymes synthesized in ER.
Golgi modifies enzymes.
Lysosome buds from Golgi.
Lysosome fuses with food
vacuole and enzymes
digest food.
Contractile vacuoles of
freshwater protists
• Contains a pore to release excess liquid and salts acquired
through osmosis.
Vacuoles
• Sacs of cellular membrane filled with fluid
containing various molecules.
– Temporary vacuoles include food and recycling
vacuoles visited by lysosomes.
– Permanent vacuoles help maintain cell integrity
by regulating water.
•Contractile vacuoles
of freshwater protists.
•Central vacuoles of
plant cells.
Central vacuoles of plant cells
• Regulator of
water balance.
• Dump site for
toxins.
• Storage for
sugars and
amino acids.
• Provides rigidity
for cell shape.
Energy Generation in Cells
• Through two organelles:
– Mitochondria
•Convert sugar to ATP.
– Chloropasts
Mitochondria
• “Powerhouse of the cell”
• Allow eukaryotic cells to use oxygen in the
otherwise anaerobic digestion of food, obtaining
16x more ATP.
•Capture energy from sunlight.
• Both thought to be evolved from bacterial
endosymbionts.
– Organisms living within another organism for the
mutual benefit of both species.
– Ribosomal RNA of both organelles matches that
of bacteria, not eukaryotes.
Mitochondria
• Found in higher numbers in very active cells.
• Example: Muscles
• Less abundant in less active cells.
• Example: Bone and cartilage.
Chloroplast
• Organelle where photosynthesis occurs.
• Found in all plant cells and some protists.
• Contain chlorophyll which directly captures
energy from the sun.
Bioflix Animations
of Animal and Plant Cells
Bioflix can be found in the Study Area of Mastering Biology.
Homework
Read the article by Keiichi Namba on the
Prokaryotic flagella, and the section in your
book titled "Cilia and Flagella…" with Figure 4-6
and 4-7 on the Eukaryotic flagella.
Compare and contrast how the Prokaryotic and
Eukaryotic flagella are made and organized, and
how they move a cell. Be sure to discuss one
thing unique about each structure.