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2.2, 2.3 Ultrastructure of cells
Light Microscopes• Has resolution that is
sufficient to view images up to 0.2 micrometers, due to the limitations of the wavelength of light.
• Scientists ran in to problems when they wanted to see smaller things, such as in Figure 1.
New technology was needed, and thus came the Electron Microscope
Figure 1. Image from www.cytochemistry.net
Electron Microscopes• Uses beams of
electrons, rather than light, so a much clearer resolution can be achieved.
• Useful to view images down to 1 nm (0.001 micrometers)
• Useful to see images such as those of viruses and small organelles.
2.2 – Ultrastructure of cellsProkaryotes
What are they?• Prokaryotes are cells that
have no membrane-bound organelles
• Smaller than animal or plant cells
• Very Old! ~3.5 billion years old
Basic Prokaryote Structure – E.coli• One BIG
compartment
Diagrams vs Reality
Vs.
Functions of the named structures in prokaryotes
• Cell wall – provides structure, protection for the cell
• Cell membrane – provides shape, allows materials in and out of the cell (selectively permeable)
• Pili – allow attachment to other bacteria in order to share DNA
• Ribosomes – synthesize proteins for the cell• Nucleoid – region containing DNA, instructions for
cell processes• Cytoplasm – space in which metabolic reactions
can take place• Flagella – utilize whip-like motion to move the cell
Reproduction• Prokaryotes use a
method of asexual reproduction termed Binary Fission.• Binary fission allows
prokaryotes to divide in to two identical bacterium
2.3 Ultrastructure of cellsEukaryotes
Comparison of structures in Prokaryotic vs. Eukaryotic
Size DNA Nucleus Organelle
Ribosomes
Mitochondria
Prokaryote
1-3 micrometer
Closed loop
DNA in cytoplasm
“cell parts”
70S (small)
No
Eukaryotes
10-100 micrometer
Double helix
Has nuclear membrane
Membrane bound
80S (big) yes
Eukaryotic cells - Liver Cell Diagram• Draw overall
structure and label the following based on the diagram:• Golgi Apparatus• Lysosome• Mitochondrion• Free Ribosomes• Chloroplast• Vacuoles• Microtubules• Centrioles• Cilia/flagella (not
pictured)• Rough ER• Nucleus
Comparing images to diagrams
vs.
Compartmentalization• Eukaryotic cells are compartmentalized• Advantages of being so include:• Enzymes and substrates for a particular process can be
much more concentrated than if they were spread out• Potentially harmful substances can be quarantined• pH and other homeostatic levels can be managed much
more effectively• Organelles with their contents can be moved around
within the cell
Organelles and their functions• Nucleus – contains chromosomes, which are
organized raw DNA• Most of the time, they are visible as chromatin, an
unorganized form of DNA
Rough Endoplasmic Reticulum• Consists of flattened
sacs – cisternae• Ribosomes attach to
them, and fulfill protein synthesis
Golgi Apparatus• Consists of flattened membrane sacs called
cisternae, similar to the rough ER• These cisternae are shorter, have no ribosomes
attached, and have many vesicles nearby• Golgi Apparatus processes proteins brought to it
from the rER
Lysosomes• Little spherical
organelles, formed out of golgi vesicles
• Have a high concentration of protein, mostly digestive enzymes that they use to break down food particles
• Also responsible for breaking down “old” organelles and intruders, such as bacteria
Mitochondrion• Double membrane! – inner membrane is
invaginated (folded inwards) to form structures called cristae
• Produce ATP (energy for the cell) by aerobic respiration
Free Ribosomes• No membrane! – same size as ribosomes attached
to the rER, only 20 nm in length• Synthesize proteins for the cell and its
surroundings• Produced in the nucleolus
Chloroplast• Only found in photosynthetic cells• Double membrane! – performs photosynthesis• Photosynthesis produces a wide variety of compounds,
including glucose
Vacuoles• Vacuoles vary widely in size
– • Very small in animals (generally)• Very large in plants (generally)
• Used for a variety of purposes, including digestion, water balance, transport
• What do you think the function of this palisade mesophyll cell is?
Microtubules/Centrioles• Small, cylindrical fibers called microtubules that
provide structure to the cell• Centrioles are present in animal cells, and provide
an anchoring point for microtubules during mitosis
Cilia/Flagella• Whip-like structures that allow the cell to move• Comprised of a ring of double microtubules and
two central ones• While cilia and flagella can both be used for
locomotion, cilia can also be used to create a current next to the cell
Structure/Function• What do you think these
structures indicate about the cell’s function in Figure 1? SOC
What about the cell in Figure 2?SOC
Figure 1.
Figure 2.
Plant Cells• Eukaryotic, and
therefore have all the characteristics of a eukaryotic cell
• In addition to the organelles present in animal cells, plant cells also have chloroplast, a cell wall, and an enlarged vacuole.
plant
SOC