Bacteria are procaryotes|
Blue-Green algae (cyanobacteria) are also procaryotes
(one of several kinds of photosynthetic bacteria, that used to be classified with the algae)
The differences between procaryotes and eucaryotes are much more important than the differences between you and an amoeba,
or you and a pine tree, or kelp, or mushrooms, etc.
Procaryotes don't have nuclei; they have circular DNA chromosomes just floating in their cytoplasm.
Procaryotes don't have other organelles, either (mostly)
Also no histone proteins, no microtubules, no mitotic spindles.
Bacterial "flagella" (by which they swim) turned out to be completely different from eucaryote flagella.
Only about 5,000 species of procaryotes have been "described"!
Archaea are a recently-discovered taxonomic group, somewhat more complex that procaryotes, but almost like bacteria.
Archaea DO have histone proteins, for example.
All other living things, animals, plants, fungi, protozoa, etc.
Eucaryotes have their genes on multiple linear chromosomes
Nuclei have nuclear pores. These control stuff going in & out
The DNA of eucaryotes is tightly bound to special kinds of protein called histones (which are extremely conservative in evolution, with almost exactly the same amino acid sequence in humans as in, say, peas; only 2 different, out of hundreds)
Another organelle that (almost) all eucaryotic cells have are mitochondria. These also have inner and outer membranes.
Plant cells have chloroplasts, which are yet another organelle.
Another organelle is the Endoplasmic Reticulum
One of the major researchers on the ER was George Palade,
There are other organelles, including vacuoles, lysosomes, and something called the Golgi Apparatus.
Each kind of organelle has its own special kinds of proteins.
"Put me in the nucleus" is: Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val
Special proteins already in each kind of organelle membrane grab any copy of "their" signal peptide, and pull it and all the rest of whatever protein it is attached to, and pull it into that organelle.
This was proven by experiments in which genes were changed so that certain proteins began with the 10 or 20 amino acid sequence that some other protein would normally have; which caused these altered proteins to get put in the wrong organelle.
"Motor proteins" several kind of cytoplasmic proteins in eucaryotes can exert mechanical forces by sliding along fibers.
Myosin protein slides actively along fibers of the protein actin
Actin and myosin were first discovered in muscle cells, the active contraction of which is caused by sliding of large myosin fibers relative to actin fibers.
Dynein sliding relative to microtubules is what causes the bending of cilia and flagella; and also transports membranes and other materials from place to place in the cytoplasm.
Actin and microtubules form a meshwork called the "cytoskeleton" in most eucaryote cells, including nearly all human cells.
Questions that you should now be able to answer:
1) Which of the following are eucaryotes?
2) What structures do eucaryotes have that procaryotes don't?
*3) Which have flagella? Procaryotes or eucaryotes?
4) Where is DNA located? In procaryotes? In eucaryotes?
5) Who has circular chromosomes?
*6) About how many different species of bacteria are known to science? About how many species of animals? Which probably actually has more species? Are any still to be discovered?
7) What did mitochondria and chloroplasts evolve from?
8) What are some other organelles?
9) What are nuclear pores, and how many layers of membrane are there in nuclei?
10) By what sort of mechanism are mitochondrial proteins, nuclear proteins, or other organelle proteins caused to become located in these organelles?
11) What kind of mutation could cause one of them to get put into the wrong organelle, or to go to none of the organelles?
12) What are histones; where are they located; and which kinds of organisms have them? And which don't have them?
13) Why are tubulin and actin not considered to be motor proteins, although they are the two most important cytoskeletal proteins.
*14) If microtubules usually polymerize outward from a center near the nucleus, then would you expect to find their plus or minus ends near the edges of the cell?
*15) Can you figure out what is meant by saying that a dynein is a minus end-directed motor protein, while all myosins and (almost all!) kinesins are plus end-directed?
*16) If membranes of the endoplasmic reticulum tend to contain kinesins, while membranes of the Golgi apparatus attach to dyneins, then how can that explain the positioning of these organelles in living human cells?
**17) Can you guess whether cancer cells usually exert stronger or weaker pulling forces, as compared with equivalent normal cells, as they undergo amoeboid locomotion? What about forces exerted during amoeboid locomotion of white blood cells, as compared with structural cells (i.e. stronger or weaker?) Would you expect cancer cells' amoeboid locomotion to be more like that of white blood cells, or more like that of cells in wound healing?
**18) Certain poisons specifically prevent tubulin from forming microtubules; would you expect that these poisons would be useful in treating any particular human diseases?
*19) Can you invent some alternative possible reasons why treating cells with these tubulin poisons will cause the cells to contract more strongly than before? (about 2 1/2 times as strong)
*20) These poisons prevent normal separation of the chromosomes when plant and animal cells divide: can you invent two alternative kinds of possible mechanism, one involving kinesin, and the other nicknamed the "Pac-Man Hypothesis"?
***21) Can you figure out why histone proteins and actin have changed less than any other proteins in evolution, in the sense of having almost exactly the same amino acid sequences in humans as in plants, etc. (If you can think of reasons, please tell me)
22) Nerve fibers can be as long as 2 feet (distance from nucleus to most distant parts of the cell); How would you guess that new proteins get transported to such distant locations?
23*) Based on your suggested answer to the previous question, why would you expect that all the microtubules in the longest nerve fibers would have the same orientation (+ versus - ends), even though shorter nerve fibers contain about equal numbers of microtubules oriented in both directions (= as many with one polarity as the opposite)?
24*) Several kinds of bacteria that cause food poisoning turn out to use the actin of the infected cells to move around! Guess how they do this!
25**) Just before eucaryotic cells divide, their chromosomes gravitate to positions half way between the ends of the cells: how can this be made to happen by making strengths of pulling forces toward the ends vary as functions of each chromosome's current position in the cytoplasm
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