Muscle Cells

Here's a little animation:
Sarcomere
There's a lot of great review and summary in this clip, especially at the beginning!

Here's a slide of real muscle cells. If you peer closely, you can actually see the "striations" or stripes of the sarcomeres!

Stem Cells

There are two kinds of stem cell: embryonic and adult. Both kinds can either divide to produce another stem cell like themselves...or produce a more specialized cell.

Embryonic stem cells (from embryos) are truly pluripotent, meaning that they have the potential to develop into any kind of cell.
Adults tissues have stem cells as well. These cells tend to be less plastic, meaning that they can't differentiate into the variety of cells that embryonic stem cells can. They serve the purpose of replenishing lost cells (like skin or blood) .

Bone marrow might come to mind when you think of stem cells, and this is because bone marrow contains stem cells for the creation of new blood cells and is used in the post-chemotherapy treatment of leukemia.

Some adult stem cells, like those found in the umbilical cord, are pluripotent, and this is why you might have heard about "cord blood donations." These cells can differentiate into any kind of cell just like embryonic stem cells.

What can you use stem cells for? Well, think of them the same way you would think of a transplant. You can transplant new cells for a tissue that has lost cells. Wouldn't it be cool to use stem cells and regenerate heart cells that were lost to scarring from a myocardial infarction? Re-growing nerve cells in spinal injuries would also be an exciting new therapy in medicine.

Stem cells could also be used to grow groups of a specific kind of tissue for drug testing.

Want to know more?
LINK: NIH
LINK: How Stuff Works
LINK: Stem Cells in the News

The Endosymbiotic Theory

This is to supplement the Week 3 notes.

There is a very cool theory called the Endosymbiotic Theory that was proposed in the early 1970's by cell biologist Lynn Margulis to explain the origin of two types of organelle: the mitochondrion and the chloroplast.

Dr. Margulis was studying the evolution of eukaryotic cells (the more complex cells with nuclei and membrane-bound organelles...like the cells in our bodies). Her idea was that mitochondria (the ATP producing organelles) and chloroplasts (the photosynthesizing organelles) were originally free-living prokaryotic organisms (like bacteria) that were engulfed by (taken in by) other prokaryotic organisms.

Dr. Margulis wondered if, rather than being digested by their engulfers, these precursors to mitochondria and chloroplasts might have set up a long-term symbiotic relationship with their hosts.

Symbiosis: a prolonged close relationship between two organisms that often (but not always) benefits both organisms

Dr. Margulis was widely criticized for this idea when it first came out, but since then, a large and well-accepted body of evidence has been discovered to support her idea.

Remember from Lab 1... a theory in science is not a guess! An hypothesis is a guess, a theory is supported by a vast body of evidence.

The evidence for this theory includes:

---Mitochondria and chloroplasts have their own separate DNA...and the DNA is circular, like bacterial DNA.

---Mitochondria and chloroplasts divide independently from the rest of the cell

---Mitochondria and chloroplasts have their own ribosomes, and these ribosomes resemble bacterial ribosomes

---Mitochondria and chloroplasts have two membranes with slightly different structures (the inner membrane is more similar to bacterial membranes)

---The few differences in the DNA code or "DNA language" found in living things are found in mitochondria and chloroplasts (this will make more sense later in the course).

---Mitochondria and chloroplasts are around the same size as bacteria.

Mitochondria most closely resemble modern day Rickettsia bacteria...like those that cause Rocky Mountain Spotted Fever and typhus.

Below is an image of Rickettsia invading a human cell. Interestingly, these modern bacteriahave to be engulfed by a host cell in order to survive...

Chloroplasts resemble modern day cyanobacteria...which are photosynthetic bacteria.

Below is a picture of colonies of cyanobacteria:

Atomic Bonding Animations

I found a few animations that might help you review the ideas from lecture:

Really Short Covalent Bond Video

Really Short Ionic Bond Video

Longer Video (about polarity in molecules and the special properties of water)

Covalent and Ionic Bonding

Also, for fun:

A LINK to a video on the elements...check it out!