Video 1
Archaea
More than a century, after the discovery of the cell nucleus, it was believed that there were two fundamental types of life on Earth: bacteria and everything else. Bacteria were classified as prokaryotes. These were simple, single-celled organisms with their DNA contained, not within a nucleus, but by the cell wall. All other life forms were classified as eukaryotes. Their cells carry their DNA enclosed within the nucleus. But this simple classification system was in for a shock.
In 1977, biologist Carl Woese was studying the genetic makeup of a methane-producing microbe. When he realized it was different from any known bacteria. Its cell wall was unique. It produced unusual enzymes and its genetic sequence was unlike anything he had ever seen.
" It became soon apparent with the scope of an hour, there were something, a third thing out there."
This is the moment of discovery. Carl Woese has found the third form of life- a group of single-celled organism that he called Archaea.
" We used to think there were two primary kingdoms on this planet. Now we know there are three, that was the shift, big shift. Because all of the microbiology has been structured around the idea that all the bacteria are fundamentally the same, not in their details but in their essence, their ancestry and the basic cell organization. Here is something every microbiologist and virologist firmly believed in. And it wasn’t true. So it does make us smile, doesn’t it? The life out."
What he found was a life form able to live anywhere on the planet, including the most extreme environments. Some archaea even called this home, hydrothermal vents on the ocean floor. Temperatures here fluctuate wildly within just a few inches, going from freezing to a scorching 760 degrees Fahrenheit. Archaea have also been found living in miles inside of the earth, thriving in lakes of acid where even iron minerals dissolved.
Today some biologists believe the archaea are the common ancestor from which eukaryotes evolve, and that includes you and me.
Video 2
Overview of cell structure cell
Cells are the smallest living units of an organism. All cells have three things in common, no matter what types of cells they are. All cells have a cell membrane, which separates the inside of the cell from the environment. Cytoplasm, which is a jelly-like fluid, and DNA, which is the cell’s genetic material. There are two broad categories of cells. The first category is eukaryotic cells. They have organelles, which include the nucleus and other special parts. Eukaryotic cells are more advanced complex cells such as those found in plants and animals. The second category is prokaryotic cells. They don’t have a nucleus or membrane-enclosed organelles. They do have genetic material but it’s not contained within a nucleus. Prokaryotic cells are always one-celled or unicellular organisms such as bacteria.
So what are organelles? Organelle means “little organ”. Organelles are the specialized parts of cell that have unique jobs to perform. Let’s start with the nucleus, the control center of the cell. The nucleus contains DNA or genetic material. DNA dictates what the cells is going to do and how it’s going to do it. Chromatin is the tangled spread-out form of DNA found inside the nuclear membrane. When the cell is ready to divide, DNA condenses into structures known as chromosomes. The nucleus also contains a nucleolus which is the structure where ribosomes are made.
After ribosomes leave the nucleus, they will have the important job of synthesizing or making proteins. Outside the nucleus, the ribosomes, and the rest of the organelles, float around in the cytoplasm, which is the jelly-like substance. Ribosomes may wander freely within the cytoplasm, or attach to the endoplasmic reticulum, sometimes abbreviated as “ER”. There are two types of ER, rough ER has ribosomes attached to it, and smooth ER doesn’t have ribosomes attached to it. The endoplasmic reticulum is a membrane-enclosed passageway for transporting materials such as the protein synthesized by ribosomes. Proteins and other materials emerge from the endoplasmic reticulum in small vesicles where the Golgi apparatus, sometimes called the Golgi body receives them. As proteins move through the Golgi body, they are customized in the forms that cells can use. The Golgi body does this by folding the proteins into usable shapes or adding other materials onto them such as lipids or carbohydrates. Vacuoles are sac-like structures that store different materials. Here, in this plant cell, the central vacuole stores water. Going back to the animal cell, you’ll see an organelle called a lysosome. Lysosomes are the garbage collectors that take in damaged or worn-out cell parts. They are filled with enzymes that break down the cellular debris.
The mitochondrion is an organelle that is the power house for both animal and plant cells. During a process called cellular respiration, the mitochondria make ATP molecules that provide the energy for all the cells activities. Cells that need more energy have more mitochondria. Meanwhile, the cell maintains its shape through a cytoskeleton. The cytoskeleton includes the thread-like microfilaments which are made of protein and microtubules which are thin hollow tubes. Some organisms such as plants that are photoautotrophic, meaning they capture sunlight for energy, have cells with an organelle called a chloroplast. The chloroplast is where photosynthesis happens. It is green because it has a green pigment called chlorophyll. Plant cells also have a cell wall outside their cell membranes that shape, support and protect the plant cell. Animal cells never have a cell wall.
There are many other unique structures that only some cells have. Here are just a few. In humans, for example, the respiratory tract is lined with cells that have cilia. This are microscopic hair-like projections that can move and waves. This feature helps trap inhaled particles in the air and expels them when you cough. Another unique feature in some cells is flagella. Some bacteria have flagella. A flagellum is like a little tail that can help the cell move or propel itself. The only human cell that has a flagellum is the sperm cell.
In summary, remember, eukaryotic cells are plant and animal cells with a nucleus and membrane-enclosed organelles. While prokaryotic cells are unicellular organisms without these things. All cells have a cell membrane, cytoplasm and genetic material. And even though only plant cells have chloroplast, both plant and animal cells have mitochondria.
