Thursday, November 11, 2010

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Biology4Kids.com: Microorganisms

Biology4Kids.com: Microorganisms

Ribosomes

Ribosomes - Protein Construction Teams

Cells need to make proteins. Those proteins might be used as enzymes or as support for other cell functions. When you need to make proteins, you look for ribosomes.Ribosomes are the protein builders or the protein synthesizers of the cell. They are like construction guys who connect one amino acid at a time and build long chains. 

Ribosomes are found in many places around the cell. You might find them floating in the cytoplasm (cytosol). Those floating ribosomes make proteins that will be used inside of the cell. Other ribosomes are found on the endoplasmic reticulum. Endoplasmic reticulum with attached ribosomes is called rough. It looks bumpy under a microscope. Those attached ribosomes make proteins that will be used inside the cell and proteins made for export out of the cell. 

Two Pieces Make the Whole

A ribosome is not just one piece. There are two pieces or subunits. Scientists named them 60-S (large) and 40-S (small). When the cell needs to make protein, mRNA is created in the nucleus. The mRNA is then sent into the cell and the ribosomes. When it is time to make the protein, the two subunits come together and combine with the mRNA. The subunits lock onto the mRNA and start the protein synthesis. 

The 60-S/ 40-S model works fine for eukaryotic cells. Prokaryotic cells have ribosomes made of 50-S and 30-S subunits. It's a small difference, but one of many you will find in the two different types of cells. Scientists have used this difference in ribosome size to develop drugs that can kill prokaryotic microorganisms that cause disease. 

Mixing and Matching Amino Acids


The process of making proteins is quite simple. We just explained that mRNA is made in the nucleus and sent into the cell. The mRNA then combines with the ribosome subunits. Another nucleic acid lives in the cell - tRNA, which stands for transfer RNA. tRNA is bonded to the amino acids floating around the cell. With the mRNA offering instructions, the ribosome connects to a tRNA and pulls off one amino acid. Slowly the ribosome makes a long amino acid chain that will be part of a larger protein. 

Chromosomes

Chromosomes - Pull up Those Genes

Chromosomes are the things that make organisms what they are. They carry all of the information used to help a cell grow, thrive, and reproduce. Chromosomes are made up of DNA. Segments of DNA in specific patterns are called genes. Your genes make you who you are. You will find the chromosomes and genetic material in the nucleus of a cell. In prokaryotes, DNA floats in the cytoplasm in an area called the nucleoid. 

Loose and Tight

Chromosomes are not always visible. They usually sit around uncoiled and as loose strands called chromatin. When it is time for the cell to reproduce, they condense and wrap up very tightly. The tightly wound DNA is the chromosome. Chromosomes look kind of like long, limp, white hot dogs. They are usually found in pairs. 

Completing the Sets

Scientists count individual strands of chromosomes. They count individuals not every organism has pairs. You probably have 46 chromosomes (23 pairs). Peas only have 12. A dog has 78. The number of chromosomes is NOT related to the intelligence or complexity of the creature. There is a crayfish with 200 chromosomes. Does that make a crayfish five times smarter or more complex than you are? No. There are even organisms of the same species with different numbers of chromosomes. You will often find plants of the same species with multiple sets of chromosomes. 

Chromosomes work with other nucleic acids in the cell to build proteins and help in cell division. You will most likely find mRNA in the nucleus with the DNA. tRNA is found outside of the nucleus in the cytosol. When the chromosomes are visible, cells with two complete sets of chromosomes are called diploids (46 in a human). Most cells are diploid. Cells with only one set (23 in a human) are called haploid cells. Haploids are most often found in cells involved in sexual reproduction such as a sperm or an egg. Haploid cells are created in cell division termed meiosis. 

Cell Structure

Cell Wall - What's it for?

While cell membranes might be around every cell, cell walls made of cellulose are only found around plant cells. Cell wallsare made of specialized sugars called cellulose. Cellulose provides a protected framework for a plant cell to survive. It's like taking a water balloon and putting it in a cardboard box. The balloon is protected from the outside world. Cellulose is called a structural carbohydrate (complex sugar) because it is used in protection and support. 

Cell walls also help a plant keep its shape. While they do protect the cells, cell walls and cellulose also allow plants to grow to great heights. While you have a skeleton to hold you up, a 100-foot tall redwood tree does not. It uses the strong cell walls to maintain its shape. For smaller plants, cell walls are slightly elastic. Wind can push them over and then they bounce back. Big redwoods need strength in high winds and sway very little (except at the top). 

Another Hole in the Wall   

A cell wall is not a fortress around the delicate plant cell. There are small holes in the wall that let nutrients, waste, and ions pass through. Those holes are called plasmodesmata. These holes have a problem: water can also be lost. But even when the plant cell loses water, the basic shape is maintained by the cell walls. So if a plant is drooping because it needs water, it can recover when water is added. It will look just the same as when it started. 

More Than Walls in Plants

You may hear about cell walls in other areas of biology. Bacteria also have a structure called a cell wall. Fungi and some ptotozoa also have cell walls. They are not the same. Only plant cell walls are made out of cellulose. The other walls might be made from proteins or a substance called chitin. They all serve the same purpose of protecting and maintaining structure, but they are very different molecules. 




Atomic Structure

The problems of language here are really serious. We wish to speak in some way about the structure of the atoms. But we cannot speak about atoms in ordinary language.

Werner Heisenberg


1.        John Dalton thought that an atom is a sphere of matter that is the same throughout. 
2.        J.J. Thomson discovered that all atoms contain electrons, which are tiny, negatively charged particles. Thomson proposed that an atom is a sphere of positive charge. The electrons are mixed uniformly in the sphere. 
3.        Rutherford updated the model of the atom. He hypothesized that almost all the mass and all the positive charge of an atom is concentrated in an extremely tiny nucleus at the center of the atom. 
                                                   Bohr described the atom as a planetary arrangement: electrons orbiting the nucleus


1.        Today's model of the atom has a concentrated nucleus containing the protons and neutrons surrounded by a cloud representing where the electrons are likely to be found.
1.        Protons are in the nucleus (center) of the atom
 i. Have a positive charge
2.        Neutrons are in the nucleus (center) of the atom
 i. Are neutral; have no charge
3.        Electrons move in energy levels outside of the nucleus
 i. Have a negative charge
2.        The number of protons in the nucleus of an atom is its atomic number
1.        It identifies which element you have.
2.        The number of neutrons plus protons in an atom is its mass number. 
3.        In a stable atom, the number of protons equals the number of electrons.
1.        Atoms that have lost or gained elctrons are called ions. 
4.        The number of protons plus the number of neutrons is the mass number.
5.        The atomic weight or atomic mass is the average of the mass numbers of all of the isotopes of an element. 
6.        Isotopes are atoms of the same elements that have different numbers of neutrons.
1.        Each isotope has a different mass number. 
7.        Electrons can spin in any direction; s cientists cannot tell exactly where an electron is at a given moment or where it is going. They can calculate the probability that an electron will be found in a given space. This is quantum mechanics. 
8.        The distance from the nucleus that the electron spins is called its energy shell, energy level, or orbital.
1.        Each energy level can only hold a certain amount of electrons
i. The first shell (K level) can hold 2 electrons
 ii. The second shell (L level) can hold 8 electrons
iii. The third level (M level) can hold 18 electrons
 iv. The fourth level (N level) can hold 32 electrons
v. The fifth level (O level) can hold 50 electrons
vi. The sixth level (P level) can hold 72 electrons
2.        Each energy level is completely filled before electrons fill the next level.
3.        The number of electrons in the outermost level are called valence electrons. 


1.        An atom's nucleus is held together by the strong nuclear force.
1.        If the numbers of neutrons and protons are very different, the nucleus can become unstable and undergo radioactive decay. 
2.        Some nuclei decay by emitting an alpha particle. 
3.        Other nuclei decay by ejecting a beta particle.
1.        Transmutation is a process in which one element changes into another through radioactive decay. 
4.        Half-life is a measure of the decay rate of a nucleus.
1.        It is the time needed for one half of the mass of a sample of a radioactive isotope to decay. 
5.        Radioactive isotopes are used in medicine and for the study of the environment.
1.        Tracer elements with short half-lives are followed through living systems to study certain things.

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How someone could define what is Science and Technology?

Science is search for the profound knowledge. Scientists investigate the world around us. They observe how things work and develop ideas about ways to make them work better. Sometimes they try to test an idea to explain how something works. Scientists perform experiments to find out how things work. The knowledge that they discover is useful for many things. It can help to build new machines. It can help scientists to develop new medicines or cure a disease. Technology is the use of scientific knowledge to create new things.