GMA Biology
organized (not written) by Julie Thompson Seal coachjulieseal@yahoo.com
After The Pattern
D&C 15:14 And again, I will give unto you a pattern in all things, that ye may not be deceived....
We are made from one cell. A baby starts as one complete cell that begins to furiously replicate or copy itself over and over again. This process where a cell replicates its contents and then divides into two new cells that are identical to each other is called MITOSIS.
Mitosis has been organized by scientists into 5 phases.
Prophase: A cell gets the idea that it is time to divide. First, it has to get everything ready. You need to duplicate DNA, get certain pieces in the right position (centrioles), and generally prepare the cell for the process of mitotic division.
Metaphase: Now all of the pieces are aligning themselves for the big split. The DNA lines up along a central axis and the centrioles send out specialized tubules that connect to the DNA. The DNA (chromatin) has now condensed into chromosomes. Two strands of a chromosome are connected at the center with something called a centromere. The tubules actually connect to the centromere, not the DNA.
Anaphase: Here we go! The separation begins. Half of the chromosomes are pulled to one side of the cell; half go the other way. When the chromosomes get to the side of the cell, it's time to move on to telophase.
Telophase: Now the division is finishing up. This is the time when the cell membranecloses in and splits the cell into two pieces. You have two separate cells each with half of the original DNA.
Interphase: This is the normal state of a cell. We suppose that when it comes to cell division, you could call this the resting state. It's just going about its daily business of surviving and making sure it has all of the nutrients and energy it needs. It is also getting ready for another division that will happen one day. It is duplicating its nucleic acids, so when it's time for prophase again, all the pieces are there.
The Protein Kinesin transports DNA molecules or Chromosomes down the microtubule to the spindle pole.
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. Inprokaryotes, DNA floats in the cytoplasm in an area called the nucleoid.
Chromosomes are not always visible. They usually sit around uncoiled and as loose strands called chromatin. When it is time for the cell toreproduce, 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.
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.
DNA is an essential molecule for life. It acts like a recipe holding the instructions telling our bodies how to develop and function.
What does DNA stand for?
DNA is short for deoxyribonucleic acid.
What is DNA made of?
DNA is a long thin molecule made up of something called nucleotides. There are four different types of nucleotides: adenine, thymine, cytosine, and guanine. They are usually represented by their first letter:
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A- adenine
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T- thymine
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C - cytosine
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G - guanine
Holding the nucleotides together is a backbone made of phosphate and deoxyribose. The nucleotides are sometimes referred to as "bases".
Different Cells in the Body
Our bodies have around 210 different types of cells. Each cell does a different job to help our body to function. There are blood cells, bone cells, and cells that make our muscles.
How do cells know what to do?
Cells get their instructions on what do to from DNA. DNA acts sort of like a computer program. The cell is the computer or the hardware and the DNA is the program or code.
The DNA Code
The DNA code is held by the different letters of the nucleotides. As the cell "reads" the instructions on the DNA the different letters represent instructions. Every three letters makes up a word called a codon. Every codon corrosponds with a specific amino acid. (Amino acids strung together make proteins.) A string of codons may look like this:
ATC TGA GGA AAT GAC CAG
Even though there are only four different letters, DNA molecules are thousands of letters long. This allows for billions and billions of different combinations.
Genes
Within each string of DNA are sets of instructions called genes. A gene tells a cell how to make a specific protein. Proteins are used by the cell to perform certain functions, to grow, and to survive. Genes are made of DNA, and so is the genome itself. A gene consists of enough DNA to code for one protein, and a genome is simply the sum total of an organism's DNA.. Human genes are commonly around 27,000 base pairs long, and some are up to 2 million base pairs.Very simple organisms tend to have relatively small genomes. The smallest genomes, belonging to primitive, single-celled organisms, contain just over half a million base pairs of DNA.But among multicellular species, the size of the genome does not correlate well with the complexity of the organism. The human genome contains 3 billion base pairs of DNA, about the same amount as frogs and sharks. But other genomes are much larger. A newt genome has about 15 billion base pairs of DNA, and a lily genome has almost 100 billion.
Shape of the DNA Molecule
Although DNA looks like very thin long strings under a microscope, it turns out that DNA has a specific shape. This shape is called a double helix. On the outside of the double helix is the backbone which holds the DNA together. There are two sets of backbones that twist together. Between the backbones are the nucleotides represented by the letters A, T, C, and G. A different nucleotide connects to each backbone and then connects to another nucleotide in the center.
Only certain sets of nucleotides can fit together. You can think of them like puzzle pieces: A only connects with T and G only connects with C.
