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DNA = DEOXYRIBONUCLEIC ACID blueprint of life (has the instructions for making an organism) established by James Watson and Francis Crick codes for your genes shape of a double helix made of repeating subunits called nucleotides Gene - a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color..etc), a gene is a stretch of DNA. Nucleotide - consists of a sugar, phosphate and a base . Nucleotides (also called Bases): Adenine, Thymine, Guanine, Cytosine or A, T, G, C Nucleotides pair in a specific way - called the Base-Pair Rule: Adenine pairs to Thymine Guainine pairs to Cytosine *The rungs of the ladder can occur in any order (as long as the base-pair rule is followed) How the code works For instance, a stretch of DNA could be AATGACCAT - which would code for a different gene than a stretch that read: GGGCCATAG. Those 4 bases have endless combinations just like the letters of the alphabet can combine to make different words. DNA REPLICATION Replication is the process where DNA makes a copy of itself. Why does DNA need to copy? Simple: Cells divide for an organism to grow or reproduce, every new cell needs a copy of the DNA or instructions to know how to be a cell. DNA replicates right before a cell divides. DNA replication is semi-conservative. That means that when it makes a copy, one half of the old strand is always kept in the new strand. This helps reduce the number of copy errors. RNA = Ribonucleic Acid DNA remains in the nucleus, but in order for it to get its instructions translated into proteins, it must send its message to the ribosomes, where proteins are made. The chemical used to carry this message is Messenger RNA (mRNA). RNA is similar to DNA except: 1. has on strand instead of two strands. 2. has uracil instead of thymine 3. has ribose instead of deoxyribose mRNA has the job of taking the message from the DNA to the nucleus to the ribosomes. Transcription - RNA is made from DNA Translation - Proteins are made from the message on the RNA Gene Expression Three Important Points to Remember Chromosomes are made of DNA Segments of DNA code for a protein Protein in turn, relates to a trait (eye color, enzymes, hormones, etc) How are Proteins Synthesized from DNA 1. DNA is transcribed into mRNA (messenger RNA) 2. mRNA leaves the nucleus and travels to the cytoplasm 3. Ribosomes in the cytoplasm use the code on mRNA to translate it into amino acids 4. Amino acids form a chain - a protein Sounds simple, huh? Well, you're not getting off that easy, now we will break down each step of the process. Transcription Animation of Transcription: http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html RNA is very similar to DNA with the following exceptions: it is single stranded it has uracil instead of thymine it has the sugar ribose, instead of deoxyribose The base-pair rule is followed during transcription, except, instead of pairing thymine with adenine, when creating an RNA strand, uracil is used DNA Strand: T G C A T C A G A RNA Strand: A C G U A G U C U Transcription begins on the area of DNA that contains the gene. Each gene has three regions: 1. Promotor - turns the gene on or off 2. Coding region - has the information on how to construct the protein 3. Termination sequence - signals the end of the gene RNA Polymerase is responsible for reading the gene, and building the mRNA strand. It reads only the 3' to 5' strand. Still confused: Check on these animations: http://www.ncc.gmu.edu/dna/mRNAanim.htm http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf Translation Animation of translation: http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html 1. The mRNA travels to the cytoplasm 2. Amino acids exist freely in the cytoplasm, many of them you acquire from your diet 3. Each 3 bases (codon) translates to a single amino acid. 4. The ribosome looks for the "start" codon - AUG, this is where the chain begins 5. Transfer RNA (tRNA), has an anticodon at one end and an amino acid at the other, it binds to a complementary codon. 6. Another tRNA reads the next codon, the amino acid attached to it binds with the amino acid on the previous tRNA using a peptide bond. The first tRNA falls off. 7. This process continues until the "stop" codon is reached. 8. The amino acid chain folds into a 3 dimensional structure, now a protein. 9. That protein can be an enzyme, a hormone, or any other structure in the body that gives it traits and functionality. Still confused? Check out other animations: http://www.cat.cc.md.us/biotutorials/protsyn/translat.html http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf Test for Understanding A DNA sequence has the following bases: T A C - A G A - T T A - G G G - A T T What amino acids does it code for?