DNA - DEOXYRIBONUCLEIC ACID

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1 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)

2 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) Adenine and Guanine= Purines Cytosine and Thymine= Pyrimidines How the code works Those 4 bases have endless combinations just like the letters of the alphabet can combine to make different words. Endless combinations result in different traits, appearances, and functions of the organism For example: compare these stretches of DNA for a fictional organism A A A T T A T T T = curly tails A A A T T A G G G = straight tails A A A T T A C C C = no tails 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.

3 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. Steps: 1. Enzymes called helicases separate the DNA strands. As the DNA strand separates at the hydrogen bonds, a Y-shaped region will develop. This is called a replication fork. 2. Enzymes called DNA polymerases add complimentary nucleotides to the new and the original strands. 3. DNA finish replicating and then they fall off the strands. to help you understand DNA replication. you can use this or the above diagram

4 RNA 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 RNA = ribonucleic acid. 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

5 Types of RNA: 1. mrna- messenger RNA, this carries the instructions from a gene in the nucleus to the ribosome to make a protein 2. rrna- ribosomal RNA, a part of the structure of ribosomes 3. trna-transfer RNA, transfers amino acids to the ribosome to make a protein. Steps of Transcription: Occurs in the Nucleus 1. An enzyme called RNA polymerase (catalyzes the formation of RNA on a DNA template) will bind to a promoter causes the DNA strands to unwind and separate. 2. RNA polymerase will then add RNA nucleotides that are complimentary to the DNA strand. This will only be done on a specific region on one of the two DNA strands. 3. RNA polymerase will reach a termination signal that signals the RNA to quit transcribing for that specific gene so then it can eventually move onto a new gene.

6 Translation and the Genetic Code (occurs in the cytoplasm on the ribosome) Genetic Code: the term for the rules that relate how a sequence of nitrogenous bases in nucleotides corresponds to a particular amino acid. Three adjacent nucleotides (letters) in the mrna specify an amino acid (word found of the chart below) in a polypeptide Each of these three nucleotides that come together to specific a specific amino acid or signals a start/stop signal is called a codon. There are 20 different amino acids mrna code of AUG codes for the Methionine or start DNA= TCA mrna=agu Amino Acid=Serine All genes will begin with a start codon and end with a stop codon in order to produce a protein. Translation occurs using all three types of RNA. Each trna molecule will bind up with the mrna with the complimentary bases. The nucleotides found on the trna are called the anti-codons. These anticodons will bond with the codons in the mrna to be able to form the appropriate amino acid for that codon. You can refer to pages for more details regarding this.

7 Here are some visuals to help you better understand this process.