DNA, RNA and protein synthesis

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1 DNA, RNA and protein synthesis DNA is deoxyribonucleic acid DNA contains all the genetic instructions for making proteins within the cell. Each DNA molecule is made of repeating subunits called nucleotides. One nucleotide looks like this: There are 4 types of nitrogenous bases. (*Contains nitrogen.) Adenine (A) Guanine (G) Cytosine (C) Thymine (T) Phosphate group Deoxyribose sugar DNA Structure: DNA is a double -stranded molecule, and the bases pair up in a specific way. A will only bond with T C will only bond with G **Here s a hint the straight -line letters go together and the curvy -line letters go together! The shape of the DNA molecule is called a double-helix, which looks like 2 spirals wound around each other. Rosalind Franklin was the first person to take an x-ray picture of DNA, but James Watson and Francis Crick interpreted the photo and won a Nobel prize for their work!

2 DNA is complementary, which means that bases on one strand will match up with bases on the other strand. Example: ATG GGC CTA _TAC CCG GAT During mitosis, each cell must copy its DNA so each daughter cell has a complete copy. DNA Replication is called semiconservative, which means that 2 strands of DNA are produced each new molecule has one old strand and one new strand. DNA Replication 1. The original DNA strand unzips, exposing the bases on the other side of the molecule. 2. DNA Polymerase (an enzyme) attaches to one side of the molecule. 3. Free-floating nucleotides in the nucleus match up with their complementary bases and are incorporated into the DNA molecule. Safety First! DNA NEVER leaves the nucleus!!!!! Since DNA is the master copy of the directions that a cell needs to survive, it must be protected! DNA in the nucleus is SAFE! DNA in the cytoplasm can be destroyed_!

3 Problem If DNA is the pattern for all the proteins and enzymes in the cell and all proteins are made at the ribosomes in the cytoplasm How do we get the pattern to the assembly line if it s locked in the nucleus???? Solution! DNA can t leave but a messenger can! RNA is a copy of DNA that can go out into the cytoplasm. DNA RNA nucleus RNA How many strands? RNA = ribonucleic acid (different sugar ) DNA 2 1 RNA Nucleotide subunit Phosphate Group Deoxyribose Sugar Nitrogen Base Phosphate Group Ribose Sugar Nitrogen Base Bases Deoxyribose sugar Thymine (T) Adenine (A) Guanine (G) Cytosine (C) T A G C Ribose sugar Uracil (U) Adenine (A) Guanine (G) Cytosine (C) U A G C

4 Types of RNA There are three different types of RNA and each has a specific function. mrna = Messenger RNA -- delivers the pattern to the ribosome trna = Transfer RNA delivers an amino acid to the growing protein rrna = Ribosomal RNA makes up the ribosome (site of protein synthesis ) The Birth of RNA mrna is made in a process called transcription. One segment of the DNA code is copied using RNA nucleotides -- almost like taking notes from a lecture! DNA = A C G T T G C A A RNA = U G C A A C G U U **Remember that U replaces T in RNA! Genes A gene is a stretch of DNA that codes for a particular trait. mrna The mrna detaches from the gene in DNA and moves out of the nucleus and into the cytoplasm. The mrna then attaches to a ribosome (made of RNA and protein ) and begins the process of translation. Translation takes the language of DNA bases and changes it to amino acids. DNA Sequence Each group of three bases is called a codon, and each codon provides the code for one amino acid. ***We know that many amino acids make a protein...and that the sequence of amino acids is important! It s the sequence of amino acids that determines the type of protein produced! Remember: proteins are made of LONG chains of amino acids. There are only 20 different kinds of amino acids, but billions of different types of proteins! ***The sequence of bases in DNA determines the order of amino acids in the protein!!!!

5 DNA RNA Protein The mrna has the pattern, but needs some help to bring the amino acids in the correct order! Each trna molecule can carry one type of amino acid. The other end has 3 unpaired bases called the anticodon. The anticodon is complementary to a codon on the mrna. The trna can only attach where the anticodon matches the mrna codon! So the mrna directs the order of trna molecules, which assembles the amino acids in a specific sequence!

6 nucleus Quick Summary: 1. _DNA is the pattern for making _mrna 2. mrna leaves the _nucleus and attaches to a ribosome DNA { } cytoplasm mrna transcription 3. _trna decodes the mrna message and brings amino acids to build the protein. ribosome trna anticodon amino acid trna Amino acid Anticodon_ (3 bases on trna): Matches up to codon on mrna translation protein 4. Protein_ detaches from the ribosome and goes off to work in the cell