<p> Protein Synthesis</p><p> A gene is a segment of DNA that is located on a chromosome and codes for a hereditary characteristic. The gene directs the making of the protein melanin in hair follicle cells.</p><p> Transcription-The synthesis of RNA from DNA</p><p> Translation – RNA directs the assembly of proteins</p><p> Protein synthesis- Forming proteins based on information in DNA and carried out by RNA</p><p>RNA Structure </p><p>1. RNA contains the sugar ribose instead of deoxyribose</p><p>2. RNA contains the nitrogenous base uracil in place of thymine</p><p>3. RNA is usually single stranded not double stranded</p><p>4. RNA is much shorter than DNA, usually the length of one gene</p><p>5. Adenine pairs with uracil and cytosine pairs with guanine</p><p>Types of RNA</p><p>Cells have three major types of RNA. Each plays a different role in protein synthesis.</p><p>1. messenger RNA (mRNA)- a single stranded molecule that carries the instructions from a gene to make a protein. It carries the genetic message from DNA to the ribosomes.</p><p>2. ribosomal RNA (rRNA)- It is part of the structure of the ribosome and help in building the structure of proteins.</p><p>3. transfer RNA (tRNA)- They transfer amino acids from the cytosol to the ribosomes.</p><p>Transcription</p><p> The process by which the genetic instructions in a specific gene are transcribed into an RNA molecule.</p><p> It takes place in the nucleus of eukaryotic cells and in the cytosol of prokaryotic cells</p><p>Steps of Transcription</p><p>1. RNA polymerase binds to a promoter on DNA. A promoter is specific nucleotide sequence of DNA.</p><p>2. When RNA polymerase binds to DNA it unwinds and unzips the area that needs to be copied. 1 3. RNA polymerase adds free RNA nucleotides that are complementary to the nucleotides on one side of the DNA strand. The resulting chain is an RNA molecule.</p><p>4. If the DNA strand is ATCGAC the corresponding RNA strand would be UAGCUG.</p><p>5. As RNA polymerase passes a DNA region during transcription the region rewinds.</p><p>6. When RNA polymerase gets to the end of a gene it reaches a termination signal, a specific sequence of nucleotides that marks the end of a gene.</p><p>7. Upon reaching a stop signal, RNA polymerase releases the DNA and newly formed RNA molecules.</p><p>8. Transcription can make mRNA, rRNA, and tRNA.</p><p>The Genetic Code</p><p> Three adjacent nucleotides in mRNA specify an amino acid. </p><p> Each group of three nucleotide sequence in mRNA is called a codon.</p><p> There are 64 mRNA codons. The genetic code is nearly universal to all living things and supports the idea that all organisms share an ancient common ancestor.</p><p> Some amino acids are encoded by 2,3,or more different codons.</p><p> No codon encodes more than one amino acid.</p><p> AUG is the amino acid methionine and also is the start codon and tells a ribosome to start translation.</p><p> UAA, UAG, and UGA are stop codons and tell the ribosome to stop translation. They do not code for an amino acid.</p><p>Translation- the decoding of the genetic instructions to make a protein</p><p> All three types of RNA are involved in making a protein.</p><p> Every protein is made of one or more polypeptides.</p><p> Polypeptides are chains of amino acids. There are 20 different amino acids found in the proteins of living things.</p><p> Each protein may consist of hundreds or thousands of the 20 different amino acids arranged in a specific to each protein.</p><p> The amino acid sequence will determine the proteins three dimensional shape. 2  The shape of a protein determines its function.</p><p>Steps of Translation</p><p>1. Initiation</p><p> a. mRNA enters the ribosome.</p><p> b. rRNA reads the mRNA strand and assists in the assembly of proteins</p><p> c. tRNA has a 3 nucleotide anticodon on one end and its corresponding amino acid attached to its other end. It gets the amino acid from the cytosol.</p><p> d. tRNA carrying the amino acid methionine at one end and the anticodon UAC on the other end pairs with the start codon AUG on the mRNA. </p><p> e. The first amino acid in all polypeptides is methionine but it can be removed later.</p><p>2. Elongation</p><p> a. A tRNA carrying the appropriate amino acid pairs its anticodon with the second mRNA codon.</p><p> b. The ribosome then detaches methionine from the first tRNA and a peptide bond forms between methionine and the second amino acid.</p><p> c. The first tRNA then exits the ribosome.</p><p> d. The ribosome then moves a distance of one codon along mRNA.</p><p> e. Steps a through d continues to add amino acids lengthening the polypeptide.</p><p>3. Termination</p><p> a. The process ends when a stop codon is reached. </p><p> b. A stop codon is one for which there is no tRNA that has a complementary anticodon.</p><p>4. Disassembly</p><p> a. The newly made polypeptide is released</p><p> b. The last tRNA leaves the ribosome</p><p> c. The ribosome moves away from the mRNA</p><p>*Several ribosomes may translate the same mRNA transcript at the same time. As a ribosome moves along to the next mRNA codon another ribosome can attach to the same mRNA. This allows a ribosome to make many proteins in a short period of time. 3 The Human Genome</p><p>Genome- entire gene sequence, complete genetic content</p><p> There are 3.2 billion base pairs in 23 chromosomes</p><p> There are approximately 30,000 genes</p><p> Each gene codes for a protein</p><p> We know what some of the genes control. Having this knowledge may help us to diagnose, treat, and prevent genetic disorders, cancer, and infectious diseases.</p><p>4</p>