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Genetics Exam Review #2 DNA & Protein Synthesis DNA • Structure of DNA was discovered in the 1950’s by James Watson and Francis Crick in England. • They were able to determine the structure of DNA as a double helix by stealing a photograph of work done by Rosalind Franklin. DNA • DNA is made up of subunits called nucleotides. • A nucleotide is made up of three parts: sugar, phosphate and nitrogen base. • The sugar in DNA is called deoxyribose. • The four nitrogen bases in DNA are: adenine, cytosine, guanine and thymine. • DNA has base pairing rules: Adenine always pairs with Thymine and Guanine always pairs with Cytosine. DNA • What is the complementary DNA strand? T-A-C-A-G-T-C-T-A-G-G-C-A-T-C-C-A-G-C-A-T A-T-G-T-C-A-G-A-T-C-C-G-T-A-G-G-T-C-G-T-A DNA Replication • DNA replication is the process by which DNA makes an exact copy of itself prior to cell division. 1. DNA double helix unwinds. 2. DNA strand is unzipped between the nitrogen bases. The point at which it is unzipping is called the replication fork. 3. DNA Polymerase adds nucleotides to each side of the original DNA strand. 4. When DNA Polymerase reaches the ends of the strands, two identical copies of the DNA have been made. 5. Each new strands winds back up into the double helix structure. RNA • There are three main differences between DNA and RNA: 1. RNA has the sugar ribose / DNA has the sugar Deoxyribose. 2. RNA is single stranded / DNA is double stranded. 3. In RNA, adenine pairs with uracil / in DNA, adenine pairs with thymine. RNA • There are three types of RNA: 1. Messenger RNA (mRNA) – carries message from DNA in the nucleus to the ribosome for protein synthesis. 2. Transfer RNA (tRNA) – brings amino acids to the ribosome for protein synthesis. 3. Ribosomal RNA (rRNA) – makes up the structure of the ribosome. Transcription • Protein synthesis is broken down into two processes: transcription and translation. • Transcription occurs in the nucleus. It is the process of making mRNA from DNA. • Transcribe the following DNA segment: T-A-C-A-G-T-C-T-A-G-G-C-A-T-C-C-A-G-C-A-T A-U-G-U-C-A-G-A-U-C-C-G-U-A-G-G-U-C-G-U-A Translation • Translation occurs in the cytoplasm at the ribosome. It is the process of making a protein from the mRNA. • The ribosome reads the mRNA 3 nucleotides at a time (a codon). • A tRNA molecule brings the correct amino acid to the ribosome based on its anti-codon. • The ribosome continues adding amino acids until it reaches a “stop” codon. • It then releases the protein and begins again. Translation • Break the mRNA segment from above into codons: A-U-G U-C-A G-A-U C-C-G U-A-G G-U-C G-U-A • What is the amino acid sequence for the protein? Met – Ser – Asp – Pro – Stop – Val – Val • This diagram shows the process of translation which occurs in the cytoplasm. • Molecule 1 represents mRNA, which is made in the nucleus during transcription. • Molecule 2 is a ribosome (tRNA). • Molecule 3 is an amino acid, which are bonded together to make proteins (Molecule 4). • Molecule 5 is tRNA, which contains the anti-codons and brings amino acids to the ribosomes. Translation Mutations • A mutation is any change in a DNA sequence. These changes can result in the wrong sequence of amino acids in a protein – which will cause the protein to function incorrectly. 1. 2. 3. 4. Insertion – an extra nucleotide is added to the sequence. Deletion – a nucleotide is removed from the sequence. Inversion – a sequence of nucleotides is switched. Duplication – a nucleotide or sequence of nucleotides is repeated. 5. Substitution – a nucleotide is replaced with a different nucleotide.