What Do Proteins do? * Enzymes that catalyze reactions. * Determine physical characteristics, phonotypical characteristics. * Manifest genetic disorders by their absence or presence. * Create hormones and antibodies.
What was Garrod’s hypothesis? * One gene creates one Enzyme. * Error in gene results in error in enzyme. * Hereditary material directs enzyme production.
George Beadle and Edward Tatrum * Lack of particular enzyme corresponds to a mutation in a specific gene. * Confirmed one-gene-one enzyme hypothesis.
Vernon Ingram * Studied amino acid sequence of hemoglobin from individuals with sickle cell anemia. * Hemoglobin consists of more than one polypeptide chains joined together. * A different gene controls each polypeptide and its sequence. * In sickle cell anemia, one hemoglobin polypeptide chain has glutamic acid replaced with Valine. * A gene specifies the kind and location of each amino acid in a given polypeptide chain.
5.2: Protein Synthesis: An Overview * Protein are synthesized outside the nucleus, in the cytoplasm, on ribosomes.
The Central Dogma * DNA never leaves the nucleus since it is too precious for the cell. * DNA is the organelle that allows the cell to live hence if it dies it won’t live no more. * DNA data is transferred into the cytoplasm by mRNA. * Ribosomes translate mRNA into polypeptide chains, which are synthesized into proteins. * The process of Protein synthesis consists of three stages: (1) Transcription, (2) Translation, (3) Termination. * Transcription: Is the process during which DNA is coded into mRNA and sent out of the nucleus into the cytoplasm. * Translation: involves using ribosomes the mRNA is translated and amino acids are synthesized. * Basic summary of both stages is DNA is transcribed into mRNA, complementary strand, and then ribosomes translate the RNA into specific sequences of amino acids, which are used to build proteins.
Ribonucleic Acid (RNA) * RNA is a carrier like DNA of genetic information. * The difference between DNA and RNA is:
Deoxyribonucleic Acid | Ribonucleic Acid | * Contains deoxyribose sugar | * Contains ribose sugar | * Double stranded | * Single Stranded | * A=T,C=G | * A=U,C=G | * In the nucleus | * Both in the Nucleus and Cytoplasm. |
* There are three major types of mRNA, tRNA, and rRNA. Types of RNA | Characteristics and Key Functions | Messenger RNA (mRNA) | * Varies in length, depending on the gene that has been copied. * Acts as the intermediary between DNA and the ribosomes. * Translated into protein by ribosomes. * RNA version of the gene encoded by DNA. | Transfer RNA (tRNA) | * Functions as the delivery system of amino acids to ribosomes as they synthesize proteins. * Very short, only 70 – 90 base pairs long. | Ribosomal RNA (rRNA) | * Binds with proteins to form the ribosomes. * Varies in the length. |
Transcription and Translation: An Overview * Transcription can be divided into three steps: initiation, elongation, and termination. * During initiation, the RNA Polymerase binds to DNA at a specific site known as the promoter region, * RNA polymerase puts together the appropriate ribonucleotides and builds the mRNA transcript, a process known as elongation. * Soon after transcribing the process of termination is started. * Translation is also divided into three steps: initiation, elongation, and termination.
The Genetic Code * Each triplet of nucleotides is called a codon. * Codon is a sequence of three bases in DNA or complementary mRNA that serves as a code for a particular amino acid.
7.3.1 The direction of transcription on the DNA molecule.