Nucleic Acids & Protein Synthesis

The Genetic Code Biologists call the program of the cell the genetic code. The Genetic Code, is the way in which cells store the program that they need to pass from one generation to the next.

Discovering the Code Fredrick Griffith used bacteria and mice to first to theorize about the Genetic Code. Proves that information from one strain is being transferred to the other strain thus proving there is a transferring factor. Oswald Avery decided to repeat Griffith’s work to see if he could find the transferring factor in Griffith’s experiment. Treated the bacteria with enzymes, each destroying a specific structure of the cell. When they destroyed DNA the experiment didn’t work, proving DNA was the transferring factor.

Discovering the Code DNA: is the nucleic acid that stores and transmits the genetic information from one generation of organisms to the next. Hershey & Chase, Further tested Avery’s conclusion, using viruses called a bacteriophage. Bacteriophage- Made of DNA and a protein coat (covering). They “labeled” the two parts of the bacteriophage with radioactive isotopes. They found the radioactive material used to label DNA inside the bacteria, proving that the DNA was the transferring factor.

The Structure of DNA DNA is made of units called nucleotides. Nucleotides are made up of; a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base. Nitrogenous bases are; Adenine, Guanine, Cytosine, and Thymine. Adenine and Guanine are Purines. Cytosine and Thymine are Pyrimidines. Individual nucleotides are joined together to make D.N.A. the sugar and the phosphate group make to backbone of the chain while the nitrogenous base sticks out.

Scientists and the Structure of DNA Rosaliand Franklin & Maurice Wilkins tried to use x-ray beams to determine the structure of DNA. At the same time as Franklin & Wilkins two other scientists name James Watson and Francis Crick were also trying to determine the structure of DNA. Watson & Crick, using Franklin’s X-ray pattern, built a 3-dimensional model of DNA, the model was made of two strands twisted or spiraled around each other, they called this shape a Double Helix.

Franklin’s D.N.A. X-ray

The Double Helix In the double helix the nitrogenous bases are positioned exactly opposite each other. This positioning allows for a weak Hydrogen bond to from between; Adenine(A) + Thymine(T), and Cytosine(C) + Guanine(G). Base Pairing is the force that hold the two strands of the DNA double helix together.

The Double Helix

DNA and the Chromosome In eukaryotes the chromosome contains both DNA and proteins, they are packed tightly together to form a chromatin. Chromatin: consists of DNA that is tightly packed around a protein called histone

The Replication of DNA The two strand in the double helix are complementary. Complementary means that they have all the information necessary to reconstruct the other strand. Each strand of DNA serves as a template against which a new strand can be made. Before a cell divides it must copy DNA to ensure that each new cell has a complete set of DNA. The process of copying DNA is known as replication or DNA synthesis and is carried out by enzymes.

The Replication of DNA Enzymes separate the two strands of DNA by breaking the H bonds of the base pairs. The main enzyme of replication is DNA Polymerase The enzymes; 1.) Separates the strands. 2.) Reads the strands. 3.) Insert the appropriate (complementary) base. 4.) Produce the sugar-phosphate backbone. 5.) proofreads the bases to make sure they are correct. Example: If a strand reads: T-A-C-G-T-T it will produce the strand: A-T-G-C-A-A and vice versa.

Replication Replication results in two DNA molecules both of which are identical to the original.

The Structure of RNA Is made of nucleotides. RNA is used to carry out the process of Protein Synthesis. Three differences between RNA & DNA. The 5-carbon sugar in RNA is Ribose. RNA is single stranded. RNA contains a nitrogenous base called uracil instead of thymine.

Types of RNA Three main types Messenger RNA (mRNA) carries copies of instructions to assemble proteins. Ribosomal RNA (rRNA) found in at the ribosome, is the site of protein construction. Transfer RNA (tRNA) transfers amino acids to the ribosome where they are assembled into protein.

Transcriptions (RNA Synthesis) Transcription- Process by which RNA is produced by copying part of the sequence of DNA into a complimentary sequence in RNA. Transfers information from DNA to RNA. RNA Polymerase- Enzyme used in transcription to make RNA from DNA. RNA polymerase binds to regions of DNA called: promoters - Base sequences that signal where in the DNA the polymerase should bind. The polymerase creates the complimentary strand of mRNA . mRNA carries information from DNA to the ribosome to create proteins.

RNA Editing Before the mRNA leaves the nucleus it must be edited. DNA contains sequences of nucleotides called introns (not used in protein synthesis) and exon (are used in protein synthesis). When the RNA is made it contains both. Before the mRNA leaves the nucleus, it is edited to remove the introns.

The Genetic Code The language of the mRNA. It is written using four different letters in combinations of 3 letters at a time. These different 3 letter combinations are called codons. Each codon specifies a single amino acid that is to used to form the protein chain. The codons can be decoded using a chart. There is a start codon that begins protein synthesis (AUG), and three that stop it (UGA, UAA, UAG).

Translation Translation-The decoding of mRNA to make protein. Starts when mRNA reaches the Ribosome. As mRNA moves through the ribosome the codons are decoded. tRNA then brings the amino acid specified by the codon to the ribosome. At the ribosome the amino acids are assembled to make the protein. Each tRNA carries a specific amino acid, and has three unpaired bases called anticodons which are complimentary to a codon.