DNA, RNA & Protein Synthesis BIO 138
History of DNA Before the 1900’s scientists suspected that our physical characteristics were programmed into our cells; they just didn’t know how and where it was located.
1928: Frederick Griffith was working on how bacteria make people sick with pneumonia. He figured out that a ‘factor’ is passed from one bacteria to the next and makes people sick. He thought this factor might be a ‘gene’.
1944: Oswald Avery repeated Griffith’s experiments to try and identify exactly what molecule in the bacteria caused the spread of pneumonia. The isolated different structures within the bacteria and figured out the nucleic acid DNA was responsible for the spread of pneumonia.
1952: Alfred Hershey & Martha Chase worked with viruses and bacteria to verify that the genetic material was in fact DNA and not something else.
1950: Erwin Chargaff figured out the nitrogen base pairings of DNA. Adenine (A) always pairs with Thymine (T) Guanine (G) always pairs with Cytosine (C)
1952: Rosalind Franklin took an X-ray photo of a molecule, but did not know what she had discovered. Photo 51
1953: James Watson and Francis Crick were shown photo 51 by Maurice Wilkins. They took the information and wrote a single-page paper in April of 1953 describing the structural shape of DNA, the double-helix.
DNA Function Function- carries biological instructions for making proteins. Location- found in chromatin and chromosomes along with other histone proteins inside the nucleus of eukaryotic cells.
DNA Structure -made up of repeating subunits called nucleotides: deoxyribose sugar, phosphate and nitrogen base group. -the complimentary nitrogen base groups are bonded together via hydrogen bonds. -the sugars and phosphates are held together by covalent bonds. -double stranded to form a double helix. (Video Clip)(Video Clip)
Nitrogen Base Groups Pyrimidines: Purines:
DNA Replication -DNA must replicate itself in order to go through Mitosis. -DNA replication occurs during the ‘S’ phase of Interphase -The double helix splits apart in numerous places by the enzyme helicase and is copied with the help of an enzyme called DNA polymerase. -The newly formed DNA fragments are connected together by the enzyme ligase. (Video Clip)(Video Clip)
Prokaryotic DNA Replication -prokaryotic cells (bacteria) have DNA that is generally only one chromosome and circular. -replication occurs at two forks moving in opposite directions around the circle until they meet up and replication is complete.
Errors with DNA Replication -DNA polymerase also acts as an error-checking enzyme, fixing errors with replication. -Not all errors are fixed, can result in mutations. -Some mutations are from environmental factors; UV light, pollution, toxins, smoking. -Mutations can lead to tumors and cancer.
RNA (Nucleic Acid) Types of RNA: 1. Messenger RNA (mRNA) 2. Ribosomal RNA (rRNA) 3. Transfer RNA (tRNA) All RNA is made from DNA through the process of Transcription.
Structure of RNA -Single stranded -Ribose sugar -much shorter than DNA -Adenine pairs with Uracil -Guanine pairs with Cytosine
Protein Synthesis Overview: Function: make all proteins as needed for all the processes of the cell. Two Step Process: 1.Transcription 2.Translation Transcription occurs in the nucleus. Translation occurs in the cytoplasm at a ribosome. Video Clip
Transcription Steps: 1. RNA Polymerase binds to a promoter region of a segment of a DNA molecule. (gene) 2. RNA Polymerase begins adding new RNA nucleotides corresponding to the DNA nucleotides. 3. RNA Polymerase reaches a termination signal and stops transcribing. The newly formed RNA is released and sent out of the nucleus.
Outcome of Transcription: -The “Genetic Code” has been transcribed from DNA inside the nucleus to mRNA that can now leave the cell to be translated into a protein. -The exact “Genetic Code” is the sequence of the nitrogen bases. This is why we are all different! -Each set of three nitrogen bases is called a mRNA codon. -Each mRNA codon represents an amino acid.
Translation 1. Ribosome, mRNA, and tRNA all bond together in the cytoplasm. Translation begins at a start codon on the mRNA. 2. tRNA’s bring amino acids to the ribosome as the ribosome translates the mRNA. 3. A chain of amino acid begins to grow (polypeptide). 4. Ribosome reaches a stop codon and the polypeptide is released and forms into a protein for use by the cell.
Outcome of Translation: -Translation forms all the proteins that are needed for our cells and our bodies. -Each cell contains hundreds of ribosomes meaning translation occurs non-stop! -Proteins are only produced as needed, your cells try to be very efficient! -The translated mRNA breaks apart into individual nucleotides to be reused again in the future for transcription. -Each cell in your body has 23 pairs of chromosomes made up of approx. 3.2 billion nitrogen bases pairs. It’s all about the order! -There are approx. 30,000 genes in our genome and approx. 20,000 proteins.