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. (Outbreak in London) He figured out that a ‘hereditary factor’ is passed from one bacteria to the next and makes people sick.

1944: Oswald Avery repeated Griffith’s experiments to try and identify exactly what molecule in the bacteria caused the spread of pneumonia. (DNA, RNA, or protein?) They isolated different molecules within the bacteria and figured out the nucleic acid DNA was responsible for the spread of pneumonia.

1949: 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: Alfred Hershey & Martha Chase worked with viruses to identify if DNA or protein was the hereditary material viruses transfer when viruses enter a bacterium. -Used radioactive isotopes: S and P -Their tests showed the answer was DNA.

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.

1962: Watson, Crick, and Wilkins won the Nobel Prize for Medicine for their work on the discovery of the structure of DNA. 1958: Rosalind Franklin died in 1958…cancer.

DNA Function Function- carries biological instructions for making proteins. Location- found in the nucleus. -DNA + Histone proteins = chromatin -chromatin coils up into chromosomes

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. (A double bonded to T; G triple bonded to C) -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 during the ‘S’ phase of Interphase in order to go through Mitosis. -Steps of Replication: 1. The double helix is splits apart in numerous places by the enzyme helicase. 2. New complementary fragments of DNA are assembled by the enzyme DNA polymerase. 3. The new 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.