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How Many Scientists Does it Take to Discover a Molecule?

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Presentation on theme: "How Many Scientists Does it Take to Discover a Molecule?"— Presentation transcript:

1 How Many Scientists Does it Take to Discover a Molecule?

2 Erwin Chargaff (Born 1905) Russian
Moved to the U.S. Discovered that there could not be only one base attached There was always an equal number of A’s to T’s and C’s to G’s. There could be different amounts of these two groupings.

3 Rosalind Franklin (1920 – 1958) British
Worked under Maurice Wilkins Used X-ray diffraction to get images of DNA Her work was passed along to Watson and Crick by Wilkins. She did not get recognized for her work possible because she was a woman in science when it was not fully acceptable


5 Watson and Crick Crick (Born 1916) British Watson (Born 1928) American
Used images and papers produced by Franklin Discovered double helix shape They got the Nobel Prize in 1953 along with Wilkins

6 DNA Replication DNA replicates when the cells divide and when the sex cells are formed Groups of proteins guide the process, but DNA polymerase is the major functioning enzyme.

7 Three major events to begin DNA replication
The two nucleotide chains must separate forming a replication fork. The chains are separated by enzymes called helicases DNA polymerase binds to the separated chains of DNA and assembles complimentary nucleotides to the old strand The new strand of DNA hydrogen bonds with the old strand and winds back to form a helix


9 Checking the System Incoming nucleotides bind to the DNA polymerase and the polymerase checks to see if the incoming nucleotide pairs correctly with the DNA template. Error rate is about 1 error in base pairs (108)

10 Direction of Replication
Replication takes place in both directions. DNA polymerase begins replication simultaneously at many points along the separated nucleotide.

11 The Other Nucleic Acid Remember that:
DNA is located in the nucleus and under no circumstances can leave the nucleus. Proteins are manufactured in the cytoplasm at the ribsomes. DNA is the instructions for making those proteins.

12 RNA: Ribonucleic Acid Sugar: Ribose Phosphate group Nitrogen bases
Single Stranded Made of nucleotides Sugar: Ribose Phosphate group Nitrogen bases The nitrogen bases in RNA have one difference. Thymine is replace by uracil So A pairs to U; G pairs to C


14 Three Types of RNA Messenger RNA (mRNA) Transfer RNA (tRNA)
Carries the code from DNA to the ribosome Transfer RNA (tRNA) Picks up individual amino acids in the cytoplasm and carries them to the ribosome to be delivered Ribosomal RNA (rRNA) Helps bind mRNA and tRNA together during protein synthesis

15 RNA Transcription DNA transcribes a copy of mRNA in the nucleus of the cell. The mRNA takes the DNA code out of the nucleus and to the ribosomes.

16 Steps of Transcription
RNA polymerase makes RNA copies of specific segments of DNA. This begins at a promotor site on DNA Only the DNA template is used for transcription

17 Steps of Transcription
RNA polymerase adds complimentary RNA nucleotides to form a new RNA molecule. Complimentary base pairing determines the nucleotide sequence

18 Steps of Transcription
Transcription ends at the DNA terminator. Both DNA and RNA are released by the RNA polymerase. All three types of RNA molecules are transcribed by this process.


20 Protein Synthesis – Structure and Composition
Proteins are polymers made of amino acids bonded by peptide bonds Proteins are made up of specific sequences of amino acids There are 20 kinds of amino acids

21 Protein assembly Codon (AUG) means “Start” or can code for the amino acid methinone MRNA codon is paired with tRNA anticodon Amino acids are bonded with peptide bonds and the polypeptide chain grows into a protein At the stop codon (UAA, UAG, UGA) translation ends and the protein is finished The protein folds up Several ribosomes can translate the same mRNA transcript at the same time


23 Mutations A change in the nucleotide sequence is one spot


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