DNA Notes PDF

DNA Notes History A chromosome is basically chromatin that is wound up tightly to form a visible structure (remember my yarn example). If you unwind the chromatin, you get DNA. So what is DNA? DNA stands for ____Deoxyribonucleic Acid__. Its existence was discovered in 1869 by a man named Friedrich...

DNA Notes History A chromosome is basically chromatin that is wound up tightly to form a visible structure (remember my yarn example). If you unwind the chromatin, you get DNA. So what is DNA? DNA stands for ____Deoxyribonucleic Acid__. Its existence was discovered in 1869 by a man named Friedrich _Miescher______________. The importance of DNA as a “transformative factor” (meaning it was the chemical responsible for passing on information) was discovered in 1944 by ___Oswald Avery_______. It wasn’t until 1953 that the structure of DNA was finally discovered by James _Watson_ and Francis _Crick___. Watson and Crick borrowed from the works of many scientists (most notably Rosalind __Franklin____) to conclude that DNA was in the form of a double helix. (think a twisted staircase). Watson and Crick received the Nobel Prize for their findings, but Franklin was excluded because she died prior to the award being given. The rules of the Nobel committee state that the award cannot be given posthumously. DNA can be thought of as the __blueprint_____ for designing an organism. Your DNA is unique to you. Nobody else in the world has the same DNA unless they are your identical twin. Structure DNA is a large molecule (_polymer_____) that falls under the category of __nucleic acid_____. Remember a polymer is a large molecule made up of monomers put together. The monomers in nucleic acids are called ___nucleotides_____. So, a nucleic acid (like DNA) is made of nucleotides linked together. What is a nucleotide? It is a 3-part structure that looks like this: 1 - phosphate 1 - deoxyribose (5-sided sugar) 1 - nitrogenous bases The phosphate and deoxyribose always stay the same in the nucleotide, but the nitrogenous bases can vary. They are either ___adenine__, _guanine___, __cytosine___, or _thymine____). Adenine and Guanine are known as __purines_. Cytosine and Thymine are known as __pyrimidines__. __Erwin Chargaff___ work also helped Watson and Crick. Chargaff discovered that Adenine always binds with Thymine and that Guanine always binds with Cytosine. _A_ - _T_ and __G_ - _C__ This is known as Chargaff’s Rule. The bonds between the bases are ___hydrogen____ bonds. It is the sequence of the __bases________ that equal genes and thus determine the traits or characteristics in living things. DNA Replication We have already said that the copying of DNA happens during __interphase___. This must occur before the cell can divide. Big picture-wise, here is what happens. 1. The DNA __unzips____. The enzyme ___helicase____ separates the hydrogen bonds between the base pairs. The unzipped strands now become templates. 2. The enzyme DNA ____Polymerase___ grabs free-floating nucleotides and begins to pair them with the unzipped templates. 3. The two strands are called the ____leading___ strand and the __lagging___ strand (depending on the direction their deoxyribose molecules are pointing). 4. The leading strand builds __towards____ the replication fork whereas the lagging strand builds _away_____ from the replication fork. The lagging strand is laid down in segments called Okazaki Fragments. 5. The original DNA molecule continues to separate while new strands are simultaneously assembled. 6. The result is that when the entire molecule has completely separated, two identical DNA molecules are created.