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Replication

DNA codes for proteins, and proteins make up everything important about an organism.  Every time a new cell is made, it must have the correct instructions for all of the proteins in the body.  Replication is the process of copying DNA.

  • It occurs during interphase

  • It is "semiconservative" - each side of the molecule is used as a template to make the other side correctly.

  • It involves many enzymes and steps that may require a deeper dive

  • Sometimes, mistakes are made:  mutations.

Copying DNA

Replication takes place in the nucleus during the "S" phase of interphase when a cell starts preparing to divide.

  • At many points along a chromosome, Helicase enzymes attach to the DNA and start to separate the weak hydrogen bonds between the bases.

    • As they move away from each other, they create a bubble in the DNA

    • This exposes all of the bases that would like to form hydrogen bonds with their complementary nucleotides

  • DNA polymerase is an enzyme that will attach ​to the middle of the bubble and start reading the exposed bases.

    • As it reads each base, it brings in the complementary nucleotide (A with T and G with C)​ and builds the opposite side of the molecule.

    • Each original strand is saved as a new strand is built on the other side,  so the process is called "semi-conservative" (semi- half; conserve - to save)

  • Eventually, all of the helicase enzymes will meet and release, and all of the polymerase enzymes will finish their sides of the new molecules resulting in two identical copies of DNA.​

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Mutations

A mutation is a change in DNA.  Sometimes DNA polymerase will make a mistake that can be anywhere from deadly to beneficial to not noticeable.  The effects of mutations may require an understanding of Transcription and Translation.

  • Substitution mutations - the wrong nucleotide is added on the new strand

    • Missense mutations - code for the wrong amino acid when making a protein​

    • Nonsense mutations - code for stopping the protein before it is finished

    • Silent mutations - code for the same amino acid, so the protein is not affected

  • Frameshift mutations - the new strand has the wrong number of nucleotides which causes all amino acids to be changed​

    • Addition - an extra nucleotide is put into the new strand​

    • Deletion - a nucleotide is skipped, and the new strand comes up short

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