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12-3 Protein Synthesis

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DNA vs. RNA

Double stranded Sugar =

deoxyribose Thymine (no

Uracil)

Stays in nucleus One type

Same copy in the cell all the time

Single stranded Sugar = ribose Uracil (instead of

Thymine) Nucleus &

cytoplasm 3 types (mRNA,

tRNA, rRNA) Disposable copies

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Ribose vs. Deoxyribose

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RNAmany functions but mostly just

protein synthesis

three main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA

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Types of RNA

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mRNA

RNA molecules that carry copies of the DNA instructions = mRNA

messenger RNA (mRNA) = serve as “messengers” from DNA to the rest of the cell

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rRNA

Ribosomes are made up of several dozen proteins, as well as a form of RNA known as ribosomal RNA (rRNA).

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tRNA

During the construction of a protein, a third type of RNA molecule transfers each amino acid to the ribosome – as specified by coded messages in mRNA.

These RNA molecules are known as transfer RNA (tRNA).

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Transcription (DNA mRNA)

RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA

required enzyme = RNA polymerase RNA polymerase binds to DNA (in

nucleus) separates the DNA strands RNA polymerase then uses one strand

of DNA as a template nucleotides are assembled into a strand

of mRNA

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Where does RNA start?

enzyme will bind only to regions of DNA known as promoters

promoters are signals in DNA that indicate to the enzyme where to bind to make RNA (“start sequence”).

Similar signals in DNA cause transcription to stop when the new RNA molecule is completed.

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The “language” of mRNA instructions is called the genetic code

RNA contains four different bases: A, U, C, and G

Letters read “3” at a time = codon Codon = a group of three

nucleotides on messenger RNA that specify a particular amino acid.

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