protein synthesis 1 background information all information is stored in dna all information is...

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Protein Synthesis

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Background Information

All information is stored in DNA RNA “reads” the DNA code DNA is found in base triplets (sets of

three letters) Complimentary sequence of RNA

(after reading DNA) will be called a codon

Done in the cell Nucleus

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Transcription In this phase the genetic information represented

by the sequence of each DNA base triplet serves as a template for copying the information into a complimentary sequence of RNA

Three kinds of RNA will be made from the DNA template

1. Messenger RNA (mRNA) directs protein synthesis

2. Ribosomal RNA (rRNA) joins with ribosomal proteins to make ribosomes

3. Transfer RNA (tRNA) binds to an amino acid and holds it in place on a ribosome until it is incorporated into a protein during translation

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Transcription Cont.

The process is catalyzed by the enzyme RNA polymerase

This enzyme needs to be told where to begin and where to end

The PROMOTER is the nucleotide sequence of DNA that instructs RNA polymerase where to begin.

During the transcription process the bases are paired up in a complimentary manner

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Cont.

The bases C, G, and T from DNA pair up with G, C, and A in the RNA.

However, adenine in the DNA template pairs up with U (uracil) and not thymine in the RNA sequence

So, DNA (CGA) reads (GCU) in RNA. Transcription continues until the

terminator sequence is read Once this happens RNA Polymerase

detaches and the process ends.

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Translation

Process where the nucleotide sequence in an mRNA molecule specifies the amino acid sequence of a protein

Occurs on a ribosome in the cytosol

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Stages of Translation mRNA binds to the small part of a

ribosome at the mRNA binding site Initiator tRNA binds to the start codon

(AUG) on mRNA. The tRNA anticodon (UAG) attaches to the

mRNA codon (AUG) by pairing between the complementary bases

AUG is the start codon, and it is the codon for methionine, which means that methionine is always the first amino acid in the protein building process

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Stages Cont. From this point, the ribosome will continue

to add amino acids in the sequence that is given to it by the mRNA strand.

The ribosome reads the remainder of the strand one codon at a time, and from here the protein lengthens

The process moves in what we call a 3’ to 5’ direction

The process ends when a stop codon is read, which leads to the detachment of the protein from the final tRNA.

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Final Translation Facts

Occurs at about a 15 peptide bond per second rate

As one ribosome finishes with a strand of mRNA, another one usually picks it up and translates it, so that more than one copy of protein can be made

Process constantly occurs.

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