DNA TO PROTEIN genotype to phenotype Look deep into nature, and then you will understand everything better. Albert Einstein

one-gene, one-enzyme hypothesis Many enzymes are composed of more than one polypeptide chain, or subunit (that is, they have a quaternary structure). In this case, each polypeptide chain is specified by its own separate gene. Thus, it is more correct to speak of a one-gene, one-polypeptide relationship: The function of a gene is to control the production of a single, specific polypeptide.

Expression of Hereditary Material Information is useless without required machinery CENTRAL DOGMA OF MOLECULAR BIOLOGY. The central dogma, simply stated, is that DNA codes for the production of RNA, RNA codes for the production of protein, and protein does not code for the production of protein, RNA, or DNA

2 entities modify the central dogma RNA VIRUSES: Synthesis of DNA from RNA is called reverse transcription, and not surprisingly, such viruses are called retroviruses PRIONS:

Hypotheses of the Dogma Messenger Hypothesis: RNA molecule forms a complementary copy of one DNA strand and this mRNA moves to cytoplasm to serve as a template for protein synthesis. Adapter Hypothesis: An adapter molecule binds a specific amino acid with one region and recognizes nucleotide sequence with a different region. tRNA acts as an intermediary between nucleotide sequence of mRNA and AA sequence in protein.

Transcription of a Eukaryotic Gene DNA of a eukaryotic cell is confined to the nucleus, but proteins are synthesized in the cytoplasm.

TRANSCRIPTION DNA-Directed RNA Synthesis

The synthesis of RNA molecules using DNA strands as the templates so that the genetic information can be transferred from DNA to RNA. Transcription

DNA regions that can be transcribed into RNA are called structural genes. only one of the two strands of DNA—the template strand—is transcribed. non-template strand, remains untranscribed

Template The template strand is the strand from which the RNA is actually transcribed. It is also termed as antisense strand. The coding strand is the strand whose base sequence specifies the amino acid sequence of the encoded protein. Therefore, it is also called as sense strand.

Promoter

Three phases: initiation, elongation, and termination. Transcription Process

Transcription in Prokaryotes Initiation phase: RNA-polymerase recognizes the promoter and starts the transcription. Elongation phase: the RNA strand is continuously growing. Termination phase: the RNA-polymerase stops synthesis and the nascent RNA is separated from the DNA template.

Transcription in Eukaryotes Transcription initiation needs promoter, a special sequence of DNA to which RNA polymerase binds very tightly. There is at least one promoter for each gene Promoters are important control sequences that “tell” the RNA polymerase three things:Promoters are important control sequences that “tell” the RNA polymerase three things: where to start transcriptionwhere to start transcription which strand of DNA to readwhich strand of DNA to read the direction to take from the startthe direction to take from the start Part of each promoter is the initiation site, where transcription begins Initiation

RNA-polymerase does not bind the promoter directly. RNA-polymerase associates with six transcription factors, TFII A - TFII H. Transcription factors

The elongation is similar to that in prokaryotes. The transcription and translation do not take place simultaneously since they are separated by nuclear membrane RNA Pol moves 3’ to 5’, synthesis 5’ to 3’, no primer, Unwinds 20 bp at a time Elongation

Transcription Elongation Transcript antiparallel to DNA template strand No proofreading error rate 1 in 10, ,000

Transcription Termination The termination sequence is AATAAA followed by GT repeats Translation starts before termination in prokaryotes Pre-mRNA initial product of transcription in eukaryotes

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