Transcript The Central Dogma of Molecular Biology

Transcription of the DNA code into mRNA
http://www.ncbi.nlm.nih.gov/Class/MLACourse/Modules/MolBioReview/central_dogma.html
 The classic view of the central dogma of biology states
that "the coded genetic information hard-wired into
DNA is transcribed into individual transportable
cassettes, composed of messenger RNA (mRNA); each
mRNA cassette contains the program for synthesis of a
particular protein (or small number of proteins)."
 Lodish, et al (2000) Molecular Cell Biology, 4th edition
 http://www.learnerstv.com/animation/animation.php
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?ani=16&cat=biology
http://wps.prenhall.com/wps/media/objects/1552/158
9869/web_tut/21_04/21_04_01a.swf
The role of a particular gene is to produce one enzyme
that has a role in a metabolic pathway
One gene/one enzyme theory was proven by Beadle
and Tatum in the 1930’s
Has since been altered since proteins may be made of
more than one polypeptide
 1. The DNA replicates information in a process that
involves many enzymes: replication
 2. the DNA codes for the production of messenger
RNA (mRNA) during transcription
 3. In eucaryotic cells, the mRNA is processed and
migrates from the nucleus to the cytoplasm
 4. Messenger RNA carries coded information to the
ribosomes. The ribosomes “read” this information and
use it for protein synthesis. This process is called
transcription
 Is a carrier of genetic information
 Contains a ribose sugar rather than a deoxyribose
 Ribose sugar has a hydroxyl group on its 2´ sugar
 Instead of thymine, RNA contains uracil
 RNA is single stranded
 There are three major classes of RNA:
 Messenger RNA (mRNA)
 Transfer RNA (tRNA)
 Ribosomal RNA(rRNA)
 Not all genes are transcribed all the time.
 Genes are controlled so that transcription occurs only
when the product of the gene is required
 There are three phases to transcription:
 Initiation
 Elongation
 Termination
http://schoolworkhelper.net/2010/07/protein-synthesis-transcription/
 http://vcell.ndsu.edu/animations/transcription/movie
-flash.htm
 RNA polymerase binds to the DNA molecule upstream
of the gene at the gene’s promoter region
 A promoter region has a high number of A and T bases
 DNA strand is unwound exposing the template strand
 The RNA that is polymerized will be complementary
to the template strand
 RNA builds the single stranded RNA in the 5´ to 3 ´
direction
 DNA already transcribed rewinds into the double helix
http://www.mun.ca/biology/scarr/2250_DNA_replication_&_transcription.html
 RNA polymerase reaches the terminator sequence
 The newly formed RNA disassociates from the DNA
template strand
 RNA polymerase leaves and is free to bind to another
promoter region
 Before mRNA can be used by ribosomes as a template
for building proteins, it must first be processed.
 Soon after RNA polymerase begins transcription, a
methylated cap is added to the 5' end.
 Poly A polymerase synthesizes the polyadenylated tail
by adding adenine residues to the 3´ end.
 The poly-A tail makes the RNA molecule more stable
and prevents its degradation.
 The processed mRNA is now ready to undergo splicing
in preparation for translation.
 http://vcell.ndsu.edu/animations/mrnaprocessing/mo
vie-flash.htm
 http://vcell.ndsu.edu/animations/mrnasplicing/movie
-flash.htm
 Introns are non-coding RNA sequences that must be
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removed before translation.
The process of removing the intron is called splicing
The intron is looped out and cut away from the exons
by snRNPs (small nuclear ribonucleoprotein) (snurps)
The exons are spliced together to produce the
translatable mRNA
The mRNA is now ready to leave the nucleus and be
translated into protein
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http://www.phschool.com/science/biology_place/biocoach/transcription/premrna.html
http://www.ncbi.nlm.nih.gov/Class/MLACourse/Modules/MolBioReview/alternative_splicing.html
 There are only 4 nucleotide bases in RNA but 20
amino acids
 The minimum combination of bases to code for 20
amino acids was a triplet code called a codon
http://scienceblogs.com/oscillator/2010/02/expanding_the_genetic_code.php
://www.sparknotes.com/biology/molecular/geneticcode/section1.rhtml
 The genetic code is nearly universal.
 Almost all organisms build proteins with the same
genetic code
 Fruit fly codon will code for the same amino acid as in
a human
 This is important in cloning
 The genetic code is redundant
 More than one codon can code for the same amino
acid
 Three codons do not code for an amino acid – these are
“stop” codons to end protein synthesis
 Stop codons are: UGA, UAA, UAG
 The genetic code is continuous
 It reads as a series of 3-letter codons without spaces,
punctuation or overlap