Transcript Translation
Basics of Molecular Biology Central Dogma: - DNA replication - Transcription - Translation Metabolic regulation: - Genetic level - Metabolic pathway control Central Dogma Central Dogma: universal - Genetic information is stored on the DNA molecule. - DNA replication: The genetic information can be replicated directly to form a second identical molecule. - Transcription: Segments information on the DNA molecule can be transcribed to yield m-, t, r-RNAs. - Translation: Using RNAs, this information is translated into proteins. DNA Replication in Cell Division Cycle (Mitosis) Transcription The primary product of transcription: m-RNA, t-RNA and r-RNA. Transcription requires: RNA polymerases - Growth of RNA polymers is energy requiring. e.g. ATP, GTP, The base-sequence of RNA is the precise complement of the DNA template sequence. DNA template RNA product A U T A G C C G Transcription DNA template Promoter Operator Gene 1 Gene 2 Gene 3 m-RNA RNA polymerase http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html Transcription Process - Initiation: The sigma factor of RNA polymerase recognizes a specific sequence of nucleotides on a DNA strand – promoter region. the strands unwound. - Elongation: Transcription starts with the core enzyme of the RNA polymerase then the sigma factor is released. - Termination: RNA polymerase encounter a stop signal or transcription terminator (e.g. rho protein in procaryotes). - the RNA polymerase dissociate from the DNA template - the RNA transcript is released. Translation Translation is the final step on the way from DNA to protein. - It is the synthesis of proteins directed by a mRNA template. - The information contained in the nucleotide sequence of the mRNA is read as three letter words (triplets), called codons. - Each word stands for one amino acid. - During translation amino acids are linked together to form a polypeptide chain which will later be folded into a protein. Translation Translation: Message to Product Universal three-letter codons on mRNA: A, G, C, U - 64 codes for 20 standard amino acids - more than one codon can specify a particular amino acids. - Nonsense codons: UAA, UAG and UGA - Do not encode normally for amino acids. - Act as stop points in translation. - encoded at the end of each gene. Translation Important Components: Ribosome: The ribosome is the cellular factory responsible for the protein synthesis. It consists of two different subunits, one small and one large and is built up from rRNA and proteins. Inside the ribosome the amino acids are linked together into a chain through multiple biochemical reactions. Translation-Components t-RNA: The charged t-RNA (aminoacyl-t-RNA) carries an amino acid at one end and has a triplet of nucleotides, an anticodon, at the other end. It is formed by the energy from two phosphate bonds and enzymes (aminoacyl-t-RNA synthetases) The anticodon of a t-RNA molecule can basepair, i.e form chemical bonds, with the m-RNA's three letter codon. The t-RNA acts as the translator between m-RNA and protein by bringing the specific amino acid coded for by the m-RNA codon. t-RNA Translation-Components • m-RNA template • The translation process also involves a large number of protein factors that facilitate binding of mRNA and tRNA to the ribosome. • Protein synthesis consumes a large part of the energy produced in the cell. Translation Processes Translation consists of Initiation, Elongation and Termination. http://www.phschool.com/science/biology_place/biocoach/translation/init.html Initiation results in the formation of an initiation complex in which the ribosome is bound to the specific initiation (start) site on the mRNA while the initiator tRNA charged with (Nformyl)methionine is annealed to the initiator codon and bound to the ribosome. - Protein synthesis begins with a AUG codon (less frequently GUG) on the m-RNA AUG encodes for a modified methionine, N-formylmethionine (fMet). In the middle of protein, AUG encodes for methionine. Translation Processes Elongation joins amino acids to the growing polypeptide chain according to the sequence specified by the message. - The formation of the peptide bond between the two amino acids occurs on adjacent sites on the ribosome: the P or peptidyl site and the A or aminoacyl site. - The growing protein occupies the P site, while the next amino acid to be added occupies the A site. - As the peptide bond is formed, the t-RNA associated with the P site is released. http://www.phschool.com/science/biology_place/biocoach/translation/elong1.html Translation Processes Termination - At a stop codon, a release factor reads the triplet, and polypeptide synthesis ends. - the polypeptide is released from the tRNA. - the tRNA is released from the ribosome, the two ribosomal subunits separate from the mRNA. http://www.phschool.com/science/biology_place/biocoach/translation/term.html Posttranslation • Posttranslational modification means the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis. • It may involve the folding of a proper structure, the formation of disulfide bridges and attachment of any of a number of biochemical functional groups, such as phosphate, acetate, various lipids and carbohydrates. e.g. phosphorylation catalyzed by enzymes such as with kinase. (e.g. phosphorylated TP53 protein functions as tumor suppressor). Summary of Central Dogma • • • • DNA replication DNA-RNA transcription RNA-Protein translation Posttranslation components, processes, features