Figure: 10.2 Title: Cells synthesize three major types of RNA Caption: RNA consists of a single nucleotide strand whose bases are complementary to the bases within the template strand of the gene. There are three major types of RNA: (a) Messenger RNA (mRNA) carries within its base sequence the information for the amino acid sequence of a protein. (b) Ribosomes contain both ribosomal RNA (rRNA) and proteins. The ribosome is divided into a small and large subunit that join together during protein synthesis. The small subunit binds the mRNA; the large subunit binds tRNA and catalyzes the formation of bonds between amino acids to form a protein. (c) One side of transfer RNA contains an anticodon, which is a sequence of three nucleotides that can form base pairs with a codon in mRNA. Enzymes within the cytoplasm attach a specific amino acid to the opposite side of the tRNA so that it can carry the proper amino acid to the ribosome for incorporation into a new protein.
Figure: 10.3 Title: Genetic information flows from DNA to RNA to protein Caption: Cellular information is stored within the base sequence of DNA. Transcription, the process of RNA synthesis, occurs in the nucleus. During transcription, the nucleotide sequence in a gene specifies the nucleotide sequence in a complementary RNA molecule. For protein-encoding genes, the product is an mRNA molecule that exits from the nucleus and enters the cytoplasm where translation occurs. During translation, the sequence in an mRNA molecule specifies the amino acid sequence in a protein.
Figure: 10.4ab Title: Intiation and elongation of RNA transcription Caption: Intiation and elongation of RNA transcription
Figure: 10.4cd Title: Termination of RNA transcription Caption: Termination of RNA transcription
Figure: 10.5 Title: RNA transcription in action Caption: This electron micrograph shows the progress of RNA transcription in the egg of an African clawed toad. In each treelike structure, the central “trunk” is DNA and the “branches” are RNA molecules. A series of RNA polymerase molecules are traveling down the DNA, synthesizing RNA as they go. The beginning of the gene is on the left. Therefore, the short RNA molecules on the left have just begun to be synthesized; the long RNA molecules on the right are almost finished.
Figure: 10.6 Title: Translation is the process of protein synthesis Caption: Protein synthesis, or translation, decodes the base sequence of an mRNA into the amino acid sequence of a protein.
Figure: 10.6abc Title: Initiation of protein synthesis Caption: Initiation of protein synthesis
Figure: 10.6def Title: Elongation during protein synthesis Caption: Elongation during protein synthesis
Figure: 10.6ghi Title: Termination of protein synthesis Caption: Termination of protein synthesis
Figure: 10.7 Title: Complementary base pairing is critical at each step in decoding genetic information Caption: (a) DNA contains two strands: the template strand is used by RNA polymerase to synthesize an RNA molecule; the other strand, which is complementary to the template strand, is needed for DNA replication. (b) Bases in the template strand of DNA are transcribed into a complementary mRNA. Codons are sequences of three bases that specify an amino or a stop during protein synthesis. (c) Unless it is a stop codon, each mRNA codon forms base pairs with the anticodon of a tRNA molecule that carries a specific amino acid. (d) The ribosome links the amino acids together, forming the protein.
Figure: 10.8 Title: An overview of “information flow” in a cell Caption: This simplified diagram shows the major steps from DNA to protein to chemical reactions catalyzed by enzymes. Regulation of gene expression may occur at any or all steps.
Transcripción del ADN
Three Types of RNA Sitio Catalítico tRNA docking sites Attached amino acid Transfer RNA Subunidad ribosomica pequeña Ribosome contains rRNA mRNA Subunidad Ribosomica grande mRNA Met anticodon 1 2 C A G A U G G A G U U A U G G A G U
Translation: Initiation (1) A tRNA with an attached methionine amino acid binds to a small ribosomal subunit, forming an initiation complex.
Translation: Initiation (2) The initiation complex binds to end of mRNA and travels down until it encounters an AUG codon in the mRNA. The anticodon of the tRNA in the initiation complex forms base pairs with the AUG codon.
Translation: Initiation (3) The large ribosomal subunit binds to the small subunit, with the mRNA between the two subunits. The methionine tRNA is in the first tRNA site on the large subunit.
Translation: Elongation 1 The second tRNA enters the second tRNA site on the large ribosomal subunit. Which tRNA binds depends on the ability of its anticodon (CAA in this example) to base pair with the codon (GUU in this example) in the mRNA. tRNAs with a CAA anticodon carry an attached valine amino acid, which was added to it by enzymes in the cytoplasm.
Translation: Elongation 2 The "empty" tRNA is released and the ribosome moves down the mRNA, one codon to the right. The tRNA that is attached to the two amino acids is now in the first tRNA binding site and the second tRNA binding site is empty.
Translation: Elongation 3 The catalytic site on the large subunit catalyzes the formation of a peptide bond linking the amino acids methionine to valine. The two amino acids are now attached to the tRNA in the second binding position.
Translation: Elongation 4 Another tRNA enters the second tRNA binding site carrying its attached amino acid. The tRNA has an anticodon that pairs with the codon. (Here, the CAU mRNA codon pairs with a GUA tRNA anticodon.) The tRNA molecule carries the amino acid histidine (his).
Translation: Elongation 5 Binding of tRNAs, & formation of peptide bonds continues. Ribosome reaches STOP codon (UAG). Protein "release factors" signal the ribosome to release the protein. The mRNA is also released and large & small subunits separate.
Translation: Termination The catalytic site forms a new peptide bond, in this example, between the valine and the histidine. A three-amino acid chain is now attached to the tRNA in the second tRNA binding site. The empty tRNA in the first site is released and the ribosome moves one codon to the right.
Complementary Base Pairing Methionine Glycine Valine etc. template DNA strand (a) complementary DNA strand (b) mRNA (c) tRNA (d) protein amino acids anticodons codons gene etc. etc. etc. etc. G G G A G C G A U U U C A A C A U C C U G G G A G T T C T G A G T C C C C A A A T C
Overview of Information Flow Amino Acids Active Protein Inactive Protein (Cytoplasm) DNA (Nucleus) rRNA tRNA 1 Transcription + Proteins Ribosomes tRNA tRNA-AA mRNA mRNA 2 Translation 3 Modification Product Substrate 4 Degradation