Bio Chapter 17

• the synthesis of RNA using information in the DNA.
• DNA -> mRNA
• mRNA - carries a genetic message from the DNA to the protein-synthesizing machinery of the cell

• synthesis of a polypeptide using theinformation in the mRNA.
• RNA -> Proteins

move through Ribosome, mRNA(3 letters) are translated to 1 amino acid

• The initial RNA transcript from any gene, including those specifying RNA that is not translated intoprotein
• In eukaryotic, pre-mRNA, is processed in various ways before leaving the nucleus as mRNA

• DNA->(transcription) RNA ->(translation) Protein
• Francis Crik

The genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, three-nucleotide words. 4^3

• mRNA nucleotide triplets
• customarily written in the 5' - 3'direction
• codons are complementary to the template strand and thus identical in sequence tothe mRNA
• 64 codons, 61 = amino acids, 3 are stop signals
• AUG (Met) - start signal
• Redundacy(GAA, GAG)

ability to extract the intended message from a written language depends on reading the symbols in the correct groupings

• enzyme assemble a polynucleotide only in its 5' -3' direction
• don't need primer to start

where RNA polymerase attaches and initiates transcription

in bacteria, the sequence that signals the end of transciption

stretch of DNA that is trancribed into RNA molecule

• Initiation - RNA polyerase binds to promoter, unwind, initiates RNA synthesis at starting point
• Elongation - polymerase move downstream, 5'-3', DNA strands reform double helix
• Termination - RNA transcription released and polymerase detaches

collection of proteins mediate the binding of RNA polymerase and initiate transcription

the whole complex of transciption factors and RNA Pol II bound to the promoter

• Eukaryotic promoter - includes a TATA box( a nucleotide sequence contains TATA, about 25 nucleotide upstream from the start point
• Several transcription factors - one recognizing TATA box, must bind to the DNA before RNA Pol II can can bind in correct postion
• Additional Transcription factors - bind to the DNA along with RNA polymerase II, forming th etranscription initiation complex. RNA polymerase II then unwinds the DNA double helix,

• RNA polymerase II transcribes a sequence on the DNA called the polyadenylation signal sequence in the pre-mRNA.
• Then, at a point about 10–35 nucleotides downstream from the AAUAAA signal, proteins cut it free from the polymerase,
•  pre-mRNA. The pre-mRNA then undergoes processing,the topic of the next section

• both ends of the primary transcript are altered
• 5' cap - guanine (G) nucleotide added
• 3' end - an enzyme adds 50–250 more adenine (A) nucleotides, forming a poly-A tail
• facilitate the export of the mature mRNA
• help protect the mRNA from degradation
• they help ribosomesattach to the 5' end of the mRNA
• RNA splicing certain interior sections of the RNA molecule are cut out and the remaining parts spliced together

• not continuous; it is split into segments
• introns -(intervening) The noncodingsegments of nucleic acid that lie between coding regions
• exons - they are eventually expressed,usually by being translated into amino acid sequences
• introns are cut out adnd exons joined together

• Several different snRNPs join with additional proteins to form an even larger assembly
• interacts with certain sites along an intron,releasing the intron, which is rapidly degraded, and joining togetherthe two exons
• snRNAs catalyze these processes, as well as participating in spliceosome assembly

• RNA molecules that function as enzymes
• without proteins: The intron RNA functionsas a ribozyme and catalyzes its own excision

• Itcan form a three-dimensional structure because of its ability to base pair with itself
• Some bases in RNA contain functional groups
• RNA may H-bond with other nucleic acid molecules

Many genes are known to give rise to two or more different polypeptides, depending on which segmentsare treated as exons during RNA processing

Proteins often have a modular architecture consisting ofdiscrete structural and functional regions

• transfer amino acids from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome
• arrives at a ribosome bearing a specific amino acid at one end
• At the other end of the tRNA is a nucleotide triplet called an anticodon(base-pairs with a complementary codon on mRNA)

enzyme that matching up of tRNA and amino acid

• the flexible base pairing at thsi codon position
• differ in the third nucleotide base

• made up of a large subunit and a small subunit
• 1/3 = proteins, 2/3 = rRNA
• has three binding sites for tRNA:
• P site -holds the tRNA carrying the growing polypeptide chain
• A site - holds the tRNA carrying the next amino acid to be added to the chain
• E site - exit site

• Joins mRNA, a tRNA with the first amino
• acid, and the two ribosomal subunits
• Proteins called initiation factors  are required to bring all thetranslation components together
• GTP provides the energyfor the assembly

• Amino acids are added one by one to form a chain
• Codon recognition
• Poltide bond formation- bond betweed A site with P site
• Translocation -  more one to the left, P to A, P to E

• When a stop codon reaches the A site
• Release factor protein adds H2O

enable a cell to make many copies of a polypeptide very quickly

• changes in the genetic material of a cell or virus
• point mutations - changes in a single nucleotide pair of a gene
• sickle cell disease
•    -single nucleotide-pair substitutions and (2) nucleotide-pair     insertions or deletions

which has no observable effect on the phenotype. (Silent mutations can occur outside genes as well.

• Substitutions that change one amino acid to another one
• may have little effect on the protein: The new amino acid may have properties similar to those of theamino acid it replaces,
• it may be in a region of the protein where the exact sequence of amino acids is not essential tothe protein’s function
• •Still code for an amino acid, but not necessarily the right amino acid

• Change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
• causes translation to be terminated prematurely; the resulting polypeptide will be shorter

• Additions or losses of nucleotide pairs in a gene
• cause frameshift mutation
• result will be extensive missense, usually ending sooner or later in nonsense and premature termination
• -> nonfunctional

incorrect base will be used as a template in the next round of replication,

• A number of physical and chemical agents, interact with DNA in ways that cause mutations
• Ex. X-ray/ radiation

• A discrete unit of inheritance - Mendel
• A region of specific nucleotide sequence in a chromosome -Morgan
• A DNA sequence that codes for a specific polypeptide chain
• A region of DNA that can be expressed to produce a final functional product, either a polypeptide or an RNA molecule