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Ch.16 The Molecular Basis of Inheritance and Ch.17 Gene Expression: From…
Ch.16 The Molecular Basis of Inheritance and Ch.17 Gene Expression: From Gene to Protein
DNA is the genetic material
Evidence that viral DNA can program cells
Additional evidence that DNA was the genetic material came from studies of viruses that infect bacteria
called bacteriophages ("bacteria-eaters")
or phages for short
Viruses are much more simpler than cells
A virus is little more than DNA or sometimes RNA enclosed by a protective coat
often simply a protein
to produce more viruses, a virus must infect a cell and take over the cells metabolic machinery
Double helix
the presences of two strands
Antiparallel
subunits run in opposite directions
DNA Sequences
Genetic information is carried in DNA as a linear sequence of nucleotides that may be transcribed into mRNA
translated into polypeptide
each nucleotide can be represented simply as the letter of its base A,T,C, or G
Addition of a nucleotide to a DNA strand
DNA polymerase catalyzes the addition of a nucleotide to the 3' end of a growing DNA strand with the release of two phosphates
origins of replication
replication of chromosomal DNA begins at particular sites
Helicases
Enzymes that untwist the double helix at the replication forks separating the two parental strands and making them avablive as template strands
single strand binding proteins
topoisomerase
The stages if transcription: intintaition, elongation and termination
transcription applies to both bacteria and eukaryotes
termination differ
in a bacterium the RNA transcript is immediately useable as mRNA
In a eukaryote the RNA transcript must first undergo processing
The elongated cycle of translation
The hydrolysis of GTP plays an important role in the elongated process
codon recognition
Peptide bond formation
translocation
Synthesis of the leading strand during DNA replication
DNA polymerase III
associated with a protein called the sliding clamp that encircles the newly synthesized double helix like a doughnut
The sliding clamp moves DNA pol lII along the DNA template strand
Synthesis of the lagging strand
primase joins RNA nucleotide into a primer
DNA pol lll adds DNA nucleotides to the primer forming okazaki fragment 1
after reaching the next RNA primer to the right DNA pol lll detaches
fragment 2 is primed the DNA pol lll adds DNA nucleotides detaching when it reaches the fragment 1 primer
DNA pol l replaces the RNA with DNA adding nucleotides to the 3' end fragment 1 and later of fragment 2
DNA ligase forms a bond between the newest DNA and the DNA of fragment 1
The initiation of transcription at a eukaryotic promoter
in eukaryotic cells proteins called transcription factors mediate the initiation of transcription by RNA polymerase ll
Eukaryotic promoter
several transcription factors
Additional transcription factors
Transcription elongated
RNA polymerase moves along the DNA template strand
Joining complementary RNA nucleotides to the 3' end growing RNA transcript
Behind the polymerase the new RNA peels away from the template strand, which re-forms a double helix with the nontemplate strand