Ch.16 The Molecular Basis of Inheritance and Ch.17 Gene Expression: From Gene to Protein

DNA is the genetic material

Addition of a nucleotide to a DNA strand

The stages if transcription: intintaition, elongation and termination

The elongated cycle of translation

Evidence that viral DNA can program cells

Additional evidence that DNA was the genetic material came from studies of viruses that infect bacteria

Viruses are much more simpler than cells

called bacteriophages ("bacteria-eaters")

or phages for short

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

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

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

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 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

The hydrolysis of GTP plays an important role in the elongated process

codon recognition

Peptide bond formation

translocation

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