Ch.10 Molecular Biology of the Gene

HOW DO BACTERIOPHAGES EAT BACTERIA?
A bacteriophage has a head, containing DNA and a hollow tail with six jointed fibers extending from it. Bacteriophage attaches to bacterial cell, and injects DNA. It can reprogram its host cell to produce new pages, by their proteins. When the bacteria had been infected with T2 phages containing labeled protein, the radioactivity ended up mainly in the liquid, which contained phages but not bacteria. This result suggested that the phage phage protein did not enter the cells. But when the bacteria had been infected, then most of the radioactivity was in the bacteria pellet. When these bacteria were returned to liquid growth medium, the bacterial cells were destroyed, lysing and releasing new phages that contained radioactive phosphorus in their DNA but no radioactive sulfur in their proteins.

WHAT IS NUCLEOTIDE MADE OF?
DNA nucleotide is a long molecule of nucleotides, consisting of 3 parts. These 3 parts include a pentose sugar, a phosphate group, and a nitrogenous base. The nitrogenous bases include purines (adenine and guanine) and pyrimidines (cytosine and thymine). DNA includes adenine, guanine, cytosine, and thymine. RNA includes adenine, cytosine, guanine, and uracil instead of thymine.

WHAT ARE THE DIFFERENCES BETWEEN DNA AND RNA?
DNA and RNA are slightly different. In the cell RNA is usually single stranded, while DNA is double stranded. RNA nucleotides contain ribosome while DNA contains deoxyribose, which is a type of ribose that lacks one oxygen atom. In RNA the nucleotide uracil substitutes for thymine, which is present in DNA. DNA can be found in nucleus, but RNA can be found in nucleus and cytoplasm. A job of DNA is medium of long-term storage and transmission of genetic information. THe main job of RNA is to transfer the genetic code need for the creation of proteins from the nucleus to the ribosome. This process prevents the DNA from having to leave the nucleus, so it stays safe. Without RNA protein would never be made.



SUMMARY:
Frederick G. discovered that a transforming factor could be transferred into a bacterial cell. Alfred Hershey and Martha Chase used bacteriophages to show that DNA is the genetic material. DNA and RNA is the nucleotide, which contains 1) nitrogenous base, 2) 5-carbon sugar, and 3) phosphate group. DNA is a double-stranded helix, and it is composed of two polynucleotide chains joined together by hydrogen bonding between bases, twisted into a helical shape. DNA replication follows a semiconservative model. It begins at the origins of replication. It always occurs in the 5' to 3' direction. A gene is a sequence of DNA that directs the synthesis of a specific protein. DNA is transcribed into RNA, and RNA is translated into protein. The sequence of nucleotides in DNA provides a code for constructing a protein. Protein construction requires a conversion of a nucleotide sequence to an amino acid sequence. Transcription rewrites the DNA code into RNA, using the same nucleotide language. Each word is a codon, consisting of three nucleotides. Translation involves switching from the nucleotide language to amino acid language. The basic steps of transcription is, 1) the two DNA strands separate, this stage is called initiation 2) One strand is used as a pattern to produce an RNA chain, using specific base pairing, this stage is called elongation 3) RNA polymerase catalyzes the reaction, this stage is called termination.
Translation occurs on the surface of the ribosome.  During initiation, mRNA binds to a small ribosomal subunit and the first tRNA binds to mRNA at the start codon. And a large ribosomal subunit joins the small subunit, allowing the ribosome to function. During elongation, next tRNA binds to the mRNA at the A site. And joining of the new amino acid to the chain occurs. tRNA is released from the P site and the ribosome moves tRNA from the A site into the P site. Elongation continues until the ribosome reaches at stop codon. Mutations can be spontaneous, and induced by mutagens. Viruses have two types of reproductive cycles, lytic cycle and lysogenic cycle. Both DNA viruses and RNA viruses cause disease in animals. Some animal viruses reproduce in the cell nucleus. Aids is caused by HIV, human immunodeficiency virus. HIV is a retrovirus, containing two copies of its RNA genome, and reverse transcriptase. Three mechanisms let transfer of bacterial DNA, transformation, transduction, and conjugation.

KEY TERMS:
1) Bacteriophages: bacterial viruses that eat bacteria
2) Nucleotides: chemical units that DNA and RNA are consisting of
3) Semiconservative model: When each strand separates and each has one old strand with one new strand
4) DNA polymerases: the enzymes that link DNA nucleotides to a growing daughter strand
5) Promoter: a nucleotide sequence of the "start transcribing" signal
6) RNA splicing: the cutting-and-pasting process
7) Mutation: any change in the nucleotide sequence of DNA
8) Mutagen: a source of mutation is a physical or chemical agent
9) Plasmid: a small, circular DNA molecule separate from the bacterial chromosome
10) Conjugation: the physical union of cells and the DNA transfer between them

This is a diagram of DNA transcription. The first step, initiation, the attachment of RNA polymerase to the promoter and the start of RNA synthesis. The second step, elongation, the RNA elongates. As RNA synthesis continues, the RNA strand peels away from its DNA template, allowing the two separated DNA strands to come back together in the region already transcribed. The third step, termination, finally the RNA polymerase reaches a sequence of bases in the DNA template called a terminator. At that point, the polymerase molecule detaches from the RNA molecule and the gene, sense it signals the end of the gene.

http://www.youtube.com/watch?v=ztPkv7wc3yU&feature=related



5 FACTS:
1) Central dogma shows the processes of replication/transcription/translation to make DNA to protein.
2) During DNA replication, DNA strands separate and random nucleotides come in so they can make two identical daughter molecules of DNA
3) During transcription, as DNA strands separate, RNA nucleotides come in so they can make RNA strand
4) During translation, anticodon with amino acid come in to make polypeptide and the anticodon leaves, so they can make protein
5) DNA nucleotides: A bonds with T, T bonds with A, G bonds with C, and C bonds with G.
RNA nucleotides: A bonds with T, U bonds with A, G bonds with C, and C bonds with G.