1.What contains the genetic material?
Experiments showed that DNA is the genetic material.
2.What are the four nucleotides found in DNA?
They are thymine (T), cytosine (C), adenine (A), and guanine (G).
3.What are the four nucleotides found in RNA?
They are uracil (U), cytosine (C), adenine (A), and guanine (G).
Five main facts from the reading:
1.DNA is a double-stranded helix.
2.DNA replication depends on specific base pairing.
3.Genetic information written in codons is translated into amino acid sequences.
4.Transcription produces genetic messages in the form of RNA.
5.Transfer RNA molecules serve as interpreters during translation.
Diagram:
This diagram represents the process of DNA transcription to RNA.
Link: http://www.sequencing-gene.com/sequencing-gene/dna-transcription
Summary:
The introduction of this chapter talked about the way viruses enter a host, and start multiplying and making new copies of themselves, based on the host's provisions. A virus is simply nucleic acid wrapped in a coat of protein and for herpesviruses and some other animal viruses, a membranous envelope. This chapter taught us about molecular biology, the study of DNA and how it serves as the chemical basis of heredity. In the past scientists had hard time to find out which part was the genetic material. They were in front of a dilemma between the DNA and the protein. However, experiments showed that DNA is the genetic material. We can trace the discovery of the genetic role of DNA back to 1928. British medical officer Frederick Griffith was studying two strains of a bacterium: a harmless strain and a pathogenic strain that causes pneumonia. Griffith was surprised to find that when he killed the pathogenic bacteria and then mixed the bacterial remains with living harmless bacteria, some living bacterial cells were converted to the disease-causing form. Most biologists doubted that DNA could be Griffith's transforming factor, primarily because there was not a lot of information for DNA. However, in 1952, Alfred Hershey and Martha Chase performed a set of experiments, which shows that DNA is the genetic material of a virus called T2, which infects the bacterium E. coli. Bacterial viruses are called bacteriophages or just phages. DNA and RNA are polymers of nucleotides. One year after Hershey and Chase published their results, scientists figured out the three-dimensional structure of DNA and the basic strategy of how it works. The four nucleotides found in DNA differ only in their nitrogenous bases. Thymine (T) and cytosine (C) are single-ring structures called pyrimidines. Adenine (A) and guanine (G) are larger, double-ring structures called purines. The one-letter abbreviations can be used for either the bases alone of for the nucleotides containing them. In RNA, instead of thymine, RNA has a nitrogenous base called uracil (U). James Watson and Francis Crick discovered that the DNA is a double-stranded helix in 1953. DNA replication depends on specific base pairing. The most famous model for DNA replication is knows as semi-conservative model, because half of the parental molecule is maintained in each daughter molecule. This model was confirmed by experiments performed in the 1950s. DNA replication proceeds in two directions at many sites simultaneously. Each strand has a 3' end and a 5' end. The enzymes that link DNA nucleotides to a growing daughter strand called DNA polymerases, add nucleotides only to the 3' end of the strand, never to the 5' end. So, a daughter DNA strand can only grow in the 5' to 3' direction. Another important enzyme, called DNA ligase, links the separated pieces together into a single DNA strand. The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits. The two main stages that take place after replication are transcription, the transfer of genetic information from DNA into an RNA molecule, and translation, the transfer of the information in the RNA into a protein. Genetic information written in codons is translated into amino acid sequences. Experiments have verified that the flow of information from gene to protein is based on a triplet code: The genetic instructions fro the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of three-base words, called codons. The genetic code is the set of rules giving the correspondence between codons in RNA and amino acids in proteins. The Genetic code is also called the Rosetta stone of life. Transcription produces genetic messages in the form of RNA. The "starting transcribing" signal is a nucleotide sequence called a promoter. Eukaryotic RNA is processed before leaving the nucleus. The kind of RNA that encodes amino acid sequences is called messenger RNA (mRNA) because it conveys genetic information from DNA to the translation machinery of the cell. The RNA has internal noncoding regions called introns, and coding regions called exons. Before the RNA leaves the nucleus, the introns are removes, and the exons are joined to produce an mRNA molecule with a continuous coding sequence. This cutting-and-pasting process is called RNA splicing. Transfer RNA molecules serve as interpreters during translation. To convert the three-letter words (codons) of nucleic acids to the one-letter, amino acid words of proteins, a cell employs a molecular interpreter, a special type of RNA called transfer RNA (tRNA). Ribosomes build polypeptides. A ribosome consists of two subunits, each made up of proteins and a kind of RNA called ribosomal RNA (rRNA). An initiation codon marks the start of an mRNA message. Transcription and translation have three stages: initiation, elongation, which adds amino acids to the polypeptide chain until a stop codon terminates translation, and termination. Mutations can change the meaning of genes. Any change in the nucleotide sequence of DNA is called a mutation. Viral DNA may become part of the host chromosome. Many viruses cause disease in animals and plants. bacteria can transfer DNA in three ways: transformation, transduction, and conjugation. Also bacterial plasmids can serve as carriers fro gene transfer.
Key Terms:
1. Virus - simply nucleic acid wrapped in a coat of protein.
2. Molecular biology - the study of DNA and how it serves as the chemical basis of heredity.
3. Nucleotides - long chains of chemical units.
4. DNA Polymerases - the enzyme that links DNA nucleotides to a growing daughter strand.
5. DNA Ligase - the enzyme that links the pieces together into a single DNA strand.
6. Transcription - the transfer of genetic information from DNA into an RNA molecule.
7. Translation - the transfer of the information in the RNA into a protein.
8. Genetic code - the set of the rules giving the correspondence between codons in RNA and amino acids in proteins.
9. RNA splicing - the process of cutting-and-pasting introns and exons.
10. Mutation - any change in the nucleotide sequence of DNA.
