Central Dogma of Molecular Biology

CENTRAL DOGMA OF MOLECULAR BIOLOGY

Molecular Biology Laboratory, Biological Sciences Department
College of Science and computer Sciences, De La Salle University-Dasmarinas
ABSTRACT:
The central dogma of biology holds that genetic information normally flows from DNA to RNA to protein. In the experiment, DNA and RNA bead kits were used. Different coloured beads correspond to different nitrogenous bases, sugars and phosphates. Different structures of DNA and RNA were formed based on the sequences that were given.
INTRODUCTION:
DNA contains the complete genetic information that defines the structure and function of an organism. Proteins are formed using the genetic code of the DNA. Three different processes are responsible for the inheritance of genetic information and for its conversion from one form to another:
1. Replication: a double stranded nucleic acid is duplicated to give identical copies. This process perpetuates the genetic information.
2. Transcription: a DNA segment that constitutes a gene is read and transcribed into single stranded sequence of RNA. The RNA moves from the nucleus into the cytoplasm.
3. Translation: the RNA sequence is translated into a sequence of amino acids as the protein is formed. During translation, the ribosome reads three bases (a codon) at a time from the RNA and translates them into one amino acid.
The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred back from protein to either protein or nucleic acid. (Crick,1958) In other words, once information gets into protein, it can 't flow back to nucleic acid.

Prokaryotes and eukaryotes mainly undergo these processes but differ in how they perform these mechanisms.
This activity aims to achieve the following objectives: 1. Demonstrate the processes of replication, transcription and translation. 2. To be able to identify the enzymes, substrates and materials needed for each processes to occur.
MATERIALS AND METHODS:
DNA and RNA bead kits were used for this experiment. In the DNA kit: red beads corresponds to the phosphates, white beads for deoxyribose sugar, blue beads for cytosine, green beads for guanine, orange beads for adenine and yellow beads for thymine. In the RNA kit all are in the same color except yellow beads that represent thymine were replaced by purple beads for Uracil. The deoxyribose represented by the white bead was also changed with pink beads that represent ribose sugar. Hydrogen bonds are represented by small plastic rods. Enzymes were also represented by different shapes of beads. By using these materials, different sequences of DNA and RNA were produced.

RESULTS AND DISCUSSION:
As was given in the hand-out, the sequence provided (3’ C A G T T A A G G C T C C T A G G T T A T A A T T C G T T T C 5’) was done using the beads in the kit. After the DNA sequence was formed, it was transcripted into RNA:

In the first of these processes, DNA sequences are transcribed into messenger RNA (mRNA). Messenger RNA is then translated to specify the sequence of the protein. DNA is replicated when each strand of DNA specifies the sequence of its partner to make two daughter molecules from one parental double-stranded molecule. ANSWERS TO WORKSHEET:
The application of this is as follows: (Answers to worksheet questions) Given a particular sequence of DNA Polymer
3’ C A G T T A A G G C T C C T A G G T T A T A A T T C G T T T C 5’ * The first 5 bases at the 3” end of the complementary strand is 3’ CAAAG 5’ * The first 10 bases at the 5’ end of the complmentary strand is 5’ G T C A A T T C C G 3’
The different proteins involved in replication and their functions: Protein | Function | Helicase | unwinds parental double helix at replication forks | SSBP | binds to and stabilizes single-stranded DNA until it can be used as a template | Topoisomerase | relieves "overwinding" strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands | Primase | synthesizes an RNA primer at the 5 ' end of leading strand and of each Okazaki fragment of lagging strand | DNA pol III | using parental DNA as a template, synthesizes new DNA strand by covalently adding nucleotides to the 3 ' end of a pre-existing DNA strand or RNA primer | DNA pol I | joins 3 ' end of DNA that replaces primer to rest of leading strand and joins Okazaki fragments of lagging strand | DNA ligase | joins 3 ' end of DNA that replaces primer to rest of leading strand and joins Okazaki fragments of lagging strand | Assuming the presence of the complementary strand, the percentage composition of the polymer with respect to the A-T base pair with respect to the G-C base pair is as follows:
Total nucleotides: 31 % A-T base pair = (19/31) x 100 = 61.29%
A-T base pair: 19 % G-C base pair = (12/31) x 100 = 38.71%
G-C base pair: 12 In the segment, the following illustrates and indicates the direction of the synthesis of a. A 5-nucleotide RNA-primer
5’ G U C A A 3’ – leading strand
3’ G U U U C 5” – lagging strand b. A 12-nucleotide Okazaki fragment
3’ A G G T T A T A A T T C 5’ – lagging strand only Even if the organisms are different, the 20 amino acids can be decoded into 64 different combinations of nucleotide. Meaning that there are 4 different combination in a particular amino acid at maximum suggesting the principle that they have very similar compositions. After mRNA is transcribed, it undergoes post-translational modicfication. This includes capping at the 5’ end, tailing at the 3’ end, splicing and edicting of mRNA strand. But before the mRNA leave the nucleus, a surveillance occurs-that means that only “good” mRNAs are exported out to the cytoplasm, while the “bad” ones are degraded. Once the good mRNA arrives to the cytoplasm, it is now directed to a ribosome to construct a protein, thus translation begins. RNA polymerase identifies the promoter site. Ϫ-subunit of RNA polymerase detaches from RNA polymerase. Termination happens if RNA polymerase recognizes a termination sequence(UUUUU)

REFERENCES:

http://users.ugent.be/~avierstr/pdf/principles.pdf

http://www.cliffsnotes.com/study_guide/The-Central-Dogma-of-Molecular-Biology.topicArticleId-24998,articleId-24953.html

http://quizlet.com/3472699/table-161-bacterial-dna-replication-proteins-and-their-functions-flash-cards/

References: http://users.ugent.be/~avierstr/pdf/principles.pdf http://www.cliffsnotes.com/study_guide/The-Central-Dogma-of-Molecular-Biology.topicArticleId-24998,articleId-24953.html http://quizlet.com/3472699/table-161-bacterial-dna-replication-proteins-and-their-functions-flash-cards/