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BIO SCI 99 Chapter Notes -Purine, Heterocyclic Compound, Furanose

Biological Sciences
Course Code
Brian Sato

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[Week 01]
MONDAY - Class Intro., Central Dogma, Nucleic Acids
The Central Dogma: Information Flow from DNA to RNA to Proteins
1: Turning point in understanding how info. flows in bio. sys.
Watson & Crick's determination of DNA structure
a) Their model of DNA structure:
• reasoned from data collected by other scientists
• consisted of 2 strands of DNA wound about one another in a spiral,
double helix.
- each strand composed of
• a long string of the 4 nucleotides containing the bases:
adenine (A)
guanine (G)
cytosine (C)
thymine (T)
- Nucleotides in one strand pair with those in the other.
• A - T
• G - C
- the strands are said to be complementary b/c the sequence of
one strand contains info. about the sequence of the other strand.
b) Watson & Crick realized the DNA could logically be replicated by separating the 2
strands & using each as a template to synthesize a new, complementary strand
2: Genetics could be described in chemical terms with the discovery of the DNA structure.
a) DNA & Proteins are linear polymer
Idea is that sequence of nucleotides in DNA sequence of amino acids in protein, but...
pgs. 47-50

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DNA is in the nucleus
Proteins are synthesized in cytoplasm
need intermediate to shuttle info. between the 2 locations
intermediate = RNA
3: Crick proposed:
biological info. flows in the direction of
DNA RNA Proteins
DNA acts as a template for its own synthesis (DNA DNA)
a) ex. of exceptions to the central dogma:
• certain enzymes can synthesize DNA from RNA
• some viruses use RNA as a template to make more RNA
4: RNA is widely accepted to be the molecule that mediates the transfer of info. from DNA in the
nucleus to the site of protein synthesis in the cytoplasm.
3 different types of RNA req. for the process
Ribosomal RNA:
1: Ribosomes
• Particles in the cytoplasm where protein synthesis occurs.
• Are large structures composed of both protein and RNA.
• Consists of a large subunit and small subunit.
The Central Dogma of Information Flow: DNA RNA Protein
The info. to replicate DNA is inherent in its structure (curved arrow).
Info. flows from DNA to RNA by transcription.
Info. flows from RNA to protein by translation.
In some instances info. can flow backwards from RNA to DNA (reverse
No evidence exists for info. flow from protein to nucleic acid.

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2: Ribosomal RNA (rRNA)
• The RNA component in ribosomes
Messenger RNA (mRNA):
1: Why rRNA is not the carrier of information from DNA to protein:
• rRNA is an integral part of the ribosomes which makes specific proteins.
• The nucleotide composition of rRNA is pretty much the same in different organisms where as
the nucleotide composition of chromosomal DNA varies greatly from organism to organism.
2: Messenger RNA (mRNA)
a template used by ribosomes (protein-synthesizing factories) to direct the construction of the
protein sequence.
• Only needed short-term to instruct the synthesis of proteins.
3: RNA Polymerase:
• Enzyme that carries out RNA synthesis by the process of transcription.
4: Transcription:
• The process of making single-stranded RNA copies of a DNA strand
• RNA polymerase Synthesizes RNA by reading one strand of the duplex DNA, paring RNA
bases to the bases in the DNA strand, to synthesized a single-stranded RNA molecule that has
a sequence directed by the DNA sequence.
The Process of Transcription:
RNA polymerase opens the DNA duplex and uses one strand as a template for RNA synthesis.
The Polymerase matches incoming nucleotides to the DNA template strand by base pairing and joins them together to form an RNA chain.
As RNA polymerase advances along the template strand, the two DNA strands reassociate behind it to re-form to double helix.
When the gene has been completely transcribed, the polymerase dissociates from DNA, releasing the completed RNA transcript.
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