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BIOLOGICAL BACKGROUND
? Central Dogma ? DNA and RNA Structure ? Replication, Transcription and Translation ? Techniques of Molecular Genetics
? Using restriction enzymes ? Using PCR
THE CENTRAL DOGMA OF MOLECULAR BIOLOGY
Genetic information flow: 1) From DNA to DNA during its transmission from generation to generation. 2) From DNA to Protein during its phenotypic expression in an organism.
Transcription: DNA to RNA (sometimes reversible). Translation: RNA to protein (irreversible). Occassionally, genetic information flows from RNA to DNA (reverse transcription).
HEREDITARY MATERIAL
Major structural differences between DNA and RNA are: 1) Hydrogen vs. Hydroxide
2) Thymine (T) vs. Uracil (U)
Most organisms and viruses have DNA as their hereditary material. Some viruses have RNA (single and double stranded).
BUILDING BLOCKS
? Phosphodiester links: Nucleotides are linked
together by phosphodiester
backbone.
? DNA molecules are typically composed of two strands that are related through complementary base pairs (Hydrogen bonds).
Anti-parallel strands
Purines ? A, G Pyrimidine ? C, T (U)
TYPES OF RNA
Four different classes of RNA molecules play essential roles in gene expression: ? Messenger RNA (mRNA): intermediaries that carry genetic information from DNA to the ribosomes where proteins are synthesized. ? Transfer RNA (tRNA): small RNA molecules that function as adaptors between amino acids and the codons in mRNA during translation. ? Ribosomal RNA (rRNA): structural components of the ribosomes, the intricate machines that translate nucleotide sequences of mRNAs into amino acid sequences of polypeptides. ? Small Nuclear RNA (snRNA): structural components of spliceosomes, the nuclear structures that excise introns from nuclear genes.
ORGANISMS
Organisms (including bacteria and blue-green algae) that lack true nuclei in their cells and that do not undergo meiosis Coupled transcription and translation
Organisms that have nuclei enclosed by a membrane within
their cells
CHROMOSOMES
Prokaryotic chromosome: ? Most contain a single, double stranded, circular DNA molecule. ? The DNA is mostly naked, but is supercoiled and looped.
Eukaryotic chromosome: ? Consist of very long, linear double stranded DNA. ? The DNA is complexed with twice as much protein (histones organized in nucleosomes). ? The protein helps compact it into the nucleus.
GENE
? Region of DNA that controls a hereditary characteristic. ? It usually corresponds to a sequence used in the production of a specific protein or RNA. ? A gene carries biological information in a form that must be copied and transmitted from each cell to all its progeny. This includes the entire functional unit: coding DNA sequences, non-coding regulatory DNA sequences, and introns. ? Genes can be as short as 1000 base pairs or as long as several hundred thousand base pairs.
GENE
Intron and Exon
Exon: segment of a eukaryotic gene that corresponds to the sequences in the final processed RNA transcript of that gene. In some species (including humans) exons are separated by long regions of DNA (introns).
Intron: Intervening sequences of DNA bases within eukaryotic genes that are not represented in the mature RNA transcript because they are spliced out of the primary RNA transcript.
TRANSFER OF GENETIC INFORMATION
Perpetuation of genetic information from generation to generation
Control of the phenotype:
Gene expression
DNA
.T. .T. .T. AAA
Transcription DNA-dependent RNA polymerase
mRNA
Replication
DNA-dependent DNA polymerase
DNA DNA
Reverse transcription RNA-dependent DNA polymerase (reverse transcriptase)
.T. .T. .T. AAA
.T. .T. .T. AAA
UUU
Translation Complex process involving ribosomes, tRNA and other molecules
Polypeptide
phe
(not folded)
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