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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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