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MOLECULAR GENETICS

RIBONUCLEIC ACID (RNA)

Distribution

Found all over the cell (nucleus, mitochondria, chloroplasts, ribosomes and the soluble part of the cytoplasm)

Types

Messenger RNA       (mRNA)          <5%
Ribosomal RNA       (rRNA)            Up to 80%
Transfer RNA            (tRNA)            About 15%

In eukaryotes small nuclear ribonucleoproteins (snRNP)

Structure
Single polynucleotide strand which may be looped or coiled (not a double helix).
Sugar Ribose (not deoxyribose).
Bases used: Adenine, Guanine, Cytosine and Uracil (not Thymine).

mRNA
A long molecule 1 million Daltons
Ephemeral
Difficult to isolate
mRNA provides the plan for the polypeptide chain.
rRNA
Coiled
Two subunits:

a long molecule 1 million Daltons
a short molecule 42 000 Daltons

Fairly stable
Found in ribosomes
Made as subunits in the nucleolus
rRNA provides the platform from protein synthesis

tRNA
Short molecule about 25 000 Daltons
Soluble
At least 61 different forms each has a specific anticodon as part of its structure.
tRNA translates the message on the mRNA into a polypeptide chain.

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© Paul Billiet 2014