RNA Structure and Function

I RNA

A. Def- Ribonucleic acid.

B. Components

1. Ribose, a sugar

2. Phosphate, a negatively charged group

3. Nitrogenous base, a complex organic structure that sits “away” from the sugar and phosphate

Phosphate

Nitrogenous

Bases

Sugar

C. Nitrogenous bases- Types

1. Adenine

2. Guanine

3. Uracil (in RNA), Thymine (in DNA)

4. Cytosine

D. Functions of RNA

1. The RNA represents a copy of a small segment of the information contained within the DNA. It is convenient to view the DNA as a giant “recipe book” that contains all of the information necessary to “make” the organism in which it is found. The “recipes” each specify the ingredients and their order of addition to make a needed protein. The protein “ingredients” are the 20 amino acids that serve as sub units of all proteins.The RNA is then a “xerox copy” of a single recipe within the book. This copy can then be transferred to the location within the cell where proteins are made.

2. This system allows the DNA to be held in a protected area of the cell, yet still be used. It is analogous to a “reference book” within a library. The information must be copied from the master copy to be removed from the protective location and used in a remote location.

3. The information is contained within the order of nitrogenous bases along the RNA strand. The sugar/ phosphate string functions to “hold” the “letters” (N bases) in the proper order to spell out the recipe for the protein to be made. The N bases are the letters in the genetic code and the sugar/phosphate backbone is the “paper” on which the code is “written”.

E. Types of RNA

1. Messenger RNA (mRNA)

a. Encodes a protein

b. refers to the “recipe copies” discussed above.

2. Ribosomal RNA (rRNA)

a. A structural component of the cellular machinery that “reads” the code contained on a messenter RNA

b. Does NOT encode a protein

3. Transfer RNA (tRNA)

a. Functions as a “carrier” of amino acids into the portion of the cell where the “recipe” is being decoded and the specified protein is being built.

b. Does NOT encode a protein

F. Comparisons between DNA and RNA

DNA

/

RNA

Found in the nucleus of Eukaryotic cells or the nucleoid region of prokaryotic cells / Found primarily within the cytoplasm of all cells
Contains deoxyribose as the sugar in its backbone / Contains ribose as the sugar in its backbone
Contains the nitrogenous base thymine as a letter in the code / Contains the nitrogenous base uracil as a letter in the genetic code
Contains all of the information necessary to manufacture an entire organism / Contains a small sub set of information from the DNA. This subset of information is usually the code that directs the manufacture of a single protein. (mRNA)
Double stranded helical structure / Single stranded structure with occasional “folding back” upon itself
Stable- Does not degrade easily / Unstable- Degrades readily

G. Processes that employ RNA within the cell

1. Transcription- Manufacture of RNA from a DNA template

` 2. Translation- manufacture of a protein using the information contained within a mRNA molecule

H. Handling RNA in the lab

1. Sterile techniques must be applied

2. No contact with skin, body fluids or unsterile surface. All skin and body fluids (saliva, tears, etc.) contain enzymes that degrade RNA.

I. Important research uses for RNA

1. Reverse transcriptase reading to make “clonable” genes.

2. Marker for gene expression- Genes that are “turned on” will be actively manufacturing RNA molecules that are “copying” them.

3. Regulation of gene expression through small interfering RNA molecules

II. Links for further exploration of RNA structure and function.

http://www.web-books.com/MoBio/Free/Ch3C.htm

http://www.ncc.gmu.edu/dna/rna.htm

http://www.ncc.gmu.edu/dna/mRNAanim.htm requires shockwave

http://www.pwc.k12.nf.ca/wadey/biotech/dna1.swf Construction of a DNA molecule

http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html Click and drag game for transcription and translation