Notes: Ribonucleic Acid

RNA is a copy of a gene in DNA that is responsible for delivering genetic information from the DNA in the cell nucleus to the ribosome in the cytoplasm and the completion of the process of protein synthesis (also known as translation.)  There are several distinctive differences between DNA and RNA.

RNA and DNA comparison

RNA

DNA

Its sugar molecule is ribose.

DNA has the deoxyribose sugar

Is single stranded

Is double stranded

Uses Uracil

Uses Thymine

Is smaller and leaves the nucleus

Remain in the nucleus

Has 3 basic types

There is only one kind of DNA

Is a copy of the genetic code

Is THE genetic code

 

Common Types of RNA:

 

  1. Messenger RNA - mRNA - a single uncoiled strand that transmits information from DNA to the ribosomes during protein synthesis; a sequence of three bases that codes for one amino acid is called a codon.
  2. Transfer RNA - tRNA - a single folded strand that bonds with a specific amino acid. A sequence of three bases on one end of a tRNA molecule is called an anti-codon.
  3. Ribosomal RNA - rRNA - a globular form that is the major constituent of the ribosomes.

 

 

Transcription - the process of forming a mRNA strand from a DNA strand.

Step 1: DNA Transcription

The image below is a mRNA table for determining which codons will code for each amino acid. You may download the table for offline reference as a .pdf, .rtf, or .doc file.

A detailed codon chart

 

 

Transcription of mRNA from DNA.

transcription of mRNA from DNA

Image source

Protein synthesis - the formation of proteins using information coded on DNA and carried out by RNA.

Watch the Teacher's Domain From DNA to Protein video and animation of transcription and translation at the link below. It is a narrated presentation that illustrates the process of protein synthesis, starting with chromosomal DNA inside the cell's nucleus. You'll learn how a gene is transcribed into messenger RNA and leaves the nucleus.

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Now, read the rest of the notes detailing the process of translation.

Translation - the assembling of protein molecules from information encoded in mRNA.

Now watch the short Protein Synthesis video clip. Pay close attention to references to codons.

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Afterward, think about what you've learned about how proteins are assembled. In what ways are RNA and DNA similar? Different?

 

The three essential processes involving nucleic acids are:

  • DNA duplicates itself in replication.
  • DNA produces RNA in transcription.
  • RNA produces proteins in translation.

 

 

Replication Transcription or Translation Errors can result in Mutations: any change in the DNA of an organism. Truths about mutations:

Mutations by cell type:

Mutations within chromosomes:

Deletion - a piece of a chromosome breaks off and is lost.

Image of deletion

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Inversion - a piece of a chromosome breaks off and reattaches itself in reverse order.

Image of inversion

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Translocation - a broken piece attaches to a nonhomologous chromosome.

Image of translocation

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Nondisjunction - a pair of chromosomes fail to separate during Anaphase I of meiotic cell division; results in trisomy (three of one kind in a diploid cell) or monosomy.(one of one kind in a diploid cell)

Image of nondisjunction

Image source

This karyotype shows three of the 21st chromosome; this results in the condition known as Down Syndrome

 

Gene mutations:

Point mutations - a change in a single nitrogen base in DNA. If the last letter is changed it may not cause a change in the amino acid (see table); however if the first letter is changed, it could result in a "nonsense" mutation;

This example shows a normal sequence:

Normal sequence of DNA

 

This shows what could happen if the first letter is changed:

Another sequence of DNA

 

The third codon now code for the Stop sequence instead of Arginine; the protein would be severely deformed. Cystic Fibrosis disease is caused by this type of mutation.

Adapted from the Wikipedia entry, Nonsense Mutation.

 

Frame-shift mutation - the addition or deletion of a nitrogen base, causing a shift in the sequence of codons so that the amino acid sequence is nonsense, coding for all the wrong amino acids.

This is the normal sequence:

3rd DNA sequence

 

This shows the deletion of the C-G pair in the DNA:

4th DNA sequence

A deletion of the C - G in the DNA here caused the first letters in the next codon to be included in this codon...all codons from here on have their first letter shifted to the previous codon and now code for different amino acids.

 

Mutagen: anything that causes a mutation. Some well known environmental examples are:

 

Here is a short video clip that covers additional information about mutations.

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