RNA Structure and Function

Ribonucleic acid (RNA) also consists of nucleotides, but these nucleotides contain the sugar ribose.

 RNA has A,C,G and U. 




Although both RNA and DNA are nucleic acids, there are key differences in the structure and function of RNA and DNA. 


There are three types of RNA and each is involved in protein synthesis.

Protein synthesis is the process in which the correct amino acids are connected together in the order that is written on the gene.


1. Messenger RNA

 Messenger RNA (mRNA) is produced in the nucleus by a process called transcription.

 Messenger RNA carries genetic information from DNA to the cytoplasm where the amino acids will be connected together.


2. Transfer RNA

Transfer RNA (tRNA) is a carrier molecule for amino acids, delivering them to the site of protein synthesis.



As there are 20 different amino acids, there are at least 20 different types of tRNA (at least one for each type of amino acid).


3. Ribosomal RNA

Ribosomal RNA (rRNA) and proteins are the parts of ribosomes.


Ribosomes help to build proteins

11.2 Gene Expression

DNA and RNA are involved in the synthesis of proteins. 

The genes in DNA contain the instructions for the amino acid sequence of a protein. 

Since enzymes are proteins, an error in the gene for that enzyme could render the enzyme non-functional. 

If an enzyme is defective, then the cell may not be able to perform a chemical reaction. 

This can create inborn errors in metabolism that lead to metabolic diseases.

Structure and Function of Proteins

Proteins differ in the number and sequence of amino acids. 

This sequence of amino acids gives each protein a unique shape and function


From DNA to RNA to Protein

In order to synthesize a protein, the genetic information in the DNA must be converted to an amino acid sequence.  Its similar to the way that someone needs to read a recipe and mix the correct ingredients together.


Step 1- Transcription involves the synthesis of mRNA from template DNA. Think of this step as making a RNA photocopy of a recipe from your DNA cookbook

Step 2- During translation, the correct amino acids are dropped off by tRNA's according to the instructions written on the mRNA.



 Toggle open/close quiz question

Which of the following statements is true?
    a.Ribosomes are made of mRNA
    b.Proteins store the information that is used to make DNA
    c.DNA contains the information to make proteins
    d.tRNA's carry lipids



The Genetic Code

Within a gene, information for the amino acid sequence of a protein is encoded in a triplet code. The triplet code means that three bases are read at a time and each three bases request one of the twenty amino acids.

Imagine if you had a recipe that used 3 letter abbreviations for the ingredients water, sugar and flour. It might look like this: WATSUGFLO 

This triplet code is transcribed into the codons in mRNA. Each codon specifies one of the twenty different amino acids.

Amino acids can be requested by more than one codon.




During transcription, a strand of mRNA is formed that is complementary to the sequence within the DNA. 

Transcription begins when RNA polymerase to the DNA. 

The DNA helix is unwound and the primary mRNA strand is made by RNA polymerase.

The primary mRNA strand is then processed to remove introns.

The remaining sequence of genetic information, the exons, are retained in the mature mRNA for protein synthesis. 

Exons contain the information to build a protein, introns are just extra DNA- like advertisements in a cooking magazine. 




Translation: An Overview

The translation of a mature mRNA into proteins requires several enzymes, tRNA, and rRNA.

The tRNA is a single-stranded RNA molecule with an amino acid bound to one end and an anticodon on the other end.

The anticodon is complementary to the corresponding mRNA codon and can temporarily match up to it. This is how the tRNA knows when to drop off its amino acid as a protein is being made.

As a mature mRNA moves to a ribosome, the sequence of codons in the mRNA determines the sequence of anticodons that can match up.

The order that the tRNA molecules drop off their amino acids determines the order of the amino acids of the protein that is being made. 





 Toggle open/close quiz question

Which of the following lists are needed for a protein to be made?
    a.DNA polymerase, mRNA, mutation
    b.codon, ribosome, DNA polymerase
    c.tRNA, gene, DNA polymerase
    d.a gene, RNA polymerase, tRNA, ribosome