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DNA, RNA, and Proteins

Page history last edited by Darrell Sharp 12 years, 5 months ago


        The Central Dogma of Molecular Biology

Central Dogma

  • The DNA information is transferred to RNA.
  • The RNA information is used to build a specific protein.
  • The protein has a specific function.
  • The DNA information can be copied into another DNA molecule by proteins (replication) 


  • The central dogma of biology explains how information moves and is used by cells and organisms. It explains how life works.




California Science Standards


Cell Biology

  •  Students know the central dogma of molecular biology outlines the flow of information from transcription of ribonucleic acid (RNA) in the nucleus to translation of proteins on ribosomes in the cytoplasm.
  • Students know how genetic engineering (biotechnology) is used to produce novel biomedical and agricultural products. 






  • The information in DNA is in the sequence of bases of the nucleotides.

  • The bases are the "letters" of the "words."

  • Only one strand of the DNA is used for information.

  • DNA words are three letters long (triplets):  TACCAGGGCACATTC

  • One "sentence" is called a gene.

  • A gene has information for making one protein.

  • DNA has billions of nucleotides which make thousands of genes.


The central dogma of biology states that:

  • The information of a gene is copied into an RNA molecule.
  • The RNA contains the same information as the gene.
  • The information of the RNA is used to build a protein. 
  • The protein performs a function for the cell.





    Human DNA has approximately 25,000 to 35,000 genes.










    Central Dogma: DNA ----> RNA ----> Protein 



RNA Structure 


RNA is like DNA except it is

  • single-stranded,
  • has a ribose sugar,
  • and has the base U instead of T.


The base uracil (U) is almost identical in structure to thymine (T).


  • U pairs with A.










  • DNA ----> RNA
  • in the nucleus 
  • by the enzyme RNA polymerase 


Transcription: copying the information in a gene into an RNA molecule       

  1. RNA polymerase, an enzyme, unzips the DNA at the beginning of a gene       
  2. Free RNA nucleotides pair with complementary DNA nucleotides (A::U & C::G)   
  3. RNA polymerase bonds the nucleotides together           
  4. At the end of the gene, RNA polymerase releases the DNA and the new RNA molecule           




         Transcription animation





    DNA  ----(transcription)----> RNA  ----(translation)----> Protein  




        Transcription diagram







There are three kinds of RNA molecules made by transcription:       


  1. mRNAmessenger RNA contains the information from the gene                       
  2. rRNAribosomal RNA is used to make a ribosome     
  3. tRNAtransfer RNA is attached to a specific amino acid






  • Ribosomes are made of rRNA and protein. 
  • Ribosomes use mRNA and tRNA to build proteins.
  • They do the work of translation







rRNA - a ribosome is made of rRNA and protein. 

70s ribosome











  • RNA ----> Protein
  • in the cytoplasm 
  • by ribosomes 


Translation: using mRNA information to build a protein.    


  • The mRNA reading frame has 3 nucleotide “words” called codons.           
  • Each codon codes for a specific amino acid or for starting or stopping translation.
  • Ribosomes carry out the process of translation in the cytoplasm of the cell.       
  • The ribosome holds the mRNA and tRNA molecules.
  • The tRNA anticodons match the mRNA codons by complementary base pairing.           
  • The amino acids on the tRNA molecules are bonded together by the ribosome.
  • At the stop codon, the ribosome releases the mRNA and the new protein molecule.





The Genetic Code


  • Each mRNA codon matches a specific tRNA anticodon.
  • Each tRNA is bonded to a specific amino acid.
  • The codons have the information for the specific amino acid sequence in the protein.


  • Each gene has a unique sequence of nucleotides.
  • Transcription makes a unique mRNA.
  • Each mRNA codes for a specific protein.
  • 1000s of genes produces 1000s of proteins that build and maintain cells and organisms.



This table shows the mRNA codons and the amino acids they code for during translation.

This is called the genetic code.

Each codon represents an amino acid.

There are 20 different amino acids.

The amino acid names are abbreviated, like Phe, Ser, Met, etc.





How to use the genetic code


Look at the sequence of bases of the nucleotides of a gene of DNA.

Write the sequence of bases of the complementary RNA made by transcription.

Write the abbreviations of the amino acids in the protein made by translation.





protein = Met--Ser--Asp--Pro-Glu--Tyr--Arg  [stop]



  • Usually proteins are 100s or 1000s of amino acids in length.


  • The structure and function of the protein is determined by the sequence of amino acids.





Peptide syn.png


Another image of Translation

external image translation3.gif








    Transcription and Translation video








Vocabulary - define these terms in your notebook. Write the word and a definition.

  1. gene
  2. nucleus
  3. transcription
  4. RNA polymerase
  5. mRNA
  6. translation
  7. ribosome
  8. cytoplasm
  9. codon
  10. amino acid
  11. protein
  12. central dogma of biology 







Assignment - Part I


Click Animations from The University of Utah


Click Tour the Basics



Click "What is DNA?"


    Read the questions: 


    1. Where are the instructions for a cell? 

    2. What does DNA stand for?

    3. What are the letters of the DNA alphabet?

    4. How many letters are in a DNA word?

    5. What are the "sentences" of DNA called? 

    6. The DNA "sentences" are instructions for making what molecule? 


    Watch the animation. Use the "Next" button to continue. 


    Write the questions and the answers in your notebook.




Click "What is a gene?"


    Read the questions: 


     7. What are genes?

     8. What are genes made of?

     9. What are three examples of proteins in the animation?


    Watch the animation. Use the "Next" button to continue. 


    Write the questions and the answers in your notebook.




Click "What is a protein?"


    Read the questions: 


    10. Where are receptor proteins located on cells? 

    11. What do receptor proteins do?

    12. What do structural proteins do?

    13. What molecule has the information for making proteins?

    14. What molecule carries the information - the message - from the nucleus to the cytoplasm?

    15. What structure in the cytoplasm uses the message to build the protein? 

    16. How many proteins does a cell need? 


    Watch the animation. Use the "Next" button to continue. 


    Write the questions and the answers in your notebook.





Assignment - Part II


Click Animations from The University of Utah


Click DNA to Protein



Click Transcribe & Translate a Gene or the image


Click "Click Here To Begin"


Write the questions and the answers in your notebook.


   17. What is the first thing that happened to the DNA?

        (Refresh the page if you miss it) 


   Type the complementary bases for the transcribed RNA molecule.


   18. What RNA base pairs with the DNA base "A"?


   Move the mouse over the RNA strand. Move the green box over the AUG sequence.


   19. AUG is the start codon. What amino acid corresponds to AUG?

        (Use the genetic code to find AUG)


   Move the green box over AUG, click on it. 

   Find the codon in the genetic code.

   Find the three letter abbreviation for the amino acid next to the codon.

   Click and drag the amino acid to the flashing box.

   Repeat until you reach the stop codon.


   20. List the names of the amino acids in the protein. 









Mutation is a change in the DNA code.  


Gene mutations happen in a single gene.                       

  • Point mutation is a change in a single nucleotide, like A is changed to C. 
  • Frameshift mutation is an insertion or deletion of a nucleotide which changes the reading frame.     


Chromosomal mutations are large changes in chromosomes that affect many genes.

  • Duplication and deletion happen during unequal crossing over causing one chromatid to have repeated genes and one chromatid to have missing genes. 
  • Translocation is the exchange of pieces of chromosomes between nonhomologous pairs which can cause duplications and deletions. 


Mutations can have no effect (silent), a small effect, or a large effect.                      

  • Mutations in noncoding regions or mutations that don’t change the amino acids in the proteins do not affect the phenotype.     
  • Point mutations may change one amino acid in the protein which could have a small or large affect on the function of the protein.
  • Frameshift mutations usually have a large affect on the protein because many amino acids are changed.   
  • Chromosomal mutations always have a large affect on phenotypes because many genes are duplicated or deleted



Only mutations that happen in sex cells are passed on to offspring; mutations in body cells are not passed on.   



Mutations are caused by mistakes in DNA replication and by mutagens.

  • Mutagens are things in the environment that cause mutations. 
  • Examples are UV radiation from sunlight, nuclear radiation, industrial chemicals, and natural chemicals like nicotine in tobacco.





Mutation Review Questions


  1. Compare gene mutations: point mutations and frameshift mutations - how are they similar and different? 
  2. Which gene mutation has a larger effect, point mutation or frameshift mutation? Why?
  3. What is a chromosomal mutation? 
  4. Which has a larger effect, gene mutation or chromosomal mutation? Why?
  5. What are the possible effects of a mutation?
  6. How does a point mutation affect transcription and translation?
  7. How does a frameshift mutation affect transcription and translation?
  8. Are all mutations in a parent passed on to an offspring?
  9. How are mutations passed on to offspring? (In what kind of cell do they have to occur?)
  10. What causes mutations?





Genetic Engineering and Biotechnology






  • genetic engineering: changing the genes of an organism to create new functions or substances.


  • genetically modified organism (GMO): an organism that has been genetically engineered.


  • transgenic organism: an organism with genes from another species.


  • biotechnology: the scientific methods used to make GMOs and their by-products. 







Biotechnology WebQuest




Use this webpage to answer the questions: Explore More - Genetic Engineering 


Write the questions and your answers in your notebook.


Click on "Uses"



1-3. Find three different ways that genetic engineering is used and describe them.



Click on "GE In-Depth" (Move you mouse over each picture to see how cloning happens)


4. What is recombinant DNA technology?



5-8. How are genes transferred? (4pts: all accurate. 3pts: one error. 2pts: several errors 1pt: partially accurate)



9-12. How was the first mammal, a sheep named Dolly, cloned? (4pts: all accurate. 3pts: one error. 2pts: several errors 1pt: partially accurate)




Click on "Search"



13. What is bioremediation?



14. How can genetic engineering be used to help people with genetic diseases?










Biotechnology Practice Quiz 



Comments (4)

San said

at 4:18 pm on Feb 3, 2012

Mr. Sharp! Is cloning part of genetic engineering?

Darrell Sharp said

at 6:35 pm on Feb 3, 2012

Cloning is not part of genetic engineering.
Biotechnology includes both genetic engineering and cloning.
(Some people may include cloning with genetic engineering, but most people do not because the genes of the cloned organism haven't been changed.)

Katrina said

at 7:52 pm on Jun 5, 2012

mr. sharp! Point mutation and frameshif mutation. which one has larger effect and why?

Darrell Sharp said

at 10:20 pm on Jun 5, 2012

Frameshift mutations have larger effects because they change how the codons are read, so the whole protein is messed up and doesn't function. Point mutations only change one letter, so the protein isn't affected that much.

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