The Central Dogma of Molecular Biology

• 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 DAN 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. 

Genes

• 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.

http://www.biologycorner.com/bio1/DNA.html

Transcription    

• 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

     http://www.biologycorner.com/bio1/DNA.html

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

        Transcription diagram

    http://biology12-lum.wikispaces.com/Transcription--Danis+Wang

There are three kinds of RNA molecules made by transcription:       

1. mRNA: messenger RNA contains the information from the gene                       
2. rRNA: ribosomal RNA is used to make a ribosome     
3. tRNA: transfer RNA is attached to a specific amino acid

Ribosomes

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

mRNA

http://leavingbio.net/HEREDITY-HIGHER%20LEVEL.htm

rRNA - a ribosome is made of rRNA and protein. 

http://www.t6.lanl.gov/kys/

tRNA

http://www.wiley.com/college/boyer/0470003790/structure/tRNA/trna_intro.htm

Translation

• 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.

        http://www.nature.com/scitable/content/the-genetic-code-6903567 

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.

gene =     TAC AGG CTA GGG CTT ATA GCA ACA

mRNA =   AUG UCC GAU CCC GAA UAU CGU UGU 

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.

Translation

Another image of Translation

    Transcription and Translation video

Homework

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

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 question and the answer in your notebook.

Click "What is a gene?"

     7. What are genes?

     8. What are genes made of?

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

Click "What is a protein?"

    10. What happened to the person's foot?

    11. Where are receptor proteins located on cells? 

    12. What do receptor proteins do?

    13. What do structural proteins do?

    14. What molecule has the information for making proteins?

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

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

    17. How many proteins does a cell need? 

Mutation

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.