The CENTRAL DOGMA in BIOLOGY



HOW does DNA determine our traits?

The Central Dogma in Genetics

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Trait

The CENTRAL DOGMA in BIOLOGY:

Introduction to how proteins are made.

We have learned to predict inherited traits, we have learned the structure of DNA, and we have learned to analyze DNA, but the biggest question of all is how does DNA code for our traits? What does DNA actually do?

Think about some of the diseases and conditions you have studied in class and in your reading. List the disease/condition, its symptoms and then its molecular cause (what is happening with the protein?).

|Condition |Symptoms |Molecular Cause: what is happening with the protein? |

|Tay Sachs | | |

|Sickle Cell Anemia | | |

|Cystic Fibrosis | | |

| | | |

Based on this information what types of molecules does DNA code for

____________________________

CENTRAL DOGMA OVERVIEW

Cells in our body use the recipes written in your genes to make proteins - just like you use recipes from a cookbook to make dinner. Proteins do much of the work in your cells and your body as a whole. Some proteins give cells their shape and structure. Others help cells carry out biological processes like digesting food or carrying oxygen in the blood. Using different combinations of the As, Cs, Ts and Gs, DNA creates the different proteins - just as you use different combinations of the same ingredients to make different meals.

The ‘Central Dogma’ in biology states that DNA provides a code for proteins. It is the proteins in our body that determine all of our traits. Humans have tens of thousands of different kinds of proteins, each with a specific structure and function. Hormones, antibodies, insulin, and digestive enzymes are all different types of proteins. Proteins are the key to your functioning and traits. It is our DNA tells our bodies what proteins to make.

PROTEIN STRUCTURE

So exactly what is a protein? Proteins are highly complex molecules made up of smaller subunits called amino acids. There are about 20 different amino acids. Amino acids link together to form chains which make-up the protein. A typical protein may contain 500 or more amino acids. Each protein has its own unique number and sequence of amino acids which determines its particular structure and function.

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THE ROLE OF DNA IN MAKING PROTEINS

Since DNA is the genetic material that we inherit, but proteins are actually responsible for determining our traits, then DNA must provide our cells with the information on what proteins should be made or synthesized. DNA provides a code, in the language of base pairs (A, T, G, and C) that instructs the cells to make specific proteins.

DNA is safely stored in the nucleus of a cell, but a messenger is needed to take the information to the place where proteins are assembled. The information from the DNA in the nucleus is carried to the site where proteins are manufactured. The sites of protein manufacturing are called ribosomes.

The messenger of this information is called mRNA or messenger-RNA (RNA stands for ribonucleic acid). The process of reading a DNA strand and creating RNA is called transcription. The process of using the code of RNA to assemble a protein is called translation.

DNA transcription mRNA translation protein

RNA:

RNA is made from the DNA and has a fairly similar structure to DNA, with a few differences we can summarize below in a Venn Diagram:

TRANSCRIPTION: creating mRNA from DNA

1. First, the 2 strands of DNA ‘unzip’ exposing the gene (section of DNA holding the code for that particular protein)

2. Using one strand of DNA as a template, a complimentary strand of RNA is produced. Wherever a thymine (T) would have been used for DNA, uracil (U) is used instead.

3. Messenger RNA (mRNA) carries the message to a ribosome, where the protein is then manufactured.

4. Inside the nucleus, the 2 strands of DNA rejoin and recoil.

Here is an example of an RNA strand made from a DNA molecule:

1. 2. 3. 4.

______________ ______________ ______________ ______________

ATAGATCTCACCTAT ATAGATCTCACCTAT ATAGATCTCACCTAT ATAGATCTCACCTAT

TATCTAGAGTGGATA UAUCUAGAGUGGAUA TATCTAGAGTGGATA

TATCTAGAGTGGATA TATCTAGAGTGGATA UAUCUAGAGUGGAUA

1.Original DNA 2. DNA strand 3. mRNA, messenger, 4. Original DNA

strand-stays in separates . makes a copy of it- safely in nucleus.

nucleus of cell. and unzips. self from one strand mRNA travels to

of the DNA. ribosome where

proteins are made.

Translation: Creating a Protein from RNA

Translation is the process that creates, or synthesizes, proteins from the genetic code, which is now in mRNA form. The mRNA is read in triplet, _________ base pairs at a time. Each triplet, called a ________________, codes for a specific amino acid that will be added to the protein.

For example: consider the following sequence of mRNA:

A u g g a u c c u c g u …

This sequence would be read, 3 bases at a time, as

- - -

The codons above represent the following different amino acids.

- - -

We use the following chart to determine which amino acids are coded for each of the ______ possible triplet combinations of A, U, C, and G.

Note that some triplet combinations code for the same amino acids!

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Somethings to understand about the mechanics of protein synthesis:

Protein are built in the _____________________ which are organelles in a cell.

The ribosome begins adding amino acids when it finds the mRNA ‘start’ codon: _______

The protein is ‘complete’ when the ribosome reaches on of the 3 STOP codons: __________ ____________ & ___________

This synthesis uses another set of RNA, known as transfer RNA, or tRNA. Each tRNA has 2 ends: an ___________________________________ (which is complementary to a codon) and the corresponding _________________________________________

The Steps of PROTEIN SYTHESIS

1. The ribosome begins at the start codon AUG. It attracts the tRNA with the correct anti-codon. Remember each tRNA has a anticondon that mirror a code on the protein wheel found on the previous page and has a specific amino acid (in the case of the start codon, it would be methionine).

2. The tRNA attaches to the start codon.

3. The ribosome then reads the next codon, and attracts the corresponding tRNA, which attaches to the corresponding codon.

4. The two amino acids (attached to each tRNA) bond together – the beginning of a protein.

5. The ribosome releases the first tRNA, then reads next codon.

6. The ribosome continues this process, growing a chain of amino acids. The resulting chain of amino acids is the primary structure of the protein.

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7. The process ends once the ribosome reaches one of the 3 STOP codons – UGA, UAA or UAG.

8. The protein folds to obtain its secondary, tertiary, and quaternary structure.

9. The protein is complete![pic]

Central Dogma Analysis Questions (also reference text chapter 12-3 (pages 300-306)

1. Summarize the ‘Central Dogma’ of biology.

2. Describe the structure of a protein (what are proteins made of? What makes proteins different from each other? How is its final structure formed?)

3. Where is DNA stored in a cell? Where are proteins manufactured in a cell? What molecule delivers the ‘message’ between those 2 places?

4. Compare and contrast RNA and DNA (give both similarities and differences)

Use the following base sequence of ONE strand of a DNA molecule to answer 5-9:

…T A C A A T G C C A G T G G T T C G C A C …

Draw the complete DNA: provide both the strand given above and its complementary strand.

5. Give the base sequence of the strand of mRNA that will be read from the original DNA strand

6. What sequence of amino acids (protein fragment) would this mRNA code for? Why do you think I only had you do a fragment rather than a whole protein?

7. If the seventh nucleotide in the original DNA strand was replaced with a cytosine, what would the resulting mRNA look like?

8. What would the resulting protein fragment (sequence of amino acids) look like?

9. What is the start codon? What then is always the first amino acid of any protein?

10. Which 3 codons cue the ribosome to stop adding more amino acids (stop codons)?[pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic][pic]

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“He has is Dad’s curly hair” –OR-“He appears to have inherited a gene or genes from his father that makes a protein that causes his hair to curl.”

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RNA

DNA

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