TRANSCRIPTION & RNA

SDK

February 16, 2013

Proteins/ Gene Expression

• Proteins make up all living materials

• Proteins are composed of amino acids – there are 20 different amino acids

• Different proteins are made by combining these 20 amino acids in different combinations

• Proteins are manufactured in the ribosomes under the strict control and order of DNA.

• The DNA language is made up of letters which are ATGCATATGGAATCAG

• These letters forms Words• ATC GCA GGA AUU AUG

• These words make sentences

•

Protein Synthesis

DNA, Transcription and Protein Synthesis

• DNA contains the genetic information to make amino acids•Amino acids combine to make proteins

• These proteins determine the physical traits of an organism and control cellular functions.

• Proteins do everything, and DNA gets all the credit!

• Transcription is the Reading of the DNA and

Changing the code to mRNA.• Translation is changing the mRNA into a trait by

Using tRNA to interpret the mRNA.

Transcription & Translation

• DNA has regions of coding and non-coding. The regions of DNA that code for proteins or traits are called EXONS, while the regions that do not code for proteins are called INTRONS.

Introns & Exons

Making a Protein—Transcription•First Step: Copying of genetic information from DNA to RNA called Transcription

•Part of DNA temporarily unzips and is used as a template to assemble complementary nucleotides into messenger RNA (mRNA).

• Transcription occurs inside the nucleus in a two step sequence of events.– Pre-mRNA includes both introns and exons for the

gene.– mRNA is only the coding portion (exons).

• Translation occurs in the cytoplasm at the ribosomes.– Reminder: The are three (3) types of RNA

• Messenager (mRNA)• Transfer (tRNA)• Ribsomal (rRNA)

Site of Transcription&Translation

Process of Transcription

Transcription- process that makes mRNA from DNA

1. DNA unzips into 2 separate strandsA. DNA Helicase is the enzyme that breaks H-bond

2. Free floating RNA NITROGEN BASES in the nucleus pair up w/unzipped DNA NITROGEN BASES:

A. Cytosine(C) pairs with Guanine(G)

* (G) with (C)

B. Uracil(U) pairs with Adenine(A)

* (A) with (U)

C. Thymine (T) pairs with Adenine (A)

***remember (T) is only with DNA

3. After all the pairing is done:

• a single strand of RNA has been produced.

4. Genetic code from DNA is transferred to mRNA

5. The code obtained from DNA lets the mRNA know which amino acids to pick up:

• code is a set of 3 nitrogen bases = Codon

A U G G G C U U A A A G C A G U G C A C G U U

This is a molecule of messenger RNA.

It was made in the nucleus bytranscription from a DNA molecule.

mRNA molecule

codon

Messenger RNA

A U G G G C U U A A A G C A G U G C A C G U U

A ribosome on the rough endoplasmic reticulum attaches to the mRNA

molecule.

ribosome

Ribosome

A U G G G C U U A A A G C A G U G C A C G U U

It brings an amino acid to the first three bases (codon) on the mRNA.

tRNA molecule

anticodon

U A C

A transfer RNA molecule arrives.

The three unpaired bases (anticodon) on the tRNA link up with the codon.

Transfer RNA

A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule comes into place, bringing a second amino acid.

U A C C C G

Its anticodon links up with the second codon on the mRNA.

Transfer RNA

A U G G G C U U A A A G C A G U G C A C G U U

A peptide bond forms between the two amino acids.

Peptide bond

C C G U A C

Transfer RNA

A U G G G C U U A A A G C A G U G C A C G U U

The first tRNA molecule releases its amino acid and moves off into the cytoplasm.

C C G U A C

Transfer RNA

A U G G G C U U A A A G C A G U G C A C G U U C C G

The ribosome moves along the mRNA to the next codon.

Transfer RNA

A U G G G C U U A A A G C A G U G C A C G U U

Another tRNA molecule brings the next amino acid into place.

C C G

A A U

A U G G G C U U A A A G C A G U G C A C G U U

A peptide bond joins the second and third amino acids to form a polypeptide chain.

C C G C C G

Polypeptide chain

A U G G G C U U A A A G C A G U G C A C G U U

The polypeptide chain gets longer.

G U C

A C G

The process continues.

This continues until a termination (stop) codon is reached.

The polypeptide is then complete.

Termination (stop) codon

DNA and Protein Synthesis - Summary

Use one of the codon charts on the next page to find the amino acid sequence coded for by the following mRNA strands.

CAC/CCA/UGG/UGA

___________/___________/___________/____________

AUG/AAC/GAC/UAA

___________/___________/___________/____________

CAC/CCA/UGG/UGA

___________/___________/___________/____________Histidine1st

Bas

e

2nd Base

3rd Base

Proline Tryptophan Stop

AUG/AAC/GAC/UAA

___________/___________/___________/____________Methionine Asparagine Aspartic Acid Stop

DNA and Mutations

Mutations are any changes that take place in DNA:

• Can be spontaneous or caused by mutagens• ex: Chemicals, high temperatures, UV light, radiation

• Can change the genetic code, and be replicated when forming new body cells.

• In sex cells, can be passed on to offspring.

DNA and Mutations – Lets looks at different mutations

THE DOG BIT THE CAT

DNA and Mutations - Substitution

THE DOG BIT THE CAT

• Substitution - Replace just one letter:

THE DOG BIT THE CAR

DNA and Mutations - Deletion

THE DOG BIT THE CAT Deletion: Delete just one letter (T):

THE DOG BIT HEC AT

DNA and Mutations-Insertions

THE DOG BIT THE CAT

• Insertion - Add just one letter (E):

THE DOE GBI TTH ECA T