Transcription, & Synthesis Do you remember what are made of ?

• Hundreds of Amino Acids link together to make one Protein • There are 20 types of amino acids, some we can make, and some we can’t • There are infinite combinations of amino acids • Can be hundreds or thousands monomers long These long chains are called polypeptide chains

Protein Synthesis

• Protein synthesis is the process in which a makes protein based on the message contained within its DNA. • However: – DNA is only found in the nucleus – Proteins are only made outside the nucleus – in the . • Houston, we have a problem. Protein Synthesis

• How do the many different messages within the DNA molecule get to the many outside the nucleus? • A molecular cousin of DNA – RNA – is used to carry these messages. Ribonucleic Acids (RNA)

• The job of RNA (ribonucleic acid) is to carry messages from the DNA (in the nucleus) to the ribosomes (in the cytoplasm). • There are three types of RNA: 1. mRNA – carries a message from the DNA to the cytoplasm 2. tRNA – transports amino acids to the mRNA to make a protein 3. rRNA – make up ribosomes, which make protein. Ribonucleic Acids (RNA)

• RNA is almost exactly like DNA, except: – Contains a ribose sugar, instead of a deoxyribose sugar (hence the name…) – Contains instead of . – RNA is single-stranded, not double-stranded (usually…) Ribonucleic Acids (RNA) Protein Synthesis

• Occurs in TWO steps: 1. – the genetic information from a strand of DNA is copied into a strand of mRNA 2.Translation – the mRNA, with the help of the , forms a chain of amino acids (eventually forming a protein) based on the information contained on the mRNA. The Central Dogma

. This order of events is called the central dogma of molecular :

R E N DNA RNA P O T I Step One: Transcription

1. DNA unzips: split apart base pairs and unwind the DNA double helix. 2. Bases pair up: Free in the cell find their complementary bases along the new strands with the help of RNA polymerase. What will be different?? 3. New backbone formed: The sugar-phosphate backbone is assembled to complete the RNA strand, and separates from the DNA strand. Step One: Transcription

. Watch this simplified animation: http://www.stolaf.edu/people/giannini/flashani mat/molgenetics/transcription.swf

. Watch the more complex animation! . http://www- class.unl.edu/biochem/gp2/m_biology/animat ion/gene/gene_a2.html

Step One: Transcription

. Try it! What RNA strand will be made from the following DNA sequence?

TACGCATGACTAGCAAGTCTAACT

Step One: Transcription

. Try it! What RNA strand will be made from the following DNA sequence?

TACGCATGACTAGCAAGTCTAACT AUGCGUACUGAUCGUUCAGAUUGA

Step 1½: RNA Editing

• An mRNA molecule has to be “edited” in order to be useful. There’s a lot of unnecessary information that needs to be removed. • An mRNA sequence that does NOT code for protein is called an interon. A sequence that is useful in making a protein is called an exon. Step 1½: RNA Editing

DNA

transcription pre-RNA (in nucleus) exon 1 interon exon 2 interon exon 3

RNA editing interon

interon RNA (in cytoplasm) exon 1 exon 2 exon 3 Step Two: Translation “to decode or decipher the meaning of”

• Now that our mRNA molecule has been made, it’s time for its message to be made into a protein sequence. • How does the mRNA sequence translate into an amino acid sequence? Step Two: Translation

. Problem: – There are 20 different amino acids. – There are 4 RNA bases.

A T C G phe ile val pro ala his asn asp cys arg leu met ser thr tyr gln lys glu trp gly Step Two: Translation

. Watch this simplified animation: http://www.stolaf.edu/people/giannini/flashani mat/molgenetics/translation.swf

. Watch the more complex animation! . http://www- class.unl.edu/biochem/gp2/m_biology/animat ion/gene/gene_a3.html

Step Two: Translation

1. So how do you exactly go about determining what protein your cells are going to make? 2. FIRST, Divide the mRNA sequence into codons. As you just saw and heard, codons are three-base sections of mRNA:

AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA Step Two: Translation

2. Since each 3-letter combination “codes” for an amino acid, you need to figure out what amino acid matches up with each codon: AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA

? The Step Two: Translation

2. Since each 3-letter combination “codes” for an amino acid, you need to figure out what amino acid matches up with each codon: AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA met ? The Genetic Code Step Two: Translation

2. Since each 3-letter combination “codes” for an amino acid, you need to figure out what amino acid matches up with each codon: AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA

met arg thr asp arg ser asp ??? The Genetic Code Step Two: Translation

2. Since each 3-letter combination “codes” for an amino acid, you need to figure out what amino acid matches up with each codon: AUG|CGU|ACU|GAU|CGU|UCA|GAU|UGA

met met thr asp arg ser asp STOP RECAP:

1. DNA is transcribed into mRNA in the nucleus. 2. The mRNA leaves the nucleus and enters the cytoplasm. 3. The protein is translated from the mRNA sequence using tRNA and amino acids.