Protein Synthesis

Unit Objectives (Chapter 12-3) By the end of this unit you will: know what transcription is know what translation is understand how proteins are made.

Transcription Transcribing or copying the coded message of DNA onto a single stranded nucleic acid called mRNA DNA’s code is contained in groups of 3 nitrogen bases called DNA triplets One side of DNA is considered the coding side, or template, and the other side is considered the complimentary side. Left side – coding side Right side – complimentary strand

To begin transcription, Helicase causes the molecule to split or “unzip”. This exposes the nitrogen bases of the coding side Free floating mRNA nucleotides attach to the coding side of DNA The whole mRNA strand is removed from the coding side of DNA The mRNA strand then moves out of the nucleus and heads for a ribosome. The DNA strand then can re-attach with the complementary side of DNA

Transcription Transcription and the TATA's

mRNA Each group of 3 nitrogen bases of mRNA are called codons.

Codon Wheel

Here is how we will “do it”! DNA Coding Triplet: ATA CGA mRNA Codons that would be transcribed: UAU GCU Amino Acids: Tyrosine + Alanine

Summary Transcription is copying the DNA code onto a mRNA molecule. mRNA leaves the nucleus and moves to the ribosome where the message is translated AUG is called the “Initiation Codon” . It begins the process and always codes for Methionine “Termination Codons” indicate the end of the process. UAG,UAA, and UGA are termination codons and don’t code for any amino acids

Let’s try Transcription: Assume the sequence of nitrogen bases below represents the coding side of DNA. ACT CCC CGA TAC Transcribe the DNA triplets into mRNA codons Draw the mRNA molecule that would be produced during Transcription. Translate the mRNA molecule into the amino acids it represents. Use your codon wheel.

Look like this?

Transcription Review DNA contains the genetic code for the production of __________. Each group of 3 nitrogen bases in DNA is called a __________. The genetic code of _____ is trapped inside the nucleus because it is ____________ to fit through the pores in the nuclear envelope. __________ is the process of copying the genetic code of _____ onto a single strand of _____. The single stranded _____ molecule falls on it’s side with it’s nitrogen bases pointing _____ and moves out of the nucleus to find a __________. Each group of 3 nitrogen bases in mRNA is called a __________. AUG is a special codon that is called an ________________. It always codes for the amino acid __________. Check you codon wheel and identify the amino acids that the following codons code for: GGC - __________ UUU - __________ CAU - __________ GUA - __________

Transcription Review Another special codon found in mRNA stops the chain of amino acids and indicates the protein is complete. These codons are called ________________. There are only 3 of the codons: _______; ________ and _______. We are always going to assume that the coding side of DNA will be the __________ side. Opposite the coding side is called the __________ side. Two enzymes play a role in transcription: ____________ unzips the DNA molecule and __________________ helps attach the free-floating mRNA nucleotides to the coding side of DNA.

Transcription Review DNA contains the genetic code for the production of Protein. Each group of 3 nitrogen bases in DNA is called a DNA triplet. The genetic code of DNA is trapped inside the nucleus because it is too big to fit through the pores in the nuclear envelope. Transcription is the process of copying the genetic code of DNA onto a single strand of mRNA. The single stranded mRNA molecule falls on it’s side with it’s nitrogen bases pointing up and moves out of the nucleus to find a ribosome. Each group of 3 nitrogen bases in mRNA is called a codon. AUG is a special codon that is called an Initiation codon. It always codes for the amino acid Methionine. Check you codon wheel and identify the amino acids that the following codons code for: GGC - Glycine UUU - Phenylalanine CAU - Histidine GUA - Valine

Transcription Review Another special codon found in mRNA stops the chain of amino acids and indicates the protein is complete. These codons are called Termination codons. There are only 3 of the codons: UGA; UAA and UAG. We are always going to assume that the coding side of DNA will be the left side. Opposite the coding side is called the complimentary side. Two enzymes play a role in transcription: Helicase unzips the DNA molecule and RNA polymerase helps attach the free-floating mRNA nucleotides to the coding side of DNA.

Translation The process where the message of mRNA is translated into sequences of amino acids. Translation happens on the surface of ribosomes. 3 codons can fit on the ribosome at one time. Remember tRNA?

tRNA Serine  amino acid (specific to tRNA)  tRNA molecule  nitrogen bases called anticodons Serine

tRNA cont… Each tRNA molecule with one specific anticodon sequence can carry only one specific amino acid. If the anticodon of tRNA is complimentary to the codon of mRNA the amino acid carried by that tRNA is dropped off. Protein Synthesis PH Let’s go back to our mRNA molecule. Draw the respective tRNA molecules that would be involved in Translation.

Translation Animations

Activity Use your codon chart to complete the following table: Codon Amino Acid Anticodon DNA triplet AUG (initiation codon) UCC AAA CGU

A few things we need to know… Gene A Gene B Exons – translatable segments of a chromosome Introns – segments of DNA that do NOT code for proteins Nonsense DNA AUG – intiation codon Codes for methionine UAA, UAG, and UGA are all termination codons

Ribosome Structure “A” Site “P” Site “E” Site Arrival Site First tRNA arrives “P” Site Peptidyl Site Amino Acids bond together “E” Site Exit site Naked tRNA goes to find another amino acid “P” Site “A” Site “E” Site

Protein Synthesis

Protein Synthesis Another look at Protein Synthesis

Quiz: Protein Synthesis Assume the strand of DNA nucleotides below represents the coding side . ACT CCA CGA TAC Draw the mRNA molecule that would be transcribed.(Value: 4) Draw the three tRNA molecules that would be complimentary to the mRNA molecule you created. Make sure the appropriate amino acid and anti-codon are positioned on the tRNA drawings. (Value: 3) Using you amino acid chart, draw the polypeptide that would be created. (Value:3)

Mutations Point Mutation: A change in one nitrogen base in DNA. EX: DNA AAA TCT CGA mRNA UUU AGA GCU Amino Acids Phen-Arg-Ala Point Mutation DNA AAA TGT CGA mRNA UUU ACA GCU Amino Acids Phen-Thre- Ala

``Lucky`` Point Mutation DNA AAA TCT CGA mRNA UUU AGA GCU A.A. Phen-Arg-Ala DNA AAA TCC CGA mRNA UUU AGG GCU A.A. Phen – Arg - Ala

Frame shift Mutations - Mutation that deletes or adds a nitrogen base pair. - The result impacts the rest of the amino acids in the chain DNA AAA TCT CGA mRNA UUU AGA GCU A.A. Phen – Arg- Ala (Deletion) AA ATC TCG_ mRNA A.A. YIKES!