By the end of this unit you will:  know what transcription is  know what translation is  understand how proteins are made.

 DNA contains the genetic code which controls the production of proteins, but it is stuck in the nucleus.  Proteins are produced at the ribosomes in the cytoplasm. Houston: We Have a Problem!  There are two important events which must happen in order to make a protein; transcription and translation

 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 and the TATA's

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

 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

 Assume the following sequence represents the coding side of DNA  ATG GCA TAC.  Assuming the coding side of DNA is the left side, transcribe a mRNA molecule. Draw the molecule horizontally.  Use your codon wheel to figure the sequence of amino acids.

 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 - __________

 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.

 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?

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

 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 Protein Synthesis PH

 Translation Translation  Translation 2 Translation 2  Translation 3 Translation 3

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

← Gene A ← Gene B  Exons – translatable seqments 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

 Another look at Protein Synthesis Another look at Protein Synthesis

 Assume the strand of DNA nucleotides below represents the coding side  ACT CCA CGA TAC  Transcribe a mRNA molecule using the coding side. Detach it and draw it hortizontally.  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.  Using you amino acid chart, draw the reactants and products of this synthesis.