Protein Synthesis Przeworski

Protein Synthesis Instructions for proteins are stored as DNA in the nucleus (one gene = one protein) The ribosomes that actually make the proteins are outside in the cytoplasm DNA is too large to exit through nuclear pores… it requires a messenger to send the instructions

Nucleus mRNA Transcription DNA Translation Cytoplasm Ribosome Protein

Transcription In transcription, a copy of a protein recipe called messenger RNA (mRNA) is made from DNA mRNA is half the width of DNA and can leave the nucleus

DNA vs RNA Deoxyribonucleic acid Contains the sugar deoxyribose Double-stranded Bases are G, C, A, T Ribonucleic acid Contains the sugar ribose Single-stranded Bases are G, C, A, U U = Uracil, replaces Thymine G still pairs with C A pairs with U T D P Thymine Nucleotide (DNA) U R P Uracil Nucleotide (RNA)

A now pairs with U (instead of T) The RNA bases are slightly different. C still pairs with G A now pairs with U (instead of T) C D P G R P G D P A D P U R P T D P C D P C R P G D P

Step One: Initiation RNA polymerase locates the section of DNA (gene) that it wants to transcribe. It attaches to the promoter region, causing DNA to unzip with the help of a Helicase. Polymerase and Helicase are enzymes (special proteins!)

Step two: Elongation Once DNA is unzipped, the Polymerase transcribes the DNA section Free-floating RNA nucleotides attach This is just like Replication, but with the base uracil instead of thymine. (A-U and C-G)

Step Two: Elongation For example, if the DNA strand read ACGT, then the RNA would be UGCA. This continues until the entire gene is transcribed, ending with the Stop sequence.

Step Three: Termination Once the stop sequence is reached, the RNA strand detaches It is then processed into mRNA by adding a 5’ cap and a poly-A tail (for protection) Finally, the mRNA leaves the nucleus! (DNA rezips)

Nucleus mRNA Transcription DNA Translation Cytoplasm Ribosome Protein

Transcription clip (real time) https://www.youtube.com/watch?v=5MfSYnItYvg

Group Poster PRoject A legible title In your groups of four (each table should work with the one behind them, and turn your chairs around) You will be given a step of transcription or DNA vs RNA For your assigned topic, make sure there is: A legible title Large writing describing what occurs in the step (or large writing that explains the differences between DNA and RNA) A large picture, colored. (All writing should be in marker)

Translation - Overview In translation, a ribosome uses an mRNA recipe to select and put together a sequence of amino acids mRNA is read 3 bases at a time (3 bases = 1 codon) Each codon = 1 amino acid DNA template: A T A G A T C C A mRNA: U A U C U A G G U Amino Acid 1 Amino Acid 2 Amino Acid 3

DNA: A T A G A T C C A mRNA: U A U C U A G G U Tyrosine Leucine Glycine

Special Codons As a ribosome reads an mRNA transcript, special codons tell it where to start and stop making a protein START codon: A U G (must memorize!) mRNA: A A G G U C A U G C C A C G U U A A Amino Acid: Methionine Proline Arginine STOP

Step onE The mRNA from the nucleus makes its way through the cell to a free-floating ribosome and attaches to it.

Step two: Each set of three RNA bases is called a codon. For this sequence: AUGCUA, AUG is a codon and CUA is another codon. Each codon codes for a single amino acid, which is the building block of proteins.

Step two: At the ribosome, the codon of mRNA pairs with its anti-codon (correct base pairs) For our earlier codons, AUG would pair with UAC and the anticodon for CUA is GAU.

Step two: tRNA (transfer RNA) translates each codon into one amino acid. Amino Acids are linked with peptide bonds to form a chain

Step three: Once the amino acids are linked with a PEPTIDE BOND, the mRNA strand moves like an assembly line, releasing the first codon and anticodon.

Step four The chain of amino acids (polypeptide chain) will then form a protein. There are 20 different amino acids, which are the codes for all living things!

Wheel of codons!! Input the mRNA codon, get out the amino acid! Special amino acids: AUG= start UGA=stop

Types of RNA Structure Function mRNA Single strand (messenger) Single strand Takes copied DNA recipe to ribosome tRNA (transfer) Has anticodon on one end, carries amino acid on the other Delivers amino acids to ribosomes rRNA (ribosomal) Folded into ribosome shape The ribosome itself is made of this

Given the mRNA codon GCU, what is the amino acid? Alanine

Practice time! Given mRNA codon of AUG, what is the amino acid? Methionine (Start!)