RiboNucleic Acid Also made of monomers called nucleotides 5 carbon sugar: Ribose Phosphate functional group: PO4 1 of 4 nitrogen bases Cytosine Guanine Adenine Uracil replaces Thymine Molecule is a single strand

Purpose of RNA There are many types of RNA, so function varies depending upon type: Determines which genes are expressed Some regulate chemical processes, so, they function like enzymes Small sections of RNA act as place holders for DNA polymerase during DNA replication Directly involved in converting genetic code on DNA into proteins

3 TYPES OF RNA USED IN PROTEIN SYNTHESIS messenger RNA(mRNA) Long, single strand Made in the nucleus Carries genetic code from DNA to ribosomes in cytoplasm

transfer RNA (tRNA) Folded chain of RNA Carries the amino acid monomers that make a protein “Translates” the genetic code

Ribosomes ribosomal RNA (rRNA) Globular strand of RNA 2 parts: large and small subunits Located on the ER and free floating in cytoplasm Site of protein synthesis

Why is mRNA needed in the first place Why is mRNA needed in the first place? DNA carries the code, however, DNA cannot leave the nucleus. RNA carries the “genetic message” to ribosomes Why change a base? The nuclear envelope “recognizes” the bases on DNA and keeps it in the nucleus; by changing a single base on RNA, its chemical signature changes, so the nuclear envelope will allow it to pass through to cytoplasm Why not just make proteins in the nucleus? Proteins are “huge” molecules. There’s just not enough room in the nucleus to make all the proteins an organism requires, so the protein factory (ribosomes, ER and Golgi Body) is out in the cytoplasm where there’s plenty of space. Why are ribosomes on the ER and in the cytoplasm? Proteins are needed for many functions. The proteins made in ribosomes on the ER are transported either to the nucleus or out of the cell(hormones). Those ribosomes in the cytoplasm make proteins that stay in the cell(replace organelles) BIKINI

RNA

MAKING mRNA 1st step in protein synthesis Messenger RNA is made in the nucleus in a process called: TRANSCRIPTION “to write across” Here the genetic code on DNA is “rewritten” in a strand of mRNA. m

Once the mRNA is formed it detaches from the DNA TEMPLATE, leaves the nucleus and enters the cytoplasm. The DNA either closes or TRANSCRIPTION continues until enough mRNA is made for protein synthesis

Let’s Transcribe! Remember; NO ‘T’ in RNA! DNA T A C C G C T A G C C C G C G T C T A A G T A C C T A A C T mRNA A U G G C G A U C G G G C G C A G A U U C A U G G A U U G A

Next Steps…. TRANSLATION The newly formed messenger RNA leaves the nucleus Together with the ribosomes and tRNA a new protein is formed during… TRANSLATION “ across languages” In this process the base code ‘language’ of the nucleic acids is translated into the amino acid ‘language’ of protein

TRANSLATION USING mRNA TO CONSTRUCT A POLYPEPTIDE CHAIN OF AMINO ACIDS TAKES PLACE IN RIBOSOMES(ROUGH E.R. OR CYTOPLASM) The BASE CODE SEQUENCE that was TRANSCRIBED from DNA to mRNA determines the sequence of AMINO ACIDS which determines the NATURE OF THE PROTEIN Now, Let’s see how the code is read…

MESSENGER RNA (mRNA) CODONS THE GENETIC CODE IS TRANSLATED IN ‘3 LETTER WORDS” On mRNA – THREE NUCLEOTIDE BASES FORM ONE CODON. EACH CODON CODES FOR A SPECIFIC AMINO ACID

TRANSFER RNA – (tRNA) The Translator THREE NUCLEOTIDES AT THE BOTTOM OF THE tRNA IS THE ANTICODON THE ANTICODON ARE THE COMPLIMENTARY BASES ON THE mRNA CODON THE TAIL OF THE tRNA CARRIES AN AMINO ACID THAT CORRESPONDS TO THE CODON.

THE RIBOSOME CELL ORGANELLE THAT IS MADE OF rRNA. SITE OF PROTEIN SYNTHESIS TWO PIECES SMALL SUBUNIT ATTACHES TO THE mRNA LARGE SUBUNIT DIRECTS tRNA HAS 2 ‘PARKING PLACES’ FOR ONLY TWO tRNA AT A TIME

THE PROCESS OF TRANSLATION STEP 1: The small subunit attaches to mRNA at the start codon, always AUG The large subunit attaches over the small subunit, encasing the mRNA strand LARGE SUBUNIT START CODON mRNA

STEP 2 The first tRNA carrying the first amino acid, always Methionine, enters the ribosome and attaches to the start codon The ribosome then shifts down one codon

STEP 3. The mRNA codon is ‘read’ by the ribosome and the second corresponding tRNA carrying the second amino acid enters STEP 4. Once the second tRNA docks, a peptide bond is formed between the two amino acids PEPTIDE BOND

The ribosome again shifts down one codon STEP 5. The first tRNA releases its amino acid and leaves the ribosome. The ribosome again shifts down one codon STEP 6. This process of building the polypeptide chain continues until the ribosome reaches the STOP codon and detaches. Many ppc’s are made continuously from one mRNA ppc’s are processed into proteins by the Golgi body POLYPEPTIDE CHAIN Protein synthesis

READING THE AMINO ACID WHEEL mRNA Codon CAU Start with first letter in center and work your way out for each letter in the codon until you identify the amino acid OR CHART HISTIDINE READING THE AMINO ACID WHEEL Match the codon with its amino acid UCA AAC GCG GAC UUC Serine SER Asparagine ASP Alanine ALA Aspartic acid ASP A Phenylalanine PHY

What might this imply about certain amino acids? There are only 20 amino acids(that is 20 monomers) for all proteins. However, there are far more than 20 codons. For example: Find LEUCINE( be careful, its listed more than once…how many codons are there for this one amino acid? What might this imply about certain amino acids? Amino acids that are used more often in proteins have more than one codon; this helps increase the rate of protein synthesis and decreases chance mutation will alter the protein. 6 Also, note that for many codons the last base can be any of the 4. This also decreases the chance that mutation will alter the protein significantly.

Let’s Practice! Write the DNA sequence below onto the table; TAC CTT AAC GAG CTA AAA GTT AGC TGG TTG ACT Now, transcribe the mRNA codons from the DNA; AUG GAA UUG CUC GAU UUU CAA UCG ACC AAC UGA Good Job! Now, what would the tRNA anticodon’s be? UAC CUU AAC GAG CUA AAA GUU AGC UGG UUG ACU Awesome! Now, let’s make a polypeptide by translating the mRNA codon’s to amino acids: MET- GLU A-LEU-LEU-ASP A-PHY-GLU-SER-THR-ASP-STOP

TRANSCRIPTION(nucleus) REPLICATION (nucleus) TRANSCRIPTION(nucleus) TRANSLATION(cytoplasm in RIBOSOME)

TRANSLATION

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