Chapter 13 –RNA and Protein Synthesis

1. Chapter 13 –RNA and Protein Synthesis Section 1 - RNA

2. RNA • RNA stands for RiboNucleicAcid • RNA is a nucleic acid; therefore, made of nucleotides • RNA works with DNA to make proteins • Proteins are made through a process called protein synthesis • Review: Proteins are made of amino acids • Review: Proteins are made by ribosomes

3. Phosphate Nitrogen Base • Guanine • Cytosine • Adenine • Thymine (only in DNA) • Uracil (only in RNA) 5 – Carbon Sugar - Ribose (if RNA) - Deoxyribose (if DNA)

4. Differences between RNA and DNA RNA • Has the sugar ribose • Single stranded • Has uracil DNA • Has the sugar deoxyribose • Double stranded - double helix • Has thymine

6. The Nucleotides of RNA

7. DNA has the 5-carbon sugar, deoxyribose. RNA has the 5-carbon sugar, ribose. DNA has thymine, adenine, cytosine and guanine. RNA has uracil, adenine, cytosine and guanine. DNA is a double stranded molecule. It has base-pairs with hydrogen bonds between the nitrogen bases. The molecule is anti-parallel. RNA is a single stranded molecule.

10. 3 types of RNA There are 3 major types of RNA: • Messenger RNA (mRNA) – carries the genetic code from DNA to the ribosome (site of protein synthesis) • Ribosomal RNA (rRNA) – makes the two subunits of ribosomes • Transfer RNA (tRNA) – transports amino acids (monomers of proteins) to the ribosomes

11. 3 types of RNA Messenger RNA (mRNA) – carries code from DNA to ribosome for protein synthesis Ribosomal RNA (rRNA) – assembles amino acids brought by tRNA in a specific order from mRNA to make proteins; made of RNA by the nucleolus Transfer RNA (tRNA) – transports specific amino acid to ribosome for protein synthesis

13. Production of RNA • RNA is made through a process called transcription • “trans” – across • “script” – to write • DNA is split and one strand forms a template • A sequence of DNA that codes for a protein is known as a gene • There are portions of DNA that do not code for protein

14. Transcription • DNA template is formed when it untwists and hydrogen bonds between nitrogen bases are broken • RNA polymerase (an enzyme) binds complementary nucleotides to the template • Places Cytosine with Guanine • Places Adenine with Thymine • Places Guanine with Cytosine . . . BUT • Place URACIL with Adenine • RNA DOES NOT HAVE THYMINE!!

15. Transcription

17. Transcription • DNA “unzips” • One side of DNA becomes a template • Free nucleotides of RNA attach to open sites of the template by RNA Polymerase (not shown) • Cytosine attaches to Guanine • Uracil attaches to Adenine • Guanine attaches to Cytosine • Adenine attaches to Thymine • Messenger RNA is produced and released • mRNA is edited • Introns removed • Exons spliced together • mRNA goes to ribosomes for protein synthesis

18. Another look at transcription . . .

20. Transcription (cont’d) • Transcription starts at a location called the promoter • Promoter is a specific sequence of DNA that starts transcription • Pre-RNA is produced • Introns are cut out and thrown out • Exons are spliced together to form mRNA • mRNA is sent to ribosomes to be decoded

22. Editing/Refining • Intronsand Exonsare processed • Introns are removed and exons are placed together • Exons are expressed; introns disappear • Purpose of introns are not known

32. A sequence of nitrogen bases on a segment of DNA of one of its strands that actually carries instructions for the order of amino acids in a protein is called a gene. When DNA separates, one side becomes the template. Which side is the template? The side that is a code for a protein! After transcription, a molecule of mRNA with codons is produced. During translation, each codon of mRNA is matched with an anti-codon on a tRNA molecule with the amino acid it carries.