Ch. 25.2- RNA

1. Ch. 25.2- RNA

2. Target #15- I can describe the structure and function of RNA • RNA ribonucleic acid • Made of nucleotides, ribose sugar, and phosphate • Nucleotide bases • Adenine • Guanine • Cytosine • Uracil  replaces the base thymine • Single stranded, no helix shape • Considered a “helper” to DNA • Allows protein synthesis to occur according to the genetic information that DNA provides • 3 major types, each with a specific function • Messenger RNA (mRNA), transfer RNA (tRNA), Ribosomal (rRNA)

3. Target #16- I can differentiate between the three types of RNA • Messenger RNA (mRNA) • Location: Produced in the nucleus • How it’s formed: DNA serves as a template for its formation during transcription • Function: Responsible for carrying genetic information from DNA in the nucleus to the ribosomes in the cytoplasm outside the nucleus

4. Target #16- cont. • Transfer RNA (tRNA) • Location: produced in the nucleus • How it’s formed • DNA serves as a template • Function: transfers amino acids to the ribosomes where amino acids are joined • Forms a protein • Each tRNA carries only one amino acid

5. Target #16- cont. • Ribosomal RNA (rRNA) • Location: produced in the nucleolus of a nucleus • How it’s formed: DNA serves as a template for its formation • Function: joins with proteins made in the cytoplasm to form the subunits of ribosomes • One large and one small • Used for protein synthesis in the cytoplasm

6. Ch. 25.3 (part 1) Gene Expression

7. Target #17- I can describe gene expression • Gene expression: the process of using a gene sequence to synthesize a protein • Requires two processes: transcription and translation • Transcription • A portion of DNA serves as a template for mRNA formation • takes place in the nucleus • Translation takes place in the cytoplasm • The sequence of mRNA bases determines the sequence of amino acids in a polypeptide

8. Target #18- I can describe the process of transcription • Transcription • A segment of DNA called a gene serves as a template for the production of an RNA molecule • In particular mRNA • Begins when the enzyme RNA polymerase binds tightly to a promoter gene • Opens up the DNA helix so that complimentary base pairing can occur on the 5’ strand • Adds free floating RNA nucleotides to make mRNA • After the mRNA is transcribed, it is processed and then enters the cytoplasm to meet with a ribosome

9. Checking for Understanding Transcription • What is the RNA base pair? • G C T A C T A

10. Target #19- I can explain an amino acid sequence • The sequence of bases in DNA is transcribed into mRNA, which codes for particular sequences of amino acids • Amino acids are written as a triplet code known as a codon • Example: GGG = glycine • Start codon  begins protein synthesis • AUG= methionine • Stop codon  ends protein synthesis • UAA, UGA, UAG

12. Target #20- I can explain the role of transfer RNA in protein synthesis • Transfer RNA (tRNA) molecules bring amino acids to the ribosomes • Each tRNA molecule is a boot-shaped polynucleotide • On one end is an amino acid • The other end is an anticodon a triplet of three bases complementary to a specific codon of mRNA • When a tRNA comes to a ribosome, it’s anticodon pairs with an mRNA codon • Ex: if mRNA codon is UGC, the anticodon is ACG • The order of the mRNA determines the order of amino acids placed in the chain, therefore determining the type of polypeptide formed

13. Ch. 25.3 (part 2) Gene Expression: Translation

14. Review • Transcription • mRNA is “written” (transcribed) from a section of DNA • Starts at a promoter gene • Occurs in the nucleus • Translation • mRNA contains codons, a triplet code, that codes for amino acids carried by tRNA • Always starts with AUG= met and stops with a stop codon • Occurs in the cytoplasm

15. Review • During translation, the codons of an mRNA base pair with the anticodons of tRNA molecules carrying specific amino acids • Order of codons determines the order of tRNAmoleculess at a ribosome and the order of amino acids

16. Target #21- I can state the steps of translation of protein synthesis • Translation of protein synthesis involves 3 steps • Initiation • Elongation • Termination • Enzymes are required for each step to function properly • Initiation & Elongation require energy in the form of ATP

17. Target #22- I can explain the process of Initiation • Initiation • The step that brings all the translation components together • Requires proteins called initiation factors • Assembles the small ribosomal and large ribosomal subunits, mRNA, and an initiator tRNA

18. Target #22- cont. • Step 1: a small ribosomal subunit attaches to the mRNA • An initiator tRNA with the anticodon UAC pairs with the mRNA start codon AUG • Step 2: the large ribosomal subunit joins to the small subunit

19. Target #23- I can identify the three binding sites for tRNA • A ribosome has three binding sites for tRNA molecules • A site  Amino Acid site • P site  Peptide site • E site  Exit site • The start codon AUG begins at the P site, all other tRNA molecules begins at the A site

20. Target #24- I can explain the process of elongation • Elongation • The step where the polypeptide sequence increases in length • Occurs in a series of 4 steps • Step 1 • A tRNA with an attached peptide is already at the P Site • A tRNA carrying the next amino acid in the chain binds to the A site

21. Target #24- cont. • Step 2 • Once the next tRNA is in place at the A site, the peptide chain will be transferred to this tRNA • Only 2 tRNA’s can be present in a ribosome at one time • Step 3 • Energy is used to transfer the amino acid chain • Creates the peptide bonds • Step 4 • Translocation occurs the mRNA moves forward one codon length • The “spent” tRNA exits the ribosome

23. Target #25- I can explain the process of Termination • Termination • The final step in protein synthesis • Occurs at a stop codon • Requires a protein called a release factor • Separates the polypeptide from the last tRNA • the ribosome separates into its two pieces