RNA and Protein Synthesis

1. RNA and Protein Synthesis Chapter 12, section 3

2. The Structure of RNA • “Central Dogma” of Biology: • DNA is “read” by RNA which then travels to the ribosomes to make proteins. • DNA  RNA  Proteins

3. The Structure of RNA • RNA, like DNA, is made up of nucleotides • However, there are 4 major differences between DNA and RNA: • RNA has ribose instead of deoxyribose • RNA has uracil instead of thymine • RNA is single-stranded instead of double-stranded • RNA is able to leave the nucleus.

4. 3 Types of RNA • Messenger RNA (mRNA) – carries the message from the DNA to the ribosomes • Ribosomal RNA (rRNA) – make up part of the structure of a ribosome • Transfer RNA (tRNA) – transfers amino acids to the ribosomes

5. Transcription • DNA  mRNA • Making RNA from DNA (in the nucleus) • RNA polymerase binds to DNA and begins building a complementary strand of mRNA • A will now pair with U, T still pairs with A • C and G still pair with each other • Why mRNA? mRNA can leave the nucleus!

6. Transcription

7. The Genetic Code • DNA and RNA are “read” 3 bases at a time • A codon is a 3 base sequence that codes (“signals”) for a specific amino acid • There are 64 possible codons (3 letter combinations) • Proteins are made of amino acids • There are 20 different amino acids

8. Practice Transcription… • DNA – AGC TCC GAT GCA TAC TTG CCA • mRNA– UCG AGG CUA CGU AUG AAC GGU • DNA – GCC AGT GCT TAC GAA CTG AGT • mRNA– CGG UCA CGA AUG CUU GAC UCA

9. The Genetic Code • RNA sequence: • UCGAGGCUA • Separate into codons: • UCG-AGG-CUA • Identify the “signaled” amino acids: • Serine-Arginine-Leucine

10. The Genetic Code

11. Translation • mRNA  Proteins • Making of proteins using the instructions from the mRNA message (“translating the code”) • Occurs at the ribosomes

12. Translation • Following transcription, mRNA leaves the nucleus and enters the cytoplasm. • The mRNA attaches to the ribosome • The tRNA brings the proper amino acid to the ribosome • Anticodon – sequence of bases on the tRNA that pair with the mRNA

13. Translation • The amino acids form a peptide bond to hold them together The next amino acid is brought in and is attached • This continues until the ribosome reaches a stop codon • The completed protein (polypeptide chain) is then released

14. Translation

15. Mutations • Changes in the DNA sequence that affect genetic information • Gene mutations – result from changes in a single gene. A gene carries the “recipe” for a single protein. • Chromosomal mutations – involve changes in whole chromosomes

16. Mutations Body-cell v. Sex-cell Mutation • Somatic cell mutations are not passed on to the next generation. • Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.

17. Gene Mutations • Point mutations – a mutation that occurs at a single point (only 1 nitrogen base) • Substitution – a single nucleotide is substituted for another one (A instead of G) • Frameshift mutations– a mutation that occurs when a nucleotide is inserted or deleted • Insertion – a nucleotide is added • Deletion – a nucleotide is removed

18. Gene Mutations • Insertions and deletions cause frameshift mutations because they shift the “reading frame” of the genetic message.

19. Gene Mutations