Ribonucleic Acid (RNA) & Protein Synthesis Ms. Napolitano & Mrs. Haas CP biology

Think About It! Imagine that we (Ms. Napolitano & Mrs. Haas) are the best bakers ever, and we made a cookbook of delicious cookie recipes. You all would like a copy of our famous chocolate chip cookie recipe, but we only have one cookbook. So, we decide to loan it out to one student at a time. The cookbook can be around from person to person. 1. What are some of the problems with this form of sharing information? 2. What is a more efficient way of getting the recipe to each student? 3. What problems can occur during the copying process?

Recall: DNA Structure A  T C  G Double helix

Genes Genes – coded DNA instructions that control the production of proteins within the cell

Part I: RNA Structure

RNA Structure Long chain of nucleotides Sugar Phosphate Nitrogenous base Differences between DNA & RNA: In RNA: 1. Sugar is ribose (instead of deoxyribose) 2. Single stranded (instead of double stranded) 3. Contains uracil (instead of thymine)

Types of RNA Messenger RNA (mRNA) Carries copies of DNA instructions out of the nucleus Ribosomal RNA (rRNA) Make up ribosomes Transfer RNA (tRNA) Transfers amino acids to the ribosome that are coded in the mRNA

Part II: Protein Synthesis

Protein Synthesis How proteins are made Need instructions from DNA Made of 2 parts: 1. Transcription 2. Translation

Transcription Copying of the DNA sequence Occurs in the nucleus Makes a complimentary strand of mRNA Uses protein RNA Polymerase Separates DNA strand Uses 1 strand of DNA as a template to make mRNA Starts at a promoter – specific sequence of DNA

RNA Editing DNA contains segments of introns Not involved in protein coding Exons code for proteins Introns are cut out of the mRNA sequence after transcription Exons are spliced together

The Genetic Code The genetic code is read just 3 letters at a time Codon – 3 consecutive nucleotides that specify for a single amino acid Ex: Consider the RNA sequence UCGCACGGU This would be read UCG-CAC-GGU 3 different codons: UCG, CAC, & GGU Codons represent different amino acids UCG= serine CAC = histidine GGU = glycine

The Genetic Code Since 4 different bases, 4 3 = 64 possible codons Some amino acids have more than one codon choice AUG is always a “start” codon Where protein synthesis begins 3 stop codons (end of protein synthesis): 1. UGA 2. UAA 3. UAG

Codon Wheel

Codon Chart

Translation Recall: During transcription, mRNA code was made from DNA, mRNA proofread (introns cut out) Translation – decoding of mRNA to produce proteins mRNA moves from the nucleus to the ribosomes

Steps of Translation 1. mRNA attaches to the ribosome. 2. As each codon moves through the ribosome, the proper amino acid is brought in by tRNA. Each tRNA carries only 1 type of amino acid tRNA has 3 unpaired bases ( anticodon ) that is complementary to mRNA codons 3. Peptide bonds form between amino acids & tRNA is released. 4. Polypeptide chain grows until a stop codon is reached.

Translation

Example of Protein Synthesis DNA strand: TAACGAGGTACT Transcription (nucleus): mRNA formed by base pairing mRNA strand: AUUGCUCCAUGA Translation: mRNA moves to ribosome, read as codons AUU-GCU-CCA-UGA Using codon chart, find amino acids that match Isoleucine-Alanine-Proline-Stop this is our new protein!

Part III: Mutations

Mutations Mutations – changes in genetic material Point mutations – occur at a single DNA point Substitutions Frameshift mutations – shift the reading frame of the genetic message Dangerous! Could change every following amino acid Insertions Deletions

Substitution Point mutation One base is changed to a different base May/may not affect the protein code

Insertions Frameshift mutation An extra base pair is (or extra base pairs are) added

Deletions Frameshift mutation A base pair is (or base pairs are) removed

Chromosomal Mutations Chromosomal mutations – changes in the number or structure of chromosomes Types: Deletion – loss of part of a chromosome Duplication – extra copies of part of a chromosome Inversion – reverses the direction of part of the chromosome Translocation – part of the chromosome breaks off & attaches to another

Chromosomal Mutations

Significance of Mutations Most mutations do not have an effect on gene expression Can be very harmful or fatal Cystic fibrosis Sickle cell anemia Cancer Source of genetic variability Resistance to HIV Polyploidy – extra sets of chromosomes Beneficial in plants – larger and stronger than diploid plants