Transcription, Translation, and Mutations

1. Transcription, Translation,and Mutations

2. Quick Review … • DNA is sometimes called "the blueprint of life" because it contains the code, or instructions for building an organism and ensuring that organism functions correctly. Just like a builder uses a blueprint to build a house, DNA is used as the blueprint, or plans, for the entire organism. • It is the chemical component of chromosomes, which are located in the nucleus of every eukaryotic cell.

3. The shape of the DNA molecule is a double-helix (like a twisted ladder). The sides of the ladder are composed of alternating sugars (deoxyribose) and phosphates. The rungs of the ladder are composed of nitrogenous bases. A Nucleotide consists of deoxyribose, phosphate, and a base. • Adenine, Thymine, Guanine, Cytosine or A, T, G, C • Chargaff’s Rules: Adenine pairs to Thymine: A=T Guanine pairs to Cytosine: G=C *bases are held together by weak hydrogen bonds* • The rungs of the ladder can occur in any order (as long as Cargaff’s Rules are followed). • For instance, a stretch of DNA could be AATGACCAT - which would code for a different gene than a stretch that read: GGGCCATAG. All in all, there are billions of nucleotides in cells, which code for all the things an organism needs to function.

4. Groups of Bases • Purines (larger) • Adenine • Guanine • Pyrimidines (smaller) • Cytosine • Thymine

5. DNA-RNA Relationship • DNA remains in the nucleus, but in order for it to get its instructions translated into proteins, it must send its message to the ribosomes (outside the nucleus), where proteins are made. Messenger RNA is used to carry this message. • RNA is similar to DNA except: 1. has one strand instead of two strands. 2. has uracil instead of thymine 3. has ribose instead of deoxyribose

6. 3 Types of RNA • Messenger RNA (mRNA) • RNA that carries copies of DNA instructions • Ribosomal RNA (rRNA) • Make up ribosomes (along with proteins) • Transfer RNA (tRNA) • Transfers or carries each amino acid to the ribosomes as coded for by the mRNA

7. Transcription • RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence of RNA • DNA strands are separated, RNA polymerase uses one strand of DNA as a template and assembles RNA • Uses base pairing to assemble RNA • A – U (instead of T) • C - G

9. Genetic Code • The “language” of mRNA is sometimes called the Genetic Code. • The genetic code is read 3 letters (or bases) at a time, called codons. • A codon is made up of 3 nucleotides that specify for a single amino acid • Amino acids are strung together to form proteins (polypeptides)

10. Genetic Code, cont. • Ex: • UCGCACGGU Would be read 3 bases at a time… • UCG-CAC-GGU Using the code → Serine-Histadine-Glycine

11. Start and Stop Codons • AUG codon codes for the assembly of amino acids to begin. It also codes for methionine • Three codons code for the assembly of amino acids to stop – UAA, UAG, and UGA

12. Protein Synthesis (Translation) • Proteins are assembled on ribosomes using information from mRNA • Steps: • 1 – mRNA transcribed • 2 – mRNA attaches to ribosome. tRNA matches anticodons to codons and brings in amino acids. • 3 – amino acids are joined together by peptide bonds. Free tRNA molecules float away. • 4 – polypeptide chain grows until stop codon.

14. Mutations • Gene mutations: • Point mutations – involve changes in one or a few nucleotides • Substitutions • Insertions • Deletions • Frameshift mutations – shift the “reading frame” of the genetic message • Ex: AUG UGG CCU UAC → AUG UGG ACC UUA C

15. DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA Amino Acids: Met-Arg-Thr-Leu SUBSTITUTION DNA: TAC GTA TGG AAT mRNA: AUG CAU ACC UUA Amino Acids: Met-His-Thr-Leu DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA Amino Acids: Met-Arg-Thr-Leu INSERTION DNA: TAT CGC ATG GAA mRNA: AUA GCG UAC CUU Amino Acids: Ile-Ala-Tyr-Leu Point Mutations

16. Chromosomal Mutations • Deletions • Duplications • Inversions • Translocations