DNA - Transcription, Translation, and Mutations

DNA Two strands coiled called a double helix Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO4) groups by phosphodiester bonds Center made of nitrogen bases bonded together by weak hydrogen bonds 2

DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone 3 3

Antiparallel Strands One strand of DNA goes from 5’ to 3’ (sugars) The other strand is opposite in direction going 3’ to 5’ (sugars) 4

DNA P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A 5 5

Synthesis Phase (S phase) S phase during interphase of the cell cycle Nucleus of eukaryotes Mitosis -prophase -metaphase -anaphase -telophase G1 G2 S phase interphase DNA replication takes place in the S phase. 6

DNA Replication Begins at Origins of Replication Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forks Replication Fork Parental DNA Molecule 3’ 5’ 7 7

Proofreading New DNA DNA polymerase initially makes about 1 in 10,000 base pairing errors Enzymes proofread and correct these mistakes The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors 8

DNA Damage & Repair Chemicals & ultraviolet radiation damage the DNA in our body cells Cells must continuously repair DAMAGED DNA Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA DNA polymerase and DNA ligase replace and bond the new nucleotides together 9

The three-base code in DNA or mRNA is called a codon. DNA, RNA, and Protein The Code Experiments during the 1960s demonstrated that the DNA code was a three-base code. The three-base code in DNA or mRNA is called a codon. 10

Central Dogma DNA is copied as RNA – Transcription RNA uses U instead of T RNA is read to make proteins – Translation Read by using the reverse of RNA, similar to DNA’s 2nd strand

Each anticodon is complementary to a codon on the mRNA. DNA, RNA, and Protein Translation In translation, tRNA molecules act as the interpreters of the mRNA codon sequence. At the middle of the folded strand, there is a three-base coding sequence called the anticodon. Each anticodon is complementary to a codon on the mRNA. 12

Activity The first number tells you where the mutation starts, followed by the number or what is deleted Ex: 487del7 means starting at base 487 7 bases are deleted.

What Are Mutations? Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring) May occur in gametes (eggs & sperm) and be passed to offspring 14

Chromosome Mutations Five types exist: Deletion Inversion Translocation (don’t worry) Nondisjunction (don’t worry) Duplication 15

Deletion Due to breakage A piece of a chromosome is lost 16

Inversion Chromosome segment breaks off Segment flips around backwards Segment reattaches 17

Duplication Occurs when a gene sequence is repeated 18