Chapter 12 DNA & Proteins

Components & Structure of DNA DNA is a long molecule made up of nucleotides which contains: Deoxyribose – 5 Carbon sugars Phosphate 1 of four Adenine – purine = double ring of C & N Thymine – pyrimidine = single ring of C & N Guanine – purine Cytosine - pyrimidine

Chargraff – Amt. of A = Amt. of T Important research that contributed to the discovery of the structure of DNA Chargraff – Amt. of A = Amt. of T Amt. of C = Amt. of G Amt. of A, T, C, G varies between different organisms Wilkins & Franklin- Studied X-ray diffraction Studied the structure of DNA fibers Revealed a tightly coiled helix w. 2 or 3 strands (one of the first illustrations of DNA)

Watson & Crick Model was made of cardboard & wire Used Chargraff’s & Franklin’s findings

Structure of DNA Double helix – 2 strands twisted around a central axis Each strand made of nucleotides Held together by Hydrogen bases Base pairing A = T linked w/ 2 hydrogen bonds G= C linked w/ 3 hydrogen bonds This keeps the 2 strands together Strands are complementary – sequence of bases on 1 strand determines the sequence of bases on the other

12-2 Chromosomes & DNA Replication Prokaryote DNA single circular DNA = cell’s chromosome Eukaryote DNA 1000x more than prokaryotes Is in the form of chromosomes Chromosome = chromatin=DNA +proteins One DNA molecule = single chromosome

12-3 RNA & Protein Synthesis DNA carries the messages for protein synthesis Genes – coded DNA instructions that control the production of proteins in all cells Proteins carry out all the functions of the cell To get this done: DNA must be decoded → RNA

Ribonucleic acid Structure (RNA) (Compares/Contrast) Single strand of nucleotides Ribose is sugar that alternates w/ phosphate Nitrogen bases – adenine, cytosine, guanine, uracil No thymine Can leave the nucleus Has 3 Forms mRNA – messenger RNA – carries instructions for making proteins tRNA – transfer RNA – carries an amino acid to the ribosome rRNA – ribosomal RNA – make up the ribosome

Protein synthesis – entire process by which proteins are made based on DNA info Stage 1 – transcription Stage 2 – translation Transcription Using DNA info to make mRNA Occurs in nucleus Translation mRNA info is used to make a protein Occurs in cytoplasm at the ribosome

12-4 Mutations Mutation – any change in DNA Occurs in Gene mutations Somatic cells – affect the individual Gametes – affect the offspring Gene mutations Point mutation – changes 1 or more nucleotides in a gene Substitution – one nucleotide is replaced by another Can result in no protein or nonfunctioning protein Some result in little or no effect Frame shift mutation Insertion – one or more nucleotides are added Deletion – 1 or more are deleted Results in message being read out of order

HECTHEERCATATERRAHCTHEACEACRARAT=gene THE CAT ATE THE RAT normal sequence THE CAT ATE THE HAT Substitution THE CCA TAT ETH EHA Insertion THC ATA THE HER AT Deletion

Chromosomal Mutation – change in the number or structure of chromosomes: Deletion – loss of all or part of chromosome Duplication – extra copies of parts of chromosomes Inversion – reverse direction of parts of chromosomes Translocation – one part breaks off & reattaches to a different chromosomes

Importance of Mutations Most are neutral – have little or no effect Some are harmful – make defective proteins that disrupt normal biological activity Ex. Sickle cell anemia, cystic fibrosis, cancer Some are beneficial – are the source of genetic variation Ex. *resistance to HIV *Polyploidy – an organism w/ an extra set of chromosomes - often larger and stronger than diploid plants = bananas