II. DNA (Deoxyribonucleic acid) A) Contains code to make proteins which determine phenotype of org B) Contained in nucleus of eukaryotic cells. Loose in cytoplasm of prokaryotes C) When supercoiled makes chromosomes D) Shape“discovered” by Watson and Crick-1953

III. Structure of DNA molecule-double helix (twisted ladder shape) A) Polymer of nucleotide subunits B) Parts of nucleotide 1. deoxyribose (5 Carbon sugar) 2. Phosphate 3. nitrogen base

C) Double stranded ladder shape 1. Sides of “ladder” are made of alternating sugars and phosphate groups (PO4) a) held tog by phosphodiester bond b) 3’ end sugar. 5’ end phosphate

2. “rungs” of ladder – nitrogen bases 2. “rungs” of ladder – nitrogen bases a)purines (double ringed molecules) 1. Adenine (A) 2. Guanine (G) b) pyrimidines ( single ring) 1. Cytosine (C) 2. Thymine (T)

4. bases bonded together w/ hydrogen bonds 5. The ORDER of nitrogen bases determines the type of protein which will be made to determine the phenotype!

IV. DNA Replication – DNA must be copied every time a cell divides so daughter cell has directions for new cell! A) Helicase (an enzyme) breaks H bonds bt nucleotides. B) Now have portions of 2 exposed strands with exposed nitrogen bases

C) Free floating nucleotides in cytoplasm enter thru nuclear pores D) Land on exposed strands, complementary bases pair up E)DNA polymerase connects nucleotides w/a phosphodiester bond between the sugars and phosphates F)End result 2 DNA molecules. Each has one old and one new strand

V. Limits on cell size – Why do they divide? A) Diffusion – slow, cell needs to be small to get materials quickly B) Lack of enough DNA to direct protein synthesis C) Surface area : Volume ratio 1. Volume increases faster than surface area 2. p. memb can’t supply big volume

VI. Cell Cycle A) Interphase 1.most of life cycle 2. Grows, protein synthesis 3. DNA is loose as chromatin 4. At end DNA & all organelles are copied to get ready to divide B) Mitosis – Cell division of somatic (body) cells

1. Prophase a) chromosomes double (humans 46  92) 1. 2 sister chromatids (identical) 2. chromatid pairs held together by centromere 2. chromatid pairs held together by centromere b) nuclear memb dissolves c) spindle fibers form d) centrioles move to opposite poles

2. Metaphase a) Dbld chromos attach to spindle fibers with centromere b) Pulled to equator of cell

3. Anaphase a) Centromeres split b) Sister chromatids separate & move on spindle fibers to opposite poles

4. Telophase a) Sister chromatids arrive at opp poles b) Chromosomes unwind to chromatin c) spindle dissolves d) nuc. membs form e) p. membs form bt 2 nuclei

5. Cytokinesis – splitting into 2 a) Animal cells – p. memb pinches tog b) Plant cells – cell plate forms bt 2 nuclei

VII. RNA - Ribonucleic acid - helps to convert code in DNA (genes) to proteins. A) Structure 1. Single stranded! 2. nucleotide structure a) Sugar is ribose b) Phosphate c) Nitrogen bases 1. Guanine 2. Cytosine 3. Adenine 4. Uracil

VIII. Transcription- DNA code is copied by formation of RNA strand in nucleus!!! A) DNA strand unwinds at certain site (“start codon”) B) RNA nucleotides (GCAU) attach to exposed nucleotide bases of DNA C) RNA polymerase connects RNA nucleotides tog D) Transcription is complete when you reach a stop codon in DNA sequence. E) RNA strand detaches, SNA strand “zips” back tog

F) RNA is modified into mRNA or tRNA

IX. Translation – RNA translates DNA code into a protein which determines the phenotype A) Structure of Protein 1. polymer of amino acids 2. a.a.’s joined tog w/ peptide bond 3. may also be called polypeptide B) mRNA (messenger RNA) 1. attaches to ribosome in the cytoplasm of the cell

2. mRNA contains codons – a triplet of bases which code for a certain amino acid Ex: DNAC – T – A – T – G – T mRNAG – A – U – A – C - A mRNAG – A – U – A – C - A Use chart to see what a a coded for! Use chart to see what a a coded for! Ex: codon 1aspartic acid codon 2threonine

C) tRNA – brings amino acid to mRNA 1. structure – special sequence of nucleotides which folds in on itself 2.anticodon is complementary to a specific codon of Mrna 3. Each tRNA carries a specific type of amino acid

D) Protein assembly – in cytoplasm at a ribosome 1. mRNA codons “read” by ribosome 2 codons at a time 2. tRNA brings amino acid to mRNA 3. tRNA anticodons bind to codons of mRNA 4. Peptide bond forms bt 2 amino acids 5. Ribosome moves 1 codon down mRNA

6. Process repeats, adding amino acids in correct sequence 7. Stops when stop codon is reached 8. Protein is released a) Sent to golgi apparatus to be

** DNA sequence→ determines RNA sequence →determines type of protein→ phenotype!