Part I Genes on DNA DNA consists of two antiparallel strand

Part I: Genes on DNA • DNA consists of two antiparallel strands, each with polarity determined by the 5’ and 3’ carbons of the deoxyribose ring. For a given gene encoding a protein, one strand operates as a template for messenger RNA (mRNA transcription), while the other coding strand reads similar to the mRNA code. • The coding region of a gene is composed of codons, sets of 3 nucleotides, each of which codes for a specific amino acid.

• A gene has a promoter immediately upstream of the DNA coding sequence. (How big? Varies) • The coding sequence always starts with a START codon. What is it? _____, codes for _____ • Coding sequence always ends with a STOP codon. Typically 3 options: ____ ____ ____ Here is the chromosomal coding strand sequence of a small gene from yeast S. cerevisiae, PBI2 (protease B inhibitor 2), including 50 bases of promoter sequence before coding sequence.

1 5’—CGGTAACCAG AAGGTAATCT TAAATATACA AACAAAAAAC AAGGTCCATA

51 ATGACAAAGA ATTTCATCGT CACTTTGAAA AAGAACACTC CAGATGTGGA 101 AGCTAAGAAG TTCTTGGATT CAGTTCATCA CGCAGGTGGC TCTATTGTAC

151 ACGAATTCGA CATCATTAAA GGGTACACCA TCAAGGTACC AGATGTTCTC 201 CACTTGAACA AGTTGAAGGA AAAGCACAAT GATGTCATCG AGAACGTCGA

251 AGAAGACAAA GAAGTTCATA CAAATTGA—3’ (Last nucleotide here: # 278)

ANNOTATE the above gene, marking: 1) the promoter region, 2) the start codon, and 3) stop codon.

Q1: How many bases make up the coding sequence? ____ Q2: So how many codons? ____ Q3: How many AAs are encoded? (Tricky: does a stop codon encode an amino acid?) ______

Part II: mRNA TRANSCRIBE the first 7 codons of the above gene (21 nucleotides of coding sequence): —Hint: remember to change Thymine to Uracil (T to U) in mRNA

Codon1 Codon2 Codon3 Codon4 Codon5 Codon6 Codon7

Solution

A gene has a promoter immediately upstream of the DNA coding sequence. (How big? Varies) • The coding sequence always starts with a START codon. What is it? _ATG___, codes for _Methionine____ • Coding sequence always ends with a STOP codon. Typically 3 options: __TAG_TAA_ _TGA___ ____

1. Promoter region - TAAATA sequence

5’—CGGTAACCAG AAGGTAATCT TAAATATACA AACAAAAAAC AAGGTCCATA

51 ATG ACA AAG AAT TTC ATC GTC ACT TTG AAA AAG AAC ACT CCA GAT GTG GAA GCT AAG AAG TTC TTG GAT TCA GTT CAT CAC GCA GGT GGC TCT ATT GTA CAC GAA TTC GAC ATC ATT AAA GGG TAC ACC ATC AAG GTA CCA GAT GTT CTC CAC TTG AAC AAG TTG AAG GAA AAG CAC AAT GAT GTC ATC GAG AAC GTC GAA GAA GAC AAA GAA GTT CAT ACA AAT TGA—3

How many bases make up the coding sequence? ____ 228 bases

So how many codons? ____76 codons -

How many AAs are encoded? 75 amino acids.