III. What do genes do? Gene expression A. Genes 1. specific sequences of nucleotides within a molecule of DNA 2. occupy a specific locus on a chromosome 3. can mutate (change nucleotide sequence) 4. specify genetic information – regulation and protein synthesis a. DNA used to make RNA (transcription) i. RNA structure – like DNA except ribose replaces deoxyribose ii. types of RNA mRNA = messenger RNA specifies info needed to make proteins rRNA = ribosomal RNA combines with proteins to make ribosomes (organelle that synthesizes proteins) tRNA = transfer RNA transport amino acids to ribosome during protein synthesis http://www.youtube.com/watch?v=41_Ne5mS2ls transcription and translation b. RNA used to make proteins (translation) why you need proteins i. enzymes are proteins – catalyze cellular reactions ii. structural proteins – ex: collagen iii. storage proteins – store nutrients ex: ovalbumin in egg white zein in corn iv. transport proteins hemoglobin transports oxygen proteins in cell membrane transport substances into and out of cell v. regulatory proteins some hormones are proteins some proteins turn genes on and off vi. motile proteins actin filaments (made of protein) in spindle fibers actin and myosin in muscles vii. protective proteins antibodies B. Transcription = mRNA synthesis using DNA as a template to make RNA 1. the basic rules – for all types of cells a. only genes are transcribed (not all DNA is used) genes are identified by: i. a promoter sequence (in front of the gene) ii. a terminator sequence at the end b. only one strand of DNA is transcribed (though genes are not all on the same DNA strand) c. sequence of RNA is complementary to DNA i. if DNA is C then RNA complementary base is G ii. if DNA is G then RNA complementary base is C iii. if DNA is T then RNA complementary base is A iv. if DNA is A then RNA complementary base is U d. new nucleotides are added to the 3’ end of the RNA e. synthesis is antiparallel f. requires RNA polymerase (an enzyme) i. unwinds double-stranded DNA ii. separates double-stranded DNA into 2 strands of single-stranded DNA iii. reads DNA template iv. adds RNS nucleotides v. recognizes promoters and terminators 2. Additional rules for eukaryotes a. RNA polymerase needs transcription factors to locate and attach to promoter transcription factors are proteins that attach to the DNA near the promoter and form a transcription complex b. introns must be removed from RNA (primary transcript) = RNA splicing produces mRNA introns = non-coding regions (not used to make protein) exons = coding regions (used to make protein) accomplished by spliceosomes c. add 5’ cap - a modified guanine attaches to 5’ end of RNA protects RNA from degradation d. create poly-A tail - the addition of many (hundreds) of adenine to the 3’ end of the RNA. required to transport RNA out of the nucleus C. Translation = polypeptide synthesis using mRNA as a template to make polypeptides/proteins translation from nucleotide sequence to amino acid sequence 1. the genetic code a. 4 different nucleotides need to code for 20 different amino acids b. codon = series of 3 RNA nucleotides that specify an amino acid c. 3 codons do not specify any amino acid = STOP codons 2. the basic rules a. use a ribosome to capture and hold mRNA b. translate 3 RNA nucleotides (1 codon) at a time into 1 amino acid this requires a tRNA to bind to codon and bring the appropriate amino acid c. read RNA from 5’ end to 3’ end d. always start at AUG chose the 5’AUG3’ closest to the 5’ end of the mRNA e. continue until reach a STOP codon a codon that can’t be recognized by a tRNA STOP codons: UAG, UAA, UGA