BIO 325 Study Guide - Fall 2018, Comprehensive Midterm Notes - Dna, Protein, Genome
BIO 325
MIDTERM EXAM
STUDY GUIDE
Fall 2018
Gene Expression
A gene’s nucleotide sequence is co-linear with the amino acid sequence
Yanofsky – how do mutations in DNA correspond to mutations in protein
• Mutagenized E. coli
• Grew on media that contains tryptophan
• Replica plated to find colonies that don’t grow without tryptophan
• Isolated trpA auxotrophs – point mutants
• Mapped sites of mutations in DNA by recombination
• Purified mutant trpA proteins and determined amino acid sequences
o A gene’s nucleotide sequence is co-linear with the amino acid sequence of the
encoded polypeptide
▪ The positions of mutations in DNA nucleotides corresponded with the
positions of the amino acid substitutions
o Each nucleotide is part of only a single codon (non-overlapping codons)
▪ Each point mutation only altered one amino acid
o A codon is composed of more than one nucleotide
▪ Different point mutations may differ the same amino acid
Crick & Brenner’s experiment with phage rIIB gene
• Proflavin inserts or deletes a single base pair
• A gene has a reading frame
o Reversion occurred when a first proflavin-induced mutant was exposed to
proflavin for the second time (+1 and -1)
• A codon is a triplet
o Gene can still function with three or multiples of three changes
Wild-type phenotype may result when the reading frame is restored through frameshift
mutations, which are insertions or deletions that shift the reading frame.
Transcription
• New phosphodiester bond forms at the 3’ end (like in DNA replication)
• RNA is also made in 5’ → 3’ direction
Translation
• mRNA is read in 5’ → 3’ direction
Only one DNA strand is transcribed for a gene, but either top or bottom strand is used to
transcribe different genes
• RNA-like strand = sense strand = coding strand
• Template strand = antisense strand = noncoding strand
The genetic code is universal
- In vitro translation with synthetic mRNAs reveal the first codon identities
- Polymononucleotides
- Polytrinucleotides
- Polytetranucleotides
- Deduced codons from amino acid sequence
- Some ambiguities
find more resources at oneclass.com
find more resources at oneclass.com
Ribosome binding experiments with synthetic mini-mRNA identified remaining codons
The genetic code is degenerate and unambiguous
• Unambiguous – a certain codon always codes for the same amino acid
• Degenerate (reduntant) – several codons can code for the same amino acid
The opening frame in DNA is defined by the start codon (ATG)
Central concepts in gene expression
• Transcription (DNA to RNA)
o Initiation, elongation, termination
o Initiation in prokaryotes vs. eukaryotes
• RNA processing in eukaryotes
o 5’ cap
o splicing
o poly-A tail
• Translation (RNA to protein)
o Initiation, elongation, termination
o Initiation in prokaryotes vs. eukaryotes
o tRNAs, wobble and redundancy
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
A gene"s nucleotide sequence is co-linear with the amino acid sequence. Yanofsky how do mutations in dna correspond to mutations in protein. Gene expression: mutagenized e. coli, grew on media that contains tryptophan, replica plated to find colonies that don"t grow without tryptophan, mapped sites of mutations in dna by recombination, purified mutant trpa proteins and determined amino acid sequences. Wild-type phenotype may result when the reading frame is restored through frameshift mutations, which are insertions or deletions that shift the reading frame. Transcription: new phosphodiester bond forms at the 3" end (like in dna replication, rna is also made in 5" 3" direction. Translation: mrna is read in 5" 3" direction. Only one dna strand is transcribed for a gene, but either top or bottom strand is used to transcribe different genes: rna-like strand = sense strand = coding strand, template strand = antisense strand = noncoding strand. In vitro translation with synthetic mrnas reveal the first codon identities.
