Lecture 12 - Gene Expression Flashcards
Where is DNA stored in eukaryotes?
nucleus
- flow into the cell is undirectional
What is a gene?
- a region of DNA that directs the synthesis of an RNA molecule
- unit of heredity
- encode for proteins
What is a promoter?
- a DNA sequence that directs/regulates transcription
What is transcription (DNA-RNA)?
- encoding DNA to RNA
What is a template?
- strand of DNA that is used in transcription
What direction is RNA made?
- made 5’ - 3’
- antiparallel and complementary to the template
What is the coding strand?
- complementary and antiparallel to the template
- not used in transcription
What is the transcript?
- RNA product of transcription
What does RNA polymerase do?
- catalyzes phosphodiester bonds between RNA nucleotides
- RNA pol synthesizes 5’ - 3’
- does not require a primer
Where do transcription and translation occur in eukaryotes?
transcription = nucleus translation = cytoplasm
What are the three modifications in the nucleus?
- addition of a methyl-guanosine cap at the 5’ end
- addition of 100-200 adenosines to the 3’ end, poly-A tail
- RNA splicing (removal of introns)
What is translation?
- process in which the genetic code carried by a mRNA directs the synthesis of proteins from amino acids
What is the genetic code?
- 3 nucleotides = one amino acid
- 3 “letter” word = codon
- universal
What was the Nirenberg Experiment?
- synthesized an artificial mRNA with repeating UUU codons using translation
What is the codon table?
- 64 possible codons
- 61 encode amino acids
- 3 are non-associated
- start codon (AUG)
- stop codons (UAA, UGA, UAG)
What is tRNA?
transfer RNA
- has a.a binding region and mRNA base-pairing region
- not translated but functions in translation
What is Aminoacyl tRNA synthetase?
-pairs correct a.a based on anticodon sequence (covalently link a.a to tRNA in the sequence-dependent matter)
What are ribosomes?
- catalyze peptide bonds
- consists of three important sites (A,P,E)
- proteins are synthesized from N-C by reading mRNA 5’-3’
What are the large and small subunits of ribosomes?
- large = contains rRNA and is catalytic
- small = contains rRNA and is recognition
What are the steps in translation?
- initiation
- elongation
- termination
What happens in the initiation phase?
- ribosomal binding site positions the small subunit such that AUG sits in the P site
- mRNA associates with ribosome vis base pairing with mRNA and rRNA = specificity
What happens in the elongation phase?
- bind = tRNA a.a approaches A site and binds to the mRNA
- bond = peptide bond forms between #1 tRNA and #2tRNA and the growing chain moves to tRNA in A site
- shift = ribosome shifts down mRNA (to 3’ end) in a one codon step
What happens in the termination phase?
- STOP codons
- when the ribosome encounters a stop codon in A site the ribosome stalls unless a release factor enters
- ribosome components dismantle and are recycled
What transcription and translation coupling?
- prokaryote only
- translation occurs at the same place, therefore can occur at the same time
What are mutations?
- heritable changes in base sequences that modify the information content of DNA
What are substitutions?
- base-pair substitutions in the replacement of one nucleotide and its partner with another pair
What are silent mutations?
- because of redundancy in the genetic code
- no change in the primary sequence
What are missense mutations?
- encode wrong amino acid
- change in the primary sequence
- may affect protein function
What are nonsense mutations?
- premature stop codon
- shortened protein
- may affect protein function
What are frameshift mutations?
- single bp addition or deletion that changes the reading frame of a protein
What is the difference between spontaneous and induced mutations?
- spontaneous = errors in DNA replication
- induced = caused by mutagens
