3. Nucleic Acids and Gene Expression Flashcards
Define: Gene
Specific sequence of nucleotides in DNA molecule coding for a specific sequence of amino acids
Feature of Genetic Code
- Degenerate
- Non-overlapping
- Triplet code
- Universal
- Punctuated
Genetic code - degenerate
- more than 1 codon on mRNA can code for same amino acid
- 1st and 2nd bases the same, 3rd is a wobble base
Genetic code - non-overlapping
Each nucleotide has in a triplet code is only read once by ribosomes
Exception: some viruses
Genetic code - triplet code
Sequence of 3 nitrogenous bases along DNA codes for 1 amino acid
Genetic code - universal
Same triplet of nucleotides codes for same amino acid in all organisms
Genetic code - punctuated
- start codon: AUG
- stop codon: UGA,UAA, UAG
Name of strand used for transcription
Template / non-coding / sense strand
Name of strand not used for transcription
Non-template / coding / antisense strand
Direction of transcription
5’→3’
Direction in which template strand is read
3’→5’
Stages of transcription
1) Initiation
2) Elongation
3) Termination
Transcription - Initiation
- In eukaryotes, basal transcription factors bind to promoter before RNA polymerase; TFIID first to bind followed by other basal TFs
- RNA polymerase binds, forming transcription-initiation complex; binding causes DNA double helix to unwind and unzip at transcription start site
Transcription - Elongation
- RNA polymerase moves along non-coding strand and continues to unwind and unzip DNA double helix
- Selects rNTPs with nitrogenous bases complementary to those on non-coding strand; catalyses phosphodiester bond formation between adjacent ribonucleotides
Transcription - Termination
Proceeds till terminator sequence is transcribed; mRNA dissociates and DNA rewinds to form DNA double helix
