Gene Expression Flashcards
What are the two steps of gene expression?
Transcription and translation
Transcription
Information in a DNA sequence (gene) is copied into complementary RNA sequence
Translation
RNA sequence used to create amino acid sequence of a polypeptide
Central dogma
DNA can be used to create a protein, but a protein can never be used to create DNA
Central dogma process
DNA goes to replication or transcription — RNA— translated into protein
What are the 3 types of RNA that have roles in the information flow of DNA to protein?
Messenger (mRNA)
Ribosomal (rRNA)
Transfer (tRNA)
Messenger RNA
Nucleotide sequence determines ordered sequence of amino acids in a polypeptide chain
Ribosomal RNA
Found in ribosome (protein synthesis factory) catalyzes peptide bond formation between amino acids to form polypeptide
Transfer RNA
Bind specific amino acid, recognize mRNA sequence, recognize which amino acid should be added to polypeptide chain
Does HIV have RNA or DNA? Describe the HIV virus in terms of RNA and DNA
RNA retrovirus
No transcribing, instead infects host cell and makes a DNA copy of genome- host cell transcription makes more RNA- translated and incorporated
What does transcription need?
1 strand of DNA, 4 ribonucleoside triphosphates as substrates, RNA polymerase enzyme, salts and pH buffer
Reverse transcription
Synthesis of DNA from RNA
RNA polymerases
- catalyze the synthesis of RNA from the DNA template
- catalyze the addition of nucleotides in 5’ to 3’ direction and are processive (like DNA)
- don’t require primer
What are the 3 steps of transcription?
Initiation
Elongation
Termination
Promoter
Special sequence of DNA that tell RNA where to start transcription and which strand of DNA to transcribe
Initiation site
Start
Sigma factors and transcription factors
Proteins that help determine which specific genes are expressed at a particular time in cell
Initiation simplified
RNA polymerase binds to the promoter and starts to unwind the DNA strands
Elongation simplified
RNA polymerase moves along the DNA template strand from 3’ to 5’ and produces the RNA transcript by adding nucleotides complementary to the DNA template to the 3’ end of the growing RNA
Termination simplified
When RNA polymerase reaches the termination site, the RNA transcript is released from the template
Genetic code
Holds information for protein synthesis Relates genes (DNA) to mRNA and mRNA to the amino acids that make up proteins
Codon
Specifies a particular amino acid
Nirenberg and Matthale
Use a simple artificial polynucleotide to identify the polypeptide that the artificial messenger encoded
What do the 64 different 3 letter codons determine?
20 amino acids
Start codon
AUG (methionine)
Stop codons
UAA, UAG, UGA
The base sequence of the DNA strand that is transcribed to produce the mRNA is what to mRNA codons
Complementary and anti parallel
What is known as the “coding strand”?
Non-template strand of DNA that has the same sequence as mRNA
