Gene Expression Flashcards
Gene
Portion of DNA providing instructions for making a functional product (RNA or Protein).
Gene Expression
The flow of genetic info in cells. From DNA to RNA to protein.
Central dogma of molecular biology.
What are the steps of Gene expression?
Transcription
Translation
What are the steps of Gene expression?
Transcription
Translation
What is the purpose of transcription in gene expression?
To copy a particular portion of the DNA nucleotide sequence (Gene) into an RNA nucleotide sequence. 3 steps: Initiation Elongation Termination
Transcription initiation
Cells regulate which proteins are to be produced and at what rate. General Transcription Factors: Recognize promoter. Position RNA polymerase. Unwind DNA. Release RNA polymerase.
Distal gene regulating protein
Activation | Repression of specific genes. (Part of initiation transcription).
Promoter
Stretch of DNA upstream from a gene.
Transcription Elongation
-Capping of the 5’ end of the RNA with a modified guanine nucleotide, in order to protect the 5’ end and so that ribosome can recognize it.
-Splicing: Removal of introns leaving the exons(contain the info to make protein).
Position of the 3’ end of each mRNA is specified by a signal encoded in the genome. The signals are transcribed into RNA and recognized by RNA-processing enzymes.
- RNA cleaved at the 3’ end, Poly-A polymerase added on. 200-300 Adenine nucleotides added to primary transcript. Important for translation and stability of mRNA.
Transcription termination
Unprotected RNA attached to RNA polymerase (no 5’ cap). RNA is degraded an exonuclease which causes the RNA polymerase to
dissociate from the DNA.
RNA polymerase
Enzyme that performs transcription.
Unwinds DNA, immediate release of RNA, synthesis in 5’ to 3’ direction.
Translation
Passage of info encoded in the mRNA into a protein sequence.
Genetic code
Set of rules that assign how the 4 letter co code of DNA can be translated in the 20 letter language of proteins.
- Universal: all living organism use the same code.
- Unambiguous: each codon codes for 1 amino acid, or a START or STOP signal.
- Redundant: most AA are encoded by more than one codon
mRNA in translation
Specify the sequence of the proteins.
Ribosome in translation
Catalyze formation of peptide bonds.
Site of translation.
A site: bind to a tRNA loaded with an amino acid.
P site: contains the tRNA with the growing polypeptide chain attached
E site: contain the tRNA without an amino acid, which is ready to exit.
tRNA in translation
Anticodon reads the codon on mRNA to specify which amino acids should be brought into the ribosome. Attached to the 3’ end.
Codon
3 nucleotide sequence.
mRNA is composed of 4 letters
and needs codons to code for 20 amino acids.
64 codons for 20 AA.
Translation initiation
Initiatior tRNA binds to the small subunit of the ribosome. Binds to the 5’ end of mRNA. Finds start codon and binds. Large subunit of ribosome recruited to form initiation complex (initiator tRNA in P site). Protein synthesis can begin.
Translation Elongation
Codon recognition.
New tRNA enter A site.
Formation of peptide bonds.
Translocation: tRNA in A site with protein attached. in P site the protein is released and in E site tRNA leaves the ribosome.
Translation Termination
Stop codon enters A site.
Codon recognized by a releasing factor.
Ribosome adds water molecule instead of amino acid, releasing the newly synthesized protein.
Ribosome dissembles.
