BIOL 2050 - Transcription, RNA Postprocessing, Translation, and Gene Regulation

transcription

process in which a DNA message (a segment of DNA that codes for specific proteins) is converted into an RNA molecule

translation

the process in which a RNA molecule is used to assemble amino acids into a polypeptide

transcription initiation

the first step of transcription where RNA polymerase binds to the promoter region containing a recognition site. Separates the strands of DNA
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transcription elongation

second step of transcription where RNA polymerase moves along the template strand in 3' to 5' direction. RNA polymerase zips the DNA up as it moves forward. The mRNA is made in 5' to 3' direction

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transcription termination

the third phase of transcription where RNA polymerase hits the terminator sequence and transcription stops

mRNA

type of RNA that carries genetic information from DNA into the nucleus to direct protein synthesis in the cytoplasm

intron

noncoding sequences that are transcribed from the DNA and are removed in post processing

exon

sections of the DNA that are transcribed and code for proteins

post processing

following transcription, introns are removed from mRNA and exons are spliced back together. A 5' cap is made of guanine and phosphate. A 3' poly-A tail is made of 50-250 adenines. These both facilitate the export of mRNA from the nucleus and protect it from degradation in the cytoplasm
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RNA splicing

the removal of introns in the mRNA by the spliceosome

codon

three-nucleotide sequence on messenger RNA that codes for a single amino acid in translation. Multiple can code for the same amino acid.

reading frame

on an mRNA, the start and stop codon defines which codons will be transcribed, specifying which amino acids will be created

ribosome

cell organelles made of rRNA and proteins which slot where mRNA can be read and tRNA can deliver amino acids

tRNA

RNA molecules that use complimentary anticodons to match specific codons on the mRNA and deliver amino acids

translation initiation

first step of translation where the ribosome assembles around the mRNA to be read. The first tRNA is brought in.

translation elongation

second step of translation where the mRNA is read one codon at a time, and the amino acid matching each codon is added to the growing protein chain

translation termination

third step of translation where a stop codon enters the reading frame and release factors bind to the stop codon at the A site, releasing the polypeptide chain

post-translational modifications

after translation, phosphates, carbohydrates, and lipids are added to the new polypeptide chain which is then folded

constitutive genes

genes that are always expressed, having essentially constant levels of expression

gene regulation

cells have the ability to control their level of gene expression. This ensures proteins are produced at the correct time and amount. This is necessary to respond to differences in the environment.

cell differentiation

for eukaryotes, different cell types with different proteomes are created from the same genome through gene regulation, allowing cells to perform specific tasks

bacteria gene regulation

gene regulation that mostly occurs at the level of transcription and can be regulated at the protein or post-translational level

eukaryote gene regulation

gene regulation is most common at transcription, but, gene regulation is still common at other levels of protein synthesis

repressors

proteins that inhibit transcription (negative control)

activators

proteins that increase the rate of transcription (positive control)

small effector molecules

molecules that bind to activators and repressors to cause confrontational change. Similar to an on/off switch for transcription factors

operons

in bacteria, a cluster of genes under transcriptional control of one promoter

lac operon

a common operon that codes for transport and metabolism of lactose. Lac repressor binds to its operator in absence of a small effector molecule. Inducible, meaning genes are turned off until necessary

trp operon

a common operon that codes for the enzymes to produce tryptophan. Trp repressor binds to its operator in the presence of its small receptor molecule. Repressible, when enough tryptophan enzyme is present, genes are turned off to prevent overproduction