Gene Expression, Transcription, Translation

DNA

nucleic acid that carries genes that instruct cellular production (eukaryotes - nucleus; prokaryotes - cytoplasm)

DNA makeup

deoxyribose, double helix, 4 bases (cytosine, guanine, adenine, thymine)

RNA

nucleic acid that facilitates protein synthesis by transferring genetic info from DNA to ribosomes (located in nucleus, cytoplasm and ribosomes)

RNA makeup

ribose, single stranded, 4 bases (cytosine, guanine, adenine, uracil)

types of RNA

mRNA, rRNA, tRNA, miRNA/siRNA

mRNA

molecule produced at the end of transcription that carries genes (in the form of codons) that instruct protein synthesis

codon

group of 3 nucleotides

rRNA

molecule that assists mRNA in attaching to the right spot during translation (for proper expression); can also act as an enzyme

tRNA

molecules that bring amino acids to the ribosome; ensuring the right one is being added per mRNA instruction

miRNA/siRNA

small regulatory RNA molecules that population control mRNA

the central dogma

the process of information flowing from DNA → RNA → protein (transcription then translation)

transcription

when the DNA sequence of a gene is unwound and used as a template to make mRNA (eukaryotes - nucleus; prokaryotes - cytoplasm)

transcription steps

initiation, elongation, termination

initiation (transcription - eukaryotes)

DNA unwinds and transcription factor assists RNA polymerase in binding to the TATA box

elongation (transcription)

RNA polymerase slides down the template strand in the 3’ to 5’ direction unzipping the DNA strand and synthesizing an RNA strand by adding the complementary nucleotides based on the template strand

termination (transcription - eukaryotes)

RNA polymerase reaches the terminator sequence (polyadenylation signal) and detaches

initiation (transcription - prokaryotes)

RNA polymerase binds to promoter on its own

termination (transcription - prokaryotes)

RNA polymerase reaches the terminator sequence (G-nucleotides) which triggers protein Rho to bump into mRNA releasing it

post transcriptional modifications

only occurs in eukaryotes; step for maturing pre-mRNA so it is ready for translation (5’ capping, polyadenylation, splicing)

5’ capping

post translational modification where a modified guanine is added to the 5’ end to protect it from degradation and aid in rib

polyadenylation

post translational modification where 200 adenine nucleotides are added to the 3’ end of the strand to protect it from degradation, export to cytoplasm, and aid in translation

splicing

post translational modification where introns are removed from the strand leaving only protein coding exons

promoter

region of DNA that tells RNA polymerase where to attach

TATA box

part of the promoter that is recognized by the transcription factor

transcription factor

helper protein that binds to the TATA box and signals RNA polymerase to come

RNA polymerase

transcription enzyme that binds to the DNA at the signaled site

coding strand

the strand the RNA transcript is modeled after (opposite template strand)

template strand

the strand of DNA used to synthesize the RNA transcript

recognition sites (-35 element and -10 element)

sequences of DNA that RNA polymerase recognizes and directly binds to

rho-dependent termination

prokaryote RNA transcript contains a rho binding site that a rho factor recognizes and cleaves

rho-independent termination

prokaryote RNA transcript folds on itself and cleaves when the termination sequence is reached

DNA encoding binding site

sequence of DNA that codes for Rho binding site onto the RNA transcript

rho factor

rho protein that recognizes binding site and cleaves RNA transcript

rho binding site

cleavage site

transcription STOP point

DNA sequence that says to stop RNA polymerase so Rho can catch up

translation

protein synthesis based on mature mRNA instructions (eukaryotes - ribosomes; prokaryotes - cytoplasm)

translation steps

initiation, elongation, termination

initiation (translation - eukaryotes)

1) initiator tRNA connects to small ribosomal subunit and connects to mRNA

2) tRNA starts scanning for start codon

3) tRNA latches on to start codon

4) large ribosomal subunit joins to complete initiation complex

elongation (translation)

tRNA binds to the codon and adds amino acids to a chain and it runs down the mRNA (chain is passed through the A, P, and E slots on the ribosome)

termination (translation)

the final amino acid chain is released when the stop codon enters the ribosome which is recognized by a release factor and the tRNA detaches

initiation (translation - prokaryotes)

1) initiator tRNA connects to small ribosomal subunit and connects to mRNA

2) tRNA starts scanning for shine dalgarno sequence

3) shine dalgarno signals to ribosome where start codon is

4) tRNA latches on to start codon

5) large ribosomal subunit joins to complete initiation complex

post translational modifications

processes to chemically mature proteins and extend function (eukaryotes - endoplasmic reticulum; prokaryotes - cytoplasm)

types of post translational modifications

proteolysis, glycosylation, phosphorylation, ubiquination, lipidation/prenylation

proteolysis

cutting the polypeptide chain

glycosylation

addition of a carbohydrate to a protein (can act as cell surface marker)

lipidation

addition of a lipid to protein (can help anchor protein to cell membrane)

ubiquination

linking of two proteins together to mark it for degradation by the proteasome

phosphorylation

addition of a phosphate group to a protein (exclusive to serine, thyrosine, and threonine)