the expression of genes Flashcards
what is rRNA
ribosomal RNA, makes ribosomes, it is the last set of genes to be turned off before cell division
What is tRNA
transfer RNA, carries amino acids to ribosome during protein synthesis
- they have an anticodon on one and carry the amino acid on the other. the anticodon will connect to the codon on the mRNA
- it is RNA that is all folded up
mRNA
messenger RNA, a copy of DNA that contains the information for protein synthesis.
How does transcription work
DNA is used to make mRNA,
- only genes are transcribed not all DNA; in front, there is a promoter sequence and a terminator sequence at the end (prokaryotes)
- RNA sequence is complementary to DNA
- new nucleotides are added on the 3’ end of the RNA and the synthesis in antiparallel
what is complementary to what (nitrogenous bases)
A - T (U in RNA)
G - C
what do polymerase do
unwind and separate double-stranded DNA, read DNA template, adds RNA nucleotides, and reorganized promoters and terminators.
rules for eukaryotes
- 5’ cap is added at the for it to last longer and help transport; a modified guanine
- introns are removed by spliceosomes, exons are kept (pre-mRNA to mRNA)
- poly-A-tail at 3’ end to help transport mRNA (it is in back, it is the motor, propulsion); multiple adenine (poly-A)
- caps are put because they need to get out of the nucleus therefore last longer.
what is translation
assembly of amino acids into polypeptides
how are amino acids polymerized
they have an N-terminal and a C-terminal (nitrogen on one end and carbon of the order) and they are arranged so the N-terminal is in front.
what direction is mRNA read
5’ to 3’, 5’cap to poly A tail (tail is at the end)
where are amino acids taken
in enzymes, tRNA goes and gets the amino acid
what is a stop codon
codons that cannot be recognized by a tRNA, UAG, UAA, UGA are stop codons. when they have seen the ribosome breaks into subunits
What is a start codon
AUG (also an amino acid)
how are tRNA molecule produced
They are synthesized by RNA polymerase III (does like a ribosome but for RNA), (reads DNA and makes an RNA copy)
What are genes
section of DNA, from promoter to terminator. Read from 3’ to 5’ because you add basses on the 3’ end of RNA (so 5’ end of RNA is in front and they are antiparallel)
Types of mutation
Somatic mutation; mitosis in daughter cells
Germline mutation; before meiosis and end up in gametes
base substitutions
Silent mutation: base mutation but codon still codes for the same protein so phenotype stays the same
missense mutation: new codon; so new protein, may change phenotype
non-sense mutation: creates a stop codon, protein is shortened
frameshift mutations
deletion: a base pair is deleted; will shift the next amino acid creating new codons (changes all aa in exon after frameshift)
insertion; same but add one
Triplet deletion: lost one entire codon
triplet duplication or insertion
what is an inducible system?
a repressor is attached to the operator, this DNA is called an operon (genes). when an inducer attaches to the repressor it falls of allowing RNA polymerase to start transcription. This mRNA will be translated by ribosome creating the proteins needed.
If glucose is present no lac operon is needed
lactose is sugar so if there is already glucose no need for more
lacZ
a first structural gene on the operon; codes for enzyme B. galactosidase; breaks down lactose into glucose and galactose (lacZ, lacY, lacA) antialphabetical
what is the lac operon
an inducible system that only exists in E. Coli; genes in this operon are normally turned off, they turn on in the presence of lactose (procaryote regulation)
lacY
second structural gene on the operon; enzyme opens up the cell to let lactose enter (protein channel)
lacA
last structural gene in the operon; codes for enzyme transacetylase
O
operator; sequence of DNA; binding side of the repressor protein
lacI (i)
repressor; blocks transcription;
P lac
promoter, binding site of RNA polymarase
what happens when there is no glucose
cAMP increses; cAMP attaches to CAP and activate it (catabolite activator protein); cAMP-CAP binds to DNA and helps initiate transcription (cAMP-CAP regulate other operons too)
Epigenome
genetic control that is not DNA, external factor (environmental cues); gans change phenotype
transcription regulation (affect the production of mRNA)
- chromatin remodeling: gene is turned of by chromatin compaction; when it decondenses allows access points for RNA polymerase:
Heterochromatin: condensed and inaccessible by polymerase
Euchromatin: relaxed and accessible - multiple copies of genes: ex; more rRNA, greater capacity of making ribosome
transcription factors (part of transcription regulation)
can increase and decrease (how often, how quick), turn on or off gene expression:
- activators turn on genes; bind to DNA near promoter or bind to the enhancer region and uses mediators to activate
- repressors turn genes off; bind to DNA near promoter
DNA methylation
CH3 added to cytosine (methyl group added to C base)
lots of is in promoter region turn genes off (silencing)
and it can be transferred to next generation: imprinting
Post-transcriptional regulation
regulate of change mRNA:
- alternative splicing: cutes pre-mRNA to produce alternative proteins, allows 1 gene to make many genes products
- RNAi (interference): gene silencing: when there is a lot of a mRNA, special RNA polymerase produces double-stranded mRNAn (micro RNA) that will bind to mRNA and prevents translation (cuts or just stays there); this may be produced when high levels of mRNA
Translational control
- translational repression: gene expression down, Proteins bind to the mRNA
- change poly-a tail: if it is lengthed: increase translation, shortened: decrease
post-translational control
turn proteins from inactive to active; by cutting segments that prevent protein from forming; also can add sugars
no activators in translation
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