Module 4 Flashcards
- Sequence of genomic DNA or RNA that is
essential for a specific function - Used to be defined as giving rise to an enzyme
Gene
(3) Types of Genes and functions
- protein-coding genes – TRANSLATED
- RNA-specifying genes – TRANSCRIBED ONLY
- untranscribed genes – do not get transcribed but affect the expression of other genes
Type of mRNA as a transcription unit:
– contains 1 gene only
– common in eukaryotes
Monocistronic mRNA
Type of mRNA as a transcription unit:
- contains several genes in tandem array
– common in prokaryotes
Polycistronic mRNA
States that not all genes within a cell are active at the same time.
Regulation of Gene Expression
Stages where gene regulation occurs
*Transcription
*Post-transcription
*Translation
*Post-translation
In Transcriptional Regulation these are:
- genes that are transcribed continuously
– not affected by the environment
Constitutive Genes
In Transcriptional Regulation these are:
genes governed by REGULATORY proteins
Non-constitutive genes
Types of regulatory proteins
- Repressor
- Activator
Protein that prevents transcription
Binds to an OPERATOR sequence upstream of the gene in the
DNA
Negative control
Repressor
Protein that promotes transcription
Binds to either PROMOTER or ENHANCER sites in the DNA
Positive control
Activator
Sequences found at the 5’ flanking region of a gene
Signals initiation of transcription
Promoters
Promoter sequences in eukaryotes
- TATA Box – (TATAAA), Hogness-Goldberg box
- CAAT Box – (CAAT)
- GC Box – (GGGCGG)
Promoter in Eukaryotes found 19-27 bp upstream of start of transcription
TATA Box (TATAAA)
sequence that is translated
Exon
intervening sequence, eventually spliced off
intron
mRNA domains that control critical post-transcriptional gene regulation processes
untranslated
UTR (untranslated region)
Promoter sequences in prokaryotes
Pribnow Box (TATAAT)
TTGACA
Found 10 bp (technically 7 in the lab) from the start of transcription in prokaryotes
TATAAT
Found 35-bp upstream of start of transcription
TTGACA
- unit of bacterial gene expression & regulation
- Polycistronic
- Contains regulatory elements
Operon
Site to which RNA polymerase binds
Promoter
Site to which repressor protein binds
Operator
Structural Genes for lac operon:
Lac Z - beta-galactosidase
Lac Y - permease
Lac A - transacetylase
Codes for repressor protein
Repressor
T or F: In the absence of lactose, the repressor protein does not bind and transcription of structural
genes proceeds.
F: In the PRESENCE of lactose, the repressor protein does not bind and transcription of structural genes proceeds.
T or F: In the absence of lactose, the repressor protein binds to the operator gene and blocks transcription.
T: In the absence of lactose, the repressor protein binds to the operator gene and blocks transcription.
The lac operon is NEGATIVE INDUCIBLE CONTROL, why?
Negative control because of presence of repressor protein that prevents transcription; Inducible because it is based on the presence of lactose
Structural genes of the trp operon.
*Trp E
*Trp D
*Trp C
*Trp B
*Trp A
Regulates mRNA transcription
Attenuator
T or F: In the absence of tryptophan, the repressor protein trpA-repressor can bind to the operator causing allosteric transition. The trp-Repressor complex binds to the operator and transcription is blocked.
F:In the absence of tryptophan, the repressor protein alone cannot bind to the operator. Transcription proceeds to form a Polycistronic mRNA. If tryptophan is present, the repressor protein, trpA-repressor, binds to tryptophan, causing allosteric transition. The trp-Repressor complex binds to the operator and transcription is blocked.
The trp operon is under NEGATIVE REPRESSIBLE CONTROL, why?
Presence of tryptophan represses transcription of structural genes
Negative control because of presence of repressor that prevents transcription
Regulator several hundreds or thousands of bp upstream or downstream of gene it regulates
Enhancer
proteins encoded by separate
genes
bind to specific DNA sequences
also known as trans-acting
factors
Transcription Factors
3 types of Transcription Factor DNA binding sites:
- Helix-turn-helix
- Zinc finger
- Leucine zipper
immediate product of
transcription; edited before use or translation
pre-mRNA
pre-mRNAs found in
nucleus of eukaryotes
hnRNA
lends protection and stability to 5’ end; UNIQUE TO EUKARYOTES
5’ capping
Addition of poly-A tail
to protect the 3’ end from exonucleases
3’ polyadenylation
removal of introns
splicing
In translation, prokaryote or eukaryote:
Formylmethionine as first amino acid
Shine-Dalgarno sequence – where 16S rRNA binds
AGGAGG 10 bases
upstream of AUG codon
Prokaryote
In translation, prokaryote or eukaryote:
Methionine as first amino acid
7mGppp – where rRNA binds
Eukaryote
Methods of Translational Regulation
- Altering the half-life or stability of mRNA for translation
- Controlling the initiation and rate of translation
- Regulation by microRNA (miRNA)
removal of _______ reduces the half-life of mature mRNAs and decreasing their stability
poly-A binding protein (PABP)
Small non-coding RNA molecule found in plants, animals, some viruses
Short, 19-23 nts in length
Encoded by eukaryotic nuclear gene (DNA)
Base pairs with complementary sites of mRNA in the cytoplasm; silences by prevention or delay of translation
Double or single stranded?
microRNA (miRNA); Double stranded
Methods of Post-translational Regulation by Modification of protein product
- Ubiquitination
- Phosphorylation
- Glycosylation
- Enzymatic cleavage
Post translational regulation where there is
attachment of protein ubiquitin to other
proteins
and
protein becomes target of destruction
by proteosome
Ubiquitination
Post-translational regulation
carried out by kinases
by addition of phosphate group to amino acids affecting the activity of protein
Phosphorylation
Post-translational regulation where there is
addition of carbohydrate group
also affects protein activity
Glycosylation
Post-translational regulation where there is
breakdown of protein into smaller functional units carried out by PEPTIDASE
Enzymatic Cleavage
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