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30 Cards in this Set

  • Front
  • Back
Gene Expression in Eukaryotes
* Genes are split into introns and exons

* mRNA splicing and transcription occur in the nucleus

* translation occurs in the cytoplasm
Gene Expression in Prokaryotes
* transcription and translation are coupled

* mRNA is translated immediately after transcription
RNA polymerase in Bacteria
* consists of a core enzyme with four subunits (α, α, β, β')

* promotes or catalyzes polymerization

* utilizes accessory proteins, sigma (σ) factors
Sigma (σ) Factors
* participate in the initiation of polymerization

* may have a major σ factor that regulates gene expression under normal conditions and a σ factor that regulates gene expression under alternative conditions
* where the σ factor and RNA polymerase bind to start txn

* consist of consesus sequences:
- 35 box
- 10 box (TATA or Pribnow box)
Terminator Sequences:
- Intrinsic Terminator
- Rho-dependent Terminator
* sequence where txn is terminated

* Intrinsic: forms a stem-loop structure in the RNA transcript that signals the RNA polymerase to stop txn

* Rho-dependent: takes advantage of a protein that scans along the DNA
Unit of Transcription
* region between the promoter sequence and terminator sequence

* mammals: one gene = one unit of txn

* bacteria: one unit of txn = several genes costranscribed together in a polycistronic mRNA (operon)
* multiple genes are encoded in the same mRNA
* one unit of transcription in bacteria

* goes through the promoter, genes of interest, until the terminator sequence
Polar Effect
* a mutation in an upstream gene can stop txn, gene expression, and possibly tln of a downstream gene
Complement Test
* allows you to figure out if you have a mutation in gene one or a mutation in gene one that has a polar effect on genes two and three

* introduce normal copies of gene one, two, or three and see which one restores your phenotype
* refers to a set of operons that are coregulated

* when a cell is responding to a change in conditions, you need to regulate multiple operons simultaneously
Lac Operon
* regulated in response to nutrient conditions

* if no glucose, but lactose is present, genes for metabolizing lactose are upregulated

* lactose absent: repressor binds to the operator

* lactose present: inducer binds to the repressor, which falls off the operator = txn of lac genes
Mal Operon
* bacteria want to upregulate the genes for maltose when present

* no maltose (the inducer): without binding of the inducer to the activator, the activator cannot bind to RNA polymerase; the RNA pol doesn't bind efficiently

* maltose present: maltose (the inducer) binds to the activator, which then binds to the RNA polymerase = txn
Global Control Systems
* systems that regulate the expression of many different genes at the same time

* Ex: Catabolite Repression System
Catabolite Repression System
* allows cells to regulate the expression of genes in response to glucose levels

* low levels of glucose: high levels of cAMP, which bind to CAP, which binds to the activator near the promoter region = txn of lac operon

* high levels of glucose: low cAMP levels = no txn of lac operon
* cyclic AMP

* regulates the Catabolite Repression System

* starvation signal

* can bind to catabolite activator protein (CAP)
Quorum Sensing
* regulated in response to bacterial number

* uses a small signal molecule called acyl homoserine
Stringent Response
* like catabolite repression, senses nutrient levels

* regulated in response to AA levels and mediated by ppGpp

* ppGpp signals bacteria to halt process of protein synthesis and synthesize AA instead
* an alarmone involved in stringent response that signals the environment is AA poor

* signals bacteria to halt protein synthesize and initiate amino acid synthesis instead
Two Component Systems
1) signal produced by binding of signalling molecule to histidine kinase
2) binding causes dimerization of HK
3) dimerization causes autophosphorylation of histidine residue
4) phosphotransfer rxn: the phosphate group is transferred to an aspartic acid on the response regulator
5) activated response regulator activates or represses txn
Histidine Kinase
transmembrane protein that can sense extracellular conditions

Ex. pH, divalent cations [ ]
Response Regulator
* DNA binding protein

* could be a positive or negative regulator:
- activate txn
- repress txn
Bacterial Ribosome
* smaller number of protein components and RNA

* targeted by gentamicin and erythromycin

* 80% remain in the cytoplasm
* 20% in membrane, periplasm, secreted
Sec Pathway Summary
* all proteins have a signal sequence (30 AA tag at N terminus)

* signal recognition protein (SRP) Sec B helps to recognize the signal sequence of the unfolded protein and target it to the secretory machinery

* Sec A is an ATPase
- ATP hydrolysis helps thread the protein through a pore in the membrane

* Sec Y, E, and G make up the transmembrane pore

* as the protein is targeted to the pore and threaded through, sometimes the SS is cleaved
Sec Pathway - Gram Positive
* the pathway delivers proteins to the outside of the cell
Sec Pathway - Gram Negative
* they have an additional membrane, so the general secretory pathway only delivers proteins as far as the periplasm
Type III Apparatus
* consists of 20 proteins that form a needle that spans both membranes and punctures the eukaryote membrane
Type III Secretory Pathway
* contact with host cell mediated by a host receptor and bacterial adhesin

* needle is inserted with a special tip complex that mediates insertion into host cell membrane

* a pore is created, allowing bacterial proteins (effector molecules) to enter the eukaryotic cell
Effector Molecules
* bacterial proteins that enter the host cell

* can prevent the membrane from undergoing changes in shape (prevents phagocytosis)

* can cause changes in host cell that allows the bacteria to be engulfed