Flashcards
Transport Across membrane
Cards in this deck (32)
- 1Which bacteria is monoderm and which is diderm?Gram positive = monoderm
Gram negative = diderm - 2What is the function of the cytoplasmic membrane?-Microorganisms maintain an intracellular environment- Homeostasis
-Membrane is a permeability barrier
-Internal pressure higher than outside, maintains cell structure =Turgor
-Permeability barrier is essential for creating an electrical and chemical gradient of proton. PMF - 3What is the structure of cytoplasmic membrane?-The membrane consists mainly of phospholipids
-amphipathic: hydrophilic and hydrophobic regions
-Uptake and secretion of charged, hydrophilic molecules require transport proteins
-Protein export also requires transport mechanisms
- 4What affects molecules permeability?The more ionic the molecule the less permeable the membrane is to it
- 5How is the cytoplasmic membrane a protein anchor?Site of many proteins involved in transport, bioenergetics, and chemotaxis
- 6What do transport proteins do?Accumulate solutes against the concentration gradient
-high specificity for the solute and tightly regulated - 7Which is better transport or diffusion?Simple diffusion- rate too slow for cells to achieve conc. of nutrients they need
-Conc of nutrients in nature often very low
-Cells need to concentrate the nutrients
-Cells need transport (uptake) systems
-Transport systems can become saturated with nutrients so rate of uptake reaches maximum levels
- 8What do all transport systems have?A membrane spanning protein
-12 alpha helices spanning membrane and forming a channel
-Conformational change in protein following substrate binding which shuttles nutrients across the membrane
-Hydrophobic internal part
-Hydrophilic sticking out of membrane
- 9What is visible in the centre of this protein?Gated pore visible in the empty centre of the membrane spanning protein
- 10What is a Uniporter?Proteins that transport a molecule unidirectionally across the membrane, either in or out
- 11What is a Symporter?Cotransporters; they transport one molecule along with another substance, typically a proton
- 12What is an Antiporter?protons that transport one molecule into the cell while simultaneously transporting a second molecule out of the cell
- 13What are some examples of more complex transporters?
- 14What can uptake be driven by?-PMF (electrical and/or chemical gradient)
-ATP
-Chemical gradient of the transported molecule
-A combination of the above - 15What are transport system?-Usually highly specific for particular nutrients
-Transport systems often react with only one molecule
>Glucose specific transporter
>Single amino acid transporter
>Branched chain amino acids transporter - 16How causes specific transporter systems?-The expression of genes encoding the protein transporter is highly regulated
-A transporter for a specific nutrient is produced in a cell in response to its presence in the environment
-The concentration of the nutrient also dictates the type of transporter
>high affinity transporter at low concentration of substrate
>low affinity transporter at high concentration of substrate - 17What are the three classes of transport systems?1. Simple transport
2. Group translocation
3. ABC transporter - 18What is Simple transport?-Driven by the energy in the PMF
-requires a protein spanning the membrane
-Energy source = PMF
- 19What is a group translocation?-Chemical modification of the substrate to be transporter, Driven by phosphoenolpyruvate
-Transport system involved a series of protein
- 20What is an examples of Group translocation?Phosphotransferase system
-proteins are phosphorylated and dephosphorylated until enzyme II phosphorylates the sugar
-Examples Nonspecific components participate in the transport of any sugar
-Examples specific components to a particular sugar e.g. glucose transporter, mannose transporter, fructose transporter
-Phosphoanhydride bond in PEP provides energy for phosphorylation
-Phosphorylation of glucose is the first step in glucose metabolism
-Glucose-6-P is ready to enter into metabolic route immediately
- 21What is cAMP?When glucose levels drop, cyclic AMP (cAMP) begins to accumulate in the cell. The cAMP molecule is a signaling molecule that is involved in glucose and energy metabolism in E. coli
- 22What is the ABC (ATP binding cassette) system?Periplasmic binding proteins are involved and energy comes from ATP
- 23What are the required three components of ABC transport systems?1. Periplasmic protein
2. Membrane spanning protein
3. ATP hydrolyzing protein (kinase) which provides energy for transport - 24What do ABC transporters transport?>200 different types- ABC transporters are a family of proteins
ABC system transports:
-sugars
-amino acids
-Inorganic nutrients- sulphate and phosphate
-Multidrug resistance (cancer treatment)
ATP consumed to drive the transport of the substrate - 25What is the difference in ABC transport systems in Gram negative and gram positive bacteria?-Periplasmic binding proteins = very high affinity for substrate to be transporter
-Gram negative BPB are free and move in periplasmic space
-Gram positive (no periplasm) have binding proteins anchored in the cytoplasmic membrane
- 26How do bacteria get Iron into cell?-Bacteria produce siderophores to scavenge iron
-Siderophores have an extremely high affinity for iron
-After binding to iron, the bacterium takes up the siderophore iron complex
-Carried out by ABC transporters in an ATP dependent manner
-Siderophores are produced by pathogenic bacteria to obtain iron from the host
-Fe+2 present in low conc- as it goes to Fe +3 in O2 presence
- 27How is protein secreted from microbes-The microbial cell is very complex with many distinct locations
-The function of proteins an the cell depend on proteins being in the correct location and only the corrected location
-Virulence factors need to be in the correct location relative to their host target cells
-Microbes deploy sophisticated protein secretion systems containing targeting signals for each subcellular location - 28How does the protein export- secretion systems look like in bacteria?
- 29How does the sec system work?-Proteins destined for secretion in a two-step process have a signal sequence, which is cleaved off after translocation across the inner-membrane
-N: a positively charged amino terminal
-H: a hydrophobic core
-C: polar carboxyl-terminal
-The pre-protein is kept unfolded following translation by SecB, a chaperone protein
-The unfolded protein travel to the motor protein SecA, which guides the protein to the SecYGE translocase which forms a pore
-SecA is an ATPase providing energy for protein translocation (The PMF also plays a role)
-Following translocation the signal sequence is cleaved off by signal peptidase I, and the mature protein folds
-The sec system is conserved in Bacteria, Eukarya (mitochondria, chloroplasts) and Archaea
- 30What is the Type II secretion system of Shigella flexneri?The needle complex
-Two domains:
>needle like structure protruding from the cell
> Cylindrical base that anchors structure to outer and inner membrane
- 31What is TIISS?secretion into extracellular milieu
- 32What is TIIISS?secretion from bacterial cytoplasm into cytoplasm of the host (plant or animal cells)
-Yersinia pestis = bacteria that causes plague (works like this)
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- University Microbiology Flashcards on Transport Across membrane, created by Adrianna Bialecka on 08/02/2025.
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- Adrianna Bialecka · Feb 2025
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- Feb 8, 2025
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