The document discusses various mechanisms of nutrient transport in cells, including simple diffusion, facilitated diffusion, active transport, and group translocation. It provides details on the concentration gradients, carrier proteins, and energy requirements that facilitate the different transport methods. Specific examples covered include sodium-hydrogen antiport, sodium-glucose symport, the phosphotransferase system for sugar phosphorylation during transport, and microbial iron uptake via siderophore secretion and receptor-mediated transport.

1. Reaacredited with B grade with a CGPA of 2.71 in the second cycle of NAAC
affiliated to manomanium sundaranar university, tirunelveli.
Post graduate & Research Centre – Department of Microbiology
(government aided)
ACADEMIC YEAR 2021-2022
I SEM CORE: PHYSIOLOGY AND METABOLISM
UNIT-1
NUTRIENT TRANSPORT MECHANISM
M.ANTONY SELVAM SUBMITTED TO
REG NO:20211232516103 GUIDE:DR.S.VISWANATHAN
I M.SC MICROBIOLOGY ASSISTANT PROFFESSOR&HEAD
ASSIGNED ON: 08/12/2021 SPKC - ALWARKURUCHI

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Nutrient transport mechanism
▪ It is the process of intake transports nutrients to the cell and discharge waste
and toxic materials from the cell .
▪ CELLULAR PROCESS :
▪ Metabolism
▪ Respiration
▪ Diffusion
▪ Osmosis
▪ Destruction

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TYOES OF TRANSPORT MECHANISM
▪ Simple diffusion:
▪ It is the process in which molecule move from region of high concentration
to region of low concentration across the plasma membrane.
▪ Rate of diffusion depends on size of concentration gradient between the
interior and exterior of cell.
▪ External nutrient concentration ---High
▪ Internal nutrient concentration--- Low
▪ Rate of uptake as more nutrients is required.
▪ It is mostly used to transport very small molecules H20,02,Co2

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FACILITATED DIFFUSION:
▪ Diffusion involving carrier proteins to transport nutrients is called
facilitated diffusion.
▪ Rate of diffusion across selectively permeable membrane
increased by using carrier protein (permeable) which are
embedded in plasma membrane.

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Carrier proteins :
▪ It resembles enzymes, in their specificity for the substance to
transport.
▪ It is selective and will transport only related solutes.
▪ Some are related to major intrinstic protein (mIp) family of
proteins.

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CONCENTRATION GRADIENT:
▪ A concentration gradient spanning the membrane drives the
movement of molecules and no metabolic energy input is
required.
▪ If the concentration gradient disappears net inward movement
ceases.
▪ In eukaryotes gradient can be maintained by transport nutrients
to another membrane compound.

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MECHANISM OF FACILITATED
DIFFUSION:
▪ Carrier protein complex spans the membrane after the molecules
binds to the outside.
▪ The Carrier may change confirmation and release the molecules on
the cell interior.
▪ The carrier subsequently changes to its orginal shape and is ready
to pic up the another molecules.
▪ It is responsible If the solute concentration is greater inside the
cell,it will move outward.
▪ This facilitated diffusion is mostly used by eukaryotic cells,to
transport a variety is sugars and amino acids.

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ACTIVE TRANSPORT
▪ Is the transport of solute molecules to higher concentration
against concentration gradient, with input of energy.
▪ Active transport is also characterized by the carrier saturation
effect at high solute concentration.

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PERIPLASMIC SPACE
▪ Protons are pumped to outside of plasma membrane during
electron transport .
▪ Proton gradient drives NA+ ions explains by an antiport
mechanism.
▪ The carrier confirmation then alters so that NA+ is released ,
inside the cell along with sugar by an symport mechanism.

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MECHANISM OF ACTIVE TRANSPORT
▪ Antiport transport of two (or) more different molecules or ions
across a (phospholipid membrane such as ) plasma membrane.
▪ Antiports – NA+/H+
▪ Symport – transport of 2 different molecules across plasma
membrane is some Direction symports – NA+ / Glucose.

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GROUP TRANSLOCATION
▪ Group translocation is a type of transport, chemically modifies the solute
molecules as it is brought into the cell.
▪ A molecules is modified and transport from periplasm with the help of group
of carrier proteins.
▪ Equ : PEP + sugar (outside) –pyruvate + sugar phosphate ( inside)
▪ Phosphotransferase system consists of 2 enzymes and heat stable
Proteins .
▪ Enzyme 1 and heat stable proteins (HPR) are cytoplasmic.
▪ Enzyme 2 more variable in structure and ofter composed of 3 sub units .

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▪ enzyme 2 A is cytoplasmic and soluble.
▪ Enzyme 2 B is hydrophilic and attached to 2 C.
▪ 1 C is hydrophobic proteins,that is embedded in the membrane.
▪ A phosphate is transferred from PEP to enzyme 2 which the help of E1 And
HPR ,Then a sugar molecules is phosphorylated as it is carried across the
membrane by enzyme 2.E2 transports only specific sugars and varies with
the PTS
▪ E1 HPR are common to all Pts.

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IRON UPTAKE
▪ Microorganisms require iron for use in cytochrome and many
enzymes iron – uptake is made difficult by the exterme
insolubility of ferric iron and it’s derivatives, which leaves little
fferric iron available for transport.
▪ Bacteria or fungi evercome this difficulty by secreting
siderophores.

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Siderophores
▪ They are low molecular weight, organix molecules that are able
to complex with ferric iron and supply it to the cell.
▪ The iron transport molecules are normally either in the form of
hydrocarbon or Phenolates catecholates .
▪ Ferrichrome – is a hydroxamates ,produced by many fungi.
▪ Enterobactin – is a catecholate , produced by E.Coli.

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MECHANISM OF IRON UPTAKE
▪ Microorganisms secrete siderophores ,when iron is source in the
medium .
▪ Ferric iron probably complexes with 3 siderophores groups to form a 6 –
coordinate actoherital complex.
▪ Once the iron sIderiphores complex reach the cell surface.
▪ It is bind to siderophore – receptor Protein.
▪ Then the iron is either releases directly into the cell or whole iron
siderophore complex is transported inside by an ABC transport.
▪ After the iron has entered into the cell ,it is reduced to 6 ferrous form.

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REFERENCE
▪ Presscott 7 th edition
▪ Harley And Klein’s

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