Chapter 3 - Cells: The living units (part b). The main contents of this chapter include all of the following: Membrane transport: active processes, active transport, primary active transport, secondary active transport, vesicular transport, endocytosis and transcytosis,...and other contents.
Trang 1Cells: The Living Units: Part B
Trang 3 Requires carrier proteins (solute pumps)
Moves solutes against a concentration gradient
◦ Primary active transport
◦ Secondary active transport
Trang 4 Energy from hydrolysis of ATP causes shape
change in transport protein so that bound solutes (ions) are “pumped” across the membrane
Trang 6Copyright © 2010 Pearson Education, Inc. Figure 3.10
Extracellular fluid
K + is released from the pump protein and Na + sites are ready to bind Na + again.
The cycle repeats.
Binding of Na+ promotes phosphorylation of the protein by ATP.
Cytoplasmic Na + binds to pump protein.
Phosphorylation causes the protein to change shape, expelling Na + to the outside.
Extracellular K + binds to pump protein.
6
Trang 7Copyright © 2010 Pearson Education, Inc. Figure 3.10 step 1
Trang 8Copyright © 2010 Pearson Education, Inc. Figure 3.10 step 2
Binding of Na+ promotes phosphorylation of the protein by ATP.
Trang 9Copyright © 2010 Pearson Education, Inc. Figure 3.10 step 3
Phosphorylation causes the protein to
Na+ released
P
3
Trang 10Copyright © 2010 Pearson Education, Inc. Figure 3.10 step 4
Extracellular K+ binds to pump protein.
P
K+
4
Trang 11Copyright © 2010 Pearson Education, Inc. Figure 3.10 step 5
K+ binding triggers release of the phosphate Pump protein returns to its original conformation.
Pi
5
Trang 12Copyright © 2010 Pearson Education, Inc. Figure 3.10 step 6
The cycle repeats.
K+ released
6
Trang 13Copyright © 2010 Pearson Education, Inc. Figure 3.10
Extracellular fluid
K + is released from the pump protein and Na + sites are ready to bind Na + again.
The cycle repeats.
Binding of Na+ promotes phosphorylation of the protein by ATP.
Cytoplasmic Na + binds to pump protein.
Phosphorylation causes the protein to change shape, expelling Na + to the outside.
Extracellular K + binds to pump protein.
6
Trang 14 Depends on an ion gradient created by primary
active transport
Energy stored in ionic gradients is used
indirectly to drive transport of other solutes
Trang 15 Cotransport—always transports more than one substance at a time
◦ Symport system: Two substances transported in
same direction
◦ Antiport system: Two substances transported in
opposite directions
Trang 16Copyright © 2010 Pearson Education, Inc. Figure 3.11
The ATP-driven Na+-K+ pump
stores energy by creating a
steep concentration gradient for
Na+ entry into the cell.
As Na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient
into the cell (ECF = extracellular fluid)
Na+-glucose symport transporter loading glucose from ECF
Na+-glucose symport transporter releasing glucose into the cytoplasm
Trang 17Copyright © 2010 Pearson Education, Inc. Figure 3.11 step 1
The ATP-driven Na+-K+ pump
stores energy by creating a
steep concentration gradient for
Na+ entry into the cell.
Trang 18Copyright © 2010 Pearson Education, Inc. Figure 3.11 step 2
The ATP-driven Na+-K+ pump
stores energy by creating a
steep concentration gradient for
Na+ entry into the cell.
As Na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient
into the cell (ECF = extracellular fluid)
Na+-glucose symport transporter loading glucose from ECF
Na+-glucose symport transporter releasing glucose into the cytoplasm
Trang 19 Transport of large particles, macromolecules, and fluids across plasma membranes
Trang 21 Involve formation of proteincoated vesicles
selective
Trang 22Copyright © 2010 Pearson Education, Inc. Figure 3.12
Coated pit ingests substance.
coated vesicle detaches.
Coat proteins detach and are recycled to plasma membrane
Uncoated vesicle fuses with a sorting vesicle called an endosome vesicle containing Transport
membrane components moves to the plasma membrane for recycling.
Fused vesicle may (a) fuse with lysosome for digestion
of its contents, or (b) deliver its contents to the plasma membrane on the
opposite side of the cell (transcytosis).
Protein coat (typically clathrin)
Extracellular fluid Plasma
membrane
Endosome
Lysosome
Transport vesicle
(b) (a)
Uncoated endocytic vesicle
Trang 23Copyright © 2010 Pearson Education, Inc. Figure 3.12 step 1
Coated pit ingests substance.
Protein coat (typically clathrin)
Extracellular fluid Plasma
membrane
Cytoplasm
1
Trang 24Copyright © 2010 Pearson Education, Inc. Figure 3.12 step 2
Coated pit ingests substance.
coated vesicle detaches.
Protein-Protein coat (typically clathrin)
Extracellular fluid Plasma
membrane
Cytoplasm
1
2
Trang 25Copyright © 2010 Pearson Education, Inc. Figure 3.12 step 3
Coated pit ingests substance.
coated vesicle detaches.
Coat proteins detach and are recycled to plasma membrane
Protein coat (typically clathrin)
Extracellular fluid Plasma
Trang 26Copyright © 2010 Pearson Education, Inc. Figure 3.12 step 4
Coated pit ingests substance.
coated vesicle detaches.
Coat proteins detach and are recycled to plasma membrane
Uncoated vesicle fuses with a sorting vesicle called an endosome.
Protein coat (typically clathrin)
Extracellular fluid Plasma
membrane
Endosome Uncoated
Trang 27Copyright © 2010 Pearson Education, Inc. Figure 3.12 step 5
Coated pit ingests substance.
coated vesicle detaches.
Coat proteins detach and are recycled to plasma membrane
Uncoated vesicle fuses with a sorting vesicle called an endosome.
Protein coat (typically clathrin)
Extracellular fluid Plasma
membrane
Endosome
Transport vesicle
Uncoated endocytic vesicle
Trang 28Copyright © 2010 Pearson Education, Inc. Figure 3.12 step 6
Coated pit ingests substance.
coated vesicle detaches.
Coat proteins detach and are recycled to plasma membrane
Uncoated vesicle fuses with a sorting vesicle called an endosome.
Fused vesicle may (a) fuse with lysosome for digestion
of its contents, or (b) deliver its contents to the plasma membrane on the
opposite side of the cell (transcytosis).
Protein coat (typically clathrin)
Extracellular fluid Plasma
membrane
Endosome
Lysosome
Transport vesicle
(b) (a)
Uncoated endocytic vesicle
Trang 29 Phagocytosis—pseudopods engulf solids and
bring them into cell’s interior
◦ Macrophages and some white blood cells
Trang 30Copyright © 2010 Pearson Education, Inc. Figure 3.13a
Phagosome
(a) Phagocytosis
The cell engulfs a large particle by forming pro- jecting pseudopods (“false feet”) around it and en-
closing it within a membrane sac called a phagosome
The phagosome is combined with a lysosome
Undigested contents remain
in the vesicle (now called a residual body) or are ejected
by exocytosis Vesicle may
or may not be coated but has receptors capable of binding to
protein-microorganisms or solid particles.
Trang 31 Fluidphase endocytosis ( pinocytosis)—plasma
membrane infolds, bringing extracellular fluid and solutes into interior of the cell
◦ Nutrient absorption in the small intestine
Trang 32Copyright © 2010 Pearson Education, Inc. Figure 3.13b
Vesicle
(b) Pinocytosis
The cell “gulps” drops of extracellular fluid containing solutes into tiny vesicles No receptors are used, so the process is nonspecific Most vesicles are protein-coated.
Trang 33 Receptormediated endocytosis — clathrin
coated pits provide main route for endocytosis and transcytosis
◦ Uptake of enzymes lowdensity lipoproteins, iron, and
insulin
Trang 34Copyright © 2010 Pearson Education, Inc. Figure 3.13c
ingest and concentrate specific substances (ligands) in protein-coated vesicles Ligands may
simply be released inside the cell, or combined with a lysosome to digest contents Receptors are recycled to the plasma membrane in vesicles.
Trang 36Copyright © 2010 Pearson Education, Inc. Figure 3.14a
1
The bound vesicle migrates to the plasma membrane.
membrane-2
There, proteins
at the vesicle surface (v-SNAREs) bind with t-SNAREs (plasma membrane proteins).
Secretory
vesicle Vesicle SNARE
(v-SNARE) Molecule to
be secreted
Cytoplasm
Fused v- and t-SNAREs
3
The vesicle and plasma membrane fuse and a pore opens up.
4
Vesicle contents are released to the cell exterior.
Fusion pore formed
Trang 37 Also see Table 3.2
membranes Secondary active
transport
Ion gradient Movement of polar or charged
solutes across membranes
neurotransmitters
Receptor-mediated