The energy of the Na gradient can be used to move other molecules across the cell membrane against their concentration gradients.

(1)

Chapter 5b

(2)

Energy Transfer in Living Cells

Figure 5-16

ATP Secondary active transport Primary active transport Metabolis m

The chemical bond energy is converted into high-energy bonds of ATP through the process of metabolism.

The energy in the high-energy phosphate

bond of ATP is used to move K+ and Na+ against their concentration gradients. This creates potential energy stored in the ion concentration gradients.

The energy of the Na+ gradient can be used to move other molecules across the cell membrane against their concentration gradients.

Energy is imported into the cell as

energy stored in chemical bonds of nutrients such as glucose. Glucos e Pyruvat e CA cycl e Hea t

H₂O CO₂

ADP+P_i O₂

High [K+] Low [Na+]

Na + Na + Glycolysi s ET S K + K +

2 Cl– Low [K+] High [Na+] Glucos

e

ATP ATP

ETS = Electron transport system = Citric acid cycle

CA cycle

(3)

Carrier-Mediated Transport

• Specificity

• Competition

• Saturation

(4)

Carrier-Mediated Transport Competition

(5)

Carrier-Mediated Transport Competition

Figure 5-18

(b) Maltose

(a) The GLUT

transporter

Maltose

Glucose

GLUT

transporter

(6)

Carrier-Mediated Transport Saturation

(7)

Vesicular Transport

• Phagocytosis

• Cell engulfs bacterium or other particle into

phagosome

• Endocytosis

• Membrane surface indents and forms vesicles

• Active process that can be nonselective

(

pinocytosis

) or highly selective

• Potocytosis uses caveolae

(8)

Phagocytosis

Figure 5-20

1

Bacteriu m

Lysosome Phagocyte

The phagocytic white blood cell encounters a bacterium that binds to the cell

membrane.

The phagocyte uses its cytoskeleton to push its cell membrane around the bacterium, creating a large vesicle, the phagosome.

The phagosome containing the bacterium separates from the cell membrane and

moves into the cytoplasm.

The phagosome fuses with lysosomes containing digestive enzymes.

The bacterium is killed and digested within the

vesicle. 2

3

4

(9)

Phagocytosis

Figure 5-20, step 1

1

Bacteriu m

(10)

Phagocytosis

Figure 5-20, steps 1–2

1

Bacteriu m

membrane.

(11)

Phagocytosis

Figure 5-20, steps 1–3

1

Bacteriu m

membrane.

2

(12)

Phagocytosis

Figure 5-20, steps 1–4

1

Bacteriu m

membrane.

2

3

(13)

Phagocytosis

Figure 5-20, steps 1–5

1

Bacteriu m

membrane.

The bacterium is killed and digested within the

vesicle. 2

3

4

(14)

Figure 5-21

Receptor-Mediated Endocytosis and Exocytosis

1Ligand binds to membrane receptor. Clathrin-coate d pit Recepto r Extracellular fluid Intracellular fluid To lysosome or Golgi complex

Receptor-ligand migrates to clathrin-coated pit.

Endocytosis

Vesicle loses

clathrin coat.

Ligands go to lysosomes

or Golgi for processing. Transport vesicle

(15)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, step 1

1Ligand binds to membrane receptor.

Recepto r

Extracellular fluid

(16)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, steps 1–2

Clathrin-coate d pit

Recepto r

Intracellular fluid

Clathri n

(17)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, steps 1–3

Recepto r

Endocytosis

Clathri n

2

(18)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, steps 1–4

Recepto r

Endocytosis

clathrin coat. Clathri

n

2

3

(19)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, steps 1–5

Recepto r

Endocytosis

clathrin coat. Clathri

n

Endosom e

Receptors and ligands separate.

2

3

4

(20)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, steps 1–6

Recepto r

To lysosome or Golgi complex

Endocytosis

clathrin coat.

or Golgi for processing.

Clathri n

Endosom e

Receptors and ligands separate.

2

3

4

5

(21)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, steps 1–7

Endocytosis

clathrin coat.

with receptors moves to the cell membrane.

(22)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, steps 1–8

Endocytosis

clathrin coat.

(23)

Receptor-Mediated Endocytosis and Exocytosis

Figure 5-21, steps 1–9

Endocytosis

clathrin coat.

(24)

Transepithelial Transport

• Polarized cells of transporting epithelia

Figure 5-22

Apical

membran

e

Tight

junction

Transporting

epithelial cell

Basolatera

l

membrane

Lumen

of intestine

or kidney

Extracellular

(25)

Transepithelial Transport of Glucose

Figure 5-23

1

[Glucose] _low

[Glucose] _high

[Glucose] _low

[Na+_] high

[Na+_] low

[Na+_] high Apical membran e Basolatera l membrane Extracellula r fluid Lumen of kidney or intestine Epithelia l cell 3 2 GLUT transporter transfers glucose to ECF by facilitated diffusion.

Na+_-K+_{- ATPase}_pumps

Na+_{out of the cell,} keeping

ICF Na+_{concentration low.}

Na+_{-glucose symporter}

brings glucose into cell against its gradient using energy stored in the Na+ concentration gradient.

1

2

(26)

Transepithelial Transport of Glucose

Figure 5-23, step 1

1

[Glucose] _low

[Glucose] _high

[Na+_] high

[Na+_] low Apical

membran e

Basolatera l membrane

Extracellula r fluid Lumen of

kidney or intestine

Epithelia l cell

(27)

Transepithelial Transport of Glucose

Figure 5-23, steps 1–2

1

[Glucose] _low

[Glucose] _high

[Glucose] _low

[Na+_] high

[Na+_] low Apical

membran e

Basolatera l membrane

Extracellula r fluid Lumen of

kidney or intestine

Epithelia l cell

GLUT transporter transfers glucose to ECF by facilitated diffusion.

1

2

(28)

Transepithelial Transport of Glucose

Figure 5-23, steps 1–3

1

[Glucose] _low

[Glucose] _high

[Glucose] _low

[Na+_] high

[Na+_] low

[Na+_] high Apical membran e Basolatera l membrane Extracellula r fluid Lumen of kidney or intestine Epithelia l cell 3 2 GLUT transporter transfers glucose to ECF by facilitated diffusion.