Membrane Structure and Function

Page
8

The main electrogenic pump of plants, fungi, and bacteria is a proton pump

Slide 64

Fig. 7-18

EXTRACELLULAR

FLUID

H+

H+

H+

H+

Proton pump

+

+

+

H+

H+

+

+

H+

–

–

–

–

ATP

CYTOPLASM

–

Slide 65

Cotransport: Coupled Transport by a Membrane Protein

Cotransport occurs when active transport of a solute indirectly drives transport of another solute

Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell

Slide 66

Fig. 7-19

Proton pump

–

–

–

–

–

–

+

+

+

+

+

+

ATP

H+

H+

H+

H+

H+

H+

H+

H+

Diffusion

of H+

Sucrose-H+

cotransporter

Sucrose

Sucrose

Slide 67

Concept 7.5: Bulk transport across the plasma membrane occurs by exocytosis and endocytosis

Small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins

Large molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesicles

Bulk transport requires energy

Slide 68

Exocytosis

In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents

Many secretory cells use exocytosis to export their products

Animation: Exocytosis

Slide 69

Endocytosis

In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane

Endocytosis is a reversal of exocytosis, involving different proteins

There are three types of endocytosis:

Phagocytosis (“cellular eating”)

Pinocytosis (“cellular drinking”)

Receptor-mediated endocytosis

Animation: Exocytosis and Endocytosis Introduction

Slide 70

In phagocytosis a cell engulfs a particle in a vacuole

The vacuole fuses with a lysosome to digest the particle

Animation: Phagocytosis

Slide 71

Fig. 7-20

PHAGOCYTOSIS

EXTRACELLULAR

FLUID

CYTOPLASM

Pseudopodium

“Food”or

other particle

Food

vacuole

PINOCYTOSIS

1 µm

Pseudopodium

of amoeba

Bacterium

Food vacuole

An amoeba engulfing a bacterium