053 working cell

BIOLOGYCONCEPTS & CONNECTIONS

Fourth Edition

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor

From PowerPoint® Lectures for Biology: Concepts & Connections

CHAPTER 5The Working Cell

Modules 5.10 – 5.21


• Membranes organize the chemical reactions making up metabolism

5.10 Membranes organize the chemical activities of cells

MEMBRANE STRUCTURE AND FUNCTION

Cytoplasm

Figure 5.10


• Membranes are selectively permeable

– They control the flow of substances into and out of a cell

• Membranes can hold teams of enzymes that function in metabolism


• Phospholipids are the main structural components of membranes

• They each have a hydrophilic head and two hydrophobic tails

5.11 Membrane phospholipids form a bilayer

Head

Symbol

TailsFigure 5.11A


• In water, phospholipids form a stable bilayer

Figure 5.11B

Hydrophilicheads

Hydrophobictails

Water

Water

– The heads face outward and the tails face inward


• Phospholipid molecules form a flexible bilayer

– Cholesterol and protein molecules are embedded in it

– Carbohydrates act as cell identification tags

5.12 The membrane is a fluid mosaic of phospholipids and proteins


• The plasma membrane of an animal cell

Fibers of the extracellular matrix

Figure 5.12

Glycoprotein Carbohydrate (of glycoprotein)

Microfilaments of the cytoskeleton

Phospholipid

Cholesterol

Proteins

CYTOPLASM

Glycolipid


• Some membrane proteins form cell junctions

• Others transport substances across the membrane

5.13 Proteins make the membrane a mosaic of function

TransportFigure 5.13


• Many membrane proteins are enzymes

Figure 5.13

• Some proteins function as receptors for chemical messages from other cells

– The binding of a messenger to a receptor may trigger signal transduction

Enzyme activity Signal transduction

Messenger molecule

Receptor

Activated molecule


• In passive transport, substances diffuse through membranes without work by the cell

– They spread from areas of high concentration to areas of lower concentration

5.14 Passive transport is diffusion across a membrane

EQUILIBRIUMMolecule of dye

Figure 5.14A & B

Membrane

EQUILIBRIUM


• In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration

5.15 Osmosis is the passive transport of water

Hypotonicsolution

Figure 5.15

Solutemolecule

HYPOTONIC SOLUTION

Hypertonic solution

Selectivelypermeablemembrane

HYPERTONIC SOLUTION

Selectivelypermeablemembrane

NET FLOW OF WATER

Solute molecule with cluster of water molecules

Water molecule


• Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution

– The control of water balance(osmoregulation) is essential for organisms

5.16 Water balance between cells and their surroundings is crucial to organisms

ISOTONIC SOLUTION

Figure 5.16

HYPOTONIC SOLUTION

HYPERTONIC SOLUTION

(1) Normal

(4) Flaccid

(2) Lysing

(5) Turgid

(3) Shriveled

(6) Shriveled

ANIMALCELL

PLANTCELL

Plasmamembrane


• Small nonpolar molecules diffuse freely through the phospholipid bilayer

• Many other kinds of molecules pass through selective protein pores by facilitated diffusion

5.17 Transport proteins facilitate diffusion across membranes

Figure 5.17

Solutemolecule

Transportprotein


• Transport proteins can move solutes across a membrane against a concentration gradient

– This is called active transport

– Active transport requires ATP

5.18 Cells expend energy for active transport


• Active transport in two solutes across a membrane

Figure 5.18

Transportprotein

1

FLUIDOUTSIDECELL

Firstsolute

First solute, inside cell, binds to protein

Phosphorylated transport protein

2 ATP transfers phosphate to protein

3 Protein releases solute outside cell

4 Second solute binds to protein

Second solute

5 Phosphate detaches from protein

6 Protein releases second solute into cell


• To move large molecules or particles through a membrane

– a vesicle may fuse with the membrane and expel its contents (exocytosis)

5.19 Exocytosis and endocytosis transport large molecules

Figure 5.19A

FLUID OUTSIDE CELL

CYTOPLASM


– or the membrane may fold inward, trapping material from the outside (endocytosis)

Figure 5.19B


• Three kinds of endocytosis

Figure 5.19C

Pseudopod of amoeba

Food being ingested

Plasma membrane

Material bound to receptor proteins

PIT

Cytoplasm


• Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors

5.20 Connection: Faulty membranes can overload the blood with cholesterol

Figure 5.20

LDL PARTICLEPhospholipid outer layer

Protein

Cholesterol

Plasma membraneCYTOPLASM

Receptor protein

Vesicle


• Enzymes and membranes are central to the processes that make energy available to the cell

• Chloroplasts carry out photosynthesis, using solar energy to produce glucose and oxygen from carbon dioxide and water

• Mitochondria consume oxygen in cellular respiration, using the energy stored in glucose to make ATP

5.21 Chloroplasts and mitochondria make energy available for cellular work


• Nearly all the chemical energy that organisms use comes ultimately from sunlight

• Chemicals recycle among living organisms and their environment

Figure 5.21

Sunlight energy

Chloroplasts,site of photosynthesis

CO2

+H2O

Glucose+O2

Mitochondriasites of cellular

respiration

(for cellular work)

Heat energy

053 working cell

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