PowerPoint PresentationCopyright © 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 5
5.10 Membranes organize the chemical activities of cells
Membranes organize the chemical reactions making up metabolism
MEMBRANE STRUCTURE AND FUNCTION
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
5.11 Membrane phospholipids form a bilayer
Phospholipids are the main structural components of membranes
They each have a hydrophilic head and two hydrophobic tails
Head
Symbol
Tails
In water, phospholipids form a stable bilayer
Figure 5.11B
The heads face outward and the tails face inward
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
5.12 The membrane is a fluid mosaic of phospholipids and proteins
Phospholipid molecules form a flexible bilayer
Cholesterol and protein molecules are embedded in it
Carbohydrates act as cell identification tags
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The plasma membrane of an animal cell
Fibers of the extracellular matrix
Figure 5.12
Some membrane proteins form cell junctions
Others transport substances across the membrane
Transport
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
5.14 Passive transport is diffusion across a membrane
In passive transport, substances diffuse through membranes without work by the cell
They spread from areas of high concentration to areas of lower concentration
EQUILIBRIUM
5.15 Osmosis is the passive transport of water
In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration
Hypotonic
solution
Water molecule
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5.16 Water balance between cells and their surroundings is crucial to organisms
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
ISOTONIC SOLUTION
Figure 5.16
HYPOTONIC SOLUTION
HYPERTONIC SOLUTION
(1) Normal
(4) Flaccid
(2) Lysing
(5) Turgid
(3) Shriveled
(6) Shriveled
5.17 Transport proteins facilitate diffusion across membranes
Small nonpolar molecules diffuse freely through the phospholipid bilayer
Many other kinds of molecules pass through selective protein pores by facilitated diffusion
Figure 5.17
5.18 Cells expend energy for active transport
Transport proteins can move solutes across a membrane against a concentration gradient
This is called active transport
Active transport requires ATP
Active transport in two solutes across a membrane
Figure 5.18
3
4
Second solute
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
5.19 Exocytosis and endocytosis transport large molecules
To move large molecules or particles through a membrane
a vesicle may fuse with the membrane and expel its contents (exocytosis)
Figure 5.19A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
or the membrane may fold inward, trapping material from the outside (endocytosis)
Figure 5.19B
Three kinds of endocytosis
PIT
Cytoplasm
5.20 Connection: Faulty membranes can overload the blood with cholesterol
Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors
Figure 5.20
LDL PARTICLE
5.21 Chloroplasts and mitochondria make energy available for cellular work
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
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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