lecture notebook to accompany principles of life...life concepts sadava sinauer associates morales...

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Cell Membranes and Signaling 5

2

POL HillisSinauer AssociatesMorales Studio Figure 05.01 Date 06-28-10

Carbohydrates are attached to the outer surface of proteins(forming glycoproteins) or lipids (forming glycolipids).

In animal cells, some membrane proteins associate with filamentsin the extracellular matrix.

Peripheral membraneproteins do not penetratethe bilayer at all.

Some membrane proteins interact with the interior cytoskeleton.

Cholesterol molecules interspersed among phospholipid tails in thebilayer influence the fluidity offatty acids in the membrane.

Some integral proteins cross the entire phospholipidbilayer; others penetrate onlypartially into the bilayer.

Phospholipid

Extracellularmatrix

Outside of cell

Inside of cell

Cytoskeleton

FIGURE 5.1 Membrane Molecular Structure (Page 63)

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Chapter 5 | Cell Membranes and Signaling 3

POL HillisSinauer AssociatesMorales Studio Figure INTXT05.02 Date 06-15-10

Hydrophilic R groups (sidechains) in exposed partsof the protein interact withaqueous environments.

Hydrophobic R groups interact with the hydrophobiccore of the membrane awayfrom water.

Hydrophobicinteriorof bilayer

Outside of cell(aqueous)

Inside of cell(aqueous)

IN-TEXT-ART (Page 65)


Exposed regions of membraneglycoproteinsbind to each other, causing cells to adhere.

Cells



“Head”

“Tails”





The cells are fused together to create a heterokaryon.

The mouse cell has a membraneprotein that can belabeled with a green dye.

The human cell has a membraneprotein that can be labeled with a red dye.

Initially, the mouse and human membrane proteins are on different sides of the heterokaryon.

After 40 minutes, the mouse and human membrane proteins are intermixed.

Go to yourBioPortal.com for original citations, discussions,and relevant links for all INVESTIGATION figures.

METHOD

Membrane proteins can diffuse rapidly in the plane of the membrane.

Proteins embedded in a membrane can diffuse freely within the membrane.

METHOD

FIGURE 5.2 Rapid Diffusion of Membrane Proteins A human cell can be fused to a mouse cell in the laboratory, forming a single large cell (heterokaryon). This phenomenon was used to test whether membrane proteins can diffuse independently in the plane of the plasma membrane.

HYPOTHESIS

CONCLUSION

1

Mouse cell Human cell

Membraneproteins

RESULTS

3

2

ANALYZE THE DATAThe experiment was repeated at various temperatures

with the following results:

Plot these data on a graph of Percentage Mixed vs. Temperature. Explain these data, relating the results to the concepts of diffusion and membrane fluidity.

Temperature (°C)

0152026

Cells with mixed proteins (%)

084277

INVESTIGATION

Heterokaryon

(Page 66)



LIFE Concepts Sadava Sinauer AssociatesMorales Studio Figure 05.00 in text art #4 Date 12-27-09


LIFE Concepts Sadava Sinauer AssociatesMorales Studio Figure 05.03 Date 12-27-09

Cells lose waterand shrivel.

from the cell wall(wilting).

Cells take up water, swell, and burst.

Cell stiffens but generallyand pulls away retains its shapebecause cellwall is present.

Cell body shrinks

Animal cell(red blood cells)

Plant cell(leaf epithelialcells)

H2O

H2O

H2O

H2O

H2O

(C) Hypotonic on the outside (dilute solutes outside)

(B) Isotonic (equivalent solute concentration)

(A) Hypertonic on the outside (concentrated solutes outside)

Inside of cell

Outsideof cell

H2O

FIGURE 5.3 Osmosis Can Modify the Shapes of Cells (Page 68)




A polar substance is more concentrated on the outside than the inside of the cell.

Binding of a stimulus molecule causes the pore to open…

3 …and the polar substance can diffuse across the membrane.

2

1

Stimulusmolecule(ligand)

Hydrophobicinterior of bilayer

Binding site

Channelprotein

Outside of cell

Inside of cell

Hydrophilic pore

Closed channel

FIGURE 5.4 A Ligand-Gated Channel Protein Opens in Response to a Stimulus (9)




This oocyte does not have aquaporins in the cell membrane.

This oocyte has aquaporins inserted experimentally into the cell membrane.

AquaporinmRNA

Aquaporin channel

Water does not diffuse into the cell, so it does not swell.

Water diffuses into the cell through the aquaporin channels, and it swells.

3.5 minutes inhypotonic solution

Proteinsynthesis

Go to yourBioPortal.com for original citations, discussions,and relevant links for all INVESTIGATION figures.

Aquaporin increases the rate of water diffusion across the cell membrane.

Aquaporin increases membrane permeability to water.

METHOD

FIGURE 5.5 Aquaporins Increase Membrane Permeability to Water A protein was isolated from the membranes of cells in which water diffuses rapidly across the membranes. When the protein was inserted into oocytes, which do not normally have it, the water permeability of the oocytes was greatly increased.

HYPOTHESIS

CONCLUSION

RESULTS

ANALYZE THE DATA

INVESTIGATION

Oocytes were injected with aquaporin mRNA (red circles) or a solution without mRNA (blue circles). Water permeability was tested by incubat-

ing the oocytes in hypotonic solution and measuring cell volume. After time X in the upper curve, intact oocytes were not visible:

A. Why did the cells increase in volume?B. What happened at time X?C. Calculate the relative rates (volume increase per minute) of swelling in the control and experimental curves. What does this show about the effectiveness of mRNA injection?

Rel

ativ

e vo

lum

e

1 2 3 4 5

X

Time (min)

1.1

1.0

1.2

1.3

1.4 With mRNA

Without mRNA

For more, go to Working with Data 5.1 at yourBioPortal.com.

(0)




…releasing the glucose.

The carrier protein returnsto its original shape, readyto bind another glucose.

3 …which then changes the protein’s shape…

Glucose binds to the protein…

The carrier protein has a glucose binding site.

4

21

5

All carriers are occupied.

Some carriers are occupied.

Outside of cell

Inside of cell

Low glucose concentration

High glucose concentration

Glucose concentrationoutside the cell

Glucose carrier protein

Glucose

Rat

e of

diff

usio

nin

to th

e ce

ll

(A)

(B)

FIGURE 5.6 A Carrier Protein Facilitates Diffusion (Page 71)

TABLE 5.1 Membrane Transport Mechanisms FACILITATED DIFFUSION (CHANNEL OR CARRIER SIMPLE DIFFUSION PROTEIN) ACTIVE TRANSPORT

Cellular energy No No Yes required?

Driving force Concentration Concentration ATP hydrolysis (against gradient gradient concentration gradient)

Membrane protein No Yes Yes required?

Specificity No Yes Yes

(Page 71)




Hydrolysis of ATP phosphorylates thepump protein and changes its shape.

3 Na+ and 1 ATP bind to the protein “pump.”

3 The shape changereleases Na+ outsidethe cell and enables K+ to bind to the pump.

Release of Pi returns thepump to its original shape,releasing K+ to the cell'sinterior and once againexposing Na+ binding sites.The cycle repeats.

4

2

1

We can’t make these as smooth and oval as previous proteins because we need to attach the molecuels on the edges and we need the room to squeeze them in. I took off a few irrregularities.

Outside of cell

High Na+ concentration,low K+ concentration

Inside of cell

High K+ concentration,low Na+ concentration

ADPNa+

Na+

K+K+

K+

Na+–K+ pump

Pi

PiPi

Pi

ATP

FIGURE 5.7 Primary Active Transport: The Sodium–Potassium Pump (Page 72)




A vesicle fuses with the plasma membrane. The contents of the vesicle are released, and itsmembrane becomes part of the plasma membrane.

The plasma membranesurrounds a part of theexterior environment and buds off as a vesicle.

(A) Endocytosis

(B) Exocytosis

Plasma membraneOutside of cell

Inside of cell Endocytotic vesicle

Secretory vesicle

FIGURE 5.8 Endocytosis and Exocytosis (Page 73)




The protein clathrin coats the cytoplasmic side of the plasma membrane at a coated pit.

The endocytosed contents are surrounded by a clathrin-coated vesicle.

Coatedvesicle

Coatedvesicle

Coatedpit

Cytoplasm

Outsideof cell

Outsideof cell

Specificsubstancebinding toreceptorproteins

Clathrinmolecules

Clathrinmolecules

Specificsubstancebinding toreceptorproteins

Cytoplasm

Coated pit

FIGURE 5.9 Receptor-Mediated Endocytosis (Page 74)




Circulating signalssuch as hormones are transported by the circulatory system and bind to receptors on distant cells.

Autocrine signals bind to receptors on the same cell that secretes them.

Cells without receptors for a particular signal do not respond to that signal.

Paracrine signals bind toreceptors on nearby cells.

Circulatory vessel(e.g., a blood vessel)

Target cell

Target cell

Target cell

ReceptorSecreting cell

FIGURE 5.10 Chemical Signaling Concepts (Page 75)


A signal moelculearrives at the target cell.

1

A signal molecule binds to a receptor protein in the cell surface or inside the cytoplasm.

2

Signal binding changes the three-dimensional shape of the receptor and exposes its active site.

3

The activated receptor activates asignal transduction pathway tobring about cellular changes.

4

Signal molecule

Receptor

Inactivesignal transductionmolecule

Activatedsignal transductionmolecule

Short-termresponses:enzyme activation,cell movement

Long-termresponses:altered DNAtranscription

FIGURE 5.11 Signal Transduction Concepts (Page 76)




Growth factor (ligand) fits noncovalently into receptor.

Two receptor subunits are transmembrane proteins.Outside of cell

Ligand

Inside of cell

Cell membrane

FIGURE 5.12 A Signal Binds to Its Receptor (Page 76)


Signal molecule

Receptor

R + L RL





Hormone binding to the receptoractivates the G protein. GTP replaces GDP.

2The G protein and effectorprotein are inactive until thesignal arrives.

1

The GTP on the G protein is hydrolyzed to GDP but remains boundto the G protein.

4

Part of the activated G protein activates an effector protein that converts thousands of reactants to products, thus amplifying the action of a single signal molecule.

3

Outside of cell

Inside of cell

Signal (hormone)

G protein-linkedreceptor Inactive

G proteinInactive effectorprotein Reactant Product

Amplification

ActivatedG protein

Activatedeffector protein

GDP GTP GDP

FIGURE 5.14 A G Protein–Linked Receptor (Page 78)


A conformational change in the receptor transmits the signal tothe cytoplasm.

2

The receptorbinds thesignal.

1

…which phos-phorylates targets, triggering a cas-cade of chemical responses insidethe cell.

3

4

The signal activates the receptor’s protein kinase domain in the cytoplasm…

Cellular responses

Target

Outside of cell

Inside of cell

Receptor

Proteinkinasedomain(inactive)

Signal(insulin)

P

Phosphategroups

PPPP

ATPADP

FIGURE 5.13 A Protein Kinase Receptor (Page 77)




2

Cytoplasm containsinactiveglycogen phosphorylase

Membranes containepinephrine receptors

Liver

3 The membranes are removed by centrifugation, leaving only the solution in which they were incubated.

4 Drops of membrane-freesolution areadded to thecytoplasm.

The hormone epinephrine is added to the membranes and allowed to incubate along with the substrate for synthesis of a second messenger.

Liver tissue is homogenizedand separated into plasma membrane and cytoplasm fractions.

2

1

The activity of previously inactive liver glycogen phosphorylasewas measured with and without epinephrine incubation,with these results:

A. What do these data show?

B. Propose an experiment to show that the factor that activates the enzyme is stable on heating and give predicted data.

C. Propose an experiment to show that cAMP can replace the particulate fraction and hormone treatment and give predicted data.

Condition

HomogenateHomogenate + epinephrineCytoplasm fractionCytoplasm + epinephrineCytoplasm + membranesCytoplasm + membranes + epinephrine

Enzyme activity (units)

0.42.50.20.40.42.0

For more, go to Working with Data 5.2 at yourBioPortal.com.

INVESTIGATION

A second messenger mediates between receptor activation at the plasma membrane and enzyme activation in the cytoplasm.

A soluble second messenger, produced by hormone-activated membranes, is present in the solution and activates enzymes in the cytoplasm.

Go to yourBioPortal.com for original citations, discussions, and relevant links for all INVESTIGATION figures.

HYPOTHESIS

FIGURE 5.15 The Discovery of a Second Messenger Glyco-gen phosphorylase is activated in liver cells after epinephrine binds to a membrane receptor. Sutherland and his colleagues observed that this activation could occur in vivo only if fragments

of the plasma membrane were present. They designed experi-ments to show that a second messenger caused the activation of glycogen phosphorylase.

METHOD

CONCLUSION

ANALYZE THE DATA

Active glycogen phosphorylase is present in the cytoplasm.RESULTS

(Page 79)




CH2O–O P

O

O–PP O

O

O–O

O

O–H H

OH OH

NH2

N

N

N

N

C

CH

O CH2

H H

O OH

NH2

N

N

N

N

C

CH

O

HC

C

C

C

C

CH

HC

O

O

–O

P

HC

CHHC

ATP cAMP PPi+

ATP

Phosphate groups

Cyclic AMP (cAMP)

Adenylylcyclase

Adenine

FIGURE 5.16 The Formation of Cyclic AMP (Page 79)

LIFE The Science of Biology 9E Sadava Sinauer AssociatesMorales Studio Figure 07.20 Date 04-20-09

Phosphorylation activates glycogen phosphorylase, releasing stored glucose molecules from glycogen.

Release of glucose by carrier transport fuels “fight-or-flight” response.

Phosphorylation, inducedby epinephrine binding,inactivates glycogensynthase, preventing glucose from being stored as glycogen.

1

The protein kinase cascade amplifies the signal. Here, for every molecule of epinephrine bound, 20 molecules of cAMP are made, each of which activates a molecule of protein kinase A.

2

3

4

Epinephrine

cAMP

Active phosphorylase kinase

Glucose 1-phosphate

Inactive protein kinase A

Inactive phosphorylase kinase

Inactive glycogen phosphorylase

Glycogen

Glucose

Blood glucose

Epinephrinereceptor

Inside of cell

Plasmamembrane

Outside of cell

Outside of cell

10,000

10,000

1,000

100

20

20

1

ATP

ActivatedG proteinsubunit

Activatedadenylylcyclase

Active protein kinase A

Active glycogen phosphorylase

Active glycogensynthase

Inactive glycogensynthase

GTP

FIGURE 5.17 A Cascade of Reactions Leads to Altered Enzyme Activity (Page 80)




Inactiveenzyme

InactiveG protein

ActiveG protein

Adenylylcyclase

(A)

(B)

(C)

Activeenzyme

GDP

ATP

ATP

GTP

P

Protein kinase

Proteinphosphatase

Receptor binding

GTPase

cAMPPhosphodiesterase

AMP

Pi

FIGURE 5.18 Signal Transduction Regulatory Mechanisms (Page 81)

LIFE The Science of Biology 9E Sadava Sinauer AssociatesMorales Studio Figure 07.04 Date 05-18-09

N

N

N

N

NH2

H HHH

N

N

N

O

O

N

H3C

CH3

CH3

OH

OH

OH

ON

AdenosineCaffeine

Outsideof cell

Plasmamembrane

Insideof cell

The similar structures of caffeine and adenosine allow them both to bind to the receptor, but only adenosine triggers signal transduction.

The adenosine receptoroccurs in the brain cells.

(B)(A)

Adenosine and caffeine both fit the receptor.

FIGURE 5.19 Caffeine and the Cell Membrane (Page 82)

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