Cells: The Living Unitsdrjerrycronin.weebly.com/uploads/5/9/7/4/5974564/... · PowerPoint® Lecture Slides prepared by Karen Dunbar Kareiva ... •Sodium-potassium pump –Most studied

PowerPoint® Lecture Slides

prepared by

Karen Dunbar Kareiva

Ivy Tech Community College© Annie Leibovitz/Contact Press Images

Chapter 3 Part B

Cells:

The Living

Units

© 2017 Pearson Education, Inc.

3.4 Active Membrane Transport

• Two major active membrane transport

processes

– Active transport

– Vesicular transport

• Both require ATP to move solutes across a

plasma membrane for any of these reasons:

– Solute is too large for channels, or

– Solute is not lipid soluble, or

– Solute is not able to move down concentration

gradient


Active Transport

• Requires carrier proteins (solute pumps)

– Bind specifically and reversibly with substance

being moved

– Some carriers transport more than one

substance

• Antiporters transport one substance into cell while

transporting a different substance out of cell

• Symporters transport two different substances in the

same direction

• Moves solutes against their concentration

gradient (from low to high)

– This requires energy (ATP)© 2017 Pearson Education, Inc.

Active Transport (cont.)

• Two types of active transport:

– Primary active transport

• Required energy comes directly from ATP hydrolysis

– Secondary active transport

• Required energy is obtained indirectly from ionic

gradients created by primary active transport



• Primary active transport

– Energy from hydrolysis of ATP causes change in

shape of transport protein

– Shape change causes solutes (ions) bound to

protein to be pumped across membrane

– Example of pumps: calcium, hydrogen (proton),

Na+-K+ pumps



• Sodium-potassium pump

– Most studied pump

– Basically is an enzyme, called Na+-K+ ATPase,

that pumps Na+ out of cell and K+ back into cell

– Located in all plasma membranes, but especially

active in excitable cells (nerves and muscles)



• Leakage channels located in membranes result

in leaking of Na+ into the cell and leaking of K+

out of cell – Both travel down their concentration gradients

• Na+-K+ pump works as an antiporter that pumps

Na+ out of cell and K+ back into cell against their

concentration gradients

• Maintains electrochemical gradients, which

involve both concentration and electrical charge

of ions– Essential for functions of muscle and nerve

tissues© 2017 Pearson Education, Inc.

Figure 3.1 Cell diversity.

Erythrocytes

Fibroblasts

Epithelial cells

Skeletal

muscle

cell

Smooth

muscle cells

Nerve cell

Macrophage

Fat cell

Sperm

Cell of reproduction

Cell that stores

nutrients

Cells that connect body parts, form linings,

or transport gases

Cells that move organs and body parts

Cell that gathers information and controls

body functions

Cell that fights

disease


Three cytoplasmic Na+ bind to

pump protein.

Focus Figure 3.1 Primary active transport is the process in which solutes are moved across cell membranes against electrochemical gradients using energy supplied directly by ATP. The action of the Na+-K+ pump is an important example of primary active transport.

Extracellular fluidNa+

Na+ –K+

pump

ATP-binding site

Cytoplasm

ATPK+

1

Slide 2


Na+ binding promotes hydrolysis

of ATP. The energy released during thisreaction phosphorylates the pump.


pump protein.



Na+ –K+

pump

ATP-binding site

Cytoplasm

ATPK+ Na+ bound

ADP

P

1

2

Slide 3


Phosphorylation causes the

pump to change shape, expelling

Na+ to the outside.




pump protein.



Na+ –K+

pump

ATP-binding site

Cytoplasm

ATPK+ Na+ bound

ADP

Na+

released

P

P

1

2

3

Slide 4




Na+ to the outside.




pump protein.



Na+ –K+

pump

ATP-binding site

Cytoplasm

4

ATPK+ Na+ bound

ADP

Na+

released

P

P

P

K+

1

2

3

Two extracellular K+ bind to pump.

Slide 5


K+ binding triggers release of

the phosphate. The dephosphorylated

pump resumes its original

conformation.



Na+ to the outside.




pump protein.



Na+ –K+

pump

ATP-binding site

Cytoplasm

4

K+ bound

ATPK+ Na+ bound

ADP

Na+

released

P

P

P

PiK+

1

2

5 3


Slide 6


Pump protein binds ATP; releases

K+ to the inside, and Na+ sites are readyto bind Na+ again. The cycle repeats.

K+ binding triggers release of

the phosphate. The dephosphorylated

pump resumes its original

conformation.



Na+ to the outside.




pump protein.



Na+ –K+

pump

ATP-binding site

Cytoplasm

4

K+ bound

K+ released

ATP

ATPK+ Na+ bound

ADP

Na+

released

P

P

P

PiK+

6

1

2

5 3


Slide 7


A&P Flix™: Resting Membrane Potential



• Secondary active transport

– Depends on ion gradient that was created by

primary active transport system

– Energy stored in gradients is used indirectly to

drive transport of other solutes

• Low Na+ concentration that is maintained inside cell

by Na+-K+ pump strengthens sodium’s drive to want to

enter cell

• Na+ can drag other molecules with it as it flows into

cell through carrier proteins (usually symporters) in

membrane

– Some sugars, amino acids, and ions are usually

transported into cells via secondary active transport© 2017 Pearson Education, Inc.

Figure 3.10 Secondary active transport is driven by the concentration gradient created by primary active transport.

Extracellular fluid

Cytoplasm

ATP

Na+-K+

pump

Na+

Na+Na+

Na+

Na+

Na+

K+

Na+

Na+

Na+

Na+

Na+

The ATP-driven Na+-K+ pumpstores energy by creating a steepconcentration gradient for Na+

entry into the cell.

Primary active transport

Slide 2

1


Figure 3.10 Secondary active transport is driven by the concentration gradient created by primary active transport.

Extracellular fluid

Cytoplasm

ATP

Na+-K+

pump

Na+-glucosesymporttransporterloads glucosefrom extracellularfluid

Na+-glucosesymport transporterreleases glucoseinto the cytoplasm

Glucose

Na+

Na+Na+

Na+

Na+

Na+

K+

Na+

Na+

Na+

Na+

Na+

The ATP-driven Na+-K+ pumpstores energy by creating a steepconcentration gradient for Na+

entry into the cell.

Primary active transportAs Na+ diffuses back across the membranethrough a membrane cotransporter protein, itdrives glucose against its concentration gradientinto the cell.

Secondary active transport

Slide 3

1 2


Vesicular Transport

• Involves transport of large particles,

macromolecules, and fluids across membrane

in membranous sacs called vesicles

• Requires cellular energy (usually ATP)


Vesicular Transport (cont.)

• Vesicular transport processes include:

– Endocytosis: transport into cell

• 3 different types of endocytosis: phagocytosis,

pinocytosis, receptor-mediated endocytosis

– Exocytosis: transport out of cell

– Transcytosis: transport into, across, and then out

of cell

– Vesicular trafficking: transport from one area or

organelle in cell to another



• Endocytosis

– Involves formation of protein-coated vesicles

– Usually involve receptors; therefore can be a

very selective process

• Substance being pulled in must be able to bind to its

unique receptor

– Some pathogens are capable of hijacking

receptor for transport into cell

– Once vesicle is pulled inside cell, it may:

• Fuse with lysosome or

• Undergo transcytosis


Figure 3.11 Events of endocytosis mediated by protein-coated pits.

1

2

3

4

5

6

(a) (b)

Fused vesicle may (a) fusewith lysosome for digestion ofits contents, or (b) deliver itscontents to the plasmamembrane on the oppositeside of the cell (transcytosis).

Transport vesiclecontaining membrane components moves tothe plasma membranefor recycling.

Uncoated vesicle fuses with

a sorting vesicle called an

endosome.

Coat proteins are recycled

to plasma membrane.

Protein-coated

vesicle detaches.

Coated pit

ingests substance.Extracellular fluid

Cytoplasm

Plasmamembrane

Protein coat(typically clathrin)

Uncoatedendocyticvesicle

Transportvesicle

Endosome

Lysosome



(a) (b)

Coated pit


Cytoplasm

Plasmamembrane


Slide 2

1



(a) (b)

Protein-coated

vesicle detaches.

Coated pit


Cytoplasm

Plasmamembrane


Slide 3

1

2



(a) (b)


to plasma membrane.

Protein-coated

vesicle detaches.

Coated pit


Cytoplasm

Plasmamembrane


Slide 4

1

2

3



(a) (b)



endosome.


to plasma membrane.

Protein-coated

vesicle detaches.

Coated pit


Cytoplasm

Plasmamembrane



Endosome

Slide 5

1

2

3

4



(a) (b)




endosome.


to plasma membrane.

Protein-coated

vesicle detaches.

Coated pit


Cytoplasm

Plasmamembrane



Transportvesicle

Endosome

Slide 6

1

2

3

4

5



(a) (b)

Fused vesicle may (a) fusewith lysosome for digestion ofits contents, or (b) deliver itscontents to the plasmamembrane on the oppositeside of the cell (transcytosis).




endosome.


to plasma membrane.

Protein-coated

vesicle detaches.

Coated pit


Cytoplasm

Plasmamembrane



Transportvesicle

Endosome

Lysosome

Slide 7

1

2

3

4

5

6



• Phagocytosis: type of endocytosis that is

referred to as “cell eating”

– Membrane projections called pseudopods form

and flow around solid particles that are being

engulfed, forming a vesicle which is pulled into

cell

– Formed vesicle is called a phagosome

– Phagocytosis is used by macrophages and

certain other white blood cells

• Phagocytic cells move by amoeboid motion where

cytoplasm flows into temporary extensions that allow

cell to creep© 2017 Pearson Education, Inc.

Figure 3.12a Comparison of three types of endocytosis.

Phagocytosis

The cell engulfs a large particle by forming

projecting pseudopods (“false feet”) around

it and enclosing it within a membrane saccalled a phagosome. The phagosome iscombined with a lysosome. Undigestedcontents remain in the vesicle (now called aresidual body) or are ejected by exocytosis.

Vesicle may or may not be protein-coated

but has receptors capable of binding to

microorganisms or solid particles.

Phagosome

Receptors



• Pinocytosis: type of endocytosis that is

referred to as “cell drinking” or fluid-phase

endocytosis

– Plasma membrane infolds, bringing extracellular

fluid and dissolved solutes inside cell

• Fuses with endosome

– Used by some cells to “sample” environment

– Main way in which nutrient absorption occurs in

the small intestine

– Membrane components are recycled back to

membrane


Figure 3.12b Comparison of three types of endocytosis.

Pinocytosis

The cell “gulps” a drop of extracellular fluid

containing solutes into tiny vesicles. No receptors

are used, so the process is nonspecific. Most

vesicles are protein-coated.

Vesicle



• Receptor-mediated endocytosis involves

endocytosis and transcytosis of specific molecules

– Many cells have receptors embedded in clathrin-coated

pits, which will be internalized along with the specific

molecule bound

• Examples: enzymes, low-density lipoproteins (LDL), iron,

insulin, and, unfortunately, viruses, diphtheria, and cholera

toxins may also be taken into a cell this way

– Caveolae have smaller pits and different protein coat

from clathrin, but still capture specific molecules (folic

acid, tetanus toxin) and use transcytosis


Figure 3.12c Comparison of three types of endocytosis.

Receptor-mediated endocytosis

Extracellular substances bind to specific receptor

proteins, enabling the cell to ingest and concentratespecific substances (ligands) in protein-coatedvesicles. Ligands may simply be released insidethe cell, or combined with a lysosome to digest

contents. Receptors are recycled to the plasma

membrane in vesicles.Vesicle


Exocytosis

• Process where material is ejected from cell

– Usually activated by cell-surface signals or

changes in membrane voltage

• Substance being ejected is enclosed in

secretory vesicle

• Protein on vesicle called v-SNARE finds and

hooks up to target t-SNARE proteins on

membrane

– Docking process triggers exocytosis

• Some substances exocytosed: hormones,

neurotransmitters, mucus, cellular wastes © 2017 Pearson Education, Inc.

Figure 3.13a Exocytosis.

The process of

exocytosis

The membrane-

bound vesicle migrates

to the plasma

membrane.

There, proteins atthe vesicle surface(v-SNAREs) bind witht-SNAREs (plasmamembrane proteins).

The vesicle and

plasma membrane fuse

and a pore opens up.

Vesicle contents

are released to the cell

exterior.

Fusion pore formed

Fusedv- andt-SNAREs

Vesicle

SNARE

(v-SNARE)

Secretory

vesicle

Cytoplasm

Extracellular

fluid

Plasma membraneSNARE (t-SNARE)

1

2

3

4

Molecule to

be secreted



The process of

exocytosis

The membrane-


to the plasma

membrane.

Vesicle

SNARE

(v-SNARE)

Secretory

vesicle

Cytoplasm

Extracellular

fluid


Molecule to

be secreted

Slide 2

1



The process of

exocytosis

The membrane-


to the plasma

membrane.


Fusedv- andt-SNAREs

Vesicle

SNARE

(v-SNARE)

Secretory

vesicle

Cytoplasm

Extracellular

fluid


Molecule to

be secreted

Slide 3

1

2



The process of

exocytosis

The membrane-


to the plasma

membrane.


The vesicle and



Fusion pore formed

Fusedv- andt-SNAREs

Vesicle

SNARE

(v-SNARE)

Secretory

vesicle

Cytoplasm

Extracellular

fluid


Molecule to

be secreted

Slide 4

1

2

3



The process of

exocytosis

The membrane-


to the plasma

membrane.


The vesicle and



Vesicle contents

are released to the cell

exterior.

Fusion pore formed

Fusedv- andt-SNAREs

Vesicle

SNARE

(v-SNARE)

Secretory

vesicle

Cytoplasm

Extracellular

fluid


Molecule to

be secreted

Slide 5

1

2

3

4


Figure 3.13b Exocytosis.

Photomicrograph

of a secretory

vesicle releasing

its contents

by exocytosis

(100,000)


3.5 Membrane Potential

• Resting membrane potential (RMP)

– Electrical potential energy produced by

separation of oppositely charged particles across

plasma membrane in all cells

• Difference in electrical charge between two points is

referred to as voltage

• Cells that have a charge are said to be polarized

– Voltage occurs only at membrane surface

• Rest of cell and extracellular fluid are neutral

• Membrane voltages range from –50 to –100 mV in

different cells (negative sign (–) indicates inside of cell

is more negative relative to outside of cell)


K+ is Key Player in RMP

• K+ diffuses out of cell through K+ leakage

channels down its concentration gradient

• Negatively charged proteins cannot leave

– As a result cytoplasmic side of cell membrane

becomes more negative

• K+ is then pulled back by the more negative

interior because of its electrical gradient

• When drive for K+ to leave cell is balanced by its

drive to stay, RMP is established

– Most cells have an RMP around –90 mV

• Electrochemical gradient of K+ sets RMP© 2017 Pearson Education, Inc.

K+ is Key Player in RMP (cont.)

• In many cells, Na+ also affects RMP

– Na+ is also attracted to inside of cell because of

negative charge

• If Na+ enters cell, it can bring RMP up to –70 mV

– Membrane is more permeable to K+ than Na+, so

K+ primary influence on RMP

• Cl– does not influence RMP because its

concentration and electrical gradients are

exactly balanced


Figure 3.14 The key role of K+ in generating the resting membrane potential.

Na+

K+

K+

K+

K+ K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

Na+ Na+

Na+

Na+

Na+

Na+

Na+

Na+

A−

A−

−

CI−

Extracellular fluid

Potassiumleakagechannels

Protein anion (unableto follow K+ through themembrane)Cytoplasm

++

+ + + ++

+

−−−−−

−−

3

1

2

K+ diffuse down their steep concentration gradient (out of the cell) via leakage channels. Loss of K+ results in a negative charge on the inner plasma membrane face.

K+ also move into the cell

because they are attracted to the

negative charge established on

the inner plasma membrane face.

A negative membrane potential (–90 mV) is established when the movement of K+ out of the cell equals K+ movement into the cell. At this point, the concentration gradient promoting K+ exit exactly opposes the electrical gradient for K+ entry.

CI−



Na+

K+

K+

K+

K+ K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

Na+ Na+

Na+

Na+

Na+

Na+

Na+

Na+

A−

A−

−

CI−

Extracellular fluid



++

+ + + ++

+

−−−−−

−−


CI−

1

Slide 2



Na+

K+

K+

K+

K+ K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

Na+ Na+

Na+

Na+

Na+

Na+

Na+

Na+

A−

A−

−

CI−

Extracellular fluid



++

+ + + ++

+

−−−−−

−−






CI−

1

2

Slide 3



Na+

K+

K+

K+

K+ K+

K+

K+

K+

K+

K+

K+

K+

K+

K+

Na+ Na+

Na+

Na+

Na+

Na+

Na+

Na+

A−

A−

−

CI−

Extracellular fluid



++

+ + + ++

+

−−−−−

−−






A negative membrane potential (–90 mV) is established when the movement of K+ out of the cell equals K+ movement into the cell. At this point, the concentration gradient promoting K+ exit exactly opposes the electrical gradient for K+ entry.

CI−

1

2

3

Slide 4


Active Transport Maintains Electrochemical

Gradients

• RMP is maintained through action of the Na+-K+

pump, which continuously ejects 3Na+ out of cell

and brings 2K+ back inside

• Steady state is maintained because rate of

active pumping of Na+ out of cell equals the rate

of Na+ diffusion into cell

• Neuron and muscle cells “upset” this steady

state RMP by intentionally opening gated Na+

and K+ channels


3.6 Cell-Environment Interactions

• Cells interact with their environment by

responding directly to other cells, or indirectly to

extracellular chemicals

• Interactions always involves glycocalyx

– Cell adhesion molecules (CAMs)

– Plasma membrane receptors


Role of Cell Adhesion Molecules (CAMs)

• Every cell has thousands of sticky glycoprotein

CAMs projecting from membrane

• Functions:

– Anchor cell to extracellular matrix or to each

other

– Assist in movement of cells past one another

– Attract WBCs to injured or infected areas

– Stimulate synthesis or degradation of adhesive

membrane junctions (example: tight junctions)

– Transmit intracellular signals to direct cell

migration, proliferation, and specialization© 2017 Pearson Education, Inc.

Roles of Plasma Membrane Receptors

• Membrane receptor proteins serve as binding

sites for several chemical signals– Contact signaling: cells that touch recognize

each other by each cell’s unique surface

membrane receptors• Used in normal development and immunity

– Chemical signaling: interaction between

receptors and ligands (chemical messengers)

that cause changes in cellular activities• In some cells, binding triggers enzyme activation; in

others, it opens chemically gated ion channels

• Examples of ligands: neurotransmitters, hormones,

and paracrines© 2017 Pearson Education, Inc.

Roles of Plasma Membrane Receptors (cont.)

– Chemical signaling (cont.):

• Same ligand can cause different responses in different

cells depending on chemical pathway that the receptor

is part of

• When ligand binds, receptor protein changes shape

and thereby becomes activated

• Some activated receptors become enzymes; others

act to directly open or close ion gates, causing

changes in excitability


Roles of Plasma Membrane Receptors (cont.)

– Chemical signaling (cont.):

• Activated G protein–linked receptors indirectly

cause cellular changes by activating G proteins,

which in turn can affect ion channels, activate other

enzymes, or cause release of internal second

messenger chemicals such as cyclic AMP or calcium


Focus Figure 3.2 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause responses within the cell.

Kinase enzymes activate other enzymes. Kinaseenzymes transfer phosphategroups from ATP to specific proteins and activate a series of other enzymes that trigger various metabolic and structural changes in the cell.

Second messengers

activate other enzymes or

ion channels. Cyclic AMP

typically activates protein kinase

enzymes.

Activated effectorenzymes catalyze reactionsthat produce 2nd messengers in the cell.(Common 2nd messengers include cyclic AMP and Ca2+.)

Activated G protein

activates (or inactivates)

an effector protein by

causing its shape to

change.

Ligand*(1st

messenger) binds to

the receptor. The

receptor changes shape

and activates.

The activated receptor binds

to a G protein and activates it.

The G protein changes shape (turns

“on”), causing it to release GDP

and bind GTP (an energy source).

1 2

Ligand

(1st messenger)

Receptor G protein Enzyme 2nd

messenger

Extracellular fluid

Effector protein

(e.g., an enzyme

Intracellular fluid

Ligand Receptor

G protein

GDP GTP

GTP

GTP

Inactive 2nd

messenger

Active 2nd

messenger

Activated

Kinase

enzymes

Cascade of cellularResponses

(The amplificationeffect is tremendous.

Each enzyme catalyzeshundreds of reactions.)

* Ligands includehormones andneurotransmitters.

3

4

5

6



Ligand

(1st messenger)


messenger

Extracellular fluid

Effector protein

(e.g., an enzyme

Intracellular fluid

Ligand Receptor

G protein

GDP GTP

GTP

GTP

Inactive 2nd

messenger

Active 2nd

messenger

Activated

Kinase

enzymes





Ligand*(1st

messenger) binds to

the receptor. The


and activates.

1

Slide 2



Ligand

(1st messenger)


messenger

Extracellular fluid

Effector protein

(e.g., an enzyme

Intracellular fluid

Ligand Receptor

G protein

GDP GTP

GTP

GTP

Inactive 2nd

messenger

Active 2nd

messenger

Activated

Kinase

enzymes





The activated receptor binds





2Ligand*(1st

messenger) binds to

the receptor. The


and activates.

1

Slide 3



Ligand

(1st messenger)


messenger

Extracellular fluid

Effector protein

(e.g., an enzyme

Intracellular fluid

Ligand Receptor

G protein

GDP GTP

GTP

GTP

Inactive 2nd

messenger

Active 2nd

messenger

Activated

Kinase

enzymes





Activated G protein




change.

3The activated receptor binds





2Ligand*(1st

messenger) binds to

the receptor. The


and activates.

1

Slide 4



Ligand

(1st messenger)


messenger

Extracellular fluid

Effector protein

(e.g., an enzyme

Intracellular fluid

Ligand Receptor

G protein

GDP GTP

GTP

GTP

Inactive 2nd

messenger

Active 2nd

messenger

Activated

Kinase

enzymes






4

Activated G protein




change.






2Ligand*(1st

messenger) binds to

the receptor. The


and activates.

1

Slide 5



Ligand

(1st messenger)


messenger

Extracellular fluid

Effector protein

(e.g., an enzyme

Intracellular fluid

Ligand Receptor

G protein

GDP GTP

GTP

GTP

Inactive 2nd

messenger

Active 2nd

messenger

Activated

Kinase

enzymes





Second messengers




enzymes.

5


4

Activated G protein




change.






2Ligand*(1st

messenger) binds to

the receptor. The


and activates.

1

Slide 6



Ligand

(1st messenger)


messenger

Extracellular fluid

Effector protein

(e.g., an enzyme

Intracellular fluid

Ligand Receptor

G protein

GDP GTP

GTP

GTP

Inactive 2nd

messenger

Active 2nd

messenger

Activated

Kinase

enzymes





Kinase enzymes activate other enzymes. Kinaseenzymes transfer phosphategroups from ATP to specific proteins and activate a series of other enzymes that trigger various metabolic and structural changes in the cell.

6

Second messengers




enzymes.

5


4

Activated G protein




change.






2Ligand*(1st

messenger) binds to

the receptor. The


and activates.

1

Slide 7


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Cells: The Living Unitsdrjerrycronin.weebly.com/uploads/5/9/7/4/5974564/... · PowerPoint® Lecture Slides prepared by Karen Dunbar Kareiva ... •Sodium-potassium pump –Most studied