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Active Processes

• ATP is necessary to transport substances that

are:

– Too large

– Non-soluble

– Unable to move across its concentration gradient

• Active Transport

– Primary & Secondary Active Transport

• Vesicular Transport

– Endocytosis & Exocytosis 1

Primary Active Transport

•The energy to do

work comes directly

from the hydrolysis

of ATP

•Example: Sodium-

Potassium Pump

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The Na+ - K+ Pump

• Na+-K+ ATPase maintains ↑ [K+] inside cells &

↑ [Na+] outside cells

• Binds 3 Na+ : 2 K+

• Creates cell membrane’s electrochemical

gradient

• Crucial to cardiac & skeletal muscle, and

nervous functions

• See video

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Resting Membrane Potential

• Selective permeability

allows for the generation of

a membrane potential

(voltage)

• At rest, the cell membrane

has a (-) membrane

potential

• Important to excitable tissue

like nervous tissue

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Secondary Active Transport

• Indirectly driven by

primary active

transport through the

creation of ionic

gradients

• Molecules or ions

move from regions of

lower concentration to

regions of higher

concentration

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Vesicular Transport

• Large particles, macromolecules, and

larger volumes of fluids do not fit through

channels of protein pumps and must be

transported in and out of the cell through

vesicles

• Exocytosis: Out of the cell

• Endocytosis: Into the cell

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2

Exocytosis

• Secretions within vesicles dock at the membrane and are released as the cell & vesicular membranes fuse

• Used during hormone secretion, neurotransmitter release, mucus secretion & waste elimination 7

Endocytosis: Clathrin-mediated

• The main process used for

endocytosis

• Clathrin-mediated transport

is used during

phagocytosis, pinocytosis,

and receptor-mediated

endocytosis

• Clathrin is a lattice-like

protein that cages in cargo

for transport into the cell 8

Endocytosis: Phagocytosis

• Primarily used by defense

cells like WBCs and

macrophages

• Large, solid substances

such as bacteria and dead

cells are engulfed and

subsequently destroyed

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Endocytosis: Pinocytosis

• Droplets of extracellular

fluid containing dissolved

particles are folded into the

plasma membrane

• Nutrients dissolved in

extracellular fluid are taken

into the cell

• Particularly important in

the lining of the small

intestine 10

Endocytosis: Receptor-mediated

• Selective mechanism for

bringing specific

macromolecules into the

cell

• Receptors bind with their

specific ligands (enzymes,

insulin, hormones) and are

endocytosed

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The Cytoplasm

• Gel-like material, consistency of room temperature butter

• Contains the cytosol (viscous, clear liquid), organelles (“cell machinery”), the cytoskeleton (scaffolding & motor units), and inclusion bodies (stored nutrients, pigmentation)

• Most cellular activities take place in the cytoplasm

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3

Mitochondria

• Organelle whose inner

membrane is folded into

shelf-like partitions called

“cristae”

• Abundance depends on

cell type

• Function: "Power plants

of the cell”

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Ribosomes

• Small granules

dispersed throughout

the cytoplasm and on

the membranes of

Rough ER, composed

of ribosomal RNA and

protein

• Function: protein

synthesis

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Endoplasmic Reticulum

• Network of

interconnected

parallel membranes

that is continuous

with the nuclear

membrane

• Rough ER: Studded

with ribosomes

• Smooth ER: No

ribosomes 15

RER & Protein Synthesis

• Newly synthesized

proteins are taken into

the RER cisternae

where they undergo

modification before they

are transported where

needed

• RER is also a

“membrane factory”.

External face is site for

phospholipid synthesis

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Smooth Endoplasmic Reticulum

• Contains enzymes that

catalyze the synthesis of

lipids and steroids

• Plays a role in lipid

metabolism and drug

detoxification

• Catalyzes the

decomposition of

glycogen to release

glucose

• In muscle, stores Ca+2

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Golgi Apparatus

• Flattened

membranous sacs

("cisternae") arranged

in stacks associated

with many vesicles

• Function:

modification,

packaging, and

transport of proteins,

the cell’s “traffic

director” 18

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Lysosomes

• Spherical

membranous sacs

containing digestive

enzymes (acid

hydrolase)

• Lysosome Function:

“demolition crew of

the cell“

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Review: Endomembrane System

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Peroxisomes

• Membrane sacs that look like lysosomes

abundant in liver and kidney cells

containing oxidases

• Oxidases detoxify harmful substances &

neutralize free radicals by converting them

into hydrogen peroxide and water

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