Download Anatomy Chapter 3 section 3 Active Transport Diffusion or facilitated

Anatomy Chapter 3 section 3
Active Transport
Diffusion or facilitated diffusion- net movement is from high to low.
Active transport-movement against the concentration gradient – low to high.
 Requires energy- comes from cellular metabolism
 Uses carrier proteins-proteins w/binding sites that combine
w/particles being transported./union causes energy to be released/
alters shape of protein./passenger molecules move thru the
membrane/transported particles are released/ protein can take
another passenger/
 b/c move against gradient- called pumps. Ex. Na/K pump transports
proteins Na ions out of cell and K ions into cell. ( Na move from low
to high- lower concentration inside cell than outside).
 Sugars, amino acids, (Na, K, Ca, H ions).
 Some of these substances are actively transported in others out.
 Important to cell survival- particularly maintenance of homeostasis.

Endocytosis
Cellular energy is used to move substance into or out of a cell without actually
crossing the cell membrane.
Endocytosis- molecules that are too large to enter a cell by diffusion or active
transport are conveyed in a vesicle that forms from a section of the cell membrane.
3 forms of endocytosis- pinocytosis, phagocytosis,
receptor mediated endocytosis.
 Pinocytosis-cells take in tiny droplets of liquid from their
surroundings,.
A small portion of the cell membrane indents
( invaginates).
Open end seals off
Small vesicle forms
Vesicle detaches and moves into cytoplasm
Vesicular membrane breaks down- releasing liquid into the
cytoplasm.
Fxn: cell can take in water and the particles dissolved in it.proteins- that might otherwise be too large.
 Phagocytosis-cells take in solids-pinocytosis- cells take in
liquids.
Phagocytes- certain types of cells, including wbc, b/c they can
take in solid particles ie bacteria and cellular debris.
Particle attaches to cell membrane.
Stimulates portion of cell membrane to project outward.-surrd
particle, and draw into cell.
The part of membrane surrd solid detaches from cells surface,
forming a vesicle containing the particle.
Usually a lysosome joins newly formed vesicle and lysosomal
enzymes decompose the contents.
Products of decomposition then diffuse out of lysosome and into the
cytoplasm- used as raw materials in metabolic processes.
Exocytosis expels remaining residue.
Phagocytic cells dispose of foreign objects- dust, damaged cells, cell
parts no longer functional. destroy disease causing microorganisms,
important line of defense against infection.
Pinocytosis and phagocytosis engulf nonspecifically!!!!
 Receptor Mediated Endocytosis
Moves very specific types of particles into the cell.
Uses protein molecules that extend thru cell membrane and are
exposed on its outer surface.
Proteins are receptors to which specific molecules from the fluids
surrd cell can bind and selectively enter cell, while other types of
molecules are left behind.
Molecules that bind specifically to receptors are called – Ligands.
EX:
Cholesterol molecules enter cells by receptor mediated endocytosis.
Cholesterol molecules synthesized in liver.
Packaged into large spherical particles called – low density
lipoproteins (LDL).
An LDL particle has a coating that contains a binding protein
called apolipoprotein-B.
Membranes of various body cells ( including liver cells) have
receptors for it.
When liver releases LDL particle in the blood, cells with
apolipoprotein-B receptors recognize and bind the LDL
particles.
A receptor ligand combination is formed.
Stimulates the cell membrane to indent and form a vesicle then
Surround LDL particle.
Vesicle transports LDL particle to the lysosome , where
enzymes digest it and release the cholesterol molecule for
cellular use.
Receptor mediated endocytosis- allows cells w/ appropriate
receptors to remove and process specific types of substances
from their surroundings.
Provides specificity.
Exocytosis
Reverse of endocytosis.
Substances made in cell are packaged into vesicles, fuses to cell membrane,
releasing contents outside cell.
Cells secrete some proteins like this.
Nerve cells use exocytosis to release neurotransmitter chemicals that signal
other nerve cells, muscle cells and glands.