Plasma Membrane & Movement of Materials in Cells · Transport by Carrier Proteins •Carrier proteins- bind certain molecules – •Transport them through membrane. –Facilitated

Plasma Membrane &

Movement of Materials in

Cells

Why do cells need to control

what enters and exits?

• Plasma membrane – boundary

between the cell and its

environment

• Homeostasis – maintaining the cells

environment

• Cells need to bring in nutrients, get

rid of wastes, and keep harmful

molecules out

Selective Permeability

• The plasma

membrane allows

some molecules

into the cell while

keeping others

out.

• A window screen

is also selectively

permeable.

Selective Permeability cont.

• Water freely

enters and exits

cells.

• Glucose,

sodium, and

calcium ions are

only allowed to

enter in certain

amounts at

certain times.

Membrane Models• Fluid-Mosaic Model

– Membrane -fluid phospholipid bilayer -

protein molecules partially/fully embedded.

p. 84

Plasma Membrane

Structure/Function• Hydrophilic polar heads face out

• Hydrophobic nonpolar tails face each other.

P. 85

Phospholipid Bilayer

Plasma Membrane

Structure/Function• Proteins - peripheral or integral.

– Peripheral proteins -inner membrane surface.

– Integral proteins - embedded in the membrane.

p. 86

Protein Functions• Channel Proteins – Help pass

molecules through membrane.

• Carrier Proteins – Bind to substance-

help in passage through membrane.

• Cell Recognition Proteins - Help body

recognize foreign substances.

Protein Functions (cont.)

• Receptor Proteins – Bind molecules-

protein changes shape

-causes cellular change.

• Enzymatic Proteins – cause and

speed metabolic (chemical) reactions

Plasma Membrane Permeability

• Plasma membrane- differentially

permeable.

–Passive Transport - No ATP (energy)

requirement.

• Molecules follow concentration gradient.

–Active Transport - Requires carrier

protein and ATP.

Crossing Plasma Membrane

p. 88

Diffusion

• Particles of matter are in

constant motion.

• Moving particles will

collide with each other.

• Diffusion – the net

movement of particles

from an area of high

concentration to an area

of low concentration.

Osmosis• Osmosis - Diffusion of water across

a selectively permeable membrane – caused by concentration differences.

(HIGH → Low)

Osmotic pressure- due to osmosis.• Greater the pressure, stronger the water

diffusion toward low concetration.

Osmosis

p. 90

Osmosis• Isotonic Solution - Solute and water

concentrations same (equal) inside and

outside membrane.

• Hypotonic Solution - Lower

concentration of solute on one side of

membrane.

– Cells in hypotonic solution .

• Lysis (burst)

Osmosis• Hypertonic Solution - Higher

concentration of solute on one side of

the membrane.

– Cells placed in a hypertonic solution will

• Plasmolysis

Transport by Carrier Proteins• Carrier proteins- bind certain molecules –

• Transport them through membrane.

– Facilitated Transport

• Small molecules follow concentration gradient by

combining with carrier proteins. (No Energy

Required)

p. 92

Transport by Carrier Proteins

–Active Transport

• Small molecules move against

concentration gradient by

combining with carrier proteins.

• (Requires Energy- ATP)

Membrane-Assisted Transport• Large macromolecules- transported into/out

of the cell by vesicle.

– Exocytosis - Vesicles fuse with plasma

membrane as secretion occurs.

p. 94

Membrane-Assisted Transport

– Endocytosis - Cells take in substances by

vesicle formation.

• Phagocytosis - Large, solid material.

(eat)

• Pinocytosis - Liquid or small, solid

particles. (drink)

• Receptor-Mediated - pinocytosis of

specific molecules by receptor binding.

p. 95

Cell Surface Modifications

• Junctions between Animal Cells

Adhesion Junctions

–Intercellular filaments between cells.

• Tight Junctions

–Form impermeable barriers.

• Gap Junctions

–Plasma membrane channels are

joined (allows communication).

Cell Surface Modifications

• Extracellular Matrix

–Mesh of polysaccharides and proteins

outside cells that produced them.

• Plant Cell Walls

–Permeable cell wall of cellulose

• Plasmodesmata cytoplasm strands

between cells- allow material passage

between cells.