Exchange with the Environment

Cell Transport

Cell Processes

For a cell to survive, it must get nutrients and water. It must also get rid of wastes

How can the cell get materials in and out through the cell membrane?

Cell membrane

Made up of a phospholipid bilayer and several proteins

Phospholipid: Hydrophillic phosphate head Hydrophobic fatty acid tail

Image from: http://academic.brooklyn.cuny.edu/biology/bio4fv/page/phosphb.htm

Cell membrane

Cell membrane: Proteins Integral Proteins

Embedded in lipid bilayer Receptor proteins and transport proteins Transmit signal or materials into/out of the cell

Peripheral Proteins Only on one side of membrane Some act as enzymes Some act as cell markers

Fluid mosaic model of cell membrane

Phospholipid bilayer acts as a fluid Lipids and proteins can move in the layer Sterols (including cholesterol) are used to

help keep membrane structure

Cell membrane

Cell Membrane

Diffusion

The movement of particles from an area of high concentration to an area of low concentration down the concentration gradient

Occurs outside of cells and across cell membranes

Diffusion

Picture from: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html

Osmosis

The diffusion of water across a cell membrane

If solution outside a cell has more water than the cell then water will move into the cell

Osmosis

Image from: http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html#c3

Movement of small particles

Not all particles are able to slip through a cell membrane through diffusion

Example: sugars and starches aren’t small enough to move between the phospholipid molecules

Types of solutions

IsotonicHas same concentration as a

cell, the cell neither loses nor gains water

HypotonicHas less concentration than

cell, cell gains water

Types of solutions

Hypertonic Has more concentration than cell,

cell loses water

Osmosis in cells

Paramecia Control water flow by using a contractile vacuole

Collect excess water and pump it out of the cell

Plant cells Live in hypotonic environment Survive because of cell wall Pressure of water against cell wall: turgor pressure Too much water leaves the cell: plasmolysis Water storage in Central Vacuole

Transport of particles

Some particles have to go through “doorways” to enter the cell Because they are too large or not

soluble through cell membrane These “doorways” are protein

channels These proteins are carrier proteins

Facilitated Diffusion

Diffusion of particles through protein channels in a cell membrane

Particles move from high concentration to low concentration

Example: glucose and salts Does NOT require energy

Image from: http://www.bios.niu.edu/sims/metabolism/metabolism1.htm

Ion Channels

Allow ions to move across the cell membrane

Specific to specific ions Some are “gated”

Active transport

Movement of particles against the normal direction of diffusion

Particles move from LOW concentration to HIGH

Requires energy from the energy molecule ATP

Example: sodium/potassium pump

Image from: http://www.cat.cc.md.us/courses/bio141/lecguide/unit1/prostruct/images/u1fig7a.jpg

Image from: http://www.sp.uconn.edu/~terry/images/anim/antiport.gif

Moving larger particles Endocytosis

Cell membrane surrounds a particle, and encloses it in a vesicle

PhagocytosisWhen large particles are taken in by endocytosis

PinocytosisTransport of fluids or solutes

Image from: http://www.sirinet.net/~jgjohnso/endocytosissmall.jpg

Endocytosis

Image from: http://www.sp.uconn.edu/~bi107vc/images/cell/clathrin.jpg

Exocytosis

Used to remove large particles from the cell

Vesicles formed at the ER or Golgi move to the cell membrane for release

Exocytosis

Image from: http://www.sirinet.net/~jgjohnso/exocytosis.jpg

Image from: http://cellbio.utmb.edu/cellbio/end7.jpg

Modeling the cell membrane