transport methods notes

transport by proteins

reminder... proteins are imbedded in the cell membrane

facilitated transport/diffusion

- facilitate = "to help"
- some molecules easily cross the membrane because carrier proteins facilitate their passage
- carrier proteins help only specific molecule ie glucose can enter cells much faster than other sugars
- more with the concentration gradient (from higher to lower concentration) therefore no ATP energy required
- channel and carrier proteins both do this
- AKA "passive transport"

active transport

- hint: activity requires energy so this type of transport requires ATP (energy giving molecule)
- ions or molecules moved against the concentration gradient using a protein (channel proteins don't do this type of transport)
- egs include:
a) absorption of nutrients by cells in digestive tract
b) Na+/K+ pump in nerve cells
- up to 40% of a cell's energy may be used for active transport

transport by vesicles

- molecules too large for proteins are brought in and out by vesicles eg. proteins (hormone secretion)
- always requires ATP energy
- can move both with and against the concentration gradient

exocytosis

- exo = exit
- vesicles from the golgi body, etc contain molecules for body's use
- vesicles move to and fuse with membrane during secretion eg. digestive enzyme amylase from pancreas or human growth hormone from anterior pituitary
- fusing with membrane adds to it (increases total area of cell membrane)

endocytosis

- take in substances by vesicles
- membrane "lost" by endocytosis is balanced by membrane gained by exocytosis
- occurs in one of 3 ways

3 types of endocytosis

phagocytosis, pinocytosis, receptor-mediated endocytosis

phagocytosis

- "cell eating"
- large material is taken in such as a food particle or invader
- common in some human white blood cells
- when an endocytic vesicle fuses with a lysosome, digestion occurs

pinocytosis

- "cell drinking"
- vesicles form around liquid or very small particles
- performed by blood cells or cells lining the kidney tubule

receptor-mediated endocytosis

- form of pinocytosis
- specific receptor sites on outer membrane surface binds with a particular peptide hormone, vitamin, or lipoprotein
- involved in intercellular exchange (transport between cells)
- commonly occurs across the membranes of the placenta between fetal and maternal blood