EXAM2 Chapter 5A: Cell Membranes

How do we know about cells?

Technology enables discoveries (late 17th century microscope) --> humans draw the implications (Theodore Harvey, mid 18th century)

Why are all living organisms composed of cells?

Define a place where living things can do the processes of life

store/use information

store/use energy sources

make things happen in a non-random way

A place that can be copied/propagated through time

A place that's different from the surrounding environment - need a barrier

cells divide and divide and divide and divide

to keep some things out/some things in

to do things and make things happen

membranes also used for transformation of energy and info (ATP synthase; G-Protein coupled receptor)

Cell membranes are a mix of lipids, proteins, carbohydrates

lipid bilayer

proteins: transport vesicle

carbohydrates: outer surface on the membrane

Phospholipids

are AMPHIPATHIC: has BOTH polar heads and nonpolar tails

have SHAPE

saturated (cone shape): NO double bonds, straight tails, make micelles

unsaturated (cylinder shape)

micelles: lipids with bulky heads and ONE tail are wedge-shaped, pack into spherical structure

image

Phospholipids with unsaturated tails form DOUBLE membranes

Phospholipids shape influences shape that comes from interaction with water: liposomes

liposome: an enclosed spherical bilayer structure spontaneously formed by phospholipids in environments with neutral pH (i.e. water)

liposomes are aqueous INSIDE

Membranes are not static - they are FLUID

continual movement of lipids, what controls fluidity?

temperature

higher temp: MORE fluid

lower temp: LESS fluid

Ratio of saturated vs. unsaturated tails

Van Der Waals are strongest when they're closer together (STRAIGHT TAILS ARE MORE TIGHTLY BONDED)

unsaturated: MORE fluid

Length of fatty acid tails

saturated: LESS fluid

Van Der Waals: the longer the tail, the more chances to interact, more tightly bonded

long: less fluid

short: more fluid

Cholesterol stiffens membranes

cholesterol sits in spaces between unsaturated lipids, fill up space, tighten membrane

Membranes are stuffed with proteins

Integral membrane proteins

Peripheral membrane proteins

include transmembrane proteins that span the entire membrane

3 regions: transmembrane, extracellular, cytoplasmic

temporarily associated with either the internal or external side of the membrane (ATTACHED to membrane, NOT IN the membrane)

holding on tightly to the membrane by hydrophobic regions

Membrane proteins could be a: transporter, receptor, enzyme, anchor