hw 2

Cell membranes are composed principally of

phospholipid

Molecules that traverse a membrane against their concentration gradient do so by _______ transport.

active

Active transport differs from facilitated diffusion in that

active transport involves the transport of molecules up their concentration gradient

Cholesterol is present in the membranes of all

animal cells

Plasma membrane phospholipids are

asymmetrically distributed between the two membrane halves.

Lipids with unsaturated fatty acids

increase fluidity of membranes

Phospholipid bilayers are permeable only to molecules that are _______ and _______.

small & uncharged

passive transport across a membrane refers to

transport in the energetically favorable direction

The sugar groups of glycolipids and glycoproteins are found on the outer surface of the plasma membrane T/F

true

Active transport is transport in an energetically

unfavorable direction, always coupled to another reaction or source of energy

Channels form pores through which molecules of appropriate size and charge can cross a membrane. By contrast, carrier proteins

selectively bind the molecule to be transported, change configuration, and release it on the other side.

What is the primary reason that mammalian red blood cells are used in the study of the plasma membrane?

They lack nuclei and membrane-bounded organelles.

While small, uncharged molecules can diffuse through the hydrophobic core of a phospholipid bilayer, larger polar molecules such as glucose must enter cells by binding to

carrier proteins that facilitate the passage of specific molecules across membranes

Cholesterol affects membrane fluidity by

decreasing membrane fluidity at high temperatures and increasing membrane fluidity at low temperatures

Integral membrane proteins are those that

directly associate with membrane lipids.

In the fluid mosaic model of biological membrane structure, transmembrane proteins are

embedded nearly randomly in the lipid bilayer

Introducing a double bond into a fatty acid puts a(n) _______ into the conformation of the molecule.

kink

Phospholipids in a membrane commonly

move laterally in the plane of the bilayer & rotate within the bilayer.

A feature common to most transmembrane proteins is a(n)

α-helical region of about 20 to 25 hydrophobic amino acids.

The resting potential of a typical eukaryotic cell is _______ mV.

-60