BIOL 212 Study Guide - Quiz Guide: Cell Membrane, Membrane Transport, Integral Membrane Protein

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6 Feb 2017
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1. Explain why the unique molecular structure of the
phospholipid molecules form a bi-layer. Also, be
able to describe how small lipid-soluble substances
cross and small water-soluble substances cross the
plasma membrane
Bullet point version!!!
Amphipathic design, ability to be hydrophobic
or hydrophilic
Fatty acid tail is nonpolar and uncharged =
hydrophobic, water fearing making them turn
towards each other to avoid contact with water
Phosphate glycerol head is polar and - charged
= hydrophilic, water loving and will face the
ECF and ICF
ICF and ECF reacts with water so the water
fearing tails turn in and the water loving
heads face out making a bilayer
Lipid soluble pass through because the bilayer
is made of mostly lipid so it can get through
really easily
Water soluble substances must use integral
proteins to pass through, to avoid contact with
the tails
The unique molecular structure of the
phospholipid molecules forms a bilayer because the
design is amphipathic, meaning that it has the ability
to be both hydrophilic and hydrophobic. The fatty acid
tail is nonpolar and uncharged making it water fearing
so it will turn away from the fluid and the tails will
face each other to stay away from water. On the other
hand, the phosphate-glycerol head is polar and
negatively charged making it water loving and will face
the extracellular and intracellular environment where
there is water. The ICF and ECF reacts with the water
molecules, which are polar and charged, and the small
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amounts of water inside the fluid make it so that the
tails will face each other and the heads facing out,
making a bi-layer
Small lipid-soluble substances are able to
cross the plasma membrane because the bilayer is made
up of mostly lipids. Water soluble substances pass
through channels in the integral proteins to cross the
membrane, they will not cross the lipid tails.
2. Describe the two main differences between a passive
and an active process of membrane transport. Also,
describe EACH of the 4 passive processes and each
of the 3 active processes
Bullet point version!!!
Passive processes do not require any ATP
[cellular energy], and will go down a
concentration gradient [from high to low
concentration]
Active processes do require ATP and can act
independent of the concentration gradient,
often going against it
Passive processes
Filtration - movement down the gradient by
outside forces, like gravity
Osmosis - movement of water molecules
specifically
Diffusion - moving down the concentration
gradient by thermal kinetic energy
Facilitated diffusion - a substance will
bind to a protein making it move and
deposit the substance on the other side
Active processes
Active transport - substances are carried
via membrane carrier protein usually
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