Download Oct_7

Midterm 1
Oct 17
Chapters 1-7
Key on lectures
RCH 101
8:30 – 9:20
40 MC
o
Computer card
o
Recognize structures like phosphatidylethanolamine
Kin 217 – Oct 7
-
[structure of major phospholipids in cell membranes]
-
Different types of membrane lipids (we talked about this last time)
[ chart of Phospholipid composition of organelles ]
o
Note that sphingomyelin high in plasma membrane
[ Inner / Outer membranes - curvature stress - phosphatidyl choline, big methyl group  on outer
membranes. Which ones on the inside? –those with small head group  phosphotidyl serine (?) ]
Cholesterol Fig 7.4
o
Going to stick into a membrane
o
Cholesterol doesn’t like to ‘dance’ – it’s a wallflower
What is cholesterol doing in membranes?
o
Prevents close packing
o
Lowers the melting temperature
o
Melting transition is less sharp
o
Animal cell membranes have cholesterol

Example – 25% for red cells

Plasma membranes have more cholesterol
Diagram of Biomembrane structure
o
[Series of proteins sticking in, sticking on…sea of proteins in membrane]
Fluid Mosaic Model
o
[Like surfing on waves—
o
Water  phospholipids
o
Surfers  some are in it, some on top]
Lipid Rafts
o
[Research is showing that phospholipids AREN’T randomly arranged]
o
[Microdomains that associate with proteins, domain has its own control…area around
lipid very different from other areas]
o
[Controversial – some people believe in these, some don’t ]
Transmembrane Protein Fig 7.7
o
Glycophorin

10 amino acids span bilayer

Hydrophobic

[What controls the hydrophobic and hydrophilic tendencies of an AA? – the
residue groups! ]

If you see a hydrophilic region on a transmembrane, you know you’ve got some
sort of porin
Porin
o
Beta barrel structure

Forms a pore

Allows a selective small molecule movement

Hydrophilic interior

[ what’s coming in and out is essential for survival]
Peripheral membrane proteins [not actually embedded in bilayer ]
o
Attachment

Hydrogen bonding and ionic interactions in some cases
o
Anchoring

[nice big] hydrophobic fatty acids (14,16 or 18 carbons)

Covalently attached to the protein
o
N–terminal amino acid, via cysteine, via a hydroxy amino acid
Fig 7.10
Transport Processes
o
Passive Transport

Simple Diffusion

No control [well…indirect control], follows concentration gradient
-
-
-
-
-
-
-
o
o

Rate
o
o
o
-
-
Hydrophobicity
Ions need to lose hydration [ ions associated with a lot of
water molecules…it’s hard to transport such a big molecule]
[any thing with a high charge in an aqueous environment has
reacted with water..we talked about this last class as well]
Passive Transport

Facilitated diffusion – requires protein

Follow concentration gradient

Enzyme like
o
Specific
o
Saturable [ can only do so much work before it hits a plateau
]

Fast!

Transporter – glucose

Channel – Na+, K+, Ca2+, Cl-, H2O
Gated ion channels
o
Gated pores or channels

Open and close in response to a signal
o
Ligand

Acetylcholine [ it binds and then the gate will open ]
o
Charge

Change in membrane charge

Voltage-gated pores

Na+, K+ channel
Mechanism of the selectivity of the potassium channel (Fig. 7.17)
o
[ Hydrated sodium is a lot smaller than potassium (?) can’t go into transition stage –
requires energy to remove water molecules; won’t react with outside channel groups
Transport Processes
o
Active Transport

Requires energy

Against gradient [most of the time], larger molecules, cell movement

Enzyme like

Specific

Saturable

Slower than channels [facilitated] [ ie: facilitated diffusion is running downhill,
active transport -> run uphill ]

Primary

Use ATP directly

Secondary

Electrochemical gradient or membrane potential drive transport
o
Generated by primary active transport
o
[if you want to get Ca into cell, make cell very negative and
it’ll pull Ca into it ]

Uniport [one substrate moving across]

Active (Ca2+ ATPase)

Facilitated Diffusion (blood glucose)

Symport [two substrates coming in at different directions]

Uptake of one substrate linked with uptake of another

Antiport

On substrate in, one substrate out
Fig 7.2
o
[Active transport of sodium by ATP
o
Sodium brings glucose in as well]
Diagram of Movement of solutes across membrane
Look at Sodium-Potassium ATP channel…
o
[ Change in confirmation and moves things across… ]
o
-
Oxygen, carbon dioxide, nitrogen, urea, ethanol, even water
[ don’t have to spend any ENERGY to transport oxygen and all
those ]