They seperate cell interior from external environment 

They enclose organelles inside cells - concentrate molecules

They make cells and organelles selectively permeable

List what is composed in a phospholipid (its structure)

List whether its hydrophilic, or hydrophobic

What does ampiphipathic mean?

Polar Unit, Phosphate group and Glycerol make up the HYDROPHILIC head

The Fatty acid chains make up the HYDROPHOBIC tail

Amphipathic means that the structure has both a hydrophilic and hydrophobic region

The hydrophobic effect is the tendency of polar molecules like water to exclude hydrophobic molecules (repel, non polar molecules aggregate)

Look at lec 7 pg 6 and remember what micelle and stuff look like

Look at pg 7 and remember the frye-edinin expirement! (Youtube if have to)

All fatty acids start out as saturated (ONLY single bonds)

A more fluid cell membrane is an unsaturated cell membrane. (Has double bonds and maybe triple) C=C instead of C-C. AND THE ELEMENTS ARE C AND H

Can organisms regulate their fatty acid saturation (Cell membrane fluidity)?

How?

Yes they can.

They do this by regulating the proportion of unsaturated fatty acids via the desaturase transcript.

Decrease the temperature -> Increase the desaturase mRNA -> Increase unsaturated fatty acids.

TL;DR The lower the temp, the higher the fluidity. 

What do sterols do?

What are their three main parts?

Sterols act as membrane buffers 

At high temperatures they help restrain movement of lipids

At low temperatures they disrupt fatty acid association

Sterols have a hydrophilic end (OH group)

Hydrophobic end

Hydrophobic tail - Pg.11 for diagram

Pg 13 lec 7

memorize this model!

What are integral membrane protein?

What are they also called?

Integral membrane protein traverse the lipid bilayer 

They have three distinct domains : Extracellular (outside cell), Transmembrane (TM), and Intracellular (Cytoplasmic)

The TM domain is a stretch of 17-20 nonpolar amino acids that form an alpha helix

They are also called transmembrane protein. Remember INtegral are IN the cell membrane

What are peripheral membrane protein?

How do they stay attached to the cell?

Peripheral are positioned on the membrane surface - THEY ARE OUTSIDE OF THE CELL MEMBRANE. = Do not interact with the hydrophobic section

They are held to the membrane by interacting with integral membrane protein or lipids

1. Transport

2. Enzymatic activity

3. Signal Transduction

4. Attachment

Why do we need transport through the cell membrane?

What are the two main types of transports and their subtypes?

Hydrophobic nature of membrane prevents free movement of molecules.

O2 can diffuse in, but Ions, macromolecules etc cannot come in.

1. Active Transport

a) Primary

b) Secondary

2. Passive transport

a) Simple

b) Facilitated

Passive transport is movement across a membrane without using energy

It does this via diffusion : A net movement of a substance from a higher concentration to a lower concentration.

Rate of diffusion depends on how large the concentration gradient is ; The higher the gradient, the faster the rate.

What is simple diffusion?

Simple diffusion is the movement of things through the membrane without the use of a transporter 

Rate depends on molecular size and lipid solubility

Nonpolar molecules can use

Small polar uncharged molecules can use

Large polar unchared molecules cannot use

Ions cannot use

What is facilitated diffusion?

What are the two things that help this type of diffusion?

Facilitated diffusion is a form of passive transport that uses a transmembrane protein.

1. Channel Protein 

- Form hydrophilic pathways in the membrane

- Molecules are shielded from hydrophobic core of bilayer

- Transport of water and ions ( Aquaporin - water, voltage gated channels - ions )

2. Carrier proteins

Both of those are integral protein

What are aquaporin?

Aquaporin are highly specific channel protein that do not allow ions to pass through. They do this by a positive charges in its centre repelling transport of protons.

They only let water through, at a single file line. This is through a VERY narrow channel.

They are channel protein that move ions (Na+, K+ Cl-)

They OPEN and CLOSE through changes in their protein shape

They take part in helping in nerve conduction and muscle contraction 

1) Protein binding site exposed to region of higher concentration

2) Solute molecule binds to protein

3) Protein change shape, binding site now exposed to lower concentration region

4) Solute molecules is released to lower concentration site, and protein changes shape back to where its site faces higher concentration region

1. Size of concentration gradient

2. Number of channel and carrier protein in membrane

What is active transport?

What are its three main functions?

What are its two main classes?

Active transport is transport of a molecule across a membrane AGAINST a concentration gradient therefore requiring energy

Almost 25% of a cell's ATP is used for active transport 

Functions :

1) Uptake of essential nutrients

2) Removal of secretary or waste materials

3) Maintenance of intracellular concentration of ions 

(H+, Na+, K+, Ca2+)

Two main classes : 1) Primary actve transport,  2)Secondary active trasport

What is Primary active transport?

What do they only transport?

Primary active transport - Transports a substance and also hydrolizes ATP to power its own transport

ALL primary active transport proteins transport ONLY positively charged ions

H+ pumps pushes hydrogen ions from cytoplasm to outside of cell membrane - Keeping lysosome PH low, also generate membrane potential

Ca2+ pumps Calcium ions from cytoplasm to the cell 

exterior and from the cystol to the ER

NA+ / K+ pumps - Pushes 3 Na+ ions out and 2 K+ ions in creating a membrane potential (Voltage)

What is secondary active transport?

What are the two types of secondary active transports? Briefly describe?

Transport proteins use ion concentration (caused by primary transport) to transport another molecule

IE. Concentration gradient of Phosphate, transports Mercury (not a real world example!)

1) Symport - Transports driving ion from higher concentration to lower concentration , also brings the target solute from low to high concentration (TOGETHER)

2) Antiport - Transports driving ion from higher concentration to lower concentration, which brings target solute from higher concentration to lower concentration (Opposite)

What's high concentration for one substance will be low for the other substance and vice versa! 

Explain exocytosis

Exocytosis is a form of transportation to the outside of a cell

1) Secretory Vesicle approaches a cell membrane

2) Vesicle fuses with cell membrane

3) Protein inside vesicle are released and proteins attached to vesicle are part of membrane now

Pinocytosis is a bulk/fluid phase form of endocytosis

1) Solute molecules and water molecules are outside of cell membrane

2) Cell membrane pockets inwards and encloses the solute and water molecules 

3) Pocket piches off as endocytotic vesicle

1) Substances attach to membrane receptors 

2) Membrane pockets inwards

3) Pocket pinches off as endocytotic vesicle

pg 37 for junction types

Membrane protein respond to environmental stimuli

1) Ligand attatches to cell receptor, causing a signal

2) Different molecules transfer the signal in a chain down a pathway 

3) Signal finally hits the molecule that causes a response