Lipids

What are lipids and their functions?

• structural - membranes

• Energy - source/storage

• signaling ex. steroid hormones

• structurally diverse

• not soluble/sparingly soluble in H20

What are the 5 types of lipids?

• free fatty acids - Energy source, component of other lipds

• Tryiglycerols (triglycerides/fats) - store energy, insulation

• phospholipids - component of membranes, have a phosphate group

• glyclolipids/sphingolipids - have a sugar, membrane components

• sterols - hormones (signalling), most different structure

What are fatty acids? What are the difference between saturated and unsaturated fats?

• E source lipids

• amphipathic (hydrophilic, polar head and hydrophobic nonpolar tail)

• usually even number of carbons, 12 to 20 long

• carboxyl group at head, hydrocarbon tail

• saturated - alkane tail, more VDW interactions, higher meltin gpoint

• unsaturated - tail has an alkene in it, usually cis, causing a kink. lower melting point

What makes a trans fat different from a normal saturated fat?

has a trans double bond instead of a cis double bond

What end of the fatty acid does the omega naming system start from?

the end of the tail

What is the essential Omega-3/6 fatty acid that we can sparingly make other fatty acids from?

linolenic acid

What are eicosanoids? What effects do they have?

• hormones derived from free fatty acids

• omega-6 produces eicosanoids with pro-inflammatory effects

• omega-3 produces eicosanoids with anti-inflammatory effects

What are triacylglycerols? How are they structured?

• fats; long term E storage and insulation; not in membrane

• glycerol backbone with 3 fatty acid chains attached to an ester bond

• often mixture of saturated/unsaturated fats

Why store Energy as fat (triacylglycerols) rather than sugars?

• fats store more energy per gram that carbohydrates do - less oxidezed that glucose, so it can be oxidizes more and release more energy

• store fat anhydrously - don’t require water to surrond it, ligher to storev

What are the types of membrane lipids? What makes them different

• phospholipids - glycerol backbone, 2 fatty acid chains, phosphate group and maybe head

• sphingolipids - sphingosine backbone with amine, 1 fatty acid chain, and head group with a sugar

Describe the structure of phospholipids

• glycerol backbone, 2 fatty acids, and a polar phosphate, potentially a head group

• fatty acid chains added via condensation reactions, forming esters

Describe the structure of sphingo/glycolipids

• long sphingosine backbone with amine

• sphingosine, 1 fatty acid chain, and a head group with a sugar

How are sphingolipids often used in cells?

as signaling molecules, sugars on head group change to signal

Describe the structure of sterol lipids and the types

• 4 fused rings, 3 6C and 1 5C, with different groups on it

• cholesterol - membrane component

• bile acids/salts - amphipathic, solubilize fat by forming a polar coat around them

• steroid hormones

How are lipid bilayers fluid in the fluid mosaic model?

• lateral diffusion - proteins and lipids on the same side of the bilayer can switch positions quickly

• flipflop diffusion - lipids move from outer to inner side of bilayer via an enzyme

How are lipid bilayers a mosaic in the fluid mosaic model?

• made of different kinds of lipids

• have different proteins embedded in membrane

• proteins have specific orientations

• inner/outer side are asymmetric/different

• sugars on lipids/proteins stick off outer leaflet of membrane for signalling/recognition

• composition/amount (esp. of proteins) varies between types of membranes ex. plasma vs nuclear

• cholesterol for support

What are the types of proteins associated with lipid membranes?

• integral: tightly associated with membrane

• peripheral: loosely associated with membrane

What are integral proteins?

• proteins tightly associated with membrane, usually transmembrane proteins

• have nonpolar exterior for region that travels through nonpolar section of membrane

• requires a detergent, both polar and nonpolar, to remove/dissociate from membrane

What are transmembrane proteins?

• type of integral protein, tightly associated with membrane

• have nonpolar exterior for region that touches nonpolar inside of membrane

• at least 1 part of the protein spans the entire membrane

What are peripheral proteins?

• proteins loosely associated with plasma membrane via hydrogen or ionic bonds

• attach via charged heads of lipid or w/ proteins embedded in the membrane

• may have a nonpolar fatty acid “anchor” into the membrane

• don’t require detergent to remove

Why do cells need to adjust membrane fluidity? How do cells adjust membrane fluidity?

• control in response to temperature changes in environment, lipids get more solid in cold and more fluid in heat

• change chain length, degree of unsaturation, and amount of cholesterol

How does changing the chain length of membrane lipids affect membrane fluidity?

• increase length: more solid (more VDW interactions increase MP)

• decrease length: more fluid (fewer VDW interactions, lower MP)

How does changing the degree of unsatuation of membrane lipids affect membrane fluidity?

• increase saturation (fewer double bonds): more liquid (more VDW, higher MP)

• decrease saturation (more double bonds): less liquid (fewer VDW, lower MP)

How does changing the amount of cholesterol in a membrane affect membrane fluidity?

• increase cholesterol = more rigid

• decrease cholesterol = less rigid

Is a fatty acid chain with double bonds saturated or unsaturated?

unsaturated

A cell moves to colder temperatures. What does the cell need to do to membrane fluidity and how will it do so?

• increase fluidity

• decrease length of fatty acids

• decrease amount of saturation (more double bonds and more unsaturated fats)

A cell moves to warmer temperatures. What does the cell need to do to membrane fluidity and how will it do so?

• decrease fluidity

• increase fatty acid chain length

• increase saturation (fewer double bonds and more saturated fats)

What are transport proteins?

• translocase enzyme

• more hydophilic molecules into cell by providing a hydrophobic path through the membrane

• can be passive or active transport

Describe passive transport

• no Energy required (spontaneous)

• molecules move from high to low concentration

• driven by entropy

• can be simple or facilitated diffusion

• move cells both in/out of cell, no directionality (even with facilitated diffusion proteins)

Compare simple and facilitated diffusion

• simple: passive diffusion, no transport protein, mols move from high conc to low conc, molecules pass straight through membrane (ex. sterols)

• facilitated: passive diffusion, requires transmembrane protein, for polar molecules (ex. ions)

Describe active diffusion

• requires E, either through ATP hydrolysis (1’) or movement of another ion down its conc gradient (2’)

• moves from low to high conc

• requires transmembrane protein

Compare 1’ active transport and 2’ active transport

• both require transmembrane proteins

• require Energy

• 1’ - ATP hydrolysis occurs, causing a conformational change in the molecule that moves molecule

• 2’ - pay for transport of molecule with movement of another molecule down concentation gradient, increaseing overall entropy of system

What is symport and antiport transport?

• symport - moves 2 molecules in the same direction

• antiport - moves 2 molecules in opposite directions

• can be active or passive transport

Describe facilitated diffusion of glucose

• uses glucose transporters

• glucose moves down concentration gradient into cell

• glucose molecules bind protein, causing a conformational change in the protein to shuttle glucose across

• protein now inwardly open, glucose enters cell

• new glucose can now exit cell using same transporter

Describe facilitated diffusion of potassium

• uses channels

• K+ enters hydrophobic pore and passes through membrane protein down concentration gradient

• gated protein

What are two methods of facilitated diffusion in cells?

• transporters

• channels

Describe Na/K ATPase

• primary active transport

• moves Na out of cell and K into cell, both against concentration gradeitn to maintain high K conc. and low Na conc in cell

• type of antiport

Describe the Na/K ATPase model of ion movement

• 1. sodium inside cell binds to ATPase

• 2. ATP phosphorylates enzyme (aspartate binding phosphate group of ATP), causing conformation change that opens up the protein to the outside of the cell

• 3. Na leaves cell

• 4. K outside of cell bind to protein

• 5. ATP hydrolysis of phosphorylated group (removal of phosphate group for aspartate) causes conformational change and protein reverts to inward-facing shape

• 5. K released into cell

What state is the Na/K ATPase pump in when its phosphorylated? When its not phosphorylated?

• phosphorylated - open to outside, ready to bind K

• not phosphorylated - open to inside, ready to bind Na

Describe generally how enzymes use ATP to move molecules in and out of cell

converts energy of ATP phosphorylation/dephosphorylation to cause a conformational change to move things (like a turbine)

How does the sodium linked glucose transporter work?

• secondary active transport

• uses Na+ leaving cell down concentration gradient to move glucose up concentration gradient

• transporter has directionality