Lipids

What is a lipid?

Category that includes many different types of hydrophobic molecules

What are the three functional types of lipids?

1. Storage → triacylglycerols

2. Structural → sphingolipids/glycerophospholipids

3. Signaling → hormones

What are fatty acids?

Carboxylic acids with long hydrocarbon chains 14-20 carbons long

What are the three types of fatty acids? What are their characteristics?

1. Saturated: Full of H, no double bonds, fully reduced

2. Unsaturated: Double bonds, usually cis (kink)

3. Polyunsaturated: 2 or more double bonds

Why are fatty acids called fatty acids?

Because of the carboxylic acids at the top

Properties of saturated fatty acids

Packed tightly together with higher melting temperature

Properties of unsaturated fatty acids

Side chains flow freely past each other due to kink in chain resulting in lower melting temperature

Do cis or trans fats have higher melting temps

Trans due to their linear structure

Naturally ocurring unsaturated fatty acids almost always have ____ double bonds, putting a ____ bend in the hydrocarbon chain.

Cis

30 degree

Where are trans double bonds found?

In processed foods

How to name fatty acids

Delta

• # of C: # of double bonds

• Count from COOH, indicate first position of change

• Indicate positions of ALL double bonds

Omega: # of C: # of double bonds

• # of C: # of double bonds

• Count from end

• Indicate position of first double bond only with (-)

If not indicated, should you assume a fatty acid is cis or trans?

Cis

How to indicate trans omega and delta nomenclature?

trans Δ, trans ω

Structure of glyceraldehyde

What is the backbone for carbohydrates and lipids

Glyceraldehyde and glycerol

What lipids are used as energy storage

Triglyceride = triacylglycerol (TAG)

• 3 fatty acids attached to glycerol backbone

• How the body stores energy as fat

What are adipocytes

Fat cells specialized to store TAGS

How are triglycerides formed?

condensation reaction

How are triacylglycerols (TAGS) broken down?

Lipase enzymes that hydrolyze fatty acids off a TAG

What classification of enzyme is a lipase?

Hydrolase

Do triacylglycerides, proteins or carbohydrates store energy better?

Triacylglycerides

What is SDS page?

Separating proteins based on molecular weight using an electric field and gel. SDS denatures proteins and coats them with a negative charge and PAGE provide matrix for proteins to migrate.

What are peripheral proteins?

Proteins present in the plasma membrane transiently associated with the membrane by H bonding and have electrostatic interactions.

• Can be disrupted with salt or pH change

What are integral proteins?

Proteins in the plasma membrane tightly associated with the membrane by inserting itself by hydrophoboc interactions and require disruption with harsh conditions (detergent)

In what ways can membrane lipids change their orientation?

1. Transverse diffusion (flip-flop)

2. Lateral diffusion

What is transverse diffusion?

The movement from one leaflet of membrane to another (outer → cytosolic) and requires ATP or enzyme to occur

What is lateral diffusion?

Movement within the same leaflet and happens readily

What does it mean when something is fat soluble?

Can easily cross the membrane

What does it mean when something is water soluble?

Hard to cross membrane

When a molecule has more OH, is it more polar or non polar?

Polar

What is a glycerophospholipid?

• Glycerol backbone

• 2 fatty acid tails

• 1 phosphate head group

What is phosphatidic acid?

• Fatty acids

• Glycerol backbone

• Phosphate

What is phosphatidylethanolamine?

• Fatty acid chains

• Glycerol backbone

• Phosphate

• OCH₂CH₂NH₃⁺

What is phosphatidylcholine?

• Fatty acid chains

• Glycerol backbone

• Phosphate

• OCH₂CH₂N⁺(CH₃)₃

What is phosphatidylserine?

• Fatty acid chains

• Glycerol backbone

• Phosphate

• OCH₂NH₃⁺COOH

Net charge of phosphatidic acid at pH 7

-2

Net charge of phosphatidylethanolamine at pH 7

0

Net charge of phosphatidylcholine at pH 7

0

Net charge of phosphatidylserine at pH 7

-1

What are sugar alcohols?

No carbonyl, instead have CH₂OH at top and bottom of fischer projection, no O in ring

What is phosphatidylinositol?

Diacylglycerol (DAG) + phosphate + inositol inserted into membrane with fatty acid

How does phosphatidylinositol signaling work?

Pip2 is cleaved by phospholipase C to release DAG and IP3

What are glycerophospholipids?

Ether lipids: 1 fatty acid chain linked to diacylglycerol by ether (R-O-R) linkage instead of ester

What are galactolipids?

No phosphate head group, instead have galactose

Most abundant membrane lipid

What role do galactolipids play in plants?

They are essential for thylakoid membranes in chloroplasts, and are involved in photosynthesis and chloroplast development

What are waxes?

Alcohol + fatty acids via ester linkage with no glycerol backbone (hydrophobic)

What are sphingolipids?

Fatty acids with a sphingosine

What are sphingosines?

18 carbon amino alcohol with trans double bonds and long fatty acid chains

What are glycosphingolipids?

Sugar + sphingolipid

What role do glycosphingolipids play in the body?

Determining blood type

How do O, A, and B blood types differ?

1 sugar difference

O = missing last sugar

A = GelNAc last sugar

B = Gal last sugar

For people with A blood type, what antibodies do they have and what antigens are present on their RBCs?

Anti-B antibodies in plasma

A antigen in RBC

For people with B blood type, what antibodies do they have and what antigens are present on their RBCs?

Anti-A antibodies in plasma

B antigen in RBC

For people with AB blood type, what antibodies do they have and what antigens are present on their RBCs?

No antibodies in plasma

A and B antigens in RBC

For people with O blood type, what antibodies do they have and what antigens are present on their RBCs?

Anti-A and Anti-B antibodies in plasma

No antigens in RBC

What allows AB blood types to get blood from any blood type?

No antibodies against any other blood types

What allows O blood types to donate to all blood types?

No antigens on RBCs

What are antigens?

Molecules that generate an antibody response

What are sterols?

Lipids with 4 fused rings

• 3 are 6-membered

• 1 is 5-membered

When more OH are present on a molecule is it more hydrophobic or hydrophilic?

Hydrophilic

What do bile acids do?

Surround fat to make it more soluble

What are steroid hormones?

Oxidized derivatives of sterols and more soluble due to polar substituents

What are the fat soluble vitamins?

A, D, E, K

What is retinal?

A form of vitamin A and a required cofactor covalently bound to rhodopsin (GPCR)

What is rhodopsin?

A photoreactive protein with a G protein couple receptor formed in the retina from B-carotene

• When interacting with light: cis → trans isomerization of cofactor retinal and induces a conformational change G protein cascade = vision