Biochem 406-lecture 1,2

What is the purpose of lipid droplets

Lipid droplets are used to store fats and act as an energy reservoir

What are lipid droplets made of

Phospholipid monolayer and periipin proteins on the outside. Cholesterol esters and triacylglycerols on the inside

Why are fats better for long term energy storage than carbohydrates

Triacylglycerols can pack closely together, excluding water.

Fats are more reduced

How do bile salts help in lipid digestion

Bile salts are amphipathic and can emulsify lipids in aqueous environments like the small intestine, forming mixed micelles

what does human pancreatic lipase do and what is its cofactor

works outside of the cell at the lipid/water interface to break down fats

And colipase is the cofactor

What does colipase do

Co lipase is a cofactor of HPL which binds the lid exposing the active site

What conformation changes occur in the human pancreatic lipase when it shifts from closed to open conformation

In the inactive form the lid region blocks accesses to the active site

In the active form the conformational change creates a large hydrophobic surface on HPL that allows it to insert into to the monolayer of the mixed micelle

What are Fatty Acid Binding Proteins (FABP)

Make fats soluble inside of the cell

How does inhibiting HPL through drugs like Orlistat work?

Orlistat inactivates HPL by forming a covalent bond with a key serine residue in the active site. Inhibiting HPL prevents dietary fats from being broken down so they pass through the digestive system un digested and end up being excreted as waste.

where are fatty acids synthesized in the body

Fatty acids are synthesized from acetyl-CoA in the liver and adipose tissue. Fatty acid synthesis occurs in the cytoplasm

What is the first step of the citrate shuttle which transports acetyl-CoA from the mitochondria matrix to the cytoplasm

Citrate synthase catalyzes the reaction where oxaloacetate and acetyl CoA combine to make citrate

Whats the second step of the citrate shuttle mechanism

Citrate is transported through the mitochondrial membrane via the citrate shuttle

Whats the third step of the citrate shuttle

Citrate lyase catalyzes the break down of citrate into Acetyl-CoA and oxaloacetate

what happens to the Acetyl CoA and Oxaloacetate in the cytoplasm

Acetyl-CoA goes on to be used for fatty acid biosynthesis

oxaloacetate is converted into malate (by malate dehydrogenase) which is then converted into pyruvate and sent back to the mitochondria to regenerate oxaloacetate

What are the products and reactants of the citrate shuttle

Uses 2 ATP, 1 NADH

Generates 1 NADPH

what is the reaction catalyzed by Acetyl-CoA Carboxylase

First committed step of Fatty Acid Synthesis -> carboxylation of acetyl CoA to form Malonyl-CoA (highly exergonic reaction and essentially irreversible)

By how much does each of the 6 enzyme activities in Fatty Acid Synthase extend the fatty acyl chain by

Each enzyme extends the chain by 2 Carbon units

How does the ACC enzyme catalyze the reaction of acetyl-CoA to malonyl CoA

1. HCO3- is activated by ATP

2. Biotin cofactor with swinging arm takes the reactive CO2 to Acetyl-CoA

3. Acetyl-CoA with the CO2 attached becomes Malonyl-CoA

What is ACP

ACP = acyl carrier protein.

Intermediates in fatty acid synthesis are attached to an ACP

What is the overall reaction catalyzed by fatty acid synthase

Acetyl-CoA and Malonyl-CoA form Palmitate (16C saturated FA) in the cytosol.

Uses 8 acetyl-CoA, 7ATP, and 14 NADPH

What is the first step of Fatty Acid Synthase

Malonyl/Acetyl-CoA ACP transacylase (MAT) catalyzes the transfer of Acetyl CoA and Malonyl CoA onto ACP (drops off Acetyl-CoA in KS first)

What is the second step of Fatty Acid Synthase

KS catalyzes the condensation of malonylACP and AcetylACP, releasing a CO2

What is the third step of fatty Acid synthase

KR catalyzes the reduction of the fatty acid chain using NADPH which turns a ketone to an alcohol

What is the fourth step of fatty acid synthase

DH catalyzes a dehydration reaction in which a water molecule is released, and the alcohol becomes an alkene

what is the 5th step of fatty acid synthase

Enoyl-ACP reductase (ER) reduces the fatty acid chain using an NADPH turning the alkene into an alkane

what is the 6th step of fatty acid synthase

The cycle repeats (and a new malonyl CoA is added) until the chain reaches 16 carbons long (palmitate)

How is the growing chain released once it reaches 16 carbons

The fatty acid acyl chain can only properly bind in the C16 pocket of thioesterase once the carbon chain is 16 carbons long. Then it will be properly positioned for hydrolysis

How are longer fatty acid chains synthesized

Palmitate is the primary product and longer chain FA are built off of it. Elongation mostly happens in the ER and sometimes in mitochondria and separate enzymes are used

What do desaturases do

add cis double bonds, important for the synthesis of unsaturated fatty acids

why is arachidonate important

Serves as the precursor for important signaling molecules (the eicosanoids powerful hormones that break down quickly)

How does Asprin help with pain

By inhibiting the COX enzymes which are the enzymes responsible for pain/inflammation