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Biochemistry > Lipid Metabolism - BIOCHEM 432 > Flashcards

Lipid Metabolism - BIOCHEM 432 Flashcards

1
Q

Why is Acetyl-CoA a key metabolite in cells?

A

It links energy conversion pathways, amino acid metabolism and lipid metabolism

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2
Q

Acetyl-CoA helps to derive fatty acids and cholesterol which happen to be precursors to what 4 molecules?

A

Triacylglycerols, membrane lipids, steriods and bile acids

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3
Q

Name the three important role that lipids serve

A

Energy storage, cell membrane structure and endocrine signaling.

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4
Q

What lipid molecules have the funtion of energy storage?

A

Fatty acids and Triacylglycerols

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5
Q

What lipid molecules function in the hydrophobic barriers of cell membranes?

A

Glycerophospholipids and Sphingolipids

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6
Q

What lipid molecules function in the endocrine system to activate a variety of signaling pathways?

A

Steriods and eicosanoids

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7
Q

Describe a fatty acid

A

A fatty acid is a carboxylic acid with a long hydrocarbon chain (typically within 4-36 carbons).
The most abundant fatty acids have unbranched chains of 12-20 carbons which are even-numbered.
A distinction between fatty acids is the position and number of double bonds between carbons.
Fatty acids are able to form covalent bonds with proteins to tether them to membranes.

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8
Q

What functional group is important for the formation of ester linkages?

A

The carboxyl group (CO2-) of a fatty acid

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9
Q

How are the carbons of fatty acid numbered?

A

The first carbon is the carboxyl carbon. The second carbon is in the alpha position immediately after the first carbon. The beta carbon is the third carbon in the chain. The last carbon is a methyl group (CH3).

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10
Q

Where does the hydrocarbon tail of a fatty acid begin?

A

From the beta carbon to the end methyl group

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11
Q

What constitutes the fatty acyl group of a fatty acid?

A

First carbon (not including the oxygen of the carboxyl group) to the end methyl group

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12
Q

What constitutes a saturated fatty acid?

A

No double bonds are present in the hydrocarbon tail–fully reduced methylene groups

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13
Q

What constitutes an unsaturated fatty acid? Monosaturated fatty acid? Poly unsaturated fatty acid?

A

An unsaturated fatty acid contains at minimum one double bond between carbons in the hydrocarbon tail.
Monosaturated hydrocarbon tails only have one double bond present.
Polyunsaturated hydrocarbon chains contain 2+ double bonds between carbons.

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14
Q

What is a Trans fatty acid

A

Where the hydrogens on the carbons on either side of a carbon-carbon double bond in the hydrocarbon tail are opposite sides of the double bond.

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15
Q

What is a Cis fatty acid?

A

Where the hydrogens on the carbons on either side of a carbon-carbon double bond in the hydrocarbon tail are the same side of the double bond.

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16
Q

True or false: Almost all living organisms synthesize and incorporate trans-fatty acids.

A

FALSE: Almost all living organisms synthesize and incorporatecis-fatty acids. Trans-fatty acids are often produced during commercial food production.

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17
Q

Describe Omega Fatty Acids

A

Omega fatty acids are unsaturated.
The terminal carbon in the methyl group at the end of the hydrocarbon tail is the omega carbon
To determine what kind of omega fatty acid there is, count from the omega carbon to the first double bond within the hydrocarbon tail
Omega fatty acids are associated with reduced cardiovascular disease

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18
Q

What is the most common saturated fatty acid found in animals, plants and microorganisms?

A

PALMITIC ACID (16:0; Hexadecanoic acid) is the most common saturated fatty acid found in animals, plants and microorganisms. Over consumption of palmitic acid increases the risk of developing cardiovascular disease in humans.

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19
Q

What is the symbol, systematic name and structure of palmitic acid?

A

Symbol: 16:0 (16 carbons:0 double bonds)
Systematic name: Hexadecanoic acid
Structure: CH3(CH2)14COOH

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20
Q

True or false: Linoleic acid and a-Linolenic acid are both essential omega fatty acid

A

Linoleic acid and α-Linolenic acid are two essential fatty acids. Linoleic acid (LA) is a polyunsaturated omega-6 fatty acid used in the biosynthesis of arachidonic acid (AA). α-Linolenic acid (ALA) is a polyunsaturated omega-3 fatty acid. Both are necessary for health and cannot be produced within the human body.

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21
Q

What is the symbol, systematic name and structure of Linoleic acid?

A

Symbol: 18:2 (18 carbons:2 double bonds)
Systematic name: 9,12-Octadecadienoic acid
Structure: CH3(CH2)4(CH=CHCH2)2(CH2)6COOH
Omega acid identity: w6

22
Q

What is the symbol, systematic name and structure of a-Linoleic acid?

A

Symbol: 18:3 (18 carbons:3 double bonds)
Systematic name: 9,12,15-Octadecadienoic acid
Structure: CH3CH2(CH=CHCH2)3(CH2)6COOH
Omega acid identity: w3

23
Q

What is arachidonic acid a precursor to?

A

Arachidonic acid is a precursor of eicosanoid involved in cellular signaling as a lipid second messenger

24
Q

What is the symbol, systematic name and structure of Arachidonic acid?

A

Symbol: 20:4 (20 carbons:4 double bonds)
Systematic name:5,8,11,14-Eicosatetraenoic acid
Structure: CH3(CH2)4(CH=CHCH2)4(CH2)2COOH
Omega acid identity: w6

25
Q

True or false: The mammalian fatty acid synthase (FASN) catalyzes the rate-limiting step of fatty acid synthesis?

A

FALSE: Acetyl Co-A carboxylase (ACC) catalyzes the rate-limiting step in fatty acid synthesis

26
Q

True or False: Excess glucose can be converted into fatty acids in our bodies?

A

TRUE

27
Q

True or False: One of the important functions of citrate shuttle is to provide NAPDH for fatty acid synthesis in the cytosol

A

TRUE

28
Q

True or False: Some unsaturated fatty acids are essential to humans because our cells do not express certain desaturating enzymes

A

TRUE

29
Q

True or False: TAGs synthesized by the liver cells are transported to adipose tissue via chylomicrons for storage?

A

FALSE: TAGs synthesized in the liver are packed in VLDL particles to deliver them to adipose tissue for storage or other organs for use.

30
Q

True or False: Citrate allosterically activates Acetyl-CoA Carboxylase

A

TRUE

31
Q

True or False: AMPK is fully active when it’s phosphorylated and bound to AMP

A

TRUE

32
Q

True or False: Bile acids are produced from cholesterol

A

TRUE

33
Q

What kind of TAGs are transported by chylomicrons?

A

Dietary TAGs are transported by large lipoportien complexes call chylomicrons

34
Q

How are TAGs stored in adipose tissue released?

A

Triacylglycerols stored in adipocytes are released as free fatty acids in response to hormone signaling and are transported by the carrier protein albumin.

35
Q

What are the carbon sources of fatty acids?

A

Glucose and amino acids

36
Q

Name the five major steps in converting glucose into TAGs

A
  1. Glucose import
  2. Glycolysis
  3. Citrate shuttle
  4. Fatty acid synthesis
  5. TAGs synthesis and VLDL export for storage
37
Q

Name three benefits of the citrate shuttle for fatty acid synthesis

A
  1. Provides acetyl CoA for fatty acid synthesis
  2. Generates NAPDH for fatty acid synthesis
  3. Restores mitochondrial oxaloacetate

Bonus: regulates glycolysis and gluconeogenesis

38
Q

When the citrate cycle is inhibited by a high energy charge in the cell, what provides a mechanism to transport excess acetyl lunits from the mitochondria to the cytosol and why?

A

Under conditions when the citrate cycle is inhibited by a high energy charge in the cell, the citrate shuttle provides a mechanism to transport excess acetyl units from the mitochondria to the cytosol for fatty acid synthesis.

39
Q

How is NADPH produced in the citrate shuttle for fatty acid synthesis?

A

The oxidation of malate to pyruvate by malic enzyme generates NADPH, which is used in the fatty acid synthesis pathway.

40
Q

Overview the citrate shuttle

A

Fatty acids oxidation in mitochondrial matrix;

When cell energy is high, citrate is exported from mitochondrial matrix to cytosol to provide acetyl-CoA;

The oxidation of malate to pyruvate generates NADPH used in the fatty acid synthesis;

Malate and pyruvate are transported back into mitochondria.

41
Q

Overview Acetyl-CoA carboxylase (ACC) and its functions

A
  • Catalyzes the rate-limiting step in fatty acid synthesis
  • Requires carbon source, biotin, and energy
  • Regulated by reversible phosphorylation and allosteric mechanisms
42
Q

Overview Fatty Acid Synthase (FASN) and its functions

A
  • Catalyzes a series of reactions that add C2 units to a growing fatty acid chain
  • Has multiple functional domains
  • It uses acyl carrier protein (ACP) as the hydrocarbon anchor
43
Q

What three activities does ACC carry out?

A
  1. Acts as a biotin carrier
  2. Acts as a biotin carboxylase
  3. Acts as a carboxytransferase
44
Q

What are the three functional domains of ACC in eukaryotes?

A
  1. Biotin carrier domain
  2. Biotin carboxylase domain
  3. Carboxyltransferase domain
45
Q

Describe the production of malonyl-CoA

A

The production of malonyl-CoA by acetyl-CoA carboxylase involves a two-step ATP-dependent reaction that carries a carboxyl group from the biotin carboxylase active site to the carboxyltransferase active site using a carboxybiotin arm attached to the biotin carrier protein domain.
1. The acetyl-CoA carboxylase reaction.
2. Domain structure of acetyl-CoA carboxylase showing the three functional domains in eukaryotes, which are encoded on three separate polypeptides in prokaryotes.

46
Q

How is ketogenesis regulated?

A

via glucagon, cortisol and insulin (they’re all hormones)

47
Q

What is the main hormonal regulator of ketogenesis?

A

Insulin is the main hormonal regulator of ketogenesis. A low insulin state leads to increased production of ketone bodies through different mechanisms

48
Q

What is diabetic ketoacidosis?

A

An overproduction of ketone bodies through increased ketogenesis that decreases the blood pH

49
Q

Why would a diabetic patient have breath the smells fruity or like nail polish remover?

A

acetone is produced by ketogenesis

50
Q
A

Biochemistry (16 decks)

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