Lipid and Amino Acid Metabolism

Question 1

Dietary fat composition

Answer 1

Contains:
1) Triacylglycerols
2) Cholesterol
3) Cholesterol esters
4) Phospholipids
5) Free fatty acids

Question 2

Lipid digestion occurs?

Answer 2

Lipid digestion is minimal in the mouth and stomach; transported to small intestines essentially intact.

1) Emulsification occurs in small intestines.

Question 3

Emulsification

Answer 3

The mixing of two normally immiscible liquids (in this case, fat and water).

Question 4

Lipid digestion: First steps

Answer 4

1) Lipids enter duodenum intact
2) Form micelles from emulsification via bile
3) Broken down by pancreatic lipase, colipase, and cholesterol esterase.

Question 5

What enzymes does the pancreas secrete in the duodenum?

Answer 5

ogether, these enzyme hydrolyze the lipid into 2-monoacylglycerol, free fatty acids, and cholesterol.

1) Pancreatic lipase
2) Colipase
3) Cholesterol esterase

Question 6

Micelle formation

Answer 6

The broken down components of dietary fat (2-monoacylglycerol, free fatty acids, and cholesterol) forms micelles with bile salts

Question 7

Micelle absorption
(Steps)

Answer 7

1) Micelle diffuse to brush boarder of intestinal mucosal cell where they are absorbed.

2) Digested lipids pass through the brush boarder, where they are absorbed into the mucosa, and re-esterified to form triacylglycerols and cholesteryl esters, and packaged with fat-soluble vitamins (ADEK) into chylomicrons.

Question 8

Chylomicron secretion

Answer 8

Chylomicrons leave the mucusal cell via lacteal (the vessels of the lymphatic system) and reenter the blood stream at the thoracic duct.

Question 9

Thoracic duct

Answer 9

collects lymph from the left side of the head and neck, the upper left quadrant of the trunk, the left arm, and the entire lower portion of the trunk and both legs; empties into the left subclavian vein

Question 10

Lipid Mobilization

Answer 10

Lipids are mobilized from adipocytes by hormone-sensitve lipase

Question 11

Adipocytes

Answer 11

specialized fat cells whose cytoplasm contains nothing but triglycerides

Question 12

Lipid transport

Answer 12

Lipids are transported in combination with proteins

Question 13

Lipoproteins

Answer 13

clusters of lipids associated with proteins that serve as transport vehicles for lipids in the lymph and blood.

Types:
1) Chylomicrons
2) VLDL
3) IDL (VLDL remnants)
4) LDL
5) HDL

Question 14

Chylomicrons

Answer 14

A type of lipoprotein; the form in which absorbed fats from the intestines are transported to the circulatory system.

Forms in the Smooth ER of intestine.

Transport dietary triaclyglycerols, cholesterol, and cholesterol esters from intestines to tissues.

Question 15

VLDL

Answer 15

Transports triacylglycerols and fatty acids from liver to tissues.

Question 16

IDL

Answer 16

Picks up cholesterol esters from HDL to become LDL. Picked up by the liver.

Question 17

LDL

Answer 17

Deliver cholesterol to the cell

Question 18

HDL

Answer 18

Picks up cholesterol accumulating in the blood vessels. Delivers cholesterol to the liver and steridogenic tissues. Transfers apolipoproteins to other lipoproteins.

Question 19

Lipoprotein overview

Answer 19

chylomicrons - least dense
HDL - most dense

Question 20

Lipid transport in lipoproteins

Answer 20

Question 21

Apoproteins

Answer 21

Form the protein component of lipoproteins and control interactions between lipoproteins.

Question 22

Cholesterol Metabolism

Answer 22

Can be derived from HDL and LDL but also made de novo.

1) Citrate shuttle brings mitochondrial acetyl-CoA into cytoplasm.

2) Acetyl-CoA + acetacetyl-CoA combine with HMG CoA reductase (RATE LIMITING STEP). NADPH supplies reducing equivalents

Cholesterol plays major role in synthesis of cell membranes, steroid hormones, bile acids, and vitamin D

Question 23

Specialized enzymes for cholesterol transport

Answer 23

1) LCAT (lecithin-cholesterol transferase) catalyzes formation of cholesteryl esters for transport with HDL.

2) CETP catalyzes the transition of IDL to LDL by transferring cholesterol esters from HDL.

Question 24

Fatty Acids

Answer 24

Carboxylic acids with a long chain. Saturated (no double bonds) or Unsaturated.

Question 25

omega fatty acids

Answer 25

type of polyunsaturated fat that is required by the body; the numbering of the carbon omega starts from the methyl end (end fartest from carboxylic end)

Question 26

Fatty Acid Synthesis

Answer 26

Synthesized in cytoplasm from acetyl-CoA transported out of the mitochondria.

Occurs in 5 steps:
1) Activation
2) Bond Formation
3) Reduction
4) Dehydration
5) Second Reduction

These steps are repeated eight times to form palmitic acid, the only fatty acid that humans can synthesize.

Question 27

What causes Fatty Acid Synthesis

Answer 27

The build up of Acetyl-CoA caused it to be used in the fatty acid mechanism

Question 28

How does Acetyl-CoA leave mitochondria for fatty acid synthesis when in abundance?

Answer 28

1) Acetyl-CoA is combined with oxaloacetate to make citrate in mitochondria.

2) Citrate is transported out of mitochondria via citrate shuttle.

3) Once in the cytoplasm, citrate is broken down by citrate lyase into acetyl-CoA and Oxaloacetate.

4) -Acetyl-CoA enters Fatty Acid Metabolism cycle
- Oxaloacetate goes back into mitochondria to start process over.

Question 29

Beta Oxidation

Answer 29

The breakdown of fatty acids in the mitochondria into their component Acetyl-CoAs.

Attacks the beta carbon!

Oxidation, Hydration, Oxidation, Cleavage

Question 30

Regulation of beta oxidation?

Answer 30

Malonyl-CoA can block the carnitine transporter preventing beta oxidation.

Question 31

Even number vs Odd number chains?

Answer 31

Odd number chains can be converted to glucose!

Question 32

Unsaturated fatty acids in beta oxidation?

Answer 32

Unsaturated fatty acids use an isomerase and an additional reductase during cleavage.

Question 33

Protein Digestion

Answer 33

Begins:

1) Stomach - pepsin breaks peptide bonds

2) Small intestines - zymogens secreted from pancreas are activated and continue to cleave polypeptide chains. (protein digestion mostly occurs in small intestine)

3) Dipeptidase and amino-peptidase break down protein further at brush-boarder of small intestines.

Carbon skeletons of amino acids are used for energy, either through gluconeogenesis or ketone body formation. Amino groups are fed into the urea cycle for excretion and the fate of the side chain depends on its chemistry

Question 34

Protein Absorption

Answer 34

Proteins enter into the blood stream by coupling with Na+ down the concentration gradient via facilitated diffusion.

Question 35

Fasting States

Answer 35

In the fasting state, proteins and other alternative energy resources are utilized to provide energy.

Catabolism of cellular proteins only occurs during starvation

Question 36

Ketogenic Amino Acids

Answer 36

Can be converted into ketone bodies to be used as an alternative fuel, usually during periods of starvation.

Question 37

Glucogenic Amino Acids

Answer 37

An amino acid that can be converted to glucose via gluconeogenesis.

Question 38

Which AA are only Ketogenic? Both Keto/Glucogenic?

Answer 38

Only Keto: The AA that start with Letter L

Both Keto/Gluco = PITTT

Question 39

Ketone bodies

Answer 39

brain’s energy source during starvation, when glucose is not available
ketone bodies form during starvation state due to excess acetyl-CoA in the liver
ketolysis regenerates acetyl-CoA for use as an energy source in peripheral tissue
the brain can derive about 2/3 of its energy from ketone bodies during prolonged starvation

Question 40

Urea cycle

Answer 40

The ammonia and basic AA side chains go into urea cycle and yield urea to be excreted from the body, preventing damaging ammonia and completing protein metabolism.