Energy Storage and use: Metabolism of Carbs, fats, and proteins

Question 1

What is the largest substrate storage in the body?

Answer 1

Lipids.

Question 2

Types of Lipids. 3. What do each do.

Answer 2

1. Simple Lipids: Acylglycerol

• ( Unsaturated, Saturated)
  
  • Formed from one glycerol and free fatty acids
• Mostly participate in energy production by entering into the Beta-oxidation cycle to produce acetyl-CoA, and ultimately, ATP

2. Complex Lipids:

• Phospholipids
• glycolipids
• lipoproteins
• important role in cell functions as they constitute the major part of the cell barrier and are involved in signal transduction and lipid transport

3. Precursors and derived lipids.

• Hormones
• Ketone bodies
• Glycerol
• Steroids
  *

Question 3

Fatty acids are stored as what?

Answer 3

Triacylglycerol

Question 4

During fasting, what do fatty acids do

Answer 4

Enter Beta oxidation to produce acetyl Co-A

Question 5

What is glycogen? What is it composed of?

Answer 5

Branched chain molecule found in animal cells. Similar to startch. Is composed of glucose molecules joined together to form polymere.

Question 7

What is the first stage of fat breakdown? What is this? What happens to glycerol after this? What happens to fatty acids during this?

Answer 7

Lypolysis. Seperation of fatty acids from glycerol molecule. Enters glycolysis pathway and then procedes to krebs cycle and oxidative phosphorylation. Fatty acids are catabolized to acetyl CoA by Beta Oxidation (mitochondrial Matrix)

Question 8

Everytime fatty acids are converted to Acetyl CoA what happens?

Answer 8

Coenzymes are reduced to generate one NADH+H+ and one FADH2. The acetyl CoA then enters Kreb cycle and oxidative phosphorylation.

Question 9

When fats are broken down for energy, what is waste product?

Answer 9

Ketones. Synthesized from Acetyl CoA

Question 10

What is the significance of ketones? Why does this help?

Answer 10

Ketones can be utilized by the nervous system as partial alternative to glucose. Helps conserve body’s supply of glucose if energy becomes limited.

Question 11

What is synthesis of fat from nutrients?

Answer 11

Lipogenesis.

Question 12

Where does digestion of Triaglycerides occur? Facilatated by what?

Answer 12

Duodenum.
•Bile salts (emulsification)
•Alkaline medium (pancreatic juice)

Question 13

In Fed state, adipose tissue does what

Answer 13

converts glucose via pyruvate and acetyl–CoA into fatty acids which are stored as fat globules of TG

Question 14

In humans, FA synthesis occurs where? Adipocytes store FA’s as?

Answer 14

•FA synthesis occurs in the liver – adipocytes store FAs arriving from liver as VLDL and directly from intestine

Question 15

Explain Lipid Catabolism.

Answer 15

Two pathways: Broken into glycerol and 3FFA

1. Glycerol heads towards fast glycolytic pathway to form one glycerole 3 phosphate via glycerole kinase.
2. 3 FFA enter beta-oxidation to form Acetyl CoA and later on ATP

Question 16

What is one of the major mechanisms leading to fat storage?

Answer 16

The reversal of Acetyl-coA into fatty acids

Question 17

In fasting state, what happens to TG in adipose tissue? This process is regulated by what?

Answer 17

TGs are hydrolysed by lipases to release free Fas, and are delivered through bloodstream to skeletal muscle and heart.
•Adrenaline which stimulates activity of TG lipase
•Insulin which inhibits the activity of TG lipase

Question 18

Walk through catabolism of triglycerol.

Answer 18

. First the TAG is broken by TAG lipase into one DAG and one free fatty acid. In the next step, the DAG is catabolized by the DAG lipase to form one MAG and one free fatty acid, and the last step will release with the action of the MAG lipase, the last free fatty acid and one glycerol.

Question 19

Walk through the action of hormones on lypolysis

Answer 19

when glucagon binds with it cell receptor it triggers the activation of the adenylyl cyclase with the addition of one ATP that in turn will activate the cAMP with the result of triggering lipase activity. These enzymes will then catabolize the TAG into FFA and one glycerol. Note that insulin will block the activity of the lipases.

Question 20

During Lipid metabolism, what do the liver and muscle do? What are the two major fates of this fatty acid?

Answer 20

take up non-esterified fatty acids from plasma.

1. oxidation (energy source for liver –production of ketone bodies; for muscle – production of Acetyl-CoA)
2. triacylglycerol formation (local store in the liver and muscle for energy needs)

Question 21

Once in the cell cytosol, fatty acid forms fatty acetyl CoA and what two paths can it take? (during Fasting and then during post meal)

Answer 21

1. in the fasting state or energy deficit, through the action of CPT-1 the fatty acyl CoA enters into the b-oxidation cycle to form acetyl-CoA and ketone bodies.
2. in postprandial state or energy surplus, the fatty acyl CoA forms new triacylglycerol that will be stored in the cel

Question 22

What effect does glucacon have on fatty acid metabolism? What about insulin?

Answer 22

The glucagon promotes fatty acyl CoA oxidation by activation of CPT-1 while Insulin will promote glucose as prime substrate leading to a higher formation of Malonyl-CoA, an intermediate that inhibits CPT-1

Question 23

Explain mechanism to form fatty Acetyl-CoA

Answer 23

Carnitine transports long-chain acyl groups from fatty acids into the mitochondrial matrix, so they can be broken down through β-oxidation to acetyl CoA to obtain usable energy via the citric acid cycle. It requires to shuttle an acyl and carnitine from the matrix to the cytosol under the action of the CTP I and II.

Question 24

What happens when the fatty acid is a long chain?

Answer 24

The long chain fatty acid must pass through an additional biochemical step before being shuttle to the mitochondria. The fatty acids longer than 20 carbon enter into the peroxisomes to form two components; the acetylcarnitine and octanoylcarnitine that will be released in the cytosol and picked up by the mitochondria. So, the structure of fatty acids play a role in the cascade of biochemical steps that leads to the formation of ATP

Question 25

Beta oxidation breaks fats down into what? and these are used for what?

Answer 25

–Acetyl coenzyme A –> Krebs Cycle
–FADH2 –> Oxidative Phosphorylation
–NADH –> Oxidative Phosphorylation

Question 26

Steps of beta oxidation.

Answer 26

1. The first reaction is driven by the acyl-CoA dehydrogenase to produce beta-enoyl-CoA. It oxidizes simple Carbon bond into double bond, reason why it is called beta-oxidation
2. The second biochemical reaction involves enoyl-CoA hydratase that forms a b-hydroxy product.
3. The third step of the cycle oxidizes a secondary alcohol to form a ketone and produce a NADH
4. The final biochemical reaction of the cycle uses another co-Enzyme A through its reaction with the thiolase that produces one acetyl-CoA for the Kreb cycle and releases one Acyl-CoA for the next b-oxidation cycl

Question 27

How much ATP is yielded from beta oxidation?

Answer 27

14

Question 28

What is the most abundent fatty acid in our diets? How much ATP is yielded in the oxidation of this?

Answer 28

Palmatic Acid. 107.

Question 29

Function of adipocytes.

Answer 29

fat cell makes up and stores the fat in postprandial state and breaks it down and releases it in fasting state as well as during and after exercise

Question 30

What is proteolysis?

Answer 30

Proteins broken down into amino acids.

Question 31

After proteolysis, what occurs? What happens to the substance that is produced?

Answer 31

Amino acids are then deaminated (amino group removed). This process produces amonia NH3 and is toxic. Carried by the bloodstream to the liver where is converted to Urea.

Question 32

After amino group is removed from protein, what occurs to the remainder of the molecule?

Answer 32

Either converted to pyruvate, acetyl CoA(which goes to the krebs cycle) or converted to intermediate which directly enters the krebs cycle.

Question 33

Which tissue provide glucose for other tissues?

Answer 33

Liver and kidneys

Question 34

What is gluconeogenesis? What are the sources? Occurs where?

Answer 34

Formation of new glucose.Glycerol(produced by breaking down triglycerides), lactate, amino acids. Occurs in liver

Question 35

What is glycogenesis?

Answer 35

Covalent bond formation between glucose molecules. When glucose is abundent in supply, stored as glycogen.

Question 36

In cytosol, how is fatty acid produced? In Smooth endoplasmic reticulum how is trigliceride produced?

Answer 36

• Acetyl CoA+Acetyl CoA+………—>Fatty acid

•Glycerol + 3 Fatty Acids à Triglyceride

Question 37

Where is cholesterol synthesized from?

Answer 37

Most comes from diet, some synthesized in smooth ER from acetyl CoA.

Question 38

What is the role of creatine?

Answer 38

Acts as a buffer store of ATP.

1. during heavy activity phosphocreatine is converted to creatine and ATP
2. during recovery period the reverse reaction generates phosphocreatine