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MCAT Biochemistry > Glucose, Fatty Acids, and Metabolism > Flashcards

Glucose, Fatty Acids, and Metabolism Flashcards

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MCAT flashcards
1
Q

How does ATP store energy?

A

High-energy phosphate bonds

ATP powers most reactions that require a driving force in the cells including muscle contraction and the activity of the Na+/K+ pump

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2
Q

How does NADH store energy?

A

High-energy electrons of the hydride ion

Primarily produced during glycolysis and citric acid cycle

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3
Q

Where are carbohydrates primarily stored in the body?

A

In the muscle and the liver as glycogen

Storage process is called glycogenesis
Glucose -> glycogen
Breakdown process is called glycogenolysis
Glycogen -> glucose
Breakdown of glucose is called glycolysis
Glucose -> ATP

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4
Q

Where are lipids primarily stored in the body?

A

Primarily stored in adipocytes (fat cells) in form of triglycerides

Breakdown of fatty acids is called beta-oxidation
Fatty acid -> energy, Acetyl-CoA

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5
Q

Glycolysis

A

Series of reactions that converts 6-C glucose molecule into two 3-C molecules of pyruvate
Most common chemical pathway for this process
Can occur with or without presence of oxygen
Occurs in cytosol of cells
First half adds two phosphate groups from 2 ATP to glucose and split in half, second half converts two 3-C molecules into pyruvate

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6
Q

Describes the steps of glycolysis in the energy input half.

A
  1. Glucose converted to Glucose 6-phosphate with addition of ATP
  2. Converted to Fructose 6-phosphate
  3. Converted to Fructose 1,6-bisphosphate with addition of ATP
  4. Split to two Glyceraldehyde 3-phosphates
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7
Q

How does insulin affect glycolysis?

A

Increases the rate of glycolysis

Insulin is released when there is an excess of glucose in the blood

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8
Q

How does glucagon affect glycolysis?

A

Glucagon inhibits glycolysis and will slow it down

Glucagon is released when there is a scarcity of glucose in the blood

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9
Q

Describe the steps of glycolysis in the energy output half.

A
  1. Each Glyceraldehyde 3-phosphate is converted to 1,3-Bisphosphoglycerate w/ production of 1 NADH from NAD+
  2. Converted to 3-Phosphoglycerate w/ production of 1 ATP
  3. Converted to 2-Phosphoglycerate
  4. Converted to Phosphoenolpyruvate
  5. Converted to pyruvate w/ production of 1 ATP
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10
Q

What is the net energy product of glycolysis?

A

2 ATP and 2 NADH

2 ATP are used, 4 ATP are produced and 2 NADH are produced

Called substrate-level phosphorylation for ATP production here

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11
Q

Substrate-level phosphorylation

A

Phosphate group being donated to ADP is initially attached to another molecule and is transferred to ADP by a kinase enzyme

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12
Q

What monosaccharides feed into glycolysis in addition to glucose?

A

Fructose and galactose can enter glycolysis as an intermediate of the 6-C phase

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13
Q

Fermentation

A

Metabolism in the absence of Oxygen
Includes glycolysis as well as the reduction of pyruvate to ethanol or lactic acid and the oxidation of NADH back to NAD+ (for use in glycolysis)

Lactic acid, ethanol, or CO2 dispelled from cell as waste product

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14
Q

Cori Cycle

A

Lactic acid expelled from cells is transported through the blood to the liver
In liver, lactic acid is oxidized back to pyruvate
Pyruvate is converted to glucose and can be sent back to other tissues to help produce ATP

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15
Q

Pentose Phosphate Pathway (PPP)

A

Alternative pathway to glycolysis
Diverges from glycolysis after glucose is phosphorylated and rejoins at glyceraldehyde-3-phosphate (PGAL or G3P)
Main purpose is to create NADPH and 5-C sugars (ribose) to build DNA and RNA
Ensures the oxidative state of all cells remains in balance, greatest levels of PPP in liver & fat cells

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16
Q

How is the PPP regulated?

A

By levels of NADPH

High levels of NADPH inhibit first step in oxidative half of PPP

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17
Q

Gluconeogenesis

A

Synthesis of glucose from non-carbohydrate products, such as proteins and lactic acid

Only liver cells can perform this process

Glucose is released for use by other cells

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18
Q

Glycogen

A

Polymer of glucose molecules linked by alpha-1,4’ glycosidic bonds

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19
Q

Glycogenesis

A

Production of glycogen from glucose

Primary substrate: glucose 6-phosphate, product of first step of glycolysis

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20
Q

Glycogenolysis

A

Breakdown of glycogen to glucose
Uses UTP, equiv. To ATP
Adds inorganic phosphate to each alpha-1,4’ bound glucose

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21
Q

What processes help to maintain blood-glucose levels many hours after a meal?

A

Gluconeogenesis and Glycogenolysis

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22
Q

Gluconeogenesis

A

Similar to glycolysis run in reverse (enzymes catalyze forward and reverse reactions, except when deltaG is very large)
Substrates: molecule must have a 3-C backbone
Glycerol, lactic acid, some amino acids
Glucagon increases gluconeogenesis

23
Q

Which processes will increase when blood-glucose is low?

A

As blood-glucose drops, glucagon will be released, which will stimulate processes that increase free glucose
These processes include gluconeogenesis and glycogenolysis
Considered more catabolic processes, because breaks down molecules and uses to power ATP synthesis

24
Q

Do saturated or unsaturated fats have a higher reducing potential? How about higher energy storage?

A

Saturated fats have a higher reducing potential, as they have more electrons to reduce other compounds. Unsaturated fats have two less electrons for every double bond present, and therefore they also store less energy.

25
Q

How can fatty acids be used in the body?

A

They can be broken down into acetyl-CoA in beta-oxidation

In liver, hey can be converted into a ketone body for ketogenesis- prolonged fast after body cannot synthesize enough glucose from gluconeogenesis

26
Q

Describe what happens to fatty acids in the initial fasting state

A

Fatty acids are freed from adipocytes as triglycerides by enzyme lipase into bloodstream via lipoproteins
Fatty acids diffuse through cell membrane into mitochondria for beta-oxidation where they are oxidized two carbons at a time

27
Q

Beta-Oxidation

A

Fatty acids are first converted into acyl-CoA with 1 ATP in outer membrane of mitochondria
Acyl-CoA cleaved two carbons at a time to acetyl-CoA in mitochondrial matrix
- produces FADH2 and NADH for every acetyl-CoA
Acetyl-CoA -> Citric Acid Cycle

28
Q

What are the Four steps of Beta-Oxidation?

A
  1. Oxidation
  2. Hydration
  3. Oxidation
  4. Thiolysis
    OHOT
29
Q

What is the yield of Beta-Oxidation?

A

108 ATP / 16-C fatty acid

For odd fatty acids, last 3-C molecule can be used as substrate for gluconeogenesis

30
Q

Ketone Bodies

A

Produced by ketogenesis from fatty acids when in prolonged fast

Three primary in humans: acetone, acetoacetic acid, beta-hydroxybutyrate
- carbonyl allows dissolution in blood stream
Spare glucose for the brain and RBCs with alternative source of energy

31
Q

Ketogenesis

A

Fatty acid eneters liver and is processed into ketone body that can be sent to other organs
Ketone bodies are not substrates for gluconeogenesis

Ketone bodies can be converted back into acetyl-CoA and fed into Citric acid cycle for synthesis of ATP

32
Q

Where are lipoproteins primarily produced?

A

Liver, intestines, and adipocytes- expelled via exocytosis

33
Q

How do intestine cells transport lipids to the liver?

A

Intestines produce chylomicrons (higher lipid to protein ratio) which carry lipids to liver

Liver repackages chylomicrons as VLDL and HDL

34
Q

What do Very low density lipoproteins carry (VLDL)?

A

Triglycerides, phospholipids, cholesterol from liver to other parts of the body such as muscle and adipocytes

35
Q

What do high density lipoproteins (HDL) carry?

A

Pick up stray fatty acids and triglycerides from periphery and bring them to the liver

36
Q

How can the liver generate fatty acids out of non-lipids?

A

Excess of sugar and carbohydrates after a meal can produce an excess of acetyl-CoA
With insulin, acetyl-CoA can be converted into fatty acids in cytosol

37
Q

Lipase (Hormone sensitive and intestinal)

A

HS: Enzyme that hydrolyzes triglycerides and releases free fatty acids into the bloodstream

Intestinal: Also an enzyme in intestine that breaks down triglycerides in intestines

Fatty acids are then taken around body to various tissues to use for beta-oxidation

38
Q

Is there a storage form of amino acids analogous to glycogen or triglycerides?

A

Amino acids have no storage form and are either present in proteins or as a pool of amino acids

39
Q

How does protein breakdown begin in the small intestine?

A

Trypsin, chymotrypsin, and carboxypeptidase cleave proteins into mono-, di-, or tri-amino acids by hydrolysis
Small amino acid chains are cleaved by enzymes of the brush border and then absorbed and released into circulation by intestinal epithelial cells

40
Q

How does amino acid breakdown begin?

A

Removal of nitrogen group, producing ammonia and a carbon chain
Ammonia -> urea cycle to become urea (excreted in urine)
Carbon chain -> substrate for various stages of CAC

41
Q

What are uses of amino acids besides synthesis of proteins?

A

Substrates for gluconeogenesis, ketogenesis
Form neurotransmitters, hormones, heme, and other amino acids
11/20 amino acids can be formed from other amino acids, 9 are essential and must be obtained from diet

42
Q

What processes occur when your intestine is your main store of glucose?

A

Blood-glucose levels are high so insulin is released from pancreas
Glycolysis occurs in all tissues
Glycogenesis occurs in liver and muscle cells to store glycogen
Extra glucose converted to fatty acids and stored as triglycerides in adipocytes (fatty acid synthesis)

43
Q

What processes occur when your liver is your main store of glucose (a few hours after eating)?

A

Blood-glucose levels start to drop and the pancreas releases glucagon
Glucagon stimulates glycogenolysis in liver and muscle cells, gluconeogenesis in liver, fatty acid release in adipocytes, and beta-oxidation in all cells

44
Q

In late starvation, what processes occur?

A

Ketogenesis begins in the liver, which is the production of ketone bodies which can be produced by any molecule that can be converted to acetyl-CoA. Beta-ox, glycogenolysis also occur
Ketone bodies can be used by all organs and tissues except for RBCs.
Gluconeogenesis produces glucose primarily for RBCs at this point.

45
Q

How do stress responses affect metabolism?

A

Epinephrine and Cortisol are both released by stress response
Epinephrine has a quick response and promotes glycogenolysis
Cortisol is later and more sustained and promotes gluconeogenesis

46
Q

Where do the hormones insulin, epinephrine, glucagon, and cortisol have receptors in the cell?

A

Insulin, epinephrine, and glucagon are hydrophilic hormones and therefore have receptors on outside of membrane
Cortisol is a glucocorticoid, is hydrophobic and therefore has receptors in the nucleus

47
Q

Through what enzymatic mechanisms do insulin and glucagon exert their effects?

A

Usually via reversible phosphorylation, but can use regulation of synthesis of enzymes, or use of control enzymes

48
Q

What is an example of a Control Enzyme and how does it work?

A

Phosphofructokinase-2 is activated by insulin and catalyzes the creation of a molecule that is a potent activator of glycolysis.
Therefore insulin activates phosphofructokinase-2, phosphofructokinase-2 catalyzes creation of a molecule, the molecule then activates glycolysis

49
Q

What is an example of regulating the synthesis of enzymes?

A

Cortisol and glucagon regulate glucose 6-phosphatease, the last enzyme of gluconeogenesis, by increasing its synthesis

50
Q

What are four ways hormones control metabolic enzymes?

A
  1. Phosphorylation
  2. Regulation of the synthesis of enzymes
  3. Use of control enzymes
  4. Local metabolic effects
51
Q

Name the anabolic processes that occur during a fed state:

A

Glycolysis
Glycogenesis
Fatty acid synthesis

52
Q

Name the catabolic processes that occur a few hours after eating:

A

Gluconeogenesis
Glycogenolysis
Beta-Oxidation

Prolonged hunger- then ketogenesis

53
Q

Which processes will increase when blood-glucose is high?

A

As blood-glucose levels raise, insulin is released to use the glucose and processes that reduce free glucose are stimulated.
These processes include glycolysis and glycogenesis
These processes are more anabolic (uses molecules to synthesize glycogen, fatty acids, nucleic acids, steroids)

54
Q

NADPH

A

Used in various synthetic or anabolic functions of the body (making cholesterol and fatty acids)

Acts as antioxidant

MCAT Biochemistry (11 decks)

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