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Physiology > Carbohydrate Metabolism > Flashcards

Carbohydrate Metabolism Flashcards

1
Q

Body’s energy sources

A

Food intake
- carbs, fats, proteins
Metabolism

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2
Q

Why do cells need energy?

A
  • survival/homeostasis
  • growth
  • reproduction
  • repair
  • movement
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3
Q

Adenosine triphosphate

A

Main energy source

  • present in cytoplasm and nucleoplasm of all cells
  • combo of adenine, ribose, and 3 phosphate radicals
  • obtained by CHO, protein, and fat
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4
Q

ATP break down

A

Breaking of phosphate molecule from ATP causes a large energy release, which powers the muscle
- result = adenosine di-phosphate and an unattached phosphate molecule

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5
Q

Why does ATP provide so much energy?

A

Removal of each of the last 2 phosphate radicals liberates 12,000 calories of energy
= high energy bonds

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6
Q

ATP is used for _____, and ADP + Pi is used for _____

A

Energy utilization; energy production

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7
Q

Kinases

A

Adds a phosphate

- ex: glucokinase and hexokinase

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8
Q

Phosphatases

A

Removes a phosphate

- ex: glucose phosphatase

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9
Q

Phosphorylase

A

Spills a compound by adding phosphate

- similar to hydrolysis, but uses phosphate instead of water

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10
Q

_____ of carbs used by the body are used for ATP formation

A

90% or more

- final products of CHO digestion in the gut = fructose, galactose, and glucose (80%)

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11
Q

What is the final common pathway for transport/supply of CHO to all tissues?

A

Glucose
- after absorption from GIT, most of fructose and galactose are rapidly converted to glucose in liver via glucose phosphataes

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12
Q

Fate of glucose in the liver: option 1

A

CHO processed in liver –> glucose formation –> transport out of liver to needy tissues for energy use

  • glucose has to go thru cell membrane
  • then goes thru reactions inside the cell to produce ATP (glycolysis, citric acid cycle)
  • H atoms that are released concurrently yield even more ATP (glycolysis, citric acid cycle)
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13
Q

Option 2

A

CHO processed in liver –> glucose formation –> glycogenesis (energy storage)
- glycogen is simply a large polymer of glucose: liver and muscle glycogen

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14
Q

Option 3

A

Glycogenolysis in the liver

- breakdown of stored glycogen in times of energy needs

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15
Q

Can glucose freely move into the cell?

A

No, its too large

  • requires facilitated diffusion via carrier proteins in the cell membrane
  • glucose transporter (GLUT) on outside and releases it intracellularly
  • glucose moves from area of high concentration to low concentration
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16
Q

Insulin

A

Anabolic hormone secreted by pancreatic beta cells

  • speeds up process of facilitated diffusion = increased efficiency and efficacy
  • rate of CHO utilization by most cells is controlled by rate of insulin secreation
17
Q

What cells do not require insulin for glucose transport?

A

RBC, brain, liver

18
Q

GLUT transporters

A 
GLUT 1 
- RBCs
GLUT 2 (most common)
- liver
- pancreas
- GIT
- kidney
GLUT 3 
- brain
GLUT 4
- muscle
- fat
19
Q

First step after glucose is in the cell

A

It has to be “locked” in the cell

  • phosphorylation via glucokinase (liver) or hexokinase (other tissues)
  • glucose —-> glucokinase + ATP —> glucose 6 phosphate
20
Q

Glycolysis

A

Splitting of glucose to form 2 pyruvic acid molecules

  • occurs via 10 successive chemical reactions inside the cell
  • does not require oxygen, but mostly occurs in the presence of oxygen
  • process starts with glucose to create 2 pyruvic acid molecules = 2 ATP used, 4 ATP made and 4 H atoms are released*
21
Q

Phophofructokinase (PFK)

A

Converts fructose-6-phosphate to fructose-1,6-diphosphate

- ATP inhibits PFK, while ADP activates PFK

22
Q

Step 2

A

Citric acid cycle

  • acetyl CoA is degraded into CO2 and H atoms in the mitochondria
  • requires oxygen
  • for each molecule of glucose, 2 acetyl CoA + H2O molecules enter TCA cycle
23
Q

Citric acid cycle products

A
  • 4 CO2
  • 16 H atoms
  • 2 coenzyme A
  • 2 ATP (1 ATP per acetyl CoA molecule that enters cycle)
24
Q

How many H atoms have been formed after step 2?

A

24

  • most combine with nicotinamide adenine dinucleotide (NAD+) to form NADH+
  • NADH+ will enter into multiple oxidative chemical reactions that form lots of ATP
25
Q

Oxidative phophorylation

A

Oxidation of H atoms released from all previous stages of glucose metabolism

  • forms 90% of ATP that comes from glucose metabolism
  • *this process yields the most energy from glucose metabolism**
  • requires oxygen!
26
Q

Step 3 products

A

Net ATP produced per 2 H atoms = 3 ATP

  • 20 H atoms enter this step
  • 30 ATP are formed from oxidative phosphorylation
27
Q

Recap of ATP formed so far:

A
  • glycolysis = 2 ATP
  • TCA cycle = 2 ATP
  • oxidative phosphorylation = 30 ATP
  • so: 34 ATP *
  • 4 remaining H atoms produce 4 more ATP
  • 38 ATP possible per glucose molecule!!!!*
28
Q

What happens if oxygen is low?

A

Glycolysis can occur without oxygen (anaerobic glycolysis)

- most of pyruvic acid is converted to lactic acid, to provide energy for several minutes

29
Q

Anaerobic glycolysis

A

Produces net gain of 2 ATP
- when oxygen becomes available again, lactic acid converts back to pyruvic acid and NADH+
= formation of ATP and re-formation of glucose

30
Q

Pentose phosphate pathway

A

Alternative pathway for glucose

  • responsible for 30% of glucose breakdown in liver and more in fat cells
  • does not require same enzymes as TCA cycle
  • cyclical process in which one molecule of glucose is metabolized per revolution of cycle
31
Q

Pentose phosphate products

A

Yields:

  • CO2
  • H atoms
  • 5 carbon sugar, D-ribulose
32
Q

Glycogenesis

A

Glucose is stored in liver and muscle as glycogen
- any excess glucose after a meal is converted to glycogen
- any monosaccharide, including glucose, can enter into reactions that lead to glycogen formation
= glycogen is a polymer of glucose

33
Q

Glycogenolysis

A

Breakdown of stored glycogen to re-form glucose in the cells

  • occurs via phosphorylation, catalyzed by enzyme phosphorylase
  • splits glucose molecules away from glycogen polymer
  • phosphorylase enzyme inactive at rest, so glycogen remains stored
34
Q

What activates phosphorylase?

A

Epinephrine
- sympathetic nervous system response
Glucagon
- triggered by hypoglycemia

Physiology (33 decks)

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