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Flashcards in Carbohydrate Metabolism Deck (34)
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1

Body's energy sources

Food intake
- carbs, fats, proteins
Metabolism

2

Why do cells need energy?

- survival/homeostasis
- growth
- reproduction
- repair
- movement

3

Adenosine triphosphate

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

4

ATP break down

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

5

Why does ATP provide so much energy?

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

6

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

Energy utilization; energy production

7

Kinases

Adds a phosphate
- ex: glucokinase and hexokinase

8

Phosphatases

Removes a phosphate
- ex: glucose phosphatase

9

Phosphorylase

Spills a compound by adding phosphate
- similar to hydrolysis, but uses phosphate instead of water

10

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

90% or more
- final products of CHO digestion in the gut = fructose, galactose, and glucose (80%)

11

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

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

12

Fate of glucose in the liver: option 1

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)

13

Option 2

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

14

Option 3

Glycogenolysis in the liver
- breakdown of stored glycogen in times of energy needs

15

Can glucose freely move into the cell?

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

16

Insulin

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

What cells do not require insulin for glucose transport?

RBC, brain, liver

18

GLUT transporters

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

19

First step after glucose is in the cell

It has to be "locked" in the cell
- phosphorylation via glucokinase (liver) or hexokinase (other tissues)
- glucose ----> glucokinase + ATP ---> glucose 6 phosphate

20

Glycolysis

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

Phophofructokinase (PFK)

Converts fructose-6-phosphate to fructose-1,6-diphosphate
- ATP inhibits PFK, while ADP activates PFK

22

Step 2

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

Citric acid cycle products

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

24

How many H atoms have been formed after step 2?

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

Oxidative phophorylation

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

Step 3 products

Net ATP produced per 2 H atoms = 3 ATP
- 20 H atoms enter this step
- 30 ATP are formed from oxidative phosphorylation

27

Recap of ATP formed so far:

- 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

What happens if oxygen is low?

Glycolysis can occur without oxygen (anaerobic glycolysis)
- most of pyruvic acid is converted to lactic acid, to provide energy for several minutes

29

Anaerobic glycolysis

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

Pentose phosphate pathway

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