Chapters 12 - 20 Metabolism

Front 1

۞ -----CHO:

Back 1

• Primary metabolic fuel for humans is glucose
o Diet CHO
o Body glycogen stores
o Biosynthesis from non-hexose precursors
• Constant rate of blood glucose balance between;
o Glucose oxidation
o Glucose biosynthesis
o Glucose storage

Front 2

۞ -----CHO:
Pathway of glucose metabolism varies with the type of cell and physiological demand

Back 2

• Liver plays a central role
~ Glucose can be oxidized for energy
~ Glucose can be stored as glycogen
~ Can supply carbons for biosynthesis of fatty acids or amino acids
~ Can release glucose from glycogen
~ Synthesize new glucose

• Other tissues (Adipose tissue, skeletal and heart muscle and brain) respond to changes in glucose by altering their internal usage but do not contribute to whole body homeostasis

~ Skeletal muscle and heart glucose can be completely oxidized or it can be stored as glycogen (for own use only not whole body)

~ Adipose tissue under conditions of need release fatty acids to blood supply.

****** Brain is completely dependent on a continuous glucose supply

Front 3

۞ -----CHO:
Glycolysis – breakdown of glucose for energy; (2 pathways)

Back 3

anaerobic breakdown= 6-8 atp

aerobic = 4-6 ATP

Front 4

۞ -----CHO:

Glycolysis – breakdown of glucose for energy

anaerobic

Back 4

1. anaerobic breakdown of glucose to pyruvate in the cytosol of the cell

a. 1 molecule of glucose to 2 molecules of pyruvate ( 4 molecules of ATP produced and 2 molecules of ATP used: net gain 2 ATP


*****net gain 2 ATP******

Front 5

۞ -----CHO:
Glycolysis – breakdown of glucose for energy
citric acid cycle

Back 5

2. citric acid cycle in mitochondria,is dependent on oxygen, in absence of enough oxygen lactate is formed – can be completely metabolized to CO2 and H2O via the Krebs cycle


****NET GAIN

Front 6

۞ -----CHO:
Glycolysis – breakdown of glucose for energy

krebs cycle

Back 6

3. Total oxidation via Krebs cycle leads to Total net ATP 38 (acetyl CoA = 2 CO2, 3 molecules of NADH; 3 ATP each and 1 molecule FADH; 2 ATP or 11 ATP). One molecule of ATP produced from GTP by substrate-level phosphorylation at succinyl CoA synthetase step) Total is 12 ATP. There are 3 acetyl CoA for each molecule of glucose or 36 ATP plus 2 ATP from step #1.

36 to 38 ATP

Front 7

۞ -----CHO:

Gluconeogenesis

Back 7

– produce glucose from pyruvate, lactate, glycerol and some amino acids.
• This is essentially a reversal of glycolysis, except that not all of the steps were reversible
• Occurs primarily in the liver (90%) and to some extent in the kidney (10%)
• Critical for tissues that depend on constant level of glucose (brain, CNS, RBC)
• Absence of dietary CHO body stores of glycogen depleted in about 18-24 hours, then liver must form new glucose
• Hormonal triggers to synthesize glucose from non-glucose sources

Front 8

۞ -----Cori cycles

Back 8

• Cori cycle – lactate generated from pyruvate is released from muscle to RBC, transported to liver, converted back to pyruvate and can be used to generate glucose and sent back to the muscle

Front 9

۞ -----alanine cycles

Back 9

• Alanine cycle – in the muscle alanine is generated from transamination of pyruvate and released. Liver cells deaminate the alanine to pyruvate, substrate for gluconeogenesis, new glucose sent back to the muscle

Front 10

۞ -----Glycogen Metabolism

Back 10

• Glucose is stored in liver and muscle as glycogen
• Glycogen is a branched chain polymer of glucose
• Liver can store 10% of its weight
• Muscle about 1% of its weight
• Muscle mass is larger than liver so muscle glycogen accounts for twice as much glycogen as contained in the liver
• Stored in postprandial state
• When blood glucose declines first to be degraded - Glycogenolysis

Front 11

۞ -----Glycogenolysis

Back 11

• Liver depleted of glycogen in 18-24 hours
• Glucagon from pancreas promotes glycogen breakdown
• Epinephrine from the adrenal medulla promotes glycogen breakdown in both liver and skeletal muscle
• Glucagon and epinephrine are insulin antagonists
• Muscle uses the glycogen breakdown for its own use
• Liver breaks down the glycogen for use by entire body
• In skeletal muscle (no glucagon receptors)

Front 12

production atp

Back 12

***krebs cycle and ETC= 38-38 ATP

***glycolisis step 1 = 6 to8 ATP

***2 NADH from pyruvate to ACOA = up tp 6

****

Front 13

from one unit of glucose

Back 13

step 1= 6 to 8 atp
step 2 = 6+ atp
step 3= 24 atp