Lecture #28: Metabolism--Carbohydrates, Lipids, and Proteins

Question 1

What is catabolic?

Answer 1

reactions break down complex organic compounds, providing energy

Catabolic reactions transfer energy from complex molecules to ATP

Question 2

What is Anabolic?

Answer 2

reactions synthesize complex molecules from small molecules, requiring energy

Anabolic reactions tranfer energy from ATP to complex molecules

Question 3

How do catabolic and anabolic exchange energy?

Answer 3

Exchange of energy require use of ATP

• Each cell has about 1 billion ATP molecules (equals ~2 sec of max contraction for skeletal muscle); rapid ADP-ATP turnover
• Over half of the energy released from ATP is lost as heat.

Question 4

What happens in Energy transfer?

Answer 4

• Energy is found in the bonds between atoms.

• Oxidation is a decrease in the energy content of a
molecule: electrons are lost, plus H+
.

• Reduction is the increase in the energy content of a
molecule: electrons gained, plus H+
.
• Oxidation-reduction reactions are always coupled
within the body.
– sometimes an intermediate molecule is involved in the
electron transfer: coenzyme (NAD + and FADH)

Question 5

What the 4 steps of glucose catabolism?

Answer 5

1. Glycolysis
2. Formation of Acetyle Coenzyme A
3. Krebs cycle
4. Electron Transport Chain (ETC)

Question 6

What is the electron transport chain?

Answer 6

• The ETC is a series of integral membrane protein complexes in the inner mitochondrial
membrane of mitochondria.

• The ETC complexes are capable of oxidation/reduction
(donating/receiving electrons).

• The small amounts of energy released w/ each transfer is
used to make an H+ gradient.

• The H+ gradient is used to form
ATP, a process termed chemiosmosis

Question 7

What is Chemiosmosis?

Answer 7

1. High-energy electrons are
   delivered to ETC complexes.
2. Electrons are passed from
   ETC complex to ETC complex,
   releasing energy with each transfer that is used to
   pumps H+ ions into the space between the inner and outer
   membranes of mitochondria.
3. H+ ions are only permitted to
   move back into the matrix through special H+ channels which use the energy of H+ diffusion to power synthesis
   of ATP from ADP and Pi
   .

Question 8

In the presence of O2, what is broken down from glucose?

Answer 8

CO2,H2O, and captured high-energy electrons

Question 9

What are high energy electrons used for?

Answer 9

Used by the ETC to pump H+ ions which are used to make ATP (via chemiosmosis)

Question 10

What do all 3 (CO2, H20, and ATP) do once they reached the ETC?

Answer 10

Move out of the mitchondria and into the cell’s cytoplasm

Question 11

What does Glycolysis do?

Answer 11

(Break down of glucose)

Glucose to pyruvate/lactate

Question 12

What does glycogenolysis do?

Answer 12

(Break Down of glycogen)

Glycogen to glucose

Question 13

What does Glycogenesis do?

Answer 13

Formation of glycogen

Glucose to glycogen

Question 14

What does Gluconeogenesis do?

Answer 14

Formation of new glucose

–Other substrates to glucose

Question 15

Are polar or non polar and what must they do first before they are transported in the blood stream?

Answer 15

Most lipids are nonpolar and must be combined with protein to be transported in blood

Question 16

What are lipoproteins?

Answer 16

Are spheres containing hundreds of molecules

Are categorized by function and density

Question 17

What are the 4 major classses of lipoproteins?

Answer 17

chylomicrons,

very low-density of protein

lowdensity &high-density lipoproteins

Question 18

What is chylomicrons?

Answer 18

2% protein, 85% TG

– form in intestinal epithelial cells to transport dietary fats to adipose cells

Question 19

What is Very low density lipoprotein?

Answer 19

10% protein, 50% TG

– form in hepatocytes to transport triglycerides to adipose cells

Question 20

What is low density lipoprotein?

Answer 20

25% protein, 50% Chol.)
- bad cholesterol
–> carry blood cholesterol to body cells

Question 21

What is High density lipoprotein?

Answer 21

40% protein, 20% Chol.
- good cholesterol
– carry cholesterol from cells to liver for elimination

Question 22

What is the fate of lipids?

Answer 22

• Oxidized to produce ATP
• Excess stored in adipose tissue or liver

• Synthesize structural or other important molecules
– phospholipids of plasma membranes
– lipoproteins that transport cholesterol
– thromboplastin for blood clotting
– myelin sheaths to speed up nerve conduction
– cholesterol used to synthesize bile salts and steroid
hormones

Question 23

What is lipolysis?

Answer 23

triglycerides are broken down into
glycerol and fatty acids within liver or adipose cells
in the presence of epinephrine, norepinephrine,
cortisol

Question 24

What is lipogenesis?

Answer 24

triglycerides are synthesized from
amino acids or glucose within liver or adipose cells
in the presence of insulin

Question 25

In lipolysis, what do fatty acids undergo?

Answer 25

Beta-oxidation in mitchondria to produce Acetyle CoA and lots of ATP

Question 26

What is ketogenesis?

Answer 26

occurs in liver cells; ketone bodies are used by heart muscle & kidney cortex for ATP production

Question 27

What fuel sources are included for lipogenesis?

Answer 27

1. amino acids, glycolysis metabolites, and ketone bodies for
   fatty acid production from Acetyl-CoA
2. glycolysis metabolites for glycerol production

Question 28

What is the fate of proteins?

Answer 28

• Proteins are broken down into amino acids, which
are transported to the liver

• Amino acids may be
– deaminated to enter Krebs Cycle
– donate amino group to form new amino acids
(transamination)
– used to synthesize new proteins throughout the body

• Excess amino acids may be converted into glucose or
triglycerides (no storage)

• Absorption of AA into body cells is stimulated by
insulin-like growth factors (IGFs) & insulin

Question 29

What happens to metabolism during the absorptive state?

Answer 29

represents the time after a meal
when nutrients enter the blood and need to be
stored.

• The hepatic portal system is used for absorption of
glucose and amino acids. The liver is able to act on
these first.

• Lacteals are used for absorption of dietary fats which
are transported as lipoproteins through the lymphatic
system before reaching general circulation.

Question 30

What is the purpose of the absorptive state?

Answer 30

• Storage of excess fuels occurs in hepatocytes,
adipocytes, skeletal muscle

• Most glucose entering liver cells is converted to
glycogen (10%) or triglycerides (40%)

• Dietary lipids are stored in adipose tissue

Question 31

What happens to amino acids in the absorptive state?

Answer 31

• Amino acids are deaminated to enter Krebs cycle or
are converted to glucose or fatty acids

• Amino acids not taken up by hepatocytes are used by other cells for synthesis of proteins

Question 32

What happens to metabolism after postabsorptive state?

Answer 32

• 4 hours after a meal when absorption of all nutrients
is complete (similar to starvation)

– Maintaining normal blood glucose level (70 to 110 mg/dL
of blood) is major challenge  goal is to put glucose back into the blood or use alternative fuel sources

Question 33

What is the purpose of the postabsorptive state?

Answer 33

• Glucose enters blood from the liver
– glycogenolysis
– gluconeogenesis

• glycerol from adipose tissue
• amino acids and lactic acid from muscle

• Alternative fuel sources are
– fatty acids from adipose fed into Krebs as Acetyl CoA for
most cells*
– oxidation of ketone bodies by heart & kidney

• *Most body tissues switch to utilizing fatty acids,
except brain still prefers glucose