Lecture #28: Metabolism--Carbohydrates, Lipids, and Proteins Flashcards
What is catabolic?
reactions break down complex organic compounds, providing energy
Catabolic reactions transfer energy from complex molecules to ATP
What is Anabolic?
reactions synthesize complex molecules from small molecules, requiring energy
Anabolic reactions tranfer energy from ATP to complex molecules
How do catabolic and anabolic exchange energy?
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.
What happens in Energy transfer?
• 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)
What the 4 steps of glucose catabolism?
- Glycolysis
- Formation of Acetyle Coenzyme A
- Krebs cycle
- Electron Transport Chain (ETC)
What is the electron transport chain?
• 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
What is Chemiosmosis?
- High-energy electrons are
delivered to ETC complexes. - 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. - 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
.
In the presence of O2, what is broken down from glucose?
CO2,H2O, and captured high-energy electrons
What are high energy electrons used for?
Used by the ETC to pump H+ ions which are used to make ATP (via chemiosmosis)
What do all 3 (CO2, H20, and ATP) do once they reached the ETC?
Move out of the mitchondria and into the cell’s cytoplasm
What does Glycolysis do?
(Break down of glucose)
Glucose to pyruvate/lactate
What does glycogenolysis do?
(Break Down of glycogen)
Glycogen to glucose
What does Glycogenesis do?
Formation of glycogen
Glucose to glycogen
What does Gluconeogenesis do?
Formation of new glucose
–Other substrates to glucose
Are polar or non polar and what must they do first before they are transported in the blood stream?
Most lipids are nonpolar and must be combined with protein to be transported in blood
What are lipoproteins?
Are spheres containing hundreds of molecules
Are categorized by function and density
What are the 4 major classses of lipoproteins?
chylomicrons,
very low-density of protein
lowdensity &high-density lipoproteins
What is chylomicrons?
2% protein, 85% TG
– form in intestinal epithelial cells to transport dietary fats to adipose cells
What is Very low density lipoprotein?
10% protein, 50% TG
– form in hepatocytes to transport triglycerides to adipose cells
What is low density lipoprotein?
25% protein, 50% Chol.)
- bad cholesterol
–> carry blood cholesterol to body cells
What is High density lipoprotein?
40% protein, 20% Chol.
- good cholesterol
– carry cholesterol from cells to liver for elimination
What is the fate of lipids?
- 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
What is lipolysis?
triglycerides are broken down into
glycerol and fatty acids within liver or adipose cells
in the presence of epinephrine, norepinephrine,
cortisol
What is lipogenesis?
triglycerides are synthesized from
amino acids or glucose within liver or adipose cells
in the presence of insulin
In lipolysis, what do fatty acids undergo?
Beta-oxidation in mitchondria to produce Acetyle CoA and lots of ATP
What is ketogenesis?
occurs in liver cells; ketone bodies are used by heart muscle & kidney cortex for ATP production
What fuel sources are included for lipogenesis?
- amino acids, glycolysis metabolites, and ketone bodies for
fatty acid production from Acetyl-CoA - glycolysis metabolites for glycerol production
What is the fate of proteins?
• 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
What happens to metabolism during the absorptive state?
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.
What is the purpose of the absorptive state?
• 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
What happens to amino acids in the absorptive state?
• 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
What happens to metabolism after postabsorptive state?
• 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
What is the purpose of the postabsorptive state?
• 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
