Lecture 14 - Energy Balance and Metabolism I Flashcards
___ is a link between energy production and utilization.
ATP
___ becomes the final common pathway for the transport of almost all the carbohydrates to the tissue cells.
Note that galactose, glucose, and fructose (all hexoses) are all ___.
Note that each can be ___.
Note that galactose and glucose can be converted to __-_-___ and enter the glycolytic pathway.
Glucose
Interconvertible
Phosphorylated
Fructose-6-phosphate
Uptake of Glucose
- Via active sodium-glucose co-transport: GI TRACT AND RENAL
- Active transport of sodium provides energy for absorbing glucose against a concentration gradient.
- Via facilitated transport: TISSUES
- Only transported from higher to lower concentrations.
- Presence of insulin increases glucose transport x10.
- Phosphorylation of glucose prevents diffusion out of cell.
- Phosphorylation can be reversed in liver, renal, and intestinal cells.
role of enzymes
- Glucokinase(transfers phosphate from ATP)
- Phosphatase (removes phosphate)
- Phosphorylase (catalyzes production of glucose-1-phosphate from glycogen)
Factors that can activate phosphorylase:
- Epinephrine (from adrenal medulla)
* Glucagon (from alpha cells of pancreas)
Effects of phosphorylase
- Promotes conversion of glycogen to glucose.
* Glucose can then be released into blood.
Know end products of glycolysis
- Pyruvic acid (2 molecules)
- Hydrogens (4) Release is catalyzed by a dehydrogenase
- ATP (2 molecules) Note that 2 molecules were needed at the beginning of the pathway and that a total of 4 ATPs were produced in the pathway, giving a net gain of 2 ATPs.
Pyruvic Acid → Acetyl-CoA •Know end products of this conversion:
- Acetyl-CoA (2 molecules)
- Hydrogens (4) Release is catalyzed by a dehydrogenase
- Carbon Dioxide (2 molecules)
Citric Acid Cycle
Where does it occur and what are the end products?
In the mitochondrial matrix!
- Hydrogens (8x2 = 16) Release is catalyzed by a dehydrogenase
- ATP (2 molecules)
- Carbon Dioxide (2x2 = 4 molecules)
Net reaction (excluding glycolysis):
2 Acetyl-CoA + 6H2O + 2ADP →
4 CO2+ 16 H + 2 CoA + 2ATP
Oxidative Phosphorylation
Occurs on mitochondrial cristae
Fate of hydrogen atoms from previous cycles: •removed in pairs •One member of each pair becomes a hydrogen ion •The other member of a pair combines with NAD+ → NADH
Fate of electrons removed from hydrogen ions: •Enter electron transport chain
Major components of the electron transport chain:
- Flavoprotein
- Several iron sulfide proteins
- Ubiquinone (Q)
- Cytochrome A3 (cytochrome oxidase) •Located on inner membrane •Can give up two electrons to oxygen
Number of ATPs formed per glucose molecule;
Maximum number of ATPs per glucose molecule
- 2 ATPs from glycolysis
- 2 ATPs from citric acid cycle
- 34 ATPs from oxidative phosphorylation
=38
66% efficiency
Pentose Phosphate Pathway
cyclical pathway in which one molecule of glucose is metabolized for each revolution of the cycle
- For every six molecules of glucose that enter the pathway, five molecules of glucose are resynthesized
- mostly used for the synthesis of fats and other substances.
- Hydrogens generated from this pathway are bound to NADP+ instead of NAD+
Glucose is preferentially stored as ___ until the storage cells (___ and ___) are saturated.
Excess glucose is then converted into ___ (liver and fat cells) and stored in fat cells.
glycogen
liver, muscle
fat
Triglycerides (Neutral Fats)
Triglyceride absorption from intestinal lumen: •Most triglycerides are digested into monoglycerides and fatty acids •Intestinal epithelial cells resynthesize these into triglycerides that enter the lymph as chylomicrons. •Apoprotein B is adsorbed to the chylomicron surfaces.
Chylomicrons are removed from the blood by various tissues, especially: ___ which synthesize lipoprotein lipase.
- Adipose tissue
- Skeletal muscle
- Heart
Lipase
Is transported to surface of capillary epithelial cells
Hydrolyzes chylomicron triglycerides, releasing fatty acids and glycerol.
Chylomicrons are transported to the venous system via the ___.
thoracic duct
Fatty acids can be used for ___ or again ___ into ___.
fuel, synthesized into triglycerides
Conditions that increase utilization of fat for energy:
starvation or diabetes mellitus
Types of lipoproteins:
Synthesized by intestinal cells:
•Chylomicrons
Synthesized by liver: •Very low density lipoproteins (VLDLs) •Intermediate density lipoproteins (IDLs) •Low density lipoproteins (LDLs) •High density lipoproteins (HDLs)
Lipoproteins transport what in the blood?
lipids
Very Low Density Lipoproteins:
- High concentrations of triglycerides and moderate amounts of cholesterol and phospholipids.
- Transport lipids mainly from liver to adipose tissue.
Low Density Lipoproteins:
•High concentration of cholesterol and moderate concentration of phospholipids
High Density Lipoproteins:
•High concentration of proteins and low concentration of cholesterol and fatty acids.
Triglycerides as an Energy Source
- Triglycerides are hydrolyzed into fatty acids and glycerol, which are transported in blood to tissues.
- Almost all cells except brain cells and red blood cells use fatty acids for energy.
- Glycerol is converted to glycerol-3-phosphate.
- Fatty acids are converted to acetyl-CoA in the mitochondria
Products from beta-oxidation of one molecule of stearic acid
- 9 acetyl-CoA molecules
* 146 molecules of ATP
Degradation of fatty acids in the liver releases many acetyl-CoAs not used for metabolism:
- 2 acetyl -CoAs condense to form acetoacetic acid
* Some of the acetoacetic acid is converted to: •Β-hydroxybutyricacid •acetone
Acetoacetic acid is a __.
Acetoacetic acid, β- hydroxybutyric acid, and acetone are __ __.
keto acid
ketone bodies
If concentrations of ketone bodies increase above normal in blood:
Ketosis occurs
Conditions favoring ketosis:
- Starvation
- Diabetes
- Diet composed almost entirely of fat
Ketone bodies that diffuse back into cells are converted into ___.
acetyl-CoA
Synthesis of fatty acids is a 2-step process that is important because…
•More fat can be stored in tissues than carbohydrates. •Weight-for-weight, fat contains about 2.5x the energy of carbohydrates
Development of Atherosclerotic Plaques
- Damage to vascular epithelium
- circulating monocytes and LDLs accumulation at injury site
- Monocytes cross endo to enter intima and become macrophages
- Macrophages ingest Lipoproteins, become foam cells and form visible fatty streaks
- fatty streaks grow larger and coalesce
- surrounding fibrous and smooth muscle tissues proliferate and form larger plaques
Development of Atherosclerotic Plaques
- Damage to vascular epithelium
- circulating monocytes and LDLs accumulation at injury site
- Monocytes cross endo to enter intima and become macrophages
- Macrophages ingest Lipoproteins, become foam cells and form visible fatty streaks
- fatty streaks grow larger and coalesce
- surrounding fibrous and smooth muscle tissues proliferate and form larger plaques
Large plaques can…
- May occlude lumen
- May become sclerotic or fibrotic
- May become calcified
What are the basic causes of atherosclerosis?
- Increased LDLs
* Familial hypercholesterolemia (defective LDL receptors)
