Biochemistry Flashcards
What does each cycle of beta oxidation yield?
1 Acetyl-CoA
1 FADH2
1 NADH + H+
1 fatty acyl-CoA (shortened by 2 carbon atoms)
Where does beta oxidation occur and what is it?
Mitochondrial matrix
Cycle of reactions
Four steps of each cycle
How many oxidation cycles occur for an even numbered saturated fat?
The fat is C2n
n-1 cycles is required for complete catalysis
What are the products of the breakdown of a C14 fatty acid?
7 acetyl-CoA
6 FADH2
6 NADH + 6H+
When and where are ketone bodies formed?
Under fasting conditions (hypoglycaemia)
In liver mitochondria
What are ketone bodies formed from?
Acetyl-CoA from beta oxidation
Where do the ketone bodies go after formation?
Diffuse into blood and move to peripheral tissues
Where are ketone bodies important for metabolism?
Brain
Heart muscle
Renal cortex
What happens to ketone bodies once they reach peripheral tissues?
Converted back to acetyl-CoA which enters the TCA cycle
What do ketone bodies do in the brain?
Used in energy production
Used in neurotransmitter synthesis
What happens if ketone bodies are allowed to accumulate under extreme starvation?
Ketoacidosis
Are ketone bodies toxic to peripheral tissues which prefer glucose?
No
What process drives lipogenesis and where does it occur?
Fatty acid synthesis in the liver
What is the role of acetyl-CoA carboxylase?
Converts acetyl-CoA to malonyl-CoA
What is the role of malonyl-CoA?
A major fatty acid synthesis precursor
What is acetyl-CoA carboxylase activity regulated by?
Nutrient and energy status
Where in the cell does fatty acid synthesis occur?
Cytoplasm
What cofactors are involved in fatty acid synthesis and degradation?
Synthesis - NADPH (reductant)
Degradation - NAD+, FAD (oxidant)
Do fatty acid synthesis and degradation have length constraints?
Synthesis - Yes (stops at C16)
Degradation - No
What effect does insulin have on acetyl-CoA carboxylase?
It signals the fed state
Stimulates storage of fuels and synthesis or proteins
What do glucagon and adrenaline do?
Glucagon signals the starved state
Adrenaline signals requirement for energy
Glycogen stores are mobilised
What does citrate do?
Stimulates acetyl-CoA carboxylase allosterically
It’s levels are high when acetyl-CoA and ATP are abundant
What does palmitoyl-CoA do?
Antagonises acetyl-CoA carboxylase
It is abundant when fatty acids are in excess
Is fatty acid synthesis induced during glucagon-mediated glucose release?
No
What is the donor molecule of carbon atoms to a growing fatty acid?
Malonyl-CoA
Does the phrase “citrate stimulates allosterically” mean that citrate helps insulin to stimulate the catalytic activity of acetyl-CoA carboxylase?
No
What is the alternate name for the urea cycle?
Ornithine cycle
Where do the nitrogens come from to synthesis urea?
One from free ammonium
One from aspartic acid
Does the removal of the amino group only occur in liver cells?
No
Is free ammonium toxic?
Yes
Are amino groups from amino acids directly transferred to carbamoylphosphate?
No
What does gluconeogenesis require?
Four liver enzymes
How does gluconeogenesis proceed?
Via the synthesis of oxaloacetate in mitochondria
Oxaloacetate accepts acetyl groups in the TCA cycle
Is gluconeogenesis energy consuming or energy producing?
Consuming
What is glycogenin?
A protein at the centre of a glycogen polymer
How many glucose molecules can covalently bind to glycogenin?
Four
Why is the catalytic activity of glycogenin important?
It’s ability to bind four glucose molecules to itself is important because glycogen synthase can only add glucose molecules to an existing glycogen chain
