Metabolism Flashcards
Glycogenesis
synthesis of glycogen from glucose
Glycogenolysis
Breakdown of glycogen to form glucose
Gluconeogenesis
synthesis of glucose from metabolic precursors
Are are glucose monomers attached in a glycogen polymer (2)
straight chain: α 1-4 glycosidic links
Branches: α 1-6 glycosidic links
Which protein is a glycogen primer bonded to
glycogenin
Which enzyme adds glucose molecules in a straight chain
glycogen synthase
What does glycogen synthase use to extend the glycogen chain
UDP glucose
What enzyme is used to introduce branches in glycogen molecules
transglycosylase
What regulates the activity of glycogen synthase (2)
insulin - activates glycogen synthase
Glucagon - inhibits glycogen synthase
What are the two types of glycogen
Liver
Muscle
Describe liver glycogen (3)
broken down between meals
Used to maintain blood glucose
Released to supply energy to tissues
Describe muscle glycogen (2)
not available for blood glucose maintenance
Provides energy via cellular respiration
Which is more likely to occur overnight: glycogenolysis or gluconeogenesis
gluconeogenesis as hepatic glycogen is depleted
what enzyme is involved in glycogenolysis
glycogen phosphorylase
What is glucose-1-phosphate converted to in glycogenolysis
Glucose-6-phosphate
What happens to liver glucose-6-phosphate (2)
It is de-phosphorylated
Glucose is released into bloodstream
what happens to muscle glucose-6-phosphate (2)
it cannot be de-phosphorylated
Used to provide energy via cellular respiration
When must new glucose be synthesised
during prolonged starvation
What are the precursors of gluconeogenesis (3)
lactate
Amino acids
Glycerol
What converts lactate to glucose
the liver
How are amino acids obtained for gluconeogenesis
derived from muscle protein by proteolysis
How is glycerol obtained for gluconeogenesis
derived from triglycerides by lipolysis
What is the main site of gluconeogenesis
the liver
Why is gluconeogenesis not the reverse of glycolysis
Energetically unfavourable steps in glycolysis must be overcome
How does gluconeogenesis alter energy distribution
Reduces liver energy to distribute glucose to other tissues
How is gluconeogenesis regulated (2)
by hormones
Regulation by insulin is dominant
What does increased fat intake without increased energy expenditure lead to (2)
Increased number and size of adipocytes
What controls energy storage in adipose tissue (2)
Genetic and environmental factors
What is fat required for (3)
energy
Essential fatty acids, membranes, and vesicles
Transport of fat-soluble vitamins
What are the types of lipids (3)
Simple
Compound
Steroids
What do triglycerides consist of
one glycerol unit and three fatty acids
What types of fatty acids exist
saturated, unsaturated, or polyunsaturated
Which compound is the main energy storage form in adipose tissue
Triglycerides
What is the structure of fatty acids generally like
straight chain, aliphatic
How do the states of plant and animal fats compare
animal fats are generally solid, plants fats are generally liquid
What must happen to fatty acids before they are oxidised
they must be converted to CoA derivatives in the cytoplasm
where does further oxidation of fatty acids (after conversion to CoA derivatives) take place
Matrix of mitochondria
What is the significance of the carnitine shuttle (2)
A carrier mechanism that transports molecules into the mitochondrial matrix for further oxidation
Results in acyl-CoA inside the matrix
B oxidation (4)
Cycle of reactions resulting in oxidation of fatty acids
Occurs in mitochondrial matrix
Requires enzymes
Yields ATP
What are the products of β oxidation (4)
1 acetyl-CoA
1 FADH2
1 fatty acyl-CoA
1 NADH + H+
Where does fat absorption occur
Into mucosal cells of the intestine
What are the main products of fat absorption (3)
glycerol
Fatty acids
Monoglycerides
One absorbed by the intestine, where do fatty acids go
shorter chain - portal blood
Longer chain (+monoglycerides) - enter lymph then blood stream
Once in muscle/adipose tissue, what occurs to chylomicrons
The lipids are cleaved by lipoprotein lipases
What are free fatty acids used for in muscle
oxidation to provide energy
What are free fatty acids used for in adipose tissue
Re synthesis to triaglycerols
How are ketone bodies formed (3)
in mitochondria of liver cells
From acetyl-CoA
By β oxidation
once produced, where do ketones go (2)
blood stream
Peripheral tissues
Why are ketones important (2)
for energy metabolism of heart muscle and the renal cortex
They can be converted back to acetyl-CoA
what does fatty acid oxidation produce under normal circumstances
acetyl-CoA
In cases of starvation/diabetes, what happens to oxaloacetate
Used for gluconeogenesis
How can acidosis arise in cases of starvation/diabetes (3)
fatty acids are oxidases to acetyl-CoA
Acetyl-CoA is converted to ketone bodies
Ketone bodies accumulate
What is a sign of acidosis
acetone smell on breath
How can acidosis be managed in cases of starvation/diabetes
starvation - sugar
Diabetes - insulin
lipogenesis
synthesis of fatty acids
What can lead to fatty acid synthesis (2)
excess energy intake
Excess carbohydrate intake
What occurs during excess carbohydrate intake (3)
Excess carbohydrates are converted to fatty acids and triglycerides
Free fatty acids are bound to albumin and transported in plasma
Triglycerides are transported to adipose tissue for storage
What transports triglycerides to adipose tissue for storage
VLDL
What is required for fatty acid synthesis and why
electrons
It is a reductive process
Describe transport of acetyl-CoA for lipogenesis (2)
acetyl-CoA is synthesised in the mitochondria
Citrate transports acetyl-CoA to the cytoplasm for lipogenesis
What is the first step required for lipogenesis (2)
activation of acetyl-CoA to malonyl-CoA
Catalysed by acetyl-CoA carboxylate
Where is acetyl-CoA carboxylate generally expressed (2)
liver
Adipose tissue
What catalyses the synthesis of fatty acids from Malonyl-CoA
Fatty acid synthase
What are the four steps of fatty acids synthesis
condensation
Reduction
Dehydration
Reduction and release
Unregulated forms of fatty acid synthase is associated with what condition
cancer
What protein does fatty acid synthase contain (among others)
acyl-carrier protein
What is the longest fatty acid created by fatty acid synthase
palmitic acid
16 carbons
What does each cycle of reactions in lipogenesis require and why
NADPH as an electron donor
In lipogenesis, what is each growing acyl chain attached to
ACP
When is fatty acid synthesis maximal (2)
Abundant carbohydrates and energy
Scarce fatty acids
How does insulin affect lipid metabolism
by stimulating the storage of fuels and protein synthesis
How does citrate affect lipogenesis
allosterically stimulates acetyl-CoA carboxylate
How does palmitoyl-CoA affect lipogenesis
antagonises acetyl-CoA carboxylate when fatty acids are in excess
What compound is required for triglyceride synthesis and what is used to produce it
Glycerol-3-phosphate is required
Liver uses glycerol to produce it
Adipose tissue uses glucose to produce it
When does adipose tissue production of triglycerides occur (2)
during a fed state
When insulin stimulates adipose uptake of glucose
What type of reaction is involved in triglyceride synthesis
esterification
What does breakdown of amino acids produce (2)
ammonium
Ammonia ions
How can nitrogen be excreted
Urea
Uris acid
Creatinine
Ammonium ions
What are the three steps involved in synthesis of urea
transanimation
De-animation
Urea cycle
What occurs in the transamination step of urea synthesis
aminotransferases move the amino group from α amino acids to α keto acids
Produces glutamate
What are the two possible routes after glutamate has been produced (transanimation)
Amino group on glutamate is transferred to pyruvate, producing alanine
Or glutamine synthase adds an ammonium ion to glutamate, creating glutamine
What is the function of alanine and glutamine
to carry nitrogen from the blood to the liver
Where does deanimation occur
liver
What happens during de-animation
The amino group of glutamate/alanine is converted to a free ammonium ion
What is generated as an end product of urea synthesis
fumarate
How can carbon be transported back to the mitochondrial matrix after synthesis of urea in the cytoplasm (2)
fumarate is converted to malate
Carbon is transported via the malate-aspartame shuttle
What can ketogenic amino acids give rise to (3)
acetyl-CoA or acetoacetyl-CoA
Ketone bodies
Fatty acids
What can glycogenic amino acids be degraded to form
pyruvate or TCA cycle intermediates
