Metabolic Stores Flashcards
how are carbohydrates stored in the liver and muscle
glycogen (a branched glucose polymer)
when glucose is broken down what is it directly converted to
glucose-6-P and this is without consuming ATP
CAN ONLY OCCUR IN THE CELL IT IS FORMED
as it cannot easily pass through the cell membrane
what happens when glucose is required somewhere else in the body
the glucose-6-P is only phosphorylated when it has been transported to its destination as once phosphorylated it is not easily removed
THIS USES ATP
in the liver there is an enzyme known as glucose-6-phosphotase which can cleaves the phosphates it can escape
how may horse worth of glycogen in the body
3-5 hours
what is the major form in which fuel is stored
lipids
triglycerides/triacylglycerols
produce about 6 times s much energy as glycogen
what is fat mainly stored as
triglycerides (triacylglycerols) these are esters of glycerol and fatty acids
as esterification occurs at carbon 123
what is an ester
formed by reaction of an alcohol with an organic acid
tell me about the oxidisation of fatty acids
they are linked to coenzyme A before they are oxidised and 2-carbon fragments cleaved off (as acetyl-Co-A)
What happens during the oxidisation of fatty acids
no ATP is directly generated however hydrogen and electrons are removed and are passed along the respiratory chain so are indirectly producing ATP
where are fatty acids and glycerol released from
adipose tissue and are mainly metabolised in the liver
when there are no other fuels available, the breakdown of fatty acids leads to what
the formation of chemicals known as ketone bodies
what ketone bodies are mainly present post breakdown of fatty acids
acetoacetate
3-hydroxybutyrate
acetone
how are ketone bodies produced
acetyl-CoA formed in the breakdown of fatty acids cannot enter the citric acid cycle since oxaloacetate becomes depleted because the liver converts it to pyruvate to produce glucose by glycogenesis
so acetyl-CoA = ketone bodies
omega-3 fatty acids
double bond at three position
not metabolised
has to be acquired in the diet
vital fatty acid
What is the appearance of ketone bodies
fruity smell (often smelled on breath when fasting.)
what happens to amino acids not needed for making new proteins as they cannot be stored
they are used as metabolic fuel
some can be deaminated, yielding nh4 + a ketone acid that are intermediates of the glycolytic pathway or of the citric acid cycle
what happens to the products of transamination
the resulting ketone acids can be fed into glycolysis or the citric acid cycle (as pyruvate , acetylene-Co-A, oxalocetate
what happens to the NH4+ formed from transamination
rapidly converted to urea as it is very toxic
gluconeogenesis
formation of glucose from non-carbohydrate sources )glycerol and the carbon backbone of amino acids can be fed into this pathway)
where does the bulk of gluconeogenesis take place
the liver
where are the bulk triglycerides stored
adipose tissue
why do athletes load up on carbs before an event
fats are not used as effectively as fuel carbohydrate so energy production cannot be as high when using lipids rather than carbs
(when fasting, burns fat so produces more keto bodies hence fruity breath)
tell me about fuel in the brain
glucose is normally only source
can’t store glucose glycogen so needs constant supply in the blood
60% of all glucose used by the body
in times of starvation can use ketone bodies)acetoacetate and 3-hydroxybutyrate) formed in other tissues
CANT USED FATTY ACIDS due to BBB that protects the brain from other potentially dangerous chemicals
what stores can muscle (large glycogen stores) use
glucose, fatty acids and ketone bodies
resting muscle uses
fatty acids
tell me about the actions in muscle
glucose-6-P is formed from glycogen
Like brain, muscle cannot convert this to glucose, so
neither tissue can export glucose
When muscle is active the rate of glycolysis far outpaces the
citric acid cycle
pyruvate must be converted to lactate
The lactate passes into the blood and to the liver, where it is converted back to glucose
under conditions where muscle protein is being broken down
amino acids pass their amino group pyruvate (through transamination) to form alanine
role of alanine
enters the blood and in the liver can be converted back to pyruvate which is used to synthesise glucose
main function of adipose tissue
to synthesize and store triglycerides (=triacylglycerols) and release fatty acids and glycerol in times of need
what is the role of lipase
hydrolyses triglycerides and is HORMONE SENSITIVE
What determines the rate at which fatty acids are esterified
the availability of glucose
tell me about the role of the liver
the hepatic portal system ensures that the liver has ready access to nutrients absorbed by the gut.
readily store, release glucose and make new glucose from lactate, alanine and glycerol in the diet or released by other tissues.
what is the formation of glucose known as
gluconeogenesis
When fuel supplies are available what does the liver do
synthesizes fatty acids, esterifies them and then secretes them into the blood as very low density lipoprotein (VLDL)
