GI - biochemistry Flashcards
what is glycogenesis
the synthesis of glycogen from glucose
what enzyme causes glycogenesis
glycogen synthase
what is glycogenolysis
the breakdown of glycogen to form glucose
what enzyme causes glycogenolysis
glycogen phosphorylase
what type of reaction is glycogenolysis
phosphorolysis
what does insulin do to glycogenesis
insulin stimulates glycogenesis
what does insulin do to glycogenolysis
insulin inhibits glycogenolysis
what does glucagon do to glycogenesis
glucagon inhibits glycogenesis
what does glucagon do to glycogenolysis
glucagon stimulates glycogenolysis
where is glycogen found
liver and muscle cells
what is glycogen used for in liver cells
stoked then released to maintain blood glucose concentration
what is glycogen used for in muscle cells
consumed within the muscle cell to produce ATP by glycolysis - not available for maintenance of blood glucose
how is glycogen released from liver to maintain BSL
liver dephosphorylates glucose-6-phosphate and releases it into blood as glucose
what maintains BSL immediately following meals
dietary CHO
what maintains BSL between meals
glycogenolysis
what maintains BSL when no dietary CHO is available and liver stores of glycogen are depleted and over night
gluconeogenesis
what bonds form long straight chains of glucose
alpha-1,4-glycosidic bonds
what bonds form branches in glycogen molecule
alpha-1,6-glycosidic bonds
true/false
the more branches a glycogen molecule has the greater the rate glucose can be added or cleaved off
true - more terminal ends
what is glycogenin
glycogen primer of 4 glucose molecules for glycogenesis
true/false
glycogen synthase starts glycogenesis from scratch
false
it adds extra glucose monomers to the existing glycogen formed by glycogenin primer
how often are branches introduced to the glycogen chain
every 10 glucose
what kind of bonds does glycogen synthase introduce to the glycogen polymer
alpha-1,4-glycosidic bonds
what enzyme introduces alpha-1,6-glycosidic bonds to glycogen
transglycosylase
what bonds does glycogen phosphorylase break
alpha-1,4-glycosidic bonds
what do adrenaline, cortisol and glucagon do to the rate of glycogenolysis
increase rate
what is the name of the transporter in liver cells that transports glucose into blood
GLUT2
what enzyme converts glucose into glucose-6-phosphate
hexokinase
what are the 2 options of fate of the glucose-6-phosphate
glycolysis
or converted to glucose-1-phosphate
what enzyme converts glucose-6-phosphate to glucose-1-phosphate
phosophglucomutase
what enzyme converts glucose-1-phosphate to UDP-glucose
UDP-glucose pyrophosphorylase
what enzyme converts UDP-glucose into glycogen by adding another glucose (1 at a time)
glycogen synthase
how is UTP regenerated in glycogenesis
UDP is produced as a bi-product at the end of the reaction when UDP-glucose forms glycogen by adding a glucose
the UDP is then phosphorylated to UTP by ATP
for each glucose added to glycogen how many ATP are used
1
what is the rate limiting step of glycogenolysis
glycogen phosphatase removing a glucose from glycogen by adding a phosphate
what enzyme converts glucose-1-phosphate into glucose-6-phosphate
phosphoglucomutase
what enzyme converts glucose-6-phosphate into glucose by phosphorylating
glucose-6-phosphatase
what is gluconeogenesis
synthesis of glucose from non-CHO precursors
what is the substrate of gluconeogenesis
pyruvate
what is the first stage in gluconeogenesis
pyruvate to oxaloacetate
where is energy for gluconeogenesis obtained
oxidation of fatty acids from adipose tissue
what are the 3 precursor molecules for gluconeogenesis
lactate
amino acids
glycerol
how many ATPs and how many pyruvate are needed to form 1 glucose molecule in gluconeogenesis
6 ATP
2 pyruvate
where does gluconeogenesis occur
liver
small amount in kidneys
where is lactate produced
anaerobically respiring skeletal muscle
how is lactate converted into pyruvate for gluconeogenesis
cori-cycle
what is the cori cycle
blood transports lactate to liver where it is converted into pyruvate and then into glucose which is transported back to the muscle cell/blood
could the cori cycle go on forever
no - consumes 6 ATP and produces 2
how are amino acids produced
proteolysis of muscle protein
how do amino acids enter gluconeogenesis
either converted to oxaloacetate from pyruvate
or enter TCA cycle through Acetyl-CoA which results in the eventual formation of oxaloacetate
what is the condition for amino acids to enter the TCA cycle
oxaloacetate must be present
what is the TCA intermediate needed for gluconeogenesis
oxaloacetate
how is glycerol formed for gluconeogenesis
lipolysis of triglycerides in adipose tissue
what is the effect of glucagon on glycolysis
glucagon inhibits glycolysis
what is the effect of glucagon on gluconeogenesis
glucagon stimulates gluconeogenesis
what is the effect of insulin on glycolysis
insulin stimulate glycolysis
what is the effect of insulin on gluconeogenesis
insulin inhibits gluconeogenesis
if [ADP] or [AMP] is high in a cell what happens to gluconeogenesis
inhibited - cell has low energy
if [ATP] is high in a cell what happens to gluconeogenesis
stimulated - cell has high energy
if molecules associated with the TCA cycle are high in a cell what happens to gluconeogenesis
gluconeogenesis is stimulated
if fructose-2,6-biphosphate (high in fed state) is high in a cell what happens to gluconeogenesis
gluconeogenesis is inhibited
what do citrate, alanine and acetyl-coA do to gluconeogenesis
simulate gluconeogenesis
how many liver enzymes are required to do the reverse of the 3 irreversible steps of glycolysis
4
what are the enzymes of 3 irreversible steps of glycolysis
hexokinase
phosphofructokinase
pyruvate kinase
what are the 3 irreversible steps of glycolysis
glucose –> glucose-6-phosphate
fructose-6-phosphate –> fructose-1,6-biphosphate
phosphoenolpyruvate –> pyruvate
true/false
lipids provide 2 times the energy of CHOs
true
do fatty acids tend to be cis or trans
cis
do essential fatty acids tend to be saturated, unsaturated or polyunsaturated
polyunsaturated
where does the synthesis of fatty acids occur and from what
cytoplasm
acetyl-CoA
what bonds join triglycerides
ester bonds
what happens when fatty acids and monoglycerides are absorbed by the intestinal mucosa
converted back into triglycerides and incorporated into chylomicrons which enter the lymph
what enzyme cleaves chylomicrons to release FAs and TGIs
lipoprotein lipase
what is the fate of the free fatty acids
- converted to TGIs for storage in adipose tissue
- oxidised for energy in muscle cells
what is the effect of adrenaline on hormone sensitive lipases
fat broken down (lipolysis) for oxidation when needed
what must happen in order for fatty acids to enter the mitochondria
must form a CoA derivative
how is a coA derivative of FA formed and where
in cytoplasm
Co-A is added to form acyl-coA (requires 2 ATP)
how does the acyl-coA enter the mitochondrion
carnitine shuttle
what happens in the carnitine shuttle
acyl-group is transferred from Acyl-CoA to carnitine to form Acyl-carnitine which is transferred across the mitochondrial membrane into the matrix
in the matrix the acyl group is added to CoA forming Acyl-CoA and carnitine
carnitine then leaves through the mitochondrial membrane
what is the transporter in the carnitine shuttle
translocase
what is beta oxidation
oxidation of FAs in mitochondria into products that can be used in TCA cycle or oxidative phosphorylation
what does one cycle of beta oxidation generate
1 acetyl coA
1 FADH2
1 NADH+H+
1 fatty acyl-CoA
what happens to the acetyl-CoA produced from beta oxidation of fatty acids
oxidised in TCA cycle to form 1 FADH2 2 CO2 1 GTP 3 NADH+3H+
how do you work out how many BO cycles are needed for a fatty acid
C/2 - 1
what happens in the last cycle of BO of an odd chain FA instead of yielding 2 acetyl-CoA
acetyl-CoA and propionyl-CoA are yielded
what happens to propionyl-CoA formed from last BO of an odd chain FA
converted into succinyl-CoA which enters TCA directly
what are ketone bodies formed from
from beta oxidation of acetyl-coA in liver mitochondrion as byproduct of glycerol digestion
what happens to these ketones
diffuse into peripheral tissues where they are converted back to acetyl-coA which enter the TCA directly
what is the name of a 4C ketone
oxaloacetate
what is the name of the build up of Acetyl-CoA in diabetics/prolonged starvation and why does it occur
ketoacidosis
no oxaloacetate to deal with it
when and where does fatty acid synthesis (lipogenesis) occur
excess energy intake - excess CHO causing excess citrate
liver
what kind of process is lipogenesis
reductive
what is the function of VLDL
carried TGIs to adipose tissue
what is the function of albumin
carries free FA in plasma
what is the function of Acetyl-CoA
precursor molecule for lipogenesis
where does fatty acid breakdown to Acetyl-CoA occur
mitochondrial matrix
where does fatty acid synthesis from Acetyl-CoA occur
cytoplasm
what is the function of citrate
transports acetyl groups into the cytoplasm for lipogenesis
when is citrate formed
1st step of TCA from oxaloacetate + Acetyl-CoA
what is the regulatory enzyme for the 1st step of lipogenesis
Acetyl-CoA carboxylase
what does Acetyl-CoA carboxylase do
activates Acetyl-CoA forming malonyl-CoA which donates an atom to the lipid
what enzyme catalyses the synthesis of saturated long chain FAs from malonyl-CoA, Acetyl-CoA and NADPH
fatty acid synthase
how many acyl-carrier proteins does fatty acid synthase carry per dimer
2
what is the longest fatty acid that can be formed from fatty acid synthase
16C
what is the function of the acyl-carrier protein
carries growing fatty acid chain until 16C chain is achieved
what is the make up of palmitic acid
16:0
what is the make up of stearic acid
18:0
what is the make up of oleic acid
18:1
what is the make up of linoleic acid
18:2
what is the function of NADPH during lipogenesis
donates electrons to the growing FAC
what does insulin do to the activity to acetyl-CoA carboxylase
stimulates
what does glucagon do to the activity of acetyl-CoA carboxylase
inhibits
what does adrenaline do to the activity of acetyl-CoA carboxylase
inhibits
what is the name of the activated form of glycerol formed by liver and from glucose in adipose tissue that is required for TGI synthesis
glycerol-3-phosphate
in a fatty acid what is the alpha carbon
adjacent to carboxyl group
ina fatty acid what is the omega carbon
furthest away from carboxyl group
how many carbons does a FA need to have to be solid at room temp
> 8C
can amino acids be stored in the body
no
what 2 phases of urea synthesis occur in the liver
deamination and urea cycle
where does transamination occur and what does it involve
all cells - amino group transferred from alpha-amino acid to alpha-keto acid (usually alpha-ketoglutarate) forming glutamate
what enzyme carried out transamination
aminotransferase
what occurs in deamination
amino group from glutamate converted into ammonium ion (NADH also formed)
what occurs in the urea cycle
conversion of ammonium to urea
what is the equation of the urea cycle
ammonium ion + CO2 + aspartic acid –> urea + fumarate (byproduct used in TCA cycle
what happens once an amino group has been removed from a ketogenic AA
either degraded to acetyl-CoA which can be oxidised in the TCA cycle
or give rise to ketone bodies
what happens once an amino group has been removed from a glucogenic AA
either degraded to pyruvate or TCA cycle intermediates
or used in gluconeogenesis (converted into phosphoenolpyruvate)
what are the 2 main transporter molecules of nitrogen to the liver
alanine - pyruvate + NH4
glutamine - glutamate + NH4
what happens to alanine and glutamate once in liver
converted back to glutamic acid
what is phenylketonuria
inherited disorder with failure to breakdown phenylamine which accumulates and causes mental retardation
what is alcaptonuria
inherited disorder where the degradation of phenylalanine and tyrosine is blocked
what is maple syrup urine disease
inherited disorder where degradation of valine, isoleucine and leucine is blocked
what is the treatment of disorders of the urea cycle
low protein diet
drugs which remove nitrogen
why are urea cycle disorders bad
accumulation of ammonia in blood
how many strong phosphate bonds are broken in the urea cycle
4 - 3 ATP to 2 ADP + AMP
where are alpha and beta globulins produced and what are they used for
liver
transport molecules
what is caeruloplasmin
alpha globulin that transports copper
what is retinol binding protein
alpha globulin that transports Vitamin A
what is transferrin
beta globulin that transports iron in Fe3+ form
what can transferrin be an indication for
iron deficiency
what is the storage form of iron
ferritin (Fe2+ bound to ferritin)
true/false
when you increase altitude there is a decrease in transferrin expression
false
when you increase in altitude there is an increase in transferrin expression
how is fibrinogen activated
prothrombin
what is fibrinogen
beta globulin produced by liver
inactive form of blood blotting agent fibrin
what is the most abundant plasma protein in the blood
albumin
what is the effect of insulin on albumin production
production stimulated by insulin
what does albumin transport
FAs
bilirubin
thyroid hormones
aspirin
what is the affinity/capacity of albumin for hydrophobic molecules
low affinity
high capacity
is albumin positive negative or neutral
negative
what is transthyretin and what does it reflect
pre albumin - reflects recent intake - useful for nutritional monitoring
what happens to transthyretin levels in uraemia and dehydration
increased
what happens to transthyretin levels in APR, fasting
decreased
what is a good marker for muscle mass
urinary creatinine
steroid hormones are hydrophilic/hydrophobic
hydrophobic
where are steroid hormones produced
ovaries
testes
adrenal glands
how is thyroxine (T4) transported in blood
bound to thyroid-binding globulin
how is cortisol transported in blood
bound to cortisol-binding globulin
order the following from heaviest to lightest
Gamma globulins
albumin
beta globulins
alpha globulins
gamma globulins (immunoglobulins)
beta globulins
alpha globulins
albumin
how do plasma proteins buffer pH
donating / accepting a proton
what is the function of lipoproteins
transfer fat in blood between organs and tissues
order the following from most to least dense
Chylomicrons
LDL, HDL
VLDL, IDL
LDL, HDL
VLDL, IDL
Chylomicrons
how do plasma proteins maintain osmotic pressure of blood
dont diffuse into interstitial fluid
what is the function of chylomicrons
transport dietary fibre to liver
what is the function of LDL
transports cholesterol from liver to peripheral tissue (bad)
what is the function of HDL
transports cholesterol from peripheral tissue to liver (good)
what is the main product of cholesterol metabolism
bile salts
how are bile salts reabsorbed by the liver
enterohepatic recycling
what do bile salt sequestrants do
block bile salt absorption in terminal ileum to lower cholesterol levels
what is the only organ that can metabolise and excrete cholesterol
liver
where are red blood cells broken down and what do they produce
spleen
haem + globulin
what enzyme controls breaking down of haem
haemoxygenase
haem –> iron + porphyrin ring —> biliverdin
what enzyme converts biliverdin to unconjugated bilirubin
biliverdin reductase
how is bilirubin transported to liver
unconjugated bilirubin binds to albumin as it is lipid soluble
what enzyme conjugates bilirubin in the liver by adding glucaronic acid
uridine glucuronyl transferase (UGT)
conjugated bilirubin is then excreted into canaliculi and then to bile ducts and then to gall bladder where bile is stored and concentrated.
When bilirubin is secreted with bile into small intestine what is it converted to by intestinal bacteria
urobilinogen
stercobilinogen
what is the fate of stercobillinogen
oxidised to stercobillrubin/stercobilin (brown colour of faeces)
what is the fate of urobiliogen
reabsorbed into blood stream forming urobilin and either goes to liver or to kidneys where it is excreted giving urine its yellow colour
what gives urine its yellow colour
urobillin
what does cholesterol form an essential component of
cell membrane of animal cells
how is cholesterol synthesised and by what
all cells
acetyl-CoA (18), NADPH (16) and ATP (36)
what is the main site of cholesterol synthesis
liver
what is the rate limiting enzyme of cholesterol synthesis
HMG-CoA reductase
what does HMG-CoA reductase do
irreversibly catalyses the the formation of mevalonic acid
what does starvation do to HMG CoA reductase synthesis and activity
stimulated
what is the P/O ratio
measure of the number of ATP molecules formed per oxygen atom reduced
what has a greater redox potential NADH+H or FADH2
NADH+H
