carbohydrate metabolism Flashcards
importance of metabolism
efficient substrate (compared to fat) for high intensity exercise but limited stores
athletes try to maximise storage of carbs (muscle and liver glycogen) by fuelling prior and refuelling after exericse
carbohydrate can be provided as source of fuel during exercise (exogenous)
muscle glycogen and exercise
fast and slow twitch usages changes throughout
muscle glycogen is used throughout different intensities
most muscle glyocgen used at 60% vo2 max
least was used at 30% vo2max
low intensity= slow twitch fibres
higher intensity= fast twitch fibres
diet, muscle glycogen and exercise
high carb diet= high muscle glycogen = better exercise performane
depleting the glycogen also helped with glycogen storage and usage
energy for muscular effort
as intensity increases, more reliance on carb- increase on blood glucose and glycogen utilisation + reduction in contribution from fat
want to maximise carb
carb is a lot more efficient- loses 5.5% less o2 to provide energy
muscle glycogen- 0.4kg
liver glycogen - 0.1kg
plasma glucose-0.01kg
are quite low in the body so need to ensure you are getting enough from diet
structure of carbs
mono- glucose, fructose, galactose
dis- sucrose, maltose, lactose
oligo- maltodextrin; 8-12 units of glucose, high GI , easy absorption so used during exercise
polys- branches- more available ends for faster breakdwon- higher GI
glucose metab in fasted state
comes from liver
liver glycogen
trasnferrred into blood- transport into brain, muscle, adipocytes etc
liver uptake= glut2
adipose= glut4
brain = glut2
muscle=glut4
in fed state
carb from small intestine
into blood and stimulates pancreas to release insulin
insulin has uptake effect- glucose into liver and muscle, adipocytes
inhibitory- breakdwon of muscle glycogen in liver, released into blood
insulin is primary contorlling factor for carbohydrate
glucose absorption
glucose is source of carb
uses SGLT1
uses glut 2 to go into bloodstream
combined using fructose (using glut5) if glut 2 transporter becomes saturated
limiting rate- 1-1.2g/min
limitations to providing cho during exercise
exogenous carb oxidation limited to exercise
due to saturation of transport proteins
SGLT1 saturated at 1-1.2g/min
uses of multiple transportable carbs
GLU:FRU intake ratio of 2:1
(changing to 1:0.8)
transport in blood to the muscle
increasing uptake
during exercise (or providing more insulin) - glut 4 moves to membrane of muscle cell allowing more glucose to be transported into the muscle
once glucose is in the cell, phosphorylated by hexokinase to G6P goes to glycogenesis or glycolysis (very quick)
insulin and glut 4 translocation
increased insulin
insulin receptor has 4 subunits (2 in and 2 out of cell)
insulun binds to receptor and activates the subunits in the cell
activates insulin receptor substrate 1 (IRS1)
creates binding to PI3kinase
activates PI3k and activates AKT
AKT initiates translocation of GLUT4 to cell membrane - allowing more uptake of glucose
insulin increases glycogen stores by increase glycogen synthase activity
increases in glucose
exercise/ muscle contractions- increase glucose uptake more than insulin due ot larger increase in blood flow
glucose uptake = leg blood flow x AV difference
limitation to uptake in muscle
study
increasing blood glucose conc to 10mmol/L increased rate of blood glucose oxidation
infused glucose straight into blood
rate of oxidation massively increased when glucose was infused
shows that limitation is due to the intestinal absorption
assessing exogenous CHO oxidation during exercise
ingestion of 13CO labelled cho body stores cho both endogenous and exogenous
breath out co2 and can measure ratio or c13 and c12 (normal) in co2 produced- can look at how much cho 13 is utilised
can measure how fast we use it
gas chromotography
isotope ratio mass spectometry
- δ 13C - isotope signature- ratio of stable isotope 13C and 12C reported in ppthoussand
- C3 and C4 plants have different ratios due to no. of enzymes
glycogenesis
storage of glucose for use at a later time
storage in muscle and liver
glucose needs to be present in cell- insulin needs to be elevated
main regulatory enzyme is glycogen synthase
elongation
when glucose enters cells- forms G6P then G1P
catalysed by UDP glucose pyrophosporylase or UTP to form UDP glucose
glucose attaches to UTP to become UDP glucose
glycogen synthase attached the UDP glucose to the other glucose molecules
forms glycosidic bond, creating glycogen molecule
glycogen storage
stored as branches of glucose polymers
several branches means they can be broken down rapidly
when 11 or more chains have formed, they can be branched
glycogen synthase only forms straight bonds so this needs to be broken down to form branches
break down 1,4 glyco bond using branching enzyme (splits the bond in two and reattaches)
forms a 1,6 glyco bond on a branch
fructose
cant be transported into muscle cell
needs fructokinase to convert fructose 1 phosphate not present in muscle
fructose metabolism occurs in liver
fructose is beneficial by helpig glucose convert to glycogen
glucokinase receptor protein changes allowing more glucose to go through the pathway
fructose in liver
50%- gluconeogenesis to glucose
12-25% gluconeogenesis to glycogen
25% pyruvate oxidised or converted to lactate
regulation of glycogen synthase
insulin increases glycogen synthase
ATK inactivates glycogen synthase kinase 3
GSK-3 phosphorylates glycogen synthase
adrenaline decreases glycogen synthase
activates PKA (protein kinase A)
increased lipolysis + glycogenolysis
glycogenolysis
glycogen breakdown
glycogen phosphorylase only breaks down 1,4 bonds- process stops when 4 glucose moles left
glucan transferase takes 3 glucose molecules and attached them to end of chain- leaves free glucose molecule
10% to glucose, 90% glucose 1-P
by glycogen phosphorylase
G6P can be used in glycolysis for energy or converted in liver to glucose
role of adrenaline
adrenaline attaches to receptor on cell membrane
activates G protein
activates adenylate cyclase
converts atp to cAMP
activates an inactive PKA which activates phosphorylase kinase
activates glycogen phosphorylase
speed of glycogenolysis
can occur within 1 second
cAMP cascade is slow
increase in ca2+ directly activates phosphorylate kinase which activates phosophorylase
