carbohydrate metabolism

Question 1

importance of metabolism

Answer 1

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)

Question 2

muscle glycogen and exercise

Answer 2

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

Question 3

diet, muscle glycogen and exercise

Answer 3

high carb diet= high muscle glycogen = better exercise performane
depleting the glycogen also helped with glycogen storage and usage

Question 4

energy for muscular effort

Answer 4

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

Question 5

structure of carbs

Answer 5

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

Question 6

glucose metab in fasted state

Answer 6

comes from liver
liver glycogen
trasnferrred into blood- transport into brain, muscle, adipocytes etc
liver uptake= glut2
adipose= glut4
brain = glut2
muscle=glut4

Question 7

in fed state

Answer 7

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

Question 8

glucose absorption

Answer 8

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

Question 9

limitations to providing cho during exercise

Answer 9

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)

Question 10

transport in blood to the muscle

Answer 10

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)

Question 11

insulin and glut 4 translocation

Answer 11

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

Question 12

increases in glucose

Answer 12

exercise/ muscle contractions- increase glucose uptake more than insulin due ot larger increase in blood flow
glucose uptake = leg blood flow x AV difference

Question 13

limitation to uptake in muscle

Answer 13

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

Question 14

assessing exogenous CHO oxidation during exercise

Answer 14

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

Question 15

gas chromotography

Answer 15

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

Question 16

glycogenesis

Answer 16

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

Question 17

elongation

Answer 17

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

Question 18

glycogen storage

Answer 18

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

Question 19

fructose

Answer 19

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

Question 20

fructose in liver

Answer 20

50%- gluconeogenesis to glucose
12-25% gluconeogenesis to glycogen
25% pyruvate oxidised or converted to lactate

Question 21

regulation of glycogen synthase

Answer 21

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

Question 22

glycogenolysis

Answer 22

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

Question 23

role of adrenaline

Answer 23

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

Question 24

speed of glycogenolysis

Answer 24

can occur within 1 second
cAMP cascade is slow
increase in ca2+ directly activates phosphorylate kinase which activates phosophorylase