MCBG (mostly topic 6 carbohydrates) Flashcards
which pathways are activated when ATP conc high
anabolic
which pathways are activated when ATP conc LOW
catabolic
List HIGH energy signals, activate which pathways?
ATP NADH NADPH FAD2H activate anabolic
List LOW energy signals, activate which pathways?
NAD+ FAD NADP+ ADP/AMP activate catabolic
clinical relevance of Creatine Kinase
marker for MI
Role of Creatine Kinase
converts creatine into phosphocreatine.
Requires ATP, produces ADP
Reversible reaction, can provide ATP when low in cell.
What can be used as marker for urine dilation?
Creatine excretion
Describe the 4 stages of catabolism
stage 1- complex molecules to building blocks e.g. carbohydrates to monosaccharides.
stage 2- building blocks to simpler (fewer) molecules e.g. monosaccharides to pyruvate.
oxidative (require coenzymes NAD+) some ATP produced.
stage 3- mitochondrial. TCA cycle. oxidative.
stage 4- mitochondrial. Electron transport and ATP synthesis (large yield). Oxygen required. NADH and FAD2H reoxidised.
Describe the absorption of monosaccharides into epithelial cell and uptake into target cells
uses SGLT1 (sodium glucose transporter) into epithelial cell. Glucose uptake into cells via facilitated diffusion using transport proteins (GLUT1-5) GLUT 1-5 all have different affinities and tissue distribution.
Describe glycolysis
Glucose C6 oxidation. Requires 2x ATP.
Reduction of 2x NAD+ –> NADH
4x ADP –> ATP
pyruvate C3 (Two produced)
yield = 2x ATP per glucose
which enzymes are important in glycolysis.
hexokinase (glucokinase in liver): glucose –> glucose 6P
Phosphofructokinase 1: Fructose 6P –> fructose bisphosphate.
Pyruvate kinase: phospoenolpyruvate –> pyruvate.
why so many steps in glycolysis?
- chemistry easier in smaller steps
- efficient energy conversion
- allows interconnections with other pathways
- can be controlled
List some important intermediates in glycolysis
1,3 bisphosphoglycerate feeds out pathway to 2,3 BPG which is produced in RBC, regulator of Hb O2 affinity (promotes release of O2)
glycerol phosphate -important to triglyceride and phospholipid biosynthesis. produced from DHAP in adipose tissue and liver
Which glucose transporter is regulated by insulin
GLUT4
describe what each glucose transporters main role is
GLUT1- in erythrocytes and also in endothelial cells of the blood–brain barrier. Required to sustain respiration
GLUT2- liver allowing the hepatocytes to export glucose made by gluconeogenesis into the blood. primary glucose transporter in pancreatic beta cells.
GLUT3-main transporter in brain. high affinity isoform for times of low glucose plasma conc.
GLUT4-insulin-regulated glucose transporter expressed by skeletal muscle and adipose tissue
Which enzyme is crucial for the regeneration of NAD+ from NADH in red blood cells?
Lactate dehydrogenase.
No mitochondria so no normal regeneration in stage 4 (electron transport chain). regenerate NAD+ by converting pyruvate to lactate.
Lactate is transported to the liver and converted back to pyruvate and used in gluconeogenesis to produce glucose.
monomers of maltose
2x glucose
monomers of lactose
glucose and galactose
monomers of sucrose
fructose and glucose
how does glycogen differ from cellulose
Glycogen- alpha glucose 1,4 and 1,6
Branched chains
made/used in humans
fuel reserve
cellulose- beta glucose 1,4
linear chains
made by plants
structural role
what are the possible fates of lactate?
- converted back into pyruvate via LDH in liver
- converted into acetyl-coA in heart muscle to feed into TCA cyle
- converted into glucose via glucneogenesis in liver
- converted to acetyl-coA for lipid biosynthesis in liver.
why may lactic acidosis occur
heavy eating
vigorous exercise
shock
congestive heart disease
role of pyruvate dehydrogenase. when is this enzyme activated?
converts pyruvate into acetyl-coA. feed into TCA cycle.
activated when there’s high conc of glucose to be catabolised. (insulin activates)
ADP activates
symptoms of lactase deficiency, why do these happen?
stomach cramping
diarrhoea
unhydrolyzed lactose is fermented by gut bacteria.irritates GI tract.
how does liver disease/alcohol affect the conversion of lactate?
lactate –> pyruvate via LDH inhibited/impaired as no NAD to use. As alcohol converts NAD+ into NADH
how does Glucose-6-phosphate dehydrogenase deficiency effect RBCs?
dec NADPH disulphide bonds form aggregated proteins Heinz bodies (RBCs with denatured Hb) haemolysis (breakdown RBC as unable to transport O2)
How does dinitrophenol (DNP) affect oxidative phosphorylation?
uncoupler of oxidative phosphorylation.
protonophore- allows protons to leak across the inner mitochondrial membrane. Bypass ATP synthase.
Temp inc as energy is released as heat.
cyanide effect on electron transport chain?
Inhibits enzyme (cytochrome oxidase) complex so no longer able to facilitate acceptance of e- by O2.
prevents flow of e- through the e- transport chain. no p.m.f generated.
ATP production stops.
how are dietary carbohydrates are digested? which enzymes
Starch, glycogen, cellulose, lactose, sucrose.
- salivary amylase. Pancreatic amylase. polysaccharide into disaccharide. Release glucose and maltose, leave smaller polysaccharides.
- Glycosidases (membrane bound) break disaccharides into monosaccharides.
- enzymes: sucrase, glycoamylase, lactase
enzyme that converts galactose to galacticol
aldose reductase
why is the pentose phosphate pathway an important metabolic pathway in some tissues.
produces NADPH. Biosynthetic reducing power, lipid biosynthesis > high activity in liver/adipose tissue.
produce C5 nucleotides for nucleic acid synthesis > high activity in bone marrow
compare oxidative phosphorylation with substrate level phosphorylation
Oxidative:
- requires membrane associated complexes
- energy uncoupling occurs indirectly through use of proton gradient (pmf)
- REQUIRES O2
- major ATP synthesis process
Substrate level:
- requires soluble enzymes
- energy uncoupling occurs directly through formation of high energy of hydrolysis bond
- can occur to some extent w/o O2
- minor ATP synthesis process
Describe how uncoupling occurs in brown adipose tissue
thermogenic (UCP)- uncoupling protein.
response to cold:
- noradrenalin activates lipase, releases fatty acids to be oxidised and activate UCP
- produces NADH/FADH2 for electron transport
- UCP transports H+ into mitochondria bypassing ATP synthase.
> energy released as heat
