Session 6 - Energy Production: Carbohydrates Flashcards
Why can’t cellulose be used as a fuel source
There are no enzymes that break down the Beta 1-4 Links in cellulose. Only Alpha 1-4 enzymes present in the GI tract
Define a catabolic pathway
the breakdown of larger molecules into smaller ones, releasing large amounts of free energy
What is the convergence point for many catablic reaction of amino acids, glucose, fatty acids, Acohol?
Acetyl CoA
Outline the 4 stages of catabolism
1) breakdown of fuel molecules to building block molecules
2) Degredation of buiding block materials into small number of organic precursors
3) Kreb cyle
4) Electron transport and oxidative phosphorylation
At what stage does respiration turn mitochondrial?
Stage 3, Pyruvate is transported into the mitochondria
What sugars make up: sucrose, Maltose and Lactose
Sucrose: Glucose and Fructose
Maltose: Glucose and Glucose
Lactose: Glucose and Galactose
What cell have an absolute requirement for glucose? and what is the normal blood glucose level?
Blood glucose = 5mM
RBC, Neutrophils, Innermost cells of the kidney medulla, Lens of the eye
Where are disaccharidases found in the GI tract?
They are found attached to the brush border membrane of epithelial cells of the small intestine
What is the difference between primary, secondary and congenital lactose intolerance?
primary - absence or persistence allele
secondary - injury to small intestine
Congenital - Autosomal recessive defect in lactase gene. can’t digest breast milk
How is glucose absorbed from through the intestines?
Active - SGLT1 utilises the Na+ gradient set up by active Na+/K+ ATPase pump
Passive - Glut 2 allows facilitated diffusion into blood
what are the two main glucose transporters and why are they relevant?
GLUT 2 - pancreatic Beta cells
GLUT 4 - insulin regulated in striated muscle
outline the main features of glycolysis
- Glucose is converted to pyruvate (x2)
- Synthesis of 2 ATP (2 invested 4 produces)
- 2 NADH produces
- Irreversible pathway
Name 3 key enzymes of glycolysis and what they are involved in
1- Hexokinase
2- Phosphofructokinase
3- Pyruvate Kinase
Why does glycolysis occur in so many stages?
1) it can be controlled
2) Efficient energy conservation
3) Versatility (interconnections between pathways)
Name 2 important intermediates of glycolysis
glycerol phosphate - important to lipid biosynthesis
2,3 diphosphoglycerate (2,3 BPG) - Produced in RBC and decreases there affinity to O2
RBS can’t perform oxidative phosphorylation. How are NADH and Reduced carriers oxidised?
Anearobic respiration ultilising Lactose Dehydrogenase. Which converts pyruvate to lactate. Lactate is then metabolised by liver to reform pyruvate
What are the main causes of lactic acidosis?
1) over production of lactate
2) Lack of metabolism
3) Renal function hindered
Where do galactose and fructose enter glycolysis?
Fructose - G-3-P
Galactose -> G-1-P -> G-6-P
What causes “essential fructosuria” and fructose intolerance
Essential fructosuria - caused by missing fructose kinase and as such fructose can’t be used at all and is excreted in the urine
Fructose intolerance - Aldose B is non functioning meaning fructose 1-P accumulates in the liver and causes liver damage
What are the 3 enzymes (or lack there of) that cause galctosaemia?
Galactokinase
Uridyl Transferase
UDP galactose epimerase
Why is having non-fucntioning Uridyl Trandferase problematic?
This would lead to a build up of galactose 1-p which is damaging to the liver but also a build up of galactose (galactosaemia). This promotes the conversion of galactose to Galactitol which converts NADH to NADP+. The depletion of NADPH results in the formation of cataracts as there is inappropriate disulphide bridge formation
What are pentose phosphates requires for?
they are required for the biosynthesis of nucleotides DNA, RNA and coenzymes
What are the key factors in the pentose phosphate pathway?
Starts from Glucose-6-P
source of NADPH
C5-sugars important in synthesis
CO2 produced so reaction is unidirectional
Rate limiting enzyme is called - Glucose-6-Phosphate Dehydrogenase
Why aren’t reversible steps sites of regulation?
If you inhibit these steps the reaction will still come to equilibrium. So inhibition would have no effect on levels of product
What is product and feedback inhibition?
If sufficient product is available then that product will reduce the action of the enzyme as to slow the pathway down and not to build up intermediates
What is a committing step?
This is a step that can’t be reversed and as such it is important that it is controlled so that it can be diverted down another pathway. Not wasted
In catabolic pathways what are inhibiting and what are activating signals?
Inhibitory = high energy signals - ATP, NADH, FAD2H the product Activating = low energy signals - ADP, AMP, NAD+, FAD, the reactant
What is feed forward regulation?
Where an early pathway provides activating stimulation to an enzyme later in the pathway
What is the role of pyruvate dehydrogenase?
Reacts pyruvate with CoA to form acetyl CoA which is fed into the TCA cycle
Why is the conversion of pyruvate to acetyl CoA sensitive to Vitamin B1 deficiency?
Vitamin B1 is used to provide many of the factors such as FAD when the reaction takes place
name 2 enzymes involved in the regulation of the TCA cycle
Isocitrate dehydrogenase
Alpha- ketoglutarate dehydrogenase
(both these stages involve the removal CO2)
Describe the stages in Oxidative phosphorylation
1) electrons from NADH and FAD2H transfered to a series of electron transfer carrier molecules
2) Energy released pumps H+ into intramembranous space
3) H+ diffuse back down [H+] gradient (pmf) and pass through synthetase enzyme which synthesises ATP
Explain the action of cyanide
CN- inhibits the electron transport chain by preventing O2 from accepting e-. As such there is no flow of electrons to generate the p.m.f and ultimately no ATP synthesis
Explain the action of “uncouplers”
Uncouplers increase the permeability of the inner membrane to protons as such dissipating the p.m.f. Also lots of heat is emitted leading uncontrolled thermogenesis
What is themogenin and how does it relate to brown adipose tissue?
Themogenin (UCP-1) is a naturally occurring uncoupling protein in brown adipose tissue. As such it is found in new-born infants to generate heat particularly around vital organs
