Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

sem 1- MCBG > Carbohydrate Catabolism (glyc to ETC) > Flashcards

Carbohydrate Catabolism (glyc to ETC) Flashcards

1
Q

What cells have an absolute glucose requirement?

A

Red blood cells, neutrophils, innermost cells of kidney medulla, lens of the eye, cells of brain
uptake depends on glucose concentration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does the brain cope during periods of starvation?

A

-it can use ketone bodies for some energy requirements but needs time to adapt.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Stage 1 of carbohydrate catabolism is breakdown to monosaccharides. What enzymes are involved here?

A
  • salivary amylase breaks down starch & glycogen into dextrins.
  • pancreatic amylase further breaks them down into monosaccharides
  • membrane bound disaccharidases on brush border of SI contain lactase, sucrase & amylase and aid breakdown to monosaccharides.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why can’t humans hydrolyse cellulose?

A

-we lack the enzyme to break down the beta 1-4 linkages

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

There are three types of lactose deficiency. Name them & describe them.

A

1- primary lactase deficiency= absence of lactase persistent allele, only in adults, most common
2- secondary lactase deficiency= caused by injury to SI, eg coeliac disease, Crohns, usually reversible.
3- congenital lactase deficiency= autosomal recessive gene defect in lactase gene, can’t digest breast milk, v rare

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are symptoms of a lactase deficiency?

A

-bloating, flatulence, vomiting, diarrhoea.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How are Na+ absorbed into the intestinal epithelial cells ?

A
  1. Active transport (low to high conc)- via Na+ dependant glucose transporter SGLT1
  2. Passive transport (high to low conc)- via GLUT2 into blood
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is glucose taken into blood & then target cells ?

A
  • first into the intestinal cell via active transport ie Na+ Glucose co transporter, then from intestinal cell into blood via passive transport via GLUT2.
  • then from blood to target cells via facilitated diffusion using transport proteins (eg GLUT1, GLUT2! GLUT3 etc)
  • GLUT4 is insulin regulated
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is stage 2 of carbohydrate catabolism and what is the key thing that happens here? Where does glycolysis happen?

A
  • breakdown to metabolic intermediates
  • the release of ‘reducing power’ (NADH) and some ‘energy’
  • intracellular, cytosolic (cytoplasm of the cell)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Say the steps of glycolysis.

A

-6C glucose phosphorylated with ATP to glucose-6-phosphate. This increases reactivity of glucose. Enzyme needed for first phosphorylation= hexokinase
Then from glucose6phosphate to fructose6phosphate
, then fructose6phosphate to fructose 1,6-bisphosphate which is a phosphorylation using ATP. 2nd enzyme=phosphofructokinase-1 ie PFK. THIS IS THE COMMITING STEP because it’s where glucose is first committed to the metabolic pathway.
-then glucose is cleaved into x2 3C molecules
- small amount of NADH captured
-then, substrate level phosphorylation to return the Pi for ATP production.
-again, another molecule of ATP produced (2 for a glucose). Large exothermic reaction so is irreversible
-in the end we have x2 pyruvate, x2 ATP net, x2 NADH. all for x1 glucose molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the products of glycolysis?

A
  • x2 NADH
  • x2 ATP
  • x2 pyruvate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Features of glycolysis:

A
  • occurs in all tissues (cytoplasm)
  • exergonic, oxidative
  • no loss of CO2
  • can operate anaerobically with the aid of lactate dehydrogenase
  • irreversible pathway
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the benefit of having many steps in glycolysis?

Hint- metabolic benefit

A
  • chemistry is easier in smaller steps
  • efficient energy conservation
  • gives versatility (allows interconnections, allows, part can be used in reverse)
  • can be controlled
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the two important intermediates in glycolysis?

A

1) Glycerol phosphate(made from DHAP, via enzyme glycerol-3-phosphate dehydrogenase): important to triglyceride and phospholipid biosynthesis, produced in adipose and liver.
2) 2,3-bisphosphoglycerate
(2,3-BPG)-made from 1,3 bisphosphoglycerate via enzyme bisphosphoglycerate mutase ): produced in RBC , regulator of Hb O2 affinity i.e promotes release of O2, reduces oxygens affinity for Hb.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the enzyme responsible for the production of a) glycerol phosphate
b) 2,3-BPG

A

a) glycerol-3-phosphate dehydrogenase

b) bisphosphoglycerate mutase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is glycolysis dependant upon to continue?

A
  • when all NAD is converted to NADH

- this is why when the NAD runs out it must be found another way. (Lactate)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How & why is lactate produced?

A

NADH+pyruvate-> NAD+Lactate
ENZYME= lactate dehydrogenase
-in skeletal muscle & RBCs, pyruvate -> lactate via LDH to restore NAD+ needed for glycolysis to continue.
-lactate metabolised in liver and heart (in heart, lactate-> pyruvate via LDH for energy as it has lots of O2, in liver lactate-> pyruvate via LDH is NOT used for energy, instead pyruvate is converted back to glucose via GLUCONEOGENESIS) - if enzyme/ vitamins deficient eg thiamine, won’t work.
-main aim to regenerate NAD w/o O2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Define hyperlactaemia & lactic acidosis.

A
  • normal lactate conc in blood is less than 1mM
  • hyperlactaemia= 2-5mM, below renal threshold, no change in blood pH
  • lactic acidosis=above 5mM, above renal threshold, blood pH lowered
19
Q

Outline fructose metabolism & location of metabolism. Give a clinical example of this going wrong

A
  1. Fructose phosphorylated by fructokinase to fructose-1P.
  2. Aldolase breaks it down into DHAP & glyceraldehyde. (Metabolised in liver)
    - essential fructosuria- fructokinase missing so fructose passes into urine, no other problems
    - fructose intolerance= aldolase missing, fructose-1P accumulates in liver, liver damage, must remove fructose from diet.
20
Q

Outline galactose metabolism & give location of metabolism.

A
  • in liver
  • galactose phosphorylated to galactose-1P by galactokinase.
  • then, galactose-1P converted to glucose-1P via galactose-1-P uridyl transferase. This requires UDP-glucose conversion to UDP-galactose via UDP-galactose4’-epimerase.
21
Q

How does galactosaemia develop?

A

happens bc of deficiency in any of the enzymes.

  • galactokinase deficiency=rare, galactose accumulates
  • transferase deficiency= common, galactose & galactose-1P accumulate- harms liver, kidney & brain.
  • this causes galactose to enter other pathways:galactose covered to galactitol (unwanted) via enzyme aldose reductase in the process converting NADPH -> NADP+
  • depletes NADH levels, prevents maintenance of free SH groups on proteins, improper disulphides bond formation, loss of structural & functional integrity, forms cataracts
  • remove lactose from diet
22
Q

Outline the pentose phosphate pathway.

A

1-starts w glucose-6-P oxidatively decarboxylated to C5 sugar & CO2 via reduction of NADP -> NADPH. ENZYME= glucose-6-P-dehydrogenase
2-then 5C sugar rearranged to Fructose 6 phosphate (the next step in glycolysis) or G-3-P (further down in glycolysis) which then enter glycolysis.
CO2 expulsion means this process is irreversible
*no ATP produced, controlled by NADP/NADPH ratio-if NADPH high, it will stop as the NAD+ will be low.

23
Q

What are the functions of the pentose phosphate pathway?

A

1-produces NADPH in cytoplasm which is a reducing power used in lipid & steroid synthesis so lots found in adipose AND maintains free -SH groups, preventing inappropriate bonds.
2-produces C5 sugar for nucleotides so lots found in dividing tissues

24
Q

How does a glucose-6-phosphate deficiency affect the pathway?

A
  • cannot convert NADP+ to NADPH so there’s a low conc of NADPH in blood.
  • this means it cannot maintain a proteins structural integrity & inappropriate S-S bonds formed, cataracts & RBC clump together causing haemolysis.
25
Q

What is meant by allosteric regulation of enzymes?

A
  • activator/inhibitor binds away from the active site.

- covalently modifies the enzyme(phosp/dephospry) which alters its activity

26
Q

Metabolic pathways can be regulated. What is the significance of an irreversible step?

A
  • irreversible steps are potential sites of regulation, reduced activity reduces flux of substrates through the pathway directly.
  • reversible steps cannot be regulated
27
Q

Feedback inhibition is a type of product inhibition. Explain its mechanism.

A
  • where the final product of a pathway inhibits the enzyme at the start of the pathway.
  • reduces substrate and more intermediates reduce the build up
28
Q

What is the committing step?

A
  • the step at which the pathway branches

- inhibition of the commuting step allows the substrate to be diverted into other pathways.

29
Q

How are inhibitory & stimulators regulators activated?

A
  • inhibitory= activated by high energy signals eg ATP, NADH, FAD2H.
  • stimulatory= activated by low energy signals eg AMP, ADP NAD+, FAD
30
Q

Outline hormonal regulation of metabolic pathways. Give 2 examples.

A

-hormone receptor binding activated signalling pathway.
-Protein kinase phosphorylates or protein phosphotase dephosphorylates.
-alters protein conformation.
eg adrenaline stimulates glycogenesis
eg insulin stimulates glucose utilisation AND inhibits glycogen breakdown

31
Q

What does the term ‘feed forward’ mean in relation to metabolic pathway regulation?

A

-substrate at start of pathway provides positive allosteric signal to a later enzyme to activate the pathway

32
Q

What enzyme is the key regulator of glycolysis? What process does it catalyse? Where is the committing step of glycolysis?

A

phosphofructokinase-1 (PFK1)
fructose-6P -> Fructose1,6-bisphosphate
-committing step= PFK1
hexokinase is not the committing step as its products are diverted to other pathways eg pentose phosphate pathway

33
Q

What is the process of phosphoregulation of PFK1 & pyruvate kinase?
Hint; insulin & glucagon.

A
  • insulin (well fed hormone)- activates protein phosphotase1 which activates PFK1
  • glucagon (starvation hormone), activates protein kinase A and inhibits PFK1 to save precious glucose from entering glycolysis
34
Q

Outline metabolic regulation of PFK1.

A
  • high energy signals will inhibit PFK eg ATP,NADH

- low energy signals activate PFK eg AMP,ADP,NAD+

35
Q

Before pyruvate app an enter the Krebs cycle, it must be converted to Acetyl CoA. How does this occur?

A

Pyruvate+CoA+NAD+ -> acetyl CoA+CO2+NADH via ENZYME pyruvate dehydrogenase

  • happens in mitochondrial matrix, enzymes require vitB cofactors
  • irreversible
36
Q

Outline regulation of the Link reaction (pyruvate dehydrogenase)

A
  • PDH activated by low NAD+, pyruvate, ADP, insulin (dephosphorylation)
  • PDH inhibited by Acetyl CoA, ATP, citrate, NADH (phosphorylation)
37
Q

Outline the Krebs cycle.

allows interconversion to supply other pathways

A

MITOCHONDRIAL

  • oxaloacetate (C4) + Acetyl CoA (C2) -> citrate (C6), co2 removed& NAD-> NADH, co2 removed& NAD-> NADH, GDP to GDT (ATP), FAD -> FADH, NAD-> NADH
  • oxidative therefore requires O2 to work
38
Q

What are the products of the Krebs cycle for 1 glucose molecule?

A 
x2 GTP (ATP)
x6 NADH
x2 FADH
x4 CO2
x1 glucose
39
Q

How is the Krebs cycle regulated by the different signals?

A
  • activated by low energy signals eg ADP,AMP,NAD+, pyruvate, FAD+, insulin
  • inhibited by high energy signals eg ATP, citrate, NADH,FADH
40
Q

How is reducing power used in ATP synthesis?

A

1- electron transport

2- oxidative phosphorylation

41
Q

Outline the electron transport chain.

What’s the difference in energy between NADH &FADH?

A
  • electrons are transferred from NADH & FADH to O2., releasing energy.
  • some of this energy is used to drive H+ across the membrane into the inter membrane space. The gradient formed here is called the proton motive force.
  • H+ ions must return into the mitochondria down its electrochemical gradient.
  • they travel through the ATP synthase using energy from the pmf & this drives ATP synthesis.
  • NADH has x3 proton carriers, FADH has x2 therefore 2NADH makes 5ATP compared to 2FADH makes 3ATP
42
Q

How is oxidative phosphorylation regulated?

A

-when [ATP] high, [ADP] is low so there’s no substrate for ATP synthase, inward flow of H+ stops & stays in IMS, pumping stops.

43
Q

Describe inhibition & uncoupling of oxidative phosphorylation.

A
  • inhibitors eg cyanide. Has higher affinity than O2 so acts as a competitive inhibitor. Blocks flow of e into IMS so no pmf created, no ATP made.
  • uncouplers increase permeability of inner mitochondrial membrane to H+ so dissipates gradient & reduces pmf, no drive for ATP synthesis
  • rest of energy lost as heat eg brown adipose tissue has uncouplers*
44
Q

Compare & contrast substrate level and oxidative phosphorylation.

A

Oxidative- needs membrane, indirect coupling (via pmf), needs O2, makes most ATP
Substrate level- requires soluble enzymes (cytosolic), direct (phosphoryl group transfer), can happen for a little w/o O2, only produces a little of ATP

sem 1- MCBG (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions