Carbohydrates Flashcards
In what tissue do we find the enzyme glucose-6-phosphatase Select one: a. Muscle b. Liver c. Adipose, liver and muscle d. Adipose tissue
b. Liver
What type of carbohydrate is cellulose? Select one: a. A simple sugar b. A disaccharide c. A polysaccharide d. A monosaccharide
c. A polysaccharide
Sucrose comprises of a Select one: a. a glucose and a glucose molecule b. a glucose and a galactose molecule c. a glucose and a fructose molecule d. a fructose and a fructose molecule
c. a glucose and a fructose molecule
How is a polysaccharide made? Select one: a. dehydration synthesis b. glycolysis c. beta oxidation d. hydrolysis
a. dehydration synthesis
Ca++ and Mg+ contribute to regulation of PDH by activating \_\_\_\_\_\_\_\_\_\_\_ and inhibiting \_\_\_\_\_\_\_\_\_. Select one: a. PDH phosphatase, PDH kinase b. PDH kinase, glycogen phosphorylase c. PDH kinase, lactate dehydrogenase d. PDH mutase, PDH kinase
a. PDH phosphatase, PDH kinase
How much glycogen can we store in our liver? Select one: a. 200 g b. 400 g c. 100 g d. 10 g
c. 100 g
What is McArdles disease? Select one: a. The inability to undertake glycogenolysis b. Lack of glycogen stores in the muscle c. Reduced blood glucose d. The inability to undertake glycolysis
a. The inability to undertake glycogenolysis
For the average individual, how much glycogen can be stored in the muscle? Select one: a. 30 – 50 g b. 800 – 1000 g c. 80 – 100 g d. 300 – 500 g
d. 300 – 500 g
Glycogen is formed from glucose, catalysed by which enzyme? Select one: a. phosphofructokinase b. Phosphorylase c. Glycogen synthase d. phosphoglucomutase e. Hexokinase
c. Glycogen synthase
Glycogen phosphorylase is inactivated by Select one: a. Intramuscular creatine kinase b. ATP c. Ca++ d. All of the above
b. ATP
How long do glycogen stores last during hard exercise? Select one: a. 0.5-1 hour b. 4-5 hours c. 3-4 hours d. 1-2 hours
d. 1-2 hours
What does glycogen synthase do? Select one: a. Converts glycogen to glucose b. Converts glucose to glycogen c. Converts glucose to pyruvate d. Converts pyruvate to lactate
b. Converts glucose to glycogen
The hormone that stimulates glycogenolysis and gluconeogenesis is: Select one: a. Glucagon b. Insulin c. Somatostatin d. Secretin
a. Glucagon
Glut4 translocation is stimulated by Select one: a. AMP and Acetyl CoA b. insulin and phosphate c. ATP and Ca++ d. Ca++ and insulin
d. Ca++ and insulin
Phosphorylation of glucose to glucose-6-phosphate in the liver is catalysed by Select one: a. Phosphofructokinase b. Myokinase c. Glucokinase d. Hexokinase
c. Glucokinase
Pyruvate dehydrogenase activity is not regulated by Select one: a. Acetyl CoA b. ATP c. Citrate d. NADH
c. Citrate
Pyruvate dehydrogenase is regulated by Select one: a. Allosteric regulation b. Substrate availability c. Product inhibition d. All answers are correct
d. All
Which hormone is responsible for the transport of glucose into cells? Select one: a. glucagon b. insulin c. catecholamine d. albumin
b. Insulin
Which of the following is true?
Select one:
a. Pyruvate can diffuse across membranes without a transporter
b. Pyruvate is present in the mitochondrial matrix only
c. Pyruvate is decarboxylated to acetyl-coA by PDH
d. Pyruvate is a two carbon molecule
c. Pyruvate is decarboxylated to acetyl-coA by PDH
During prolonged exercise blood glucose uptake by skeletal muscle is: Select one: a. 1g/min b. 0.1g/min c. 10g/min d. 80g/min
a. 1g/min
What effect would an increase in glycogenolysis have on glucose uptake and why?
More glycogenolysis = increased glucose-6-phosphate
Increased levels of glucose -6-phosphate inhibit the enzyme hexokinase.
Glucose uptake will decrease because there is a large amount of glucose-6-phosphate.
Therefore, there is less glucose uptake into the cell.
During exercise PDH is activated, describe how.
PDH active form can be activated by PDH phosphatase.
You get more active PDH when there are large amounts of pyruvate, CoA and NAD+ (metabolites) and the product amounts are low: acetyl-CoA, NADH and CO2
Calcium is also a stimulant as it is released during muscle contraction
What are the three main disaccharides, the monosaccharides that make them up and the enzymes which hydrolyze them.
Maltose: glucose and glucose, hydrolyzed by maltase
Lactose: glucose and galactose, hydrolyzed by lactase
Sucrose: glucose and fructose, hydrolyzed by sucrase
What is the benefit of having different membrane transporters for glucose and fructose and what are they?
Into the enterocytes: glut 2 or SGLT1: glucose, glut 5: fructose
Into blood: glut2 for both
Into the brain: glut 1
Important to have both as it means that more ‘sugar’ can be absorbed than if they used the same transporter.
What are the two forms of starch in the human diet, what is their prevalence and how do they differ?
Amylose (15-20% in diet) Amylose is straight chain and only has 1,4 bonds.
Amylopectin (80-85% in diet). Amylopectin is branched and has two types of bonds (1,4 and 1,6).
Which of the following cannot be formed from pyruvate in human beings? a. Glucose
b. Fructose
c. Lactic acid
d. Linoleic acid
d. Linoleic acid
The series of reactions involving the conversion of glucose to pyruvate is known as
Glycolysis
Which of the following is a feature of aerobic metabolism?
a. Little or no oxygen is consumed
b. Lactic acid is a major byproduct
c. Energy is produced more slowly than in anaerobic metabolism
d. Pyruvate is converted to glucose by reverse glycolysis to yield a net of 2 ATPs
c. Energy is produced more slowly than in anaerobic metabolism
Your roommate is participating in a weightlifting course and complains of a burning pain during workouts. You explain to that the rapid breakdown of glucose in his muscles produces large amounts of pyruvate, which the muscle converts to…..
Lactate
Which of the following is not a possible fate of metabolized glucose?
a. Urea
b. Acetyl CoA
c. Amino acids
d. Muscle glycogen
Urea
Which of the following nutrients can be made from compounds composed of 2-carbon skeletons?
a. Glucose
b. Fructose
c. Glycogen
d. Fatty acids
d. Fatty acids
Which of the following is a possible fate of acetyl CoA?
a. Degradation to urea
b. Synthesis to glycerol
c. Synthesis to fatty acids
d. Degradation to ammonia
c. Synthesis to fatty acids
An immediate consequence of a cellular deficiency of oxaloacetate is a slowing of…..
The TCA Cycle
In addition to energy, what are the principal end products of cellular oxidation of carbohydrates?
Water and carbon dioxide
Which of the following products is not generated via the TCA cycle or electron transport chain?
a. Water
b. Energy
c. Ammonia
d. Carbon dioxide
c. Ammonia
Products from the electron transport chain pathway include all of the following except
a. CO2.
b. urea.
c. water.
d. energy.
b. urea.
Outline the metabolic fates of pyruvate (produced in glycolysis).
Converted to lactate in anaerobic conditions.
Converted to acetyl CoA in aerobic conditions, and then metabolised to CO2 in the TCA cycle.
Total energy yield of one ATP? (aerobic)
30 ATP + 2 GTP
What ensures the TCA cycle is driven in the correct direction?
Three of the enzyme stages are irreversible.
What is the beta oxidation pathway?
Pathway for fatty acid metabolism.
Products of beta-oxidation?
> fatty acid CoA (which re-enters the pathway to be broken down further)…
…and acetyl CoA (which goes to the TCA cycle).
Which enzyme, involved in glycogen breakdown, is present in the liver but not in muscles?
glucose-6-phosphatase
Why is glucose-6-phosphatase not present in muscles?
The liver has this enzyme, and so can break down glucose-6-phosphatase into glucose, which can be released into the blood.
Muscle cells cannot do this, and so do not contribute to blood glucose concentration..
Benefit of glycogen branching?
Allows enzymes to cleave off entire branches. Also more ends to cleave from, so faster release.
How does glycogenolysis continue in prolonged exercise, without the need for hormonal interaction?
ATP conc is reduced and AMP conc rises.
AMP is an allosteric activator of glycogen phosphorylase.
(ATP is an allosteric inhibitor, so when energy levels are high, glycogenolysis is inhibited).
What is gluconeogenesis, and where does it take place?
Synthesis of glucose from non-carbohydrate sources. Takes place in the liver, in periods of carbohydrate deprivation.
In gluconeogenesis, what can and cannot be used as the substrate?
Sources include lactate, glycerol, glucogenic amino acids (all except leu, lys).
NOT FATTY ACIDS- because link reaction is completely irreversible.
Why is gluconeogenesis not simply the reversal of glycolysis?
There are 3 irreversible reactions in glycolysis that must be bypassed.
What type of oxidation is the most efficient way of using O2 to produce energy
Glucose oxidation
How much energy does 1 oxygen molecule burn
5 Kcals
Explain why we need to maintain glucose levels (for the brain)
glucose is the primary fuel source for brain cells, as well as neurotransmitter synthesis
Which glucose transporter is present in the blood-brain barrier?
a. glut 1
b. glut 2
c. glut 4
d. glut 5
a. glut 1
Which glucose transporter is present in the neuron?
a. glut 1
b. glut 2
c. glut 3
d. glut 5
c. glut 3
Which glucose transporter is present in the muscle cell?
a. glut 1
b. glut 2
c. glut 4
d. glut 5
c. glut 4
which hormone causes glut 4 translocation in the muscle
insulin
Muscle contraction can also stimulate GLUT4 translocation to plasma membrane. What are the two suggested signals
Calcium
AMP
For storage, what is glucose-6-phosphate converted into
glucose-1- phosphate (G1P) by phophoglucomutase
What is the purpose of UDP glucose
to bind to pre-existing glycogen to release UDP
What can activate PKA to deactivate glycogen synthase (3 things)
Ca2+, Adrenaline and Glucagon
When glycogen synthase (inactive) is phosphorylated into its active form, what happens in terms of glucose/glycogen
G-6-P is converted into glycogen
When glycogen synthase (active) is dephosphorylated into its active form, what happens in terms of glucose/glycogen
Glycogen is converted to g-6-p
At rest, glucose uptake is: a. 0.1 g/min B. 1 g/min c. 0.5 g/min d. 100 g/min
a. 0.1 g/min
Liver glycogenolysis and glucose output is what during prolonged exercise:
a. 10 g/min
b. 1 g/min
c. 2 g/min
d. 0.1 g/min
b. 1 g/min
Why does liver glycogenolysis/glucose output increase during prolonged exercise?
- AMP- the more the more glycogenolysis
* Glycogen P is activated by the presence of Ca and adrenaline
Which of the following is true:
a. When liver glycogen decreases, blood glucose decreases, so blood glucose uptake increases.
b. When liver glycogen increases, blood glucose decreases, so blood glucose uptake decreases.
c. When liver glycogen decreases, blood glucose increases, so blood glucose uptake increases.
d. When liver glycogen decreases, blood glucose decreases, so blood glucose uptake decreases.
When liver glycogen decreases, blood glucose decreases, so blood glucose uptake decreases.
How long does the glycolytic flux remain elevated for, after exercise?
a. 24 hours
b. 48 hours
c. 72 hours
d. It’s not raised in the first place
b. 48 hours
During exercise what does CHO oxidation increase up to roughly:
a. 1 g/min
b. 2 g/min
c. 5 g/min
d. 10 g/min
b. 2 g/min
