Biochemistry (Gareth's Section) Flashcards
- Describe the ‘Glycemic Index’ and how it’s obtained.
Describes the postprandial glucose response: The area under the ‘test’ food glucose curve divided by the area under a ‘reference’ food glucose curve (normally 50 g glc).
Expressed as a %, it’s essentially the RATIO of test:reference.
- Glycogen structure: If all the glycogen molecules in a liver cell had up to four tiers of branches, what would be the most effective way of increasing glycogen stores in that cell?
a) Adding more branches
b) Increasing the length of individual branches
c) Having more glycogenin
d) Making more glycogen synthase enzymes
e) none of the above
c) Having more glycogenin
- Bile Salts: What statement about bile salts is INCORRECT?
A made in the liver, stored in the gall bladder
B represent the end point of cholesterol metabolism
C most pass into lower bowel after secretion into gut
D have both charged & hydrophobic portions
E none of the above
C most pass into lower bowel after secretion into gut
- Lipase inhibitors: Lipase inhibitors are potentially useful for weight loss. Which statement about them is INCORRECT?
A they inhibit the release of fatty acids from adipose tissue
B they discourage people from eating fat
C they reduce the digestion of dietary fat
D they reduce energy intake
E all of the above
A they inhibit the release of fatty acids from adipose tissue
- Lipoprotein Lipase (LPL): What statement about chylomicrons is INCORRECT?
A they are made in the intestinal epithelial cells
B they enter the bloodstream at lymph nodes
C they encounter peripheral tissues before the liver
D they have the highest density of all the lipoproteins
E all of the above
D they have the highest density of all the lipoproteins
- Which is NOT a non-essential amino acid?
a) asparatine
b) arginine
c) leucine
d) glutamine
e) serine
f) they are all non-essential
c) leucine - it is essential
Non-essentials (11): alanine, arginine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, and tyrosine.
(AlArAsAsCyGlGlGlPrSeTy)
Essentials (9): Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine.
- Fat substitutes: What would be an effect of consuming chips that had been fried in OLESTRA?
A fat soluble vitamins would be stripped from the body B impossible: the chips would not fry properly
C no OLESTRA would be absorbed from the gut
D blood chylomicrons would contain OLESTRA
E none of the above
C no OLESTRA would be absorbed from the gut
- Glycemic Index: First the subject consumes 50 g of pure G & their BG response is recorded. A day later, the same measurements are made after they consume 50 g apple. How do you then calculate the GI of apple?
a) express area apple as % area glucose
b) express peak glucose as % peak apple
c) express peak apple as % peak glucose
d) measurement not done properly
e) none of the above
d) measurement not done properly
Test food needs to be given in an amount that will give 50 g digestible carbohydrate (not just 50 g weight of the test food…)
- Lipogenesis, like other anabolic pathways, needs ATP. However, it also needs something else. What is that thing and where does it come from?
A acetyl CoA from the Krebs Cycle B NADPH from the Pentose Phosphate Pathway C reductant from glycolysis D NADH from the Krebs Cycle E none of the above
B NADPH from the Pentose Phosphate Pathway
- Essential amino acids: Which statement is CORRECT?
A. Egg proteins contains all the essential amino acids except methionine
B. A high quality protein is one that contains 18 out of the 20 amino acids
C. A high quality protein contains less than <5% non-essential amino acids
D. A food that contained twice the amount of lysine as egg protein would be low quality
E. Certain types vegetable tend to be deficient in at least one essential amino acid
E. Certain types vegetable tend to be deficient in at least one essential amino acid
- Glycemic Index: What statement is FALSE?
a) adding fructose to foods lowers their GI
b) soft drinks have a lower GI than rice
c) some foods have a GI of >100
d) low GI foods give you slow burning energy
e) none of the above
d) low GI foods give you slow burning energy
- Lipid Transport: What best represents the disposal of cholesterol?
a) reverse cholesterol transport
b) chylomicron remnants
c) VLDL remnants (IDL)
d) a & c
e) none of the above
a) reverse cholesterol transport
- Glycogen structure: What is glycogenin?
a) A form of glucose
b) A protein
c) A phospholipid membrane anchor
d) A form of glycogen synthase
e) none of the above
b) A protein
- Lipid transport: Where does CETP act?
a) reverse cholesterol transport
b) VLDL
c) VLDL remnants (IDL)
d) LDL
e) c & d
a) reverse cholesterol transport
Cholesterol Ester Transfer Protein (CETP) is a problem for the action of HDL (high-density lipoprotein), as it impedes its cholesterol-collecting action. It can intercept HDLs on their way back to the liver and remove CE, putting them back into things like VLDLs & chylomicrons.
- Cholesterol Metabolism: Consuming certain ‘resins’ binds bile salts & stops their re-absorption from the gut. This affects blood cholesterol levels. What is a MISCONCEPTION?
A. The resins will reduce blood LDL B. The liver will make more bile salts C. Tissues will express more LDL receptors D. Fat will no longer be digested E. All of the above
D. Fat will no longer be digested
- Glucose Uptake: Glucose doesn’t simply diffuse into cells. It needs transporters (GLUTs). Which is FALSE?
a) GLUT-1 are present on all cells
b) GLUT-1 catalyse a continual trickle of glucose uptake
c) Insulin increases number of GLUT-4 in cell membrane
d) Glucose CAN’T move back out into the blood
e) none of the above
d) Glucose CAN’T move back out into the blood
- G disposal in liver: What is the key difference bw ‘push’ & ‘pull’ models of glycogen synthesis (GS)?
a) Insulin stimulates ATP levels to ‘push’ GS
b) Insulin creates more glycogenin to ‘pull’ GS
c) G stimulates glycogen synthases to ‘push’ GS
d) Insulin stimulates G uptake to ‘pull’ GS
e) none of the above
c) G stimulates glycogen synthases to ‘push’ GS
‘Push’ mechanism in the LIVER. Glycogenesis responds to BG w/o the need of insulin. (insulin however will stimulate glycogenesis further.)
‘Pull’ mechanism in MUSCLES. Insulin stimulates GS to convert G into glycogen.
- First few hours of starvation: What process is MOST RESPONSIBLE for keeping blood glucose steady during the first five hours of starvation?
A. The secretion of insulin
B. The mobilisation of liver glycogen
C. The release of glucose from muscles
D. The inhibition of muscle glucose oxidation by fatty acids
E. A reduction in the rate of glucose oxidation by the brain
B. The mobilisation of liver glycogen
- Esterification: The final step of fat synthesis is esterification. What does this mean?
A The reaction of fatty acids with glucose
B The release of the fatty acyl CoA from FAS
C The attachment of fatty acids to a glycerol backbone
D The formation of glycerol 3-phosphate from glucose
E none of the above
C The attachment of fatty acids to a glycerol backbone
- Which of the following does NOT describe something about the way in which FAS converts malonyl CoA into fatty acyl CoA ?
A ATP is consumed
B NADPH is consumed
C during synthesis, the fatty acid is anchored to FAS
D FAS is a single protein with many enzyme activites
E none of the above
A ATP is consumed
Each round of 2C addition requires 2 molecules of NADPH, but NO ATP.
It also requires the release of the CO2 that went on during the production of malonyl-CoA
- Glucogenic & Ketogenic amino acids: What statement is INCORRECT?
A. Carbon skeletons that are anaplerotic to the Krebs Cycle CAN ALL contribute to gluconeogensis
B. Ketogenic skeletons can NOT be made into glucose C. Every carbon skeleton is ultimately converted into pyruvate
D. Ketogenic skeletons are NOT anaplerotic to the Krebs Cycle
E. Ketogenic skeletons can be made into fatty acids
C. Every carbon skeleton is ultimately converted into pyruvate
- Following consumption of 50 g of glucose, what blood glucose level would indicate that a person was GLUCOSE INTOLERANT?
a) >10 mM after 30 min
b) >8 mM after 120 min
c) <4 mM at time zero
d) 5 mM at time zero
e) none of the above
b) >8 mM after 120 min
- When does the PPP make reductant?
A As G6P is made into 5-carbon sugar phosphates
B As 5-carbon sugar phosphates are rearranged
C As PPP products enters glycolysis
D Only when glycogen synthase is inhibited
E none of the above
A As G6P is made into 5-carbon sugar phosphates
- Glycolysis: How is muscle phosphofructokinase (PFK) stimulated after a meal?
a) By an increase in insulin
b) By a rise in cell glucose concentration
c) By an increase in the demand for ATP
d) in response to higher glycogen levels
e) none of the above
c) By an increase in the demand for ATP
PFK is regulated allosterically; stimulated by low energy charge; the balance of ATP, ADP & AMP. An increase in cellular ADP/AMP and a decrease in ATP creates an ‘energy demand’ for ATP.
Thus, insulin ‘indirectly’ stimulates PFK & glucose oxidation, but its direct effect first creates the low energy charge.
- What is lipogenesis?
A formation of fat cells B storage of dietary lipid C formation of fatty acids from acetyl CoA D disposal of glucose by adipose tissue E all of the above
C formation of fatty acids from acetyl CoA
- What best represents the distribution of endogenously made cholesterol to body tissues?
a) Chylomicrons
b) VLDL
c) LDL
d) b & c
e) none of the above
d) b & c (VLDL & LDL)
- Glycogenesis: What statement about glycogen synthase (GS) is FALSE?
a) GS is switched off when it is phosphorylated
b) GS uses UDP-glucose as a substrate
c) GS adds glucoses to an existing glycogen chain
d) GS uses ATP to drive glycogen synthesis
e) all of the above
d) GS uses ATP to drive glycogen synthesis
I think: Using UTP releases PP (pyrophosphate?); PP hydrolysis pulls the reaction to completion - the driving factor.
GS doesn’t use ATP to drive glycogen synthesis, but it does contribute in making UDP back into UTP:
UDP + ATP -> UTP + ADP
(??? unless PP uses ATP rather than GS?)
- Early starvation: Imagine the situation 24 hours into starvation. Which statement is TRUE?
A. At this stage, the brain is using about 5 g glucose per hour
B. The glucagon levels will go back down to zero over the next few hours
C. The Cori-cycle represents de novo synthesis of glucose
D. The contribution of protein to the maintenance of blood glucose is negligible at this stage
E. The contribution of glycerol to the maintenance of blood glucose is negligible at this stage
A. At this stage, the brain is using about 5 g glucose per hour
*Proteins have a negligible contribution of AMINO ACIDS, but they do contribute to the conversion of pyruvate to lactate for the Cori-cycle (I think).
- PDH in starvation: Which feature of pyruvate dehydrogenase (PDH) is FALSE?
A. PDH is stimulated by dephosphorylation
B. PDH is activated by PDH phosphatase
C. PDH is inhibited when fatty acids are being oxidised
D. PDH is switched off by cAMP-dependent protein kinases
E. PDH kinase is activated by acetyl CoA
D. PDH is switched off by cAMP-dependent protein kinases
- Lipoproteins: Two hours after a fatty meal, blood plasma turns milky. Why?
A the presence of chyme in the plasma
B more free fatty acids in the plasma
C lots of bile salts are co-absorbed in fat uptake
D increased levels of very large lipoproteins
E don’t know
D increased levels of very large lipoproteins
i.e. chylomicrons
- What is the most important role of cholesterol ?
A. Making female & male sex hormones
B. Burnt for energy
C. Making bile salts to aid fat digestion
D. Ensuring structural integrity of membranes
E. All of the above
D. Ensuring structural integrity of membranes
- Which does NOT describe the problem of postprandial hyperglycemia?
a) protein glycosylation
b) lipid glycosylation
c) root cause may be impaired ability of tissues to respond to insulin
d) glucose intolerance is outlined by high blood glucose levels after each meal and persisting for several hours
e) euglycemic levels are not maintained
b) lipid glycosylation
(I don’t think this occurs but only 90% sure)
Insulin resistance and hyperglycemia underpin Type II diabetes.
Euglycemic is what we call the maintained 5 mM blood glucose concentration
- Amino acid digestion & tissue uptake/release: Which statement is TRUE?
A. After digestion in the gut, amino acids directly enter the lymphatic system
B. The enzymes involved in amino acid degradation are classic rate limiting steps (slow, irreversible, highly controlled)
C. Excess amino acids are stored in special membrane vesicles in the liver
D. In the liver, the first step of amino acid processing is to release the amine group as ammonia
E. The amino acid composition of the blood entering the liver is very different to the amino acid composition of the blood leaving the liver
E. The amino acid composition of the blood entering the liver is very different to the amino acid composition of the blood leaving the liver
- Glycogenesis: How does insulin stimulate the rate of glycogen synthase (GS)?
a) It activates the enzymes that make UDP-glucose
b) It increases the rate of glycolysis
c) It stimulates protein phosphatases
d) It drives glucose uptake which then stimulates GS
e) all of the above
f) none of the above
c) It stimulates protein phosphatases
GS is regulated by reversible phosphorylation. As it is active when dephosphorylated (and inactive when phosphorylated), Insulin stimulates dephosphorylation catalysed by phosphatases, specifically protein phosphatase I, PPI.
- Catabolic meltdown: Very high rates of lipolysis and proteolysis are associated with metabolic inefficiency. What is NOT a reason for this?
A. Ketone bodies can decarboxylate and be lost from the breath, sweat or via the urine
B. Energy is used in converting amine groups into urea for excretion
C. Energy is used in converting amino acid carbon-backbones into glucose
D. Ketone bodies are much less efficient than glucose as a fuel
E. Energy is used in converting glycerol into glucose
D. Ketone bodies are much less efficient than glucose as a fuel
(not a strong option but the best answer, as A,B,C,E are true)
- Which of the following is CORRECT?
a) We get the majority of our dietary carbohydrate from amylose
b) Amylose & amylopectin are starch derivatives that are branched and easy to digest
c) Amylopectin is a linear polymer of glucose, that forms helices and can be difficult to digest, causing flatulence
d) none of the above
d) none of the above
We get the majority of our dietary carbohydrate from starch in general, this includes both amylose AND amylopectin (not just amylose). They are both polymer chains of glucose.
Amylose: linear, forms helices, difficult to digest, flatulence.
Amylopectin: branched, easy to digest.
They are both completely different types of molecules in shape but still consist of glucose monomers end to end.
- How is glycogenesis similar in liver & muscle?
- Energy is required (ATP)
- Branch points
- There is a limit to the size the glycogen molecule can get to bc the branches start to bump into each other
