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MCAT Biochemistry > Chapter 9: Carbohydrate Metabolism l: Glycolysis, Glycogen, Gluconeogenesis, and Pentose Phosphate Pathway > Flashcards

Chapter 9: Carbohydrate Metabolism l: Glycolysis, Glycogen, Gluconeogenesis, and Pentose Phosphate Pathway Flashcards

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MCAT flashcards
1
Q

GLUT 2 is found in __ for glucose storage and it has a __ Km value

A

liver, high Km

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2
Q

GLUT 4 is found in __ and __ tissues and it has a __ Km value

A

found in adipose and muscle tissues. Low Km

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3
Q

Where does glycolysis occur in cells? Does it need Oxygen?

A

Glycolysis occurs in cytoplasm. No it’s an anaerobic form of respiration.

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4
Q

Glycolysis is what form of respiration. it yields _ ATP per glucose molecule

A

anerobic respiration. 2 ATP per/glucose

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5
Q

Name the glycolytic enzymes in order

A

Glucokinase, hexokinase, Phosphoglucose isoemrase, Phosphofructokinase-1 (PFK-1), Aldolase, Trisphosphate Isomerase (TIM), Glycerladhyde-3-phosphate dehydrogenase (GAP), Phosphoglycerate kinase, phosphoglycerate mutase, enolate, pyruvate kinase

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6
Q

Which three enzymes catlyze irreversible reactions?

A

Glucokinase/hexokinase, PFK-1, pyruvate kinase

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7
Q

NADH produced in glycolysis is oxidized by mitochondrial ___ when oxygen is present

A

ETC

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8
Q

when oxygen or mitochondira are absent, the NADH produced in glycolysis is oxidized by cytoplasmic __ (2 words)

A

lactate dehydrogenase

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9
Q

__ comes from lactose in milk. It is trapped in the cell by ___ and covnerted to glucose-1-phosphate via ___ (3 word) and an epimerase

A

Galactose, galactokinase, galactose-1-phosphate uridyltransferase

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10
Q

__ comes from honey, fruit, and sucrose. It is trapped in the cell by __, and then cleaved by __ to form glyceraldehyde and DHAP

A

Fructokinase

aldolase B

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11
Q

__ refers to a complex of enzymes that converts pyruvate to acetyl-CoA

A

pyruvate dehydrogenase

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12
Q

Pyruvate dehydrogenase is stimulated by __ and inhbited by __

A

insulin

acetyl CoA

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13
Q

__ is the production of glycogen

A

glycogenesis

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14
Q

__ (2 words), creates a-1,4 glycosidic links between glucose molecules (linear amylase)

A

glycogen synthase

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15
Q

__ (2 words) moves a block of oligoglucose from one chain and adds it tot he growing glycogen as a new branch using a-1,6 glycosidic link (amylopectin)

A

Branching enzyme

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16
Q

__ is the breakdown of glycogen using two main enzymes

A

glycogenolysis

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17
Q

__ (2 words) removes single glucose 1 phosphate moelcules by breaking a-1,4 glycosidic links in the liver. Activated by glucagon to rpevent low blood sugar. activated by epinephrine and AMP for skeletal muscles

A

glycogen phosphorylase

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18
Q

Glycogen phosphorylase is activated by what in the (1) liver and (2) skeeltal muscle

A

In the liver it’s glucagon

In the muslces it’s epinephrine and AMP

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19
Q

__ (2 words) moves a block of oligoglucose form one branch and connects it to the chain using an a-1,4 glycosidic link. Removes the branchpoint, which is connected via an a-1,6 linkage, releasing free glucose

A

Debranching enzyme

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20
Q

__ occurs in both cytoplasm and mitodhondira, but mainly in the liver with a small contribution from kidneys

A

Gluconeogenesis

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21
Q

Gluconeogenesis is basically the reverse of glycolysis but the dilemma is we must bypass the irreverisble steps of glycolysis. Gluconeogenesis has 4 enzymes that can do this, state them

A

Pyruvate carboxylase
Phosphoenolpyruvate carboxykinase (PEPCK)
Fructose-1,6-bisphosphatase
Glucose-6-phosphatase

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22
Q

Pyrvuate carboxylase converts pyruvate to __

A

oxaloacatate

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23
Q

Phosphoenolpyruvate carboxykinase (PEPCK) converts oxaloacetate to __

A

Phosphoenolpyruvate

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24
Q

Pyr carboxylase is activated by what. PEPCK is activated by what?

A

Pyr carboxylase is activated by Acetyl CoA from B-oxidation

PEPCK is activated by glucagon and cortisol

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25
Q

F16BPase converts F16BP to ___

A

fructose 6-phosphate

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26
Q

What is the RDS of gluconeogenesis? What activates it? Inhibition feedback?

A

F16BPase. Activated by ATP and Glucagon. Inhibited by AMP and insulin

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27
Q

G6Pase converts glucose-6-phosphate to free __. Found only in __ (2 words)

A

glucose

Endoplasmic reticulum of liver

28
Q

The pentose phsphate pathway (PPP) also known as ___. Occurs in the ___ to generate ___ (2 words)

A

Hexose monoposphate shunt (MHP)
cytoplasm of cells
NADPH and sugars (from rubulose-5-phsphate)

29
Q

The RDS of he PPP/HMP shunt is __ (2 words). Which is activated by ___ and inhibited by ___ and ___

A

glucose-6-phosphate dehydrogenase
NADP+
NADPH and insulin

30
Q

Normal range of blood-sugar concentration

A

4-6 mM

31
Q

What drives glucose entry into most cells?

A

By concentrations and is independent of sodium

32
Q

Glut 2
__ Affinity transporter in __ and __ cells
Captures excess glucose from the ___ ___ __ (3 words) from the intestine and primarily stores it
When glucose levels drop below the Km for the transporter, remaining glucose will ___ the liver and enter peripheral ___

A

Low affinity
Hepatic and Pancreatic cells
Hepatic portal vein
bypass the liver and enter peripheral

33
Q

Liver will pick up glucose and store it as ___

A

glycogen

34
Q

Glut 4
Responds to glucose concentration in ___ ___
Found in ___ and ___ tissues
Dependent on ___
Km of GLUT 4 is similar to __
At higher glucose levels, transporters will permit only a constant rate of glucose ___
Muscles store glucose as ___ and adipose tissues needs glucose to store ___ ___ as ____

A 
peripheral circulation
Adipose and muscle
Insulin
BS = 5mM 
influx 
glycogen
Fatty Acids as triacylglycerides
35
Q

Mnemonic for the function of insulin and glucagon?

A

Insulin “Inside the cell” so BS goes down because glucose gets absorbed into cells
Glucagon “glucose be gone” so BS goes up because glucose goes away from cells and into bloodstream

36
Q

GLUT transporters work at baseline levels but insulin causes what?

A

Increase rate of take up because more GLUT4 are now on the surface of adipose and muscle tissues

37
Q

What is glycolysis and where does it occur?

A

Converts glucose into two pyruvate molecules, two NADHs, two ATP. Occurs in cytoplasm

38
Q

If a cell has mitochondira and oxygen, the product of glycolysis NADH can be fed into ___ ___ (what type of respiration or ___ in order to generate ATP for the cell

A

aerobic respiration or ETC in order to generate energy for the cell

39
Q

If not mitochondira or oxygen, then glycolysis can occur ___ or by ___which results in smaller energy output

A

anaerobic or by fermentation

40
Q

In general what two enzymes transports glucose and traps it into cells?

A

GLUT 2/4 and phosphorylating it with either Hexokinase (many cells) or glucokinase (liver and pancreatic)

41
Q

What enzume is the rate limited enzyme and the main control of glycolysis?

A

Phosphofructokinase 1

42
Q

What does phosphofructokinase 1 act on and what is the product?

A

Fructose 6 phosphate + ATP–> Fructose-1,6,bisphosphate + ADP

43
Q

what is PFK-1 inhbited by and what is it activated by? (Hint think negative inhibtion due to excess amount of product). Why?

A

Inhibited by ATP (has enough energy) and citrate (TCA cycle is full and has enough energy) so glycolysis should turn off and turn on gluconeogenesis
Activated by AMP and insulin (cell is starved for ATP so turn off gluconeogenesis and turn on glycolysis
Reason: Cell should turn off glycolysis when it has too much energry and turn it on when it needs energry (high AMP). Citrate is an intermediate in Krebs Cycle, implies that cell is producing enugh energy for the O2 reactions

44
Q

What stimulates and inhbibits PFK-2 in hepatocytes?

A

Insuline stimulates and glucagon inhibits PFK-2
Insuline activates PFK-2: F6P –> F2,6-BP
F2,6-BP activates PFK-1: F6P –> F1,6-BP
Glucagon inhbits PFK-2: lowers F2,6BP (which activates F26BPase for gluconeogenesis)

45
Q

where is PFK-2 found? Where is PFK-1 found?

A

PFK-2 liver

PFK-1 other cells in roder to override inhibtion caused by ATP sot hat glycolysis can continue

46
Q

Role of glyceraldehyde-3 Phosphate DH

A

catlyzes oxidation and addition of P to glyceraldehyde 3 phosphate. High 1,3 biphosphoglycerate and reduction of NAD+ to NADH. NADH oxidized by mitochondrial eelctron transport, if oxygen is present

47
Q

Glyceraldehyde 3 Phosphate DH
Catalyzes an __ and addition of an __ to its substrate glyceraldehyde 3-phosphate
Results in producitn of a high energy intermediate ___
and the reduction of ___ to ___
___ can be oxidized by mitochondiral ETC if ___ is present

A

oxidation, Phospahte
1,3 biphosphoglycerate, reduction of NAD+ to NADH
NADH oxygen

48
Q

3 Phosphoglycerate kinase
Transfers high energy phosphate from ___ to ADP
Results in the formation of __ and __
This is an example of a substrate level ____ rxn: ADP is direcrly phosphorylated using a high energry intermedaite

A

1,3 Biphosphoglycerate to ADP
ATP and 3-PG
substrate level phosphorylation reaction

49
Q

Pyruvate Kianse
the __ enzymes in aerobic glycolysis
Catalyzes a substrate level phosphorylation of ___ using high energry substrate ___
It is acrivated by ___ from the PFK-1 reaction
Exhibits feed-forward activation: products of an earlier reaction fo glycolsyis, ___ a later reactions in glycolysis

A

the last enzyme in aerobic glycolysis
ADP using high energy susbtrate phosphoenolpyruvate (PEP)
activated by 1,5 biphosphate
stimulate the alter reactions

50
Q

When does fermentation occur?

A

Occurs in the absence of oxygen

51
Q

Lactic fermentation involves ___
which oxidizes ___ to ___ in order to replenish the coenzyme for glycerladehyde 3 phosphate DH
without mitochondira/oxygen, glycolysis would stop when all NAD+ is converted to ___
Thus, ____ can prevet this from occurring by reducing pyruvate to ____

A

lactate dehydrogenase
oxidizes NADH to NAD+
when all NAD+ is converted to NADH
thus, lactate dehydrogenase can rpevent this from occurring by reducing pyrviate to lactate

52
Q

What are the threee important intermediates of glycolysis that bridges to other metabolic pathways?

A 
dihydroxyacetone phosphate (DHAP) : used in ehtapic and adipose tissue to triacylglyceride synthesis
1,3 BPG and PEP: High energy intermedaites to generate ATP by substrate level phosphorylation (only ATP gained in anaerobic respiration
53
Q

Aneorbic glycolysis yields a net __ per glucose

A

2 ATP/glucose

54
Q

RBCs have what enzyme that produces 2,3 biphosphoglycerate from 1,3 BPG in glycolysis?

A

Biphosphoglycerate mutaase

55
Q

where does 2,3BPG bind to in hemoglobin and what affect does it have on its affinity? What can be seen in the oxygen dissociation curve?

A

Binds to the beta chains of Hemoglobin
Decreases affinity (higher Km value) for oxygen thus oxygne unloading into tissues for circulation
2,3 BPG causes a rightward shift on the Hb dissociation curve

56
Q

2,3 BPD does not bind to ___ Hb. Explain why. Why is this beneficial?

A

2,3 BPG does not bind to fetal Hb because there’s a negatively charged gamma subunit instead so it repels it. This is beneficial because it allows for Hb ti have higher affinity (lower Km) for oxygen then materal Hb

57
Q

Galactose is a ___ of glucose

A

C4 epimer of glucose

58
Q

Lactose is a disaccharide made up of __ and __ with the glycosidic linkage at ___

A

glucose and galactose

B (1–>4)

59
Q

Steps in lactose galactose metabolism

A

Lactose = galactose and glucose with B (1–>4) linkages

(1) Lactase acts on the B (1–>4) linakges and splits it into lactose and glucose
(2) galactose reaches liver through hetaptic protal vain, and transproted to tissue
(3) galactose phosphorylated by galactokinase –> galactose-1-P
(4) Galactose-1-phosphate uridyltransferase is an epiermase and converts galactose-1-phosphate to glucose-1-P
(5) Glycogen or Glucose 6-P
(6) If glucose 6-P then glycolysis or revert back to glucose

60
Q

Steps in fructose metabolism. Start with sucrose

A

Sucrose = fructose and glucose a (1–2) linakges

(1) Sucrase acts on a(1–2) linkages and splits it into fructofruanose and glucopyranose which is absorbed via the hepatic portal vein
(2) Fructokinase: phosphorylates fructose and traps it in cell –> fructose 1 P
(3) Aldolase B cleaves F1P into glycerladehyde and DHAP
(4) glycolysis, glycogenesis, glyconeogeneis

61
Q

In aerobic glycolsyis what does pyrvuate enter and what is it converted to?

A

It enters the mitochodnria and is converted into Acetyl-CoA such that it can enter the TCA/Krebs cycle or for fatty acid synthesis

62
Q

Pyruvate Dehydrogenase complex
Considered to be a ___ reaction so cannot be sued to covnert acetyl CoA back to pyruvate
Activated by ___ in the liver and is not responsive to hormones in the nervous system
High Insulin levels signal that individal is in ___ state
Liver should ___ glucose for energy
Shifts ___ ___ equilirbium towards production and stoage

A 
Irreversible reaction
activated by insulin
high insulin = well fed state
liver should burn glucose
shfits fatty acid
63
Q

What are the three fates of pyruvate

A

(1) PDH to covnert it to acetyl-CoA
(2) lactate dehydrogenase to become lactate
(3) pyrvuate carboxylase to become oxaloacetate

64
Q

PDH is inhbited by

A

its product Acetyl CoA

65
Q

Glycogen

A 
Homopolymer of glucose 
Lienar at (1-->4)
Branchning at (1-->6)
66
Q

Synthesis and degradation of glycogen occurs in ___

A

liver

MCAT Biochemistry (3 decks)

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