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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

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
F16BPase converts F16BP to ___
fructose 6-phosphate
26
What is the RDS of gluconeogenesis? What activates it? Inhibition feedback?
F16BPase. Activated by ATP and Glucagon. Inhibited by AMP and insulin
27
G6Pase converts glucose-6-phosphate to free __. Found only in __ (2 words)
glucose | Endoplasmic reticulum of liver
28
The pentose phsphate pathway (PPP) also known as ___. Occurs in the ___ to generate ___ (2 words)
Hexose monoposphate shunt (MHP) cytoplasm of cells NADPH and sugars (from rubulose-5-phsphate)
29
The RDS of he PPP/HMP shunt is __ (2 words). Which is activated by ___ and inhibited by ___ and ___
glucose-6-phosphate dehydrogenase NADP+ NADPH and insulin
30
Normal range of blood-sugar concentration
4-6 mM
31
What drives glucose entry into most cells?
By concentrations and is independent of sodium
32
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 ___
Low affinity Hepatic and Pancreatic cells Hepatic portal vein bypass the liver and enter peripheral
33
Liver will pick up glucose and store it as ___
glycogen
34
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 ____
``` peripheral circulation Adipose and muscle Insulin BS = 5mM influx glycogen Fatty Acids as triacylglycerides ```
35
Mnemonic for the function of insulin and glucagon?
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
GLUT transporters work at baseline levels but insulin causes what?
Increase rate of take up because more GLUT4 are now on the surface of adipose and muscle tissues
37
What is glycolysis and where does it occur?
Converts glucose into two pyruvate molecules, two NADHs, two ATP. Occurs in cytoplasm
38
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
aerobic respiration or ETC in order to generate energy for the cell
39
If not mitochondira or oxygen, then glycolysis can occur ___ or by ___which results in smaller energy output
anaerobic or by fermentation
40
In general what two enzymes transports glucose and traps it into cells?
GLUT 2/4 and phosphorylating it with either Hexokinase (many cells) or glucokinase (liver and pancreatic)
41
What enzume is the rate limited enzyme and the main control of glycolysis?
Phosphofructokinase 1
42
What does phosphofructokinase 1 act on and what is the product?
Fructose 6 phosphate + ATP--> Fructose-1,6,bisphosphate + ADP
43
what is PFK-1 inhbited by and what is it activated by? (Hint think negative inhibtion due to excess amount of product). Why?
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
What stimulates and inhbibits PFK-2 in hepatocytes?
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
where is PFK-2 found? Where is PFK-1 found?
PFK-2 liver | PFK-1 other cells in roder to override inhibtion caused by ATP sot hat glycolysis can continue
46
Role of glyceraldehyde-3 Phosphate DH
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
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
oxidation, Phospahte 1,3 biphosphoglycerate, reduction of NAD+ to NADH NADH oxygen
48
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
1,3 Biphosphoglycerate to ADP ATP and 3-PG substrate level phosphorylation reaction
49
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
the last enzyme in aerobic glycolysis ADP using high energy susbtrate phosphoenolpyruvate (PEP) activated by 1,5 biphosphate stimulate the alter reactions
50
When does fermentation occur?
Occurs in the absence of oxygen
51
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 ____
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
What are the threee important intermediates of glycolysis that bridges to other metabolic pathways?
``` 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
Aneorbic glycolysis yields a net __ per glucose
2 ATP/glucose
54
RBCs have what enzyme that produces 2,3 biphosphoglycerate from 1,3 BPG in glycolysis?
Biphosphoglycerate mutaase
55
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?
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
2,3 BPD does not bind to ___ Hb. Explain why. Why is this beneficial?
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
Galactose is a ___ of glucose
C4 epimer of glucose
58
Lactose is a disaccharide made up of __ and __ with the glycosidic linkage at ___
glucose and galactose | B (1-->4)
59
Steps in lactose galactose metabolism
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
Steps in fructose metabolism. Start with sucrose
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
In aerobic glycolsyis what does pyrvuate enter and what is it converted to?
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
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
``` Irreversible reaction activated by insulin high insulin = well fed state liver should burn glucose shfits fatty acid ```
63
What are the three fates of pyruvate
(1) PDH to covnert it to acetyl-CoA (2) lactate dehydrogenase to become lactate (3) pyrvuate carboxylase to become oxaloacetate
64
PDH is inhbited by
its product Acetyl CoA
65
Glycogen
``` Homopolymer of glucose Lienar at (1-->4) Branchning at (1-->6) ```
66
Synthesis and degradation of glycogen occurs in ___
liver

MCAT Biochemistry (3 decks)

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