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Biochemistry > glycolysis > Flashcards

glycolysis Flashcards

1
Q

glycolysis involves a sequence of reactions that metabolizes:

A

1 molecule of glucose to 2 molecules of pyruvate and generates 2 molecules of ATP

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2
Q

under aerobic conditions, pyruvate is

A

completely oxidized generating much more ATP

aerobic system is more efficient than anaerobic

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3
Q

complete oxidation is more energy efficient than

A

anaerobic glycolysis

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4
Q

sources of glucose in diet:

A

disaccharides (especially sucrose and lactose)

starch

glycogen

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5
Q

in mammals:

glucose is the only fuel that brain uses under

glucose is the only fuel that ______ cells can use

A

conditions of non-starvation

red blood

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6
Q

pyruvate and lactate can be salvaged and resynthesized to glucose via

A

gluconeogenesis

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7
Q

glucose uptake occurs via protein transporters called

A

glucose transporters (GLUTs)

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8
Q

GLUT 1

A

ubiquitous but expressed highly in brain, RBCs, cornea, placenta, and cancer cells

high affinity

unregulated

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9
Q

GLUT 2

A

main transporter in liver (also pancreas)

low affinity

unregulated

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10
Q

GLUT 3

A

main transporter in neurons

high affinity

unregulated

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11
Q

GLUT 4

A

present in skeletal muscle, heart, and adipose tissue

insulin dependent

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12
Q

largest GLUT transporter

A

GLUT 2

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13
Q

smallest GLUT transporter

A

GLUT 1/3

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14
Q

location of glycolysis

A

occurs in cytoplasm of eukaryotic cells

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15
Q

two stages of glycolysis

1.

2.

A
  1. trapping of glucose and its cleavage into 2 interconvertible 3-carbon molecules
  2. generation of ATP
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16
Q

first stage of glycolysis begins with:

ends with

A

the phosphorylation of glucose

the isomerization of dihydroxyacetone phosphate to glyceraldehyde 3-phosphate (GAP)

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17
Q

trapping of glucose (through GLUTs) and preparation phase:

ATPs consumed:

ATPs generated:

A

2 ATPs consumed

no ATPs generated

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18
Q

strategy of stage 1 is to:

and form a compound that can be readily cleaved into:

A

trap the glucose in the cell

2 phosphorylated 3-carbon units

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19
Q

stage 1 step 1

ATP:

enzyme:

A

glucose phosphorylated to glucose-6-phosphate (G6P)

ATP is consumed

enzyme: hexokinase (in all tissues) and glucokinase (in liver)

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20
Q

stage 1 step 2

ATP:

enzyme:

A

G6P isomerized to fructose-6-phosphate (F6P)

no ATP

enzyme: phosphoglucoisomerase

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21
Q

stage 1 step 3

ATP:

enzyme:

A

F6P phosphorylated to fructose-1,6-bisphosphate (F1,6BP)

ATP is consumed

enzyme: phosphofructokinase (rate limiting enzyme of glycolysis)

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22
Q

stage 1 step 4

ATP:

enzyme:

A

F1,6BP broken down to glyceraldehyde-3-phosphate (G3P/GAP) and dihydroxyacetone phosphate (DHAP)

no ATP

enzyme: aldolase

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23
Q

stage 1 step 5

ATP

enzyme:

A

DHAP isomerized to G3P (GAP)

no ATP

enzyme: triose phosphate isomerase

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24
Q

second stage of glycolysis:

energy harnessed in _____ used to form _____

A

GAP

ATP

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25
Q

stage 2 step 1

NAD+

enzyme:

A

oxidative phosphorylation of GAP to form 1,3-bisphosphoglycerate (1,3-BPG)

NAD+ reduced to NADH

enzyme: glyceraldehyde 3-phosphate dehydrogenase (GAPDH)

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26
Q

NADH contains

A

a pair of “high energy” electrons

sent to ETC, plays role in oxidative phosphorylation

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27
Q

stage 2 step 2

ATP:

enzyme:

A

1,3 BPG is converted to 3-phosphoglycerate (3-PG)

ADP is phosphorylated to form ATP

enzyme: phosphoglycerate kinase

28
Q

stage 2 step 3

ATP

enzyme:

A

3-PG is converted to 2-phosphoglycerate (2-PG)

no ATP

enzyme: phosphoglycerate mutase

29
Q

stage 2 step 4

water:

enzyme:

A

2-PG is dehydrated to form phosphoenolpyruvate (PEP)

water is formed

enzyme: enolase

30
Q

stage 2 step 5

ATP:

enzyme:

A

PEP is converted from unstable enol to pyruvate, a stable ketone

ATP is formed

enzyme: pyruvate kinase

this step is irreversible

31
Q

pyruvate can be reduced to

A

lactate, with the generation of NAD+

32
Q

pyruvate can be oxidized aerobically via the

A

citric acid cycle after first undergoing an oxidative decarboxylation to form acetyl CoA and producing CO2

33
Q

yeast and some other microorganisms can convert pyruvate to

A

ethanol

fermentation

34
Q

pyruvate –> lactate produces NAD+ that can be used in what step of glycolysis?

A

GAP –> 1,3 BPG

35
Q

sucrose is a disaccharide of

A

glucose and fructose

36
Q

lactose is a disaccharide of

A

glucose and galactose

37
Q

fructose and galactose can be converted into

A

glycolytic intermediates

38
Q

fructose quickly turned into ______ in times of high energy

A

fat

39
Q

what is important about fructose metabolism?

A

it bypasses the rate limiting step of glycolysis

40
Q

fructose metabolism:

A
  1. fructose –> fructose 1-phosphate via enzyme fructoskinase (ATP –> ADP)
  2. fructose 1-phosphate –> glyceraldehyde + DHAP via enzyme fructose 1-phosphate aldolase
  3. glyceraldehyde –> G3P/GAP via enzyme triose kinase
41
Q

galactose metabolism

A
  1. galactose –> galactose 1-phosphate via galactokinase
  2. galactose 1-phosphate + UDP-glucose –> glucose 1-phosphate via enzyme: galactose 1-phosphate uridyl transferase
  3. glucose 1-phosphate –> glucose 6-phosphate via phosphoglucomutase
42
Q

major regulatory enzymes of glycolysis and reactions they catalyze

A

hexokinase: glucose –> glucose 6-phosphate (ATP –> ADP)

phosphofructokinase (rate-limiting step): fructose 6-phosphate –> fructose 1,6 bisphosphate (ATP –> ADP)

pyruvate kinase: phosphoenolpyruvate –> pyruvate (ADP –> ATP)

43
Q

glycolysis in at rest muscles (major regulatory enzymes)

A

glycolysis is inhibited

glucose 6-phosphate inhibits action of hexokinase

high ATP : AMP ratio inhibits PFK and PK

44
Q

glycolysis in muscles during exercise (major regulatory enzymes)

A

glycolysis is stimulated

glucose 6-phosphate is continuing on in pathway (does not inhibit hexokinase)

low ATP : AMP ratio activates PFK and PK

45
Q

goal of glycolysis in muscle

A

to generate ATP during activity (ATP levels regulate glycolysis)

46
Q

goals of glycolysis in liver

A

to maintain blood glucose levels

to provide building blocks for other pathways

47
Q

glycolysis in liver (major regulatory enzymes)

A

glucokinase is not inhibited by glucose 6-phosphate (glucose is permanently trapped)

(very little hexokinase in live)

PFK is activated by F-2,6-BP (inhibited by citrate)

PK is regulated by allosteric effectors and covalent modifications (F-1,6-BP activates and ATP inhibits)

48
Q

hexokinase has a ______ affinity for glucose

A

high

49
Q

glucokinase has a ______ affinity for glucose

A

low

50
Q

excessive fructose has been linked to

A

fatty liver, insulin insensitivity, obesity, type II diabetes

51
Q

actions of fructokinase and triose kinase bypass

A

hte most important regulatory step in glycolysis (PFK rate limiting step)

52
Q

fructose-derived G3P and DHAP are processed by

A

glycolysis to pyruvate and acetyl CoA in an unregulated fashion

53
Q

excess acetyl CoA (from excess fructose) is converted to

A

fatty acids which can be transported to adipose tissue to form triacylglycerols, resulting in obesity ; and liver also begins to accumulate fatty acids resulting in fatty liver

54
Q

activity of fructokinase and triose kinase (from fructose consumption) can deplete the liver of

A

ATP and inorganic phosphate, compromising liver function

55
Q

lactose intolerance

A

inability to metabolize lactose

drinking milk causes disturbances in GI function

56
Q

lactose intolerance is caused by

A

deficiency in enzyme lactase (which breaks down lactose to glucose and galactose)

57
Q

galactosemia

A

disruption of galactose metabolism

58
Q

classic galactosemia (most common form)

A

is an inherited deficiency in galactose 1-phosphate uridyl transferase activity

59
Q

defects in galactose metabolism results in:

A

failure to thrive

vomiting/diarrhea after consuming milk

enlargement of liver and jaundice

cataracts

lethargy and retarded mental development

significant elevation of blood-galactose levels and presence of galactose in urine

60
Q

how do you diagnose defect in galactose metabolism

A

absence of galactose 1-phosphate uridyl transferase in RBCs

61
Q

how to you treat defect in galactose metabolism

A

remove galatose (and lactose) from diet

62
Q

although elimination of galactose from diet (in patients with defect in galactose metabolism) prevents liver disease and cataract development, many patients still suffer from

A

CNS malfunction, most commonly a delayed acquisition of language skills

63
Q

cataracts results from

A

galactose being unable to enter glycolysis and instead being turned into galactitol

64
Q

warburg effect (aerobic glycolysis)

A

rapidly growing tumor cells metabolize glucose to lactate even in the presence of oxygen

65
Q

visualization of tumor and effectiveness of treatment:

a non-metabolizable glucose analog, 2-F-2-D-deoxyglucose detected by a combination of

A

positron emission tomography (PET) and computer-aided tomography (CAT)

Biochemistry (32 decks)

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