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Biochemistry > Exam 3 November 9 Lecture > Flashcards

Exam 3 November 9 Lecture Flashcards

1
Q

Why are carbohydrates important?

A

they are the most abundant biomolecule in nature and have functions in energy, structure, communication, and precursors for other biomolecules

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2
Q

Carbohydrates are a direct link between what?

A

between solar energy and chemical bond energy

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3
Q

What are the inputs and outputs of photosynthesis?

A

inputs: sunlight, water, carbon dioxide
outputs: oxygen, sugar

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4
Q

What are monosaccharides and what are they for?

A

one sugar molecule → for metabolism and circulation

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5
Q

What are some examples of monosaccharides?

A

glucose, fructose, galactose

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6
Q

What are disaccharides?

A

two sugar molecules

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7
Q

What are some examples of disaccharides?

A

sucrose (sweetener), lactose (nutrition), maltose (digestion)

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8
Q

What are oligosaccharides and what are they for?

A

two to ten sugar molecules → signal and structure recognition in which they attach to protein to act as an external recognition signal

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9
Q

What are some examples of oligosaccharides?

A

raffinose and stachyose

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10
Q

What are polysaccharides and what are they for?

A

ten or more sugar molecules → for nutrition, structure and lubrication, and energy storage

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11
Q

What are some examples of polysaccharides?

A

starch, glycogen, cellulose

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12
Q

What is catabolism?

A

the breakdown of fuels (like carbohydrates, lipids, proteins) into usable forms of energy (like ATP) → often coupled with generation of reducing equivalents like NADH

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13
Q

In catabolism in mammals, how is energy generated by?

A

oxidation of carbon compounds to carbon dioxide using oxygen

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14
Q

What is anabolism?

A

the biosynthesis of molecules from smaller molecules (like the synthesis of macromolecules, muscle contraction, active ion transport, thermogenesis) → requires energy in the form of ATP or NADPH

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15
Q

What is the overall reaction of oxidative respiration?

A

carbon fuel + O2 → CO2 + H2O + ENERGY
(carbon fuel is glucose, other carbohydrates, amino acids, fatty acids), (CO2 from the TCA cycle), (H2O from the ETS), (energy from glycolysis, TCA cycle, ETS, oxidative phosphorylation)

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16
Q

How is oxidative respiration achieved?

A

by a series of removal of electrons from carbohydrates and intermediates (aka oxidation) → the electrons pass through carriers NADH and FADH2 to the ETS and this drives ATP synthesis by oxidative phosphorylation

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17
Q

What is the general idea behind redox reactions?

A

A-oxidized + B-reduced ↔ A-reduced + B-oxidized (can be broken down to 2 half reactions: A-oxidized + n e- + n H+ ↔ A-reduced AND B-reduced ↔ B-oxidized + n e- + n H+)

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18
Q

Many redox reactions have both what?

A

an electron (e-) and a proton (H+) transferred

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19
Q

What type of reaction will it be if it generates ATP or even NADH?

A

a redox reaction

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20
Q

What are some important things to keep in mind for redox reactions?

A

reduced reactant → will be oxidized

oxidized reactant → will be reduced

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21
Q

What is an example of a redox reaction?

A

pyruvate + NADH + H+ ↔ lactate + NAD+

A-oxidized + B-reduced ↔ A-reduced + B-oxidized

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22
Q

What are some other important things about redox reactions?

A
  1. not oxygen dependent
  2. involved in both catabolism (energy-releasing process) and anabolism (energy-capturing process)
  3. if protons are gained, electrons are also gained
  4. the conversion of pyruvate and NADH to lactate and NAD+ is under anaerobic conditions
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23
Q

What is the difference between an irreversible and a reversible reaction?

A

irreversible: can only go in one direction
reversible: can go in either direction

24
Q

What are the 3 regulated steps in glycolysis from glucose to pyruvate?

A

hexokinase (traps it in the cytosol), PFK-1, pyruvate kinase

25
Q

What makes a certain step irreversible?

A
  1. hydrolysis of ATP has a large negative ΔG
  2. steps requiring ATP are irreversible
  3. ATP + H2O → ADP + pi (phosphate) + free energy
  4. ΔG for the hydrolysis of 1 mole of ATP is -57 kJ/mol
26
Q

Why is the pyruvate kinase step irreversible?

A

the transfer of phosphate to ADP is normally energetically unfavorable but the tautomerization of the enol to the ketone is so highly energetically unfavorable that the ΔG for the reaction is large and negative (-61.9 kJ/mol which is larger than the energy required to make ATP) → enols are unstable so they will quickly tautomerize to its keto form

27
Q

How are biochemical reaction commonly regulated?

A

by feedback or feed-forward control → normally at rate-limiting or commitment steps

28
Q

What is the difference between the rate-limiting step and the commitment step?

A

rate-limiting step: the SLOWEST step in the pathway
commitment step: the first IRREVERSIBLE step unique to the pathway → will now be committed to go through the entire pathway

29
Q

Irreversible steps usually involve what?

A

high-energy substrates (like ATP)

30
Q

What are the 5 different regulations of metabolism?

A
  1. transcriptional/translational regulation (slow)
  2. protein degradation (slow)
  3. allosteric regulation (fast)
  4. post-translational modification (fast)
  5. compartmentation (fast)
31
Q

What is the main way metabolism is regulated?

A

through allosteric regulation (fast)

32
Q

What is transcriptional/translational regulation?

A

the induction of genes for enzymes involved in metabolism (slow since it is a big complex to regulate)

33
Q

How does protein degradation regulate metabolism?

A

through 2 pathways: ubiquitin-proteasome pathway (takes a lot to make protein go away) and the lysosomal proteolysis (slow)

34
Q

How does allosteric regulation regulate metabolism?

A

through activators and inhibitors in which the molecule/protein binds to the enzyme not at the active site (fast)

35
Q

How does post-translational modification regulate metabolism?

A

by adding or removing phosphorylation (fast)

36
Q

What is compartmentation?

A

shuttling substrates to a compartment for biochemical reactions (like moving an enzyme from 1 part of the cell to another → fast) → example is fatty acid biosynthesis in the cytosol and oxidation in the mitochondria

37
Q

What is the difference between feedback and feedforward mechanisms?

A

feedback is product inhibition where there is enough of the product so we don’t need to make more whereas feedforward is product activation in which we can use the extra product

38
Q

What are futile cycles?

A
  1. formed by irreversible reactions/pathways in opposite directions
  2. activation of both reactions would waste cellular energy
  3. reaction in only one direction should be active at a given time to minimize energy loss (ex. glycolysis vs gluconeogenesis)
39
Q

What is the exception of the rule for futile cycles?

A

the liver → uses a futile cycle between glucose and glucose-1-phosphate as a buffer to maintain blood glucose levels

40
Q

Why is the step by PFK-1 irreversible?

A

due to a large decrease in free energy and commits the molecule to glycolysis → since un-phosphorylated molecules/metabolites can leave the cell so it needs to be phosphorylated to trap both molecules in the cell

41
Q

Where does glucose come from?

A

the digestion and absorption of carbohydrates (aka diet) in the form of monosaccharides, disaccharides, and polysaccharides

42
Q

Disaccharides, oligosaccharides, and polysaccharides must be what to be absorbed at the intestine?

A

must be hydrolyzed to monosaccharides

43
Q

What makes up lactose?

A

galactose + glucose (lactase breaks down lactose)

44
Q

What makes up sucrose?

A

fructose + glucose (sucrase breaks down sucrose)

45
Q

What makes up maltose?

A

glucose + glucose (maltase breaks down maltose)

46
Q

What makes up cellubiose?

A

glucose + glucose (β-D-glucosidase breaks down cellubiose) → only in plants and microbes

47
Q

What are the 4 glucose transporters?

A

GLUT-1, GLUT-2, GLUT-3, GLUT-4

48
Q

What is GLUT-1?

A

basal non-insulin stimulated glucose uptake into many cells

49
Q

What is GLUT-2?

A
  1. glucose sensing
  2. β-cell in pancreas (and liver, intestine, and kidney)
  3. together with glucokinase, it forms the β cell’s glucose sensor and allows glucose to enter the β-cell at a rate proportional to the extracellular glucose level
50
Q

What is GLUT-3?

A

non-insulin mediated glucose uptake into brain neurons

51
Q

What is GLUT-4?

A

responsible for insulin-stimulated glucose uptake in muscle and adipose tissue → the classic hypoglycemic action of insulin (senses insulin and sends signal to take up glucose)

52
Q

What is the only organ that can complete gluconeogenesis?

A

the liver

53
Q

What is the take home message regarding the fate of glucose?

A
  1. all tissues can take up glucose constitutively
  2. muscle and adipose tissue can increase glucose uptake in response to insulin (both skeletal muscle and adipose tissue have GLUT-4)
  3. glucose has different fates in different tissues!!!
54
Q

How is type 2 diabetes a result of insulin resistance?

A
  1. downregulation of insulin receptors → glucose can’t bind to the receptors
  2. defects in intracellular signaling → can’t respond correctly to signals but glucose can bind to the receptor
55
Q

What is the first line treatment for type 2 diabetes?

A

metformin

56
Q

What is the mechanisms of action for metformin?

A
  1. suppressing liver gluconeogenesis
  2. activation of AMP-activated protein kinase (AMPK)
  3. inhibition of glyceraldehyde-3-phosphate dehydrogenase → glycolytic enzyme

Biochemistry (18 decks)

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