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Biochem > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

CHO general

A

Named so because many have formula Cn(H2O)n

Produced from CO2 and H2O via photosynthesis in plants

Range from as small as glyceraldehyde (Mw = 90) to as large as amylopectin (Mw > 200,000,000)

Fulfill a variety of functions, including: energy source and energy storage, structural component of cell walls and exoskeletons, informational molecules in cell-cell signaling

Can be covalently linked with proteins and lipids

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2
Q

basic nomenclature

A

number of carbon atoms in the carbohydrate + -ose

Three carbons = triose
Four carbon = tetrose
Five carbon = pentose
Six carbon = hexose

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3
Q

CHO functional group

A

all CHO initially had a carbonyl functional group.
aldehydes = aldose H-C=O
ketones = ketose C=O

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4
Q

CHO as constitutional isomers

A

an aldose is a carbohydrate with aldehyde functionality

a ketose is a carbohydrate with ketone functionality

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5
Q

glycosidic bond

A

2 sugar molecules can be joined via a glycosidic bond - joins 2 monomers

disaccharides can be named by the organisation and linkage or a common name.

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6
Q

CHO polysaccharides

A

natural CHO are usually found as polymers.

  • homo or hetero polysaccharides (one vs multiple monomer units)
  • linear or branched (one type vs many types of glycosidic bond)
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7
Q

metabolism (anabolic and catabolic rn)

A

sum of all chemical reactions in the cell

anabolic: monomeric subunits polymerised into complex macromolecules, requires chemical energy eg AA –> proteins

catabolic: nutrients broken down into individual molecular components, polymers –> monomers and further smaller products, releases energy
eg CHO –> CO2, H2O, NH3

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8
Q

laws of thermodynamics applying to living organisms

A
  • Living organisms cannot create energy from nothing.
  • Living organisms cannot destroy energy into nothing.
  • Living organism may transform energy from one form to another.
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9
Q

free energy elm constant ΔG

A

ΔG -ve, chem r’n proceeds
ΔG 0 = eqm
ΔG +ve: no r’n.

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10
Q

energetics of chemical reactions

A

Hydrolysis reactions tend to be strongly favorable (spontaneous).

Isomerization reactions have smaller free-energy changes.
o isomerization between enantiomers: ΔGº= 0
o isomerization r’n rearrange molecule

Complete oxidation of reduced compounds is strongly favorable.
o This is how chemotrophs obtain most of their energy.
o the oxidation of reduced fuels with O2 is stepwise and controlled.
** being thermodynamically favorable is not the same as being kinetically rapid.

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11
Q

addition-elimination reactions

A

Condensation: H & OH (=H2O water) is removed from the molecule and released.

Hydrolysis: hydro means water, lysis means to cut or break, so H2O (water) is split and added to the molecule as H + OH

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12
Q

key energy carriers in the cell

A

Phosphoryl transfer from ATP

ATP is frequently the donor of the phosphate in the biosynthesis of phosphate esters
ATP hydrolysis has a very high negative ΔG = - 30.5kJ/mol

Cellular ATP concentration is usually far above the equilibrium concentration, making ATP a very potent source of chemical energy.

ATP, NADH, NADPH, FADH2: High energy bonds or e- carriers
Main source of chemical energy

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13
Q

NAD, NADP, NADH, NADPH

A

NAD+ : Nicotinamide adenine dinucleotide

NAD+ and its phosphorylated analog NADP+ reduce to NADH and NADPH respectively

accepting a hydride ion (two electrons and one proton) from an oxidizable substrate.

The hydride ion is added to either the front (the A side) or the back (the B side) of the planar nicotinamide ring

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14
Q

metabolism overview

A

glycogenolysis: glyc –> gluc
glycolysis: gluc –> pyruvate
oxidation: pyruvate –> acetyl CoA
acetyl CoA –> ketone bodies –> NADH & FADH2 –> ETC

lipolysis: triglyceride –> FFA
B-oxidation: FFA –> acetyl CoA
acetyl CoA –> TCA Cycle

proteolysis: protein –> AA
deamination & oxidation: AA –> acetyl CoA
acetyl CoA –> fatty acids

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15
Q

glycolysis

A

gluc –> glyc

harnessing energy from glucose

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16
Q

gluconeogenesis

A

synthesis of glucose from glycogen

glyc –> gluc

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17
Q

pentose phosphate pathway

A

oxidation of glucose in PPP

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18
Q

glucose importance

A

excellent fuel - yields good amount of E upon oxidation (2840 kJ/mol glucose)
efficiently stores in polymeric form
many organisms and tissues can use glucose as fuel, to generate AA, membrane lipids, nucleotides for DNA and RNA, cofactors needed for metabolism

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19
Q

organised vs disorganised release of energy - step wise oxidation

A

a cell overcomes Ea by using stepwise process, capture energy and don’t produce too much heat. each step help to overcome Ea and allow r’n to move forward in a controlled way

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20
Q

four major pathways of glucose utilisation

A
  1. Storage: can be stored in the polymeric form (starch, glycogen), used for later energy needs
  2. Energy production: generates energy via oxidation of glucose, short-term energy needs
  3. Production of NADPH and pentoses: generates NADPH for use in relieving oxidative stress and synthesizing fatty acids, generates pentose phosphates for use in DNA/RNA biosynthesis
  4. Structural carbohydrate production: Extra Cellular Matrix (ECM), Proteoglycans, Glycosaminoglycans.
21
Q

glycolysis defn and fn

A

Definition: Sequence of enzyme-catalyzed reactions by which glucose is converted into pyruvate
o Pyruvate can be further aerobically oxidized.
o Pyruvate can be used as a precursor in biosynthesis.

  • Some of the free energy is captured by the synthesis of ATP and NADH.
22
Q

glycolysis energy investment/prepatory phase

A
  1. priming r’n: traps glucose in the cell
  2. glucose phosphorylation by ATP: glucose –> glucose-6-phosphate ** hexokinase
  3. 2nd phosphorylation by ATP: glucose-6-phosphate –> fructose-6-phosphate
  4. cleavage 6C mol –> 2x 3C mol: fructose-6-phosphate –> fructose-1,6-biphosphate ** PFK
  5. isomerisation: glyceraldehyde-3-phosphate + dihydroxyacetone phosphate 2x glyceraldehyde-3-phosphate

(every mol x2 from now on)

23
Q

glycolysis pay-off phase

A
  1. oxidation and phosphorylation: produces 2xNADH
    2x glyceraldehyde-3phosphate 2x 1,3biphosphoglycerate
  2. P transferred to ATP, 2x ATP produced: 2x 1,3biphosphoglycerate 2x 3-phosphoglycerate
    8&9: rearrangment reactions and condensation
  3. P group removed, final 2x ATP produced ** pyruvate kinase
    2x phosphoenolpyruavte –> 2x pyruvate
24
Q

summary of glycolysis

A

Used: 1 glucose; 2 ATP; 2 NAD+

Made: 2 pyruvate (various different fates), 4 ATP (2ATP net) used for energy-requiring processes within the cell, 2 NADH: must be re-oxidized to NAD+ for glycolysis to continue

Glycolysis is heavily regulated. ensure proper use of nutrients, ensure production of ATP only when needed

Net equation: Glucose + 2 NAD+ + 2 ADP + 2 Pi  2 Pyruvate + 2 NADH + 2 H+ + 2 ATP

25
Q

feeder pathways for glycolysis

A

Glucose molecules are cleaved from glycogen and starch by glycogen phosphorylase.
o yielding glucose-1-phosphate
o uses inorganic phosphate as phosphate source

Disaccharides are hydrolyzed.
o lactose: glucose and galactose
o sucrose: glucose and fructose
o Monosaccharides fructose, galactose, and mannose enter glycolysis at different points.

if a molecule can be converted into a glycolytic intermediate it can enter glycolysis and produce energy

26
Q

fates of molecules for glycolysis

A

Central pathway: 1st part of glycolysis. Glucose converted into glyceraldehyde 3-phosphate.

Glucose 1-phospahte from breakdown of starch, enzyme converts into glucose 6-phospahte. From then on, glucose processed in glycolytic cycle.

Galactose can be rearranged to glucose 1-phosphate.

Sucrose converted to glucose or fructose.

27
Q

fates of pyruvate

A

Three possible catabolic fates of the pyruvate formed in glycolysis

pyruvate –> lactate (anaerobic)
pyruvate –> acetyl-CoA –> CO2 + H2O (aerobic)
pyruvate –> ethanol + 2CO2 (anaerobic)

28
Q

anaerobic glycolysis (fermentation)

A

Generation of energy (ATP) without consuming oxygen or NAD+
No net change in oxidation state of the sugars
Reduction of pyruvate to another product
Regenerates NAD+ for further glycolysis under anaerobic conditions

29
Q

lactic acid fermentation

A

Reduction of pyruvate to lactate, reversible
During strenuous exercise, lactate builds up in the muscle, (generally less than 1 minute)
Acidification of muscle prevents its continuous strenuous work.
Lactate can be transported to the liver and converted to glucose there.
Requires a recovery time
o high amount of oxygen consumption to fuel gluconeogenesis
o restores muscle glycogen stores

Acidification – significant change in pH – interferes with the chemical processes in muscle contraction.
- Large –ve ΔG’˚ so favourable reaction

NAD+ within cytosol, is available for glycolysis to continue occurring.
- Main function is to recycle NADH – keeps glycolysis going (diagram below)

30
Q

glycolysis vs gluconeogenesis

A

Opposing pathways that are both thermodynamically favourable
o operate in opposite direction
o end product of one is the starting compound of the other

Reversible reactions are used by both pathways.

Irreversible reaction of glycolysis must be bypassed in gluconeogenesis.
o no ATP generated during gluconeogenesis (uses ATP)
o different enzymes in the different pathways
o differentially regulated to prevent a futile cycle

processes highly regulated, glyc has 3 points and GNG regulated at the 3 points going back the other way. Occur at different points (counterproductive to occur at same time

glycolysis: occurs mainly in muscle and brain
gluconeogenesis: occurs mainly in liver

31
Q

gluconeogensis (main enzymes and points at which energy is used)

A
  1. pyruvate carboxylase: pyruvate –> oxaloacetate
  2. phosphoenolpyruvate carboxykinase: oxaloacetate –> PEP
  3. fructose bisphosphatase-1: fructose 1,6-bisphosphate –> fructose 6-phosphate
  4. glucose 6-phosphatase: glucose 6-phosphate –> glucose
32
Q

gluconeogenesis ATP expense

A

2 Pyruvate + 4 ATP + 2 GTP + 2 NADH + 2 H+ + 4 H2O –> Glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+

“Costs” 4 ATP, 2 GTP, and 2 NADH

Physiologically necessary: Brain, nervous system, and red blood cells generate ATP ONLY from glucose.

Allows generation of glucose when glycogen stores are depleted:
o during starvation
o during vigorous exercise
o can generate glucose from amino acids, lactate, glycerol but not fatty acids
**(expensive from an energy/ATP point of view)

33
Q

precursor to gluconeogenesis

A

animals can produce glucose from sugars or proteins

sugars: pyruvate, lactate or oxaloacetete
protein: AA converted to Krebs cycle intermediates

animals cannot produce glucose from FA

  • produce of FA degradation is acetyl CoA
  • can’t have net conversion of acetylCoA to oxaloacetate
34
Q

pentose phosphate pathway

A

alternate use for glucose, how body generates ribose sugar (for DNA and RNA) and NADPH, pentose phosphates can be regenerated into glucose-6-phosphate, which requires no ATP.

glucose-6-phosphate –> ribose-5-phosphate

  • utilised to synthesise nucleotides (important precursor)
  • NADHPH is main e- carrier

The main products are NADPH and ribose 5-phosphate.
- NADPH is an electron donor.
o reductive biosynthesis of fatty acids and steroids
o repair of oxidative damage
-Ribose-5-phosphate is a biosynthetic precursor of nucleotides.
o used in DNA and RNA synthesis
o or synthesis of some coenzymes

35
Q

metabolic pathways purpose

A

biochemical reactions in the living cell - metabolism, organised into metabolic pathways

purpose: extraction of energy, storage of fuels, synthesise of important building blocks, elimination of waste

36
Q

metabolic regulation principles

A

flow of metabolites through pathways is regulated in order to maintain homeostasis.

metabolite levels can be altered very rapidly to inc/dec glycolysis during/after action or to inc capacity of glujconeogeneis after successful action

37
Q

feedback inhibition

A

products of metabolic pathways directly or indirectly inhibit their own biosynthetic pathways
eg: high ATP synthesise inhibits the glycolysis step that prevents glucose degradation

38
Q

factors that offed reaction rates

A
  • [reactants] vs [products]
  • activity of catalyst
  • [enzyme]
  • rate of translation vs rate of degradation
  • intrinsic activity of enzyme
  • substrate, effectors, phosphorylations state

[effectors]
- allosteric regulators, competing substrates, ph, Ionic environment

temperature

39
Q

effect of [substrate] on RR

A

The rate is more sensitive to concentration at low concentrations.
o Chemical kinetics: Frequency of substrate meeting the enzyme matters.

The rate becomes insensitive at high substrate concentrations.
o The enzyme is nearly saturated with substrate.

40
Q

enzyme phosphorylation

A

Phosphorylation is catalyzed by protein kinases.

Dephosphorylation is catalyzed by protein phosphatases, or can be spontaneous.

Typically, proteins are phosphorylated on the hydroxyl groups of Ser, Thr, or Tyr.

41
Q

enzyme regulation by regulatory proteins

A

Binding of regulatory protein subunits affects specificity

enzymes recognise several target proteins, its specificity provided by the regulatory subunit. Each of several regulatory subunits fits the scaffold containing the catalytic subunit, and each regulatory subunit creates its unique substrate binding site.

42
Q

ATP and AMP cellular regulation

A

10% decrease in [ATP] can greatly affect the activity of ATP utilizing enzymes.

10% decrease in [ATP] leads to a dramatic increase in [AMP].
- AMP can be a potent allosteric regulator.

ATP and AMP (adenosine monophosphate) can both be allosteric effectors

43
Q

hexokinase (glycolysis)

A

converts glucose –> glucose-6-phosphate
has a high affinity for glucose
inhibition: inc FA and its product (-ve feedback) - important because ATP used in this step, prefer to use glycogen to produce product so HK is inhibited to spare blood glucose and ATP

44
Q

phospho-fructokinase (PFK) (glycolysis)

A

fructose-6-phosphate –> fructose1,6biphosphate
key rate limiting step

activation: inc fructoste-6-phospahte, inc ADP, inc AMP
inhibition: inc H+, inc citrate, inc ATP

45
Q

pyruvate kinase (glycolysis)

A

phosphoenolpyruvate –> pyruvate

activation: inc fructose-1,6-biphosphate
inhibition: inc ATP, alanine

46
Q

pyruvate carboxylase

A

pyruvate –> oxaloacetate

activation: inc acetyl CoA
inhibition: ADP

replenishing Krebs cycle intermediates in the mitochondrial matrix.

47
Q

PEP carboxylase (GNG)

A

oxaloacetate –> phosphoenolpyruvate

activation: n/a
inhibition: ADP

48
Q

fructose 1,6 biphosphatase (GNG)

A

fructose 1,6 bisphosphate –> fructose-6-phosphate

activation: citrate
inhibition: AMP, fructose-2,6-biphosphate

49
Q

glucose-6-phosphatase (GNG)

A

also known as G6Pase

hydrolyzes glucose 6-phosphate

glucose-6-phosphate –> glucose + Pi

Biochem (17 decks)

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