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The Dynamic Cell > Metabolism > Flashcards

Metabolism Flashcards

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1
Q

What is bioenergetics?

A

the quantitative study of energy transduction occurring in living cells

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2
Q

What is Gibbs free energy?

A

the amount of energy in a system available to do work

G=H-TS

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3
Q

What kind of reaction occurs when G is negative?

A

exergonic –> the reaction can occur spontaneously

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4
Q

What kind of reaction occurs when G is positive?

A

endergonic –> requires an energy input

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5
Q

What are chemoorganotrophs?

A

extract energy from organic compounds by oxidation

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6
Q

Describe each stage of the extraction of energy from food

A

Stage 1:
- large molecules broken down

Stage 2:
- small molecules degraded into a few simple units –> some ATP generated

Stage 3:
- ATP produced from the complete oxidation of simple units

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7
Q

Describe the reducing agent and oxidising agent in redox reactions

A

reducing agent –> electron donor, is oxidised
oxidising agent –> electron acceptor, is reduced

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8
Q

What are dehydrogenases

A
  • oxidise organic compounds by abstracting 2H+ and 2e- and passing them to a mobile carrier in biodegradation and energy abstraction
  • can reduce organic compounds by adding 2H+ and 2e- from a mobile electron carrier typically in biosynthetic pathways
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9
Q

What is NADH

A
  • an electron carrier
  • produced in catabolic reactions and by TCA cycle
  • used in the generation of ATP by OxPhos
  • usually found in mitochondria
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10
Q

What is NADPH?

A
  • an electron carrier
  • produced by the pentose phosphate pathway (PPP)
  • used for reductive biosynthesis
  • found in the cytoplasm
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11
Q

What is FADH2?

A
  • an electron carrier
  • produced in catabolic reactions and by TCA cycle
  • used in generation of ATP by OxPhos
  • found in mitochondria
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12
Q

Describe the structure of ATP

A

contains 2 phosphoanhydride bonds on its triphosphate unit

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13
Q

List the unfavourable reactions driven by ATP hydrolysis

A

glucose + Pi –> G-6-P

ATP + H20 –> ADP + Pi

Glucose + ATP –> G-6-P + ADP

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14
Q

Describe the process of substrate level phosphorylation

A

transfer of phosphoryl group from metabolites with high-phosphoryl transfer potential to ADP producing ATP

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15
Q

Describe the process of oxidative phosphorylation

A

ATP formation as a result of transfer of electrons from fuels via electron carriers –> carried out in the mitochondria

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16
Q

What are the functions of metabolism

A
  • obtain energy
  • convert nutrients into own characteristic molecules
  • polymerise monomeric precursors
  • synthesise and degrade molecules required for special cellular functions
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17
Q

What are the features of catabolic reactions

A
  • degradative
  • produces ATP
  • negative free energy change
  • produces reducing potential
  • generates NADH and FADH2
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18
Q

What are the features of anabolic reactions?

A
  • synthetic
  • requires ATP
  • positive free energy change
  • requires reducing potential
  • uses NADPH
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19
Q

List the three principal ways that metabolic pathways are regulated

A
  1. levels and accessibility of substrates (thermodynamics and compartmentalisation)
  2. amounts of metabolic enzymes (rate of transcription and degradation)
  3. modulation of catalytic activities of enzymes (allosteric regulation, covalent modification, association with regulatory proteins)
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20
Q

What determines enzyme turnover?

A
  • alteration of transcription factor by external signals
  • stability of mRNA species
  • rate of translation
  • rate of protein degradation
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21
Q

What are allosteric enzymes?

A
  • has a site distinct from the substrate-binding site that allosteric effectors/modulators bind to
  • binding causes conformational change
  • can be positive (activator) or negative (inhibitor)
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22
Q

What are regulatory enzymes?

A
  • contain several regulatory sites –> each selectively binds a ligand
  • conformation of active site reflects summation of signals
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23
Q

Describe adenylate control

Study These Flashcards
A

ATP generating pathways (catabolic) - inhibited by a high energy charge

ATP utlising pathways (anabolic) - stimulated by a high energy charge

24
Q

List three types of covalent modification

Study These Flashcards
A
  • adenylation
  • methylation
  • phosphorylation
25
How does phosphorylation/dephosphorylation alter a protein?
- changes Vmax and/or Km of the enzyme - sensitivity to substrate - sensitivity to inhibitors or activators
26
Where does glycolysis take place?
cytosol
27
In simple terms, what is glycolysis?
conversion of glucose to pyruvate
28
What are the two stages of glycolysis?
Stage 1L - trapping and destabilising glucose --> produces 2 x 3C molecules (5 steps) - energy required: 2 ATPs per glucose molecule Stage 2: - oxidation of the 3C molecules to pyruvate (5 steps) - energy generated (4 ATPs and 2 NADH per glucose molecule)
29
Describe Step 1 of Stage 1 (trapping glucose)
- glucose enters cells via facilitated diffusion - once in cell, glucose is trapped by phosphorylation --> produces glucose 6-phosphate + ADP + H+ - glucose 6-phosphate is negatively charged and cannot freely diffuse out of cell
30
What is hexokinase?
- used to phosphorylate hexose sugars - induced fit enzyme action - inhibited by glucose 6-P (feedback inhibition)
31
Describe Step 2 of Stage 1 (formation of fructose 6-phosphate)
- isomerisation of glucose 6-P to fructose 6-P - carried out by phosphoglucose isomerase - convert one isomer (glucose) to another (fructose) by tautomerisation
32
Describe Step 3 of Stage 1 (phosphofructokinase)
- a second phosphorylation reaction - carried out by enzyme phosphofructokinase - allosteric enzyme sets pace of glycolysis - inhibited by ATP, citrate and H+ ions - stimulated by AMP, ADP and Fruc 2,6-bisP - F-6P forms F-1,6-BP + ADP + H+
33
Describe steps 4 and 5 of Stage 1 (trapping and detabilising)
- splitting fructose 1,6-bisP into 3C fragments - cleavage of F-1,6-BP catalysed by enzyme aldolase --> yields 2 triose phosphates (DHAP and GAP) - DHAP is converted into GAP
34
What is triose phosphate isomerase (TIM)
- catalyses the conversion of DHAP into 3-P
35
Describe Step 6 of Stage 2 (formation of a high energy bond)
- G 3-P is oxidised and phosphorylated by the enzyme G 3-P dehydrogenase - Dehydrogenase transfer high energy electrons from complex organic molecule to NAD+ to form NADH - results in 1,3-bisphosphoglycerate sum of two processes: - oxidation of the aldehyde to a carboxylic acid by NAD - joining of orthophosphate to the carboxylic acid
36
Describe stage 7 of stage 2 (ATP generation from 1,3-bisPglycerate)
- substrate level phosphorylation - forms 3- phosphoglycerate and ATP
37
Describe steps 8,9,10 of Stage 2 (generation of additional ATP and pyruvate ATP)
- phosphoryl group on 3-Pglycerate shifts position, followed by dehydration and formation of a C=C bond - increases transfer potential of phosphoryl group
38
What is the function of pyruvate kinase?
- involved in last step of glycolysis - catalyses transfer of phosphoryl group to form ATP - activated by Fructose 1,6bisP and inhibited by ATP and alanine
39
List the catabolic fates of pyruvate
- acetaldehyde --> ethanol - lactate - acetly CoA
40
Describe the catabolic fates of pyruvate when oxygen is present and when it isnt
oxygen present - electrons on NADH transferred to oxygen --> produce H20, ATP, NAD+ no oxygen - electrons on NADH transferred to pyruvate to form lactase or ethanol and NAD+
41
List the two major sites of storage of glycogen
- liver - muscle
42
What is GLUT 2?
- present in liver and B cells of pancreas - high capacity, low affinity transporter --> takes up a lot of glucose when there is a lot around
43
What is GLUT 4?
- present in muscle and fat cells - insulin leads to rapid increase in number --> increasing uptake
44
What is glycogenesis
the conversion of glucose to glucose 6-P
45
What is glucokinase?
- isozyme present in the liver - not inhibited by glucose 6-P - provides glucose 6-P for synthesis of glycogen and formation of fatty acids
46
Which enzyme catalyses the conversion of glucose 6-P to glucose 1-P
phosphoglucomutase
47
Which enzyme catalyses the conversion of glucose 1-P to UDP-glucose
UDP-glucose pyrophosphorylase (UDP)
48
Which reaction is catalysed by glycogen synthase?
- glycosyl units added to the non-reducing end of glycogen molecule --> form a a-1,4 glycosidic bond - a primer is required (glycogenin)
49
How is glycogen synthase regulated?
- by the enzyme protein kinase A - phosphorylation converts it from active alpha form to inactive beta form - this is counteracted by insulin
50
What catalyses the formation of a-1,6 glycosidic bonds>
- branching enzyme - removes 7 glucose units from end of chain and re-attached it at interior site - must be 4 residues away from a branch point
51
Describe the steps of glycogenolysis
- glycogen phosphorylase (dimeric protein) cleaves a-1,4 glycosidic bonds by addition of orthphosphate - releases glucose 1-P (negative charge) - a debranching enzyme is cleaves the a-1,6 linkages --> contains 2 actives: transferase and a-1,6-glucosidase activity - glucose 1-P converted to glucose 6-P by phosphoglucomutase
52
List some hormones that glycogen phosphorylase is responsive to
insulin adrenaline glucagon
53
What is the role of protein phosphatase 1?
- activated by high insulin levels --> reverses effect of protein kinase A - inactivates phosphorylase kinase by removing covalent P group - activates glycogen synthase by removing covalent P group
53
What is Von Gierke's disease
- glucose-6-phosphatase missing - hypoglycemia
53
What is Cori's disease?
- deficiency of glycogen debranching enzyme
54
What is MacArlde's disease
- muscle phosphorylase missing --> cannot break down stored glycogen in muscle
55
What is the major site of gluconeogenesis?
the liver

The Dynamic Cell (8 decks)

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