1: Cell metabolism and integrity Flashcards
Glycolysis
2 stages -
forming high energy compound
splitting a high energy compound
Where does glycolysis occur
Cytoplasm
Glycolysis is
Anaerobic
Converts one molecule of glucose into two pyruvate molecules
Isomerase enzymes are used for
making an isomer
Kinase enzymes are used for
movement of a phosphate group (generally)
First step of glycolysis
Glucose –(hexokinase)–> glucose-6-phosphate
irreversible reaction, commits glucose to glycolysis
uses ATP in order for reaction to start
Fructose bisphosphate splits into
via Aldolase
DHAP (dihydroxyacetone phosphate)
into
G3P (glyceraldehyde-3-phosphate)
via TPI
-2 molecules from now on-
Net result of glycolysis
2 pyruvate molecules
Net gain of 2 ATP
2 NADH
Pentose Phosphate Pathway
When ATP isn’t needed, glucose enters PPP
produces Ribose or NADPH
NADPH produced by the PPP
- electron rich
involved in antioxidant reactions:
RBCs produce Reactive Oxygen Species and glutathione
NADPH is an electron supplier for glutathione
3 fates of pyruvate
Alcoholic fermentation
Lactate production
(Regenerate NAD+ for glycolysis to continue) - Anaerobic processes
Acetyl CoA production (create Acetyl CoA to enter TCA cycle)
-Aerobic process
Pyruvate in alcoholic fermentation
Pyruvate –(pyruvate decarboxylase)–> acetaldehyde –(alcohol dehydrogenase)–> ethanol
occurs in yeast, anaerobic process
NAD+ regenerated for glycolysis
Pyruvate in lactate production
pyruvate–(lactate dehydrogenase)–> lactate
- used in muscles during intense activity
NAD+ regenerated
Pyruvate in Acetyl CoA Production
Pyruvate –(pyruvate dehydrogenase complex)–> acetyl CoA + CO2
- occurs in mitochondria
- acetyl CoA enters TCA cycle
Beri Beri is
Thymine deficiency
(Vit B1)
(thymine needed to form TPP - prosthetic group forming pyruvate dehydrogenase complex)
less TPP=less ATP prod.
Loss of H+, carbanion attacks pyruvate
cannot convert pyruvate into acetyl CoA
so cannot enter TCA cycle
Symptoms of Beri Beri
damage of peripheral nervous system
muscle weakness
Decreased cardiac output
BRAIN particularly vulnerable
TCA cycle occurs in the
mitochondria
Each TCA (Krebs) cycle produces
2x CO2
3x NADH
1x GTP
1x FADH2
Where are TCA cycle enzymes found
Soluble proteins found in mitochondrial matrix space
except for succinate dehydrogenase (inner mitochondrial membrane)
Glucogenic amino acids
amino acids which eventually form glucose
Ketogenic amino acids
amino acids which eventually enter Krebs cycle as Acetyl CoA
How many amino acids are there
20
How many molecules do amino acids give rise to
7
pyruvate
Acetyl CoA
Acetoacetyl CoA
a-ketoglutarate
Succinyl CoA
Fumarate
Oxaloacetate
two groups of amino acids
Glucogenic
Ketogenic
Transamination reaction
Transferral of amino group
Transamination reaction of alanine and a-ketoglutarate
forms : pyruvate (alanine) (acetyl CoA enters krebs) and glutamate (re-converted to a-kg)
Alanine undergoes transamination by action of alanine aminotransferase enzyme
Role of NADH
enter mitochondrial matrix to regenerate NAD+
used in oxidative phosphorylation in mitochondria
How does NADH form NAD+
NADH moved into mitochondria, oxidised in electron transport chain, NAD+ moved out of mitochondria
NADH shuttles
Glycerol phosphate shuttle - brain, skeletal muscle
Malate-aspartate shuttle - liver, kidney, heart
Process of glycerol phosphate shuttle
- Cystolic glycerol 3-phosphate dehydrogenase transfers electrons from NADH to DHAP to generate glycerol 3-phosphate
- Glycerol 3 phosphate carries electrons
- Membrane bound form of same enzyme transfers electrons to FAD, then get transferred to co-enzymeQ part of e- transport chain
- G3-phosphate drops off electrons becoming DHAP again
Malate Aspartate Shuttle
aspartate converted to oxaloacetate using AT (aspartate transaminase)
oxaloacetate converted to malate using MDH (malate dehydrogenase)
then enters mitochondria using malate-a-ketoglutarate antiporter
REVERSE reaction
aspartate leaves mitochondria via glutamate-aspartate antiporter
What types of reactions are involved in the malate aspartate shuttle
redox
transamination
How many ATP molecules are produced by :
GTP/ATP
NADH
FADH2
GTP/ATP - 1 ATP
NADH - 3 ATP
FADH2 - 2 ATP
How many ATP molecules are produced by the TCA cycle
12 :
oxidation of 1 acetyl coA molecule gives
3x NADH
1x FADH2
1x GTP
Fatty acid metabolism
1- converting fatty acids to acyl CoA
2- transporting Acyl CoA from outer mitochondrial membrane into matrix (Carnitine shuttle)
3- actual Beta Oxidation Cycle
Beta-oxidation produces
> 50% bodys energy
Predominates in time of fasting (uses fat stores instead of carbs)
Stage 1 of Fatty acid metabolism
converting fatty acid into fatty acyl CoA (using fatty acyl-CoA synthetase)
- requires 2 ATP
- occurs on outer membrane of mitochondria
Stage 2 of fatty acid metabolism
CoA and carnitine both carry acyl group at different points
Primary Carnitine Deficiency
Autosomal recessive disorder
- mutations in SLC22A5 which encodes carnitine transporter, so no CoA transported into matrix
Stage 3 of fatty acid metabolism
Beta Oxidation - in mitochondria
one cycle :
Acyl CoA –> Acyl CoA SHORTER 2C + Acetyl CoA (2C)
Steps of beta oxidation (4)
oxidation
hydrolysis
oxidation
thiolysis
Why does the glycerol phosphate shuttle produce less ATP in the process of oxidative phosphorylation compared to the malate-aspartate shuttle
Electrons passed from cytoplasmic NADH to mitochondrial FADH2 which enter electron transport chain later leading to fewer H+ pumped and less ATP produced
Example of Beta oxidation using palmitoyl CoA (16C)
palmitoyl CoA + 7FAD + 7NAD+ +7H20+ 7CoA —-> 8 acetyl CoA + 7FADH2 +7NADH
per cycle make - 1 acetyl CoA, 1 FAD2, 1NADH
Thiolyis is
reaction of adding CoA to a compound
When does Acetyl CoA from beta oxidation enter the TCA cycle
when carbohydrate metabolism = fat metabolism
Oxaloacetate needed for Acetyl CoA entry
What happens to acetyl CoA when fat metabolism predominates (during fasting)
acetyl CoA forms ketone bodies
3 examples of Ketone bodies
Acetoacetate
D-3-hydroxybutyrate
Acetone
Why is there different enzymes feeding fatty acyl CoA into the beta oxidation cycle
depends on the length of the acyl CoA
4 enzymes feeding fatty acyl CoA into B oxidation cycle
(<6C) short chain
(6-12) medium chain
(13-21) long chain 3-hydroxy
(>22) very long chain
acyl-CoA enzyme A dehydrogenase
Medium chain acyl-coenzyme A dehydrogenase deficiency MCADD
autosomal recessive - predominantly in caucasians
1 in 10,000 live births in uk
If undiagnosed - fatal : accounts for 1 in 100 deaths from SIDS
Precautions for patients with MCADD
never go without food for longer than 10-12h
adhere to high carbohydrate diet
patients with illness resulting in appetite loss or sever vomiting may need IV. glucose to make sure body isn’t solely dependent on fatty acids to make energy
Two enzymes involved in fatty acid synthesis
Acetyl CoA Carboxylase
Fatty acid synthase
What are fatty acids formed by
(process of lipogenesis)
- decarboxylative condensation reactions involving acetyl-CoA and malonyl-CoA
- following each round of elongation, fatty acid undergoes reduction and dehydration by dehydratase (DH) and enol reductase (ER) activity
- growing fatty acyl group is linked to an acyl carrier protein (ACP)
Carriers in Beta oxidation
CoA
Carriers in lipolysis
ACP (acyl carrier proteins)
Reducing power in Beta oxidation
FAD/NAD+
Reducing power in lipolysis
NADPH
Location of Beta oxidation
mitochondrial matrix
Location of lipolysis
Cytoplasm
Oxidative phosphorylation
Electron transport chain
composed of :
four complexes
two mobile carriers - act as electron carriers
Four complexes of ETC
Complex I - NADH dehydrogenase
Complex II - succinate dehydrogenase
Complex III - Q-cytochrome C oxidoreductase
Complex IV - cytochrome c oxidase
Two mobile carriers in ETC
ubiquinone (co-enzyme Q)
cytochrome C
What happens in the ETC
As electrons move between complexes, they release enough energy to transport protons from the matrix to the intermembrane space
Two subunits of ATP synthase
f0 - membrane bound
f1 - matrix
Formation of ATP by ATP synthase
- flow of H+ back into matrix
- generates mechanical rotation in the F0 subunit
- Causes conformational change in F1 subunit and forms ATP from ADP and phosphate
When is complex I bypassed
electrons donated by other FADH2 molecules (generated in glycerol phosphate shuttle and B-oxidation) bypass complex 1
fewer protons generated so fewer ATP molecules generated
most common cause of a failiure of oxidative phosphorylation
lack of oxygen e.g hypoxia (diminished), anoxia (total)
neurons - few minutes
muscle - few hours
Metabolic poisons (5)
Rotenone - Inhibits Complex I (Ox. phos. can still occur)
Malonate - competitive inhibitor of complex II
N3- / CN- - binds to haem group in complex IV, blocking electron flow
DNP
Oligomycin - inhibits ATP synthase by blocking proton channel
How does DNP work as a metabolic poison
provides alternative channel for H+ to travel through
Uncouples electron transport from ATP synth
Energy released as heat instead of for ATP
(similar mechanism in shivering thermogenesis)
Hamartoma
localised benign overgrowths of one or more mature cell types
e.g in the lung
Where is Acyl CoA generated
On outer mitochondrial membrane
How does Acyl-CoA enter the mitochondrial matrix
Coupled to carnitine to form acyl carnitine
Translocase moves acyl carnitine and carnitine to and from matrix respectively.
Allowing B oxidation of fatty acids
A child is diagnosed with carnitine deficiency. How might this condition lead to hypoglycaemia
Acyl CoA entry into mitochondria is impaired, reducing ATP production from fatty acid metabolism
Lipoprotiens are
molecules made of a phospholipid and apoprotein exterior, carrying cholesterol esters and lipids on the interior
Lipoproteins travel in
the bloodstream
Cholesterol is carried as an ester because
the molecule becomes more hydrophobic and hence can be more tightly packed
Types of lipoproteins (listed by incr. density)
Very low density lipoproteins VLDL
Intermediate density lipoproteins IDL
Low density lipoprotein LDL
High density lipoprotein HDL
What determines lipoprotein density
Level of lipid content; fewer lipids means higher density
2 most important lipoproteins
LDL and HDL
HDL is known as
Good cholesterol
as it carries lipids and cholesterol away from peripheral tissues and into liver for use or disposal
LDL is known as
Bad cholesterol
as it carries lipids and cholesterol into peripheral tissues.
What can high levels of LDLs lead to
atherosclerosis
6 factors leading to higher LDL levels
obesity
diabetes
smoking
age
sedentary lifestyle
poor diet
Which shuttle (transporter of electrons) from cytoplasmic NADH into mitochondria produce a lower net ATP production? why?
Glycerol phosphate: e- passed from cytoplasmic NADH to mitochondrial FADH2
FADH2 donates e- directly to second e- transporter in ox. phos.
skipping first transporter in ETC
fewer H+ pumped so less ATP produced
Non-shivering thermogenesis is the bodys response to temperature drop. How does this mechanism lead to an incr. in body temp.?
Uncoupling of oxidative phosphorylation dissipates proton gradient (allowing H+ to bypass ATP synthase channel), energy dissipated as heat
UCP1
Upon accepting electrons, which complex does not pump protons from the matrix to intermembrane space
Complex II
succinate dehydrogenase
directly participates in ETC by transferring electrons to ubiquinone
A redox couple with a positive E0 is more likely to
Act as an oxidising agent and accept electrons
- consistent with tendency to undergo reduction
Effective treatment for primary carnitine deficiency
Carnitine supplements
increase overall availability of carnitine, essential for transport of fatty acids into mitochondria to produce ATP
