Week 8 - Metabolism Flashcards
What are metabolites?
What is the metabolic pathway?
Reactants, intermediates and products
Series of enzyme catalysed reactions
What are the differences between degradative pathways and biosynthetic pathways?
- Converge on common intermediates
- Metabolised further in central oxidative pathway
- Few metabolites are starting point
- Carry out opposite
What do membrane-bound compartments require?
Transport systems
How is metabolic flux controlled?
- Allosteric control (enzymes regulated by effectors)
- Determined by RDS
- Covalent modification (hormonal control of ezymes)
- Substrate cycles (vary rates of opposing reaction)
- Genetic control (protein synthesis affects enzyme activity)
- Supply and demand
What is the route of carbohydrate digestion?
- Salivary amylase (to oligosaccharides)
- Small intestine digestion with pancreatic enzymes
- Mucosal cell enzymes (disaccharides to monosaccharides)
- Active transport takes glucose into cells with Na+
What is the difference between D glucose and pyranose?
What is glucose stored as?
D = linear
Pyranose = Ring structure
Glycogen
What are the properties of glycolysis?
Provides ATP
+ O2 = Pyruvate as end product –> forms Acetly CoA when oxidative phosphorylated
- O2 = Pyruvate reduced to lactate by lactate dehydrogenase
What are the 2 types of glucose transport?
Na+-independent facilitated diffusion –> Moves via concentration gradient
ATP-dependent Na+-monosaccharide transport –> Co-transport system against concentration gradient in intestinal epithelial cells
What are the proeprties of glucose phosphorylation and fructose 6-phosphate phosphorylation?
Catalysed by hexokinase
Irreversible
Rate limiting
Catalysed by phosphofructokinase-1
Inhibition of enzyme by + ATP/citrate concentration
Activation of enzyme by high AMP concentration
What are the properties of haemolytic anaemia?
- Lack of mitochondria in red blood cells
- Failure of ATP synthesis, altering cell shape
- Caused by genetic defects of glycolytic enzymes
- Regular transfusions required
When does gluconeogenesis occur?
What is glycogenolysis?
When there is insufficient glucose
Mobilisation of glucose from glycogen
What are the proeprties of glycogen?
- Main stores in skeletal muscle and liver
- Muscle fuel reserve for ATP synthesis
- 1 reducing end
- Non-reducing end on every branch
What are the 3 glycogen enzymes for degradation?
Glycogen phosphorylase:
- A dimer
- Breaks 1,4 linkages
- Allosteric interactions and ocvalent modification
- ATP, G6P, glucose = inhibitors
- AMP = activator
Glycogen debranching enzyme:
- Breaks 1,4 linkages then makes new ones on main branch, reducing branching
Phosphpoglucomutase:
- Converts glcosyl units to G1P
What are the properties of glycogen synthesis?
Glycogen synthase = makes 1,4 linkages (active form = dephosphorylated)
Glycogenin attaches to glucose
Liver synthesis accelerates during well-fed and fasting periods
Skeletal muscle synthesis accelerates during rest and exercise periods
What are the properties of insulin, glucagon and adrenaline hormonal regulation?
- Act through enzyme phosphorylated state changes
- Adrenaline and glucagon act through second messenger
- Adrenaline acts on muscle and liver
- Glucagon acts on liver
When is gluconeogenesis inhibited?
When does glyconeogenesis increase?
What activates glycogenolysis in muscle?
When substrate and energy levels are high
When glucose and energy levels are low
By calcium as it binds and activates calmodulin
What are glycogen storage diseases?
Genetic diseases caused by defective enzymes needed for synthesis / degradation
Glycogen has abnormal structure or excess accumulation
Von Gierke’s disease
Type Vlll
What are the properties of the TCA cycle?
In mitochondrial matrix
NADH + H+ + FADH2 from NAD+ and FAD+ by removing electron pairs
Biosynthesis of metabolites
No ATP produced
What are the properties of the pyruvate dehydrogenase reaction?
Pyruvate + NAD+ + CoA à Acetyl CoA + NADH + CO2
Controls glucose entry into TCA cycle
Rate limiting step
Irreversible
Regulated (allosterically, covalently, hormonally)
PDH = multienzyme complex, 3 enzyme complexes, 5 coenzymes
3 enzyme activities = Pyruvate decarboxylase, Dihydrolipoyl transacetylase, Dihydrolipoyl dehydrogenase (E1, E2, E3)
5 coenzymes = Thiamine pyrophosphate, Lipoamide, CoA, FAD+, NAD+
Mechanism = pyruvate decarboxylation –> acetyl CoA formation –> oxidised lipoamide regeneration
What are pyruvate dehydrogenase medical problems?
Beri-beri (thiamine deficiency) –> PNS damage and weakened muscle
PDH deficiency –> reduced ATP synthesis, + alenine
Mercury / arsenite poisoning
Vitamin deficiencies
What is produced for each Acetly CoA oxidised?
3 NADH
1 FADH2
2 CO2
1 GTP
4 pairs of electron
What are the properties of the elctron transport chain?
In inner mitochondrial matrix
4 protein complexes (3 proton pumps (complex 1,3,4), 1 link to TCA cycle (complex 2))
2 small components (CoQ, cytochrome c)
What are the properties of complex 1?
NADH dehydrogenase
NADH binds to it
Accepts NADH electrons
Transfers electrons to CoQ
4 H+ pumped out
What are the properties of complex 2?
Succinate dehydrogenase
Enzyme of TCA cycle
Accepts FADH2 electrons
Transfers electrons to CoQ via Fe-S proteins
What are the properties of complex 3?
Cytochrome c reductase
Heme prosthetic group
Accepts CoQ electrons
Transfers electrons to cytochrome c
2 protons pumped across
What are the properties of complex 4?
Cytochrome c oxidase
13 protein subunits with 2 heme groups and 3 copper ions
Cytochrome c electrons accepted
Electrons transferred to 1/2O2 –> reduced to H2O
8 protons pumped across
What are the properties of coenzyme Q?
Ubiquinone
Small, lipid soluble compound
Mobile carrier
Accepts Fe-S protein electrons from complex 1 and 2
Electrons transferred to complex 3
What are the proeprties of cytochrome c?
Peripheral membrane protein bound to IMM loosely
Bind to complex 3 and transfers electrons to complex 4
Highly conserved
What are the proeprties of ATP synthesis in oxidative phosphorylation?
ATP synthase is complex 5
In inner mitochondrial matrix
Composed of 2 subunits:
F1 ATPase – generates ATP, F0 coupling factor – proton channel spanning IMM
What agents affect oxidative phosphorylation?
ATPase inhibitors (oligomycin)
SSI’s of electron transport chain
Uncouplers (neutralise proton gradient and prevent ATP synthesis) à chemical = dinitrophenol, natural = uncoupling proteins
What is UCP1/ thermogenin?
In mitochondria of brown adipose tissue
Energy from electron transport chain = used to generate heat (non-shivering thermogenesis)
In new-borns and hibernating animals, is important
What is the process of fatty acid mobilisation?
Glucagon or adrenaline activate hormone-sensitive lipase
Triacyglycerol in adipose tiossue is hydrolysed
Free fatty acids and glycerol is formed
Why can’t the brain take up free fatty acids?
Cannot cross blod-brain barrier
What happens during ‘beta’-oxidation of fatty acids?
Activation in cytosol of long fatty acid chains forming fatty acyl CoA
Import of activated LCFAs into mitochondria
‘beta’-oxidation in mitochondrial matrix, generating NADH, FADH2, acetyl CoA
What is used for LCFA import into mitochondria?
Carnitine shuttle
CoA esters cannot cross mitochondrial inner membrane
What are the proeprties of carnitine?
From meat
Liver and kidney synthesise it
Kidneys supply to muscles via blood
Deficiency leads to toxic LCFA build up causing neurological damage
What are the proeprties of ketone bodies?
Brain fuel source during starvation
Acetyl CoA in liver mitochondria makes it
Happens when high AcCoA levels
Small glycogen stores in babies = can quickly become ketotic
What happens during ketone body synthesis?
Liver mitochondria
Acetoacetate and ‘beta’-hydroxybutyrate form 2 ketone bodies
Acetoacetate reduced to ‘beta’-hydroxybutyrate when high NADH (during starvation)
How are ketone bodies utilised?
Not metabolised by liver
Adaptation of brain to use them during starvation
Used by heart muscle and kidney cortex under all conditions (spares glucose)
What happens during ketoacidosis?
0.1mM = normal
7mM = tissue utilisation saturated so excreted in urine (ketonuria)
- blood pH (ketoacidosis)
Test using paper strips for ketonuria
When does gluconeogensis occur?
During exercise (lactate)
Short-term fasting (alanine)
Diabetes (insulin insensitivity)
Trauma (peripheral insulin resistance)
When glucose levels are low and ATP levels are high
When is glucose required?
Brain + RBCs for fuel
Glycogen stores (enough for 1 day (190g))
Inhibited by alcohol (ethanol = + cytosolic NADH conc. In liver –> gluconeogenesis intermediates are therefore redirected to alternate reaction pathways so – glucose synthesis)
What are the properties of gluconeogenesis?
- Glucose synthesis from non-carbohydrate precursors
- Occurs in liver, kidneys and small intestine
- Occurs in cell cytosol
- Is reversal of glycolysis
When is gluconeogenesis not the reversal of glycolysis?
Pyruvate to PEP:
Pyruvate (in mitochondria) + CO2 + ATP –> oxaloacetate (in mitochondria) + ADP + Pi
F1,6BP to F6P:
ructose 1,6-biphosphate + H2O –> Fructose 6-phosphate + Pi
G6P to glucose:
G6P + H2O –> glucose + Pi
What effect does insulin have on gluconeogenesis?
What effect does glucagon have on gluconeogenesis?
Promotes glycolytic enzyme synthesis
Inhibits PEPCK synthesis
Increases PEPCK and F1,6BPase expression
How do you form gluconeogenesis precursors from amino acids?
Remove amino group
Use carbon skeleton to form glucose
What are the 4 types of metabolic pathways?
Fuel oxidative pathways
Fuel storage and mobilisation
Biosynthetic pathways
Detoxification / waste disposal pathways
What is anabolism?
What is catabolism?
What are anabolic pathways?
What are catabolic pathways?
Synthesis
Breakdown
Synthesis of large molecules
Breakdown of large molecules
How is balance acheived in metabolism?
Blood nutrient concentration (fatty acids for example)
Hormones (epinephrine for example (fight or flight))
CNS
What are the consequences of too low or high metabolism?
Low = hypoglycaemia, brain metabolism limited
High = coma, non-enzymatic glycosylation of proteins
What is the role of insulin in metabolism?
Promotes fuel storage and use for growth
Glycogen formation in liver & muscle
Conversion of glucose to triacylglycerols (liver)
Protein synthesis (e.g. albumin) in liver
Storage of triacylglycerols (adipose)
Increases glucose uptake by muscle & adipose
Amino acid uptake & protein synthesis in skeletal muscle
What is the role of glucagon in metabolism?
Promotes mobilisation and maintains fuel availability (not in muscle as lack of receptors)
Increased Glycogenolysis, reduced glycogen synthesis in liver
Stimulates gluconeogenesis & ketogenesis
Mobilizes fatty acids from adipose triacylglycerols
Where is insulin and glucagon produced?
Pancreas:
- ‘alpha’ cells secrete glucagon
- ‘beta’ cells secrete insulin
What are the properties of glucagon in metabolism?
Produced as preprohormone in Rough Endoplasmic Reticulum
Acts on liver & adipose tissue
Degraded by liver & kidneys (~5 min ½ life)
Secretion is regulated by [glucose] & [insulin]
what are the intracellular events of glucagon and insulin in metabolism?
Hormones change substrate flux through pathway
Hormones bind to receptors on cell surface (second messengers activated, signal transduction)
3 types of transduction à receptor coupled to adenylate cyclase – receptor / kinase activity – receptor coupled to hydrolysis of PIP2
Insulin autophosphorylates cell receptor
Glucagon binding = causes formation of secondary messenger
What are cellular responses to glucagon or insulin?
Reverses glucagon-stimulated phosphorylation
Kicks off a phosphorylation cascade
Induction/repression of enzyme
Stimulate protein synthesis
Stimulate glucose & amino acid intake
What are the 3 types of memory?
Sensory memory (registration)
Working / short-term memory (limited capacity, acoustic coding, receny effect)
Permanent / long-term memory (large capacity, primary effect, semantic coding)
How can you imporve patient recall?
Organisation (good structure)
Less is more
Stress importance
Precise information
Association with visual imagery
Cues
External aids
What is adherence?
What are the forms on non-adherence?
Following advice from health professional
All aspects of self-management
Failure to make lifestyle changes necessary for health
Failure to monitor health
Failure to take up available health screening
Failure to keep appointments
What needs to be involved in a systematic review?
a clearly stated set of objectives with pre-defined eligibility criteria for studies;
an explicit, reproducible methodology;
a systematic search that attempts to identify all studies that would meet the eligibility criteria;
an assessment of the validity of the findings of the included studies, for example through the assessment of risk of bias; and
a systematic presentation, and synthesis, of the characteristics and findings of the included studies.
What is evidence based medicine?
Systematic review, appraisal and use of clinical research findings to aid optimum clinical care delivery to patients
How to formulate evidence based medicine?
Formulate a clear clinical question from a patient’s problem
Search the literature for relevant clinical articles
Evaluate (critically appraise) the evidence for its validity and usefulness
Implement useful findings in clinical practice
What happens to dietary carbohydrates during the fed state?
Turned into monosaccharides
Starch digested by ‘alpha’-amylase
Di/tri/oligosaccharides digested by enzymes
Monosaccharides absorbed by intestinal epithelial cells –> transported to hepatic portal vein
What happens to glucose, proteins, free amino acids and fats during the fed state?
Glucose = oxidised for energy –> enters biosynthetic pathways –> forms carbon skeleton of most compounds
Proteins = cleaved by pepsin in stomach and proteolytic enzymes in pancreas (absorbed into intestinal epithelial cells –> released into hepatic portal vein)
Free amino acids = absorbed from blood and used for protein synthesis and biosynthesis
Fats = insoluble –> triacylglycerols = emulsified by bile sales and pancreatic lipase converts TAGs to fatty acids and 2-monoacylglycerols –> form micelles when in contact with bile salts
What do hormones effect on metabolic pathways?
Substrate availability
Allosteric regulation of enzyme
Covalent modification of enzymes
Induction of enzyme synthesis
What is the role of liver in fed state metabolism?
Uses hepatic portal vein for venous drainage of gut and pancreas
Takes up carbs, lipids and AA’s
What happens during carbohydrate metabolism in the fed state?
+ glucose intake by hepatocytes (GLUT-2 = high Km)
+ glucose phosphorylation (glucokinase = forms glucose-6-phosphate)
Excess glucose converted into TAG (packaged into LDLs)
+ glucogenesis –> activation of glycogen synthase by allosteric effector and dephosphorylation –> glucose-6-phosphate converted into glycogen
+ pentose phosphate pathway/hexose monophosphate shunt activity
+ glycolytic enzymes as + insulin-to-glucagon conversion
- glucose production
What happens during fat metabolism in fed state?
Liver = primary fatty acid synthesis site –> acetyl CoA carboxylase activated
+ acetyl CoA
What happens during the fasting state and starved state?
2-4 hours after meal:
blood glucose falls, insulin decline, glucagon rise, fuel release
3+ days:
survival depends on protein levels and adipose tissue amounts
Protein depletion = organ malfunction and infection –> death at around 40% body protein
What are the 2 priorities during the starved state?
Maintain adequate blood glucose
Mobilise fatty acids and synthesis ketone bodies
What is the role of body stores in the starved state?
Fuels are readily oxidizable
Carbs stored as glycogen (fluctuates, binds water as polar molecule)
Triacylglycerols have more calories than carbs or protein
Body protein can be used
What fuels does the brain use?
What fuels does muscle use?
Glucose = primary fuel
Ketones = during starvation
Glucose
Fatty acids
Ketone bodies
(glycogen to glucose by glucose-6-phosphate for contraction, fatty acids used by resting muscle)
What fuels does the heart use?
What fuels does adipose tissue use?
What fuels does the liver use?
Fatty acids
Ketone bodies
Lactate
Glycerol-3-phosphate for triacylglycerol synthesis, requires glucose
provides brain, muscle and peripheral organ fuel, forms glycogen from carbs, forms ketone bodies from fatty acids
Liver
What happens during carbohydrate metabolism during the starved state?
produce glucose from gluconeogenesis or glycogenolysis and produce ketone bodies for non-glucose dependent tissues
Glycogen degradation then gluconeogenesis:
+ Glucagon to insulin ratio
PKA-mediated phosphorylation of glycogen phosphorylase kinase
+ glycogen phosphorylase phosphorylation
Gluconeogenesis skeletons = derived from glucogenic amino acids, muscle lactate and adipose tissue glycerol
Liver
What happens during fat metabolism during the starved state?
Fatty acid oxidation = liver main energy source, from triacylglycerols in adipose tissue –> TCA cycle inhibited by NADH
+ ketone body synthesis = not used by liver (as lacks thioporase)
Adipose tissue
What happens during carbohydrate metabolism during the starved state?
Depressed glucose transport as insulin sensitive
Reduced glycolysis
Reduced triacylglycerol synthesis
Adipose tissue
What happens during fat metabolism during the starved state?
Lipolysis mobilises adipose triacylglycerols –> fatty acids and glycerol released
Increased fatty acid usage with increased fasting length
Adipose tissue
What happens during fatty acid metabolism during the starved state?
Increased release as hydrolysis of triacylglycerols
Decreased uptake as adipose LDL activity is low
Resting skeletal muscle
What happens during the fasting state?
Resting muscle moves further from glucose to fatty acids and ketone bodies as become main energy source for contraction
Resting skeletal muscle
What happens during carbohydrate metabolism in the starved state?
Depressed glucose transport as insulin sensitive
Reduced glycolysis
Resting skeletal muscle
What happnens during lipid metabolism during the starved state?
First 2 weeks = fatty acids from adipose tissue and ketone bodies from liver are used
3 weeks = reduced use of ketone bodies so more for the brain
Resting skeletal muscle
What happens during protein metabolism during the starved state?
Early stages = + breakdown of muscle protein (+ liver gluconeogenesis)
Fall in insulin initiates this
Brain and kidney
What happens during the starved state?
Early = brain uses glucose
Later stages = glucose replaced by plasma ketone à some glucose needed for neurotransmitters
Reduction in protein degradation as less protein catabolism for gluconeogenesis
Kidneys = express gluconeogenesis enzymes (compensates for acidosis by ketone bodies)
What are the properties of diabetes mellitus?
Heterogeneous metabolic disease –> multifactorial, polygenic, characterised by hyperglycaemia, insulin deficiency
0.1 : 0.9 type 1 (insulin-dependent) and type 2 (non-insulin-dependent)
What are the properties of Type 1 diabetes mellitus?
‘beta’-cell autoimmune attack causes insulin deficiency
Hyperglycaemia and ketoacidosis –> + blood sugar and ketone levels, + gluconeogenesis, + fatty acid mobilisation and liver oxidation
Hypertriacylglycerolemia –> excess fatty acids converted to triacylglycerols, decreased enzyme production
What are the properties of Type 2 diabetes mellitus?
Dysfunctional ‘beta’-cells and insulin
Hyperglycaemia –> + hepatic production and reduced use, minimal ketosis
Dyslipidaemia –> Fatty acids converted to triacylglycerols and secreted as VLDLs in liver, low lipoprotein lipase
