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Nutrient metabolism Flashcards

1
Q

Define energy

A
  • The capacity for doing work

- Can be converted but cannot be broken down or created

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2
Q

What are the units of energy?

A
  • Measured by capacity to produce heat

- Measured in Joules (=1newton/m = 0.24 calories)

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3
Q

What is energy used for?

A
  • Synthesis of macromolecules and biomolecules
  • Active transport of molecules and ions across membranes
  • Mecchanical worm in cellular movements e.g. muscle contraction
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4
Q

What is the absorptive state in digestion?

A
  • Just after eating (2 hours)

- Is the period in which nutrients from food are absorbed by the body

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5
Q

What is the post-absorptive state in digestion?

A
  • Longer after eating
  • Nuritents no longer absorbed from food
  • In this state, energy is utilised from stored nutrients
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6
Q

Outline carbohydrate digestion and absorption

A
  • Alpha amylase breakdown of starch completed in SI by pancreatic amylase
  • Disaccharides broken down to monosaccharides by maltase, sucrase and lactase (brush border enzymes)
  • Glucose and galactose actively transported across intestinal mucosa
  • Facilitated transport of fructose
  • Glucose, galactose and fructose transported to the liver via the portal vein
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7
Q

Outline amino acid digestion/absorption

A
  • AAs actively transported inot epithelial cells

- From there to blood stream to portal vein to liver for first stage in metabolism

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8
Q

Outline lipid digestion/absorption

A
  • FFAs trnasported to epithelial cells
  • TAGs reformed
  • Coalesce to form chylomicrons
  • Released into lymph, then circualtion
  • Bypasses hepatic metabolism
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9
Q

List the energy sources in the absorptive state in the ruminant

A
  • VFAs
  • Amino acids
  • (Carbohydrates used by microorganisms in the rumen)
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10
Q

List the energy sources in the absorptive state in non-ruminants

A
  • Amino acid
  • Glucose
  • TAGs
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11
Q

What are the potential fates of glucose?

A
  • Energy source (almost all tissues)
  • Glycogen synthesis (liver, skeletal muscle)
  • TAG synthesis (liver, adipose)
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12
Q

What are the basic steps in aerobic metabolism of glucose?

A
  • Glycolysis producing 2 pyruvates

- Pyruvate into TCA cycle

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13
Q

What are the basic steps in anaerobic metabolism of glucose?

A
  • Glycolysis producing 2 pyruvates

- Pyruvate into Cori cycle

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14
Q

What is the role of glycolysis in nutrient metabolism?

A
  • Breakdown of glucose to pyruvate
  • Produces pyruvate
  • Need this carry out anaerobic and aerobic metabolism
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15
Q

What are the products of aerobic metabolism?

A
  • ATP
  • CO2
  • H2O
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16
Q

What are the products of anaerobic metabolism

A
  • ATP

- Lactate

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17
Q

Describe what happens to the pyruvate molecules produced by glycolysis under anaerobic conditions

A
  • 2 pyruvates produced as normal
  • Utilise 2 NADH (also produced by gycolysis) and 2 H+ to convert 2 pyruvate into 2 lactic acid molecules
  • Catalysed by lactate dehydrogenase
  • Produces 2NAD+ and 2lactic acid molecules
  • Lactic acid molecules enter cori cycle
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18
Q

Describe the process of glycolysis

A
  • Occurs the same under anaerobic or aerobic conditions
  • Glucose to 2 pyruvate using 2Pi, 2NAD+ and 2 ADP
  • This produces 2 pyruvates, 2ATP, 2NADH, 2H+ and 2H2O
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19
Q

What is the fate of the NAD+ produced by under anaerobic conditions?

A
  • Oxidative reduction cannot take place
  • NAD can be used in glycolysis
  • Get build up of lactic acid and enters bloodstream
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20
Q

Describe the TCA cycle

A
  • Aerobic conditions
  • Pyruvate to acetyl CoA by pyruvate dehydrogenase
  • Permanent change
  • Acetyl CoA ouples with oxaloacetate to form citrate
  • Citrate oxidised back to oxaloacetate => CO2
  • Produces 3NADH, 1FADH2 adn GTP
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21
Q

Where does oxidative phosphorylation occur?

A

Across the inner membrane of mitochondria

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22
Q

Describe the process of oxidative phosphorylation

A
  • NADH donates electron to electon carrier chain (ECC)
  • Electron carriers form 3 aggregates within membrane
  • 2 electron carriers shuttling electrons between aggregates
  • Ubiquinol and cytochrome C
  • Each time electron transported through an aggregate results in transport of proton from mitochondrial matrix to intermembrane space
  • Leads to proton gradient
  • protons back to inner matrix via ATP synthase = 1ATP per proton
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23
Q

How many ATP molecules can be produced per NADH molecule in oxidative phosphorylation?

A
  • 3

- 3 protons are transported, so 3 ATP are produced

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24
Q

How many ATP molecules can be produced by FADH2 molecules in oxidative phosphorylation?

A
  • 2

- Enters further down chain, donates 2 protons

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25
Q

Describe the Cori cycle

A
  • Anaerobic respiration
  • Convert lactate to pyruvate to precent acidosis
  • Lactate converted to pyruvate in liver cells
  • Pyruvate used to produce glucose -6-phosphate
  • This also requires ATP
  • Process of gluconeogenesis
  • Liver uses ATP produced by muscle cells in glycolysis
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26
Q

How many ATP molecules are produced in anaerobic conditions?

A

2 molecules

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27
Q

How many molecules of ATP are produced in aerobic conditions?

A

38 molecules

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28
Q

When are FFAs converted to TAG and laid down as fat?

A
  • In absorptive state
  • Glucose provides most of energy requirements
  • When glycogen stores make up 5% of liver mass
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29
Q

How are free fatty acids (FFAs) transported?

A
  • Bound to albumin

- Finite amount of this at any one time

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30
Q

Name the different lipoproteins

A
  • Chylomicrons
  • Very low density lipoproteins (VLDLs)
  • Low density lipoproteins (LDLs)
  • High density lipoproteins (HDLs)
  • Also less importantly intermediate density lipoproteins (IDLs)
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31
Q

Describe the structure of lipoproteins

A
  • Made up of proteins, cholesterol, phospholipids and TAG
  • Ratio of lipid to protein changes
  • More lipid = lower density
  • Size decreases as density increases
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32
Q

Describe the transport of FFAs from the gut epithelium

A
  • Chylomicrons produced in gut epithelium
  • Via lymphatic system to blood capillaries
  • Lipoprotein lipase digests mchylomicrons in blood, releases FFAs
  • FFAs diffuse across into various cells
  • In adipose tissue laid down as TAG
  • Can be absorbed by other tissues and used as energy source
  • Chylomicron remnants left following digestion by lipoprotein lipase
  • Transported to hepatocytes and recycled
  • Used to produce more lipoproteins
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33
Q

What is the role of cholesterol?

A

Forms part of cell membranes, steroid hormones and bile

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34
Q

What is the role of HDLs?

A
  • Provide proteins for production of lipoproteins
  • Mop up excess cholesterol
  • Taken up by liver and degraded for more lipoprotein production
  • Excess cholesterol sent to gall bladder for bile production
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35
Q

What are glycogen and TAGs?

A

Storage molecules of glucose

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36
Q

What is lipogenesis?

A

The production of TAG using glucose

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37
Q

What is glycogenesis?

A

The production of glycogen using glucose

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38
Q

Where does lipogenesis occur?

A
  • Cytoplasm
  • Liver
  • Adipose tissues
  • Stored long term in adipose
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39
Q

When does lipogenesis occur?

A

In the absorptive state

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40
Q

Describe the process of lipogenesis

A
  • Acetyl CoA to malonyl CoA by acetyl CoA carboxylase
  • ACA and MCA used by fatty acid sunthase to produce faty acid palmitate
  • 2 key moieties in fatty acid synthase = beta-ketoacyl and ACP
  • ACA bound to ACP (2 carbon)
  • 2 carbon moiety trnasferred to beta-ketoacyl synthase
  • ACP binds to MCA (3 carbon moiety)
  • beta-ketoacyl synthase transfers 2 carbons from ACA to ACP, releases CO2
  • Gives 4 carbon structure
  • Reduced using NADPH
  • Back to bKA part of enzyme
  • ACP takes up 3 carbons from MCA
  • Continues cycle
  • Each cycle adds 2 carbons to chain
  • 16 carbon structure, hydrolysed away from enzyme = palmitate
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41
Q

Describe the citrate-pyruvate shuttle in lipogenesis

A
  • ACA substrate
  • ACA produced in mitochondria
  • ACA converted to citrate, can be transported out
  • Increased cytoplasmic citrate
  • Converted back to ACA and oxaloacetate
  • ACA used in fatty acid synthesis
  • Oxaloacetate converted to malate and pyruvate
  • Transfers H from NADH to NADP
  • Pyruvate taken back to mitochondria
  • 2NADH needed per ACA for reduction step
  • Half reducing potential provided by oxaloacetate release
  • Half released by pentose phosphate pathway
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42
Q

Describe the pentose phosphate pathway

A
  • Glucose to glucose-6-phosphate
  • Using 2 NADP and 1H2O
  • Produce ribose-5-phosphate and 2NADPH, 2H+ adn 1CO2
  • Ribose-5-phosphate goes on to inter-conversion of sugars
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43
Q

Give a summarised pathway for TAG synthesis

A
  • Glucose to pyruvate by glycolysis
  • Pyruvate to Acetyl CoA by pyruvate dehydrogenase
  • Acetyl CoA to malonyl CoA by acetyl-CoA carboxylase
  • Malonyl-CoA to fatty acids using NADPH
  • Fatty acids to TAG using acyl transferase and glycerol-3-phosphate
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44
Q

Describe the structure of glycogen

A
  • Granules form around glycogenin protein
  • Long chains of glucose polymers attach to this protein
  • Branched chains by alpha 1,6-linkages
  • Straight chains by alpha 1,4 - linkages
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45
Q

Describe glycogenesis

A
  • Glucose enters liver and skeletal muscle cells
  • Converted to glucose-6-phosphate by hexokinase in most tissues, glucokinase in liver
  • Converted to glucose-1-phosphate by phosphoryl group switching to C1 on ring
  • G1P reacts with uriding triphosphate to form UDPG (active form of glucose)
  • UDPG added to growing chain by glycogen synthase
  • Once chain has 11 glucose molecules, brnaching enzyme trnasfers some units to other chains
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46
Q

What is the most important controlling enzyme of glycogenesis?

A

Glycogen synthase

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47
Q

Why are VFAs used as energy sources in ruminants?

A

VFAs produced by microorganisms metabolising carbohydrates

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48
Q

What are the VFAs called?

A
  • Acetate
  • Butyrate
  • Proprionate
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49
Q

Describe the VFA metabolism of acetate

A
  • 2 carbons
  • Converted to acetyl CoA
  • Use this to produce energy via TCA cycle or oxidative phosphorylation
  • Acetyl CoA produced in cytoplasm, transported into mitochondria
  • Released in mitochondria for use in TCA cycle
  • Excess acetyl CoA converted to fatty acids and triglycerides
  • Stored in adipose tissue
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50
Q

Describe the metabolism of butyrate

A
  • 4 carbon structure
  • Converted to beta-3-hydroxybutyrate
  • This is converted to acetoacetyl-CoA and then 2 acetyl-CoA molecules
  • Can be used in TCA cycle
  • Each molecule of butyrate can produce 25 ATP molecules
  • Excess ACA converted to TAG and stored in adipose tissue
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51
Q

Describe the metabolism of proprionate

A
  • 3 carbon structure
  • 2 metabolic fate
  • Each molecule can produce 18 ATPs
  • Different fates in most tissues compared to liver
  • For both pathways is converted to succinyl CoA
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52
Q

Describe the metabolism of proprionate in the liver

A
  • 2 propionates used to produce 2 succinyl CoAs
  • These converted to 2 phosphoenolpyruvates
  • These used to produce 1 glucose molecule
  • Can either go into energy stores or glycolysis/TCA/oxidative phosporylation
  • ## The net gain for this is 17 ATP
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53
Q

Describe the metabolism of proprionate in most tissues

A
  • 1 proprionate converted to 1 succinyl CoA
  • Can go direct to TCA/oxidative phosphorylation
  • Succinyl CoA converted to pyruvate
  • Pyruvate converted to Acetyl CoA
  • ACA into energy stores or TCA/oxidative phosphorylation
  • Net gain 18 ATP
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54
Q

What are the fates of amino acid in metabolism?

A
  • Energy sources
  • Production of proteins
  • Excreted if in excess
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55
Q

What are the fates of ketoacids?

A
  • Direct production of energy
  • In absorpive state in non-ruminants used to produce fatty acids to be laid down in adipose tissue as fat
  • In ruminant converted to glucose in gluconeogenesis
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56
Q

What are the 2 types of amino acid?

A
  • Glucogenic

- Ketogenic

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57
Q

Describe amino acid metabolism

A
  • Excess AAs in liver deaminated to ketoacids, ammonia produced and excreted in urea
  • Some AAs broken down to 2 moieties
  • One can form acetyl-CoA (ketogenic)
  • Other can form glucose (glucogenic)
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58
Q

What is the fate of glucogenic AAs?

A
  • Potential to metabolised to glucose
  • Broken down to pyruvate or citric acid cycle component
  • Converted via gluconeogenesis to glucose
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59
Q

What is the fate of ketogenic AAs?

A
  • Potential to be metabolised to acetylCoA

- ACA then oxidised to form energy in TCA, or converted to FFAs and laid down as TAG in adipose tissue

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60
Q

Describe the deamination of an amino acid (alanine)

A
  • Combines with alpha-ketoglutarate (ketoacid)
  • Transamination catalysed by alanine aminotransferase
  • Ketoacid produced from alanine => pyruvate
  • Amino acid produced from alpa-ketoglutarate => glutamate
  • Glutamate back to alpha-ketoglutarate by glutamate dehydrogenase
  • Produces ammonia, excreted in urea
  • End products are pyruvate and ammonia
  • Pyruvate converted as normal
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61
Q

Describe what happens in the post-absorptive state

A
  • 2-3 hours after last meal
  • No absorption of nutrients, still has energy requirements
  • Energy from breakdown of macromolecules produced in absorptive state
  • 3 main methods of maintaining glucose levels in plasma
  • Mobilisation of glycogen from liver sources (glycogenolysis)
  • Synthesise glucose in liver (gluconeogenesis)
  • Utilise lipids as energy source (lipolysis)
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62
Q

Describe the process of glycogenolysis

A
  • In skeletal muscles and liver
  • Breakdown of glycogen to produce glucose
  • Glucose-1-phosphate cleaved from chain using Pi and catalysted by glycogen phosphorylase (non-reducing end)
  • G1P to G6p by phosphoglucomutase
  • G6P undergoes glycolysis in muscle tissue
  • G6P used in liver and kidney to produce glucose directly
  • Catalysed by glucose-6-phosphatase
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63
Q

What is the controlling enzyme of glycogenolysis?

A

Glycogen phosphorylase

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64
Q

What is gluconeogenesis?

A

Synthesis of glucose in the liver

65
Q

Describe the process of gluconeogenesis

A
  • AAs, pyruvate adn lactate produced due to anaerobic metabolism used
  • Diffuse into blood, taken up by liver
  • Glycerol used (produced by breakdown of TAGs)
  • FFAs used as energy cells by most cells (glucose sparing)
66
Q

What is the most important precursor for amino acids?

A

Skeletal muscle protein

67
Q

What are the main sites of gluconeogenesis

A
  • Liver

- Kidney

68
Q

Give a rough outline of gluconeogenesis in the liver

A
  • Pyruvate/lactate/AAs/glycerol converted to oxaloacetate
  • Oxaloacetate converted to phosphoenolpyruvate
  • Converted to glyceraldehyde 3-phosphate
  • Converted to dihydroxy acetone phosphate and glucose
69
Q

Describe the way in which the substrate for gluconeogenesis enter the pathway

A
  • Pyruvate into pathway as soon as reaches liver
  • Lactate converted to pyruvate by Cori cycle
  • Glycerol converted to dihydroxyacetonephosphate (enters pathway half way up)
  • Amino acids from muscle broken into TCA cycle intermediates, then oxaloacetate, then pyruvate, then alanine for transport to liver then back to pyruvate
70
Q

In what order are the substrates for gluconeogenesis used?

A
  • Liver glycogen first
  • Then skeletal muscle proteins
  • Then glycerol from TAG
  • Then muscle glycogen
71
Q

Describe the utilisation of energy stores through protein catabolism

A
  • AA catabolism needed for gluconeogenesis
  • AA in muscle coupled with pyruvate
  • Produces ketoacids (from AAs) and alanine (from pyruvate)
  • Catalysed by alanine aminotransferase
  • Ketoacid produced converted to pyruvate to be used again in cycle
72
Q

What are the advantages of using energy stores through protein catabolism?

A
  • Alanine and glutmate taken up by hepatic cells efficiently (other AAs not as much)
  • Transamination reduces production of ammonia
73
Q

What is the importance of the transamination reaction in protein catabolism?

A
  • Reduces the production of ammonia

- No mechanisms to remove ammonia from muscle tissues

74
Q

What is glucose sparing?

A

When FFAs liberated from adipose tissue in bloodstream are used as an energy source rather than glucose (in most tissues). This leaves glucose to be used by cells that can only use glucose as an energy source

75
Q

Describe the process of lipid catabolism adn its role in the utilisation of energy stores

A
  • TAGs into glycerol adn FAs by hormon sensitive lipase
  • Lipase controlled by hormonal signals
  • Glycerol cannot be used to form TAG as is not glycerol-3-phosphate
  • Cannot form G3P from glycerol (lacks enzyme in adipose)
  • Glycerol secreted into blood, used by liver in gluconeogenesis or processed in adipose to produce energy
  • Glycerol metabolised through TCA cycle or gluconeogenesis
  • FFAs metabolised further
76
Q

Describe FFA metabolism

A
  • Activate FFAs to fatty acyl Coa (active form) on outer membrane of mitochondria
  • Transported to mitochondrial matrix throguh membrane via carnitine mediated transport system
  • In mitochondria beta-oxidation occurs to yield acetyl CoA which can be fed to TCA cycle
  • Cycles of beta-oxidation continue untill all 2-carbon residues in FFA chain are ACA
  • Produces large number of molecules which can yield energy, also yields FADH2 adn NADH
77
Q

Describe lipid catabolism during starvation

A
  • Fat is main energy source
  • Too much ACA in liver to enter TCA cycle
  • Ketone bodies produced
  • Act as additional energy source
  • FFAs pumped into bloodstream to provide energy source
  • If this continues get excess fatty acids in blood, preferentially taken up by the liver for processing
  • Liver uses these for own energy needs
78
Q

What are the sources of glucose in starvation?

A
  • Proteins from muscle

- Fats in adipose tissue

79
Q

What are the 3 ketone bodies?

A
  • Acetoacetate
  • beta-hydroxybutyrate
  • Acetone
80
Q

How are ketone bodies produced?

A
  • Excess ACA
  • Used to produce acetoacetate
  • Can be reduced to beta-hydroxybutyrate
  • OR can be spontaneously converted to acetone
81
Q

Why is there a need to coodinate pathways involved in nutrient metabolism?

A
  • To avoid futile cycles
  • Ensure flow of molecules through the most appropriate metabolic pathways
  • To avoid futile cycles
82
Q

What are futile cycles?

A
  • When oppostie pathways are on or off at the same time, yielding no benefit e.g. gluconeogenesis and glycolysis
83
Q

How are futile cycles avoided?

A
  • Caused by opposite pathways
  • In each case some reactions in both pathways are reversible and catalysed by the same enzyme
  • Will also have irreversible reactions catalysed by different enzymes
  • These provide a point of control
  • Can turn each pathway on or off independently, rather than both on or both off
84
Q

What is meant by the integration of metabolism?

A
  • Ensure flow of molecules through most appropriate metabolic pathways
  • All pathways are linked
  • There are key metabolites at key junctions of several pathways e.g. pyruvate, glucose-6-phosphate etc
85
Q

What are the control strategies that can be used to modify key enzymes in pathways to control those pathways?

A
  • Hormone regulation
  • AMPK
  • Substrate/product concentrations
86
Q

What are the main hormones used in control of nutrient metabolism?

A
  • Insulin
  • Glucagon
  • Epinephrine
  • Glucocorticoids
87
Q

When is insulin released?

A
  • Times of plenty
  • Absorptive state
  • High glucose in plasma and want to reduce this
88
Q

When in glucagon released?

A
  • Post absorptive state

- Want to increase plasma glucose levels

89
Q

When is epinephrine released?

A
  • Fight or flight
  • Times of stress and high muscle activity
  • Want to increase glucose in muscle
90
Q

Describe the action of insulin in nutrient metabolism

A
  • Counteracts increased plasma glucose
  • Acts by binding to receptors of cell (not present on all cells)
  • Evokes 2nd messenger system to promote dephosphorylation of key enzymes in metabolic map
  • Increases glucose entry to cells tissue specific)
  • Inhibits hormone sensitive lipase and lipid catabolism
  • Stimulates fat synthesis
  • Increases consumption of glucose for ATP production (glycolysis)
  • Inhibits gluconeogenesis
  • Inhibits glycogenolysis
  • Stimulates trasport of AAs into cells
91
Q

What tissues have insulin dependent glucose uptake?

A
  • Muscle
  • Adipose tissue
  • Not affected by insulin are brain, liver and RBCs
92
Q

Give a summary of the processes affected by insulin and in what way

A
  • Glycolysis, glycogenesis, lipogenesis increased

- Glycogenolysis, lipolysis, gluconeogenesis decreased

93
Q

Describe the action of epinephrine in hormonal control of nutrient metabolism

A
  • Maximises energy to muscles cells and counteracts decreased plasma glucose
  • Promotes phosphorylation of key enzymes
  • Increases catabolism of glycogen
  • Inhibits glycogenesis
  • Activates hormone sensitive lipase and increase catabolism of lipids
  • Stimulates secretion of glucagon and inhibits insulin secretion (exaggerates own effects)
94
Q

Give a summary of the pathways affected by epinephrine and in what way

A
  • Increases: glycogenolysis, lipolysis, action ofhormon sensitive lipase, secretion of glucagon
  • Decreases: glycogenesis, insulin secretion
95
Q

Describe the action of glucocorticoids in the control of nutrient metabolism

A
  • Counteracts decreased plasma glucose (in starvation, stress)
  • Phosphorylates key enzymes
  • Stimulates gluconeogenesis in the liver
  • Increases AA uptake by liver (decreased in other tissues)
  • Increased synthesis of specific enzymes in long term effect
  • Activates hormone sensitive lipase and increases catabolism of ipids
  • Stimulates protein catabolism (and inhibits synthesis)
  • Decreases glucose entry into cells (tissue specific)
96
Q

Describe the action of glucagon in the control of nutrient metabolism

A
  • Counteracts decreased plasma glucose
  • Main target is liver
  • 2nd messenger system
  • Results in phosphorylation of key enzymes (same ones dephosphorylated by insulin)
  • Increases glycogenolysis
  • Inhibits glycogenesis
  • Stimulates gluconeogenesis
  • Blocks glycolysis
  • Activates hormone sensitive lipase (increasing catabolism of lipids)
  • Inhibits fatty acid synthesis
97
Q

What does AMPK stand for?

A

AMP activated protein kinase

98
Q

What is the role of AMP?

A

It is the energy sensor of the cell

99
Q

How does AMP carry out its role?

A
  • If energy is too low, AMP builds up and get activation of AMPK
  • Leads to glucose transport into cell
  • Glycolysis and fatty acid oxidation activated to generate ATP
  • Inhibits ATP-using reactions (anabolic reactions and production of macromolecules)
100
Q

Describe the role of AMPK in fatty acid synthesis

A
  • ATP builds up in cell
  • ACA builds up in mitochondria
  • Converted to citrate, citrate to cytoplasm
  • Build up of citrate in cytoplasm feeds forward, activates acetyl-CoA carboxylase, drives forward conversion of acetyl CoA to Malonyl CoA
  • Increased production of fat
  • AMP is product of fat synthesis
  • Build up of AMP leads to binding to acetyl CoA carboxylase and inhibits its action
  • Low ATP, AMPK activated, phosphorylates acetyl CoA carboxylase, inhibits it and turns off fat production
101
Q

What is the effect of product build up in a pathway?

A

Feedback inhibition (negative feedback)

102
Q

What is the effect of substrate build up in a pathway?

A

Feedforward activation

103
Q

How can enzymes be modified?

A
  • Covalent modification
  • Dephosphorylation or phosphorylation of hydroxyl groupds of specific serine or threonine residues
  • Alters conformation and activity of enzyme
  • Can activate or deactivate enzymes (will do the opposites of each other)
104
Q

How is enzyme modification controlled?

A
  • Usually extracellularly by hormones

- Sometimes intracellularly by AMPK

105
Q

Describe the hormonal control of hormone sensitive lipase

A
  • HSL cleaves fatty acids from glycerol moiety
  • Dephosphorylates is inactivated version (insulin action on protein phosphatase which dephosphorylates HSL_
  • No breakdown of TAGs
  • Glucagon, epinephrine and glucocorticoids stimulate breakdown of TAGs in adipose tissue to release FFAs and promote glucose sparing (hormones activate protein kinase, phosphorylates HSL)
106
Q

Describe the hormonal control of fructose-2,6-bisphosphate in the liver

A
  • F-2,6-BP produced by phospho-fructokinase 2 (PFK2)
  • PFK2 has 2 activities
  • Dephosphorylated produces F-2,6-BP
  • Phosphorylated at serine residues actively destroys F-2,6-BP
  • Insulin: dephosphorylates PFK2, lots of F-2,6-BP produced, PFK1 activated and glycolysis occurs
  • Glucagon: via cAMP dependent protein kinase phosphorylates PFK2, F-2,6-BP destroyed, PFK1 inhibited, gluconeogenesis activated, glycolysis inhibited
107
Q

Describe PFK1 vs F-1,6-BP in the liver and muscle

A
  • Compartmentation (don’t want same effect in all tissues)
  • Glucagon acts mainly on liver, epinephrine mainly at muscle
  • Both through cAMP
  • In liver, cAMP-activated-protein-kinase turns on gluconeogenesis, inhibits glycolysis
  • This would be negative in muscle cels
  • Use isoenzymes
  • PFK2 in muscle does not have serine, cannot be phosphorylated, F-2,6-BP always present so glycolysis will continue and gluconeogenesis will not
108
Q

Explain the role of fructose-2,6-bisphosphate in glycolysis and gluconeogenesis

A
  • PFK1 vs F-1,6-BP in liver
  • Presence of F-2,6-BP stimulates PFK1 and stimulates glycolysis
  • Absence of F-2,6-BP, ATP inhibits PFK1 so no glycolysis (promotes gluconeogenesis)
  • Glycolysis or gluconeogenesis in cell directly related to level of F-2,6-BP in
109
Q

By what mechanisms are enzymes modified to control metabolism?

A
  • Enzyme levels
  • ALlosteric modification
  • Covalent modification
110
Q

How can compartmentation be acheived?

A
  • Tissue differences (e.g. liver/skeletal muscle)
  • Intracellular (cytosol/mitochondria)
  • Chemical (NAD+ in lipolysis and NADP+ in lipogenesis)
111
Q

What is the function of compartmentation?

A
  • Further potential control of metabolism

- Substrate level within compartment is major control stratefy for some pathways

112
Q

Describe intracellular compartmentation using the cytosol and mitochondria as an example

A
  • TCA/oxidative phosphorylation controlled by NAD+ and ADP levels within mitochondria
  • Fate of metabolites dictated by transport across mitochondrial membrane
  • Normally low NAD+, so low rate of TCA, low levels of NADH produced
  • Low NADH => less pushed into oxidative phosphorylation
  • Low ADP slows oxidative phosphorylation, need ADP to produce ATP thorugh ATPsynthase at end of OP
  • FFAs in cytosol esterified to TAG, transported out of cell or into mitchondrial matrix to produce acetyl-CoA through beta-oxidation
  • Uses carnitine mediated transpor system adn direction of transport dictates what is produced
113
Q

Give an example of compartmentation between tissues

A
  • Liver and muscle
  • Different versions of PFK2 mean that where epinephrine leads to the phosphorylation of PFK2 in the liver to turn off glycolysis, this is not possible in the muscle due to a lack of serine residues
114
Q

Describe the insulin dependent glucose uptake by cells in the post-absorptive state

A
  • Glucagon dominant
  • GLUT4 not active
  • Les uptake of glucose into muscle and adipose
  • Some uptake in insulin independent transporter systems in liver, brain adn erythrocytes
  • In liver, glucokinase is main enzyme for glucose uptake
  • In other tissue, hexokinase
  • Convert glucose to G6P (cannot escape cell in this form)
  • In PA state want less glucose uptake in liver, more gluconeogenesis
  • Therefore glucokinase has lower affinity for glucose than hexokinase
115
Q

Describe the insulin dependent glucose uptake by cells in the absorptive state

A
  • High uptake of glucose into muscles and adipose tissue
  • Moderate to liver and brain
    High glucokinase, high efficiency, low affinity no problem
  • Prevents brain adn erythrocytes accumulating glucose as these cannot store it
  • Prevented by action of G6P
  • High levels of G6P inhibit hexokinase, prevent glucose trapping
  • Less effective against glucokinase
116
Q

Explain the hormonal control in high blood glucose

A
  • Insulin dominant
  • Dephosphorylation of glycogen synthase = production of glycogen
  • Through PFK2 insulin inhibits F-1,6-BP activity => stimulation of PFK1
  • Leads to direct dephosporylation (activation) of pyruvate kinase
  • Prolonged insulin leads to lowered PEPCK
117
Q

Explain the hormonal control in fatty acid synthesis and degradation in high glucose

A
  • Insulin dominant
  • Inhibits hormone sensitive lipase
  • No FFAs liberated
  • No accumulation of FFAs in liver cells
  • No allosteric inhibition of acetyl-CoA carboxylase from fatty acyl-CoA
  • Glucose plentiful, high glycolysis and TCA, high ATP, no AMP inhibition allosterically or via AMPK activation
  • Overall get stimulation of fat production when blood glucose high
118
Q

Explain hormonal control in low blood glucose

A
  • Glucagon => phosphorylation of glycogen synthase and glycogen phosphorylase
  • Activates glycogen phosphorylase (breakdown to produce glucose)
  • Inhibits production of more glycogen
  • Through PFK2 activity through F-2,6-BP, stimulates gluconeogenesis
  • F-1,6-Bp inhibits glycolysis by inhibiting PFK1
  • Phosphorylation of pyruvate kinase, inhibiting glycolytic enzyme
  • Prolongs glucagon signalling, increases PEPCK in liver cells
  • Low blood glucose in liver => stimulation of breakdown of glycogen and gluconeogenesis inhibiting opposite pathways
  • Leads to more G6P in liver, converted to glucose by glucose-6-phosphatase
  • Glucose secreted into blood and distributed to cells that need it
119
Q

Explain the role of substrate/product concentrations in the coordination of fatty acid synthesis/degradation

A
  • Acetyl-CoA carboxylase most important in fat synthesis control
  • In degradation most important is hormone sensitive lipase and carnitine acyltransferase 1
  • High blood glucose, accumulation of pyruvate in liver due to increased glycolysis
  • More Acetyl CoA produced from pyruvate
  • Accumulates in mitochondria and is converted to citrate and then transported to cytoplasm
  • High citrate in cytoplasm allosterically activates acetyl-CoA carboxylase to stimulate increased fat production
120
Q

Describe the role of substrate/product conentration in the liver during high blood glucose

A
  • Glucose enters liver cells, made into G6P, little inhibition of glucokinase by G6P, accumulation of G6P, end up with accumulation of G1P, G6P adn F6P in cell due to equilibrium
  • Various allosteric controls
  • G6P binds to glycogen phosphorylase slowing breakdown of glycogen
  • F6P binds to PFK1, activates it, more glycolysis, more F-1,6-BP, activates pyruvate kinase, drive glycolysos allosterically and inhibits glycogen breakdown
121
Q

Describe the allosteric coontrol of fatty acid synthesis/degradation in low blood glucose

A
  • Glucagon
  • In adipose stimulates HSL, lots of FFAs liberated from TAG
  • Into plasma, taken up by range of cell types
  • leads to accumulation of fatty acyl-CoA in different cells
  • Fatty acyl-CoA allosterically inhibits acetyl-CoA carboxylase needed in fat production
  • Shut down fat synthesis, stimulate fat break down
  • Phosphorylates acetyl-CoA carboxylase = inhibition
  • Low AMP inhibits this further allosterically and via AMPK
122
Q

List some metabolic diseases caused by a negative energy balance

A
  • Bovine ketosis
  • Bovine fatty liver disease
  • Bovine pregnancy toxemia
  • Ovine pregnancy toxemia (twin lamb disease)
  • Equine hyperlipaemia and hepatic lipidosis
  • Feline idiopathic hepatic lipidosis
123
Q

Describe metabolic pathways present in a lactating cow with no negative energy balance

A
  • Enough nutrients to meet requirements
  • Absorbing AAs and VFAs
  • Some AAs bypass liver to mammary glands to produce milk proteins
  • In liver gluconeogenesis from AAs adn proprionate to produce glucose
  • Glucose to brain (and mammary glands to produce lactose) via circulation or be made into glycogen if there is an excess of glucose in liver
  • Some breakdown of TAG to fatty acids in adipose, to mammary glands for milk production
124
Q

Describe the metabolic pathways in a lactating cow with a negative energy balance

A
  • Glucagon high
  • Acetate and butyrate taken in (ketogenic), energy substrate for most tissues
  • AAs and proprionate to liver for gluconeogenesis
  • Some AAs to mammanry glands
  • Glycogenolysis, glucose in plasma
  • Protein catabolism to AAs, to liver for gluconeogenesis or mammary glands
  • Lipolysis, FFAs used for energy
  • Glycerol used in liver for gluconeogenesis
  • Long time -Ve balance: FFAs build up, taken in by liver
  • Used for energy, if build up then build up of acetyl CoA in liver, ketone body production, secreted
  • Ketone bodies not used in brain, build up of ketone bodies = ketosis
  • Continued TAG build up in liver = fatty liver disease
125
Q

What could increased the chance of ketosis?

A
  • If over conditions (fat)
  • More fatty acids that can be liberated
  • Build up of FFAs and ketone bodies
126
Q

What are the clinical signs of ketosis?

A
  • Diminished appetite
  • Decreased milk production
  • Weight loss
  • Dry faeces
  • Moderate depression
  • Decreased rumen motility
  • Odour of acetone (pear drops) on breath and milk
127
Q

What are the subtypes of ketosis?

A
  • Primary
  • Secondary
  • Nervous
128
Q

Describe primary ketosis

A
  • Not enough feed to meet energy requirements
  • Occurs at peak lactation (4-6 weeks)
  • Body reserves all used up
129
Q

Describe secondary ketosis

A
  • Secondary to other diseases
  • Lots of diseases
  • Retained placenta, hypocalcaemia, displaced abomasum, mastitis, metritis,, traumatic calving
130
Q

Describe nervous ketosis

A
  • Clinical signs likely due to hypoglycaemia

- Staggering, blindness, circling,proprioceptive deficits, head pressing, excessive grooming, pica, hyperesthesia

131
Q

How can ketosis be diagnosed?

A
  • Clinical signs vague and non-specific
  • Acetone smell may be present
  • Elevated ketone levels in urine adn milk (dipsticks, tablets, Rother’s agent milk test)
  • Blood sampling (most reliable)
132
Q

Why is a negative energy balance around calving/early lactation common?

A
  • Energy demands greatly increased
  • At same time, energy intake will be decreased
  • Leads to overall negative energy balance
133
Q

Briefly describe hepatic lipidosis

A
  • When liver overwhelmed with FFAs
  • Over produces ketone bodies
  • Takes up large amounts of FFAs and tries to store these as TAGs
  • Liver function impaired
  • Interrelated with but not as common as ketosis
134
Q

Describe the epidemiology of ketosis

A
  • Mortality low
  • Morbidity variable
  • Lactation low risk of clincial ketosis
  • If there are a few cases of subclinical ketosis, likely to have large number of sub-clinical
  • Can be realted to many diseases
135
Q

List some of the risk factors that increase the chance of ketosis

A
  • First 6 weeks after calving
  • Increased incidence with parity
  • High producers
  • Fat cows (greater decrease in feed intake as less drive to eat due to insuline resistance, more fat to mobilise)
  • Concurrent disease
  • Dairy cows
136
Q

Describe the treatment of ketosis

A
  • May spontaneously disappear
  • Intravenous glucose (ideally continuous infusion)
  • Propylene glycol
  • Glucocorticoids
137
Q

Explain why propylene glycol is used in the treatment of ketosis

A
  • Decreases ratio of acetate to proprionate
  • Part of propylene glycol metabolised to proprionate in rumen
  • Increased proprionate speeds up TCA cycle, other VFAs oxidised properly and less ketone bodies produced
  • Remaining propylene glycol absorbed directly from rumen without alteration and enters gluconeogeneis via pyruvate
138
Q

Discuss the use of glucocorticoids in the treatment of ketosis

A
  • Short term solution to manage extreme symptoms
  • Descreases tissue uptake of glucose
  • Reduces milk production
  • Increases appetite
  • Stimulates protein breakdown to AAs supplying more gluconeogenetic precursors
  • Increased lipolysis and thereby exacerbates ketosis and possibly fatty liver
139
Q

Describe the prevention and control of ketosis

A
  • Reduce stress, no sudden changes
  • Prevent cows being too fat in dry period (ideally BCS 3)
  • Introduce lactation diet in last 14 days of dry period (adapt rumen flora)
  • TLC for transition cows (more trough space)
  • Monitor
140
Q

Define homeostasis

A

Regulation of internal environment within a set range. The aim is to maintain a stable, constant condition

141
Q

Define enantiostasis

A

The ability of an organism to maintain physiological function in response to an unstable environment e.g. estuarine organisms exhibit enantiostasis in order to survive constantly changing salt concentrations.

142
Q

Define homeorhesis

A

Dynamic change which retusn a system to its original trajectory as opposed to returning to aparticular state.

143
Q

Define a genetic adaptation

A

Traits that have been selected for by natural selection.

  • Underlying genetic basis for adaptive trait did not arise as a consequence of the environment.
  • The genetic variant pre-existed and was subsequently selected becuase it provided a seective advantage in a given environment
144
Q

Define a physiological adaptation

A
  • A system wide response made by an organism that is necessary in order to maintain the constancy of the internal environment
  • Despite fluctuating external environment
145
Q

Define a compensatory adaptation

A
  • Physiological adaptation to compensate for environmental (external) change
  • E.g. more bronw fat so if very cold weaher dont have to use shivering thermogenesis
146
Q

Define an exploitative adaptation

A
  • Genetic/physiological/behavioural adaptation to exploit a new ecological niche
  • E.g. sex of offspring of crocodiles dependent on temperature of eggs
147
Q

Define accomodation

A
  • A temporary change to cope with changing environmental conditions (individual)
148
Q

Define adaptation

A

A permanent change in genetic make up of a population

149
Q

Describe hibernation in bears

A
  • Not really hibernation - torpor
  • Female bears can gesate, give birth adn lactate in torpor
  • Body fat supplies substrate for metabolism
  • Ketosis does not occur
  • Metabolic water is sufficient to maintain normal hydration
  • If non-reproductie then no loss of lean mass
  • Ketone bodies are produced but ketosis does not occur
  • Hardly any protein used for energy
  • protein turnover continues, but less urea formed
150
Q

Explain why very little protein is used for energy in hibernating bears

A
  • Loss of protein = loss of function
  • Avoids build upp of ammonia/urea
  • No net build up in plasma of total AAs, total protein, urea, uric acid
  • Therefore metabolic-end products are recycled back into lean mass
  • AAs only used for protein sunthesis and synthesis of other compounds
151
Q

Explain the role of amino acids in small hibernations

A
  • No loss of lean body mass
  • AAs enter protein synthetic pathways at increased rate
  • Produces reciprocal decreases in entry to urea cycle
  • Needed in gluconeogenesis
152
Q

Describe the urea cycle in hibernation

A
  • Reduced AA entry into UC
  • Urea formed hydrolysed and nitrogen reelased combined with glycerol to form AAs
  • AA degradation leads to production of NH4+
  • NH4+ into urea and excreted
  • More efficient to recycle
  • Into gut, bacteria hydrolyse, free N into AAs
153
Q

Compare hibernation in small and large mammals

A
  • Small mammals true hibernators (mass specific metabolic rate high, would be expensive to maintain in cold winter with scarce food)
  • Larger enter torpor (absence or suspension of motive power, activity or feeling)
  • Both have hypometabolism
  • Reduce body temp to reduce metabolic rate
  • Reduced fuel usage (accumulation of fat prior to, insulation and fuel store)
  • Decreased heart rate
  • Cerebral hypometabolism
154
Q

Outline how diving mammals are adapted to an aquatic environment

A
  • Adapted metabolism to acute hypoxia and nutrient deficit
  • Similar to foetal adaptations to intrauterine life
  • Limiting factor is oxygen
  • Increased lung size, large blood volume, higher Hb content, high muscle Hb
  • Use anaerobic processes
  • Decreased metabolic rate
  • Some have aquati respiraiton
  • Diving lung volume small to prevent the bends
  • Lots of oxygen stored in blood
  • Increased PCV
  • Increased blood cell volume
  • Hypometabolism
  • Redistribution of blood
  • Post dive increase ventilation
155
Q

Describe tissue specific adaptation of the heart of diving mammals

A
  • Large stores of glycogen
  • Hypoxia-tolerating enzyme systems
  • No evidence of ischaemia dilation of the left ventricle
156
Q

Describe tissue specific adaptation of the brain of diving mammals

A
  • Decreased temperature
  • Decreased Na+/K+ ATPase activity
  • Decreased voltage-gated sodium channel activity
157
Q

Describe the coordiantion of hypometabolism of divign mammals

A
  • Rapid response

- Suggests neural origin

158
Q

Describe th circulatory responses of diving mammals

A
  • Primary effects on circulation are bradycardia, diminuation of cardiac output, peripheral vasoconstriction
  • Primary response modified by reflex hyperpnea simultaneously indued in the spontaneously breathing animal
  • Secondary response to chemoreceptor stimulation, when breathing is allowed, is characterised by increased cardiac output and heart rate and changes in peripheral flow pattern

GI (31 decks)

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