Systems to Cells

Question 1

How many ppl in Uk hae diabetes?

Answer 1

4.7 million ppl have diabetes currently

Question 2

What is the 1st law of thermodynamics?

Answer 2

The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another.

Question 3

Diagram of Energy balance

Answer 3

Question 4

what is energy needed for?

Answer 4

• Cell growth and division
• Building new molecules and replacing old ones
• Movement (muscle contraction is ATP-dependant)
• Breathing, thinking

Question 5

What is our energy currency?

Answer 5

ATP is an energy currency formed by substrate-level and oxidative phosphorylation.

Question 6

Memorise ATP energy release diagram

Answer 6

Question 7

List facts about ATP NOW!

Answer 7

Uhh okay,

• The average human body has 100-250g of ATP
• Daily requirement of ATP is 50-70kg. You make more than your body weight of ATP everyday
• ATP is re-formed from ADP around 1000x a day.
• It is essential for life
• We need to keep replenishing this energy.

Question 8

what does the complete oxidation og glucose give?

Answer 8

ΔG° = -2840kJ/mol

Question 9

How is glucose broken down?

Answer 9

Broken down to pyruvate by glycolysis. Under aerobic conditions the pyruvate is converted to Acetyl-CoA and this enters the Krebs Cycle

Under anaerobic conditions, it’s converted into lactate.

can be efficiently stored as starch/glycogen

Question 10

Is glucose a key energy source?

Answer 10

Glucose is a key energy source.

The brain and nerves have an absolute requirement for glucose for enrgy. So do erythrocytes, tstes and kidney medulla.

Question 11

What is Whole blood glucose homeostasis?

Answer 11

Whole Body Glucose Homeostasis

• Blood sugar levels kept the same by a range of homeostatic mechanisms
• When in excess, glucose is stored as glycogen in liver and muscle cells or triglytcerides in adipose tissue.
• When levels are low, these tissues become net exporters of glucose/fatty acids

Question 12

What is Hyperglycaemia vs hypoglycaemia?

Answer 12

Hyperglycaemia is high blood glucose while hypoglycaemia is low blood sugar

Question 13

How are metabolic pathways involved in glucose metabolism organised?

Answer 13

They’re organised at multiple levels

• System - Human, migrating bird, hibernating brown bear
• Tissue/Organ - Brain, liver, gut
• Cellular - Liver and muscle respond differenlty to high/low glucose
• Subcellular - mitochondria, lipid droplet, cystol
• Genetic - Cells/tissues can change patterns of gene expression in response to nutritional status.

Question 14

How is glucose level controlled?

Answer 14

Blood glucose is controlled by complex mechanisms

Insulin - rel;eased from pancreatic beta cells when blood glucose inreases

Glucagon - released from pancreatic alpha cells when blood glucose falls.

Question 15

What does insulin do?

Answer 15

Increasses glucose uptake into fat and muscle cells

Increases uptake of glucose by liver and increases glycogen synthesis in the liver

Inhibits gluconeogenesis in liver

Signals the fed state and the removal of glucose from the blood

Question 16

What is gluconeogeneis?

Answer 16

Gluconeogenesis is a metabolic oathway that results in the generation of glucose from non-carb carbon substrates such as lactate or amino acids.

Question 17

What does Glucagon do?

Answer 17

• Stimulates gluconeogenesis
• Inhibits glycogen synthesis in the liver
• Triggers lipid breakdown
• Glucagon signals the release of glucose into the blood.

Question 18

Homeostasis of Blood Glucose diagram

Answer 18

Question 19

Where is glycogen mainly stored?

Answer 19

Glycogen is mainly stored in liver and muscle cells

Question 20

Memorise metabolic pathway of glucose to glycogen

Answer 20

Question 21

How does Insulin integrate into the glycogenesis pathway.

Answer 21

Insulin turns ‘on’ glycogen synthase and switches off glycogen phosphorylase. Glucagon does the opposite.

Both reactions are energetically favourable - they happen spontaneously

• Allows regulation of enzymes as neeeded
• Allows system to quickly react to changes in blood sugar levels

Question 22

How do mammals regulate enzymes?

Answer 22

• Changing the rate of biosynthesis/degradation of an enzyme levels by (takes time though)
• Changing the activity of the enzyme (the most common way)
• changing the location of the enzyme

Question 23

What is reversible covalent modification and how does it regulate key mammalian enzymes?

Answer 23

Commonly used way to quickly regulate enzyme activity in response to a signal (e.g. hormones) is used to use reversible covalent modification. Although this can be include many forms (prenylation, ubiquitation, glycosylation etc.) But most common is phosphorylation

Question 24

What does phosphorylation involve?

Answer 24

Phosphorylation involves the covalent addition of a phosphate, transferred from ATP by the action of a class of enzymes called kinases.

This is reversible, and the removal of the phosphate is catalysed by a group of enzymes called phosphatases.

Question 25

What does phosphorylation do?

Answer 25

Phosphorylation may turn an enzyme on/off,

It alters the 3D conformation of the target protein because of the high charge density of the protein-bound phosphoryl group, -2 at physiological pH (quite a large charge). These often make salt bridges with nearby Arginine and Lysine residues which are positively charged

Question 26

What are the different tyoes of kinases?

Answer 26

Two main classes of kinase: those that phosphorylate Tyrosine residues and those that phosphorylate Serine/Thereonine residues

Question 27

Memorise the 20 amino acids and their side chains

Answer 27

Question 28

How does glucagon cause glycogen degradation?

Answer 28

Glucagon increases glycogen degradation by activating Protein Kinase A which goes on to phosphorylate Glycogen synthase a (active form) into Glycogen synthase b (inactive form).

Simultaneously, Glycogen phosphorylase b (inactive form) is phosphorylated into Glycogen phosphorylate a (active form).

Conversion of both Glycogen synthase a and Glycogen phosphorylase b into their alternate forms uses one molecule of ATP

• ATP + H2O = ADP + Pi + H⁺ + ENERGY

Question 29

How does insulin increase glycogen production?

Answer 29

Insulin increases glycogen synthesis by activating Protein phosphotase-1 which goes on to dephosphorylate Glycogen synthase b (inactive form) into Glycogen synthase a (active form).

Simultaneously, Glycogen phosphorylase a (active form) is phosphorylated into Glycogen phosphorylate b (inactive form).

Conversion of both Glycogen synthase b and Glycogen phosphorylase a into their alternate forms uses a molecule of water and produces a Phosphate ion.

ATP + H2O = ADP + Pi + H+ + ENERGY

Question 30

What is gluconeogenesis?

Answer 30

Gluconeogenesis is the metabolic process by which organisms produce sugars (namely glucose) for catabolic reactions from non-carbohydrate precursors. Glucose is the only energy source used by the brain (with the exception of ketone bodies during times of fasting), testes, erythrocytes, and kidney medulla.

Question 31

What are the general themes of metabolic pathways?

Answer 31

• Biosynthetic and degradative pathways are almost always distinct. this means that both pathways can be thermodynamically favourable.
• The rates of metabolic pathways are governed by the activities of key enzymes (and not by mass action).
  
  • Glycogen formation/breakdown is a perfect example of this
• Specific hormones induce soecific events in cells/tissues.
  
  • Allosteric modulation of enzyme activity. Reversible covalent modification is a well-used example.
• In cases where the direction of a metabolic pathway has to be reversed, the pathway is controlled at an irreversible step.
  
  • Where glycogen needs to be reversed back into Glucose 1-P for example. Glycogen synthase cannot revert glycogen back into Glucose 1-P, Glycogen phospphorylase has to instead.

Question 32

What is a rate determining step/

Answer 32

In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate-determining step or rate-limiting step

Question 33

What happens to the energy landscape of a reaction when an enzyme gets involved?

Answer 33

Question 34

What’s another way of changing enzyme activity besides phosphorylation?

Answer 34

• Enzymes can be controlled bu allosteric interactions with other molecules
• Often some of the other molecules and intermediates in the downstream pathway
• Molecules which potentiate one direction (glycolysis) are often negative regulators of the other direction (gluconeogenesis)

Allosteric regulation can be used to superimpose other control pathways on top of a metabolic pathway

Question 35

What are 2 similarities between Glucagon and Insulin?

Answer 35

Both are polypeptide hormones released from the pancreas.

Both bind to specific receptors enriched in muscle, liver and fat cells but have opposing actions.

Question 36

What symptoms can diabetes exhibit?

Answer 36

• Macular degeneration - leading cause of non-traumatic blindness
• Kidney failure - diabetes is the leading cause of kidney failure
• Stroke
• Fatty liver - fatal if untreated
• Atherosclerosis
• Foot ulcers

Question 37

What are the causes of diabetes?

Answer 37

Exercise and diet component, not enough exercise and overeating

And genetics of course

Question 38

What is the underlying nature of diabetes?

Answer 38

There are two types:

Type 2:

• 90% of diabetics have type 2
• Insulin resistance
• Beta cell dysfunction

Type 1:

• 10% of diabetics have type 1
• Characterised by beta cell destruction either an auto-immune response or idiopathic - we don’t know the cause.

Question 39

How likely are different races to develop diabetes?

Answer 39

Half of all South Asian, Black African and caribbean people in the UK will develop type 2 diabetes by the age of 80. For Europeans the figure is 20%.

South Asian men are typically 5 years younger on diagnosis and have increased risk of all complications compared to other ethnic groups

Question 40

How is insulin synthesised?

Answer 40

Insulin is produced by transcription and translation of the Human Insulin Gene.

1. Mature mRNA encodes a complex polypeptide called prepoinsulin
2. mRNA translated into protein inserted into lumen of the endoplasmic reticulum.
3. This preproinsulin undergoes proteolytic sequential cleavage.

Question 41

Diagram of how Preproinsulin is formed into Insulin

Answer 41

Question 42

Describe the genetic steps of insulin production

Answer 42

1. Ribosome sees mRNA and starts to read along
2. Sees signal sequence - tells ribosomes to pause. Transalational pause signal.
3. Pause point is just as signal sequence is just poking out of ribosome exit tunnel (insulin polypeptide in red)
4. Signal sequence is recognised by SRP (signal recognition peptide. It grabs the signal sequence very tightly.
5. SRP receptor passes ribosome to complex of proteins called Sec61 translocon complex
6. Imagine these to be a gateway into the lumen ER
7. Want to get insulin into the Endoplasmic reticulum lumen.
8. At that point, translation is carried on
9. Insulin peptide is co-translationally passed through membrane and into cystol of ER.

Question 43

Why is the preproinsulin passed into the lumen of the endoplasmic reticulum?

Answer 43

The prepreoinsulin is passed into the lumen is because the peptide needs to have disulphide bonds added to it to make it stable before it’s released into the blood

Question 44

What’s another reason the preproinsulin needs to be processed in the ER lumen?

Answer 44

Disulfide bonds play an important role in the folding and stability of some proteins, usually proteins secreted to the extracellular medium. Since most cellular compartments are reducing environments in general, disulphide bonds are unstable in the cystol as it is a reductive environment.

The peptide will only be folded and oxidised in the ER lumen. This is also where the S=S bonds are formed which are crucial for the folding of the molecule into its biologically active form.

Question 45

What happens to preproinsulin when it’s in the ER lumen?

Answer 45

Once inside, the preproinsulin can fold and the disulphide bonds can form. It is still not biologically active yet, it’s now proinsulin.

Question 47

When does proinsulin become biologically active?

Answer 47

Proinsulin only becomes active when the connecting peptide is removed.

Question 48

How are proteins processed in the cell?

Answer 48

Question 49

How do macromolecules move between different organelles?

Answer 49

Question 50

What enzyme removes the pre-sequence from preproinsulin?

Answer 50

The pre-sequence is cleaved by signal peptidase

Question 51

What are the steps of insulin production?

Answer 51

1. Preproinsulin is translated on ribosomes and is inserted across the ER membrane.
2. Inside the ER, the processing begins, the pre-sequence is cleaved by signal peptidase. Disulphide bond A and B chains which stabilises the 3D structure.
3. Proinsulun then traffics to golgi via vesicular transport.
4. Proinsulin traffics through the Golgi, before being packaged into secretory granules.
5. Proinsulin is cleaved into insulin and C-peptide by enzymes called pro hormone convertase PC1/3 and PC2. Carboxypeptidase E removes basic residues at the C-terminus.
6. High levels of insulin are packaged into the secretory vesicles by making crystalline complex with Zn²⁺ ions selectively pumped into the secretory vesicles.
7. The net result = Very high insulin concentrations in specialised packages.
8. In response to a suitable signal, secretory granules fuse with the plasma membrane and release their contents (insulin and C-peptide).

Question 53

What is regukated exocytosis?

Answer 53

Regulated exocytosis is a process in which the membranes of cytoplasmic organelles fuse with the plasma membrane in response to stimulation.

Question 54

Give a brief overview on how glucose triggers insulin release

Answer 54

Increased extracellular glucose is detected in the blood.

Glucose moves from outside of the beta cell to inside using the glucose transporter GLUT2.

Once inside the cell, it undergoes glycolysis. Phosphates get added to produce ATP.

By doing this the ratio of ATP:ADP is increased.

The ATP sensitive postassium channel detects this change and allows the movement of potassium out of the cell. It’s inhibited by ATP causing it to close, depolarising the beta cell.

This is sensed by voltage gated calcium channel causing it to open.

The No. of extracellular Ca²⁺ is 2-3 orders of magnitude higher than the intracellular Ca²⁺ and the the ions diffuse into the cell down the diffusion gradient.

Leads to increase in intraxcellular calcium ions causing the fusing of the vesicles to membrane, thus the release of insulin.

Question 55

What is vital to the mechanism of regulated exocytosis of insulin?

Answer 55

That extracellular glucose is accurately sensed.

• Vital to this mexhanism is the ability of the cell to sense the extracellular conc. of glucose and adjust intracellular metabolism in direct proportion.
• The cell needs to proportionally gauge a response to the increase in blood sugar levels.
• A key facet of this mechanism is the low-affinity glucose transporter expressed in the beta cell plasma membrane - GLUT2. It is not that effective in its role.

Question 56

Why would getting glucose across the plasma membrane on its own (without a glucose transporter) be difficult?

…

But how would it be done???

Answer 56

it would be difficult because glucose is a polar molecule so it would no tbe able to interact with the plasma membrane enough to be able to pass through its non-polar hydrophobic layer.

However, the way in which the glucose would be transported in this case, the glucose would need to be dehydrated (as it’s usually surrounded by water). The molecule becomes rehydrated within the cell.

This requires a lot more energy than with a transporter.

Question 57

What are the two gradients substances can diffuse down?

Answer 57

The two gradients a substance can diffuse down are either the chemical graident (a region of high conc. to low conc.) or the elctrical gradient (a charged particle would move from a high potential difference to a lower potential difference).

Question 58

What are glucose trasnporters AKA

Answer 58

Facilitative diffusion transporters

Question 59

What is the alternating conformation model for membrane transport?

Answer 59

The principle of which is that the protein switches conformations to present the substrate binding site to alternate sides of the membrane without ever fully opening a channel from one side to the other.

Question 60

Name some differecnes between a Transporter and a Channel NOW!

Answer 60

GLUT transporters have a turnover of about 17,000-20,000 glucose molecules per min.

Whereas channels open and allow flow of many ions quickly. This may be as high as 10⁶ ions per second.

Structures are different to reflect this.

There are 12 different GLUTs in the human genome. Even more channels

Question 61

What is a membrane channel?

Answer 61

Membrane channels are a family of biological membrane proteins which allow the passive movement of ions (ion channels), water (aquaporins) or other solutes to passively pass through the membrane down their electrochemical gradient.

Question 62

Michaelis-Menton cureve for a catalysed enzyme reaction. Which can double as a velocity/substrate curve for a trasnport protein like a glucose transporter.

…

Yes, this is a wordy question card

…

No, I will not ammend it.

Answer 62

Question 63

What does the KM in a Michaelis-Menten curve show you?

Answer 63

The KM in a Michaelis-Menton curve shows the concentration of extracellular glucose at which we see half of the maximum velocity of glucose entry into a cell.

The KM is a measure of affinity, how well this protein can trasnport glucose.

Question 64

The higher the KM of a trasnporter the…

Answer 64

The higher the KM of a transporter the lower the affinity for its substrate. As it takes a longer time for the trasnporter to reach its ¹/₂V_max.

Question 65

Using your knowledge of linearity and the Michaelis-menten curve, why would we want GLUT2 to be a low affinity transporter?

Answer 65

We would want GLUT2 to be a low affinity transporter because this means that the velocity of glucose entry per concentration of glucose is inherently more proportional than if it were a high affinity transporter with a low KM.

This allows the glucose transporter to respond to increases in extracellular glucose proportionally.

Question 66

How is glucose metabolised in beta cells?

Answer 66

In most cells ATP is relatively invariant, not for Beta cells though.

Glucose metabolism in beta cells is inefficient.

As a result, beta cells respond to changes in extracellular glucose concentrations by rapidly changing ATP:ADP ratio.

Glucose phosphorylation in beta cells use the low affinity (high KM) enzyme glucokinase. This enzyme is not as saturated as physiological glucose concentrations. So the phosphorylation rate is directly proportional to intracellular glucose concentrations.

Glycolytic rate therefore depepnds on glucose entry/blood glucose concentrations.

Question 67

What is the michaelis-menten equation?

Answer 67

Question 68

Micahelis-menten graph displaying the hexokinase and glucokinase.

Answer 68

Question 69

Michaelis-menten graph of GLUT2 and GLUT3 and GLUT4

Answer 69

Question 70

What are the 3 main targets of insulin?

Answer 70

The 3 main targets of insulin are muscle cells, liver cells and adipose tissue which express an inuslin receptor.

Question 71

What is the receptor that insuin binds to?

And how does it work?

Answer 71

The insulin receptor is an alpha₂Beta₂ polypeptide, held together by disulphide bonds.

Has two alpha subunits and two beta subunits.

Insulin binds to the alpha 2 subunits inducing a conformational change in alpha subunits.

This transmits a signal to the Beta subunits activating an intrinsic tyrosinase kinase within the cytosolic domain.

The signal has crossed the membrane at this point.

The binding is specific - only insulin can bind to the receptor.

Question 72

What are the steps inviolved in insulin signalling

Answer 72

Insulin Signalling?

1. Activation of the receptor occurs only upon insulin binding. Imparts specificity of signal to the tissues that express the receptor.
2. Amplification - a single molecule of insulin activates a kinase that cxan phosphorylate many target molecules.
3. Tyrosine kinase receptor phosphorylates specific Tyr resiudes within the receptor - auto-phosphorylation
4. These p-Tyr residues recruit signalling molecules (IRS-1 shown here) tit he receptor which are then themselves phosphorylated.
5. This forms a signalling complex.

Question 73

What happens at phosphorylated receptors?

Answer 73

Phospho-tyrosine residues are recognised by specific proteins

• SH2 domains
• PTB domains

Recruits specific set of target proteins to the activated receptor to form an active signalling complex.

Many of these targets are then phsophorylated by the activated receptors.

Question 74

What haooens in insulin signalling after the insulin receptor auto-phosphorylates/

Answer 74

When insulin receptor auto-phosphorylates:

Phosphorylated residues become docking sites for other signalling molecules

Insulin receptor recruits a big adaptor protein:

• IRS-1
• (Insulin receptor substrate 1)
• IRS-1 is phosphorylated

Selectively recruit molecules

Signalling comlex

Question 75

What does the autophosphorylateion of specific tyrosine residues do?

Answer 75

• The autophosphorylation of specific tyrosine residues function to recruit SH2 domain containing proteins to the receptor.
• These are then activated.
• Signal propagated.
• Insulin receptors selectively recruit different SH2-domain containing proteins.

Question 76

Considering SH2 domains and PTB domains are found on many other proteins how is specificity achieved?

Answer 76

All SH2 domains bind phsophotyosine.

All SH2 domains have a pocket into which the P-tyr residue fits.

But not all SH2 domains bind all P-Tyr residues; there is specificty dictated by the surrounding sequence in the target (receptor) polypeptide.

Question 77

Detailed diagram on specificty of SH2

Answer 77

• Pocket contains positively charged residues at the bottom to interact with negative phosphate
• If tyrosine isn’t phosphotylated: affinity for pocket is gone
• Second binding pocket:
  
  • E.g. hydrophobic pocket which recognises isoleucine.
  • Confers specificity

Question 78

Diagram of Signalling Complex

Answer 78

Question 79

What is an example of a key downstream target of a Ser/Thr kinase known as?

Answer 79

A key downstream target ia thw activation of a Ser/Thr kinase known as Akt.

Amplification at all steps

Insulind change the phosphorylation status of 100s of different proteins.

cAkt is an key enzyme which is activsted by insulin.

All signalling pathways amplify.

Question 80

What is the key action of insulin?

Answer 80

The key action of insulin is to increase glucose transport into muscle and fat cells.

Question 81

The effect of insulin needs to be independenet of new protein synthesis and requires ATP, how is this achieved?

Answer 81

Uses a specialised form of gluvpse transporter, GLUT4, expressed only in fat and muscle.

GLUT4 is capable of moving to the cell surface as a response to insulin binding to its receptor.

This si triggered by cAkt.

Regulated exocytosis.

Question 82

How is GLUT4 stored in the absence of insulin?

Answer 82

In the absence of insulin GLUT4 is inside the cells in specialised vesicles - GSVs

GLUT4 is the only GLUT isoform that exhibits this trafficking.

Glucose transport is low in the absence of insulin.

Question 83

Diagram of GLUT4 in GSV

Answer 83

Question 84

Insulin has cell specific effects, how is this achieved?

Answer 84

In adipose cells cAkt activates GLUT4 trafficking to the cell surface.

In liver/muscle cells cAkt phosphorylates and activates phosphatase - promoting glycogen storage.

Akt us a crucial molecule in insulin signalling. Different tissues express different Akt ‘effectors’.

Question 85

Insulin can regulate gene expression, describe how.

Answer 85

Insulin can upregulate and down regulate gene expression.

Upregulated genes are transcribed relatively quickly. However, they have a low sensitivity to insulin and require a higher dose.

Downregulated genes are transcribed slowly but have a high sensitivity to insulin sp a low dose is required.

Question 86

In detail, how does insulin modulate gene expression?

Answer 86

Insulin signals through IRS1 to a variety of transcription factors that control gene expression.

Insulin activates the LxR transcription factor (one of many) in liver and fat.

In fat, this drives increased expression of SREBP1 transcription factor.

SREBP1 controls (among others) fatty acid synthase, AcetylcoA carboxylase the lipid metabolism genes turned on.

Question 87

Describe the lipogenesis pathway.

Answer 87

• Acetyl Co-A (under the right conditions) enters the lipogenesis pathway.
• It then gets converted to triglycerides.

The genes for the enzymes involved in lipogenesis are turned on:

• Acetyl CoA carboxylase
• Fatty Acid Synthase
• SCD1

LxR turns on SREBP1 which turns on the lipid metabolism genes.

This gives co-ordinate regulation of lipogenesis as multiple enzymes upregulated by a single transcription factor.

Question 88

What is a promoter region in a gene?

Answer 88

A promoter is a sequence of DNA to which proteins bind that initiate transcription of a single RNA from the DNA downstream of it. This RNA may encode a protein, or can have a function in and of itself, such as tRNA, mRNA, or rRNA.

Question 89

What are the two types of transcription factors?

Answer 89

Activators which help general transcription factors and RNA polymerase assemble.

This promotes and increases transcription of target gene.

There are also repressors which blocks the genral transcription factors and RNA polymerase.

Question 90

What can phosphorylation do?

Answer 90

It can change the stability of a molecule and its location

Question 91

What can phosphorylated TFs do that non phosphorylated TFs do?

Answer 91

Phosphorylated TFs can travel through nuclear pore while non phosphorylated TFs cannot.

Question 92

What is a common feature of signalling cascades?

Answer 92

Amplification is a common feature of signalling cascades

Question 93

Glucagon transduction pathway

Answer 93

Question 94

What is the role of the hormone leptin?

Answer 94

Regulate feeding; it signals to the brain (hypothalamus) to control food intake.

Question 95

What have studies in the early 2000s revealed about adipose tissue?

Answer 95

• Adipose cells aree more than inert energy store, they secrete diffferent polypeptide hormones.
• These hormones act on other tissues to produce biological effects - adipocytokines; adipokines.
• Some of these molecukles are constitutively secreted.
• Most well-characterised is Leptin, but there are many others and the inter-relationships between these molecules and their targets is complex and as yet poorly understood.
• Likely to be the key to understanding obesity/diabetes

Question 96

What is a paradox of adipose tissue’s production of leptin and obesity?

What does this suggest?

And what are the implications of this paradox?

Answer 96

• Most people who are obese have increased fat depot and increased circulating leptin levels. So why are they obese?
• This suggests that obesity is asssociated with an inability of leptin to counteract feeding this could be due to leptin resistance?
• Suggests that key therapies for obesity treatment may need to target complex regulatory networks in the brain, rather than metabolic tissues like liver or fat.

Question 97

What are Endocrine cells?

Answer 97

Endocrine cells are responsible for producing and relkeasing hormone molecules into the bloodstream. Endocirne cells are typically grouped together in organs referred to as endocrine glands.

Question 98

What are Neuroendocrine cells?

Answer 98

Neuroendocrine cells are cells that recieve neuronal input (neurotransmitters released by nerve cells or neurosecretory cells) and, as a consequence of this input, release message molecules (hormones) to the blood.

Question 99

What are Enteroendocrine cells?

Answer 99

Enteroendocrine cells form the basis of the lagest endocrine system in the body. They secrete multiple regulatory molecules which control physiological and hoomeostatic functions, particularly postprandial secretion and motility.

Question 100

Diagram of Lamina propria

Answer 100

Question 101

What is GLP-1 secretion dependent on?

Answer 101

GLP-1 secretion by ileal L cells (entero-endocrine cells) is dependent on the presence of nutrients in the lumen of the small intestine. It is released in response to major nutrients such as carbs and lipids.

Question 102

Once in circulation, what is the half-life of GLP-1?

Answer 102

Once in circulation, it has a half life of only 2 minutes as it is rapidly degraded by an enzyme called dipeptidyl peptidase-4.

Question 103

What is the role of GLP-1?

Answer 103

GLP-1 is a major regulator of whole body glucose homeostasis by acting both centrally (brain) and peripherally (pancreas, adipocytes, liver etc.) to regulate metabolic profiles/fucntion of the tissues.

It also slows gastric emptying and thus can indirectly regulate appeptite.

Question 104

What is GLP-1?

What does it act on?

Why is this important?

Answer 104

Glucagon-like peptide-1 (GLP-1) is a potentn anti-hypoglycaemic hormone.

GLP-1 acts (via receptors) on the beta cell to enhance the release of insulin in response to a rise in blood glucose levels (and supresses glucagon secretion from alpha cells).

This is important as unregulated release of insulin when plasma glucose is in the normal range can cause hypoglycaemia - a dangerous fall in blood glucose. This does not happen because of GLP-1.

Question 105

How does GLP-1 act within normal blood glucose ranges?

Answer 105

When blood glucose is in the normal acting range, there is no GLP-1, and the beta cells no longer secrete insulin; this is important when blood glucose is in thr normal fasting range as it will prevent catastrophic hypoglycaemic episodes.

When you eat a meal, carbohydrates in gut cause a release of GLP-1. ‘Switches the pancreas on’.

Question 106

What is GLP-1 an example of?

Answer 106

GLP-1 is an example of homrones called incretins.

Question 107

What are some of GLP-1’s physiological actions?

Answer 107

GLP-1 has numerous physiological actions, including: potentation of glucose-stimulated insulin secretion, enhancement of beta cell growth and survival, and inhibition of glucagon release, gastric emptying and food intake.

These anti-diabetic effects of GLP-1 have led to intense interest in the use of this peptide, and other incretins, for the treatment of patients with T2D.

Question 108

What are Incretins?

Answer 108

Incretins are a group of metabolic hormones that promote a reduction in blood glucose. They achieve this by several mechanisms:

• They augment glucose-stimulated insulin release from beta cells.
• They surpress glucagon release.
• They regulate the absoprtion of nutrinets from the gut.

Question 109

What are some of the main incretins?

Answer 109

Main incretins are Glucagon-like peptide-1 (GLP-1) and gastric inhibitory peptide (GIP). Both are rapidly inactivated by the peptidase dipeptidyl peptidase-4 (DPP-4) and have very short half-life in the curculation.

Because of this, their therapeutic use is limited. Longer-lasting analogues are in clinical use as insulinotropic agents. Another approach is to inhibit the enzyme that activates GLP-1 and GIP, DPP-4.

Question 110

What are some interesting facts about platypus and GLP-1?

Answer 110

• Platypuses lack a functional stomach.
• They instead have high circulating levels of GLP-1 because its biology is rather unusual.
• There are conflicting functions of GLP-1 in the platypus: in the gut as a regulator of blood glucose, and in venom to fend off other platypus males during mating season.

Question 111

Why is platypus GLP-1 desired as a type 2 diabetes?

Answer 111

While the human version of GLP-1 degrades quickly the platypus version appears to have evolved to be long-lasting which makes it desirable for the tratment of T2D.

Question 112

What is unique about dolphins and insulin response?

Answer 112

• Dolphins and humans have co-evolved metabolic processes. reflecting brain size, - high demands for readily available glucose - and red blood cells that can transport glucose.
• Studies of populations of dolphins show that animals fasted overnight exhibit blood chemistry akin to T2D.
• When dolphins have a dextrose meal, they had an insulin deficient response - sustained post-prandial high blood glucose with no insulin. Akin to T1D.
• Dolphins can switch between T2D and T1D easily.

Question 113

How is hibernation beneficial?

Answer 113

• Hibernating animals store massive amounts of fat each autumn.
• These serve as the main source of metabolic fuel over winter.
• Fats are rich and have the advantage of generating metabolic waster as they are catabolised.
• Fat deposition occurs on an annual basis.
• This is correlated to the length of daylight.
• Cycles of natural obesity and insulin resistance.

Question 114

How do animals know when to begin hibernation process?

Answer 114

• Annual cycle of body weight fluctuation is intrinsic rhythm entrained by light.
• Depends on melatonin secretion from the pineal gland.
• Independent of temperature or food availability.
• Liver changes metabolic profile from carbohydrate to fat based metabolism.

Question 115

What is the involvement of the gut in migration?

Answer 115

• Phenotypic flexibility in the digestive system of migrating birds.
  
  • Digestive organs (gizzard, liver, smalll intestine) increase in size and capacity to convert more food into energy e.g. pre-migration
  • Atrophy when demands fall e.g. during migration.
• Many other adaptive changes exhibited:
  
  • Increased muscle size and capacity for oxidative metabolism
  • Liver metabolic profile chnages
• There is rapid, precise regulation of physiologicaal systems that is often completely reversible.
• Coordinate regulation of metabolic processes like change in diet from seeds to nectar to accumalate rapid fat deposits.

Question 116

Diagram of sources of ATP during exercise and how long do they last?

Answer 116

Stored ATP lasts about a second.

Creatine phosphate lasts for around 4 seconds,

The rest of the exercise will be using the fermentaation of glucose.

Question 117

What is GWAS?

Answer 117

Genome Wide Association Studies.

How genes effect the development of a trait/phenotype

Question 118

How to find a gene that affects a trait

Answer 118

All you need, e.g. for cystic fibrosis:

• Trait segregating in (large) families
• Behaves as a Mendelian, single gene trait
• Genetic differences across the genome

Question 119

What is a Complex trait/Quantative trait

Answer 119

Most traits are not inherited in a simple mendelian fashion.

The risk of developing a disease like autism or diabetes do not display a clear pattern of mendelian inheritnce.

Quantative traits are traits that can be quantified such as height/IQ.

These traits can have multiple genes involved or there could even be no genetic basis at all!

Question 120

What is The mendelian inheritance pattern?

Answer 120

The manner by which genes and traits are passed from parents to their children. The modes of Mendelian inheritance are autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Also known as classical or simple genetics.

Question 121

How can heritability be used to identify of genes are responsible for a trait?

Answer 121

If the trait is heritable

It would affect the risk of developing the trait

Trait is not pre-determined

A role for the environment

Could be a small number of genes or many genes which cause the trait.

• Small effect size (each make a small contribution to risk)

Question 122

How would you deterrmine heritability?

Answer 122

By utilising family history?

if a trait runs in a family it may well be tyhe case that the trait is caused by genetics and the heritability of the certain genes, however, it could be due to the shared environment.

Question 123

What sort of study provides insight into heritability of traits?

Answer 123

twin studies provide insight into heritabiloity of traits

identical twins

100% shared genes and shared environment

If one twin has multiple sclerosis for example, the odds of the other one having it is 20%

In non identical twins

50% sahared genes and shared environment.

If one twin has MS the odds of the other one having it is 5%

To calculate the heritability from the above

(Monozygiotic twins percentage - Dizygotic twins percentage) x 2 = 30

Question 124

What would 30% heritability of a trait mean? And what does it not mean?

Answer 124

30% heritability means:

For population:

30% of risk is attributable to genetics

70% of risk is non-genetic

30% heritability does NOT mean:

Each individual:

30% of trhe trait is genetic

70% of the trait is due to environment.

Question 125

What is the main source of genetic variation between humans?

Answer 125

• 99.9% of the human genome is conserved betyween ppl
• All variation is from 0.1%
• SNPs are the main source of common allele differences

Question 126

How would one identify oci contributing to complex traits?

Answer 126

• Cannot use LINKAGE mapping
  
  • No clear patterns, too few ppl
• Switch in strategy is needed
  
  • Study populations rather than families

Pre-disposing alleles should exist on limited number of haplotypes and we shouldbe ble to detect them without genotyping them i.e. if only nearby SNPs are genotyped.

Can find them even if multiple genes contrubute. As each gene contributes a small amount of risk we are esssentially looking for small effects so need huge numbers.

In essence, this is what GWAS (Genome Wide Association Studies) are.

Question 127

How is genetics important in drug discovery?

Answer 127

• New medicines: Drug targets that are backed by genetic info are approximately twice as likely to become a successful medicine
• Better medicines: Understanding how a medicine is working can help us avoid unwanted side-effects and enhance the probability the medicine will be effective.

Question 128

What is needed in a GWAS?

Answer 128

GWAS analyse small effect sizes, therefore one needs huge numbers of people.

The participants need to be separated based on the trait looking to be analysed.

Take care to match the groups for age, sex and ethnicity.

Question 129

What is Genotyping?

Answer 129

Genotyping is the technology that detects small genetic differences that can lead to major changes in phenotype, including both physical differences that make us unique and pathological changes underlying disease. It has a vast range of uses across basic scientific research, medicine, and agriculture.

Question 130

Population in GWAS must meet the associations presented in the

Hardy Weinberg equilibrium. What are these 5 assumptions of thew HW equilibrium?

Answer 130

1. Mating is random
2. No mutations are arising
3. No gene flow
4. No natural selection
5. Population size is infinitely large

Question 131

What plots are used to display GWAS?

Answer 131

MAnhattan plots are used to display GWAS.

Question 132

What are the Hallmarks of diabetes?

Answer 132

Question 133

Graph detailing the age of diagnosis of diabetes

Answer 133

Question 134

What is monogeneiuc diabetes?

Answer 134

Maturity Onset Diabetes of the Young (MODY) is an inherited form of diabetes mellitus. It is caused by a change in one of eleven genes. Up to 5% of all diabetes cases may be due to MODY. Just like other people with diabetes, people with MODY have trouble regulating their blood sugar levels.

Question 135

Is MODY diabetes more like T1D or T2D diabetes?

Answer 135

This disorder is more like type 1 diabetes than type 2, although it can be confused with either type. In type 1, the pancreas cannot make and release enough insulin. People with type 2 diabetes, on the other hand, usually make enough insulin, but their bodies cannot respond to it effectively (known as insulin resistance). Type 2 diabetes is usually associated with being overweight, but that is not true of type 1 diabetes or MODY. However, obesity does matter. An obese person with a MODY gene mutation may develop symptoms of diabetes sooner than someone of normal weight.

Question 136

What does MODY diabetes stand for?

Answer 136

maturity onset diabetes of the young. There are multiple forms (11) which are usually mistaken for T2D or T1D.

Question 137

Name 4 types of monogenic subtypes of diabetes.

Answer 137

Question 138

What is the most common subtype of MODY diabetes?

Answer 138

• HNF1A
• Transcription factor
• Drives expression of genes in endoderm, including GLUT1 and GLUT2
• Strong loss of functrion mutations (recessive)
• Treatment: low dose sulfonylurea

Question 139

What is the 2nd most common subtype of MODY diabetes?

Answer 139

• GCK= Glucokinase
• catalyses first step in glycolysis
• “traps” glucose in cells
• important for rapid uptake and metabolism of glucose
• STRONG loss of function mutations (recessive)
• Often asymptomatic requiring no treatment

Question 140

Give a brief overview of Type 1 Diabetes.

Answer 140

• ~10% of all diabetes cases
• ~0.5% of UK population
• Autoimmune condition: destruction of pancreatic beta-cells
• Presentation of insulin as ‘self-antigen’
• No strong sex bias
• Onset usually between 5 and 20 yrs old; used to be fatal rapidly
• Modern therapy – recomb. insulin injection – more or less normal lifespan now; but ….
• Some familial clustering - 20% familial cases, 80% sporadic – most familial cases are sib-pairs, not large families hints at complex inheritance

Question 141

What is an “Odds ratio”?

Answer 141

A measure of INCREASED RISK of having condition conferred by GENOTYPE at each locus/gene

Question 142

How can Genotyping assist with diagnosing diabetes?

Answer 142

Clinical signs are well established

•but only evident after development of disease

Genotyping could identify;

• High-risk subset of children with decent confidence
• 2-5 years BEFORE development of disease
• Improved clinical management
• Stratification: distinguish T1D from other forms of diabetes e.g. MODY

Question 143

Give a brief overview on T2D

Answer 143

• T2D diabetes is a complex disorder
  
  • Multifactorial
  • Polygenic
• Biggest known risk factor is obesity/ high adiposity
  
  • Causal pathway involves ectopic liver fat
• T2D genes could also affect
  
  • Behaviour- food intake
  • Metabolism, Glycaemic traits
  • Fat accumulation/ BMI (adiposity genes → T2D genes)
  • Beta-cell responses and survival

Question 144

What is the strongest risk variant for type 2

Answer 144

The strongest risk variant is TCF7L2

• Transcription factor 7-like 2
• The gene has 4 common spliced variants; when variant SNP rs7903146 is present in two copies (CT/TT risk genotypes)
• Wnt (wingless/integrated) signalling pathway
  
  • Pleiotropic effects across tissues and systems
• Has been identified across multiple ethnic groups

Question 145

Where do the majority of T2D risk variants lie?

Answer 145

The majority of T2D risk variants lie in non-coding regions.

Question 146

Can SNPs in non-coding regions affect gene expression?

Answer 146

Gene promoter or enhancer regions

Alter gene expression

(Up or Down)

Question 147

How do we calculate an Odds Ratio?

Answer 147

• Let us calculate the increased RISK: the ODDS RATIO: consider TCF7L2
• 100 people carry the risk allele vs 100 who don’t

T2D Cases Healthy Total

Carriers 7 93 100

No Risk 5 95 100

Odds ratio = ratio of affected/Unaffected

Odds for carrier of risk allele getting T2D = 7/93 = 0.075

Odds for non-carrier getting T2D = 5/95 = 0.053

Therefore the odds ratio = 0.075/0.053 = 1.4

Question 148

How does aerobic exerceise effect diabetes?

Answer 148

• Moderate intensity - unlike healthy individuals, where hepatic glucose production is matched by peripheral glucose uptake; diabetics use more than is produced (reducing blood glucose)
  
  • Lasts for between 24 - 72 hrs
• High intensity can cause hyperglycemia due to catecholamine induced glycogen production (lasting 1 - 2 hrs)
  • May be sensitive to duration of intensity?

Question 149

How does Resistance Exercise?

• Little, if no, data available on single bout of resistance exercise in diabetes.
  
  • Benefits shown in pre-diabetes (blood glucose elevated during fasting)
  • Lower blood glucose (up to 24 hours)
  • Responds to both volume and intensity

Question 150

What changed from the former diet/exercise recommendations to the current one?

Answer 150

• Moderate aerobic activity (2-3 times per week) - metabolic impact for up to 72 hrs
• Combined with resistance exercise - metabolic impact for up to 24 hrs - increased muscle mass/strength for enhanced insulin independent affect
• Compliance? - time, access to facilities, boring…. - novel strategies for HIIT

Question 151

At rest, what is the preferred substrate for ATP generation?

And why should a diabetic look to avoid certain foods based on this info?

Answer 151

At rest the preferred substrate for ATP generation are FFAs (Free Fatty Acids).

So by default the high carbohydrate content foods increase blood glucose and should be avoided.

The amount of carbohydrates is the primary determinant of blood glucose.

Question 152

The amount of carbohydrates is the primary determinant of blood glucose but what else should be considered?

Answer 152

• The type of carbohydrates (amylose vs amylopectin)
• Preperation (cooking time or method)
• Processed foodstuff vs fresh
  
  • trans fatty acids in energy dense food

Question 153

What are the two components of starch?

And how are these componenets broken down?

Answer 153

Starch is made up of two components, amylose and amylopectin.

Amylose is a straight chain of glucose units connected by alpha 1-4 bonds. These bonds are broken by the enzymes maltase and amylase

Amylopectin contains the same chains, but also has “branch points” created by alpha 1-6 bonds, these bonds are broken by the enzyme isomaltase

Question 154

What is steric hinderance?

Answer 154

Steric hindrance at a given atom in a molecule is the congestion caused by the physical presence of the surrounding ligands, which may slow down or prevent reactions at the atom.

Question 155

Which of the two starch components is digested more easily?

Answer 155

• Theoretically, amylose should be easier to digest because it does not require isomaltase, and does not have the steric hindrance caused by the branch points
• However, amylose can form a very compact physical structure, which inhibits digestion
• Therefore, amylopectin is actually digested better than amylose

Question 156

According to Macciochi what was the reason we evolved as humans?

Answer 156

“The whole reason that we evolved as humans is because we started cooking our food. When we only had a raw diet, we had to be eating constantly, because our bodies struggled to get the nutrients out of raw food.”

• Macciochi

There’s a substantial back catalogue of evidence suggesting that human evolution is directly linked to the use of fire.

Question 157

What was the benefit to our ancestors of cooking their food?

Answer 157

• When our ancestors cooked and processed their food, they made it easier to extract calories and fat (improving the gap between the amount of energy it took to digest their food and that extracted from it)
• Cooking also kills many of the potentially harmful bacteria that can grow in and on food, protecting from bouts of food poisoning

Question 158

What are the cons of cooking foods at a high temperatures for long periods of time?

Answer 158

Some health risks include: obesity, heart disease, high blood pressure and diabetes

Question 159

When is a low carb diet ineffective?

Answer 159

A low carbohydrate diet is ineffective without calorie restriction to maintain energy balance.