Basis of Molecular Disease

Question 1

Why are post translational modifications important and what are the three general types of modifications?

Answer 1

Post translational modifications (PTM) give extra functionality to proteins that the body can form beyond that possible by the 20 amino acids.

The three main types are:

Covalent - where new groups are introduced to the protein side chains,

Proteolytic - where enzymes cleave proteins to change functions

Allosteric - where weak interactions change the structure and function of proteins.

Question 2

Give the general way that covalent PTM are carried out and give the main 5 modifications.

Answer 2

A specific enzyme enacts the specific PTM and a different specific enzyme performs the reverse reaction. This can only be done on specific side chains for each PTM.

The main covalent PTMs are:

Phosphorylations

Glycosylations

Lipidations

Acetylations

Methylations

Question 3

Describe the action of phosphorylation including what groups it can occur on, the enzymes that cause the modification and where the group originates from.

Answer 3

Phosphorylation is where enzymes called kinases forms a phosphate ester group on an OH group. The OH group must be a free OH such as in serine, tyrosine and threonine.

The -PO₃ comes from ATP which becomes ADP after the phosphorylation. The reverse reaction can be done by an enzyme called phosphatases.

This PTM is key in metabolic processes, signalling pathways, transcription and movement.

Question 4

Describe the main effects of protein phosphorylation as a PTM and how they apply to the bodies processes.

Answer 4

The proteins function is changed from the phosphorylation as the OH group is transformed into a doubly negatively charged group. This can take part in hydrogen bonding as well as providing activation for enzymes.

The PTM is reversible so it can act as a temporary activator of active sites. This is key in signalling processes in complex ‘chain reactions’. Some enzymes may be able to act as both a kinase and a phosphatases.

Question 5

Describe the action of glycosylation, including what groups it can occur on and the enzymes that cause the modification.

Answer 5

Glycosylation is where some carbohydrates are attached to either an OH group (serine, tyrosine, threonine - an O-glycosylation) or an CONH₂ group (aspargine - a N-glycosylation).

Glycosylation of aspargine is the most common type and occurs on almost all human proteins.

Glycosyl groups are added with glycosyl transferases and removed with glycosyl hydrolases, but most groups are never removed.

Question 6

Describe the main roles of the PTM glycosylation and how it is involved in disease.

Answer 6

It maintains protein conformation, facilitates cell-cell contact, increases protein half-life and controls bodily functions (in competition with phosphorylation).

Glycosylation patterns are immunogenic which leads to difficulty in organ/blood transfusions but is a cancer target.

These groups can be the basis of binding/adhesion for both viruses and bacteria and can be found excessively in tumors.

Question 7

Describe the PTM of lipidation.

Answer 7

A fatty acid reacts via its -COOH group to the NH₂ N-terminus of a protein (unusually not NH₂ side chains) or thiol side chains. This is often to anchor a protein in the lipid bi-layer membrane.

Malfunctions can lead to problems in the lungs and in the eyes.

Question 8

Describe the PTM of methylation.

Answer 8

The covalent attachment of CH₃ groups to amine side chains of lysine and arginine. It is reversible and done by methylase and de-methylase enzymes.

A positive charge is retained by the nitrogen atom and it serves important roles in breaking hydrogen bonding.

Question 9

Describe the PTM of acetylation.

Answer 9

This is the covalent attachment of a -COCH₃ group on the free -NH₂ group of lysine (amide) or the -OH groups of threonine and serine (ester).

The acyl group is delivered via an acyl-co that is very reactive. The reaction is reversible and carried out by acetylases and de-acetylases.

The acetylation of lysine modulates many DNA-Protein interactions as it neutralises the positive charge it would usually carry, changing interactions. It is also in competition with phosphorylation and glycosylation on the -OH groups.

Question 10

Define the proteolytic modification of proteins as a PTM and describe the two types.

Answer 10

Proteolytic modification is where a specific peptide bond is hydrolysed in a protein. This may be to remove a part that was only required for biosynthesis, or to activate the protein, where the part removed was keeping it in its inactive form.

The two types are on non-enzymatic (such as insulin) and enzymatic proteins. Inactive forms of enzymes are called zymogens and allow enzymatic activity to be on demand, in specific locations.

Question 11

Describe allosteric modification of proteins.

Answer 11

Allosteric modifications are where the quaternary structure of proteins are modified by a non-covalently bound molecule by weak interactions. In some cases such as haemoglobin this can be a small molecule, 2,3-DPG, which alters its binding to O₂, or the ligand can be another protein to activate another protein.

Question 12

Describe where and how the human genetic material is stored. What is an allele?

Answer 12

In the nucleus via 22 autosome pairs of chromosomes and one pair of sex chromosomes and in the mitochondria with 10 copies of circular DNA. An allele is one of two copies of a gene, they perform the same function and are inherited one from each parent.

Question 13

Describe the classifications of different types of diseases.

Answer 13

1. Genetic diseases: Single gene defects in nucleus, mitochondrial mutations on the DNA not in the nucleus or chromosomal mutations affecting the number of chromosomes.
2. Infectious diseases including bacteria, viruses, etc.
3. Complex diseases from both genetic and environmental factors such as diabetes.
4. ‘Gray-Zone’ diseases such as protein misfolding.

Question 14

Generally describe single gene diseases.

Answer 14

They are diseases that are traceable to a single gene mutation. These are inherited and can be on any chromosome, autosomal or on the X-chromosome (where most mutations occur). They can also be classified by recessive or dominant.

Question 15

Briefly describe and give examples of each type of genetic disease.

Answer 15

Autosomal recessive – with both genes protein loses function such as cystic fibrosis.

Autosomal dominant – a single gene can cause proteins to take up a novel function such as Huntington disease.

Sex X chromosome – mostly recessive which affect men disproportionally as they only have a single X chromosome. Examples include haemophilia and fragile X syndrome.

Mitochondrial – mt-DNA encodes ATP production and mitochondrial ribosomes. All mitochondria are maternally inherited and mutations are typically serious. Common symptoms include diabetes, dementia, muscle weakness and other aging related symptoms (may be part of the aging process).

Chromosomal – wrong number of chromosomes, the origin of the additional chromosome affects the fatality. These can be sex (Turners) or autosome (Downs) additions.

Question 16

Describe the two types of immune responses when our bodies are attacked by pathogens.

Answer 16

The innate response is where premade phagocyte recognise the proteins hanging off the pathogen. It is cheap in energy and fast. The phagocyte then digests the pathogen.

The adaptive respone is where the immune system starts to analyse the fragments of the bacteria - the antigens. It is a slow process and uses a lot of energy, making you feel ill/tired. Antibodies are produced that bind to the pathogen and allow it to be digested by a phagocyte.

Question 17

Generally describe Pattern Recognition Receptors and the role they play in the immune system. Give examples of markers.

Answer 17

Pattern Recognition Receptors (PRR) are the part of the innate immune system which recognises the surface molecules of pathogens. These molecular patterns, or markers, include; lipopolysaccharide (LPS) in gram negative bateria, peptidoglycan mostly in gram positive bacteria, mannose, flagellin and pilin, bacterial nucleic acid and double stranded RNA.

Question 18

How can Pattern Recognition Receptors be futher classified, describing each group.

Answer 18

1. Endocytic - found on the surfaces of phagocytes to attach to pathogens such as mannose-binding lectin. The binding then activates an enzyme to produce toxins such as O₂^-, H₂O₂, O₂^•, ^•OH and NO which kill the pathogen.
2. Signalling - receptors that work via 1-9 TOLL receptors (TLRs) which bind to bacterial markers. This switches on genes to transcribe production of chemokines and cytokines which are the messengers of inflammation.

Question 19

Describe how inflammation defends against infection how it operates.

Answer 19

Inflammation isolates the bacteria from the bloodstream which is very dangerous for the body.

1. Some bacteria is destroyed by phagocyte starting the production of chemokines and cytokines.
2. Cytokines start inducing neutrophil receptors in the veins. Neutrophils are adhered to the vein by the infection and gaps form for neutrophils to pass through.
3. Chemokine receptors form a gradient to lead neutrophils to the site of infection.
4. Neutrohpils also help digest the bacteria (may burst oxidatively) and prolonged action will form pus.

Question 20

Generally describe the action of the adaptive immune system.

Answer 20

Bacterial proteins (antigens) are processed and by the phagocyte which is taken to form a complex with a T-cell in a “immune synapse”.

The T-cell produces killer T-cells to attack the infected cells (cell mediated response) and signals the B-cell to produce antibodies (Humoral response) which bind to the pathogens to allow for digestion by phagocytes.

Question 21

Describe the functions of the antibodies and generally how they bind to targets.

Answer 21

They block binding of pathogen toxins, block binding of viruses by binding to the viral surfaces, and block bacterial colonisation by binding to surface proteins.

The antibody binds to viral and bacterial antigens on the surface of pathogens.

Question 22

How do structural trends in innate and adaptive immune systems differ in signalling?

Answer 22

Innate is limited to around 100 pathogen markers and uses distinctive signalling molecules/pathways. It uses typical, well tested molecule structures.

Adaptive uses well tested, ‘Ig-fold/modules’ in different variations. Differences are achieved using mutations of the folds/modules such as dimerisations and other modifications with multiple check up points before the signal is passed on.

Question 23

Describe how microbes and pathogens are related and the ‘iceberg’ of infectious diseases.

Answer 23

Most microbes are never pathogenic, they coexist happily with our bodies. Some are potentially pathogenic but very few are always pathogenic.

The iceberg concent is that many infections cannot be indentified to a single pathogen. For poliomyelitis, 0.1-1% of infections are diagnosed as polio. For rubella this is 50% and rabies is 100% diagnosed.

Question 24

What are Koch’s postulates for identifiying a pathogen as a cause for a disease? What are the exemptions?

Answer 24

Koch’s Postulates:

• the pathogen must be present in every case of the disease
• the pathogen must be isolated from the diseased host and grown in a pure culture
• the disease must be reproduced when the culture is inoculated into a healthy host
• the pathogen must be recoverable from the experimentally infected host

The exemptions are that some microbes cannot be isolated to be grown in a culture (HIV, leprosy), they cannot be infected into a healthy human for hazard/ethical reasons (HIV), and some infections cannot be tested in an animal model (Hep B/C, yellow fever).

Question 25

Define and give examples of virulence factors.

Answer 25

Molecules produced by bacteria, viruses, etc. that assist in the colonisation, multiplication, invasion, evasion of immune system and transmition of the pathogen.

Factors include:

• Adhesins to stick to host cells
• Agressins to cause damage to cells (toxins) including enzymes to damage protiens, non-enzymes to form pores and superantigens to interfere with adaptive immune system.
• Endotoxins such as lipopolysacchiride which can cause the body to panic

Question 26

How do pathogens adhere to host cells?

Answer 26

Pathogens adhere via pili, molecular tips that stick to cells. They connect via a stem and a sticky tip. The tips may be switched to adhere to different cells and evade immune defenses.

Question 27

Describe how enzymes are used as agressin toxins by pathogens.

Answer 27

They can have 3 regions, one to fit a host cell receptor and form a vesicle, one to penetrate the cell from the vesicle and the last to enter the cell and cause damage.

These are often metalloproteases affecting the synapses and neurons.

Question 28

Describe the pore forming toxins and superantigens that pathogens produce as virulence factors.

Answer 28

The pore forming toxins are proteins that make holes in cell membranes. They are calcium dependant and destroy cells. They have a complex synthesis combining gene products.

Superantigens are also proteins that are highly toxic. They have a unique binding mode which allows them to bind to the T-cell receptor without a specific antigen present. This means they force the immune system into a huge response which undermines its specifity. The huge response causes many neutrophils to be summoned which can cause toxic shock and total organ faliure.

Question 29

Describe how cells are damaged by endotoxins from pathogens.

Answer 29

Endotoxins are lipopolysaccharides, not proteins, and induce production of cytokines and chemokines to activate the innate immune system like the superantigens.

Question 30

What is the definition and properties of viruses?

Answer 30

Viruses cannot be filtered from blood and are a-cellular; they can only ‘live’ in the hosts cells. They cannot make energy or proteins and must use the host metabolism to do it form them. They carry either RNA or DNA but not both, and may be enveloped or naked.

Viruses are unique as they must encode their DNA onto the hosts to reproduce, and as a consequence, they cannot truely be cured.

Viruses are defective particles that never work 100% correctly.

Question 31

Give the basic parts of a virus and compare the enveloped and naked viruses.

Answer 31

A virus contains; a genome (RNA or DNA), a capsid (protein coat) and sometimes an evelope (lipid membrane). It may also contain enzymes.

The naked capsid has a rigid structure that can withstand harsh conditions, resistant to drying, acid and detergents. It is released from cells by lysis where the cell bursts, spreading more virions but may be killed by antibodies.

Enveloped capsides have a lipid, glycoprotein membrane which means it is fragile and has to be wet. It is transmitted via fluids and modifies the cell membrane so that it fits the viruses needs and does not need to kill the cell to spread. This may need antibodies and killer cells to kill.

Question 32

What are the roles of viron proteins?

Answer 32

• Protect genome
• Attach to cell receptors
• Penetrate cell membrane
• Replicate genome (some viruses)
• Modify host cell (some viruses)

Question 33

Describe the different ways that viruses can contain their genome and how these are used in their reproduction.

Answer 33

Viruses have either DNA or RNA and they can both come in different forms. There are 4 ways of reproducing with different types using different methods:

• DNA can be single or double stranded and uses host proteins to form mRNA and be expressed
• (+)RNA is equivalent to mRNA and can be immediately translated
• (-)RNA has to be converted to (+)RNA via viral enzymes which acts as mRNA
• Some (+)RNA encorperates itself into host DNA which is then expressed by host

Question 34

Give the general life cycle of a virus and how this is different for enveloped and naked viruses.

Answer 34

General life cycle is: Adhesion, Penetration, Uncoating, Replication of genome, Maturation and release.

For naked virions the nucleic acid can either be injected into the cell or the whole virion can enter. The new virions are built and the cell eventually bursts.

For enveloped virions, the envelope membrane will fuse with the cell membrane and the capsid will enter and dissolve. The new capsids will be produced and released by budding, where some of the membrane is taken with each capsid to form new enveloped virions.

Question 35

How do disease-causing viruses cause damage to host cells?

Answer 35

They cause damage or kill the infected cell. The virus can persist and spread to many other cells. The cell can be transformed to become cancerous or tumourous.

Question 36

Give a general description of the influenza virus structure and outline its life cycle.

Answer 36

1. Adhesion: The virus cell adheres to the cells outer proteins with sialic acid.
2. Endocytosis: Where the cell enteres the cell in a capsule of the cell membrane.
3. Fusion and uncoating: The capsule breaks and the viron releases its genetic material into the cell.
4. Synthesis of viral proteins: The virus genetic material is transcribed (after various replication pathways) and viral proteins are formed. Genetic material is also replicated.
5. Assembly and release: New virus is made by budding the cell membrane and released once all components are present.

Question 37

Which age groups would be hit by a dangerous flu outbreak the most? How does this compare to a synthetic flu?

Answer 37

1. 1-4 years have no anti-bodies and would be severely hit.
2. 5-14 years have good immune systems so would tolerate infection better.
3. 15-35 years would feel higher impact as immune system becomes weaker (mid peak)
4. 36-64 years would have a lower impact as they have resistance to more types of flu.
5. 65+ years have weaker immune systems so would be increasingly worsely impacted.

Synthetic flus (or isolated populations) have no resistance so ages 14+ will be incerasingly affected as immune system strength is the only variable.

Question 38

Generally describe the HIV virus and how its life cycle is different to influenza.

Answer 38

HIV is enveloped with (+)RNA and can synthesis DNA with tis reverse transcriptase. The formed DNA is then integrated into the host DNA by an integrase.

The HIV virus integrates its DNA into the cellular DNA to act as a new gene which is expressed to reproduce the HIV virons. Reverse transcriptase is very error prone which leads to the rapid change of the virus structure.

Question 39

Generally describe how protein folding is favoured to occur correctly, and how this may go wrong.

Answer 39

The energy state of the protein can be described as a funnel, with the unfolded state at the top and the energy minimas at the bottom. The conformations will get lower in energy as they approach the minimas, including folding intermediates. Chaperones are present to make sure they reach the fully folded state.

Under cell stress, when charperones are blocked or not present, aggregation events can occur forming various inactive states, including amyloid fibrills which are the most stable state.

Question 40

Define an amyloid. Which secondary structure plays an important part in its formation and why?

Answer 40

An amyloid is an aggregated protein substance deposited in tissues with fibrous morphology. They are no longer soluble due to their misfolded character.

Beta sheets are the main cause of these structures as they are based on main chain interactions and side chains do not have to be optimised - they are just pointed out of the structure.

Question 41

Describe the three models for the formation of fibrils.

Answer 41

1. Refolding: Native protein must unfold then refold. The sequence of amino acids is not thought to matter and main chain interactions dictate the structure formed.
2. Native disorder: Certain proteins are poorly ordered in their native states. Without misfolding, the regions of low order form a cross-beta spine and come together to form a paralleled superplated beta-sheet.
3. Gain-of-interaction: Conformational change of a protein exposes a surface. This binds to another molecule to build up a fibril. Core stucture remains intact but function may be inhibited.

Question 42

Draw the four ways that protein aggregation can stack together.

Answer 42

Question 43

Generally define cancer.

Answer 43

Malfuction in growth mechanims of cells leads to immortality. Infiltration of cells into organs is metastasis which is very dangerous. Interference with normal organism function comes from this.

A tumour is a defined mass of abnormal tissue. Neoplasm is new autonomous growth. Cancer is generally a combination of a malignant (bad) tumor with neoplasm (tumor growth causing damage to body function).

Question 44

Generally describe the causes of cancer.

Answer 44

• Enviromental factors (80-90%) such as chemicals, drugs, radiation and viruses.
• Genetics
• Immunological defects
• Other effects such as aging, hormones, profession, pollution, sun, etc.

Question 45

Give the genetic differences between simple and complex diseases.

Answer 45

Simple: A mutation in genes cause a disease, this could be an inherited mutation or a random mutation. Often a single gene causes the disease and has a traceable inheritance (for genetic disorders).

Complex: Mutations show poor corralation to disease and their relationship are not clear cut. However the mutation may predispose to a disease. No clear pattern of inheritance but may cluster in families. This is likely a combination of environmental and genetic factors.

Question 46

Why is cancer so common? How are cell mutations containted?

Answer 46

Common cancers occur through progessive acquisition of common genetic defects (20-40). 1 in every 10 cell divisions have a mutation so over the course of a lifetime many errors accumulate.

The cell cycle has a control system composed of checkpoints for nutrient, division, mobility, etc. These factors are combined to control cell proliferation. The genes encoding checkpoints are called tumour supressors. Often mutations need to occur on both genes to cause mutations.

Question 47

Describe the action of BRCA 1/2 and how it predisposes certain cancers.

Answer 47

Cancer predepositions are located in the Zn-binding domains where cysteines are replaced with glycine which weaking ligand binding. This increases breast cancer lifetime by 20.

Question 48

Describe the two ways that mutation checkpoints can occur.

Answer 48

A transcription factor which causes gene expression binds preferentially to a protein. However mutation of proteins, such as phosporylation, can stop this binding.

The protein can be the transcription factor which is bound and inhibited by another molecule. Mutation can stop binding of inhibitor but still allow for expression as a transcription factor.

Question 49

What are the 6 basic hallmarks of cancer? How has this model been developed?

Answer 49

1. Avoiding apoptosis (cell death)
2. Self-sufficiency in growth signals
3. In sensitivity to anti-growth signals
4. Tissue invasion and metastasis
5. Limitless replication potential (normal cells die after 50 divisons)
6. Sustained angiogenesis

This model has been developed over 10 years to be more biologically precise and includes 10 factors.

Question 50

What are the main problems in anti-cancer drug design?

Answer 50

1. Side effects on healthy tissue
2. Cancer is rarely dependant on a single enzyme
3. Cancer cells are very genetically unstable
4. Many treatments will only inhibit growth of cells

Question 51

How are the adhesion and budding of influenza related? How can this be a target for medicines?

Answer 51

The virus has a haemaglutimine receptor which binds to the sialic acid from the human cells. When budding, the cell-sialic acid bond is cleaved by neuramidinase.

Drugs can mimic the sialic acid transition state to inhibit neuramidinase.

Question 52

Give the three types of hormone message and the three chemical types of hormone.

Answer 52

1. Endocrine - transfer through the blood stream
2. Paracrine - between nearby cells
3. Autocrine - within the same cell
4. Polypeptide - large hydrophillic molecules, e.g insulin
5. Amino acid derivatives - small molecules that can be hydrophilic, -phobic or both, e.g adrenaline
6. Steroids - small lipophilic molecules, e.g vitamin D

Question 53

Compare the differences between membrane receptors and nuclear receptors for the mode of action of hormones.

Answer 53

Membrane receptors are at the cell surface and interpret signals outside the cell into the cell. These signals are extremely fast and can send signals in minutes such as insulin.

Nuclear receptors require the messengers to enter the cell before they can be received. This means the signals are diffusion controlled at times and are much slower. Signals may take days, weeks or even months.

Question 54

Describe the mode of action of nuclear receptors when an external signal is sent.

Answer 54

The hormone diffuses into the cell and enters the nucleus. The nuclear receptor (NR) is held in an inactive complex to stop aggregation. The hormone acts as a ligand to the receptor and frees it from the HSP (binding protein).

The ligated NR then dimerises and interacts with co-regulators which then all bind to the nucleic acid and cause expression of the related gene.

Question 55

Why is it important to understand the structure of NRs before designing drugs to interact with them?

Answer 55

So that drug design can be rational and not random. To understand which drugs are agonists and which are antagonists and to understand their modes of action.

Question 56

How are NR domains organised?

Answer 56

The DNA binding region has an activation function regions on either side. AF2 where homone/ligands bind and AF1 whose function is not well understood.

Question 57

Briefly describe the estrogen receptor structure and how the structure of estrogen mimics affect the binding to this site.

Answer 57

The estrogen receptor (ER) is made up of many helicies with a deeply buried ligannd binding cavity.

Estrogen has a phenolic ring which is key to its binding known as a rigid region. There is a 17-OH on the opposite side of the molecule which has hydrogen bonding interactions. The area around the OH ring is the flexibel region and accomodates large extensions to the ligand core.

The length between the phenol and the 17-OH is important to avoid steric hinderence.

Question 58

What are the three major ER ligand classes?

Answer 58

1. Agonist - only small changes common such as additional methyl groups.
2. SERMs - mixed agonist/antagonist character, inhibit AF2 function as side chain is antagonistic, only inhibits AF2
3. SERDs - pure antagonist, has longer side chains (~60% longer than SERMs) and inhibits AF1 and AF2.

SER = selective estrogen receptor

M = modulators

D = downregulators

Question 59

Describe the differences between the α and β isoforms of the estrogen receptor.

Answer 59

Very similar ligand binding domains (56% similarity) but other potential differences. They have different genes so can be expressed in very different amounts depending on the conditions. Specifc are present at the ligand binding site (H3 and H6) meaning that the β-isoform has better binding.

ERα is expressed in more in mammary glands, uterus, metabolic and skeletal homeostasis.

ERβ is expressed more in the brain and in cell division.

Question 60

How can SERMs (selective estrogen receptor modulators) have specific effects in the different tissues?

Answer 60

Co-regulators (that bind to the ligated ER) can be repressors or activators and are expressed differently in different tissues. Therefore SERMs may act as a pure agonist or antagonist in some tissues.

Question 61

What two molecules control the amount of glucose in the blood? How do they work?

Answer 61

Insulin and glucagon (polymer of glucose). Insulin causes uptake of glucose into cells, the synthesis of fat, and production of glycogen.

Insulin has a large role on many aspects of the metabolism. Derangements of insulin can have widespread and devastating effects on the body.

Question 62

Describe the structure of insulin and how it is synthesised. Therefore how can the amount of insulin be detected?

Answer 62

Insulin is a small, 51 aa protein composed of two chains linked by disulfide bonds. The B chain has 30 aa and the A chain has 21 aa.

The biosynthesis of insulin is done by linking the A and B chains by a C domain which is then cleaved at multiple positive residues in the chain. This produces high quality insulin.

The concentration of the C-domain is a marker for the concentration of insulin being produced.

Question 63

How and where is insulin stored in the body?

Answer 63

Insulin is made and stored in the pancreas as crystals. Single insulin molecules form dimers, which join together to form hexamers. These hexamers then arrange into the crystal structure.

Question 64

Describe the process which releases insulin into the bloodstream.

Answer 64

Glucose is taken into the cells and ATP is produced by respiration. When there is an increase of the ATP:ADP ratio, the K⁺ ion channel closes. This causes a larger uptake of Ca²⁺ which induces synthesis and release of insulin.

Question 65

Describe the mode of action of insulin.

Answer 65

Insulin binds to the insulin receptor (IR) which is a tyrosine kinase that is located across cell membranes. Insulin binding outside the cell causes phosphorylation of the subunits inside the cell which activates them. This then causes a phosphorylation cascade which releases GLUT4 from a vesicle to the cell membrane. GLUT4 allows glucose to be transported into the cell.

Glycogen synthase is also activated by the cascade which stores the incoming glucose.

Question 66

Briefly describe diabetes and the problems it can cause.

Answer 66

Diabetes is characterised by hyperglycemia due to ineffective insulin signalling. The lack of insuliin results in high blood and urine glucose levels but intra-cellular starvation.

To gain energy, cells break down fats which produce ketones (ketosis). Accumulation of ketones lead to severe water loss and increase in blood viscosity. This also overloads the blood pH control. All of these effects result in a diabetic coma which is potentially fatal.

In the long term, lack of insulin will cause tissue damage due to oxygen superoxides forming.

Question 67

Describe the two types of diabetes.

Answer 67

Type 1 - Insulin dependant diabetes mellitus is where the β cells don’t produce enough insulin (< 3% are active). Type 1 is a auto-immune disease and may be due to viral infections.

Type 2 - Not insulin dependant diabetes mellitus is where insulin production is fine but resistance has developed. Even high insulin levels cannot push plasma glucose into fat. This means insulin is continuously produced. It is much more complex than type 1 and patients tend to be obese.

Question 68

Breifly outline three theories of the cause of type 2 diabetes.

Answer 68

1. Fatty acids phosphorylate the proteins at the start of the insulin receptor pathway meaning there is no recognition of insulin.
2. Fat cells release many biologically active molecules and proteins that contradict the action of insulin. These are called adipo (fat tissue) cytokines.
3. Genetic predisposition from mutation of at least 6 genes has been considered to be a cause of early onset diabetes.

Question 69

Describe the challenges when treating insulin and the potential solutions.

Answer 69

For diabetics injecting insulin, the problems arise between meals/injections and at night where hypoglycemia is most likely. An insulin medication with a long half-life in the body is optimal to stop these risks.

Long acting insulins have been developed with a fatty acid attachment to the B chain, making it more insoluble.

Fast acting insulins have been developed to provide fast relief after meals to shift insulin into monomeric forms by disruping dimer interactions.

Question 70

What are the challenges of full synthesis of insulin and what approach is made to semi-synthesise insulin?

Answer 70

Due to the disulfide bonds the yield of insulin is very low but the process is relatively fast (~1 hr).

Instead semi-synthesis is used where the end of porcine (pig insulin) is cleaved and modified using trypsin at pH 9 to cleave and at pH 7 to reattach the protected end chain which is deprotected to make human insulin.

Question 71

Briefly describe adipose tissue and how it can be harnessed to treat type 2 diabetes.

Answer 71

Adipose tissue is fat tissue and comes in two types - brown (smaller, lots of mitochondria and can produces lots of heat) and white (larger, fatty tissue).

There is a nuclear receptor to scavenge lipid metabolites. These can be stimulated by anti-diabetic drug (TZDs) which synthesize more adipose tissue. The new tissue accomodates fat from muscles, liver and the pancreas to make them insulin sensitive. However, losing fat is normally a better approach to reduce this fat.