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MELS301 > Proteins > Flashcards

Proteins Flashcards

1
Q

What is the primary protein structure?

A

A linear amino acid sequence

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2
Q

What is the secondary protein structure?

A

alpha helix, beta sheet or random coil

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3
Q

What is the tertiary protein structure?

A

A 3D shape governed by the different interactions in the secondary structure.

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4
Q

What is the quarternary structure?

A

Multiple proteins interacting with each other for example haemoglobin when the alpha and beta globins join together.

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5
Q

What is the function of ligands and prosthetic groups?

A

They stick on to proteins and add extra functional and structural properties for example the haem in haemoglobin.

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6
Q

What is the configuration most biologically relevant amino acids have?

A

The L configuration.

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7
Q

What is a zwitterion?

A

An amino acid which is dipolar having both a positive and negative charge.

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8
Q

What are the 4 main methods of measuring total protein in the lab?

A

Kjeldahls method
Direct photometry
Biuret method
Lowery method

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9
Q

What is the most common method to measure total protein that is used in the lab?

A

Biuret method

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10
Q

What is spectroscopy?

A

The study of how radiant electromagnetic energy and matter interact.

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11
Q

What is spectrometry?

A

The practical application of spectroscopy so that quantifiable results can be assessed.

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12
Q

What is spectrophotometry?

A

The measurement of the light spectra reflection and transmission properties of substances, as a function of wavelength.

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13
Q

What makes something appear a certain colour?

A

If it absorbs the complementary colour. For example if it absorbs blue you see orange.

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14
Q

What occurs in the kjeldahl method?

A

Protein nitrogen is converted to ammonium ion then measured by titration. There is a precipitation step to remove non-protein nitrogen such as urea and amino acids. This is used to make the reference material for the biuret method.

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15
Q

What occurs in direct photometry?

A

Absorption of UV light 200-225nm and 270-290nm depending on tryptophan and tyrosine content. This is best used on purified proteins so does not work well in complex samples such as urine or plasma.

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16
Q

What occurs in the biuret method?

A

In strong alkaline conditions copper ions form multivalent complexes with peptide bonds. Binding shifts the absorption wavelengths for Cu2+ causing a colour change from blue to purple.

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17
Q

What are the potential interferences of the biuret method?

A

Anything with absorbances around 540nm such as haemolysis, lipaemia and bilrubin.

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18
Q

How does haemolysis interfere with the biuret method?

A

Haemolysis releases haemoglobin which in turn reacts with the copper ions falsely elevating results.

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19
Q

What occurs in the Lowery method?

A

Phosphotungestic and phosphomolybdic acid are added to the sample plus alkaline copper solution which reduces the solution forming a blue colour.

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20
Q

What wavelength is the Lowery method measured at?

A

650-750nm

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21
Q

Why is the buffer important in electrophoresis?

A

It carries the current but it also controls the pH.

22
Q

What does the pH of electrophoresis determine?

A

The electrical charge on the solute, the ionisation of the solute, the electrode to which the solute migrates, the size of the ionic cloud around the molecules, the rate of migration, and the sharpness of the zones.

23
Q

What is capillary electrophoresis and how does it differ from gel electrophoresis?

A

It is electrophoresis which is performed in a capillary tube, automated, it requires smaller samples, it has an enhanced voltage capacity, enhanced separation, and therefore is faster.

24
Q

How does the serum electrophoresis create the graph visualisation?

A

The bands are visualised by a densitometer which has a light that shines through and a photodetector which measures the density of each band. A larger peak indicates a denser band.

25
Q

What is the most abundant protein in plasma?

A

Albumin

26
Q

What is the main function of albumin?

A

Maintaining osmotic pressure, keeping fluid in vessels instead of tissues. Transporter, it also has antioxidant activity and acts as a buffer.

27
Q

How is Albumin measured?

A

By dye binding BCP or BCG spectrophotometric methods.

28
Q

What is BCG?

A

Bromocresol green

29
Q

How does BCG and BCP dye binding work?

A

These are anionic dyes which bind to albumin which is an anionic protein that is enriched in Asp and Glu residues. Once they bind they create a green or purple coloured product which can be measured spectrophotometrically. Because other proteins have Asp and Glu residues specificity can be improved by measuring after 30 seconds.

30
Q

What occurs in hyperalbuminaemia?

A

Usually this does not have any clinical significance and is due to dehydration or tourniquet being left on for too long causing venoustasis.

31
Q

What causes hypoalbuminaemia?

A

Decreased production in cases of malnutrition or starvation or cirrhosis.
Increased loss in cases of nephrotic syndrome
Dilutional in pregnancy where plasma volume shifts.

32
Q

What is analbuminaemia?

A

No albumin at all

33
Q

What occurs in analbuminaemia?

A

There is up-regulation of other proteins to help maintain osmotic pressure so small problems with blood pressure but more of an issue with hyperlipidaemia which causes cardiovascular disease.

34
Q

What is bisalbuminaemia?

A

Where you have 2 albumins which are slightly different so two bands which are very close together. They are described as a fast albumin and slow albumin. Doesn’t really have any clinical implications.

35
Q

What is pre-albumin?

A

Thyroxine binding protein which transports thyroxine hormone, it complexes with retinol binding protein. Sensitive marker of nutritional status but not really relevant clinically.

36
Q

What is alpha 1 anti-trypsin?

A

A protease inhibitor which binds and inactivates trypsin. It is synthesised in the liver.

37
Q

What does alpha 1 anti-trypsin deficiency cause?

A

Emphysema in the lungs and cirrhosis of the liver.

38
Q

How is alpha 1 anti-trypsin measured?

A

Electrophoresis as a screening test to find deficiency, immunoturbidimetry and immunonephlometry.

39
Q

What is alpha 1 fetoprotein?

A

The principal fetal protein, it is used for screening for fetal abnormalities such as neural tube defects. Also elevated in some tumours so can be a useful tumour marker.

40
Q

What is acid alpha 1 acid glycoprotein (orosomucoid)?

A

An acute phase protein, synthesised in the liver. It is a carrier of basic and neutrally charged lipophilic compounds.

41
Q

What is alpha 2 macroglobulin?

A

A protease inhibitor, it inhibits plasmin and kallikrein so is antifibrinolytic and also inhibits thrombin. Because it is large it is not usually seen in the urine may be a good indication of if someone has impaired renal function.

42
Q

What is alpha 2 haptoglobin?

A

It binds to free haemoglobin and preserves it. Used to look at haemolytic disease as if there is haemolysis it all binds to free haemoglobin and is taken up by macrophages causing levels to be decreased or absent.

43
Q

What is ceruloplasmin?

A

This is a copper transport enzyme also involved in iron metabolism. Levels fluctuate with various physiological states. Decreased in Wilsons disease.

44
Q

What is Wilsons disease?

A

A failure to incorporate copper which results in unstable protein so excess copper is deposited in tissues causing problems.

45
Q

What is transferrin?

A

An iron transport protein which can also bind copper. it is increased in iron deficiency anaemia, pregnancy and estrogen therapy. Decreased in inflammation, malignancy and liver disease.

46
Q

What is beta 2 microglobulin?

A

A small protein which is filtered in the glomerulus and reabsorbed in the tubules. Can be useful when looking at renal disease, increased in renal failure, inflammation and neoplasia.

47
Q

What are complement proteins?

A

C3 and C4 they sit in the late beta, early gamma regions so can be confused if inflammation. Increased in inflammation decreased in genetic deficiencies.

48
Q

What is CRP?

A

One of the strongest acute phase reactants, binds to phosphocholine on the surface of dead and dying cells opsonising them. Increased in inflammation, trauma, infection, infarction. Sit in the gamma region.

49
Q

What are the plasma cell disorders detected by immunoassay?

A

Immunoglobulin deficiency, polyclonal hyperimmunoglobuminaemia, monoclonal gammopathy.

50
Q

What are monoclonal immunoglobulins (paraproteins)?

A

When you have a single clone which produces identical immunoglobulin which does not class switch. They are called M proteins and interfere with a lot of tests as they aggregate together.

51
Q

What does monoclonal gammopathy look like on electrophoresis?

A

A discrete band in the gamma region.

52
Q

What are Bence-Jones proteins?

A

Urinary plasma proteins when you have a lot of paraproteins that they spill over into the urine.

MELS301 (10 decks)

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