BIOCHEMISTRY - Blood and Proteins Flashcards
1
Q
What are the two main functions of albumin?
A
Non-specific transporter
Maintains oncotic pressure
2
Q
What is the role of transferrin?
A
Binds to and transports Fe3+ in the blood
3
Q
What is the role of ceruloplasmin?
A
Binds to and transports Cu2+ in the blood
4
Q
What is the difference between plasma and serum?
A
Plasma is in vivo (in the body)
Serum is in vitro (in a test tube left to clot)
5
Q
Which three lipids make up the erythrocyte membrane?
A
Phospholipids
Sphingolipids
Cholesterol
6
Q
List the peripheral proteins of the erythrocyte membrane
A
Spectrin
Ankryn
Actin
Protein 4.1
7
Q
What is the function of the erythrocyte peripheral membrane proteins?
A
Provide strength and structure
8
Q
What can occur when there is a defect in protein 4.1?
A
Elliptical erythrocytes that a more susceptible to lysis
9
Q
List the integral membrane proteins of the erythrocyte membrane
A
Glycophorin A
GLUT 1
Sodium potassium ATPase pump
Anion exchanger
10
Q
What are the function of Glycophorin A ?
A
- Prevents aggregation of the erythrocytes to one another and to the blood vessel walls
- Determines blood types
11
Q
What property in Glycophorin A determines blood types?
A
Carbohydrate bound to the glycophorin A protein
12
Q
What is the function of GLUT 1?
A
Brings glucose into the cell for glycolysis and the pentose phosphate pathway
13
Q
What is the function of the anion exchanger?
A
Exchanges bicarbonate produced from dissociation of carbonic acid with chloride to maintain the pH
14
Q
What type of metabolism occurs in erythrocytes?
A
Anaerobic (no mitochondria)
15
Q
How is ATP generated in erythrocytes?
A
Glycolysis
16
Q
How does glycolysis differ in erythrocytes?
A
2,3 BiPglycerate forms which is a negative allosteric effector of haemoglobin/O2 affinity, allowing for more O2 to reach the tissues
17
Q
How is NADPH produced in erythrocytes?
A
Pentose phosphate pathway
18
Q
Why is NADPH important in erythrocytes?
A
NADPH maintains glutathione in its reduced state
19
Q
What is methaemoglobin?
A
Oxidised haemoglobin
20
Q
What are the three consequences of methaemoglobin formation?
A
Doesn’t bind to/transport O2
Heinz body formation
Cell death
21
Q
What is the function of glutathione in erythrocytes?
A
Glutathione is readily oxidised to prevent the oxidation of the iron found in haemoglobin, preventing the formation of methaemoglobin
22
Q
Which substances ensure the regeneration of glutathione in erythrocytes?
A
NADPH
Glutathione reductase enzyme
23
Q
List the clinical signs of methaemoglobinaemia
A
Cyanosis (purple mucous membranes) due to lack of O2
Exercise intolerance
Vomiting
Chocolate brown blood
Anaemia (occasionally)
24
Q
What is the function of proximal histidine in regards to haem?
A
Proximal histidine anchors the Fe2+ in place
25
What is the function of distal histidine in regards to haem?
Distal histidine protects the O2 binding site through preventing oxidation of the Fe2+ and preventing carbon monoxide poisoning by lowering haem affinity for carbon monoxide
26
Describe myoglobin structure
Myoglobin has one polypeptide chain, one haem group and one O2 binding site
27
Describe haemoglobin structure
Haemoglobin is an allosteric enzyme with four polypeptide chains, four haem groups and four O2 binding sites
28
What is the function of myoglobin?
O2 storage in the tissues
29
What is the function of haemoglobin?
Transport of O2 to the tissues
30
Why do the functions of myoglobin and haemoglobin differ?
Myoglobin isn't allosteric so has a much higher O2 affinity than haemoglobin so does not release O2 under normal physiological conditions and thus is more useful for O2 storage rather than transport
31
What are the differences between the structure of adult haemoglobin and foetal haemoglobin?
Adult haemoglobin is made up of 2 alpha and 2 beta chains whereas foetal haemoglobin is made up of 2 alpha and 2 gamma chains (has a higher O2 affinity)
32
How is oxygen transferred in the maternal/foetal circulation?
Adult haemoglobin has less O2 affinity compared to foetal haemoglobin, so more O2 is released from the adult haemoglobin and bound to the higher affinity foetal haemoglobin
33
List the negative allosteric effectors of haemoglobin/O2 affinity
CO2
H+
2,3 BiPglycerate (2,3-BPG)
34
What is the function of the negative allosteric effectors of haemoglobin/O2 affinity?
Negative allosteric effectors bind to the haemoglobin, lowering the haemoglobin affinity for O2, increasing the O2 release into the tissues
*moves the oxygen dissociation curve to the right*
35
Where does 2,3 BiPglycerate bind to the haemoglobin?
The 2,3-BPG binds to the central compartment of haemoglobin
36
What are the three places where haem is synthesised?
Liver
Erythroblasts
Reticulocytes
37
What is congenital erythropoietic porphyria?
Defect in the formation of the pyrrole structure of haem causing severe skin photosensitivity
38
In which species is congenital erythropoietic porphyria seen most often?
Holstein Friesian calves
39
What determines amino acid properties?
R-groups
40
List the different R-groups
Hydrophobic (methyl group)
Aromatic hydrophobic (benzene group)
Hydrophilic
41
Which amino acid is always the first amino acid found in a protein sequence?
Methionine
42
Why is methionine always the first amino acid found in protein sequences?
Due to the ATG start codon
43
Which amino acid is very commonly involved in disulphide bonding and why?
Cysteine has an SH group on its R-group so is often involved in di-sulphide bonding
44
Which amino acids are commonly used in protein assays and why?
Aromatic hydrophobic amino acids (tryptophan, tyrosine, phenylalanine) have a benzene ring within their R-group so have to ability to absorb UV light at 280nm - useful for protein assays
45
Which amino acids have an OH at the end of their R-group?
Serine
Threonine
46
Which post-translational modification can involve serine and threonine?
O-linked glycosilation to produce glycoproteins
47
Which amino acid has an NH2 at the end of it's R-group?
Asparagine
48
Which amino acid has a ring structure which forces bends within protein structures?
Proline
49
How can proteins be measured?
Proteins can be measured with mean molecular mass
1 amino acid = 100 daltons
50
What is primary protein structure?
The amino acid sequence joined by peptide bonds
51
What is secondary protein structure?
Amino acids folded in alpha helices or beta sheets through hydrogen bonding
52
What is tertiary protein structure?
The overall folding of a protein through R-group interactions. When in tertiary structure the protein will be biologically active
53
What is quaternary protein structure?
Protein complexes consisting of 2 or more polypeptide subunits
54
What is protein denaturation?
Denaturation is the disruption of R-group interactions and hydrogens bond, causing proteins to unfold
55
List four different factors which can cause proteins to denature
Heat
pH
Detergents and organic solvents
Chaotropic agents
56
What are chaotropic agents?
Ions or small molecules which form hydrogens bonds with proteins, disrupting the existing hydrogen bonds, causing the protein to unfold
57
List two methods that can be used for predicting protein structure
Molecular modelling
X-ray crystallography
58
Why is the primary structure of proteins so important?
If the primary structure of a protein is maintained, then proteins that are denatured can still be refolded
59
Which proteins are essential for protein refolding?
Chaperone proteins
60
What can cause a change in the primary protein structure?
Genetic mutations
61
List the two classifications of substitution mutations
Conservative substitutions
Radical substitutions
62
Describe the effects of conservative substitution mutations
Conservative substitutions are when the same type of amino acid is substituted which has very little/no effect
63
Describe the effects of radical substitution mutations
Radical substitutions are when a different type of amino acid is substituted which can alter ligand binding and enzyme activity
64
Describe the effects of insertion and deletion mutations
Insertion and deletion mutations are the gain or loss of an amino acid which can alter protein function, have no effect if a non-essential amino acid is removed, cause new protein function
65
What is the structure of collagen?
Collagen triple helix
66
Which amino acid occupies every third position in the collagen triple helix? Why is this?
Glyceine is the only amino acid small enough to fit into the interior of the collagen triple helix
67
List all three amino acids found in the collagen triple helix structure
Glyceine
Prolene
Hydroxyprolene
68
What stabilises the collagen triple helix?
Hydrogen bonds between the hydroxyprolene amino acids
69
List two examples of diseases caused by defects in the collagen structure
Scurvy
Osteogenesis imperfecta (brittle bone disease)
70
Describe the cause of scurvy
Scurvy is caused by a vitamin C deficiency as vitamin C is a co-enzyme for the enzyme prolyhydroxylase which catalyses the conversion of prolene to hydroxyprolene. Insufficient hydroxyprolene leads to insufficient hydrogen bonds causing the collage triple helix to become unstable
71
Describe the cause of osteogenesis imperfecta (brittle bone disease)
A mutation in the glyceine codon
72
What are prion proteins?
Globular proteins found mainly in the brain and the spinal cord (central nervous system)
73
What are prion diseases?
Diseases that arise due to the globular form of prion proteins converting to the fibrous form (scrapie form)
74
How does the fibrous (scrapie) form of prion proteins cause disease?
The fibrous (scrapie) prion proteins aggregate within cells, causing tissue damage mainly within the central nervous system (brain and spinal cord) leading to interference in brain transmission
75
Give two examples of prion protein diseases
Scrapies
Bovine spongiform encephalitis (mad cow disease)
76
What are the main functions of enzymes?
Catalyse biological functions
Decreases activation energy
Stabilise the transition state
77
How do enzymes speed up the rate of biological reactions?
Enzymes form an intermediate complex (enzyme-substrate complex) which lowers the activation energy and stabilises the transition state through bringing substrates close together in the correct orientation to interact
78
What can alter enzyme activity?
pH
Temperature
79
What are co-enzymes?
Organic molecules derived from vitamin ingestion which bind to enzyme active sites to assist in the catalysis of the reaction
80
What are enzyme co-factors?
Usually metal ions which stabilise the substrate binding to the enzyme active site
81
What shape is a enzyme reaction when plotted on a graph?
Hyperbolic curve
82
What is the maximum velocity (Vmax) of an enzyme catalysed reaction?
Vmax is the point during an enzyme catalysed reaction where the enzyme is fully saturated with substrate so there can no longer be any increase in the rate of reaction
83
What is Km?
Km is the substrate concentration required to reach half the maximum velocity (Vmax)
84
What does a low Km value indicate?
Low Km indicates that there is a high substrate-enzyme affinity as a low substrate concentration is required for a reaction to reach Vmax
85
What does a high Km value indicate?
High Km indicates that there is a low substrate-enzyme affinity as a high substrate concentration is requires for a reaction to reach Vmax
86
What is the Line Weaver-Bulk plot?
The Line Weaver-Burk plot is the double reciprocal graph of the Michaelis-Menten equation
- i.e. the linear form of the hyperbolic curve
87
What are reversible enzyme inhibitors?
Competitive or non-competitive inhibitors which bind to enzymes and rapidly dissociate
88
What are irreversible enzyme inhibitors?
Inhibitors which bind to enzymes and have such a slow dissociation time that these inhibitors are described as irreversible
89
What is the difference between competitive and non-competitive reversible enzyme inhibitors?
- Competitive inhibitors bind to the active site of the enzyme and the effects of competitive inhibitors can be reversed by increasing substrate concentrations
- Non-competitive inhibitors don't bind to the enzyme active site and instead change the shape of the enzyme protein
- non-competitive inhibitors prevent reactions from reaching Vmax
90
What shape is an allosteric enzyme reaction when plotted on a graph?
Sigmoid curve
