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Plasma proteins Flashcards

1
Q

What is the normal range of total plasma protein concentration?

A

6–8 g dL–1

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2
Q

How many bands are normally formed after native, non-reduced electrophoresis of blood serum?

A

5 bands (albumin, α1-globulins, α2-globulins, β-globulins, γ-globulins)

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3
Q

What are the bands formed after native, non-reduced electrophoresis of blood serum?

A
  • albumin
  • α1-globulins
  • α2-globulins
  • β-globulins
  • γ-globulins
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4
Q

Which band formed after blood serum electrophoresis is the most negatively charged?

A

Albumin

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5
Q

Which band formed after blood serum electrophoresis is the least negatively charged?

A

γ-globulins

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6
Q

How is the albumin band of blood serum electrophoresis unique compared to the other four bands?

(In terms of constituents)

A

The albumin band is formed by only protein, while the remaining 4 bands are formed of several proteins

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7
Q

What is the decreasing order of concentration of the bands of blood serum electrophoresis bands?

A

Albumin (60%) > γ-globulins (23%) > β-globulins (15%) > α2-globulins (12%) > α1-globulins (7.2%)

Values are based on the maximum normal concentration of each band and do not add up to exactly 100

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8
Q

Which of the bands of blood serum electrophoresis is most abundant?

A

Albumin

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9
Q

Which of the bands of blood serum electrophoresis is least abundant?

A

α1-globulins

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10
Q

What proteins make up the γ-globulin band?

A

Immunoglobulins/antibodies

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11
Q

What is the main constituent of the α1-globulin band?

A

α1-antitrypsin (α1-antiproteinase)

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12
Q

What are the constituents of the α1-globulin band?

A
  • α1-antitrypsin
  • α1-fetoprotein
  • α1-acid glycoprotein
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13
Q

What are the constituents of the α2-globulin band?

A
  • Ceruloplasmin
  • Haptoglobin
  • α2-macroglobulin
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14
Q

What structural feature is shared by all proteins of the α1, α2, β, and γ bands?

A

They are all globular proteins

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15
Q

What are the main constituents of the β-globulin band?

A
  • C-reactive protein (CRP)
  • Hemopexin
  • C1q
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16
Q

Where are plasma proteins synthesized?

A
  • Liver (albumin and most globulins)
  • Plasma cells, spleen, lymph nodes, bone marrow (immunoglobulins)
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17
Q

What is the major modification that most plasma proteins share?

A

Glycosylation (whether N- or O-linked), with the notable exception of albumin

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18
Q

In what form are plasma proteins synthesized?

A

As preproproteins that are cleaved, generating the active plasma protein and a signal peptide fragment

Many preproproteins are around 300 kDa in mass, while the active proteins are around 70 kDa

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19
Q

What are the main posttranslational modifications of plasma proteins?

A
  • Proteolysis (cleaving)
  • Glycosylation
  • Phosphorylation
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20
Q

What are the general functions of plasma proteins?

A
  • Nutrition (used for energy in protein malnutrition)
  • Maintenance of blood pH
  • Contributing to the viscosity of blood (especially albumin and fibrinogen)
  • Maintaining blood pressure by generating colloid–oncotic pressure (especially albumin due to its high concentration)
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21
Q

What are the specific functions of plasma proteins?

A
  • Enzymatic catalysis (e.g. thrombin, lipases)
  • Humoral immunity (immunoglobulins)
  • Blood coagulation
  • Hormonal signaling (erythropoietin stimulates erythropoiesis)
  • Transport (albumin, thyroxin-binding globulin (TBG), apolipoproteins such as LDLs)
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22
Q

By what factor do positive acute-phase proteins increase under stress conditions?

A

Up to 1000 times

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23
Q

What conditions trigger the acute-phase reactants?

A
  • Acute inflammation
  • Chronic inflammation
  • Tissue damage
  • Cancer
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24
Q

Where is albumin synthesized?

A

Liver

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25
What is the shape of albumin?
Ellipsoid
26
How much albumin is synthesized each day?
12 g
27
In what form is albumin synthesized?
Preproalbumin
28
How is preproalbumin transformed into the albumin found in the blood?
preproalbumin → proalbumin + signal peptide (20–30 residues) _via signal peptidase_ proalbumin → albumin + hexapeptide
29
What is the structure of the mature albumin protein?
A single polypeptide with 3 domains and 17 disulfide bridges
30
Does albumin have a quarternary structure?
No, as it is formed of a single polypeptide
31
What are examples of ligands bound by albumin in the blood?
* Free fatty acids * Bilirubin * Certain steroid hormones * Plasma Trp * Metals, e.g. calcium, copper, heavy metals * Drugs, e.g. sulfonamides, penicillin G, dicumarol, aspirin, other acidic drugs
32
What is the role of albumin in congestive heart failure?
* Weak cardiac muscle leads to hypertension * Hypertension leads to loss of albumin at the glomeruli of the kidney * Lowered albumin reduced oncotic pressure, leading to increased edema * Increased edema leads to more hypertension * Continued hypertension weakens the cardiac muscle until heart failure
33
What is the diagnostic criterion for hypoalbuminemia?
< 2 g dL–1
34
What are the causes of hypoalbuminemia?
* Cirrhosis * Malnutrition * Nephrotic syndrome * GI loss of proteins (e.g. in diarrhea, vomiting)
35
What is the clinical manifestation of hypoalbuminemia?
Edema
36
What is the cause of hyperalbuminemia?
Dehydration, leading to increased blood plasma volume (though the amount of albumin stays the same)
37
What is the clinical manifestation of analbuminemia?
Moderate edema
38
Patients with hypoalbuminemia show extreme edema, while those with analbuminemia show only moderate edema. Why is this?
In analbuminemia, the levels of other plasma proteins increase compensatorily, maintaining oncotic pressure
39
What is the cause of analbuminemia?
An autosomal recessive mutation. One of the mutations affects splicing of the albumin precursors.
40
What is the alternative name of prealbumin?
Transthyretin
41
What is the alternative name of transthyretin?
Prealbumin
42
Is prealbumin (transthyretin) the precursor of albumin?
**No**, proalbumin and preproalbumin are. Transthyretin was called prealbumin since it moves faster than albumin in electrophoresis
43
What are the structural features of prealbumin (transthyretin)?
* A small glycoprotein (0.5% carbohydrate) * Rich in Trp * 62 kDa
44
What is the half-life of prealbumin (transthyretin)?
About 2 days
45
How is the half-life of prealbumin useful?
It is short (≈ 2 days) and so acts as a sensitive indicator of disease or protein malnutrition
46
What are the main functions of prealbumin (transthyretin)?
* Carrier for thyroxine (T4) and triiodothyronine (T3) * Carrier for steroid hormones * Carrier for retinol
47
What is the alternative name of α1-antitrypsin?
α1-antiproteinase
48
What is α1-antiproteinase?
α1-antitrypsin
49
What is the function of α1-antitrypsin?
Neutralizing trypsin and trypsin-like enzymes (e.g. elastase)
50
What are the four most common alleles for α1-antitrypsin?
* M * S * Z * F ## Footnote (full notation: PiM, etc.)
51
What is the most common genotype for α1-antitrypsin?
MM
52
Which genotypes for α1-antitrypsin cause deficiency with emphysema?
* ZZ * SZ
53
Which genotypes for α1-antitrypsin cause deficiency with little clinical manifestation?
* MS * MZ
54
What is the typical clinical presentation of people with an MS genotype for α1-antitrypsin?
Deficiency with little clinical manifestation
55
What is the typical clinical presentation of people with an MZ genotype for α1-antitrypsin?
Deficiency with little clinical manifestation
56
What is the typical clinical presentation of people with an SZ genotype for α1-antitrypsin?
Deficiency accompanied by emphysema
57
What is the typical clinical presentation of people with an ZZ genotype for α1-antitrypsin?
Deficiency accompanied by emphysema
58
How can α1-antitrypsin be inactivated?
Oxidation of the Met358 residue
59
What is the typical cause of α1-antitrypsin inactivation by oxidation of Met358?
Chronic lung inflammation due to smoking
60
How can α1-antitrypsin contribute to liver disease?
The ZZ phenotype polymerizes by forming a loop with a β-sheet and aggregates in the liver 10% of cases proceed to cirrhosis
61
Which genotype of α1-antitrypsin is most associated with liver disease and cirrhosis?
ZZ
62
Where is α1-fetoprotein synthesized?
* The fetal yolk sac * Later by the parenchyma of the liver
63
What are the functions of α1-fetoprotein?
* Protects the fetus from immunolytic attacks * Modulates the growth of the fetus * Transports compounds, e.g. steroids
64
What condition is a low fetal/maternal α1-fetoprotein level associated with?
Down syndrome
65
Levels of which protein can be used to screen for Down syndrome before birth?
α1-fetoprotein
66
In what cases do levels of α1-fetoprotein increase?
* Pregnancy (physiological) * Hepatomas (pathological) * Acute hepatitis (pathological)
67
What is the alternative name for α1-acid glycoprotein?
Orosomucoid
68
What is orosomucoid?
α1-acid glycoprotein
69
What is a structural feature of α1-acid glycoprotein?
Highly glycosylated (41% carbohydrate)
70
What are the functions of α1-acid glycoprotein?
* Transports progesterone * Transports carbohydrates to sites of tissue injury
71
In what conditions may α1-acid glycoprotein concentration increase?
* Inflammation and inflammatory diseases * Cirrhosis * Malignancies
72
In what conditions may α1-acid glycoprotein concentration decrease?
* Malnutrition * Liver diseases * Nephrotic syndrome
73
To which electrophoresis band does haptoglobin belong?
α2-globulins
74
To which electrophoresis band does ceruloplasmin belong?
α2-globulins
75
What are the structural features of haptoglobin?
* Tetramer (two α subunits, two β subunits) * Glycoprotein
76
How many subunits make up haptoglobin?
Four: two α subunits, two β subunits
77
What are the phenotypes of haptoglobin?
Hp 1-1: α1, α1 + 2β Hp 2-1: α1, α2 + 2β Hp 2-2: α2, α2 +2β
78
What is the function of haptoglobin?
Binding of free hemoglobin after hemolysis to prevent the loss of hemoglobin and iron into the urine
79
What is the half-life of the haptoglobin–hemoglobin complex?
90 minutes, compared to 5 days for free Hp
80
In what condition may levels of haptoglobin decrease?
Hemolytic anemia
81
What are the structural features of ceruloplasmin?
* Glycoprotein * Contains 6 atoms of copper
82
To which class of proteins does ceruloplasmin belong? | (Not electrophoresis band)
The metallothioneins: bind to metal ions and regulate their blood levels
83
What are the functions of ceruloplasmin?
* Regulate the blood levels of Cu2+ (ceruloplasmin binds 90% of serum Cu2+) * Oxidizes Fe2+ to Fe3+ for binding by transferrin | *Albumin is more important for Cu2+ _transport_*
84
In what conditions may ceruloplasmin levels decrease?
* Liver diseases, especially Wilson's disease, an autosomal recessive genetic disease
85
Abnormality in levels of which plasma protein is associated with Wilson's disease?
Ceruloplasmin
86
Where is α2-macroglobulin synthesized?
* Hepatocytes * Macrophages
87
What is the function of α2-macroglobulin?
* Inactivates proteases (e.g. thrombin) and acts as an important *in vivo* anticoagulant * Carries many growth factors
88
How does nephrotic syndrome affect levels of α2-macroglobulin?
Levels of α2-macroglobulin increase since other proteins are lost
89
Levels of which protein **increase** in nephrotic syndrome?
α2-macroglobulin
90
To which electrophoresis band does C-reactive protein (CRP) belong?
β-globulins
91
To which electrophoresis band does hemopexin belong?
β-globulins
92
To which electrophoresis band does complement C1q belong?
β-globulins
93
What is the function of hemopexin?
Binds heme formed from the breakdown of hemoglobin and other hemeproteins
94
In what conditions may hemopexin levels increase?
* Pregnancy * Diabetes mellitus * Malignancies * Duchenne muscular dystrophy
95
Levels of which protein are affected by Duchenne muscular dystrophy?
Hemopexin
96
In which conditions may hemopexin levels decrease?
* Hemolytic disorders * Low levels at birth; the adult level is reached within the first year of life * Drug induced
97
What is the function of CRP?
* Binds a polysaccharide, fraction C in the cell wall of *Staph. pneumoniae* (pneumococcus) * Helps in the defense against bacteria and foreign substances
98
How long after an incident does CRP reach its peak level?
48 hours
99
What are the functions of complement C1q?
* The first complement factor to bind an antibody * Triggers classical activation of the complement (decreased levels of C1q indicate circulating Ag–Ab complex)
100
What is the alternative name of fibrinogen?
Clotting/coagulation factor I
101
What are the structural features of fibrinogen?
* Highly elongated, axial ratio of 20:1 * Made up of 6 polypeptide chains, linked by disulfide bridges * The N-terminus is highly negative due to the presence of Glu residues. This causes its solubility and the electrostatic repulsion of plasma fibrinogen, keeping it from aggregating
102
Which plasma protein transports iron?
Transferrin
103
Which plasma proteins transport retinol (vitamin A)?
* Prealbumin (transthyretin) * Retinol-binding protein
104
Which plasma proteins transport thyroxin?
* Prealbumin (transthyretin) * Thyroxin-binding protein
105
Which plasma protein transports cortisol and corticosteroids?
Transcortin (cortisol-binding protein)
106
What are the (positive) acute-phase proteins?
* CRP * Ceruloplasmin * α1-antitrypsin * α1-acid glycoprotein * α2-macroglobulin
107
What are the negative acute-phase proteins?
* Albumin * Prealbumin (transthyretin) * Retinol-binding protein * Transferrin
108
What is the diagnostic criterion for hyperproteinemia?
> 8 g dL–1
109
What are the causes of hyperproteinemia?
Hemoconcentration (ratio of albumin to globulins remains constant), caused by * Excessive vomiting * Diarrhea * Diabetes insipidus (ADH deficiency) * Diuresis * Intestinal obstruction
110
What are the causes of hypoproteinemia?
**Conditions** * Hemodilution (ratio of albumin to globulins remains constant) * Hypoalbuminemia **General causes** * Nephrotic syndrome * Protein-losing enteropathy * Severe liver diseases * Malnutrition/malabsorption * Extensive skin burns * Pregnancy * Malignancy
111
What are the causes of hypogammaglobulinemia?
* Loss from the body (as with hypoproteinemia) * Decreased synthesis * Primary (genetic) immunodeficiency * Secondary immunodeficiency (drug induced, uremia, hematological disorders, AIDS)
112
What are the causes of hypergammaglobulinemia?
**Polyclonal** * Chronic infections * Chronic liver diseases * Sarcoidosis * Autoimmune diseases **Monoclonal** * Multiple myeloma * Macroglobulinemia * Lymphosarcoma * Leukemia * Hodgkin lymphoma

Metabolism (6 decks)

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