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proteins Flashcards

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1
Q

Amino Acids

A 
building blocks of protein 
contain amino (-NH2) & carboxyl(-COOH) functional groups

differ from one another based on the chemical composition of the R group ( side chain )

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2
Q

amino acid - formation of peptide bonds

A

the amino group of one amino acids can be linked with the carboxyl group of another to form a peptide bond

polypeptide: a chain of amino acids linked by peptide bonds
protein: a large polypeptide

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3
Q

Amino acid metabolism

A

20 amino acids are necessary for synthesis of proteins

10 of these are essential amino acids ( must come from diet)
* don’t need to memorize them

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4
Q

amino acid pool

A

pepsin & trypsin digest dietary proteins into amino acids which are absorbed from the intestine into the bloodstream

can be used to synthesize body proteins, hormones, nucleic acids, etc.

proteins provide up to 20% of daily required energy needs

deamination of amino acids produces NH4+which is converted to urea in the liver

ketoacids enter common metabolic pathway with carbs & fats & are converted to energy

ketogenic amino acids

  • can be degraded to acetly- CoA to then form ketone bodies
  • ex. leucine, lysine

Glucogenic amino acids

  • can be converted ti glucose through gluconeogenesis
  • 13 amino acids are glucogenic
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5
Q

Aminoacidopathies

A

autosomal recessive inherited errors of matabolism

an enzyme defect inhibits the ability to metabolize certain amino acids

cause severe medical complications

  • including brain damage
  • toxic amino acids or their by-products build up in the blood

newborn screening tests are available for some to provide early treatment & therapies

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6
Q

Phenylketonuria (PKU)

A

the most well know aminoacidopathy

absence of the enzyme phenylalanine hydroxylase (PAH)
- converts phenylalanine to tyrosine

chronically elevated levels of phenylalanine can cause permanent brain damage

patients have a characteristic” mousy” odor to their urine

testing is done before newborns leave the hospital

  • fluorescence of a complex formed between phenylalanine, ninhydrin & copper on a dried blood filter disk is measured
  • positive results must be verified by another method

treatment : low phenylalanine diet

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7
Q

Tyrosinemia

A

3 types caused by deficiencies in enzymes in the metabolic pathway of tyrosine

Type 1

  • most severe
  • symptoms appear in first few months of life
  • failure to thrive*, diarrhea, vomiting, jaundice
  • can lead to liver/kidney failure & nervous system problems

Type 2

  • symptoms: light sensitivity, eye pain, painful skin lesions on palms & soles of feet
  • half have impaired mental development

Type 3

  • only a few cases worldwide
  • treatment: protein-restricted diet, medications, liver-transplant
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8
Q

Alkaptonuria

A

deficiency of homogentisate oxidase ( HGD)
-needed for metabolism of tyrosine & phenylalanine

elevated levels of homogentisic acid ( HGA) in blood & urine

symptoms present during 3rd decade of life

  • blue-black pigment of ears, nose, tendons (ochronosis) casued by a build up of homogentisic
  • arthritis -like degeneration of joints
  • urine that turns black when mixed with air due to oxidation of HGA

Ferric Chloride test detects HGA in urine

treatment : high does Vitamin C to sloe accumulation of HGA in cartilage

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9
Q

Maple Syrup Urine Disease ( MSUD)

A

Absence or reduced activity of branched -chain-alpha-ketoacid decarboxylase (BCKD) enzymes
- inhibits metabolism of 3 essential amino acids : leucine, isoleucine & valine

maple syrup odor to urine

symptoms in newborns: lethargy, vomiting, lack of appetite, failure to thrive

treatment: protein-restricted diet

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10
Q

Isovaleric Acidemia

A

deficiency of isovaleryl-CoA dehydrogenase (IVD) enzyme
-involved inmetabolism of leucine

asymptomatic patients have odor of sweaty feet

symtoms in newborns: lethary, vomiting, lack of appetite & failure to thrive

treatment : protein- restricted diet

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11
Q

Homocystinuria

A

deficiency of cystathionine ß-synthase enzyme
- needed in the metabolism of methionine

symptoms : near-sightedness, dislocation of the lens in the eye, osteoporosis, mental defects

treatment: protein -restricted diet & high doses of vitamin B6

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12
Q

Cystinuria

A

Mutation of gene responsible for the synthesis of a protein complex in the kidneys that reabsorbs cystine from urine
-elevated levels of cystine in urine

cystine forms stones in the kidneys, ureters or bladder ( reoccur throughout patients life)

symptoms : hematuria, flank pain( back), UTIs

treatment : increase fluid intake to minimize stone formation

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13
Q

Amino acid analysis

A

plasma can be collected in a heparin tube after 6-8 hr fast

urine & amniotic fluid can also be analyzed

**Thin-Layer Chromatography is the method of choice

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14
Q

Protein- Basic structure

A

proteins play a key role in every function of living cells: motion, biochemical reactions, cell structure, transport, antibodies

consists of C, O, H, N, S

Macromolecules :
contain 200-300 amino acids
range in molecular mass from 6000 Daltons to several million

four levels of protein structure

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15
Q

Proteins 4 levels of structure

A

primary

  • the # & type of amino acids in a specific sequence
  • correct sequence is required to function properly

secondary

  • structures stabilized by hydrogen bonds between the amino acids within a protein
  • ex. alpha- helix ( most), ß-pleated sheet
  • adds strength & flexibility

tertiary

  • overall shape or conformation
  • 3-D resulting from interactions of side chains
  • physical & chemical properties are related to its tertiary structure

quaternary
- structure that results from the interaction of multiple protein molecules or subunits held together by non-covalent forces

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16
Q

Proteins - Properties

A

Nitrogen content: 16% by weight in serum protein

protein can contain many ionizable groups ( can be positive & negatively charged) aka amphoteric

the acid or base groups of the side chains can exist in different charged forms depending on the pH of the surrounding environment

Generally as pH increases, deprotonation (transfer of H+) occurs:
-carboxyl groups (R-COOH) are converted to carboxylate anions
(R-COO^-)
- ammonium groups (R-NH3) are converted to amino groups ( R-
NH2)

17
Q

Proteins -isoelectric point

A

isoelectric point (pI)

  • the pH at which a protein has no net charge
  • the # of positively charged groups = # of negatively charged groups

when the pH is greater than the PI, the protein has a net neg charge
when the pH is less than the PI, the protein has a net pos charge

most proteins have a PI in the pH range of 5.5-8

the solubility of a protein depends on: # & type of amino acids it has & the pH of the environment

generally the greater the charge the greater the solubility

18
Q

Protein Synthesis

A

occurs in

  • Liver for plasma protein
  • plasma cells for immunoglobulins

proteins are being rebuilt constantly

  • Hb every 120 days
  • plasma protein every 10 days

in some tissue, hormones assist in controlling protein synthesis

19
Q

Nitrogen balance

A

Amino acids cannot be stored

most proteins are repeatedly synthesized & then degraded, recycling the amino acids

a balance exists between protein synthesis ( anabolism) & protein breakdown ( catabolism )

nitrogen balance occurs through equal intake & excretion of amino acids

the excretion of excess nitrogen occurs through reversible reactions that are catalyzed by transaminases

  • ammonia is produced which is converted to urea & excreted in the urine
  • ketoacids that are produced are oxidized & converted into glucose or fat
20
Q

Protein classification - functions( osmotic pressure, enzymes, hormones, immunoglobulins, structural)

A

FUNCTION : DESCRIPTION ( EXAMPLES)

Maintain osmotic pressure: maintain water distribution 
           throughout body( Albumin)

Enzymes: catalyze biochemical reactions (Transaminases,
Dehydrogenases, Phosphotases )

Hormones: chemical messengers that control the actionof
specific cell & organs ( Testosterone, Growth hormone,
Cortisol)

Immunoglobulins: antibodies produced by B cells in bone
marrow. part of immune response ( IgG, IgM, IgA)

Structural ( Collagen, Elastin, Keratin )

21
Q

protein classification - function ( transport )

A 
Transport: 
Hemoglobin     -->O2
Albumin            --> bilirubin 
Transferrin        --> iron 
ß- globulin        --> lipids 
Ceruloplasmin  --> copper
22
Q

protein classification - functions (storage, energy source, coagulation, pH )

A

Storage: store metal ions/amino acids for later release (ferritin–
–>iron)

Energy source: supply energy to tissue ( Creatine)

Coagulation ( FIbrinogen )

Acid- Base Balance : act as buffers to maintain pH ( 7.35-7.45 )

23
Q

protein structure - simple proteins

A

Simple proteins
contain peptide chains composed of only amino acids
can be globular or fibrous

Gobular

  • globe-like, symmetrical proteins
  • soluble in water
  • function:transporters, enzymes, messengers
  • examples: Albumin, hemoglobin & immunoglobulins

Fibrous

  • long protein filaments, asymmetrical
  • water insoluble
  • Function: provides structure to cells
  • ex. troponin & collagen
24
Q

protein structure- conjugated protein

A

Conjugated Protein
consist of protein & non protein
the non amino part is called the prosthetic group
- can be lipid, carbohydrate, porphyrin, metal etc

Metalloproteins

  • metal ion attached to the protein
  • ferritin- contains iron
  • ceruloplasmin - contains copper

Lipoproteins

  • lipid attached to a protein
  • HDL, LDL

GLycoproteins
- a carbohydrate attached to a protein
10-40% carbohydrate compostion = glycoproetin
ex. haptoglobin, alpha1-antitrypsin
> 40% carbohydrate compostion = mucprotein or proteiglycan
ex. mucin-lubricant

Nucleoproteins

  • nucleic acids combined with proteins
    ex. chromatin
25
Q

Plasma Proteins

A

most frequently analyzed proteins in the clinical lab

2 main groups
Albumin (RR: 35-55g/L)
Globulins

4 types of globulins : ⍺1, ⍺2, ß, y

26
Q

Plasma protein - Prealbumin

A

Migrates ahead of albumin
transport protein of thyroid hormones
low pre-albumin indicates poor nutritional status****

decreased in

  • hepatic damage
  • acute-phase inflammatory response
  • tissure necrosis

increased in

  • steroid therapy treatment
  • alcohol abuse
  • chromic renal failure
27
Q

Plasma protein albumin

A

protein present in the highest concentration in plasma
- responsible for 80% of colloid osmotic pressure***
( maintains fluid balance in tissue)
- buffers pH
- negative acute phase reactant ( decreases during
inflammation )
-transport of various substance ( thyroid hormones,
unconjugated bilirubin, iron, fatty acids, calcium,
magnesium )

low albumin–>edema

decreased in

  • acute inflammatory response
  • liver & kidney disease
  • malnutrition or malabsorption

increased in

  • rarely clinically important
  • dehydration
  • albumin infusion
28
Q

⍺1- globulins (⍺1- Antitripsin )

A

glycoprotein synthesized in liver
positive acute phase reactant

decreased in
⍺1- antitripsin deficiency

increased in

  • inflammatory reaction
  • pregnancy

deficiency is seen on serum protein electrophoresis ( SPE) as lack of an ⍺1 band next to albumin band

29
Q

⍺1- globulins (⍺1 - fetoprotein )

A

synthesized in utero by developing embryo then by cells in the liver

may protect fetus from immunological attack by the mother

decreased in 
Trisomy 21 ( downs syndrome ) *
Trisomy 18 ( edwards syndrome )*

increased in

  • spina bifida
  • neural tube defects*
  • general fetal distress
  • twins
30
Q

⍺- globulins - Haptoglobin

A

synthesized in liver
positive acute phase reactant

binds with hemoglobin to prevent the loss of iron in the urine
used to distinguish hemolytic anemia from other anemias ( patients with hemolytic anemia will have a decreased haptoglobin )

decreased in
hemolytic anemia

increased in 
ulcerative colitis 
acute rheumatic disease 
myocradial infarction 
severe infection
31
Q

⍺2 globulins - Ceruloplasmin

A

copper- containing glycoprotein synthesized in the liver
positive acute phase reactant
90% of serum copper is bound to ceruloplasmin ( remaining 10% to albumin )

decreased in 
wilsons disease* 
malnutrition/ malabsorption
severe liver disease 
nephrotic syndrome

increased in
inflammation
severe infection
tissue damage

patients with wilson’s disease have decreased ceruloplasmin & increased urinary excretion of copper** ( excess copper is deposited in liver , brain & other porgans )

32
Q

⍺2 - Globulins( Macroglobulin )

A

synthesized in liver
**inhibits proteases ( enzymes that catalyze th breakdown of proteins

increased in

  • renal disease
  • diabetes *
  • pregnancy *
33
Q

ß globulins ( transferrin )

A

synthesized in the liver
negative acute phase reactant **
major component of ß fraction **

transport of iron

decreased in

  • liver disease *
  • low protein diet *
  • infection
  • inflammation

increased in
- iron deficiency anemia

34
Q

ß globulins ( lipoproteins )

A

complexes of lipids & proteins

transport cholesterol, triglycerides & phospholipids in the blood stream

35
Q

ß globulins- complement

A

synthesized in the liver

complement C3 is most abundant, followed by C4***

natural defense*** - protects from infection

decreased in

  • autoimmune disease
  • tissue injury
  • chronic hepatitis

increased in

  • inflammatory disease
  • tissue inflammation
36
Q

ß globulin ( fibrinogen)

A

synthesized in liver
one of the largest proteins in plasma **
positive acute phase reactant

form fibrin clots when activated by thrombin

decreased in

  • extensive bleeding
  • liver disease

increased in

  • inflammatory processes
  • pregnancy

if plasma is used instead of serum for electrophoresis, a distinct band will appear betwee the ß & y regions

37
Q

ß globulins ( c- reactive protein ( CRP))

A

synthesized in liver
indicator of inflammation
positive acute phase reactant
**elevated levels are associated with increased risk for coronary heart disease & stroke

increased in

  • acute inflammation
  • myocardial infarction
  • bacterial or viral infections
38
Q

Y- globulins ( immunoglobulins ) ( antibodies )

A

**produced by plasm a cells ( B cells)
play a role in immunity

5 classes : IgG, IgM, IgA, IgD, IgE

  • composed of heavy chains ( y,⍺, µ, ∂, ℇ )
  • *****the light chains are also known as Bence Jones Proteins - found in multiple myeloma
39
Q

Structure of immunoglobulins

A

consists of 2 identical heacy (H) chains
& two identical light (L)chains

each of the four chains has 1 variable & 1 or more constant domains

variable domains contain antigen- binding regions

constant domains of heavy chains contain sites for complement activation & receptor binding

Variation in the constant domains of the heavy chain region ( Fc) result in the different classes of immunoglobulins

IgG
-accounts fro 70-75% of total plasma immunoglobulin

IgM
-the major immunoglobulin
synthesized in neonates
- a pentamer - contain 5 monomers

chemistry (13 decks)

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