4. Amino Acids & Proteins

What is the difference between essential, conditionally essential, and non-essential amino acids?

essential: cannot be made in the body & must be obtained by diet

conditionally essential: can be made in the body unless the person is sick or has IEM (inborn errors of metabolism)

non-essential: made in the body by catabolism of body proteins

What are the 9 essential, 6 conditional, and 5 nonessential amino acids?

essential: Histidine, Isoleucine, Leucine, Lysine, Methionine, Valine, Phenylalanine, Threonine, Tryptophan (HILLMVPTT)

conditional: Proline, Arginine, Cysteine, Tyrosine, Glutamine, Glycine (PACTGG)

nonessential: Glutamic Acid, Alanine, Asparagine, Aspartic Acid, Serine (GAAAS)

What percentage of required amino acids must be obtained by diet? How are dietary proteins broken down?

About 50%

By pepsin in the stomach

What are the 2 populations that cannot metabolically produce arginine (conditionally essential a.a.)?

premature infants & people in catabolic distress

If an amino acid is produced by another amino acid, what conditions will make supplementation essential?

nutritionally deficient

inborn errors of metabolism (IEM) that prevent normal metabolic pathways

What type of aminoacidopathy is inborn errors of metabolism (IEM)? And what does it inhibit?

autosomal recessive disorder

enzyme defect that inhibits metabolism or transport of amino acids

What was the first recognized disorder for newborn screening (NBS) and what is the screening process?

Phenylketonuria (PKU)

1. Newborn is heel sticked

2. Blood is absorbed on 6-9 small circles of Guthrie’s filter paper

3. Dried blood spots placed in broth containing Bacillus subtilis, which need phenylalanine to grow

4. Growth indicates + result for PKU

What is the mutation responsible for PKU?

Gene mutation for phenylalanine hydroxylase enzyme which converts phenylalanine into tyrosine

Describe the pathophysiology of PKU (What it reduces, damages, inhibits)

1. Phenylalanine cannot be converted into tyrosine and travels to blood & eventually the brain

2. It can reduce 1) synaptic transmission 2) pyruvate kinase activity 3) HMG-CoA activity

3. It damages myelin

4. It inhibits Tyr and Trp hydroxylase (Trp is responsible for serotonin & Tyr is responsible for dopamine. Both decrease due to decrease of Tyr and Trp)

Which group of the amino acid is acidic? Which is basic?

acidic: carboxyl group

basic: amine group

What are the structures & bonds that hold together the 4 protein structures?

primary: peptide bonds create the polypeptide chain

secondary: α-helix or β-sheets are held together H-bonds along the polypeptide backbone

tertiary: 3-D folding held together by bonds between the R groups

quaternary: Multiple tertiary structures bound together

What is the term for an amino acid that can act as either an acid or base?

amphoteric

What is the term for an amino acid that contains both negative and positive charges?

Zwitterion

What is the key difference that distinguishes proteins from carbohydrates?

Proteins are composed of ~16% nitrogen

Describe the catabolic process of protein degredation?

1. transamination: transfer of an amine group from an α-amino acid → α-ketoglutarate to yield glutamate and α-ketoacid

2. Glutamate + Glutamate dehydrogenase → ammonia and α-ketoglutarate

3. Ammonia → urea by Urea cycle → excreted in urine

4. α-ketoacid enters Kreb cycle

What are the 9 primary functions of proteins?

Energy for the Krebs cycle

Distribution of water by colloid osmotic pressure

Act as buffers

Transporters of metabolic substances

Immunoglobulins

Hormone receptors

Structural function in collagen, bone, tendons, cartilage

Enzymes

Clotting factors

What are the 5 protein methods of analysis and their principle?

Biuret: Peptide bonds + Cu²⁺ ions → violet colored chelate

Turbidimetry & Nephelometry: protein precipitation → aggregates that affect light scatter

Dye binding: Protein + dye → shift in max absorbance of the dye

Protein electrophoresis: migration of proteins based on charge & density

UV absorption: proteins absorb UV @ 200 & 280 nm

What are the two most common dye’s used to analyze albumin?

BCG (bromocresol green): sensitive but overestimates low albumin levels

BCP (bromocresol purple): specific, sensitive, precise

What are the 2 main groups of proteins & what is the ratio reference range for it?

albumins & globulins

A/G ref range: 1.1-1.8

What does a decrease A/G ratio indicate? (<1.1)

indicates liver disease

What are the 3 types of acute phase proteins?

positive APP: increase with infection, tissue injury, homeostatic disturbances

negative APP: reduction during inflammation

context dependent: Alpha-fetoprotein that’s normally a negative APP but can be positive during hepatitis or certain liver conditions

What type of APP is albumin? How much does it make up in serum protein? Where is it synthesized?

negative APP

~1/2 of total protein in serum

in the liver

What are the 4 functions of albumin?

1. maintain colloid osmotic pressure

2. transport molecule for various things (thyroid/fat soluble hormones, Ca, MG, Fe, etc)

3. Anti-oxidant activity

4. Buffers pH

What are the 3 levels of albumin concentration and 1 unique albumin condition?

hyperalbuminemia: increased by dehydration & not clinically significant

hypoalbuminemia: decreased by inflammation response, impaired synthesis in liver, or malnutrition

analbuminemia: absence of albumin that’s asymptomatic

bisalbuminemia: when a person has 2 different types of serum albumin → 2 peaks on serum protein electrophoresis graph

Where are most Alpha and Beta Globulins synthesized?

In the liver

What are the 4 Alpha-1 Globulins and their key characteristics?

1. α1-Antitrypsin: Protease & neutrophil esterase inhibitor. Decreased in emphysema & cirrhosis

2. α1-Fetoprotein: Protects developing fetus from mother’s immune attacks. Deficiency of maternal AFP → increased risk of Down’s/Edwards syndrome

3. α1-Antichymotrypsin: Protease inhibitor that increases w/ inflammation response. Deficiency of ACT → increased risk of liver disease, Parkinson’s, and Alzheimer’s

4. α1-Acid glycoprotein: Inactivates progesterone & binds with basic drugs

What are the 3 Alpha-2 globulins & their key characteristics?

1. Haptoglobin: Binds free Hgb & conserves iron. Decreased in hemolytic anemia

2. Macroglobulin: Protease inhibitor & binds to hormones like insulin. Increased in liver & renal disease

3. Ceruloplasmin: Binds with copper (90%). Decreased in Wilson’s disease

What the Alpha-1 and Alpha-2 globulins positive or negative acute phase proteins?

positive

What type of globulin is fibrinogen and what type of APP is it?

γ and β globulins

positive acute phase protein

Where is fibrinogen seen in plasma electrophoresis?

in between β and γ zone as a spike

What are the 5 β globulins?

Transferrin, Hemopexin, Complement, C-Reactive Protein (CRP), Microglobulin

What is the primary function of Transferrin? When do transferrin levels increase?

transport iron to and from storage sites

increase in IDA, pregnancy, and estrogen therapy

What type of APP is transferrin? What 3 scenarios do transferrin levels decrease?

negative APP

liver disease, malnutrition, nephrotic disease

What are the 2 primary functions of Hemopexin?

Bind to free heme from hemoglobin/myoglobin breakdown

Carries hemoglobin to liver to be destroyed/recycled

What type of APP is hemopexin? What scenarios does hemopexin increase & decrease?

positive APP

increases: muscular dystrophy, Type 1 diabetes, melanomas

decrease: hemolytic anemias

What is the primary function of complement? What type of APP is it?

To trigger & amplify inflammatory responses

positive APP

What scenarios cause complement to be decreased?

malnutrition, lupus, and intravascular coagulopathies

What is the primary function of C-Reactive Protein (CRP)? What is it a risk factor for?

First response APP to inflammatory diseases

cardiovascular disease (high sensitivity CRP used to assess cardiac risk)

What is the primary function of microglobulin? Where are they found?

Help the immune system identify infected/abnormal cells

on the surface of lymphocytes

What type of APP are microglobulins?

positive APP

Memorize the structure of immunoglobulins. Where are they synthesized?

okay

B-cell lymphs

What are the causes of hypoproteinemia and hyperproteinemia?

hypo: renal disease leakage into GI tract or malnutrition

hyper: dehydration or Bence Jones protein

What are Bence Jones proteins and what are they indicative of?

An increased [ ] of free igG light chains

multiple myeloma (blood cancer formed in plasma cells)

What is unique about Bence Jones proteins related to heating?

Precipitate when heated to 40-60 ^oC and redissolve when heated to 100 ^oC

What are the normal and significant concentrations of proteinuria? What is the process of measuring urine protein?

normal: ≤ 150 mg/day

significant: >300 mg/day

Measurement based on 24-hour urine collection (1st specimen discarded, rest consecutively collected)