chem unit 2 chapter 9

Preamble

• PowerPoints are general overviews, only to assist in taking notes during video lectures
• PowerPoints do not contain detailed information required for unit exams
• Students are responsible for reading and studying the textbook to answer unit objectives
• Unit objectives are the student's study guide
• Test questions are based on unit objectives found in the textbook, not the PowerPoint

Introduction

• Proteins are complex polymers of amino acids, present in all living organisms
• Each protein is composed of a maximum of 20 different amino acids in varying numbers and sequences
• All proteins contain carbon, hydrogen, oxygen, and nitrogen and some also contain sulfur

Protein Structure (a)

• Amino acids contain an amino group (NH2), a carboxyl group (COOH), hydrogen, and an R group (a radical or side chain)
• The formula for an amino acid is RCH(NH2)COOH
• (A diagram of an amino acid structure is included).

Protein Structure (2)

• Amino acids are amphoteric, containing two ionizable sites
• A proton-accepting group (NH2) and a proton-donating group (COOH)
• When both groups are ionized, the amino acid is referred to as an ampholyte or a di-polar ion
• The isoelectric point (pI) is the pH at which the amino acid or protein has no net charge
• The positive charges equal the negative charges
• At a pH greater than the pI, the protein carries a negative charge and at a pH less than the pI, the protein carries a positive charge

Protein Structure (3)

• Peptide bonds form when a molecule of water is split between the carboxyl group of one amino acid and the amino group of another
• Peptide bonds create a covalent bond
• The N-terminal end has the amino-free group
• The C-terminal end has the carboxyl-free group

Protein Structure (4)

• Primary structure: The specific sequence of amino acids in a polypeptide chain
• Secondary structure: The interactions of adjacent amino acids
• Secondary structures include alpha-helices, beta-pleated sheets, and random coils

Protein Structure (5)

• Tertiary structure: The way the polypeptide chain folds to form a three-dimensional structure
• Tertiary structure is mainly determined by interactions between the R-groups of amino acids
• Tertiary structure specifies the chemical and physical properties of a protein
• Quaternary structure: The arrangement of two or more polypeptide chains to form a protein

Protein Structure (6)

• Denaturation: Disruption of bonds holding secondary, tertiary, or quaternary protein structures
• Factors that can cause denaturation: Heat, changes in pH, mechanical forces, exposure to chemicals (like solvents, detergents, and metals), and exposure to ultraviolet light

Protein Metabolism

• Dietary proteins are digested by proteolytic enzymes in the gastrointestinal tract
• The liver and other organs use amino acid pools to synthesize bodily proteins
• Amino acids are filtered through the renal glomeruli, then reabsorbed by the renal tubules

Protein Synthesis

• Most plasma proteins are synthesized in the liver and secreted into circulation by hepatocytes
• Double-stranded DNA molecules unfold and one strand serves as a template for messenger RNA (mRNA)
• mRNA carries the code from the nucleus to the cytoplasm
• mRNA attaches to ribosome receptor proteins
• Amino acid linked to transfer RNA (tRNA) matches the corresponding codon on the mRNA
• The next amino acid in the sequence is added
• The cycle repeats until the protein is complete

Protein Functions

• Proteins maintain water distribution between cells and tissues
• Decreased protein levels lead to decreased osmotic pressure
• Coagulation proteins are important for maintaining hemostasis
• Some proteins transport various ligands to needed locations

Box 9-1 Protein Functions

• Maintenance of colloidal osmotic pressure and water distribution
• Structural components (collagen, keratin)
• Transport proteins (transferrin, albumin, thyroid binding globulins)
• Hormones
• Enzymes
• Peptide hormones, insulin
• Coagulation factors
• Hemoglobin
• Antibodies

Aminoacidopathies (a)

• Inherited disorders of amino acid metabolism
• Over 100 aminoacidopathies have been identified

1. Alkaptonuria: A rare inherited disease that leads to a buildup of homogentisic acid in the tissues due to a defect in homogentisic acid oxidase (HGO). Leads to a darkening of body tissues.
2. Cystinuria: A defect in the amino acid transport system that causes cystine to be insoluble. This can lead to the formation of urinary calculi (kidney stones).

Aminoacidopathies (b)

3. Maple Syrup Urine Disease (MSUD) A defect in the branched chain a-ketoacid decarboxylase enzyme leading to the inability to metabolize leucine, isoleucine, and valine. This results in a distinctive odor to the urine and requires a special controlled protein diet to avoid neurological problems.
4. Phenylketonuria (PKU) An inherited condition where the body cannot metabolize phenylalanine. This leads to accumulation of phenylalanine and requires a restricted diet to avoid brain damage.

Specific Plasma Proteins (a)

• Proteins are categorized into 2 groups

1. Albumin
2. Globulin

• Globulins are further divided into a₁, a₂, β, and γ globulins

Specific Plasma Proteins (2)

• Prealbumin/Transthyretin: A transport protein for thyroxine, triiodothyronine (thyroid hormones) and retinol (vitamin A)
• Prealbumin is helpful in identifying poor protein intake. Decreased Prealbumin indicates insufficient protein intake.
• Decreased levels are also associated with acute inflammatory response, liver disease, nephrotic syndrome, and other protein-losing renal diseases

Specific Plasma Proteins (b)

• Albumin: Synthesized in the liver and makes up a large portion of serum protein
• Albumin helps maintain plasma colloidal osmotic pressure and transports a wide variety of ligands
• Hypoalbuminemia: a decrease in albumin levels, often due to increased catabolism from tissue damage or inflammation

Functions of Albumin

• Maintain plasma colloidal osmotic pressure
• Binds and transports various ligands (bilirubin, long-chain fatty acids, therapeutic drugs)
• Serves as an endogenous source of amino acids
• Plays a role in acid-base balance
• Exhibits pro-and anti-coagulatory effects

Hypoalbuminemia (a of 2)

• Increased catabolism due to tissue injury or inflammation
• Impaired synthesis of protein
• Diminished intake, malnutrition, malabsorption.
• Increased protein loss due to Nephrotic syndrome, chronic glomerulonephritis, diabetes mellitus/diabetic nephropathy, and extensive burns

Globulins (a)

• α₁-globulin: Primarily a₁-antitrypsin (AAT), crucial in neutralizing leukocyte elastase and collagenase
• AAT deficiency causes emphysema, and occasionally juvenile hepatic cirrhosis

Globulins (b)

• α₁-acid glycoprotein (Orosomucoid): An acute-phase reactant (APR) that increases during inflammation, often seen in rheumatoid arthritis, cancer, and pneumonia
• Alpha-fetoprotein (AFP): A fetal protein, useful in antenatal diagnosis of neural tube defects and as a tumor marker for hepatocellular cancer and germ cell tumors

Globulins (c)

• α₂-globulin: Haptoglobin (Hp), an acute-phase reactant that binds free hemoglobin in plasma, preventing its loss in urine and aids in the inflammatory response
• Ceruloplasmin (Cp), a copper-transport protein, found primarily in the liver, important for copper metabolism

Globulins (d)

• a₂-macroglobulin (AMG) : a type of globulin found in high concentrations in cases such as nephrotic syndrome and liver disease

Globulins (e)

• β-globulin: Transferrin is a major β-globulin that transports iron, crucial for iron-deficient anemia diagnosis
• Hemopexin: Involved in heme removal from circulation, related to hemoglobin breakdown
• B-Lipoproteins: A type of lipoprotein, that transports cholesterol

Globulins (f)

• β₂-microglobulin (BMG): Component of the MHC (Major Histocompatibility Complex) found in all nucleated cells, increased in conditions like renal failure and certain cancers
• CRP: C-reactive protein is an acute-phase reactant, which responds to inflammation, infection, and tissue injury.

Globulins (g)

• γ-globulin: Immunoglobulins (Ig) are antibodies, including IgM, IgG, IgA, IgD, and IgE.
• IgM: The largest immunoglobulin, produced during the primary immune response
• IgG: The most abundant immunoglobulin, crucial for combating bacteria and viruses
• IgA: Found in secretions like tears, saliva, milk, and gastrointestinal/bronchial fluids
• IgD: Function unknown
• IgE: Associated with allergic reactions, and hypersensitivity reactions

Hyperproteinemia

• Associated with a positive nitrogen balance
• Dietary nitrogen intake is more than excretion or loss.
• Usually occurs from hemoconcentration or dehydration

Hypoproteinemia

• Causes a negative nitrogen balance
• Due to excretion of nitrogen exceeding intake or synthesis
• Often due to an increase in plasma water volume or hemodilution

Hyperproteinemia (causes)

• Hemoconcentration/Dehydration
• Inadequate water intake
• Excess sweating
• Vomiting
• Salt-losing syndromes
• Diarrhea
• Addison's disease
• Diabetic ketoacidosis
• Increased globulins
• Multiple myeloma
• Waldenstrom's macroglobulinemia
• Chronic inflammatory conditions
• HIV/AIDS

Hypoproteinemia (causes)

• Increase in plasma water volume- Hemodilution
• Water intoxication
• Salt-retention syndromes
• Massive intravenous infusions
• Increased protein loss (kidneys, gastrointestinal tract, and skin)
• Nephrotic syndrome
• Blood loss
• Burn patients
• Trauma
• Decreased protein synthesis
• Liver disease
• Immunodeficiency disorders

Total Protein Methodologies (a of 5)

• Biuret: Relies on the presence of peptide bonds in proteins.
• A solution of protein reacts with cupric ions in an alkaline medium to form a violet-colored chelate

Total Protein Methodologies (b of 5)

• Biuret Reagents:
• Sodium potassium tartrate: Prevents precipitation of cupric ions
• Copper sulfate: Provides cupric ions
• Potassium iodide: Antioxidant stabilizing cupric ions
• Sodium hydroxide (NaOH): Provides the alkaline pH

Total Protein Methodologies (c of 5)

• Refractometry: Measures the refractive index of a solution.
• A rapid measure of protein concentration.
• Dye-binding method:
• Coomassie Blue G-250: Binds to proteins, causing a shift in absorbance from 465-595 nm

Total Protein Methodologies (d of 5)

• Reference Range: For healthy adults is 6.0-8.3 g/dL.

A/G Ratio

• Globulin concentration calculated by subtracting albumin from total protein
• Ratio calculated by dividing albumin concentration by calculated globulin concentration

Urinary Proteins

• Originate from blood filtration through the renal glomeruli and not reabsorbed by the renal tubules
• Diagnosed using urine reagent test strips
• Yellow color in the absence of protein, turns from green to blue as the protein concentration increases

Cerebrospinal Fluid Protein

• CSF is a clear, colorless fluid.
• Contains small amounts of glucose and protein
• Reference range: 15-45 mg/dL
• Elevated levels indicate various conditions like meningitis, encephalitis, subarachnoid hemorrhage, tumors, multiple sclerosis, Guillain-Barre syndrome, or brain abscesses

Albumin Methodologies (a of 2)

• Albumin methodologies are based on binding of albumin with anionic dyes
• Bromcresol green (BCG)
• Bromcresol purple (BCP)
• Reference range for Albumin: 3.4-5.0 g/dL

Albumin Methodologies (b of 2)

• Requirements of dye-binding methods
• Specific binding of the dye to albumin in the presence of serum or plasma proteins
• High binding affinity between the dye and albumin
• Substantial shift in the absorption wavelength of the dye in the bound form
• Absorption maximum for the bound form at a wavelength distinct from bilirubin and hemoglobin

Protein Electrophoresis (1 of 2)

• Methodology for separating proteins to distinguish their charges and sizes
• Proteins are ampholytes (move to anode or cathode based on their charge) separated in a liquid medium under an electric field
• Performed on serum to avoid complicating factors like fibrinogen
• Bands fixed by immersing the strip in an acid medium

Protein Electrophoresis (2 of 2)

• A normal serum protein electrophoresis (SPE) display 5 distinct bands.
• The distribution (percent) of each band (by multiplying % of the band by Total Protein) is written as g/dL
• Display of abnormalities can help in diagnosis.

Common Abnormal Protein Electrophoresis Patterns (1 of 3)

• Fusion of the β-γ bands (bridging): often due to cirrhosis, chronic infections, autoimmune disorders, or nephrotic syndrome

Common Abnormal Protein Electrophoresis Patterns (2 of 3)

• Acute phase reaction: Increases positive acute phase proteins (AAPs), including a₁-proteins (like a₁-antitrypsin, and a₁-acid glycoprotein), and a₂-proteins (like haptoglobin, ceruloplasmin, and a₂-macroglobulin) and β-proteins (like fibrinogen, and C-reactive protein)

Common Abnormal Protein Electrophoresis Patterns (3 of 3)

• Causes of Acute Phase Reaction (positive AAPs): infection, tumor growth/malignancy, rheumatoid arthritis, hepatitis, surgery, trauma, burns, and myocardial infarction

Abnormal Protein Electrophoresis Patterns

• Multiple myeloma: A cancer of plasma cells that shows up on electrophoresis due to non-functional paraproteins and an elevated y-globulin concentration

Postamble

• Read the textbook for detailed information to answer unit objectives
• Use unit objectives as a study guide
• All test questions are from the textbook, relating to the unit objectives

Test your knowledge on the functions of albumin and the principles of protein electrophoresis. This quiz covers the significance of albumin in the human body, common causes of hypoalbuminemia, and key features of α1-antitrypsin deficiency. Ideal for students studying biochemistry and clinical pathology.