Peptides and Polypeptides Quiz

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Questions and Answers

What is the primary structural characteristic that differentiates peptides from polypeptides?

Polypeptides are formed through non-covalent bonds.

Polypeptides do not have a defined sequence of amino acids.

Peptides contain less than 10 amino acids.

Peptides are made up of fewer than 50 amino acids. (correct)

Which of the following types of peptides is made up of four amino acids?

Tripeptide

Oligopeptide

Dipeptide

Tetrapeptide (correct)

What role do peptides often play in molecular biology?

They serve solely as energy sources.

They act as structural components of DNA.

They act as ligands or signaling molecules. (correct)

They are exclusively used to build carbohydrates.

Which property of peptides makes them potentially useful in food applications?

Antioxidant properties that can enhance food shelf life. Signup and view all the answers

In clinical applications, how can peptides specifically benefit diabetic patients?

By enhancing insulin sensitivity or mimicking insulin action. Signup and view all the answers

What is a common misconception about the function of antimicrobial peptides?

They function solely by lysing bacterial cells. Signup and view all the answers

What is a notable characteristic of oligopeptides regarding their size?

They typically consist of 2 to 10 amino acids. Signup and view all the answers

Which statement about peptide bonds is true?

They involve the carboxyl group of one amino acid and the amino group of another. Signup and view all the answers

Which of the following activities have been attributed to bioactive peptides from food proteins?

Blood pressure-lowering effects Signup and view all the answers

What is a primary function of lactoferricins derived from bovine and human lactoferrin?

Exhibiting antimicrobial properties Signup and view all the answers

Which statement about antioxidant peptides is correct?

Most identified antioxidant peptides come from a-casein. Signup and view all the answers

In the context of food applications, how are many bioactive peptides typically released from host proteins?

During fermentation processes Signup and view all the answers

What advantage does the use of peptides provide in molecular biology?

Peptides facilitate the creation of peptide antibodies without protein purification. Signup and view all the answers

Which of the following peptides is known for its role as an antibiotic?

Polymyxin B Signup and view all the answers

What is the primary structural characteristic of polypeptides?

They consist of many amino acids linked unbranched Signup and view all the answers

Which peptide is a well-known neuropeptide involved in pain mediation?

Substance P Signup and view all the answers

What is the mechanism of peptide bond formation?

Condensation reaction releasing water Signup and view all the answers

Which property allows peptide bonds to stabilize protein structure?

Partial double bond character Signup and view all the answers

Which of these peptides functions as a hormone involved in childbirth?

Oxytocin Signup and view all the answers

What is the role of glutathione in the body?

Regenerating itself after exposure to free radicals Signup and view all the answers

Which peptide is a notable antioxidant that also participates in cellular protection?

Glutathione Signup and view all the answers

Which peptide is known for causing hypertension?

Angiotensin II Signup and view all the answers

Which of the following peptides acts primarily as a sex-peptide in fruit flies?

Sex-peptide Signup and view all the answers

What type of bond is formed to link two amino acids in a peptide?

Peptide bond Signup and view all the answers

How does the presence of peptide hormones affect biological activities?

They are involved in various specific biological activities. Signup and view all the answers

Which peptide is known for being a protective toxin found in mushrooms?

Amanitin Signup and view all the answers

Which amino acids are involved in the synthesis of glutathione?

Cysteine, glycine, and glutamine Signup and view all the answers

Which feature of peptide bonds contributes to their inability to rotate freely?

Rigidity due to double bond character Signup and view all the answers

In molecular biology, how are large peptides typically categorized?

Polypeptides Signup and view all the answers

In which food sources is glutathione particularly abundant?

Beef, broccoli, and spinach Signup and view all the answers

What is the sequence of the tripeptide thyrotropin releasing hormone (TRH)?

Glu-His-Pro Signup and view all the answers

What is the significance of peptide toxins in biology?

They have specific roles in various biological processes. Signup and view all the answers

Which of the following peptides is classified as a nanopeptide and is secreted by the posterior pituitary?

Oxytocin Signup and view all the answers

Which peptide is NOT used for treating bacterial infections according to the information provided?

Boceprevir Signup and view all the answers

What is a primary function of C-peptide measurements in patients with diabetes?

To differentiate between diabetes types Signup and view all the answers

Which of the following is a benefit of collagen peptides?

Promotes healthy aging Signup and view all the answers

What therapeutic use does Enfuvirtide serve?

HIV treatment Signup and view all the answers

Antimicrobial peptides are used for treating which type of infections?

Both Gram-positive and Gram-negative bacterial infections Signup and view all the answers

The use of peptides in molecular biology often serves which purpose?

Studying protein structure and function Signup and view all the answers

What distinguishes type 2 diabetes from type 1 regarding C-peptide levels?

Stable C-peptide levels in type 2 Signup and view all the answers

What condition might C-peptide levels help assess in women with PCOS?

Degree of insulin resistance Signup and view all the answers

Which peptide is specifically indicated for pneumonic cases?

Bacitracin Signup and view all the answers

Inhibitory peptides are utilized in clinical research primarily for?

Inhibition of cancer proteins Signup and view all the answers

Study Notes

Peptides, Polypeptides & Biochemical Importance

Peptides are formed when fewer than 50 amino acids join together via peptide bonds. Alternatively, peptides are short polymers of amino acids. Covalent chemical bonds form between two molecules when the carboxyl group of one molecule reacts with the amino group of another molecule.
Polypeptides are peptides with more than 10 amino acid residues.

Learning Objectives

Students will be able to define peptides and polypeptides, peptide types, and biochemical function by the end of the lecture.

Patient Case Studies

Patient 1: A 16-year-old boy, a mason, presented with polyuria, polydipsia, weight loss (6kg over 3 months). Biochemical evaluations showed fasting plasma glucose (280 mg/dL), postprandial plasma glucose (380 mg/dL), HbA1c (10.5%), and a positive glutamic acid decarboxylase antibody. How to manage?
Patient 2: A 38-year-old woman with type 2 diabetes (6 years), well-controlled on metformin (1 mg twice daily) and gliclazide (40 mg twice daily), was admitted with autoimmune hemolytic anemia. She was started on prednisolone (60 mg/day). Blood glucose monitoring showed fasting glucose (360 mg/dL) and postprandial glucose (420 mg/dL), with negative urine ketones. What advice should be given?

Peptide/Polypeptides

Peptides are polymers of amino acids.
Their structure and functions depend on the nature of the amino acids present, their sequence, and their spatial relationship.
Peptides are relatively small polymers, typically 2–10 amino acids. If 2 amino acids are involved, it's a dipeptide, 3 is a tripeptide, and 10 is a decapeptide. Anything larger than 10 is an oligopeptide. Over 50 is a polypeptide.

Types

The shortest peptide is a dipeptide, made up of two amino acids joined by a peptide bond to form a dipeptide molecule.
Other types include tripeptides and tetrapeptides.

Tetrapeptide Example

A tetrapeptide (e.g., Val-Gly-Ser-Ala) has a marked amino end (L-Valine) and a carboxyl end (L-Alanine).

Peptide Naming

Peptides of defined lengths are named using IUPAC numerical multiplier prefixes.
A monopeptide has one amino acid.
Dipeptide has two, tripeptide three and so on.

Functions or Role of Peptides

Hormones and pheromones: Insulin (sugar uptake), oxytocin (childbirth), sex-peptide (fruit fly mating), etc.
Neuropeptides: Substance P (pain mediator).
Antibiotics: Polymyxin B (Gram bacteria), bacitracin (Gram bacteria).
Protection: Amanitin (mushrooms), conotoxin (cone snails), chlorotoxin (scorpions), etc.
Biologically Important Peptides: Glutathione, Thyrotropin releasing hormone (TRH), Oxytocin, Vasopressin, Angiotenins, Bradykinin, Methionine enkephalin.

Polypeptides

Poly means many.
A polypeptide is a long, continuous, unbranched peptide chain.
Proteins consist of one or more polypeptides arranged in a biologically functional manner and are often bound to cofactors or other proteins.

Peptide Bonds

Amino acids are attached covalently by the carboxyl group (COOH) of one side and the amino group (NH2) of another side.
A peptide bond is formed by an acid-amide bond.
Peptide bonds are formed through condensation reactions, where a water molecule is removed.

Peptide Bond Formation

Amino acids are linked together by condensation reactions between the carboxylic and amino groups of different amino acids.
This results in an amide bond called a peptide bond.
The resulting product is a peptide, named according to the number of amino acids involved (dipeptide, tripeptide, etc.). Peptides greater than 50 amino acids are called polypeptides..

Peptide Bond Characteristics

Peptide bonds are strong and exhibit partial double bond character.
They are resistant to typical denaturing agents like heating, high salt concentrations.
Can be broken by prolonged exposure to strong acids or bases at high temperatures, or specific enzymes (like digestive enzymes).
Peptide bonds are rigid and planar, preventing free rotation, thereby stabilizing protein structure.
Polar hydrogen and oxygen atoms are present, allowing for hydrogen bonds to form between peptide bonds in different parts of the chain.

Individual Peptides

Peptides are widespread in nature and often involved in specific biological activities (e.g., peptide hormones, peptide toxins).

Examples of Peptides

TRH: A tripeptide with Glu, His, and Pro, modified Glu forms pyroglutamic acid.
Oxytocin and Vasopressin (ADH): Nanopeptides (9 amino acids) secreted by the posterior pituitary.
Angiotensin I and II: Peptides (10 and 8 amino acids respectively) causing hypertension.
Glutathione: Widespread in animals, plants and microorganisms composed of L-glutamyl-L-cysteinyl-glycine. Rich in various foods. Plays a role as a coenzyme and antioxidant.
Cysteine, glycine, and glutamine: Produced naturally in the body, master antioxidants, and self-regenerate in the liver after free radical removal. Increasing glutathione can have benefits to strength/endurance and shifting from fat metabolism to muscle development.
Lysine Peptides: Shown to be as effective as lysine in rat growth feeding tests. Suitable for sugar-containing foods that must be heat-treated to retard/delay browning.
Nisin: An antibiotic peptide active against Gram-positive microorganisms. Used as a preservative in cheese and other food products.
Carnosine, Anserine, and Balenine: Peptides in meat extract, containing b-alanine and related histidine compounds.

Peptide Applications

Many peptides are released in vitro or in vivo from animal or plant proteins and perform health-promoting functions beyond basic nutritional needs.
Includes antimicrobial, blood pressure-lowering, cholesterol-lowering, antioxidant and mineral absorption improvement properties.

Overview of Beneficial Effects of Bioactive Peptides from Food Proteins

Includes categories for various activities (antimicrobial, etc.) as well as examples.

Antimicrobial Peptides

Identified in hydrolysates, especially from milk (e.g., lactoferricins).
Derived from bovine/human lactoferrins, a51-casein and a52-casein.
Active against Gram + and Gram - bacteria, yeasts, and fungi.
Disruption of membrane permeability is key for antibacterial action.

Antioxidant Peptides

Found in milk proteins, often encoded in α-casein sequence.
Adding leucine or proline with His-His dipeptide can enhance antioxidant activity and aid synergy with synthetic antioxidants like BHT or BHA.

Food Applications of Bioactive Peptides

Found naturally in some foods long before "bioactive" was a recognized term.
Released during milk fermentation (e.g., cheese ripening).
Generated by gut enzymatic reactions after consuming food sources.

Peptides in Molecular Biology

Used to create peptide antibodies in animals without needing to isolate the proteins of interest.
Aids in mass spectrometry by identifying proteins from peptide masses and sequences.
Often generated through in-gel protein digestion.
Can be used in probes to detect protein-peptide interactions.
Used in clinical research to study effects on cancer proteins or related diseases.

C-Peptide

Used to determine if an individual with diabetes is of Type 1 versus Type 2 origin, or Maturity onset diabetes of the young.
Diagnosed in women with PCOS as a means of determining insulin resistance.
Can diagnose gastrinomas.

Antimicrobial Peptides as Therapeutic Agents

Various peptides used in therapeutic applications (e.g., pneumonia, bacterial infections, HIV).

Benefits of Collagen Peptides

Improved joint health
Enhanced bone strength
Promotes healthy aging
Boosted skin beauty
Supporting connective tissues and preventing injury

Brain Peptides

Certain brain cells have receptors that bind opiates (endorphins).
Dynorphin is a potent peptide with 13 amino acids.
Brain peptide fragments (e.g., met- and leu-enkephalins) reduce intestinal motility.

Doping Tests (Sports Medicine)

Peptide term used for secretagogues (substances that cause another substance to be released) and peptide hormones.

Protein Functional Classification

Proteins functionally categorized as enzymes, contractile, regulation, transportation, support or defense.

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Description

Test your knowledge on the structural differences between peptides and polypeptides. This quiz covers the roles, benefits, and applications of peptides in molecular biology and food science. From understanding sizes to specific functions, engage with questions that deepen your understanding of bioactive peptides.