Endemic goiter is caused by hypertrophy of the thyroid due to a lack of iodine in the diet. Which of the following is a related physical symptom that could be observed in patients?

Antimicrobial peptides

Reasoning:

Dermcidin and cathelicidin are part of the body's innate immune system. They are antimicrobial peptides (AMPs)—small proteins secreted by epithelial cells (especially in the skin) that help protect against a wide range of pathogens.

1. What Are Antimicrobial Peptides?

• Short proteins that disrupt microbial membranes.
• Active against bacteria, viruses, and fungi.
• Provide rapid, nonspecific defense as part of innate immunity.

2. Functions of Dermcidin and Cathelicidin:

• Dermcidin:
  • Secreted by sweat glands in the skin.
  • Kills bacteria on the skin surface by disrupting their membranes.
• Cathelicidin (LL-37 in humans):
  • Found in various tissues, including skin, lungs, and the gastrointestinal tract.
  • Neutralizes bacteria and modulates immune responses (e.g., reduces inflammation).

3. Why the Other Options Are Incorrect:

• B. Chemical messengers: Typically refers to hormones or cytokines, not AMPs.
• C. Neurotransmitters: Involved in nerve signaling (e.g., dopamine, serotonin), unrelated to innate immunity.
• D. Digestive enzymes: Break down food (e.g., amylase, pepsin), not involved in pathogen defense.

4. Clinical Relevance

• Wound Healing: Cathelicidin plays a vital role in promoting tissue repair and regeneration.
• Skin Disorders: Low levels of antimicrobial peptides are associated with conditions such as eczema and psoriasis.
• Infections: Some pathogens, like Streptococcus pyogenes, can evade these peptides, allowing them to cause infections.

Carrying oxygen to other body cells.

Reasoning

Red blood cells (RBCs), also known as erythrocytes, are specialized cells in the blood with the primary role of transporting oxygen from the lungs to the tissues throughout the body. This function is critical for cellular respiration and energy production in all body cells.

1. Structure and Function:
   • RBCs are biconcave in shape, increasing their surface area for gas exchange.
   • They are filled with hemoglobin, a protein that binds oxygen in the lungs and releases it in tissues.
2. Oxygen Transport:
   • In the lungs, oxygen molecules bind to hemoglobin in the red blood cells.
   • RBCs then circulate through the bloodstream, delivering oxygen to cells for metabolism.
   • They also help transport carbon dioxide (a waste product) from tissues back to the lungs.
3. Why the Other Options Are Incorrect:
   • 1 (Fighting infection): This is the function of white blood cells (leukocytes).
   • 2 (Creating blood clots): This is primarily the role of platelets (thrombocytes) and clotting proteins.
   • 4 (Responding to antigens): This is part of the immune response, mainly involving white blood cells, particularly lymphocytes.

Fallopian tubes

Reasoning:

Fertilization in humans typically occurs in the fallopian tubes, also known as uterine tubes or oviducts. These are the narrow tubes that connect the ovaries to the uterus and serve as the site where the sperm meets the egg.

Here's how fertilization happens:

1. Ovulation:
   • An ovary releases a mature egg (ovum) during ovulation.
2. Egg enters the fallopian tube:
   • The fimbriae (finger-like projections at the end of the fallopian tube) help guide the egg into the tube.
3. Fertilization:
   • If sperm are present, fertilization typically occurs in the ampulla, the widest section of the fallopian tube.
   • The sperm penetrates the egg, forming a zygote.
4. Zygote travels to uterus:
   • The fertilized egg continues down the tube and enters the uterus, where it may implant in the uterine lining and develop into an embryo.

Other Options Explained:

• Ovaries: Produce and release eggs but are not where fertilization takes place.
• Vagina: The entry point for sperm during intercourse; not involved in fertilization directly.
• Uterus: The site of implantation and development after fertilization, but fertilization itself does not occur here.

Clinical Relevance:

• Ectopic pregnancy: If the embryo implants in the fallopian tube (often due to scarring or blockage), it can rupture the tube—a medical emergency.
• IVF (In vitro fertilization): Eggs and sperm are combinedoutsidethe body (in a lab), then the embryo is placed directly into the uterus.

Yersinia pestis

Reasoning:

Yersinia pestis is the bacterium responsible for plague, including the bubonic plague. Its primary mode of transmission is through bites from fleas, particularly rat fleas (Xenopsylla cheopis) that have fed on infected rodents.

1. Pathogen Overview – Yersinia pestis:
   • Gram-negative bacterium.
   • Causes bubonic, septicemic, and pneumonic plague.
   • Historically associated with pandemics such as the Black Death.
2. Transmission Mechanism:
   • Fleas ingest the bacteria by biting infected rodents.
   • The bacteria multiply in the flea's gut, eventually blocking it.
   • When the flea bites a human, it regurgitates infected material into the bite wound.
   • Human infection then spreads from the bite site, typically to lymph nodes.

Why the Other Options Are Incorrect:

• 1. Corynebacterium diphtheriae
  • Causes diphtheria.
  • Transmitted via respiratory droplets, not fleas.
• 2. Neisseria meningitidis
  • Causes bacterial meningitis.
  • Spread by saliva and respiratory secretions.
• 3. Plasmodium falciparum
  • Causes the most severe form of malaria.
  • Transmitted by female Anopheles mosquitoes, not fleas or rats.

Generate a hypothesis.

Reasoning:

Before beginning any experiment, a researcher must first formulate a hypothesis—a testable prediction or explanation based on prior knowledge or observations. This hypothesis guides the entire experimental design and helps determine what data will be collected.

1. Generating a Hypothesis:
   • Provides a clear focus and purpose for the research.
   • Helps define variables and expected outcomes.
2. Why Other Steps Come Later:
   • 1. Designing experimental procedures depends on the hypothesis to determine what methods are appropriate.
   • 2. Applying SI units is part of measurement but comes after the experiment is planned.
   • 4. Selecting laboratory equipment occurs once the procedures and measurements are decided.
3. Examples of Hypotheses:
   • Biology: "An increase in CO₂ concentration will enhance the growth rate of plants."
   • Chemistry: "Raising the temperature will speed up reaction X."

Steps in the Scientific Method

1. Observation
   Notice a phenomenon or pose a question based on curiosity or prior knowledge.
   Example: "Plants grow taller in sunlight than in shade."
2. Research Background Information
   Review existing studies and information to understand what is already known.
3. Formulate a Hypothesis
   Create a testable and falsifiable prediction about the relationship between variables.
   Format: "If [independent variable], then [dependent variable]."
   Example: "If plants receive more sunlight, then their growth rate will increase."
4. Design the Experiment
   • Identify variables:
     • Independent variable (what you change, e.g., sunlight exposure)
     • Dependent variable (what you measure, e.g., plant height)
     • Control variables (constants like water and soil type)
   • Plan methods to reduce bias, such as randomization or blinding.
5. Select Equipment and Materials
   Choose appropriate tools and ensure measurements follow SI units (e.g., meters, grams).
6. Conduct the Experiment
   Collect data carefully and consistently.
   Repeat trials to improve reliability.
7. Analyze Data
   Use statistical methods to evaluate whether the data supports the hypothesis.
   Visualize findings with graphs or tables.
8. Draw Conclusions
   Interpret the results relative to the hypothesis.
   Consider any limitations or errors.
9. Communicate Findings
   Share results through publications or presentations for peer review.
10. Iterate
    Refine the hypothesis or experimental design based on new insights or feedback.

Atoms are made up of protons, neutrons, and electrons:

• Protons and neutrons are located in the nucleus and have similar masses (~1 atomic mass unit each).
• Electrons are much smaller in mass (about 1/1836 the mass of a proton) and orbit the nucleus.

Since protons and neutrons are both relatively heavy compared to electrons, they account for almost all of the atom's mass. Therefore, neutrons do contribute significantly to atomic mass—just like protons.

Why the Other Options Are Incorrect:

1. The mass of each electron is the same as the mass of each proton.

• Incorrect.
• Electrons are much lighter than protons (about 1/1836 the mass of a proton).

3. Isotopes of an element differ in the number of protons in the nucleus.

• Incorrect.
• Isotopes have the same number of protons (same element) but different numbers of neutrons.
• Example: Carbon-12 vs. Carbon-14 — both have 6 protons, but different neutron counts.

4. The amount of charge on a proton is greater than the amount of charge on an electron.

• Incorrect.
• A proton has a +1 charge, and an electron has a -1 charge.
• Their charges are equal in magnitude but opposite in sign.

Proteases (also called peptidases or proteinases) are enzymes that digest or break down proteins by hydrolyzing the peptide bonds between amino acids. Since enzymes themselves are proteins, proteases can digest enzymes just like any other protein substrate.

Explanation:

What Proteases Do:

• Target proteins, including enzymes.
• Break peptide bonds.
• Convert large proteins into smaller peptides or amino acids.
• Examples: Pepsin, trypsin, chymotrypsin.

So if you put any protein — even another enzyme — in the presence of active proteases, it will get digested.

Why the Other Options Are Incorrect:

• A. Endonucleases: These cut nucleic acids (DNA or RNA) at specific internal sites. They don’t affect proteins or enzymes.
• B. Lipases: These digest lipids/fats, not proteins or enzymes.
• C. Kinases: These are enzymes that add phosphate groups to other molecules (phosphorylation). They do not digest anything.

Clinical Relevance of Proteases

Proteases in the Human Body:

• Stomach:
  • Pepsin breaks down proteins in an acidic environment (low pH).
• Pancreas & Small Intestine:
  • Trypsin and chymotrypsin function in the alkaline environment of the small intestine to continue protein digestion.
• Lysosomes (inside cells):
  • Cathepsins help break down and recycle intracellular proteins.

Medical Applications of Proteases:

• Enzyme Supplements:
  • Patients with pancreatic insufficiency (e.g., cystic fibrosis, chronic pancreatitis) may need digestive enzyme therapy.
• Protease Inhibitors in Antiviral Therapy:
  • Drugs like ritonavir are used to block viral proteases (e.g., in HIV), stopping viral replication.

Nursing Considerations:

• Monitor for Signs of Malabsorption:
  • Watch for steatorrhea (fatty stools), weight loss, and nutrient deficiencies in patients with enzyme deficiencies.
• Patient Education:
  • Teach patients to take pancreatic enzyme replacements with meals to improve digestion and nutrient absorption.

Fun Fact:

• Bacterial Proteases in Wound Care:
  • Enzymes like collagenase (from bacteria) are used in wound debridement to remove dead tissue and promote healing.

Pepsin is a critical digestive protein that accelerates the breakdown of dietary proteins into smaller peptides. Its classification as an enzyme stems from its biological role as a catalyst, its proteinaceous nature, and its specific function in the stomach. Below is a detailed explanation of why pepsin is an enzyme and how it operates:

Definition and Role of Pepsin:

Enzyme Nature:

• • Pepsin is aproteolytic enzyme(a type of hydrolase) that cleaves peptide bonds in proteins.
  • Like all enzymes, itlowers activation energyfor protein digestion, speeding up the reaction without being consumed.

Production and Activation:

• • Secreted by gastric chief cells as inactivepepsinogen.
  • Activated byHClin the stomach (pH ~1.5–2), which unfolds pepsinogen to expose its active site.

2. Why It’s Not Other Options:

2. Carbohydrate:

• • Carbohydrates (e.g., sugars, starch) are energy sources or structural molecules (e.g., cellulose). Pepsin digests proteins, not carbs.

3. Nucleic Acid:

• • Nucleic acids (DNA/RNA) store genetic information. Pepsin has no role in nucleotide metabolism.

4. Lipid:

• • Lipids (fats) are broken down bylipases, not pepsin.

3. Key Characteristics of Pepsin as an Enzyme

• Substrate Specificity:
  Pepsin primarily targets peptide bonds next to hydrophobic or aromatic amino acids, such as phenylalanine and tyrosine.
• Optimal Conditions for Activity:
  • Functions best in an acidic environment (maintained by stomach acid).
  • Becomes inactive or denatured at neutral or alkaline pH, such as in the duodenum.
• Clinical Significance:
  • Low levels of pepsin or hydrochloric acid (HCl): Can cause protein malabsorption, often seen in conditions like hypochlorhydria (low stomach acid).
  • Excess pepsin: May contribute to GERD (gastroesophageal reflux disease) by damaging the esophageal lining during acid reflux.

4. Comparison with Other Digestive Enzymes



The classification of a nucleotide as a purine or pyrimidine is based solely on the structure of its nitrogenous base, not on the sugar or phosphate group.

1. Nitrogen Base – The Defining Component:

Purines have a double-ring structure and include:

• Adenine (A)
• Guanine (G)

Pyrimidines have a single-ring structure and include:

• Cytosine (C)
• Thymine (T) in DNA
• Uracil (U) in RNA

Thus, the size and structure of the nitrogen base define whether a nucleotide is a purine or a pyrimidine.

Why Other Options Are Incorrect:

• Ribose sugar: Determines if the nucleotide is RNA-based (ribose) but not purine or pyrimidine.
• Deoxyribose sugar: Determines if the nucleotide is DNA-based (deoxyribose), again not related to base type.
• Phosphate group: Involved in forming the backbone of nucleic acids but not in determining the class of nitrogenous base.

Whether a nucleotide is classified as a pyrimidine or purine depends on its nitrogenous base. Pyrimidines (such as cytosine, thymine, and uracil) have a single-ring structure, while purines (adenine and guanine) have a double-ring structure. This structural difference is what determines the classification.

The ribose sugar and deoxyribose sugar (A & B) define whether the nucleotide is part of RNA or DNA, respectively, while the phosphate group (D) helps form the backbone of the nucleic acid but does not influence whether the nucleotide is a purine or pyrimidine.

RNA

Reasoning
To determine which molecule contains ribose sugar, we need to understand the difference between ribose and deoxyribose, the two main sugars found in nucleotides:

Key Differences:

• Ribose: Found in RNA, ATP, and GMP. It has a hydroxyl group (–OH) on the 2' carbon of the sugar.
• Deoxyribose: Found in DNA. It lacks the –OH on the 2' carbon (hence "de-oxy").

Let’s examine each choice:

1. DNA (Deoxyribonucleic Acid)

• Contains deoxyribose, not ribose.
  Incorrect.

2. ATP (Adenosine Triphosphate)

• Although ATP does contain ribose, its primary function is as an energy molecule, not a structural component of nucleic acids.
• While technically true, ATP is not the best answer in this context, because the question implies a nucleic acid context. Technically correct, but not the best answer for "nucleotide in nucleic acid."

3. RNA (Ribonucleic Acid)

• Contains ribose sugar in its nucleotide backbone.
  Correct Answer.

4. GMP (Guanosine Monophosphate)

• Also contains ribose. However, like ATP, it is not specifically a nucleic acid (RNA or DNA), but rather a nucleotide on its own. Correct chemically, but not the best answer in terms of the structural nucleotide within a nucleic acid.

RNA is the correct answer because its nucleotides inherently contain ribose and it is the nucleic acid built from ribose-containing nucleotides. While ATP and GMP do contain ribose, RNA is the most direct and complete answer to the question.