Peptide Synthesis and Cellular Structures
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Questions and Answers

What is the initial form of a peptide before it is processed in the rough endoplasmic reticulum?

  • Peptide
  • Propeptide
  • Prepropeptide (correct)
  • Amino acid

Which cellular structure is primarily responsible for synthesizing polypeptides from mRNA?

  • Golgi apparatus
  • Smooth endoplasmic reticulum
  • Transport vesicle
  • Rough endoplasmic reticulum (correct)

What happens to the polypeptide after it is synthesized in the rough endoplasmic reticulum?

  • It is transported directly to the Golgi apparatus without modification.
  • It gets cleaved into amino acids.
  • It is packaged into a secretory vesicle. (correct)
  • It is transformed into a propeptide.

What is the role of the Golgi apparatus in peptide synthesis?

<p>Processing and modification of peptides (A)</p> Signup and view all the answers

Which of the following statements about the smooth endoplasmic reticulum is true regarding peptide synthesis?

<p>It is involved in the transport and processing of propeptides. (B)</p> Signup and view all the answers

What is the initial form of a peptide before it undergoes processing in the rough endoplasmic reticulum?

<p>Propeptide (A)</p> Signup and view all the answers

Which organelle is primarily responsible for peptide synthesis?

<p>Rough endoplasmic reticulum (A)</p> Signup and view all the answers

What is the role of the Golgi apparatus in the peptide synthesis process?

<p>Modifying and packaging propeptides (A)</p> Signup and view all the answers

What triggers the synthesis of steroids?

<p>Demand-based synthesis (B)</p> Signup and view all the answers

What are steroid ligands generally derived from?

<p>Cholesterol molecules (D)</p> Signup and view all the answers

During peptide synthesis, which form does the prepropeptide eventually become?

<p>Peptide (D)</p> Signup and view all the answers

What type of vesicles transport cleaved amino acids?

<p>Transport vesicles (A)</p> Signup and view all the answers

Which of the following processes is directly associated with the rough endoplasmic reticulum?

<p>Polypeptide synthesis (B)</p> Signup and view all the answers

Which molecule is the direct product of tyrosine hydroxylation?

<p>L-Dihydroxyphenylalanine (B)</p> Signup and view all the answers

What enzyme converts L-Dihydroxyphenylalanine to dopamine?

<p>Catecholamine decarboxylase (D)</p> Signup and view all the answers

Which of the following hormones is formed from norepinephrine?

<p>Epinephrine (B)</p> Signup and view all the answers

What is the primary storage method for peptide hormones within the cell?

<p>Secretory vesicles (A)</p> Signup and view all the answers

What process is used to release hormones from secretory vesicles?

<p>Exocytosis (A)</p> Signup and view all the answers

Which term best describes the initial form of a hormone before processing?

<p>Preprohormone (D)</p> Signup and view all the answers

What is the primary method of communication used by the endocrine system?

<p>Hormones traveling through the bloodstream (B)</p> Signup and view all the answers

Which of the following statements is true regarding catecholamines?

<p>They include dopamine, norepinephrine, and epinephrine. (D)</p> Signup and view all the answers

What is the function of phenylethanolamine N-methyltransferase (PNMT)?

<p>Converts norepinephrine to epinephrine (D)</p> Signup and view all the answers

Which of the following accurately describes how signals are transmitted in the nervous system?

<p>Signals can be transmitted through both electrical and chemical means. (A)</p> Signup and view all the answers

What phenomenon occurs within a neuron that allows signals to travel along its length?

<p>Action potentials (C)</p> Signup and view all the answers

What is the role of neurotransmitters in neuronal communication?

<p>To transmit signals across the synapse to the target cell (C)</p> Signup and view all the answers

How do the distances covered by signals differ between the endocrine and nervous systems?

<p>Nervous system signals can be instant while endocrine signals take time to reach their targets. (A)</p> Signup and view all the answers

What distinguishes a paracrine chemical messenger from autocrine chemical messengers?

<p>Autocrine messengers signal the same cell that secretes them. (A)</p> Signup and view all the answers

Which of the following is an example of a neurotransmitter?

<p>Serotonin (D)</p> Signup and view all the answers

Neurohormones are produced by which type of cells?

<p>Neurons (B)</p> Signup and view all the answers

Which of the following statements accurately defines a hormone?

<p>A messenger produced by endocrine cells and secreted into the blood. (B)</p> Signup and view all the answers

What is the primary role of paracrine messengers?

<p>To initiate a local response in nearby cells. (B)</p> Signup and view all the answers

Which of the following is NOT a function of neurotransmitters?

<p>Regulate metabolic processes in the body. (D)</p> Signup and view all the answers

What differentiates neurohormones from general hormones?

<p>They are produced by neurons instead of endocrine cells. (A)</p> Signup and view all the answers

What is the main example of an autocrine chemical messenger?

<p>Histamine (D)</p> Signup and view all the answers

What is the first step lipophilic hormones take to exert their effects on target cells?

<p>Diffusion through the extracellular fluid (A)</p> Signup and view all the answers

Which component binds to lipophilic hormones once they have entered the target cell?

<p>Nuclear receptor (B)</p> Signup and view all the answers

What is the function of the hormone-receptor complex in lipophilic hormone action?

<p>To initiate changes in gene expression (C)</p> Signup and view all the answers

Where do lipophilic hormones typically exert their effects within the target cell?

<p>Nucleus (D)</p> Signup and view all the answers

What role does mRNA play in the process initiated by lipophilic hormones?

<p>Translating genes into proteins (A)</p> Signup and view all the answers

How do lipophilic hormones differ from hydrophilic hormones in their method of action?

<p>They diffuse through the cell membrane directly (A)</p> Signup and view all the answers

Which structure is essential for the transport of substances into the nucleus after a lipophilic hormone binds?

<p>Nuclear envelope (D)</p> Signup and view all the answers

What is produced as a result of mRNA translation in the presence of lipophilic hormones?

<p>Proteins that respond to the hormone (C)</p> Signup and view all the answers

Flashcards

Paracrine

A chemical messenger that acts on nearby cells.

Autocrine

A chemical messenger that acts on the same cell that secreted it.

Neurotransmitter

A chemical messenger produced by neurons and released into the synaptic cleft.

Hormone

A chemical messenger secreted by endocrine cells into the bloodstream.

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Neurohormone

A specific type of hormone produced by neurons and released into the bloodstream.

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Histamine

A paracrine messenger involved in inflammatory responses.

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Acetylcholine

A neurotransmitter that is responsible for muscle contraction.

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GABA

A neurotransmitter that inhibits nerve activity.

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Prepropeptide

A signal sequence, typically found at the N-terminus of newly synthesized proteins, that directs them to the endoplasmic reticulum (ER).

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Propeptide

A peptide that has undergone partial processing in the endoplasmic reticulum (ER), usually by the removal of the signal sequence.

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Peptide

The final, functional form of a polypeptide, often after further processing in the Golgi apparatus.

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Rough Endoplasmic Reticulum (RER)

The portion of the endoplasmic reticulum (ER) studded with ribosomes, responsible for protein synthesis and modification.

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Smooth Endoplasmic Reticulum (SER)

The portion of the endoplasmic reticulum (ER) lacking ribosomes, involved in lipid synthesis and detoxification.

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Preprohormone

A precursor molecule that is converted through a series of enzymatic steps to form the final hormone.

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Prohormone

An intermediate molecule formed by the cleavage of a preprohormone. It is closer to the final hormone form but may still require further processing.

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Cleavage

The enzymatic process that breaks down larger proteins into smaller peptides, which may be hormones.

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Secretory vesicle

A type of protein that stores peptides, including hormones, within secretory vesicles.

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Exocytosis

The process by which secretory vesicles fuse with the cell membrane and release their contents (hormones) outside the cell.

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Epinephrine

A specific type of neurohormone produced by the adrenal medulla. Its primary function is to prepare the body for stressful situations, promoting "fight-or-flight" response.

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Polypeptide

A molecule consisting of a chain of amino acids linked together by peptide bonds.

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Peptide synthesis and release

A process where a protein is synthesized and modified, ultimately leading to its secretion from the cell.

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Golgi apparatus

A stack of flattened membrane sacs responsible for further modifying, sorting, and packaging proteins.

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Action potential

Signal transmission within a neuron occurs through electrical impulses called action potentials, travelling along long axons.

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Synapse

The space between neurons where chemical signals are transmitted from one neuron to another.

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Chemical transmission

Signals travel from the axon terminal of one neuron to the dendrite or cell body of the next neuron, across the synaptic cleft.

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Electrical Transmission

Signals are transmitted electrically within the neuron along the axon using action potentials.

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Lipophilic hormone

A type of hormone that can diffuse across the cell membrane.

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Hormone receptor

A protein inside the cell that binds to a specific hormone.

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Diffusion

The process by which a lipophilic hormone moves across the cell membrane and into the cytoplasm.

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Nuclear region

The region inside the nucleus of a cell that contains DNA.

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Hormone response element (HRE)

A specific sequence of DNA that controls the expression of a gene.

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mRNA

A messenger RNA molecule that carries the genetic code from the nucleus to the ribosomes.

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Ribosome

An organelle in the cytoplasm that synthesizes proteins based on the instructions from mRNA.

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Study Notes

Chapter 5: Chemical Messengers

  • This chapter outlines mechanisms of intercellular communication, focusing on chemical messengers.
  • Two general mechanisms for intercellular communication exist: direct and indirect.
  • Direct communication involves gap junctions, allowing direct passage of ions and small molecules between adjacent cells.
  • Indirect communication uses chemical messengers, where a messenger produced by one cell travels to a target cell.

5.1 Mechanisms of Intercellular Communication

  • Gap junctions are composed of membrane proteins; they connect the cytosol of adjacent cells.
  • Particle movement between cells acts as a signal, and communication is direct.
  • Gap junctions are common in smooth and cardiac muscle.
  • Chemical messengers are produced by a source cell, released (often via secretion), travel to a target cell, bind to a receptor on the target cell, and trigger a target cell response. Communication is indirect.

5.2 Chemical Messengers

  • Chemical messengers are classified by function, chemical properties (solubility properties), and chemical classes.
  • Table 5.1 provides a functional classification of chemical messengers.

Messenger Classification by Function

  • Paracrine chemical messengers signal nearby cells; histamine is an example, responsible for inflammation responses.
  • Autocrine chemical messengers signal the same cell that secreted them.
  • Neurotransmitters are produced by neurons, released into the extracellular fluid (ECF) of the synaptic cleft, and examples include acetylcholine, GABA, and serotonin.
  • Hormones are produced by endocrine cells, secreted into the blood via interstitial fluid. Examples are insulin, estrogen, and thyroxine.
  • Neurohormones are a special class of hormones produced by neurons, secreted into the blood. Examples include antidiuretic hormone (ADH) and oxytocin.

Chemical Classification of Messengers

  • Lipophobic ligands (e.g., amino acids, amines, peptides/proteins) are water-soluble and do not cross the cell membrane. Receptors are on the cell membrane

  • Lipophilic ligands (e.g., steroids, eicosanoids) are lipid-soluble, easily cross the cell membrane. Receptors are usually intracellular.

  • Tables 5.2 provides a chemical classification of messengers, outlining chemical properties, location of receptors on target cells, and the functional classification.

Synthesis and Release of Chemical Messengers

  • Lipophobic ligands are synthesized on demand and released immediately from the source cell. Release rate depends on synthesis.
  • Lipophobic ligands are stored in vesicles until needed, released by exocytosis. The release rate is determined by exocytosis.

Steroids

  • Synthesized on demand.
  • Derived from cholesterol molecule.
  • All steroid ligands are similar.

Signal Transduction

  • Messenger binds to a receptor.
  • Binding results in a cell response.
  • Signal transduction is the process of producing a response in the target.

Receptor Binding

  • Specificity, binding is brief and reversible.
  • Affinity: strength of binding
  • Location: Lipophobic ligands bind to receptors on the cell membrane. Lipophilic ligands bind to receptors within the cell.

Receptor Properties

  • One messenger may bind to many receptor types.
  • One target may have many types of receptors.
  • Receptor number per cell varies and is dynamic.

Magnitude of Target Response

  • Concentration of the messenger, number of receptors per target cell, and receptor affinity for the messenger all affect the strength of the response.

Mechanisms: Signal Transduction

  • Intracellular-mediated responses.
  • Membrane-bound receptor-mediated responses.
  • Channel-linked receptors
  • Enzyme-linked receptors
  • G protein-linked receptors

Intracellular-Mediated Response

  • Characteristic of lipophilic ligands (except thyroid hormones).
  • Receptors are found in the cytosol or nucleus.
  • Cell response is via gene activation.

G Protein-Coupled Receptors (GPCRs)

  • G proteins are regulatory proteins that link ECF messenger to:
  • Ion channels
  • Amplifier enzymes
  • The receptor, not the external messenger, binds to guanosine (the G part of a G protein).
  • ECF messenger is the first messenger.

Signal Amplification

  • Small ligand amounts can cause a huge response in the target cell.
  • Each step in signal transduction recruits more participants.
  • Second messengers are characteristic of amplification.

Endocrine Communication

  • The endocrine target secretes a hormone.
  • The hormone enters the blood.
  • The blood spans the distance to the target.

Nervous Communication

  • Nerve cells transmit signals within a neuron via long axons.
  • Nerve cells transmit signals between cells via synapses.
  • Signals in axons are action potentials.
  • Axons via action potentials span the distance to the target.

Table 5.4 Signal Transduction Mechanisms

  • This table provides the signal transduction mechanisms for particular chemical messengers.

  • Table 5.3 provides examples of the second messengers.

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Principles of Human Physiology Chapter 5 PDF

Description

This quiz covers key concepts related to peptide synthesis in eukaryotic cells. Questions focus on the roles of the rough endoplasmic reticulum, Golgi apparatus, and smooth endoplasmic reticulum in the synthesis and processing of peptides. Test your knowledge on the initial forms of peptides and the overall synthesis process.

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