Fundamentals of Human Biology: Cell Structure

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Questions and Answers

What type of proteins are produced in the endoplasmic reticulum (ER) that are primarily involved in hormone secretion?

Water-soluble proteins

Neurotransmitters

Lipid-based proteins

Transmembrane proteins (correct)

Which function is NOT associated with the smooth endoplasmic reticulum?

Steroid synthesis

Lipid synthesis

Detoxification

Protein folding (correct)

What is the primary role of glucose-6-phosphatase found in the smooth ER regarding blood glucose levels?

Convert glucose-6-phosphate to glucose (correct)

Detoxify harmful substances

Convert glucose to glycogen

Facilitate lipid synthesis

What cellular response occurs due to chemical insult that requires increased detoxification?

Proliferation of smooth ER Signup and view all the answers

Which of the following cells is most likely to have a well-developed smooth endoplasmic reticulum?

Adrenal cortex cells Signup and view all the answers

What are the main products of the rough endoplasmic reticulum aside from proteins?

Digestive enzymes and lysosomal enzymes Signup and view all the answers

Which process involves the conversion of non-carbon sources into glucose in the smooth ER?

Gluconeogenesis Signup and view all the answers

Which of the following types of proteins typically enter the lumen of the endoplasmic reticulum?

Water-soluble proteins Signup and view all the answers

What major component defines the rough endoplasmic reticulum?

Presence of ribosomes on its surface Signup and view all the answers

What is one of the primary roles of smooth endoplasmic reticulum?

Lipid production Signup and view all the answers

Which of the following correctly describes the structure of the endoplasmic reticulum?

A series of interconnected channels and tubules, some forming cisternae Signup and view all the answers

Which of the following functions is NOT associated with the Golgi apparatus?

Lipid synthesis Signup and view all the answers

What process partially reforms the nuclear envelope after cell division?

Utilization of membranes from the rough ER Signup and view all the answers

What defines a specialized form of endoplasmic reticulum, such as sarcoplasmic reticulum?

Its role in calcium ion storage Signup and view all the answers

Which of the following statements accurately describes the relationship between rough and smooth endoplasmic reticulum?

They are part of an interconnected system typically found in the same cell. Signup and view all the answers

What feature contributes to the granulation of rough endoplasmic reticulum?

Attached ribosomes on its cytoplasmic surface Signup and view all the answers

What is one primary function of lysosomes?

Intracellular digestion/removal of unwanted elements Signup and view all the answers

Which component marks proteins for dispersion into lysosomes?

Sugar residues Signup and view all the answers

What is the pH optimum for the enzymes found in lysosomes?

5.0 Signup and view all the answers

What do primary lysosomes fuse with for digestion to occur?

Phagosomes and endosomes Signup and view all the answers

What key role does the Golgi apparatus play concerning lysosomes?

Production of hydrolytic enzymes Signup and view all the answers

Which of the following statements is true about peroxisomes?

They are also called microbodies. Signup and view all the answers

What structural feature distinguishes a secondary lysosome?

Containment of material to be digested Signup and view all the answers

How are hydrolytic enzymes synthesized before reaching lysosomes?

In the rough endoplasmic reticulum Signup and view all the answers

What is the main role of peroxisomes in the cell?

Oxidation of compounds and removal of H+ ions Signup and view all the answers

What substance is produced as a by-product during the oxidation reactions in peroxisomes?

Hydrogen peroxide Signup and view all the answers

Which enzyme is responsible for removing hydrogen peroxide in peroxisomes?

Catalase Signup and view all the answers

In what condition is there typically severe abnormalities in infancy due to defects in peroxisomes?

Zellweger syndrome Signup and view all the answers

How do secretory vesicles release their contents?

Utilizing a process called exocytosis Signup and view all the answers

Which cellular structure do all secretory vesicles arise from?

Golgi apparatus Signup and view all the answers

What triggers the release of insulin from secretory granules in beta cells?

Elevated levels of glucose in the blood Signup and view all the answers

Which type of enzyme in peroxisomes is responsible for the breakdown of fatty acids?

Beta-oxidative enzymes Signup and view all the answers

What specialized function does the sarcoplasmic reticulum serve in muscle cells?

Storage and release of Ca2+ Signup and view all the answers

Which statement about the smooth endoplasmic reticulum is NOT true?

It has ribosomes. Signup and view all the answers

Which of the following is a primary function of the Golgi apparatus?

Modification and sorting of proteins Signup and view all the answers

What is the name of the face of the Golgi apparatus that is closest to the endoplasmic reticulum?

Cis face Signup and view all the answers

What structure within the Golgi apparatus is associated with the transport of proteins?

Cisternae Signup and view all the answers

In muscle contraction, what initiates the process?

Release of Ca2+ from the sarcoplasmic reticulum Signup and view all the answers

How does the Golgi apparatus function in relation to its location within the cell?

It is located between the ER and plasma membrane. Signup and view all the answers

Which statement best describes the relationship between the sarcoplasmic reticulum and smooth endoplasmic reticulum?

The sarcoplasmic reticulum is a specialized form of smooth ER. Signup and view all the answers

What role does the Golgi apparatus play in relation to lysosomes?

It modifies and packages proteins destined for lysosomes. Signup and view all the answers

What is a characteristic of the Golgi apparatus concerning its structure?

It is made up of parallel stacks of curved cisternae. Signup and view all the answers

Study Notes

Cell Structure: Endoplasmic Reticulum (Smooth and Rough), Golgi

Course: Fundamentals of Human Biology
Code: FUNBIO.5
Lecturer: Dr Irene Oglesby
Date: October 3rd, 2024

Learning Outcomes

Discuss the appearance of the endoplasmic reticulum (ER) in the cell.
Discuss the role of smooth ER in cell activities, including lipid production and detoxification.
Describe the structure of rough ER and its role in protein production.
Describe examples of specialized ER, such as the sarcoplasmic reticulum.
List the four major functions of the Golgi apparatus, including the production of primary lysosomes.
Describe the structure and function of peroxisomes in the cell.
Discuss the presence of secretory and zymogen granules in certain cell classes.

Endoplasmic Reticulum (ER)

An elaborate membrane system that occupies up to 50% of the total membrane surface in animal cells.
Called the ER from the Greek word "rete," meaning net.
Extends from the nuclear envelope almost to the plasma membrane.
Interconnecting channels or tubules that may form flattened discs called cisternae.
Localizes the ER into specific cytoplasmic areas.

Two Types of ER

Rough ER:
- Abundantly present in cells engaged in protein synthesis.
- The "rough" appearance is due to attached ribosomes.
- Two types of proteins are synthesized:
  - Water-soluble proteins that enter the ER lumen for release elsewhere.
  - Transmembrane proteins that remain embedded in the membrane
- Synthesized proteins include digestive enzymes, hormones, plasma membrane proteins, neurotransmitters, and lysosomal enzymes.
- Post-translational processing (modifications) occurs, such as protein folding.
- Proteins are transported to Golgi apparatus.
- Could be involved in the impaired folding of proteins potentially with drastic consequences.
Smooth ER:
- Free of attached ribosomes.
- Primarily found in cells secreting lipids and steroids and in liver cells.
- Well-developed in cells that secrete steroid hormones, like those in the adrenal cortex, Leydig cells, and follicular cells.
- Functions:
  - Lipid synthesis
  - Steroid synthesis and secretion
  - Carbohydrate metabolism
  - Detoxification (including drug breakdown)
  - Calcium (Ca²⁺) accumulation, especially in skeletal muscle cells (sarcoplasmic reticulum).

Smooth ER in Rat Liver Cells

Chemical insult can cause increased detoxification activity and proliferation of the smooth ER.

Sarcoplasmic Reticulum

A specialized form of smooth ER found in smooth and skeletal muscle cells.
Stores and releases Ca²⁺.
Plays a role in excitation-contraction coupling (ECC) during muscle contraction.

Golgi Apparatus

Discovered in 1898 by Camillo Golgi.
Found in all eukaryotic cells.
Reaches its largest size and complexity in secretory and storage cells.
In some animal cells, it is near the nucleus (the centrosome).
In plant cells, Golgi bodies are dispersed throughout the cytoplasm.
It consists of parallel arrays or stacks of curved cisternae/sacs, called cisternae.
The number of cisternae varies from 3-7.
Connected by tubules.
Each cisternae is separated by a space called the lumen.
Two distinct faces: cis face (receiving) and trans face (releasing).

Functions of Golgi Apparatus

Processing: Modifies newly synthesized proteins and glycoproteins.
Sorting: Sorts and packages proteins.
Redistribution: Acts as a center for cell membrane redistribution.
Production: Produces primary lysosomes.
Synthesis: Involved in carbohydrate synthesis (e.g., polysaccharides and glycosaminoglycans - GAGs).

Golgi Apparatus - Structure

The Golgi apparatus is usually located between the ER and the plasma membrane with the cis face closest to the ER. The trans face is at the plasma membrane.
The cisternae are involved in sorting and packaging of substances.
Associated vesicles are involved in transporting substances from one face to another or to other locations within the cell.

Golgi Apparatus - Function

Acts as the "post office" of the cell, receiving proteins from the ER, modifying them, sorting them, and packaging them for transport to various destinations like lysosomes, plasma membrane, or for secretions.

Membrane-Bound Vesicles & Secretory Granules

Lysosomes:
- Found in animal cells.
- Contain powerful hydrolytic enzymes in an acidic environment for digestion.
- Originate from the Golgi Apparatus and are involved in intracellular digestion and removal of unwanted elements (like pathogens).
- Digestion occurs in lysosomes as indigestible material is accumulated as residual bodies, and lysosomes are involved in recycling or removal of old material involved in the cell pathway.
Peroxisomes:
- Round organelles in the cytoplasm, bound by a single membrane.
- Contain enzymes involved in oxidation reactions to produce hydrogen peroxide.
- Hydrogen peroxide is removed by the enzyme catalase.
- Involved in β-oxidation of fatty acids, previously thought to occur only in mitochondria.
- Zellweger syndrome is a defect in peroxisomal functions.
Secretory granules:
- Some cells specialize in rapidly secreting products, usually proteins.
- Cells concentrate and store these in secretory granules and vesicles.
- The number of granules varies.
- They are membrane-bound.
- Examples include insulin release from beta cells.

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Description

This quiz covers the key aspects of cell structure focusing on the endoplasmic reticulum, including both smooth and rough ER, as well as the Golgi apparatus. You'll explore the functions and roles of these cellular components and their significance in human biology.