Cell Biology Fundamentals

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Questions and Answers

What is the main function of the nucleolus?

Storage of genetic information

Synthesis of ribosomal RNA (rRNA) (correct)

Synthesis of proteins

Regulation of cell division

What is chromatin composed of?

DNA and proteins (correct)

RNA only

RNA and proteins

DNA only

What happens to chromatin during cell division?

It is replicated

It remains in a relaxed state

It condenses into chromosomes (correct)

It is broken down into smaller pieces

What is the function of the nuclear envelope?

To regulate the movement of molecules in and out of the nucleus (D) Signup and view all the answers

What is the significance of the fact that DNA in a single human cell, if uncoiled, would extend for about 6.5 feet?

It highlights the efficiency of DNA packaging within the nucleus (B) Signup and view all the answers

Which of the following is NOT a component of the nucleus?

Centrioles (A) Signup and view all the answers

Why are eukaryotic cells called 'eukaryotic'?

Because they have a well-defined nucleus (C) Signup and view all the answers

What is the significance of the nuclear pores?

They allow for the exchange of materials between the nucleus and the cytoplasm (B) Signup and view all the answers

Which of the following is NOT a function of lysosomes?

Produce ATP (B) Signup and view all the answers

What is the approximate pH of the lysosomal environment?

5 (B) Signup and view all the answers

Which cellular organelle is analogous to the lysosome in plant cells?

Vacuole (D) Signup and view all the answers

Which of the following statements about vacuoles is TRUE?

Vacuoles can store nutrients, water, and waste products (B) Signup and view all the answers

What structure within the mitochondria is responsible for increasing the surface area for ATP production?

Cristae (C) Signup and view all the answers

Which of the following is NOT a direct component of the endomembrane system?

Mitochondria (B) Signup and view all the answers

What is the primary function of mitochondria?

Cellular respiration (B) Signup and view all the answers

Which type of cells would you expect to have a higher number of mitochondria?

Muscle cells (C) Signup and view all the answers

What is the role of the signal recognition particle (SRP) in protein synthesis?

The SRP identifies and binds to the signal peptide of a protein, directing the ribosome to the ER membrane. (B) Signup and view all the answers

What is the primary function of the Golgi apparatus?

Modify, sort, and package proteins and lipids for transport. (B) Signup and view all the answers

How does insulin synthesis and secretion illustrate the function of the endomembrane system?

Insulin is synthesized in the ER, modified in the Golgi, and secreted from the cell via vesicles. (D) Signup and view all the answers

What is the role of the signal peptide in the synthesis of insulin?

The signal peptide directs the ribosome synthesizing insulin to the ER membrane. (B) Signup and view all the answers

Where does the process of proinsulin to insulin conversion occur?

In the Golgi apparatus. (A) Signup and view all the answers

Why is insulin secreted from the cell via exocytosis?

Exocytosis allows insulin to be secreted directly into the bloodstream, where it can regulate blood glucose levels. (B) Signup and view all the answers

What is the primary function of lysosomes within a cell?

To break down damaged or unneeded cellular components. (B) Signup and view all the answers

What role does protein modification play in the endomembrane system?

Protein modification determines the final destination of a protein within the cell. (A) Signup and view all the answers

Which of the following is NOT a characteristic of chloroplasts?

They are responsible for cellular respiration. (B) Signup and view all the answers

What is the correct order of structures within a mitochondrion, from outermost to innermost?

Outer membrane, intermembrane space, inner membrane, mitochondrial matrix (B) Signup and view all the answers

Which of the following statements accurately describes the theory of endosymbiosis?

Mitochondria and chloroplasts were originally independent organisms that were engulfed by early eukaryotic cells. (A) Signup and view all the answers

What is the primary function of the thylakoid membrane within chloroplasts?

To house pigments that capture energy from light. (C) Signup and view all the answers

Which of the following pieces of evidence supports the theory of endosymbiosis?

Mitochondria and chloroplasts have their own ribosomes and circular DNA. (C) Signup and view all the answers

What is the primary function of peroxisomes?

To detoxify harmful substances within the cell. (A) Signup and view all the answers

What is the main difference between the intermembrane space of a mitochondrion and the stroma of a chloroplast?

The intermembrane space is where ATP is produced, while the stroma is where sugars are synthesized. (A) Signup and view all the answers

Which of the following is NOT a characteristic of prokaryotes?

They have a nucleus. (C) Signup and view all the answers

Which of the following is NOT part of the endomembrane system?

Mitochondria (D) Signup and view all the answers

The endoplasmic reticulum (ER) is a network of what two primary structures?

Cisternae and tubules (B) Signup and view all the answers

What is the main function of the rough endoplasmic reticulum (RER)?

Protein synthesis for secretion (B) Signup and view all the answers

Which of these statements about the smooth endoplasmic reticulum (SER) is TRUE?

It plays a role in lipid metabolism. (D) Signup and view all the answers

What is the primary role of the Golgi apparatus in the endomembrane system?

Modification and packaging of proteins (D) Signup and view all the answers

Which of these components of the endomembrane system is responsible for breaking down cellular waste and debris?

Lysosomes (C) Signup and view all the answers

What is the main function of the plasma membrane?

Enclosing and protecting the cell (C) Signup and view all the answers

Which of these is a key difference between the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER)?

The RER is studded with ribosomes, while the SER is not. (D) Signup and view all the answers

What is the main function of ribosomes?

Synthesize proteins (D) Signup and view all the answers

What is the role of the signal peptide in protein sorting?

It directs proteins to specific organelles (B) Signup and view all the answers

Which of the following organelle destinations is specifically indicated by a signal peptide with the sequence -Lys-Lys-Lys-Arg-Lys-?

Nucleus (A) Signup and view all the answers

Imagine a protein with an altered nuclear localization signal. What would be the most likely consequence?

The protein will remain in the cytoplasm (D) Signup and view all the answers

Why is the signal sequence for the Peroxisome considered "polar + hydrophobic"?

It can interact with both the cytosol and the peroxisome membrane. (A) Signup and view all the answers

What is the primary difference between proteins synthesized by free ribosomes and those attached to the rough ER?

ER-bound ribosomes synthesize proteins for export (D) Signup and view all the answers

Which type of molecule can be transported through the nuclear pore?

All of the above (D) Signup and view all the answers

What does the presence of rRNA and proteins indicate about ribosomes?

Ribosomes are dynamic structures involved in protein synthesis (C) Signup and view all the answers

Study Notes

Biology 1 - Cells, Molecular Biology and Genetics (Biol 1000)

Course offered by Dr. Michael Cardinal-Aucoin during Winter 2025 at York University.
Course code: Biol 1000

The Eukaryotic Cell

Eukaryotic cells possess internal membranes dividing into specialized compartments called organelles.
Organelles have specific functions.
Plant, animal, and protist cells share most of the same organelles.
Organelles listed include: nucleus, endomembrane system (endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles), mitochondria, chloroplasts, and peroxisomes.
A cytoskeleton is also present.

Eukaryotes

Eukaryotic cells contain internal membranes, defining compartments known as organelles.
Each organelle is designed for a specific function.
Plant, animal, and protist cells share a majority of similar organelles.
Organelles listed include, Nucleus, Endoplasmic Reticulum(rough and smooth), Golgi apparatus, Mitochondria, Peroxisome, and the cytoskeleton.

Internal Organization of Eukaryotic Cells

Non-organellar components include the plasma membrane, ribosomes, and cytoskeleton.
Organelles (membrane-bound): nucleus, endomembrane system (nuclear membrane, ER - rough and smooth, Golgi body, lysosome, vacuoles), mitochondria, chloroplasts, and peroxisomes.

Nucleus

The nucleus is the most prominent organelle in a eukaryotic cell.
It stores DNA.
The nuclear envelope separates nucleus from the cytoplasm.
The envelope is a double membrane structure.
It has nuclear pores that serve as gateways for molecules to enter and leave the nucleus.
The nucleolus is a structure within the nucleus where ribosomal RNA (rRNA) is synthesized.
DNA is organized into chromatin, a complex of DNA and proteins.
During cell division, chromatin condenses into chromosomes.
The average human body contains enough DNA to wrap around the Earth's circumference approximately 500,000 times. The DNA in a single cell, when stretched out, would measure approximately 6.5 feet.

Nuclear Pore

The nuclear pore complex is a multi-protein structure that regulates the movement of molecules into and out of the nucleus.
The pore complex controls which molecules enter or exit the nucleus.

Ribosomes

Ribosomes are found in both prokaryotes and eukaryotes.
In eukaryotes, they are made in the nucleolus.
They are composed of rRNA and proteins.
Ribosomes are sites of protein synthesis.
Ribosomes can be free in the cytosol (cytoplasm) or bound to the endoplasmic reticulum (ER) membrane.

Protein Synthesis

Proteins synthesized by free ribosomes and those attached to the rough ER have different fates.
Proteins that are destined for secretion, organelles, or membranes usually begin to be synthesized with a short chain of amino acids called a signal peptide. The signal peptide guides the protein through the endomembrane system.

How do proteins end up where they should?

Proteins possess signal peptides which act as targeting signals.
The signal peptide guides the protein to a particular organelle or location for processing or secretion.
These signal peptides can dictate the location or destination of proteins within the cell (organelle identification).

Proteins destined for the nucleus...

Proteins destined for the nucleus have a nuclear localization signal (NLS).
The NLS is a specific amino acid sequence that directs proteins to the nucleus.
Whether or not a protein enters the nucleus or cytoplasm is dependent on the presence or absence of NLS.

Endomembrane System

The endomembrane system is composed of interconnected membranes that carry out a variety of tasks, including modifying proteins, sorting and shipping products.
These tasks include protein production, transport, modification, and sorting.

Endoplasmic Reticulum

The endoplasmic reticulum is a network of interconnected membranes.
There are two main types: rough ER and smooth ER.
The rough ER is studded with ribosomes, involved in protein synthesis.
The smooth ER lacks ribosomes, and plays a role in lipid synthesis and detoxification.

Golgi Apparatus

The Golgi apparatus processes and sorts proteins and lipids.
It modifies proteins by adding carbohydrate groups to form glycoproteins or lipoproteins.
It serves as a sorting station and ships these finished products where needed.

Lysosomes

Lysosomes are vesicles derived from the Golgi body.
They contain hydrolytic enzymes.
Lysosomes break down macromolecules (e.g., proteins, lipids, complex carbohydrates).
The acidic environment in lysosomes is ideal for the hydrolytic enzymes to work.

Vacuoles

Vacuoles are large vesicles derived from the endoplasmic reticulum and Golgi apparatus which perform a variety of functions. These include: storing nutrients, digestion and contractile functions (in many protists).

Mitochondria

Mitochondria are sites of cellular respiration.
They extract energy from sugars, fats, and other fuels to generate ATP.
Different cell types require varying numbers of mitochondria which correlates to the cell's function.
Mitochondria are enclosed by two membranes; an outer membrane and an inner membrane.
The inner membrane is highly convoluted to increase surface area, creating cristae, allowing for more space.
The inner membrane divides the mitochondrion into two compartments: intermembrane space and mitochondrial matrix.
The mitochondrial matrix contains the mitochondrial DNA, enzymes, and ribosomes vital to energy production.

Chloroplasts

Chloroplasts capture light energy and convert it into chemical energy through photosynthesis.
Chloroplasts are surrounded by a double membrane.
Inside the chloroplast, there are stacks of thylakoids called grana where the light-dependent reactions of photosynthesis take place.
The inner-most part is called the stroma, containing enzymes and chloroplast DNA, ribosomes important to photosynthesis.

Origins of Mitochondria and Chloroplasts (Theory of Endosymbiosis)

Mitochondria and chloroplasts originated from engulfed prokaryotic cells (bacteria) through a symbiotic relationship.
Evidence suggests these organelles possess their own DNA and ribosomes and are bound by a double membrane, similar to bacteria, further supporting this theory.

Peroxisomes

Peroxisomes are specialized metabolic compartments enclosed by a single membrane.
Their functions include the breakdown of fatty acids and the detoxification of harmful substances.
A byproduct of peroxisome function is hydrogen peroxide, which peroxisomes convert into water and oxygen using catalase.

Endomembrane System Example: Insulin Synthesis and Secretion

Insulin is a peptide hormone produced by pancreatic beta cells.
Insulin synthesis involves translation of preproinsulin, which is then processed into proinsulin and finally insulin.
There is a signal peptide to facilitate steps in insulin production and release.
Ultimately, insulin is secreted from the cell through exocytosis.

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Test your knowledge on cellular structures and their functions with this quiz on cell biology. Questions cover topics like the nucleolus, mitochondria, and lysosomes, among others. Perfect for students studying biology or anyone interested in understanding cell functions.