Cell Biology: Organelles, Structure, and Function

Comprehensive practice flashcards covering cell structure, eukaryotic organelles, functions of the ER, Golgi apparatus, lysosomes, mitochondria, chloroplasts, and the cytoskeleton based on the lecture notes.

What is the biological definition of a cell?

The cell is the smallest structural and functional unit of living organisms capable of maintaining homeostasis.

How is cellular homeostasis defined?

Homeostasis is the process of maintaining a constant internal environment regardless of changes in the external environment.

What is the difference between unicellular and multicellular organisms?

Unicellular organisms consist of a single cell (such as bacteria), whereas multicellular organisms consist of many cells (such as humans).

What differentiates prokaryotes from eukaryotes?

Prokaryotes ("before nucleus") lack a true nucleus (e.g., bacteria), whereas eukaryotes ("true nucleus") have a true membrane-bound nucleus (e.g., fungi, plants, and animals).

What are the primary characteristics and functions of the plasma membrane?

The plasma membrane is selectively permeable, controls what enters and exits the cell, acts as a border, and allows the internal chemical composition of the cell to differ from the outside.

What is the role of the nucleus and how is its genetic material organized?

The nucleus is the control center that protects genetic material and carries out $\text{DNA}$ replication and $\text{RNA}$ transcription. Its $\text{DNA}$ is organized into linear strands called chromosomes.

What are nuclear pores and what function do they serve?

Nuclear pores are aqueous channels embedded in the double nuclear membrane that regulate the passage of materials between the nucleus and the cytoplasm.

What is the nucleolus and what process occurs there?

The nucleolus is a specialized structure located inside the nucleus that serves as the site of ribosomal $\text{RNA}$ ($\text{rRNA}$) synthesis.

What is the composition and general function of ribosomes?

Ribosomes consist of a small and large subunit composed of $\text{rRNA}$ and proteins. Their primary function is protein synthesis by translating $\text{mRNA}$ into proteins.

How do free-floating ribosomes differ functionally from bound ribosomes?

Free-floating ribosomes synthesize proteins intended for use inside the cell, while ribosomes bound to the Rough Endoplasmic Reticulum ($\text{RER}$) synthesize proteins that will be transported out of the cell.

What is the endoplasmic reticulum (ER) and what is its internal space called?

The $\text{ER}$ is a series of membrane-bound organelles surrounding the nucleus as a continuation of the nuclear membrane. Its internal space is known as the $\text{ER}$ lumen.

What characterizes the Rough Endoplasmic Reticulum (RER) and what is its main function?

The $\text{RER}$ is studded with bound ribosomes on its surface and serves as the primary site of protein synthesis for proteins directed out of the cell.

What are the three main functions of the Smooth Endoplasmic Reticulum (SER)?

1. Lipid synthesis (phospholipids and cholesterol for the cell membrane)\n2. Detoxification of alcohol and drugs\n3. $\text{Ca}^{2+}$ storage.

Why do liver cells contain a high abundance of Smooth Endoplasmic Reticulum (SER)?

Because the detoxification of alcohol and drugs occurs primarily in the liver, requiring liver cells to possess more $\text{SER}$.

What is the Golgi apparatus and what functions does it perform?

The Golgi apparatus is the cell's shipping center made of membrane-bound flattened sacs called cisternae. It modifies proteins (e.g., by adding sugar tags to route them), packages secreted proteins, and sorts proteins.

What are the three functional regions of the Golgi apparatus?

1. Cis region: located closer to the nucleus, receives vesicles from the $\text{ER}$\n2. Medial region: middle layer\n3. Trans region: located closer to the cell membrane, packages molecules into vesicles for transport out.

What is the function and internal environment of lysosomes?

Lysosomes are small membrane-enclosed sacs containing hydrolytic digestive enzymes that break down ingested materials and damaged organelles (autophagy) at an acidic internal $\text{pH}$ of approximately $5$.

What is the structural organization of a mitochondrion?

A mitochondrion has a permeable outer membrane, a selectively permeable inner membrane folded into cristae, and an internal fluid-filled compartment called the matrix.

What unique genetic features do mitochondria possess?

Mitochondria contain their own circular, self-replicating $\text{DNA}$ encoding $13$ genes, as well as their own ribosomes.

What two critical processes are carried out by mitochondria?

1. Aerobic respiration: converting glucose into $\text{ATP}$\n2. Apoptosis: programmed cell death by activating enzymes that mediate cell destruction.

What are chloroplasts and what is their function in plant cells?

Chloroplasts are plant-specific organelles containing chlorophyll that serve as cellular solar power plants, generating energy using water, carbon dioxide, and sunlight.

What is a cell wall and in which organisms is it found?

The cell wall is a fairly rigid structure surrounding the plasma membrane found in plant and fungal cells.

What is the cytoskeleton and what is its general function?

The cytoskeleton is a complex network of protein fibers that acts as the cell highway and support system, determining cell shape, structural strength, ability to move, and facilitating intracellular transport.

What are the structural features and functions of microtubules?

Microtubules are the thickest cytoskeletal filaments ($25\,\text{nm}$ diameter) made of $\alpha$-tubulin and $\beta$-tubulin. They facilitate intracellular transport, provide the structural basis of cilia and flagella, and form the mitotic spindle.

What are intermediate filaments and what role do they play in the cell?

Intermediate filaments have medium thickness and are relatively static. They provide structural integrity, tensile strength, and prevent the cell from stretching excessively in areas subjected to mechanical stress.

What is the composition and function of microfilaments (actin filaments)?

Microfilaments are the thinnest cytoskeletal filaments, composed of two intertwined chains of actin protein subunits. They determine cell shape, drive muscle contraction, and form the contractile ring that divides cytoplasm during mitosis.