Cells and Their Organelles

Question 1

What is the structure of the cell membrane?

Answer 1

The cell membrane is composed of a double layer of phospholipids, with hydrophilic phosphate head groups facing the aqueous internal and external environments and hydrophobic lipid tails oriented towards each other. Cholesterol is also present and affects the fluidity of the membrane.

Question 2

What is the function of cholesterol in the cell membrane?

Answer 2

Cholesterol in the cell membrane helps regulate its fluidity, making it more stable and less permeable to certain molecules.

Question 3

What is the role of phosphatidylcholine in the cell membrane?

Answer 3

Phosphatidylcholine is one of the most common lipids found in the cell membrane, contributing to its structure and stability.

Question 4

What are some functions of membrane proteins?

Answer 4

Membrane proteins have various functions, including serving as catalysts (enzymes), transporters, pumps, ion channels, receptors for hormones, local mediators, neurotransmitters, and energy transducers.

Question 5

What is the relationship between the amount of proteins and cellular activity or organelles?

Answer 5

Cells or organelles that are more active tend to contain more proteins. This demonstrates that the specialization of function determines the structure.

Question 6

How are proteins arranged in the cell membrane?

Answer 6

Proteins in the cell membrane can either be integral, deeply embedded within the lipid bilayer, or peripheral, associated with the surface of the cell.

Question 7

What is the nature of phospholipid molecules in the cell membrane?

Answer 7

Phospholipid molecules are amphipathic, meaning they have both hydrophilic (water-loving) and hydrophobic (water-repelling) properties. In water, they spontaneously form bilayers with the hydrophilic head groups facing outward and the hydrophobic tail groups facing inward.

Question 8

What forces are involved in maintaining the structure of the phospholipid bilayer?

Answer 8

In the bilayer, van der Waals forces act between the fatty acid tails of the phospholipids, while electrostatic and hydrogen bonds form between the hydrophilic groups of the phospholipids and water. These forces help maintain the stability and integrity of the membrane structure.

Question 9

What is the main function of cell membranes?

Answer 9

Cell membranes have multiple functions, including forming a continuous, highly selectively permeable barrier around cells and intracellular compartments.

Question 10

Why is the control of the enclosed chemical environment important for cell membranes?

Answer 10

The control of the enclosed chemical environment by cell membranes is crucial for maintaining ion gradients, which are essential for various cellular processes.

Question 11

How do cell membranes facilitate communication?

Answer 11

Cell membranes allow communication both with the extracellular space and within different compartments of the cell. They play a role in signal transduction and the exchange of molecules and information.

Question 12

What is the significance of recognition by cell membranes?

Answer 12

Cell membranes are involved in recognition processes, including the recognition of signaling molecules, adhesion proteins, and other host cells. This recognition is particularly important in the immune system.

Question 13

How do cell membranes contribute to signal generation?

Answer 13

Cell membranes can generate signals in response to a stimulus, leading to a change in membrane potential. This electrical signal can trigger various cellular responses and functions.

Question 14

What is the main role of the rough endoplasmic reticulum (RER) in the cell cytoplasm?

Answer 14

The main role of the RER is to take developing proteins from the cytosol and continue their development prior to completion in the Golgi apparatus.

Question 15

What happens to proteins that move across the membrane of the RER?

Answer 15

Proteins that move across the membrane of the RER undergo a series of post-translational modifications, including the addition of signal sequences that target them to the correct part of the cell.

Question 16

In what cellular contexts is the rough endoplasmic reticulum (RER) abundant?

Answer 16

Cells that produce many secretory proteins, such as mucus and enzymes, will have extensive RER and mitochondria.

Question 17

What are some destinations for proteins synthesized in the RER?

Answer 17

Proteins synthesized in the RER can be destined for secretion into the extracellular matrix, association with the cell membrane (such as receptors and channels), or incorporation into membrane-bound vesicles (such as enzymes of lysosomes).

Question 18

What is the fate of correctly folded proteins in the endoplasmic reticulum (ER)?

Answer 18

Correctly folded proteins in the ER are transported to the Golgi apparatus for secretion.

Question 19

What happens to incorrectly folded proteins in the endoplasmic reticulum (ER)?

Answer 19

Incorrectly folded proteins in the ER are retained within the cell and eventually destroyed.

Question 20

What is the main function of the smooth endoplasmic reticulum (SER)?

Answer 20

The smooth endoplasmic reticulum is involved in the synthesis of lipids, phospholipids, and steroids. It is often less extensive and lacks ribosomes, but certain specialized tissues, such as steroidogenic cells and muscles, may have extensive SER.

Question 21

What is the specialized form of smooth endoplasmic reticulum found in muscle?

Answer 21

The specialized form of smooth endoplasmic reticulum found in muscle is called the sarcoplasmic reticulum (SR).

Question 22

What is the role of the sarcoplasmic reticulum (SR) in muscle?

Answer 22

The sarcoplasmic reticulum (SR) in muscle plays a major part in the sequestration of calcium ions. It modulates the tonic force of contraction and relaxation in muscle cells.

Question 23

How does the ultrastructure of the sarcoplasmic reticulum differ between muscle types?

Answer 23

In striated muscle, the sarcoplasmic reticulum is arranged around the perpendicular T tubule, forming diads in cardiac muscle and triads in skeletal muscle. The arrangement allows for the initiation of a calcium spike in response to the action potential and surface calcium influx.

Question 24

What is the main role of the Golgi apparatus?

Answer 24

The Golgi apparatus is responsible for modifying proteins and lipids received from the endoplasmic reticulum. It processes these biomolecules before they are delivered to various intracellular or extracellular targets.

Question 25

What is the process by which biomolecules leave the Golgi apparatus?

Answer 25

Biomolecules leave the Golgi apparatus through exocytosis, where they are released from the cell before being delivered to their designated intracellular or extracellular targets.

Question 26

What are the main processes involved in protein and lipid processing in the Golgi apparatus?

Answer 26

In the Golgi apparatus, protein processing involves alterations in the carbohydrate regions of glycoproteins, such as addition, removal, or modification of carbohydrates. Lipid processing includes the addition of phosphate groups and glycoproteins to lipids from the endoplasmic reticulum, resulting in the formation of phospholipids that make up the cell membrane.

Question 27

How are lysosomal proteins packaged for delivery?

Answer 27

Lysosomal proteins, including enzymes, are packaged into specific vesicles. These proteins are typically tagged with mannose-6-phosphate in the Golgi to ensure their delivery to lysosomes.

Question 28

What happens to secretory proteins in the Golgi?

Answer 28

Secretory proteins, such as hormones, are packaged into secretory vesicles in the Golgi. These vesicles are then ready for exocytosis, where they are released from the cell. The fusion of secretory vesicles with the cell membrane requires ATP and allows the proteins to be released into the extracellular space.

Question 29

What is required for the fusion of secretory vesicles with the cell membrane during exocytosis?

Answer 29

Fusion of secretory vesicles with the cell membrane during exocytosis requires ATP, as two negatively charged membranes need to merge to allow the release of the vesicle’s contents. The membrane of the vesicle becomes part of the cell membrane.

Question 30

How are cell surface proteins delivered in most cells?

Answer 30

Cell surface proteins, such as phospholipids, enter the constitutive secretory pathway present in all cells. They are transported through the Golgi and are continuously delivered to the cell membrane for incorporation into the cell’s surface.

Question 31

What is the general structure of lysosomes?

Answer 31

Lysosomes are membrane-bound organelles found within cells, typically around 1 micrometer in length. They contain numerous hydrolytic enzymes that catalyze hydrolysis reactions.

Question 32

What is the role of hydrolytic enzymes in lysosomes?

Answer 32

The hydrolytic enzymes within lysosomes are responsible for catalyzing hydrolysis reactions. They play a crucial role in breaking down foreign particles and cellular waste.

Question 33

How do lysosomes contribute to phagocytosis?

Answer 33

During phagocytosis, macrophages engulf foreign particles, forming a phagosome. The phagosome then fuses with a lysosome to create a phagolysosome, where the hydrolytic enzymes in the lysosome break down the engulfed particles.

Question 34

How do lysosomes defend against pathogen entry via endocytosis?

Answer 34

Lysosomes help defend against pathogen entry via endocytosis by degrading pathogens before they can reach the cytoplasm. The hydrolytic enzymes in lysosomes break down the engulfed pathogens, preventing their survival and replication within the cell.

Question 35

Describe the structure of mitochondria.

Answer 35

Mitochondria have an inner and outer membrane, with an intermembrane space between them. The outer membrane contains proteins called porins, which allow the movement of ions into and out of the mitochondrion. Additionally, enzymes involved in the elongation of fatty acids and the oxidation of adrenaline can be found on the outer membrane.

Question 36

What is the primary function of mitochondria in the cell?

Answer 36

The primary function of mitochondria is to synthesize ATP, serving as the powerhouse of the cell.

Question 37

How can the number of mitochondria in a cell indicate its rate of metabolic activity?

Answer 37

The number of mitochondria in a cell is often correlated with its rate of metabolic activity. Cells with high metabolic activity, such as hepatocytes, tend to have a higher number of mitochondria to meet their energy demands.

Question 38

What is the role of mitochondria in maintaining the intracellular environment?

Answer 38

Mitochondria have several roles in maintaining the intracellular environment. They can store caspases, which are responsible for triggering apoptosis, and contribute to calcium homeostasis by transiently storing calcium ions. Additionally, in brown adipose tissue, mitochondria have an alternative function of producing heat through the electron transport chain.

Question 39

What are some roles of the cytoskeleton?

Answer 39

The cytoskeleton is involved in processes such as mitosis, acts as a highway for intracellular vesicles, provides support to the plasma membrane, enables cellular locomotion, and controls the shape of the cell.

Question 40

What are the primary filament systems comprising the cytoskeleton?

Answer 40

The primary filament systems of the cytoskeleton are microtubules, actin filaments (also known as microfilaments), and intermediate filaments. These filaments are composed of dynamic protein components that assemble and disassemble, contributing to the structure and function of the cytoskeleton.

Question 41

How does the cytoskeleton contribute to the shape of a cell?

Answer 41

The cytoskeleton creates an internal architecture within the cell, linking itself, the plasma membrane, and internal organelles. Through these elaborate linkages, the cytoskeleton provides structural support and controls the shape of the cell.

Question 42

What is a unique characteristic of stem cells regarding their lifespan?

Answer 42

Stem cells have the ability to divide indefinitely, making them immortal in terms of their replication potential.

Question 43

How do stem cells differ from terminally differentiated cells?

Answer 43

Unlike terminally differentiated cells, stem cells are not committed to a specific cell lineage or function. They retain the capacity to differentiate into various cell types.

Question 44

What is the significance of the daughter cells of stem cells having a choice?

Answer 44

When stem cells divide, their daughter cells have a choice between differentiating into specialized cells or remaining as stem cells. This choice allows for the maintenance of the stem cell population and the potential for tissue regeneration and repair.