Cell Structure, Function, and Transport: A Comprehensive Biology Guide

What is cytology and when was it established?

Cytology is the study of cells, established in 1663 by Robert Hooke who observed the empty cell walls of cork.

What did Theodor Schwann conclude about cells in the 1800s?

He concluded that all animals are made of cells.

What are the key points of modern cell theory?

1. Cells arise only from other cells. 2. All organisms are composed of cells and cell products. 3. The cell is the simplest structural and functional unit of life. 4. An organism's structure and functions are due to cellular activity. 5. Cells of all species exhibit biochemical unity.

How can cells be classified based on their shapes?

Cells can be classified as squamous, cuboidal, columnar, polygonal, stellate, spheroid, ovoid, discoid, fusiform, or fibrous.

What is the relationship between cell size and surface area to volume?

Cell size is limited due to the surface area to volume relationship; as cells enlarge, volume increases faster than surface area, affecting waste excretion and nutrient uptake.

What advancements did the transmission electron microscope (TEM) bring to cell observation?

The TEM allowed for greatly increased magnification and resolution, enabling the viewing of a cell's ultrastructure.

What is the resolution of the TEM compared to light microscopes and the human eye?

The resolution of the TEM is 5 nm, while light microscopes have a resolution of 200 nm, and the human eye has a resolution of 70-100 μm.

What components make up a cell?

A cell consists of a plasma membrane, specialized organelles, and a cytoskeleton, all embedded in a gel-like solution called cytosol.

What is the difference between intracellular fluid (ICF) and extracellular fluid (ECF)?

ICF is the fluid inside the cell, while ECF is the fluid outside the cell.

What physiological processes occur at the cell surface?

Processes such as immune response, binding of egg and sperm, cell signaling, and detection of taste and smell occur at the cell surface.

What defines the boundaries of the cell?

The plasma membrane

What is the composition of the plasma membrane?

The plasma membrane consists of an oily film of lipids, primarily phospholipids (75%), cholesterol (20%), and glycolipids (5%).

How are phospholipids arranged in the plasma membrane?

Phospholipids are arranged in a bilayer with phosphate heads facing the watery regions on each side and hydrophobic tails directed toward the center.

What role do proteins play in the plasma membrane?

Proteins make up about 50% of the membrane weight and include transmembrane proteins that span the bilayer, many of which are glycoproteins.

What are glycoproteins and where are they located in the plasma membrane?

Glycoproteins are proteins conjugated with oligosaccharides that face the extracellular side of the membrane.

What is the function of the glycocalyx in the plasma membrane?

The glycocalyx, formed by glycolipids, plays a role in cell recognition and protection.

What is the difference between transmembrane proteins and other membrane proteins?

Transmembrane proteins span the bilayer, while other membrane proteins may be anchored to the cytoskeleton or drift freely.

What is the significance of the scanning electron microscope (SEM)?

The SEM produces three-dimensional images but can only view surface features of cells.

What is the importance of the cytoskeleton in a cell?

The cytoskeleton provides structural support and helps maintain the shape of the cell.

What is the primary function of the plasma membrane?

The plasma membrane regulates the movement of substances in and out of the cell, maintaining homeostasis.

How does cell size affect its ability to support activities?

As cell size increases, the ability to support activities decreases due to the limitations of surface area for nutrient uptake and waste excretion.

What is the role of cholesterol in the plasma membrane?

Helps to stabilize the membrane's fluidity and structure.

What are peripheral proteins and their association in the membrane?

Peripheral proteins adhere to one face of the membrane and are typically associated with transmembrane proteins.

List at least three functions of membrane proteins.

1. Receptors for signaling molecules. 2. Enzymes acting at the cell's surface. 3. Ion channels allowing water and dissolved ions to pass through the membrane.

What are the types of ion channels based on their regulation?

1. Always open channels. 2. Ligand-regulated gates respond to chemical messengers. 3. Voltage-regulated gates respond to changes in electrical potential. 4. Mechanically regulated gates respond to physical changes such as stretch and pressure.

What role do carriers and pumps play in membrane transport?

Carriers bind to target molecules and transport them across the membrane; pumps are specialized carriers that use ATP energy.

What are glycoproteins and their function in the cell?

Some glycoproteins serve as cell-identity markers, allowing recognition of cells as 'self'.

What are cell-adhesion molecules?

Proteins that hold cells to one another.

Explain the role of second messengers in cellular signaling.

Second messengers, like cyclic AMP, relay signals from receptors to elicit physiological responses within the cell.

What is the function of adenylate cyclase in the signaling pathway?

Adenylate cyclase converts ATP to cyclic AMP, which acts as a second messenger.

How do kinases function in relation to cyclic AMP?

Cyclic AMP activates kinases that add phosphates to enzymes, which can activate some enzymes and inactivate others.

What is the glycocalyx and its significance in animal cells?

The glycocalyx is a coating external to the plasma membrane, consisting of carbohydrate moieties of glycolipids and glycoproteins, important for cell recognition.

What are microvilli and their primary function?

Microvilli are extensions of the plasma membrane that increase a cell's surface area.

What is the brush border?

A dense fringe of microvilli on some cells that increases surface area for absorption.

Describe the structure and function of cilia.

Cilia are hairlike processes; motile cilia beat in a coordinated manner to move substances across cell surfaces.

What is the primary cilium and its function?

Nearly every human cell has a single, nonmotile primary cilium that serves as a sensory antenna.

How do motile cilia function in the respiratory tract?

Motile cilia in the respiratory tract beat in a coordinated manner to move mucus in one direction.

What is the axoneme and its role in cilia?

The axoneme is the structural basis for movement in cilia, composed of microtubules arranged in a 9 + 2 structure.

What is the function of dynein in cilia?

Dynein is a motor protein that uses ATP to move along microtubules, causing cilia to beat.

How do chloride ions contribute to cilia movement?

Chloride ions are pumped out of the cell, attracting sodium ions and causing water to follow out by osmosis, creating a saline layer for cilia movement.

What is the role of first messengers in cellular signaling?

First messengers, like epinephrine, bind to surface receptors and cannot pass through the membrane.

What happens when a first messenger binds to its receptor?

The receptor activates a G protein, which relays the signal to adenylate cyclase.

How do microvilli contribute to absorption?

Microvilli increase the surface area of cells, enhancing their ability to absorb nutrients.

What are the differences between the functions of receptors and enzymes in the membrane?

Receptors bind signaling molecules to initiate a response, while enzymes catalyze reactions at the cell's surface.

What are flagella and where do they occur in humans?

Flagella are whiplike structures longer than cilia, occurring only as the tails of sperm cells in humans.

What are pseudopods?

Pseudopods are cytoplasm-filled extensions of the cell that change in shape continually.

What is the nature of the plasma membrane?

The plasma membrane is selectively permeable, allowing materials to pass through via passive or active mechanisms.

What is filtration in the context of membrane transport?

Filtration is the process by which particles are driven through the membrane by hydrostatic pressure, as seen in blood capillaries and kidneys.

What is simple diffusion?

Simple diffusion is the net movement of particles from an area of high concentration to an area of lower concentration.

What factors affect the rate of diffusion?

The rate of diffusion is affected by temperature, molecular weight of particles, steepness of the concentration gradient, membrane surface area, and permeability to the substance.

What is osmosis?

Osmosis is the diffusion of water down a concentration gradient through a selectively permeable membrane.

What direction does water move during osmosis?

Water moves from a more dilute solution (more water) to a more concentrated solution (less water).

What are aquaporins?

Aquaporins are channel proteins that facilitate the significant entry of water into cells.

What happens to water levels in relation to nonpermeating molecules?

Water will cross the membrane toward the side with nonpermeating molecules, causing the water level to fall on one side and rise on the other.

What is reverse osmosis?

Reverse osmosis is the process where water is forced through a membrane under pressure against its concentration gradient.

What is an osmole?

An osmole is a unit used to measure the osmotic concentration of body fluids, defined as 1 mole of dissolved particles if a solute does not ionize in water.

What is the difference between osmolality and osmolarity?

Osmolality is the number of osmoles per kilogram of water, while osmolarity is the number of osmoles per liter of solution.

How are physiological concentrations typically expressed?

Physiological concentrations are usually expressed in milliosmoles per liter (mOsm/L).

What is tonicity?

Tonicity is the ability of a solution to affect fluid volume and pressure in a cell.

What occurs in a hypotonic solution?

In a hypotonic solution, water flows into the cell because it has a lower concentration of nonpermeating solutes than the intracellular fluid.

What occurs in a hypertonic solution?

In a hypertonic solution, water flows out of the cell because it has a higher concentration of nonpermeating solutes than the intracellular fluid.

What is an isotonic solution?

An isotonic solution has a total concentration of nonpermeating solutes equal to that of the intracellular fluid, allowing water to flow into and out of the cell equally.

What role do transport proteins play in cell membranes?

Transport proteins are responsible for carrier-mediated transport of substances across the cell membrane.

How do carriers exhibit specificity?

Carriers exhibit specificity for a particular solute, such as glucose, as the solute acts as a ligand that binds to a receptor site on the carrier.

What is the transport maximum?

The transport maximum is the rate of transport when all carrier sites are filled with ligand molecules.

What is the difference between uniports, symports, and antiports?

Uniports carry only one solute at a time, symports carry two or more solutes simultaneously in the same direction (cotransport), and antiports carry two or more solutes in opposite directions (countertransport).

What is facilitated diffusion?

Facilitated diffusion is carrier-mediated transport that moves a solute down its concentration gradient without consuming ATP.

What is primary active transport?

Primary active transport is carrier-mediated transport that moves a solute up (against) its concentration gradient, consuming ATP energy.

What is the sodium-potassium pump?

The sodium-potassium pump is an example of primary active transport that exchanges three Na+ for two K+ and hydrolyzes one ATP per cycle.

Why is the sodium-potassium pump important?

It compensates for the continual leakage of ions, regulates cell volume, maintains membrane potential essential for nervous system function, and helps drive secondary active transport.

What is secondary active transport?

Secondary active transport is facilitated by the ion gradient maintained by the sodium-potassium pump.

What is endocytosis?

Endocytosis is the process of bringing materials into a cell.

What is exocytosis?

Exocytosis is the process of releasing material to the outside of the cell.

What is phagocytosis?

Phagocytosis is the process by which cells engulf particles such as bacteria, dust, and cellular debris.

How do neutrophils perform phagocytosis?

Neutrophils extend pseudopods to trap bacteria in a phagosome, which merges with a lysosome to destroy the invader.

What is pinocytosis?

Pinocytosis is the process of taking in droplets of extracellular fluid containing useful molecules.

What occurs during receptor-mediated endocytosis?

In receptor-mediated endocytosis, receptors bind to specific particles from the extracellular fluid, cluster together, and the membrane sinks to form a vesicle.

What is an example of a substance taken up by receptor-mediated endocytosis?

Low density lipoprotein (LDL) is an example of a substance taken up by receptor-mediated endocytosis.

What is transcytosis?

Transcytosis is the process where endothelial cells imbibe insulin from the blood and pass it through the cytoplasm, releasing it on the other side.

What happens during exocytosis?

A vesicle containing material merges with the cell membrane, releasing the material to the extracellular space.

What structures are found in the cytoplasm?

Cytoskeleton, organelles, and inclusions, all embedded in the cytosol.

What is the function of the cytoskeleton?

It provides structural support, determines cell shape, organizes contents, moves substances, and contributes to cell movement.

What are the three main components of the cytoskeleton?

Microfilaments, intermediate filaments, and microtubules.

What are microfilaments and their function?

Thin (6 nm) filaments made of actin that form a network inside the plasma membrane, known as the membrane skeleton.

What are intermediate filaments?

Filaments (8-10 nm in diameter) that resist stress and participate in cell junctions, often composed of keratin in epidermal cells.

What are microtubules and their role?

Cylinders (25 nm in diameter) made of tubulin that hold organelles in place, form structural bundles, and guide organelles and molecules.

What is the mitotic spindle?

A structure formed by microtubules that guides chromosomes during cell division.

What are organelles?

Internal structures in a cell that carry out specialized metabolic tasks.

What is the largest organelle in a cell?

The nucleus.

What is the nuclear envelope?

A double membrane surrounding the nucleus, perforated with nuclear pores.

What is nucleoplasm?

The material within the nucleus, including chromatin and nucleoli.

What is the rough endoplasmic reticulum (RER)?

A system of flattened sacs covered with ribosomes that synthesizes phospholipids and proteins.

What is the smooth endoplasmic reticulum (SER)?

A system of tubular cisternae that lacks ribosomes and is involved in detoxification, hormone manufacture, and calcium storage.

What are ribosomes?

Small granules of protein and RNA that translate messenger RNA into protein.

What is the function of the Golgi complex?

It synthesizes and adds carbohydrate moieties to proteins, sorts them, and packages them into vesicles.

What are lysosomes?

Packages of enzymes that hydrolyze proteins and nucleic acids, aiding in digestion of bacteria and organelles.

What are peroxisomes?

Organelles that use oxygen to oxidize organic molecules, producing hydrogen peroxide for further oxidation.

What are proteasomes?

Protein complexes responsible for degrading proteins that are tagged for destruction.

What is the primary function of mitochondria?

To synthesize ATP, serving as the 'powerhouses' of the cell.

What is the structure of mitochondria?

They have a double membrane with inner folds called cristae and a matrix containing ribosomes, enzymes, and mitochondrial DNA.