unit 2

Cell Component	Functions	Enzymes/Interior Parts	Major Processes	Types of Organism
Ribosomes	Protein synthesis	rRNA, tRNA, mRNA	Translation	All organisms
Rough ER	Protein synthesis, modification, and sorting	Ribosomes	Protein folding, glycosylation	Eukaryotes
Smooth ER	Lipid synthesis, detoxification	N/A	Lipid metabolism, drug detoxification	Eukaryotes
Golgi Complex	Protein modification, sorting, and packaging	Golgi enzymes	Protein trafficking, secretion	Eukaryotes
Mitochondria	ATP production through cellular respiration	Matrix, cristae	Krebs cycle, oxidative phosphorylation	Eukaryotes
Chloroplasts	Photosynthesis, production of glucose	Thylakoids, stroma	Light-dependent reactions, Calvin cycle	Plants, algae
Lysosomes	Intracellular digestion, waste removal	Hydrolytic enzymes	Autophagy, phagocytosis	Animal cells
Vacuoles	Storage of water, nutrients, and waste	Tonoplast	Osmoregulation, storage	Plant cells, some protists

Why are cells small?

Cells are small because they need to maintain a high surface area-to-volume ratio for efficient exchange of nutrients, gases, and waste products with their environment.
Smaller cells have a larger surface area relative to their volume, allowing for more efficient diffusion of substances.

Mathematical description of cell size increase:

As cells increase in size, their volume increases at a faster rate than their surface area. This leads to a decrease in the surface area-to-volume ratio.

Processes or functions that become inefficient in larger cells:

Diffusion of substances across the cell membrane becomes slower and less efficient.
Cellular communication and signal transduction may be impaired.
Transport of molecules within the cell may become slower.

How larger cells solve these problems:

Larger cells may develop specialized structures, such as organelles, to increase surface area for specific functions.
Some cells may divide into smaller cells to maintain an optimal size.
Some cells may develop complex internal transport systems to overcome diffusion limitations.

Examples:

The presence of organelles like mitochondria and endoplasmic reticulum in eukaryotic cells increases surface area for energy production and protein synthesis.
Nerve cells (neurons) have long, thin extensions (axons) to facilitate efficient communication over long distances.
Cells in the small intestine have microvilli, finger-like projections, to increase surface area for nutrient absorption.

The importance of membranes in the cell includes:

External plasma membrane:
- Acts as a selective barrier, controlling the movement of substances in and out of the cell.
- Maintains cell shape and integrity.
- Facilitates cell-cell communication and signaling.
- Allows for attachment to other cells or extracellular matrix.
Internal membranes:
- Create compartments within the cell, allowing for specialized functions.
- Facilitate efficient organization and separation of cellular processes.
- Enable the formation of organelles, such as the endoplasmic reticulum, Golgi apparatus, and mitochondria.
- Provide surfaces for metabolic reactions and protein synthesis.

Prokaryotes compartmentalize reactions without organelles by:

Utilizing specialized regions within the cytoplasm, such as microcompartments or protein complexes, to segregate specific reactions.
Forming membrane invaginations or infoldings to increase surface area for metabolic processes.
Employing protein-based structures, like carboxysomes or magnetosomes, to localize specific reactions or functions.
Utilizing DNA supercoiling or nucleoid-associated proteins to organize genetic material within the nucleoid region.

The hydrophobic nature of the phospholipid tails causes them to orient towards the interior of the lipid bilayer, away from the aqueous environment.
The hydrophilic nature of the phospholipid heads and protein regions allows them to interact with the surrounding water molecules, either on the inner or outer surface of the membrane.
Steroids function as signaling molecules and are involved in various physiological processes such as regulation of metabolism, inflammation, and immune response.
Glycoproteins play a role in cell recognition, cell adhesion, and immune response. They have a protein backbone with attached carbohydrate chains.
Glycolipids are involved in cell recognition and cell signaling. They consist of a lipid molecule with attached carbohydrate chains.

Selective permeability refers to the property of a membrane to allow certain substances to pass through while restricting the passage of others.
The structure of the plasma membrane, specifically the lipid bilayer and embedded proteins, determines its permeability.
Small, nonpolar molecules like oxygen and carbon dioxide can freely diffuse through the membrane.
Large, polar molecules like glucose and ions cannot freely diffuse through the membrane.

Cell walls provide structural support to cells, giving them shape and preventing them from bursting under osmotic pressure.
Cell walls also play a crucial role in determining the permeability of the cell, controlling the movement of substances in and out of the cell.
Cell walls are primarily composed of cellulose, a complex carbohydrate. In addition to cellulose, cell walls may contain other polysaccharides, proteins, and lignin.
Cell walls are found in plants, algae, fungi, and some bacteria. Animal cells do not have cell walls.

Comparison	Direction of Concentration Gradient	Molecular Examples	Energy Use	Cell/Structures/Molecules Needed
Passive Transport	Moves along the concentration gradient (high to low concentration)	Diffusion of oxygen, carbon dioxide, water	No energy required	Cell membrane
Active Transport	Moves against the concentration gradient (low to high concentration)	Sodium-potassium pump, glucose transporters	Energy (ATP) is required	Carrier proteins, ATP, cell membrane

Endocytosis is the process by which cells take in substances by engulfing them into vesicles formed from the cell membrane. Exocytosis, on the other hand, is the process by which cells release substances from vesicles into the extracellular space by fusing the vesicle membrane with the cell membrane. In summary, endocytosis brings substances into the cell, while exocytosis releases substances out of the cell.

Facilitated diffusion is a type of passive transport where molecules move across the cell membrane with the help of specific transport proteins.
Cell components involved in facilitated diffusion include the cell membrane and transport proteins.
Various molecules can move through the membrane via facilitated diffusion, such as glucose, amino acids, and ions.
Aquaporins are a type of transport protein that specifically facilitate the movement of water molecules across the cell membrane.

The Na/K pump, also known as the sodium-potassium pump, is a protein found in the cell membrane.
It actively transports sodium ions (Na+) out of the cell and potassium ions (K+) into the cell.
The significance of the Na/K pump to the cell includes:
- Maintaining the resting membrane potential: The pump helps establish and maintain the electrical potential difference across the cell membrane.
- Generating action potentials: The pump's activity contributes to the generation of electrical impulses necessary for nerve and muscle cell communication.
- Regulating cell volume: By controlling the movement of ions, the pump helps regulate the osmotic balance and cell volume.
- Facilitating nutrient uptake: The pump indirectly helps transport glucose and amino acids into the cell by maintaining the concentration gradients.
Membrane potential, also known as polarity, refers to the electrical potential difference across the cell membrane.
It is generated by the uneven distribution of ions across the membrane, primarily maintained by the Na/K pump.
Membrane potential is crucial for various cellular processes, including the transmission of nerve impulses, muscle contraction, and the uptake of nutrients.

Solution
Hypotonic Solution: A hypotonic solution has a lower solute concentration compared to the cell. When a cell is placed in a hypotonic solution, water moves into the cell through osmosis, causing the cell to swell or potentially burst (lyse).
Hypertonic Solution: A hypertonic solution has a higher solute concentration compared to the cell. When a cell is placed in a hypertonic solution, water moves out of the cell through osmosis, causing the cell to shrink (crenate) or shrivel.
Isotonic Solution: An isotonic solution has the same solute concentration as the cell. When a cell is placed in an isotonic solution, there is no net movement of water, and the cell maintains its normal shape and size.

Water potential:
- Water potential is the potential energy of water molecules in a system compared to pure water at atmospheric pressure and temperature.
- The equation for water potential is Ψ = Ψs + Ψp, where Ψ represents water potential, Ψs represents solute potential, and Ψp represents pressure potential.
- Solute potential (Ψs) is the measure of the effect of solute concentration on water potential. It is always negative and decreases as solute concentration increases.
- Pressure potential (Ψp) is the measure of the effect of pressure on water potential. It can be positive or negative, depending on whether the pressure is exerted on or by the system.

The endosymbiotic theory proposes that eukaryotic cells evolved from a symbiotic relationship between different types of prokaryotic cells. Three lines of evidence supporting this theory are:

Mitochondria and chloroplasts have their own DNA: These organelles contain their own genetic material, similar to bacteria, suggesting they were once independent organisms.
Double membrane structure: Mitochondria and chloroplasts have a double membrane, which is consistent with the engulfment of one cell by another.
Replication by binary fission: Mitochondria and chloroplasts replicate independently within the cell, similar to bacteria, indicating their evolutionary origin.