Cell Structure and Function Quiz

The Cell

• The cell is the basic living unit of the body.
• Each organ is made up of many different cells held together by intercellular structures.
• Individual cells are adapted to perform specific functions.
• Although cells vary, they share common characteristics and the ability to reproduce.

Body Fluid Composition

• Approximately 60% of the adult human body is fluid, primarily water with dissolved ions and other substances.
• Most of this fluid is intracellular fluid (inside cells).
• A smaller portion is extracellular fluid (outside cells), containing ions and nutrients necessary for cell function.
• Composition of extracellular fluid:
  • Intravascular fluid (blood plasma): 7%.
  • Interstitial fluid: 26%.
  • Cerebrospinal fluid: less than 1%.

Intracellular Fluid

• Intracellular fluid is crucial for cell function.
• Proper concentrations of oxygen, glucose, ions, amino acids, fatty substances, and other nutrients are needed for cell survival, growth, and function. These are found in the extracellular fluid surrounding cells.

Cell Structure

• Cells have two main parts: the nucleus and the cytoplasm.
• The nucleus is separated from the cytoplasm by a nuclear membrane.
• The cytoplasm is separated from the surrounding fluids by a cell membrane (plasma membrane).
• Protoplasm is a collective term for the substances that make up the cell.
• Protoplasm is primarily composed of water, electrolytes, proteins, lipids, and carbohydrates.

Water in Cells

• Water is the primary fluid medium within most cells.
• Water content ranges from 70 to 85% for most cells (excluding fat cells).
• Many cell chemicals are dissolved in this water.
• Other cell chemicals are suspended in the water as solid particulates.

Ions in Cells

• Important ions in cells include potassium, magnesium, phosphate, sulfate, bicarbonate, sodium, chloride, and calcium.
• These ions are crucial for cellular chemical reactions.
• Ions acting on cell membranes are required for transmitting electrochemical impulses in nerves and muscles.

Proteins in Cells

• Proteins are the most abundant substances in cells after water, commonly comprising 10-20% of cell mass.
• Proteins can be categorized into structural proteins and functional proteins.
• Structural proteins provide the framework and support for various cellular structures.
• Functional proteins include enzymes, crucial for catalyzing cellular chemical reactions (e.g., glucose breakdown).

Structural Proteins

• Structural proteins are predominantly filamentous molecules.
• They form microtubules that act as the "cytoskeletons" of various cellular components (e.g., cilia, nerve axons, mitotic spindles).
• Extracellularly, they are found in collagen and elastin fibers, connective tissue, blood vessel walls, tendons, ligaments, etc., providing structure, support, and strength.

Functional Proteins (enzymes)

• Functional proteins (enzymes) are often mobile within the cell fluid; they catalyze specific cellular chemical reactions
• Examples of their activities include breaking down glucose and combining it with oxygen to produce energy-rich molecules for cell function.

Lipids

• Lipids are various substances grouped by their solubility in fat solvents.
• Key lipids are phospholipids and cholesterol, comprising about 2% of cell mass.
• Their primary function is forming cell membranes and intracellular membrane barriers for compartmentalization. They are hydrophobic ("water-fearing").
• Some cells contain triglycerides (neutral fat) that store energy.

Carbohydrates

• Carbohydrates play a crucial role in cell nutrition, though with limited structural roles in most cells.
• Dissolved glucose (a sugar) is available in extracellular fluid for rapid uptake.
• Glycogen, another form of carbohydrate, is stored to provide energy when needed.

Cell Membrane

• The cell membrane, also called the plasma membrane, encloses the cell and is a thin, elastic structure (7.5-10 nanometers thick).
• It primarily consists of lipids (mostly phospholipids) and proteins in a bilayer arrangement.
• Phospholipids, cholesterol, proteins, other lipids, and carbohydrates are present in specific proportions in the cell membrane.

Cell Membrane Structure

• The cell membrane's basic structure is a lipid bilayer.
• One end of each phospholipid molecule is hydrophilic ("water-loving") and soluble in water.
• The other end is hydrophobic (“water-fearing”); it's soluble in fat.
• The hydrophobic portion of the membrane is impermeable to common water-soluble substances but permeable to fat-soluble substances (e.g., oxygen).
• The hydrophilic regions ("heads") face the aqueous environments inside and outside of the cell.

Cell Membrane Proteins

• Membrane proteins are globular masses embedded in the phospholipid bilayer.
• Many are glycoproteins (proteins with carbohydrate components).
• Two main types of membrane proteins are:
  • Integral proteins: span the entire membrane, acting as channels or carriers for substance transport.
  • Peripheral proteins: are attached to one side of the membrane and do not penetrate the entire structure; mostly enzymes or transport controllers.

Membrane Protein Functions

• Many integral proteins form channels for molecules to pass between intracellular and extracellular fluids (e.g., water, ions).
• Some transport specific substances across, even against, their concentration gradient (active transport).
• Other proteins act as receptors, binding to hormones or other substances, initiating internal signals.

Cell Membrane Carbohydrates

• Carbohydrates are often attached to proteins (glycoproteins) or lipids (glycolipids) at the cell surface.
• The carbohydrate components are often arranged on the outer surface of the membrane.
• The carbohydrate-rich layer on the cell surface is called the glycocalyx, and it performs various roles (e.g., cell-to-cell recognition, cell surface characteristics).

Test your knowledge on structural and functional proteins, lipids, and their roles within the cell. This quiz covers essential concepts regarding cellular composition and the functions of various organelles and membrane proteins. Perfect for biology students focusing on cell biology!