Chapter 3: Cell Structure, Function, and Energy

Cell

The smallest unit of life that can function independently.

Prokaryotic Cells

• Unicellular organisms that lack a nucleus and many organelles, containing a circular ring of DNA.

• Example: Bacteria and Archaea

Eukaryotic Cells

• More complex cells that can be unicellular or multicellular, containing a nucleus, and membranous organelles.

• DNA is located in their nucleus, bounded by a nuclear envelope.

Compartmentalization

The presence of membrane-bound organelles in eukaryotic cells, each with specific functions.

Plasma Membrane

Separates the cell from the external environment and controls the passage of substances into and out of the cell, such as organic molecules and wastes.

Cytoplasm

• Provides structure to the cell and is the site of many metabolic reactions.

• Organelles are found here

Nucleoid

Location of DNA in prokaryotes

Nucleus

Organelle that houses DNA and directs the synthesis of ribosomes and proteins.

Mitochondria

The powerhouse of the cell responsible for ATP production and cellular respiration.

Ribosomes

Organelles responsible for protein synthesis.

Peroxisomes

Responsible for oxidizing and breaking down fatty acids/amino acids, and detoxifies poisons

Vesicles and Vacuoles

• Organelles that store and transport substances

• Acts as digestive function in plant cells.

Centrosome

• Plays a role in cell division of animal cells

• Organizing center of microtubules in animal cells.

Lysosome

Organelle that digests macromolecules and recycles worn-out organelles

Cell Wall

• Acts as protection and support for a cell’s shape

• Found in bacteria and some plants

Endoplasmic Reticulum (ER)

Modifies, sorts, tags, packages, and distributes lipids (smooth ER) and proteins (rough ER)

Cytoskeleton

Maintains a cell’s shape by securing organelles, allowing cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move independently.

Flagella and Cilia

Responsible for cellular locomotion

Solute

• A substance dissolved in a liquid

• Example: Sugar

Solvent

The liquid portion of a solution (usually water)

Concentration

The measure of how much solute is present per volume of solvent.

Hypertonic

• When a solution has a higher concentration of solute compared to solvent.

• Example: More sugar than water.

Hypotonic

• When a solution has a higher concentration of solvent compared to solute.

• Example: More water than sugar.

Isotonic

• When a solution has an equal concentration of solute and solvent.

• Example: Same amount of water and sugar

Passive Transport

• No energy required

• Movement is due to a gradient (differences in concentration, pressure, or change)

Diffusion

Movement of solute from higher concentration to lower concentration

Osmosis

Movement of water (solvent) across a semipermeable membrane

Facilitated Diffusion

Solute particles are moved across a membrane with the help of transport proteins.

Active Transport

• Energy in the form of ATP is required for this kind of transport.

• Movement is against the concentration gradient (low to high).

• Example: Sodium potassium pumps in our body are a way of active transport.

Endocytosis

The process of moving substances into a cell.

Phagocytosis

• Cell eating

• When cells engulf particles

• The cell membrane surrounds the particle and pinches off to form an intracellular vacuole

Pinocytosis

• Cell drinking

• Movement of liquids into a cell

• The cell membrane surrounds a small volume of fluid and pinches off, forming a vesicle

Receptor-mediated endocytosis

Uptake of substances by the cell is targeted to a single type of substance that binds at the receptor on the external cell membrane

Exocytosis

• The process of moving substances out of a cell.

• A vesicle transports a substance and fuses with the cell wall, releasing the substance into the extracellular fluid.

Metabolism

• All biochemical reactions taking place in an organism, including anabolic and catabolic pathways.

• Anabolic - small molecules are built into large ones, energy is required.

• Catabolic - large molecules are broken down into small ones, energy is released.

Enzymes

• Biological catalysts that lower activation energy and facilitate chemical reactions.

• Made of proteins, reusable, highly specific, have an active site, used in very small accounts.

Substrate Complex

The binding of an enzyme to its substrate, forming a complex that lowers activation energy.

Regulation of Enzyme Activity

• Environmental factors like pH, temperature, salt concentration, and in some cases, cofactors or coenzymes affect enzymes.

• Competitive inhibition - an inhibitor binds at an active site and competes with substrate.

• Non-competitive inhibition - allosteric inhibition or allosteric activation

Aerobic Cellular Respiration

The process of breaking down carbohydrates to produce ATP in the presence of oxygen.

Glycolysis

• The first step of cellular respiration where glucose (six-carbon sugar) is converted into two molecules of pyruvate (a three-carbon sugar.

• Produces about 4 ATP but 2 are used in the process, which means there are 2 net ATP.

Krebs (Citric Acid) Cycle

• Acetyl CoA (two-carbon molecule) combines with a four-carbon molecule, ultimately regenerating the four-carbon starting molecule

• Produces 2 ATP, NADH, and FADH2 while releasing carbon dioxide.

Oxidative Phosphorylation

• The final stage of cellular respiration where most ATP (32) is produced via the electron transport chain.

• NADH and FADH₂ deposit their electrons into the electron transport chain, turning back into their “empty” forms (NAD⁺ and FAD)

Anaerobic Respiration

The process of producing ATP without oxygen, including fermentation pathways.

Alcoholic fermentation

Converts pyruvate to CO₂ and ethanol

Lactic acid fermentation

Converts pyruvate to lactic acid

ATP

• The energy carrier molecule used to power cellular activities, composed of three phosphate groups, adenine, and ribose.

• Cleavage of each high energy phosphate releases energy when ATP is hydrolyzed to ADP.