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2.1 Cell Structure and Function

Syllabus
2025
Topic
2.1
Level
—

Learning objectives

2.1A—Explain how the structure and function of subcellular components and organelles contribute to the function of…Explain how the structure and function of subcellular components and organelles contribute to the function of cells.• Ribosomes are comprised of ribosomal RNA (rRNA) and protein. These non-membrane, subcellular structures are found in cells in all forms of life and reflect the common ancestry in all known life. Ribosomes synthesize proteins according to messenger RNA (mRNA) sequences.• The endomembrane system consists of a group of membrane-bound organelles and subcellular components (endoplasmic reticulum (ER), Golgi complex, lysosomes, vacuoles and transport vesicles, the nuclear envelope, and the plasma membrane) that work together to modify, package, and transport polysaccharides, lipids, and proteins intercellularly.• Endoplasmic reticulum provides mechanical support by helping cells maintain shape and plays a role in intracellular transport.- i. Rough ER is associated with membrane-bound ribosomes, allows for the compartmentalization of cells, and helps carry out protein synthesis.- ii. Smooth ER functions include the detoxification of cells and lipid synthesis.- Exclusion: Knowledge of the specific functions of smooth ER in specialized cells is beyond the scope of the AP Exam.• The Golgi complex is a membrane-bound structure that consists of a series of flattened membrane sacs. Functions of the Golgi include:- i. Correctly folding and chemically modifying newly synthesized cellular products- ii. Packaging proteins for trafficking- Exclusion: Knowledge of the role of Golgi in the synthesis of specific phospholipids and packaging of specific enzymes for lysosomes, peroxisomes, and secretory vesicles is beyond the scope of the AP Exam.• Mitochondria have a double membrane that provides compartments for different metabolic reactions involved in aerobic cellular respiration. The outer membrane is smooth, while the inner membrane is highly convoluted, forming folds that enable ATP to be synthesized more efficiently.• Lysosomes are membrane-enclosed sacs that contain hydrolytic enzymes that digest material. Lysosomes also play a role in programmed cell death (apoptosis).• Vacuoles are membrane-bound sacs that play many different roles.- i. In plant cells, a specialized large vacuole maintains turgor pressure through nutrient and water storage.- ii. In animal cells, vacuoles are smaller in size, are more plentiful than in plant cells, and store cellular materials.• Chloroplasts are specialized organelles that are found in plants and photosynthetic algae. Chloroplasts contain a double membrane and serve as the location for photosynthesis.

Cell Structures Work as a Coordinated System

A cell's organelles are a division-of-labor system: each structure creates the conditions for a particular job, and several components cooperate to move materials through the cell. Structure therefore helps explain both function and the effect of a disruption.

Component Structure linked to function Cellular contribution
Ribosome Non-membrane complex of rRNA and protein Reads mRNA sequences to synthesize proteins; its presence in all forms of life reflects common ancestry
Rough ER Membrane network associated with bound ribosomes Compartmentalizes and supports protein synthesis and intracellular transport
Smooth ER Membrane network without bound ribosomes Synthesizes lipids and contributes to detoxification
Golgi complex Series of flattened membrane sacs Folds or chemically modifies cellular products and packages proteins for trafficking
Mitochondrion Smooth outer membrane and highly folded inner membrane create compartments Supports reactions of aerobic cellular respiration and efficient ATP synthesis
Lysosome Membrane-enclosed sac containing hydrolytic enzymes Digests material and contributes to programmed cell death (apoptosis)
Vacuole Membrane-bound storage sac Stores cellular materials; a plant cell's large vacuole stores water and nutrients and maintains turgor pressure
Chloroplast Specialized double-membrane organelle in plants and photosynthetic algae Provides the location for photosynthesis

The endomembrane system includes the nuclear envelope, ER, Golgi complex, lysosomes, vacuoles, transport vesicles, and plasma membrane. For a trafficked protein, a membrane-bound ribosome makes the polypeptide at rough ER; membrane compartments and vesicles move it to the Golgi; the Golgi modifies and packages it; and vesicles deliver it to its cellular destination. This sequence shows why damaging one component can interrupt the output of the whole pathway.

Do not treat every organelle as part of the endomembrane system: ribosomes, mitochondria, and chloroplasts have distinct roles. AP does not require specialized-cell functions of smooth ER or the Golgi's synthesis and packaging of the specific excluded lipids and enzymes.