Cell Structure and Function Quiz

Cell Structure and Function

• Cells are the fundamental unit of life.
• The cell theory states cells are the basic units of structure and function in organisms. All organisms are composed of cells. All cells come only from preexisting cells.
• Cell size is small due to the important relationship between surface area and volume. Small cells have a larger surface area-to-volume ratio, enabling efficient exchange of materials.
• The unassisted human eye can generally view macroscopic organisms (large cells) and a few large cells. Microscopic cells are observed via microscopes.
• There are two basic types of cells: prokaryotic and eukaryotic.

Prokaryotic Cells

• Lack a membrane-bound nucleus.
• Structurally smaller and simpler than eukaryotic cells.
• Classified into two domains: Bacteria and Archaea.
• Bacteria can cause diseases, act as decomposers, and are used in manufacturing.
• Archaea inhabit extreme environments, like hot springs and salt lakes.
• Shape varies: coccus, bacillus, spirillum, spirochete.
• Lack membrane-bound organelles.
• DNA is located in a region called the nucleoid.
• Structures include: cell wall, plasma membrane, glycocalyx (slime layer or capsule), fimbriae, flagella, conjugation pili, ribosomes.

Eukaryotic Cells

• Possess a membrane-bound nucleus.
• Larger than prokaryotic cells.
• Contain membrane-bound organelles that perform specific functions.
• Examples of organelles: mitochondria, chloroplasts.
• Endomembrane system comprises: nuclear envelope, endoplasmic reticulum, Golgi apparatus, several types of vesicles.

The Nucleus

• Command center of the cell.
• Usually oval-shaped and located near the center of the cell.
• Separated from cytoplasm by a nuclear envelope.
• Double-layered membrane (inner and outer) with nuclear pores.
• Contains chromatin, the network of DNA and proteins that condenses into chromosomes during cell division.
• Site of gene transcription, rRNA, mRNA, and tRNA production.
• Communicates with ribosomes.

Ribosomes

• Particles responsible for protein synthesis.
• Found in both prokaryotic and eukaryotic cells.
• Eukaryotic ribosomes are 20nm by 30nm and have slightly smaller than prokaryotic ribosomes.
• Can be free in the cytoplasm or attached to the endoplasmic reticulum.
• Protein synthesis occurs in ribosomes, in mRNA's presence, the exact sequence of amino acids, following the information coded in DNA.

Endomembrane System

• Interconnected intracellular membranes that compartmentalize the cell, increasing its efficiency.
• Consists of: nuclear envelope, endoplasmic reticulum, Golgi apparatus, and various vesicles.
• Function is the transport of materials between organelles, with modifications of proteins and lipids occurring in this process.

Endoplasmic Reticulum

• Complex system of interconnected membranes and tubes.
• Rough ER is studded with ribosomes for protein synthesis.
• Smooth ER lacks ribosomes; important in lipid synthesis, detoxification (liver), and steroid hormone production.

Golgi Apparatus

• Stack of flattened, slightly curved sacs called cisternae.
• Processes, packages, and secretes modified proteins and lipids.
• Proteins and lipids received from the ER are transported, modified, and packaged into vesicles at the Golgi apparatus.

Lysosomes

• Membrane-bound vesicles found in animal cells but not plant cells.
• Contain hydrolytic enzymes for digesting macromolecules, and worn-out organelles.
• Important in cellular recycling and waste disposal.
• Acidic environment is essential for proper enzyme function.

Peroxisomes

• Membrane-bound vesicles found in both animal and plant cells.
• Contain enzymes that break down fatty acids, and produce H2O2 (a toxic by-product).
• Catalase enzyme catalyzes the breakdown of H2O2 into water and O2 to neutralize its effects.
• Necessary for detoxification of various substances.

Vacuoles

• Membrane-bound sacs, larger than vesicles; store materials.
• In plant cells, the central vacuole occupies a large portion of the cell and aids in turgor pressure maintenance and storage Functions in: storage of water, nutrients, pigments and waste products.

Mitochondria

• Double-membraned organelles.
• Contain their own DNA and ribosomes.
• Site of cellular respiration where energy (ATP) is generated.
• Highly convoluted inner membrane (cristae).
• Matrix contains enzymes for breakdown of carbohydrates.

Chloroplasts

• Found in plant cells and algae.
• Site of photosynthesis, converting light energy into chemical energy (carbohydrates).
• Contain chlorophyll and other pigments.
• Extensive internal membrane system (thylakoids arranged in stacks called grana).
• Stroma (fluid surrounding thylakoids) contains enzymes necessary for carbohydrate synthesis.

Cytoskeleton

• Network of protein filaments that maintains cell shape, enables cell movement, and facilitates intracellular transport and various cell divisions.
• Consists of actin filaments, intermediate filaments, and microtubules.
• Each type of filament has different functions (e.g., muscle contraction).

Centrioles

• Microtubule-organizing centers found in animal cells and some protists.
• Composed of microtubules arranged in a 9+0 pattern.
• Play a role in cell division, organizing microtubules to pull chromosomes apart during mitosis or meiosis and determine the plane of division.
• May give rise to basal bodies that direct microtubule organization in cilia and flagella.