Ch 3 | Cell Structure and Genetic Control

What are the three principal parts of a cell?

1) Plasma membrane, 2) Cytoplasm and organelles, 3) Nucleus.

What is the fluid mosaic model of the plasma membrane?

The concept that the membrane is a dynamic fluid where phospholipids and proteins are not trapped, but can move laterally within the bilayer.

How does the hydrophobic core of the phospholipid bilayer affect permeability?

It restricts the passage of water, ions, and water-soluble (polar) molecules.

What allows selective movement of substances across the plasma membrane?

Protein channels and transport proteins embedded in the membrane.

Distinguish between integral and peripheral membrane proteins.

Integral proteins span the entire membrane. Peripheral proteins are embedded on just one side (inner or outer surface).

List five functions of membrane proteins.

1) Structural support, 2) Transport (channels/carriers), 3) Enzymatic control, 4) Receptors for signals (e.g., hormones), 5) "Self" markers for the immune system.

What is the glycocalyx and what are its functions?

A carbohydrate-rich coating of glycoproteins, glycolipids, and polysaccharides on the outer membrane. Functions: protection, maintaining membrane shape, acting as antigens, interacting with regulatory molecules, and signal transmission.

How does cholesterol affect the plasma membrane?

It is embedded in the bilayer and provides flexibility/stability to the membrane.

What is the difference between cytoplasm and cytosol?

Cytoplasm is the entire fluid/jelly-like substance between the plasma membrane and nucleus (includes organelles). Cytosol is just the liquid matrix portion of the cytoplasm where organelles are suspended.

Compare the functions of Rough ER and Smooth ER.

Rough ER: Has ribosomes; site of protein synthesis and modification for secretion. Smooth ER: Metabolizes nonpolar compounds (like lipids), stores Ca²⁺ (especially in muscle cells), and detoxifies.

What are ribosomes and what is their function? What is the difference between free and attached ribosomes?

Granules of protein and RNA that synthesize proteins. Free ribosomes make proteins for use inside the cell. Ribosomes attached to the Rough ER make proteins destined for export or for the membrane.

What are the three main functions of the Golgi complex?

1) Modifies molecules (e.g., creates glycoproteins), 2) Packages molecules from the ER, 3) Sorts and ships molecules in vesicles to their destinations (secretion).

What is the primary function of mitochondria?

To release energy from food molecules (cellular respiration) and transform it into usable ATP.

What is the primary function of lysosomes?

To digest foreign molecules, bacteria, and worn-out or damaged organelles using digestive enzymes.

What is the primary function of peroxisomes?

Contain enzymes that detoxify harmful molecules (like alcohol) and break down hydrogen peroxide (H₂O₂).

What are the roles of microfilaments and microtubules (cytoskeleton)?

Provide structural support to the cytoplasm (cell shape) and act as tracks for transport of materials within the cell.

What is the function of the centrosome (centrioles)?

Helps organize spindle fibers and distribute chromosomes during cell division (mitosis).

Compare a primary cilium and motile cilia.

Primary cilium: Nonmotile; found on most cells; acts as a sensory antenna (e.g., for fluid movement). Motile cilia: Beat in unison to move substances along a cell surface (e.g., mucus in respiratory tract).

What is a flagellum and which human cell has one?

A long, whip-like structure for propelling a cell. The sperm cell is the only human cell with a flagellum.

What is the function of microvilli and where are they found?

They are folds in the plasma membrane that increase surface area for absorption and rapid diffusion. Found in the intestines and kidney tubules.

What is amoeboid movement and what protein is key for it?

Movement used by cells like macrophages to "crawl." It relies on the bonding of integrins (cell membrane proteins) with proteins in the extracellular matrix (ECM).

Describe the steps of phagocytosis ("cell eating").

1) Cell extends pseudopods to engulf a large particle. 2) Pseudopods fuse, forming a food vacuole. 3) Vacuole fuses with a lysosome. 4) Lysosomal enzymes digest the material. (Important for body defense and cleanup).

Compare pinocytosis and receptor-mediated endocytosis.

Both are forms of endocytosis (membrane pouches inward to form a vesicle). Pinocytosis is nonspecific ("cell drinking"). Receptor-mediated endocytosis is specific; uses receptor proteins to bind and uptake specific substances (e.g., cholesterol, viruses).

What is exocytosis and what organelle is key for it? Give an example.

The process of moving large cellular products out of the cell. The Golgi apparatus packages products into vesicles that fuse with the plasma membrane to release contents. Example: Nerve endings releasing neurotransmitters.

What is unique about the number of nuclei in muscle cells and mature red blood cells (RBCs)?

Muscle cells have hundreds of nuclei. Mature RBCs have no nucleus.

What are nuclear pores and what is their function?

Openings in the nuclear envelope formed where the inner and outer membranes fuse. They allow passage of molecules like mRNA and proteins between the nucleus and cytoplasm.

What is a gene?

A length of DNA that codes for a specific protein (or functional RNA).

Differentiate between transcription and translation.

Transcription: Occurs in the nucleus; DNA is used as a template to produce messenger RNA (mRNA). Translation: Occurs at ribosomes (in cytoplasm); mRNA sequence is used to assemble amino acids into a polypeptide (protein).

How can one gene produce more than one protein? List three mechanisms.

1) Alternative splicing: mRNA is cut and spliced in different ways after transcription. 2) Protein combinations: Polypeptide chains can associate in different combinations. 3) Posttranslational modification: Adding groups (e.g., lipids, carbohydrates, phosphate via phosphorylation) to the protein after it's made.

What are histones and what is a nucleosome?

Histones: Positively charged proteins that DNA (negatively charged) wraps around. Nucleosome: The basic unit of DNA packaging; consists of DNA wound around a core of histone proteins.

Compare euchromatin and heterochromatin.

Euchromatin: Less condensed, genetically active (being transcribed). Heterochromatin: Highly condensed, genetically inactive (not transcribed).

How do histone acetylation and DNA methylation generally affect gene expression?

Histone acetylation relaxes chromatin structure, increasing gene expression. DNA methylation (often of cytosine bases) decreases gene expression.

What is epigenetic inheritance?

The inheritance of changes in gene expression (active vs. silent) from parent to daughter cell without a change in the actual DNA base sequence. Mechanisms include histone modifications and DNA methylation patterns.