Cell Biology, Membrane Transport, and Cell Division

Comprehensive practice flashcards for Chapter 3 review covering cell structures, membrane transport, the cell cycle, mitosis, regulation of division, stem cells, and apoptosis.

What is the relationship between cell structure and cell function?

Cell structure determines cell function.

Approximately how many cells are in the human body, and what is differentiation?

There are $50\text{--}100\text{ trillion}$ cells in the human body. Differentiation is the process by which cells specialize, leading to variations in size and shape due to their unique functions.

What are the three major parts common to all composite cells?

The nucleus, cytoplasm, and cell membrane.

How is the phospholipid bilayer of the cell membrane arranged?

It has hydrophilic (water-soluble) heads facing outward toward the surfaces and hydrophobic (water-insoluble) tails facing inward toward each other. It is permeable to lipid-soluble substances.

What is the function of cholesterol within the cell membrane?

Cholesterol stabilizes the cell membrane.

What functional roles do membrane proteins play in the cell membrane?

They act as receptors, pores, channels, carriers, cell adhesion molecules (CAMs), enzymes, and self-markers.

What are cell adhesion molecules (CAMs), and what are the specific roles of selectin and integrin?

CAMs guide cells or molecules on the move so they can perform a specific task; they are also important for the growth of nerve tissue.

Selectin allows white blood cells to anchor,

and integrin guides white blood cells through capillary walls.

What are the two primary components of cytoplasm?

Cytosol = fluid/water portion, and organelles, which are the solid functional structures.

How do the Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER) differ in structure and function?

The RER is a network of membrane channels associated with ribosomes that makes proteins for the cell.

The SER has few or no ribosomes, functions in lipid synthesis, lipid absorption from the digestive tract, and the breakdown of drugs/toxins, and is essential in liver cells.

What are ribosomes, and where are they found in the cell?

Ribosomes build proteins from amino acids and provide structure; they are not membrane-bound and are found floating free in the cytoplasm or attached to the RER.

What is the function of the Golgi apparatus?

It is a stack of flattened membranous sacs that modifies, packages, and delivers proteins into vesicles for transport.

What is the structure and function of mitochondria?

Mitochondria have a double-layer membrane system with inner folds called cristae; they generate usable energy by producing $ATP$ through cellular respiration.

How do lysosomes and peroxisomes differ in function?

Lysosomes are enzyme-containing sacs that digest damged cell parts and waste.

Peroxisomes are enzyme-containing sacs that break down organic molecules; they are present in all human cells and are most abundant in liver and kidney cells.

What is a centrosome and what are its functions?

A structure containing two rod-like centrioles

it helps distribute chromosomes during cell division and is used to produce cilia and flagella.

How do cilia and flagella differ in structure and function?

Cilia are short, hair-like projections that propel substances across cell surfaces (such as moving mucus across the respiratory tract).

Flagella are long, tail-like projections that provide motility to sperm cells.

What structures compose the cytoskeleton and what is its role?

Microtubules and microfilaments (thin rods and tubules) make up the cytoskeleton, which supports the cytoplasm/cell and allows for organelle movement.

What are cellular inclusions?

Temporary collections of nutrients and pigments stored in the cell.

What are the key components of the cell nucleus?

The nuclear envelope (a porous double membrane separating nucleoplasm from cytoplasm), the nucleolus (a dense collection of RNA and proteins where ribosomes are produced), and chromatin (fibers of DNA and proteins that store genetic information and condense into chromosomes).

Can DNA leave the cell nucleus?

No, DNA can never leave the nucleus; mRNA can.

What are passive transport processes, and which four are described?

it move substances down the concentration gradient without requiring ATP

examples: simple diffusion, facilitated diffusion, osmosis, and filtration.

How does simple diffusion differ from facilitated diffusion?

Simple diffusion moves substances directly through the cell membrane from high to low concentration (e.g., oxygen, carbon dioxide, lipid-soluble molecules).

Facilitated diffusion moves substances down their concentration gradient using channel or carrier proteins (e.g., glucose, amino acids). Neither requires $ATP$.

What is osmosis and what is osmotic pressure?

Osmosis is the movement of water across a selectively permeable membrane toward a region of higher solute concentration.

Osmotic pressure is the ability of osmosis to generate enough pressure to move a volume of water, or the pressure needed to stop water movement by osmosis; it increases as nonpermeable solute concentration increases.

How do isotonic, hypertonic, and hypotonic solutions affect cell volume?

In an isotonic solution, osmotic pressure is equal and cell size stays the same. In a hypertonic solution (higher solute concentration/osmotic pressure), water leaves and the cell shrinks or crenates. In a hypotonic solution (lower solute concentration/osmotic pressure), water enters and the cell swells and may lyse (burst).

What is filtration and what pressure drives it in the human body?

Filtration occurs when smaller molecules are forced through porous membranes by hydrostatic pressure. In the body, hydrostatic pressure is the same as blood pressure; it forces molecules out of capillaries and occurs in the kidneys to make urine.

What is active transport and how does the sodium-potassium ($Na^+/K^+$) pump function?

Active transport uses carrier molecules and cellular energy ($ATP$) to move substances against their concentration gradient. The $Na^+/K^+$ pump pumps $3$ sodium ($Na^+$) ions out of the cell and $2$ potassium ($K^+$) ions into the cell ($3:2$ ratio).

What is endocytosis and what are its three types?

Endocytosis is the process by which a cell engulfs substances by forming a vesicle. Its three forms are pinocytosis (cell drinking; liquids/water), phagocytosis (cell eating; solids), and receptor-mediated endocytosis (requires binding to specific membrane receptors).

What is exocytosis?

The reverse of endocytosis, in which substances stored in a vesicle fuse with the cell membrane and release their contents outside the cell (such as neurotransmitter release from nerve cells).

What is transcytosis?

Endocytosis rapidly followed by exocytosis, which transports a substance quickly through a cell layer (such as HIV crossing a cell layer).

What are the three main stages of the cell cycle?

Interphase, Mitosis, and Cytokinesis.

What events occur during the $G_1$, S, and $G_2$ phases of interphase?

$G_1$: cell grows, synthesizes structures and organelles, and passes the $G_1$ checkpoint. S phase: DNA synthesis and replication occur. $G_2$: cell prepares for mitosis, synthesizes proteins, and passes the $G_2$ checkpoint.

What are the results of mitosis in human somatic cells?

Mitosis divides the cell nucleus (karyokinesis) to produce $2$ genetically identical diploid daughter cells, each containing $46$ chromosomes.

What are the four phases of nuclear division (mitosis) in order?

Prophase, Metaphase, Anaphase, and Telophase (PMAT).

What major cellular events occur during prophase?

Chromatin condenses into visible chromosomes, the nuclear envelope breaks down, the nucleolus disappears, and centrioles migrate to opposite poles to form the spindle apparatus.

What key event defines metaphase?

Chromosomes line up along the metaphase plate in the middle of the cell, and the spindle apparatus attaches to their centromeres.

What happens during anaphase of mitosis?

Sister chromatids separate into individual chromosomes and are pulled apart toward opposite poles by the spindle apparatus; this phase ends when chromosome movement stops.

What occurs during telophase of mitosis?

Two new nuclear envelopes reform, chromosomes relax and uncoil back into chromatin, nucleoli reappear, and the spindle apparatus disappears.

What is cytokinesis, when does it begin, and how does it differ between animal and plant cells?

Cytokinesis is the division of cytoplasm, which begins during anaphase and continues through telophase. Animal cells divide via a contractile ring that forms a cleavage furrow, while plant cells form a cell plate. It is not considered part of mitosis because it does not divide the nucleus.

Based on the provided plant cell micrograph, which mitotic or cell cycle phase is shown at each letter (A through E)?

A: Interphase, B: Telophase, C: Metaphase, D: Anaphase, E: Prophase.

Why is a higher surface area-to-volume ratio beneficial for a cell?

A higher ratio allows the cell to absorb nutrients faster and eliminate waste products more efficiently.

What are telomeres and what function do they serve in cell division?

Telomeres are protective DNA tips at the ends of chromosomes that shorten with each round of division, acting as an internal mitotic clock that limits cell division capacity.

How do cell division rates differ between skin cells and nerve cells?

Skin and blood cells divide frequently and continually, whereas nerve cells (neurons) are amitotic and stop dividing after a specific number of divisions.

What external factors stimulate cell division, and what is contact inhibition?

Growth factors and hormones stimulate cell division (e.g., epidermal growth factor stimulates skin growth, hormones stimulate uterine smooth muscle mitosis). Contact (density-dependent) inhibition is the mechanism by which cells stop dividing when they touch neighboring cells.

What are tumors, and how do benign and malignant tumors differ?

Tumors result from a loss of cell cycle control. Benign tumors remain localized, whereas malignant tumors are invasive, cancerous, and capable of metastasizing (spreading).

How do oncogenes and tumor suppressor genes relate to cancer development?

Oncogenes activate genes that promote uncontrolled cell division, while tumor suppressor genes normally regulate and limit mitosis; when inactivated, tumor suppressor genes fail to control mitosis.

What is the difference between totipotent and pluripotent stem cells, and what is a progenitor cell?

Totipotent cells can give rise to every cell type, while pluripotent cells can give rise to a restricted number of cell types. A progenitor cell is a committed, partially specialized daughter cell of a stem cell that is pluripotent.

What is apoptosis?

Apoptosis is programmed cell death that acts as a continuous protective mechanism to remove damaged, nonfunctional, or unwanted cells.