Chapter 3: Cells: The Living Units

Vocabulary flashcards covering the structural units of life, membrane transport, organelles, the cell cycle, and protein synthesis based on Chapter 3 lecture notes.

Cell

The structural units of all living things and the smallest unit of life.

Extracellular matrix

The most abundant extracellular material.

Blood plasma

An example of extracellular fluid.

Generalized human cell

A composite cell consisting of three main parts: the plasma membrane, the cytoplasm, and the nucleus.

Plasma membrane

A double layer of phospholipids with embedded proteins arranged as a fluid mosaic.

Hydrophilic head

The polar region of a phospholipid molecule that is water-loving.

Hydrophobic tail

The nonpolar region of a phospholipid molecule that is water-fearing.

Glycocalyx

A sugar-coated area at the cell surface that helps cells identify and interact with their environment.

Tight junction

An impermeable junction that prevents molecules from passing between cells.

Desmosome

An anchoring junction that helps keep cells from separating or tearing apart under tension.

Gap junction

A communicating junction that allows ions and small molecules to pass directly from cell to cell.

Passive transport

Membrane transport processes, such as diffusion and osmosis, that do not require the expenditure of cellular energy (ATP).

Concentration gradient

The difference in the concentration of a substance between two areas.

Selectively permeable barrier

A property of the plasma membrane that allow certain substances to pass while restricting others.

Osmosis

The movement of water through a membrane that is impermeable to solutes from an area of low solute concentration to high solute concentration.

Aquaporins

Water-specific protein channels in the plasma membrane.

Hypertonic solution

A solution with a higher concentration of nonpenetrating solutes than the cell, causing the cell to lose water.

Crenate

The shriveling of a cell, such as a red blood cell, when placed in a hypertonic solution.

Hypotonic solution

A solution with a lower concentration of nonpenetrating solutes than the cell, causing the cell to gain water and potentially burst.

Primary active transport

A type of transport that directly uses ATP as its source of energy to move substances against a gradient.

Secondary active transport

A type of transport where the energy source is the kinetic energy of ion gradients created by primary active transport.

Sodium-potassium pump

An active transport mechanism that pumps three $Na^+$ out of the cell and two $K^+$ back into the cell for every ATP used.

Exocytosis

The vesicular transport process responsible for the release of substances, such as hormones, from a cell.

Phagocytosis

A type of endocytosis involving the formation of pseudopods to engulf large solids or bacteria.

Pinocytosis

A transport process involving the nonselective sampling of extracellular fluid, also known as cell drinking.

Membrane potential

The voltage or electrical charge across the plasma membrane.

Resting membrane potential

The stable voltage across the membrane of a resting cell, measured at approximately $-70\,mV$ in a skeletal muscle cell.

Ligand

A chemical messenger, such as a neurotransmitter or hormone, that binds to a membrane receptor.

Inclusions

Chemical substances present in the cytoplasm such as melanin pigment granules or lipid droplets.

Cytosol

The viscous, semitransparent fluid in which cytoplasmic elements are suspended.

Mitochondria

Organelles responsible for ATP synthesis, featuring inner membrane folds called cristae.

Ribosomes

The sites of protein synthesis, which can be free in the cytosol or membrane-bound on the ER.

Rough Endoplasmic Reticulum

A membrane system studded with ribosomes that synthesizes proteins for secretion or membrane construction.

Smooth Endoplasmic Reticulum

An organelle involved in lipid and steroid synthesis, lipid metabolism, and drug detoxification.

Golgi apparatus

The organelle that modifies, concentrates, and packages proteins and lipids; its trans face serves as the shipping side.

Lysosomes

Organelles containing digestive enzymes for disposing of debris, bacteria, and worn-out organelles.

Peroxisomes

Organelles that contain enzymes to detoxify harmful substances like alcohol and neutralize free radicals.

Microfilaments

The thinnest cytoskeletal elements, consisting of strands made of the spherical protein actin.

Intermediate filaments

Tough, insoluble protein fibers that are the most stable cytoskeletal elements and strongly resist tension.

Microtubules

Hollow tubes of tubulin protein that radiate from the centrosome and help move organelles within the cell.

Basal bodies

Centrioles that have moved to the cell surface to form the bases of cilia and flagella.

Microvilli

Fingerlike extensions of the plasma membrane that function to increase surface area for absorption.

Nucleoli

Dark-staining spherical bodies in the nucleus where ribosomal subunits are assembled.

Chromatin

Threadlike structures in the nucleus composed of DNA and histone proteins.

Chromosomes

Short, barlike bodies formed when chromatin threads coil and condense during cell division.

Interphase

The period of the cell cycle from cell formation to cell division, consisting of $G_1$, $S$, and $G_2$ subphases.

Mitosis

The phase of the cell cycle during which the nucleus divides into two, consisting of prophase, metaphase, anaphase, and telophase.

DNA polymerase

The enzyme that positions complementary free nucleotides along the DNA template strands during replication.

Semiconservative replication

The process of DNA replication where each new DNA molecule consists of one old strand and one newly assembled strand.

Gene

A segment of a DNA molecule that carries instructions for creating one polypeptide chain.

Transcription

The process by which information flows from a DNA gene to messenger RNA (mRNA).

Translation

The process by which genetic information flows from mRNA to a polypeptide chain.

tRNA

Transfer RNA; the L-shaped molecule that transports specific amino acids to the ribosome.

Codon

A three-base sequence on mRNA that codes for a specific amino acid.

Anticodon

A three-base sequence on tRNA that is complementary to an mRNA codon.

Autophagy

The process of disposing of unneeded or damaged organelles using lysosomes.

Apoptosis

Programmed cell death used to dispose of unneeded, stressed, or damaged cells.

Ubiquitin

Proteins that mark other proteins for destruction in the ubiquitin-proteasome pathway.

Proteasomes

Giant protein complexes that hydrolyze proteins tagged with ubiquitin into small peptides.