Biology: Cell Structure and Function

Cell

The basic unit of structure and function in living things.

Cell theory

A fundamental concept of biology that states all living things are composed of cells, cells are the basic units of structure and function, and new cells are produced from existing cells.

Unicellular

An organism consisting of a single cell.

Multicellular

An organism consisting of many cells.

Phospholipids

Lipids with a hydrophilic head and two hydrophobic tails; they are a major component of cell membranes.

Phospholipid bilayer

A double layer of phospholipids that forms the cell membrane, providing a barrier.

Plasma membrane

Also known as the cell membrane; the barrier that separates the interior of all cells from the outside environment.

Cell membrane

Another term for the plasma membrane.

Amphipathic

Having both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region, like a phospholipid.

Fluid mosaic

The model of the plasma membrane structure where proteins are embedded in a fluid lipid bilayer.

Hydrophobic

Water-fearing; repelled by water. (e.g., the tails of phospholipids)

Hydrophilic

Water-loving; attracted to water. (e.g., the heads of phospholipids)

Saturated

Fatty acid tails with all single bonds; straight chains that pack tightly.

Unsaturated

Fatty acid tails with one or more double bonds; kinked chains that prevent tight packing.

Transport protein

A protein that moves substances across the cell membrane.

Channel protein

A transport protein that provides a hydrophilic pore through the membrane.

Carrier protein

A transport protein that changes its shape to move a specific molecule across the membrane.

Receptor

A protein on or in a cell that binds to a specific signaling molecule, triggering a response.

Enzyme

A biological catalyst (usually a protein) that speeds up a chemical reaction without being consumed.

Anchor

Membrane proteins that attach the cell to the cytoskeleton or to the extracellular matrix.

Homeostasis

The maintenance of a relatively constant internal environment by an organism.

Cell wall

A rigid layer of nonliving material that surrounds the cells of plants, fungi, and some prokaryotes.

Selectively permeable

A property of the cell membrane that allows some substances to pass through more easily than others.

Diffusion

The passive movement of molecules from an area of higher concentration to an area of lower concentration.

Simple diffusion

Passive transport where substances pass directly through the lipid bilayer without the aid of transport proteins.

Facilitated diffusion

Passive transport that uses transport proteins to move substances across the membrane.

Active transport

The movement of substances across a membrane against its concentration gradient, requiring energy (ATP).

Concentration gradient

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

Exocytosis

A process by which the contents of a cell vacuole are released to the exterior through the fusion of the vacuole membrane with the cell membrane.

Endocytosis

A process by which a cell takes material into the cell by infolding of the cell membrane.

Turgor pressure

The force exerted outward by the water against the cell wall in plant cells.

Osmosis

The diffusion of water across a selectively permeable membrane.

ATP

Adenosine triphosphate; the main energy currency of the cell.

Hypertonic

A solution with a higher solute concentration than the cell; causes water to leave the cell.

Hypotonic

A solution with a lower solute concentration than the cell; causes water to enter the cell.

Isotonic

A solution with the same solute concentration as the cell; no net water movement.

Surface area to volume ratio

A critical factor in cell size; as a cell grows, volume increases faster than surface area, limiting transport.

Rate

A measure of how quickly a process occurs.

Ratio

A quantitative relationship between two amounts.

Central vacuole

A large, membrane-bound sac in mature plant cells that stores water, nutrients, and waste.

Vacuole

A membrane-bound organelle that is used for storage, waste disposal, and maintaining water balance.

Prokaryote

A single-celled organism that lacks a nucleus and other membrane-bound organelles (e.g., bacteria).

Eukaryote

An organism whose cells contain a nucleus and other membrane-bound organelles (e.g., animals, plants, fungi).

Organelle

A tiny cell structure that carries out a specific function within the cell.

Nucleus

The organelle that contains most of the cell's genetic material (DNA) and controls cell activities.

Nucleolus

A structure within the nucleus where ribosomes are made.

Nuclear envelope

The double membrane that surrounds the nucleus, perforated with pores.

Endoplasmic reticulum (ER)

A network of membranes inside a eukaryotic cell where lipids are synthesized and proteins are modified.

Golgi apparatus/body

An organelle that modifies, sorts, and packages proteins and lipids from the ER for transport.

Lysosome

An organelle containing digestive enzymes that breaks down worn-out cell parts and waste.

Mitochondria

The "powerhouse" of the cell; site of cellular respiration and ATP production.

Cytoskeleton

A network of fibers extending throughout the cytoplasm that provides structural support and aids in cell movement.

Chloroplasts

Organelles found in plant cells and algae that are the site of photosynthesis.

Cytosol

The jelly-like fluid component of the cytoplasm, excluding the organelles.

Cytoplasm

The entire contents of the cell, enclosed within the cell membrane (in eukaryotes, this includes the cytosol and organelles, but not the nucleus).

Vesicle

A small, membrane-enclosed sac used to transport substances within a cell or to the cell membrane.

Endomembrane system

The group of organelles and membranes in eukaryotic cells that work together to modify, package, and transport lipids and proteins (includes ER, Golgi, lysosomes, and vesicles).

Bulk transport

The movement of large molecules or numerous molecules into or out of a cell (includes endocytosis and exocytosis).

Nuclear pores

Protein-lined channels in the nuclear envelope that regulate the entry and exit of molecules from the nucleus.

Ribosome

A tiny organelle that is the site of protein synthesis.

Centriole

One of two cylindrical structures in animal cells, involved in cell division.

Cilia

Short, numerous, hair-like appendages that propel protists or move fluids over the cell surface.

Flagellum

A long, whip-like tail used for movement (locomotion) in cells.

Deoxyribonucleic acid (DNA)

The double-stranded hereditary material that carries genetic instructions for development, functioning, growth, and reproduction.

Ribonucleic acid (RNA)

A single-stranded nucleic acid that is essential for protein synthesis (gene expression).

mRNA (messenger RNA)

Carries genetic information copied from DNA in the nucleus to the ribosome in the cytoplasm.

tRNA (transfer RNA)

Carries specific amino acids to the Ribosome during Translation.

rRNA (ribosomal RNA)

A primary component of the Ribosome that catalyzes peptide bond formation.

Genes

Segments of DNA that code for a specific protein or a functional RNA molecule.

Gene expression

The process by which information from a Gene is used to synthesize a functional gene product (protein or RNA).

Central dogma of molecular biology

The flow of genetic information: DNA → RNA → Protein.

Replication

The process of making an exact copy of DNA before cell division.

Mutations

Permanent, heritable changes in the Nucleotide Sequence of DNA.

Transcription

The synthesis of RNA from a DNA Template strand.

Translation

The synthesis of a protein (polypeptide) from an mRNA Sequence.

Nucleotide

The monomer (building block) of nucleic acids (DNA and RNA), consisting of a sugar, a phosphate group, and a Nitrogenous base.

Base pairing rules

Specific rules dictating which nitrogenous bases form Hydrogen bonds; A pairs with T (or U in RNA), and G pairs with C.

Adenine (A)

A purine Nitrogenous base that pairs with Thymine (T) in DNA and Uracil (U) in RNA.

Guanine (G)

A purine Nitrogenous base that pairs with Cytosine (C).

Thymine (T)

A pyrimidine Nitrogenous base found only in DNA that pairs with Adenine (A).

Cytosine (C)

A pyrimidine Nitrogenous base that pairs with Guanine (G).

Uracil (U)

A pyrimidine Nitrogenous base found only in RNA that pairs with Adenine (A).

Antiparallel

The two strands of DNA run in opposite directions (one 5

′

→3

′

, the other 3

′

→5

′

).

Sugar phosphate backbone

The structural part of the DNA or RNA molecule, composed of alternating sugar and phosphate groups.

Nitrogenous base

The part of the Nucleotide (A, T, C, G, U) that carries the genetic information.

Complementary

Describes the relationship between the two strands of a DNA molecule due to Base pairing rules.

Hydrogen bonds

Weak bonds that hold the Complementary Nitrogenous bases together in the center of the DNA helix.

Parent strands

The original DNA strands that serve as templates for the synthesis of new Daughter strands during Replication.