BIO103 - B04 VOCAB - cell structure

nucleus

This is an organelle found in eukaryotic cells. It contains the genetic material in the form of chromosomes, made up of chromatin.

nuclear envelope

In a eukaryotic cell, this double membrane surrounds the nucleus. It is perforated with pores that regulate traffic to the surrounding cytoplasm. The outer membrane is continuous with the endoplasmic reticulum.

cytosol

The semifluid portion of the cytoplasm.

cytoplasm

The contents of the cell bounded by the plasma membrane; in eukaryotes, the portion exclusive of the nucleus.

nucleoid

Found in prokaryotes, this is a non-membrane enclosed region where chromosomes are housed.

plasma membrane

The boundary of every cell that acts as a selective barrier, regulating the cell's chemical composition.

phospholipid

This molecule forms bilayers that function as biological membranes. It has a hydrophilic tail and a hydrophobic head.

organelle

Any of several membrane-enclosed structures with specialized functions, suspended in the cytosol of eukaryotic cells (not prokaryotes).

chromatin

The complex of DNA and proteins that makes up eukaryotic chromosomes; when the cell is not dividing, this exists in a dispersed (loose) form as a mass of very long, thin fibers (not visible with a light microscope).

chromosome

A cellular structure consisting of one DNA molecule and associated proteins. A eukaryotic cell typically has multiple, linear forms of this structure that are housed in the nucleus while prokaryotes often have a single, circular form found in the nucleoid.

deoxyribonucleic acid

A nucleic acid molecule, usually a double-stranded helix. It is capable of being replicated and determining the inherited structure of a cell's proteins via transcription & translation.

ribosome

A complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and small subunit. In eukaryotes, the subunits are assembled in the nucleolus.

nucleolus

A specialized region in the nucleus, consisting of chromosomal regions containing ribosomal RNA (rRNA) genes along with ribosomal proteins imported from the cytoplasm (note: information flows from nucleus to ribosomes in cytoplasm and products come back to the nucleus!). This region is the site of rRNA synthesis and ribosomal subunit assembly.

messenger RNA

A type of RNA, synthesized using a DNA template during a process called transcription, that attaches to ribosomes in the cytoplasm and specifies the primary structure (sequence of amino acids) of a protein.

transfer RNA

An RNA molecule that functions as a "translator" (during translation in protein synthesis!) between nucleic acid and protein languages. It picks up a specific amino acid and carries it to the ribosome where this molecule latches onto the appropriate codon (based on its anticodon) in the messenger RNA (mRNA) molecule.

endomembrane system

The collection of membranes inside and surrounding a eukaryotic cell, related to one another either through direct physical contact or by the transfer of membranous vesicles. It includes the plasma membrane, the nuclear envelope, the smooth and rough endoplasmic reticulum (ER), the Golgi apparatus, lysosomes, vesicles, and vacuoles.

vesicle

A membrane-bound sac in or outside a cell.

smooth endoplasmic reticulum

Portion of the endoplasmic reticulum that is free of ribosomes. Its main functions are synthesis of lipids & steroid hormones, detoxification of harmful metabolic byproducts, as well as the storage and metabolism of calcium ions within the cell. This role involving calcium is particularly evident in its modified form as the sarcoplasmic reticulum in muscle cells.

rough endoplasmic reticulum

That portion of the endoplasmic reticulum with ribosomes attached. Being an organelle, it is found only in eukaryotic cells and its primary function is to produce proteins.

Golgi apparatus

An organelle (thus, only in eukaryotic cells) consisting of stacks of flat membranous sacs that modify, story, and distribute/route products of the endoplasmic reticulum. In addition, this organelle synthesizes some products, notably non-cellulose carbohydrates.

lysosome

A membrane-enclosed sac of hydrolytic enzymes (review hydrolysis) found in the cytoplasm of animal cells and some protists.

vacuole

A membrane-bounded vesicle whole specialized function varies in different kinds of cells. Example: in a mature plant cell, the central ___________ is involved in storage, growth, and sequestration (re-distribution) of toxic substances.

mitochondria

An organelle in eukaryotic cells that serves as the site of cellular respiration; uses oxygen to break down organic materials (i.e. carbohydrates, fats, etc.) and synthesize adenosine triphosphate (ATP).

chloroplast

An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.

endosymbiont theory

The theory that mitochondria and plastids (i.e. chloroplasts) originated as prokaryotic cells engulfed by a host cell. The engulfed cell and its host cell then evolved into a single organism. Strong evidence for this theory includes the fact that both mitochondria and plastids have their own DNA and ribosomes, both of which are prokaryotic in form.

peroxisome

An oxidative organelle (formerly known as a "microbody") found in the cytoplasm of nearly all eukaryotic cells that contains enzymes involved in a variety of metabolic reactions, including several aspects of energy metabolism. A key function involves enzymes that transfer hydrogen atoms from various substrates to oxygen (O2), producing hydrogen peroxide (H2O2). Since hydrogen peroxide is particularly harmful to the cell, this organelle contains the enzyme catalase, which degrades hydrogen peroxide either by converting it to water (H2O) or by using it to oxidize (review oxidation) another organic compound. A variety of substrates are broken down by such oxidative reactions including fatty acids. Note, the oxidation of fatty acids is a particularly important example, since it provides a major source of metabolic energy (remember, fat is a great source of energy in our bodies!).

cytoskeleton

A network of microtubules, microfilaments, and intermediate filaments that extend throughout the cytoplasm and serve a variety of mechanical, transport, and signaling functions.

intermediate filament

A component of the cytoskeleton that includes filaments intermediate in size between microtubules and the smaller microfilaments.

microtubule

A hollow rod composed of the tubulin protein that makes up part of the cytoskeleton in all eukaryotic cells and is also found in both cilia and flagella.

microfilament

A cable composed of actin proteins in the cytoplasm of almost every eukaryotic cell, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction; also called an actin filament.

motor protein

A protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell.

cilia

Short appendages containing microtubules in eukaryotic cells. Specialized forms are used for locomotion. Primary versions are non-motile and play both a sensory and signaling role.

flagella

Long cellular appendages specialized for locomotion. Like motile cilia, eukaryotic forms of these structures have an "9 + 2" arrangement of microtubules ensheathed in an extension of the plasma membrane. Prokaryotes forms of these are different.

tight junction

A type of intercellular (cell-to-cell) junction between animal cells that prevents the leakage of material through the space between cells.

desmosome

A type of intercellular junction in animal cells that functions as a rivet, fastening cells together.

gap junction

A type of intercellular junction in animal cells, consisting of proteins surrounding a pore that allows the passage of materials between cells. This structure directly connects the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells.