Chapter Four: Cell Structure and Cell Function

Plasma Membrane

A cell's outermost membrane

Chromatin

A collective term for DNA molecules together with their associated proteins.

Biofilm

A community of microorganisms living within a shared mass of slime.

Central Vacuole

Fluid-filled in many plant cells.

What is a cytoskeleton?

A cytoskeleton of protein filaments is the basis of eukaryotic cell shape, internal structure, and movement. Microtubules organize eukaryotic cells and help move their parts. Networks of microfilaments reinforce their surfaces. Intermediate filaments strengthen and maintain the shape of animal cells and tissues. When organized by ATP, motor proteins move along tracks of microtubules and microfilaments. As part of cilia, flagella, and pseupdopods, they can move the whole cell.

Nuclear Envelope

A double membrane that constitutes the outer boundary of the nucleus. Pores in the membrane control which substances can cross.

Vacuole

A fluid-filled organelle that isolates or disposes of waste, debris, or toxic materials.

Flagellum

A long, slender cellular structure used for motility.

What is the function of the cell nucleus?

A nucleus protects and controls access to a eukarytoic cell's DNA. The nuclear envelope is a double lipid bilayer. Proteins embedded in it control the passage of molecules between the nucleus and the cytoplasm.

Pilus

A protein filament that projects from the surface of some bacteria and archaea.

Nucleoid

A region of cytoplasm where the DNA is concentrated inside a bacterium or archaeon.

Surface-to-Volume Ratio

A relationship in which the volume of an object increases with the cube of the diameter, and the surface area increases with the square.

Cell Wall

A semirigid but permeable structure that surrounds the plasma membrane of some cells.

Plasmid

A small circle of DNA in some bacteria and archaea.

Cell Junction

A structure that connects a cell to another cell or to extracellular matrix.

Chromosome

A structure that consists of DNA and associated proteins; carries part or all of a cell's genetic information.

Pseudopod

A temporary protrusion that helps some eukaryotic cells move and engulf prey.

How are all cells alike?

All cells start life with a plasma membrane, cytoplasm, and a region of DNA, which, in eukaryotic cells only, is enclosed by a nucleus.The surface-to-volume ration limits cell size and influences cell shape. Observations of cells led to the cell theory: All organisms consist of one or more cells; the cell is the smallest unit of life; each new cell arises from another cell; and a cell passes hereditary material to its offspring.

What do all eukaryotic cells have in common?

All eukaryotic cells start life with a nucleus and other membrane-enclosed organelles.

Ribosome

An organelle of protein synthesis

Tight Junctions

Arrays of fibrous proteins; join epithelial cells and collectively prevent fluids from leaking between them.

How are bacteria and archaea alike?

Bacteria and archaea do not have a nucleus. Most kinds have a cell wall around their plasma membrane. The permeable wall reinforces and imparts shape to the cell body. The structure of bacteria and archaea is relatively simple, but as a group these organisms are the most diverse forms of life. They inhabit nearly all regions of the biosphere. Some metabolic processes occur at the plasma membrane of bacteria and archaea. They are similar to complex processes that occur at certain internal membranes of eukaryotic cells.

Centriole

Barrel-shaped organelle from which microtubes grow.

Plastid

Category of double-membraned organelle in plants and algal cells. Different types specialize in storage or photosynthesis; e.g. chloroplast, amyloplast.

Adhering Junction

Cell junction of adhesion proteins' anchors cells to each other and extracellular matrix.

gap junction

Cell junction that forms a channel across the plasma membranes of adjoining animal cells.

Plasmodesmata

Cell junctions that connect the cytoplasm of adjacent plant cells.

What structures form on the outside of eukaryotic cells?

Cells of many protists, nearly all fungi, and all plants have a porous wall around the plasma membrane. Animal cells do not have walls. Plant cell secretions form a wavy cuticle that helps protect the exposed surfaces of soft plant parts. Cell secretions form extraceullular matrixes between cells in many tissues. Cells make structural and functional connections with one another and with extraceullular matrix in tissues.

Extracellular matrix (ECM)

Complex mixture of cell secretions; supports cells and tissues; has roles in cell signaling.

Microtubule

Cytoskeletal element involved in cellular movement; hollow filament of tubulin subunits.

Cytoskeleton

Dynamic framework of protein filaments that support, organize, and move eukaryotic cells.

Lysosome

Enzyme filled vesicle that functions in intracellular digestion.

Peroxxisome

Enzyme-filled vesicle that breaks down amino acids, fatty acids, and toxic substances.

Nucleolus

In a cell nucleus, a dense, irregularly shaped region where ribosomal subunits are assembled.

Secondary wall

Lignin-reinforced wall that forms inside the primary wall of a plant cell.

Lignin

Material that stiffens cell walls of vascular plants.

What eukaryotic organelles are specialized for producing ATP?

Mitochondria are eukaryotic organelles that produce ATP from organic compounds in reactions and require oxygen. Chloroplasts are plastids that carry out photosynthesis in cells of plants and many protists.

How do we see cells?

Most cells are visible only with the help of microscopes. Different types of microscopes reveal different aspects of cell structure.

Chloroplast

Organelle of photosynthesis in the cells of plants and many protists.

Basal Body

Organelle that develops from a centriole.

Endoplasmic Reticulum (ER)

Organelle that is a continuous system of sacs and tubes; extension of the nuclear envelope. Smooth ER makes lipids and breaks down carbohydrates and fatty acids; rough ER modifies polypeptides made by ribosomes on its surface.

Golgi body

Organelle that modifies polypeptides and lipids; also sorts and packages the finished products into vesicles.

Mitochondrion

Organelle that produces ATP by aerobic respiration.

Nucleus

Organelle with two membranes that holds a eukaryotic cell's DNA.

Microfilament

Reinforcing cytoskeletal element; a fiber of actin subunits.

Cell Cortex

Reinforcing mesh of cytoskeletal elements under a plasma membrane.

Cuticle

Secreted covering at a body surface.

Cytoplasm

Semifluid substance enclosed by a cell's plasma membrane.

Endo-membrane system

Series of interacting organelles (endoplasmic reticulum, Golgi bodies, vesicles) between nucleus and plasma membrane; produces lipids and proteins.

Cilium

Short, movable structure that projects from the plasma membrane of some eukaryotic cells.

Vesicle

Small, membrane-enclosed, saclike organelle; different kinds store, transport, or degrade their contents.

Intermediate Filament

Stable cytoskeletal element that structurally supports cells and tissues.

Organelle

Structure that carries out a specialized metabolic function inside a cell.

What is the endomembrane system?

The endomemrbane system includes rough and smooth endoplasmic reticullum, vesicles, and Golgi bodies. This series of organelles works together mainly to synthesize and modify cell membrane proteins and lipids.

Primary wall

The first cell wall of young plant cells.

Cell Theory

Theory that all organisms consist of one or more cells, which are the basic unit of life; all cells come from division of pre-existing cells; and all cells pass hereditary material to offspring.

Motor protein

Type of energy-using protein that interacts with cytoskeletal elements to move the cell's parts or the whole cell.

Nucleoplasm

Viscous fluid enclosed by the nuclear envelope.

Which one is the smallest; a protein, lipid, or water molecule?

Water molecule

What is life?

We describe the characteristic of "life" in terms of a set of properties unique to living things. In living things, the molecules of life are organized as one or more cells that engage in self-sustaining biological processes. Organisms use DNA as their hereditary material. Living things change over lifetimes, and over generations.