Chapter 4

In which of these cell types would you expect to find a membrane-bound nucleus?

fungal cell (Fungi are eukaryotes with a membrane-enclosed nucleus.)

centriole

in animal cells, a short, barrel-shaped ring consisting of nine microtubule triplets; a pair of centrioles is found near the nucleus and may play a role in the organization of the spindle; centrioles also give rise to the basal bodies at the base of each cilium and flagellum that give rise to the microtubules of cilia and flagella.

plastid

in plant cells, an organelle bounded by two membranes that may be involved in photosynthesis (chloroplasts), pigment storage, or food storage.

During what period was the cell theory developed?

in the middle 1800s; Serious work on the cell theory occurred between 1838 and 1855, when it was finalized.

endomembrane system

internal membranes that create loosely connected compartments within the eukaryotic cell. It includes the nuclear envelope, the endoplasmic reticulum, vesicles, the Golgi apparatus, and lysosomes.

Which of the components of the cytoskeleton is much more important to animal cells that to plant cells?

microfilaments (Microfilaments provide for muscle motion and animal cell division.)

Which of the functions of a cytoskeleton is unique to eukaryotic (as opposed to prokaryotic) cells?

organelle movement (Prokaryotic cells do not have organelles to organize and move about.)

intermediate filament

part of the cytoskeleton of eukaryotic cells that is composed of several types of proteins and probably functions mainly for support.

microfilament

part of the cytoskeleton of eukaryotic cells that is composed of the proteins actin and (in some cases) myosin; functions in the movement of cell organelles, locomotion by extension of the plasma membrane, and sometimes contraction of entire cells.

Which cellular structure has the most in common with the nuclear envelope?

plasma membrane (Both are membranes, both isolate their contents from their surroundings, and both control the movement of substances with the help of embedded proteins.

What is the smallest living thing in the following list: frog embryo, mitochondrion, prokaryote, virus, atom?

prokaryote (Although bacteria are larger than atoms, viruses, and sometimes mitochondria, these three things are not cells and cannot be called living things.)

archaea

prokaryotes that are members of the domain Archaea, one of the three domains of living oganisms; only distantly related to members of the domain Bacteria.

bacteria (sing., bacterium)

prokaryotes that are members of the domain Bacteria, one of three domains of living organisms; only distantly related to members of the domain Archaea.

Which of the following biological molecules accomplish work within the cell?

proteins (Proteins coordinate all movement and activity inside of a cell.)

eukaryotic

referring to cells of organisms of the domain Eukarya (plants, animals, fungi and protists). Eukaryotic cells have genetic material enclosed within a membrane-bound nucleus and they contain other membrane-bound organelles.

ribosome

a comples consisting of two subunits, each composed of ribosomal RNA and protein, found in the cytoplasm of cells or attached to the endoplasmic reticulum, that is the site of protein synthesis, during which the sequence of bases of messenger RNA is translated into the sequence of amino acids in a protein.

contractile vacuole

a fluid-filled vacuole in certain protists that takes up water from the cytoplasm, contracts, and expels the water outside the cell through a pore in the plasma membrane.

pilus (pl., pili)

a hairlike protein structure that projects from the cell wall of many bacteria. Attachment pili help bacteria adhere to structures. Sex pili assist in the transfer of plasmids.

microtubule

a hollow, cylindrical strand, found in eukaryotic cells, that is composed of the protein tubulin; part of the cystoskeleton used in the movement of orgnaelles, cell growth, and the construction of cilia and flagella.

central vacuole

a large, fluid-filled vacuole occupying most of the volume of many plant cells; performs several functions, including maintaining turgor pressure.

flagellum (pl., flagella)

a long, hair-like, motile extension of the plasma membrane; in eukaryotic cells, it contains microtubules arranged in a 9:1:2 pattern. The movement of flagella propels some cells through fluids.

organelle

a membran-enclosed structure found inside a eukaryotic cell that perfoms a specific function.

lysosome

a membrane-bound organelle containing intracellular digestive enzymes.

food vacuole

a membranous sac, within a single cell, in which food is enclosed. Digestive enzymes are released into the vacuole, where intracellular digestion occurs.

deoxyribonucleic acid (DNA)

a molecule composed of deoxyribose nucleotides; contains the genetic information of all living cells.

ribonucleic acid (RNA)

a molecule composed of ribose nucleotides, each of which consists of a phosphate group, the sugar ribose, and one f the bses adenin, cytosin, guanine, or uracil; involved in converting the information in DNA into protein; also the genetic material of some viruses.

cytoskeleton

a network of protein fibers in the cytoplasm that gives shape to a cell, holds and moves organelles, and is typically involved in cell movement.

cell wall

a nonliving, protective, and supportive layer secreted outside the plasma membrane of fungi, plants, and most bacteria and protists.

chlorophyll

a pigment found in chloroplasts that captures light energy during photosynthese; chlorophyll absorbs violet, blue, and red light but reflects green light.

cilium (pl., cilia)

a short, hair-like motil projection from the surface of certain eukaryotic cells that contains microtubules in a 9:1:2 arrangement. The movement of cilia may propel cells through a fluid medium or move fluids over a stationary surface layer of cells.

vesicle

a small, temporary, membrane-bound sac within the cytoplasm

Golgi appartus

a stack of membranous sacs, found in most eukaryotic cells, that is the site of processing and separation of membrane components and secretory materials.

basal body

a structure derived from a centriole that produces a cilium or flagellum and anchors this structure within the plasma membrane.

endoplasmic reticulum

a system of membranous tubes and channels in eukaryotic cells; the site of most protein and lipid synthesis.

cytoplasm

all of the material contained within the plasma membrane of a cell, exclusive of the nucleus.

nuclear pore complex

an array of proteins that line pores in the nuclear membrane and control which substances enter and leave the nucleus.

mitochondrion (pl., mitochondria)

an organelle, bounded by two membranes, that is the site of the reactions of aerobic metabolism.

prokaryote

an organism whose cells are prokaryotic (their genetic material is not enclosed in a membrane-bound nucleus and they lack other membrane-bound organelles.); bacteria and archaea are prokaryotes.

prokaryotic

referring to cells of the domains Bacteria or Archaea. Prokaryotic cells have genetic material that is not enclosed in a membrane-bound nucleus; they also lack other membrane-bound organelles.

Which of the following is present inside a prokaryotic cell?

ribosomes (Prokaryotic cells still use ribosomes to generate proteins.)

chromatin

the complex of DNA and proteins that makes up eukaryotic chromosones.

nuclear envelope

the double-membrane system surrounding the nucleus of eukaryotic cells; the outer membrane is typically continuous with the endoplasmic reticulum.

cytosol

the fluid portion of the cytoplasm; the substance within the plasma membrane exclusive of the nucleus and organelles.

endosymbiont hypothesis

the hypothese that certain organelles, especially chloroplasts and mitochondria, arose as mutually beneficial associations between the ancestors of eukaryrotic cells and captured bacteria that lived within the cytoplasm of the pre-eukaryotic cell.

nucleoid

the location of the genetic material in prokaryotic cells; not membrane enclosed.

nucleus (cellular)

the membrane-bound oganell of eukaryotic cells that contains the cell's genetic material.

diffusion

the net movement of solute particles from a region of high solute concentration to a region of low solute concentration, driven by a concentration gradient; may occur within a fluid or across a barrier such as a membrane.

chloroplast

the organelle in plants and plantlike protists that is the site of photosynthesis; is surrounded by a double membrane and contains an extensive internal membrane system that bears chlorophyll.

plasma membrane

the outer membrane of a cell, composed of a bilayer of phophololipids in which proteins are embedded.

nucleolus (pl., nucleoli)

the region of the eukaryotic nucleus that is engaged in ribosome synthesis; consists fo the genes encoding ribosomal RNA, newly syntesized ribosomal RNa, and ribosomal proteins.

cell theory

the scientific theory stating that every living organism is made up of one or more cells; cells are functional units of all organisms; and all cells arise from preexisting cells.

What is a feature of cells?

All cells, plant, animal, and prokaryotic, have a plasma membrane that surrounds them.)

We usually compare all eukaryotic cells as a group to all prokaryotic cells. However, some types of eukaryotic cells have characteristics that are found in prokaryotic cells, but not found in other eukaryotic cells. What feature do plant cells share with prokaryotic cells, but not animal cells?

cell wall (Plant cells and prokaryotic cells have a cell wall, whereas animal cells do not.)

What is similar about exporting proteins from a cell and digesting food particles within a cell?

Both processes involve the formation of vesicles. (Vesicles transport proteins to the plasma membrane for export and digestion requires special vesicles called lysosomes.)

Which of the following is a function of the smooth endoplasmic reticulum?

Lipid manufacture (the smooth ER serves as a workplace for enzymes. Depending on the cell type, these enzymes may make lipids, detoxify poisons, or break down glycogen chains.)

What is the purpose of mitochondria?

Mitochondria produce ATP using the energy in food. (Mitochondria don't simply produce energy in a raw form. They take the energy from food and convert it into a more useful form, ATP.)

Which statement best describes the relationship between RNA and DNA?

RNA is a copy of DNA that is used to make proteins. (A temporary copy of DNA, called RNA, is made and then used to make proteins.)

Why is the nucleus considered the control center for the cell?

The nucleus controls which proteins are made and when. (Proteins do most of the work in a cell. Because the nucleus controls protein production, it controls all the work a cell does.)