A Tour of the Cell Flashcards
A variety of microscopes have
A variety of microscopes have been developed for a clearer view of cells and cellular structure.
In the 1800s, these studies led to cell theory
cell theory
which states that
all living things are composed of cells and
all cells come from other cells
Cell size must
be large enough to house DNA, proteins, and structures needed to survive and reproduce, but
remain small enough to allow for a surface-to-volume ratio that will allow adequate exchange with the environment.
The plasma membrane
The plasma membrane forms a flexible boundary between the living cell and its surroundings.
Phospholipids form a
a two-layer sheet called a phospholipid bilayer in which
hydrophilic heads face outward, exposed to water, and
hydrophobic tails point inward, shielded from water.
Membrane proteins are either
attached to the membrane surface or
embedded in the phospholipid bilayer.
Some proteins form
channels/tunnels that allow ions and other hydrophilic molecules as they pass through the hydrophobic center of the membrane.
Other proteins serve as pumps using energy to actively transport molecules in / out of the cell.
prokaryotic
Bacteria and archaea are prokaryotic cells.
eukaryotic cells
All other forms of life are composed of eukaryotic cells.
Prokaryotic and eukaryotic cells have
a plasma membrane and
one or more chromosomes and ribosomes.
Eukaryotic cells have a
membrane-bound nucleus and
number of other organelles.
Prokaryotes
have a nucleoid and no true organelles
nucleoid
The DNA of prokaryotic cells is coiled into a region called the nucleoid, but no membrane surrounds the DNA.
The surface of prokaryotic cells may
be surrounded by a chemically complex cell wall,
have a capsule surrounding the cell wall,
have short projections that help attach to other cells or the substrate, or
have longer projections called flagella that may propel the cell through its liquid environment.
The structures and organelles of eukaryotic cells perform four basic functions.
The nucleus is involved in genetic control of the cell.
The endoplasmic reticulum, ribosomes, and Golgi apparatus are involved in the manufacture, distribution, and breakdown of molecules.
Mitochondria in all cells and chloroplasts in plant cells are involved in energy processing.
Structural support, movement, and communication between cells are functions of the cytoskeleton, plasma membrane and cell wall
The internal membranes of eukaryotic cells partition it into compartments.
Cellular metabolism
the many chemical activities of cells, occurs within organelles (inside mitochondria or chloroplasts) or out in the cytosol
Almost all of the organelles and other structures of animals cells are present in plant cells.
A few exceptions exist.
Lysosomes and centrioles are not found in plant cells.
Plant but not animal cells have
a rigid cell wall,
chloroplasts, and
a central vacuole.
The nucleus
contains most of the cell’s DNA and
controls the cell’s activities by directing protein synthesis by making messenger RNA (mRNA).
DNA is associated with many proteins in structures called chromosomes.
The nuclear envelope
is a double membrane and
has pores that allow material to flow in and out of the nucleus.
The nuclear envelope is attached to a network of cellular membranes called the endoplasmic reticulum.
The nucleolus
is a prominent structure in the nucleus and
the site of ribosomal RNA (rRNA) synthesis.
Ribosomes
are involved in the cell’s protein synthesis.
Ribosomes are synthesized from rRNA produced in the nucleolus.
Cells that must synthesize large amounts of protein have a large number of ribosomes.
Some ribosomes are free ribosomes; others are bound.
Free ribosomes are
suspended in the cytoplasm and
typically involved in making proteins that function within the cytoplasm.
Bound ribosomes are
attached to the endoplasmic reticulum (ER) associated with the nuclear envelope and
associated with proteins exported from the cell.
endomembrane system.
Many of the membranes within a eukaryotic cell are part of the endomembrane system.
Some of these membranes are physically connected and some are related by the transfer of membrane segments by tiny vesicles (sacs made of membrane).
Many of these organelles work together in the synthesis, storage, and
export of molecules.
The endomembrane system includes
the nuclear envelope,
endoplasmic reticulum (ER),
Golgi apparatus,
lysosomes,
vacuoles, and
the plasma membrane.
Smooth Endoplasmic reticulum
lacks attached ribosomes
is involved in a variety of diverse metabolic processes.
Smooth ER contains enzymes important in the synthesis of lipids, oils, phospholipids, and steroids.
Other enzymes help process (detoxify) drugs, alcohol, and other potentially harmful substances.
Some smooth ER helps store calcium ions.
Rough Endoplasmic reticulum
lines and is attached to the outer surface of the nuclear membranes (is continuous with the nuclear membrane) and is studded with ribosomes.
additional membrane for itself and proteins destined for secretions.
The Golgi apparatus
serves as a molecular warehouse and finishing factory for products manufactured by the ER.
Products travel in transport vesicles from the ER to the Golgi apparatus.
One side of the Golgi apparatus functions as a receiving dock for the product and the other as a shipping dock.
Products are modified / processed as they move through the Golgi
A lysosome
is a membranous sac containing digestive enzymes.
The enzymes and membrane are produced by the ER and transferred to the Golgi apparatus for processing.
The membrane serves to safely isolate these potent enzymes from the rest of the cell.
Lysosomes help digest food particles engulfed by a cell.
A food vacuole binds with a lysosome.
The enzymes in the lysosome digest the food.
The nutrients are then released into the cell.
Lysosomes also help remove or recycle damaged parts of a cell.
The damaged organelle is first enclosed in a membrane vesicle. Then a lysosome fuses with the vesicle, dismantles its contents, and breaks down the damaged organelle.
Vacuoles
are large vesicles that have a variety of functions.
Some protists have contractile vacuoles that help to eliminate water from the protist.
In plants, vacuoles may have digestive functions, contain pigments or contain poisons that protect the plant.
Mitochondria
are organelles that carry out cellular respiration in nearly all eukaryotic cells.
Cellular respiration converts the chemical energy in foods to chemical energy in ATP (adenosine triphosphate).
Chloroplasts
are the photosynthesizing organelles of all plants.
Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar molecules.
Mitochondria and chloroplasts have
DNA and ribosomes.
The structure of this DNA and these ribosomes is very similar to that found in prokaryotic cells.
The endosymbiont theory
proposes that
mitochondria and chloroplasts were formerly small prokaryotes and
they began living within larger cells.
cytoskeleton
Cells contain a network of protein fibers, called the cytoskeleton, which functions in structural support and motility.
Scientists believe that motility and cellular regulation result when the cytoskeleton interacts with proteins called motor proteins.
The cytoskeleton is composed of three kinds of fibers
Microfilaments
Intermediate filaments
Microtubules
Microfilaments
(actin filaments) support the cell’s shape and are involved in motility.
Intermediate filaments
reinforce cell shape & anchor organelles.
Microtubules
(made of tubulin) give the cell rigidity and act as tracks for organelle movement.
flagella and cilia
While some protists have flagella and cilia that are important in locomotion, some cells of multicellular organisms have them for different reasons.
Cells that sweep mucus out of our lungs have cilia.
Animal sperm are flagellated.
Flagella (longer than cilia) propel a cell by an undulating, whiplike motion.
Cilia work more like the oars of a crew boat.
Although differences exist, flagella and cilia have a common structure and mechanism of movement.
Both flagella and cilia are made of microtubules wrapped in an extension of the plasma membrane.
Cilia and flagella move by bending motor proteins called dynein feet.
rigid cell wall
A plant cell, but not an animal cell, has a rigid cell wall that
protects and provides skeletal support that helps keep the plant upright against gravity and
is primarily composed of cellulose.
