The cell Flashcards
How do you see specimens in a light microscope?
In a light microscope (LM), visible
light is passed through the specimen and then through
glass lenses. The lenses refract (bend) the light in such a way
that the image of the specimen is magnified as it is projected
into the eye or into a camera
What is magnification?
Magnification is the ratio of
an object’s image size to its real size.
What is resolution?
Resolution is a measure of the clarity
of the image; it is the minimum distance two points can be
separated and still be distinguished as separate points.
What is contrast?
The third
parameter, contrast, is the difference in brightness between
the light and dark areas of an image.
What are organelles?
organelles, the membrane-enclosed structures within eukaryotic
cells.
What does the electron microscope do?
electron microscope (EM) focuses a beam of electrons
through the specimen or onto its surface
What does the scanning electron microscope do?
The scanning electron microscope (SEM) is especially
useful for detailed study of the topography of a specimen. The electron beam scans the surface of the sample,
usually coated with a thin film of gold. The beam excites electrons on the surface, and these secondary electrons are
detected by a device that translates the pattern of electrons into
an electronic signal sent to a video screen. The result is an image
of the specimen’s surface that appears three-dimensional.
What does the transmission electron microscope do?
The transmission electron microscope (TEM) is used
to study the internal structure of cells (see Figure 6.3). The
TEM aims an electron beam through a very thin section of the
specimen, much as a light microscope aims light through a
sample on a slide. For the TEM, the specimen has been stained
with atoms of heavy metals, which attach to certain cellular
structures, thus enhancing the electron density of some parts
of the cell more than others. The electrons passing through
the specimen are scattered more in the denser regions, so fewer
are transmitted. The image displays the pattern of transmitted
electrons.
What do SEMs and TEMs use as lenses?
Instead of using glass lenses, both the SEM and TEM
use electromagnets as lenses to bend the paths of the electrons,
ultimately focusing the image onto a monitor for viewing.
What is cryo-electron microscopy (cryo-EM)?
A recently developed new type of TEM called cryo-electron
microscopy (cryo-EM) (see Figure 6.3) allows specimens to be
preserved at extremely low temperatures. This avoids the use
of preservatives, allowing visualization of structures in their
cellular environment. This method is increasingly used to
complement X-ray crystallography in revealing protein complexes
and subcellular structures like ribosomes
What is cytology?
the
study of cell structure.
What is cell fractionation?
which takes cells apart and separates major organelles and other subcellular structures
from one another.
What does the centrifuge do?
which spins test tubes holding
mixtures of disrupted cells at a series of increasing speeds,
a process called differential centrifugation.
What do speeds correlate with the cells during differential centrifugation?
At each speed, the
resulting force causes a subset of the cell components to
settle to the bottom of the tube, forming a pellet. At lower
speeds, the pellet consists of larger components, and higher
speeds result in a pellet with smaller components.
What are cells?
Cells—the basic structural and functional units of every
organism
What are the 2 types of cells?
prokaryotic and eukaryotic.
What do most cells have between the groups?
They are all bounded by a
selective barrier, called the plasma membrane (or the cell membrane).
Inside all cells is a semifluid, jellylike substance called
cytosol, in which subcellular components are suspended. All
cells contain chromosomes, which carry genes in the form of
DNA. And all cells have ribosomes, tiny complexes that make
proteins according to instructions from the genes.
Where is DNA located in eukaryotic cells?
In a eukaryotic cell,
most of the DNA is in an organelle called the nucleus, which
is bounded by a double membrane
Where is DNA located in prokaryotic cells?
In a
prokaryotic cell, the DNA is concentrated in a region that
is not membrane-enclosed, called the nucleoid
What does eukrayotic and prokaryotic mean?
Eukaryotic means “true nucleus” (from the Greek eu, true,
and karyon, kernel, referring to the nucleus), and prokaryotic
means “before nucleus” (from the Greek pro, before), reflecting
the earlier evolution of prokaryotic cells.
What is cytoplasm?
The interior of either type of cell is called the cytoplasm;
in eukaryotic cells, this term refers only to the region between
the nucleus and the plasma membrane.
What are mycoplasmas?
the
smallest cells known are bacteria called mycoplasmas, which
have diameters between 0.1 and 1.0 μm.
What is the plasma membrane?
the plasma membrane functions as a selective
barrier that allows passage of enough oxygen, nutrients, and
wastes to service the entire cell
Do larger organisms have larger cells than smaller organisms?
Larger organisms do not generally have larger cells than
smaller organisms—they simply have more cells
What is the flagellum (in animal cells) (diagram)
motility
structure present in
some animal cells,
composed of a cluster of
microtubules within an
extension of the plasma
membrane
What is the centrosome? (diagram)
region
where the cell’s
microtubules are
initiated; contains a
pair of centrioles
What is the cytoskeleton? (diagram)
reinforces cell’s shape;
functions in cell movement;
components are made of
protein. Includes: Microfilaments
Intermediate
filaments
Microtubules
What is microvilli? (diagram)
membrane
projections that
increase the cell’s
surface area
What is peroxisome? (diagram)
organelle with
various specialized metabolic
functions; produces hydrogen
peroxide as a by-product and
then converts it to water
What is the mitochondrion? (diagram)
organelle where
cellular respiration occurs and
most ATP is generated
What is a lysosome? (diagram)
digestive
organelle where
macromolecules are
hydrolyzed
What is the golgi apparatus? (diagram)
organelle active
in synthesis, modification, sorting,
and secretion of cell products
What are ribosomes? (diagram)
(small brown
dots): complexes that
make proteins; free in
cytosol or bound to
rough ER or nuclear
envelope
What is the plasma membrane again? (diagram)
membrane
enclosing the cell
What are the three parts of a nucleus? (diagram)
Nuclear envelope, nucleolus, chromatin
What is a nuclear envelope (diagram)
double
membrane enclosing the
nucleus; perforated by
pores; continuous with ER
What is the nucleolus? (diagram)
nonmembranous
structure involved in production
of ribosomes; a nucleus has
one or more nucleoli
What is chromatin? (diagram)
material consisting
of DNA and proteins; visible in
a dividing cell as individual
condensed chromosomes
What is endoplasmic reticulum (diagram)
material consisting
of DNA and proteins; visible in
a dividing cell as individual
condensed chromosomes
What are the 2 types of ER (diagram)
Rough ER Smooth ER
What is the cell wall? (diagram)
outer layer that maintains
cell’s shape and protects cell from
mechanical damage; made of cellulose,
other polysaccharides, and protein
What is plasmodesmata? (diagram)
cytoplasmic
channels through cell walls
that connect the cytoplasms
of adjacent cells
What is a chloroplast? (diagram)
photosynthetic
organelle; converts energy of
sunlight to chemical energy
stored in sugar molecules
What does the nuclear envelope do?
The nuclear envelope encloses
the nucleus (Figure 6.9), separating its contents
from the cytoplasm.
Where are genes located in eukaryotic cells?
The nucleus contains most of the genes in the
eukaryotic cell. (Some genes are located in
mitochondria and chloroplasts.)
What does the nuclear envelope contain (specify a description on pores)?
The nuclear envelope is a double membrane.
The two membranes, each a lipid
bilayer with associated proteins, are separated
by a space of 20–40 nm. The envelope is perforated
by pore structures that are about 100 nm in diameter. At
the lip of each pore, the inner and outer membranes of
the nuclear envelope are continuous.
What is the nuclear lamina?
the nuclear side of the
envelope is lined by the nuclear lamina, a netlike array
of protein filaments (in animal cells, called intermediate filaments)
that maintains the shape of the nucleus by mechanically
supporting the nuclear envelope.
What is the nuclear matrix and what does the lamina do together?
There is also much
evidence for a nuclear matrix, a framework of protein fibers
extending throughout the nuclear interior. The nuclear
lamina and matrix may help organize the genetic material
so it functions efficiently.
What are chromosomes?
structures that carry the genetic
information.
What are small basic proteins?
histones
What is chromatin?
The complex of DNA
and proteins making up chromosomes is called chromatin.
How many chromosomes does a typical human have (including gametes)?
For example, a typical
human cell has 46 chromosomes in its nucleus; the exceptions
are human sex cells (eggs and sperm), which have only
23 chromosomes.
What is a nucleolus?
A prominent structure within the nondividing nucleus is
the nucleolus (plural, nucleoli), which appears through the
electron microscope as a mass of densely stained granules
and fibers adjoining part of the chromatin.
What happens in a nucleolus, how are ribosomes formed?
Also in the nucleolus,
proteins imported from the cytoplasm
are assembled with rRNA into large and
small subunits of ribosomes. These subunits
then exit the nucleus through the
nuclear pores to the cytoplasm, where a
large and a small subunit can assemble
into a ribosome.
How is the mRNA formed and what does it do for the body?
the nucleus directs
protein synthesis by synthesizing messenger RNA (mRNA)
that carries information from the DNA. The mRNA is then
transported to the cytoplasm via nuclear pores. Once an
mRNA molecule reaches the cytoplasm, ribosomes translate
the mRNA’s genetic message into the primary structure of a
specific polypeptide.
What are ribosomes?
Ribosomes, which are complexes made of ribosomal RNAs
and proteins, are the cellular components that carry out
protein synthesis (they are also not considered as organelles)
Where do ribosomes make their proteins?
Ribosomes build proteins in two cytoplasmic regions:
At any given time, free ribosomes are suspended in the cytosol,
while bound ribosomes are attached to the outside of the
endoplasmic reticulum or nuclear envelope
What does the endomembrane system include?
endomembrane system,
which includes the nuclear envelope, the endoplasmic reticulum,
the Golgi apparatus, lysosomes, various kinds of vesicles
and vacuoles, and the plasma membrane.
What does the endomembrane system do?
This system carries
out a variety of tasks in the cell, including synthesis of proteins,
transport of proteins into membranes and organelles
or out of the cell, metabolism and movement of lipids, and
detoxification of poisons.
How are the membranes related to eachother in the endomembrane system?
The membranes of this system are
related either through direct physical continuity or by the
transfer of membrane segments as tiny vesicles (sacs made
of membrane).
What is the endoplasmic reticulum?
The endoplasmic reticulum (ER) is such an extensive
network of membranes that it accounts for more than half
the total membrane in many eukaryotic cells.
What does endoplasmic and reticulum mean?
The word
endoplasmic means “within the cytoplasm,” and reticulum is
Latin for “little net.”)
What is in the endoplasmic reticulum of cells?
The ER consists of a network of membranous
tubules and sacs called cisternae
What is the ER membrane and ER lumen, what do they do?
The ER membrane separates
the internal compartment of the ER, called the ER lumen
(cavity) or cisternal space, from the cytosol.
What are enzymes in the smooth ER helpful for (fatty acid wise)
Enzymes of the smooth ER are important in the synthesis
of lipids, including oils, steroids, and new membrane phospholipids.
What are enzymes,es in the smooth ER helpful for (poison-wise)
Other enzymes of the smooth ER help detoxify drugs
and poisons, especially in liver cells. Detoxification usually
involves adding hydroxyl groups to drug molecules, making
them more water-soluble and easier to flush from the
body.
What does calcium ions stored in smooth ER do in muscle and regular cells?
The smooth ER also stores calcium ions. In muscle cells, for
example, the smooth ER membrane pumps calcium ions from
the cytosol into the ER lumen. When a muscle cell is stimulated
by a nerve impulse, calcium ions rush back across the
ER membrane into the cytosol and trigger contraction of the
muscle cell. In other cell types, release of calcium ions from
the smooth ER triggers different responses, such as secretion
of vesicles carrying newly synthesized proteins.
How do primary proteins become secondary through ER?
As a polypeptide chain
grows from a bound ribosome, the chain is threaded into
the ER lumen through a pore formed by a protein complex
in the ER membrane. The new polypeptide folds into its
functional shape as it enters the ER lumen.
What are glycoproteins?
Most secretory
proteins are glycoproteins, proteins with carbohydrates
covalently bonded to them.
How are carbohydrates attached to proteins?
The carbohydrates are attached
to the proteins in the ER lumen by enzymes built into the
ER membrane.
What are transport vesicles?
Vesicles in transit from one part of the cell
to another are called transport vesicles
What can we think the golgi apparatus as?
We can think of the Golgi as a warehouse
for receiving, sorting, shipping, and even some manufacturing.
What is cisternae
flattened
membranous sacs—cisternae
What are the sides of the golgi apparatus called?
The two sides
of a Golgi stack are referred to as the cis face and the trans face;
these act, respectively, as the receiving and shipping departments
of the Golgi apparatus.
What does cis mean?
The term cis means “on the same
side,” and the cis face is usually located near the ER.
How do transport vesicles deposit their materials?
Transport
vesicles move material from the ER to the Golgi apparatus. A
vesicle that buds from the ER can add its membrane and the
contents of its lumen to the cis face by fusing with a Golgi
membrane on that side.
What does the trans face of the golgi do?
The trans face (“on the opposite side”)
gives rise to vesicles that pinch off and travel to other sites.
What does the golgi apparatus do to materials when they enter from the endoplasmic reticulum?
Products of the endoplasmic reticulum are usually modified
during their transit from the cis region to the trans region
of the Golgi apparatus. For example, glycoproteins formed
in the ER have their carbohydrates modified, first in the ER
itself, and then as they pass through the Golgi.
Does the golgi apparatus secrete macromolecules, give an example
the Golgi apparatus also
manufactures some macromolecules. Many polysaccharides
secreted by cells are Golgi products.
What is a lysosome?
A lysosome is a membranous sac of hydrolytic enzymes that
many eukaryotic cells use to digest (hydrolyze) macromolecules.
Where are hydrolytic enzymes formed?
Hydrolytic enzymes and lysosomal membrane are made
by rough ER and then transferred to the Golgi apparatus for
further processing.
What is phagocytosis?
Amoebas and many other unicellular protists
eat by engulfing smaller organisms or food particles,
a process called phagocytosis
What is autophagy?
Lysosomes also use their hydrolytic enzymes to recycle the
cell’s own organic material, a process called autophagy. During
autophagy, a damaged organelle or small amount of cytosol
becomes surrounded by a double membrane (of unknown
origin), and a lysosome fuses with the outer membrane of this
vesicle
What are vacuoles?
Vacuoles are large vesicles derived from the endoplasmic
reticulum and Golgi apparatus.
What are contractile vacuoles?
Many unicellular
protists living in fresh water have contractile vacuoles that
pump excess water out of the cell, thereby maintaining a suitable
concentration of ions and molecules inside the cell
What are food vacuoles?
Food vacuoles are membrane-bound sacs found in certain cells, primarily in unicellular organisms like amoebas. They serve as the cell’s intracellular “stomach,” responsible for digesting food particles.
How is a large central vacuole formed?
Mature plant cells generally contain a large central
vacuole, which develops by the coalescence
of smaller vacuoles.
What is the solution inside the central vacuole?
The solution inside the central vacuole,
called cell sap, is the plant cell’s main repository of inorganic
ions, including potassium and chloride.
What are the organelles in eukaryotic cells that convert energy to forms that cells can use for work?
In eukaryotic cells, mitochondria and
chloroplasts are the organelles that convert energy to forms
that cells can use for work.
What are mitochondria (mention singular form)
Mitochondria (singular,
mitochondrion) are the sites of cellular respiration, the metabolic
process that uses oxygen to drive the generation of
ATP by extracting energy from sugars, fats, and other fuels.
What are chloroplasts? and how do they use energy to support their cell?
Chloroplasts, found in plants and algae, are the sites of
photosynthesis. This process in chloroplasts converts solar
energy to chemical energy by absorbing sunlight and using
it to drive the synthesis of organic compounds such as sugars
from carbon dioxide and water.
What is the peroxisome
an oxidative organelle.
How much mitochondria is present in cells?
Some
cells have a single large mitochondrion, but more often a
cell has hundreds or even thousands of mitochondria, number correlates with the cell’s level of metabolic activity.
Describe the membranes of mitochondria
Each of the two membranes enclosing the mitochondrion
is a phospholipid bilayer with a unique collection of
embedded proteins. The outer membrane is smooth, but
the inner membrane is convoluted, with infoldings called
cristae
What is the intermembrane space of mitochondrions?
The inner membrane divides the
mitochondrion into two internal compartments. The first
is the intermembrane space, the narrow region between the
inner and outer membranes.
What is the mitochondrial matrix?
The second compartment, the
mitochondrial matrix, is enclosed by the inner membrane.
The matrix contains many different enzymes as well
as the mitochondrial DNA and ribosomes.
How is the content of a chloroplast divided?
The contents of a chloroplast are partitioned from the
cytosol by an envelope consisting of two membranes separated
by a very narrow intermembrane space.
What are thylakoids?
Inside the
chloroplast is another membranous system in the form of
flattened, interconnected sacs called thylakoids.
What is a granum?
In some
regions, thylakoids are stacked like poker chips; each stack is
called a granum
How to calculate free energy?
DH symbolizes the change in the system’s
enthalpy (in biological systems, equivalent to total energy);
DS is the change in the system’s entropy; and T is the absolute
temperature in Kelvin (K) units
What happens when ATP reacts with water?
