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Chapter 7: A Tour of the Cell
OBJECTIVES
After reading this chapter and attending lecture, the student should
be able to:
1. Distinguish between prokaryotic and eukaryotic cells.
Prokaryotic - no nucleus, organelles; lots of ribosomes and
DNA.
Eukaryotic - (the opposite)
2. Describe the structure and function of the nucleus, and briefly
explain how the nucleus controls protein synthesis in the cytoplasm.
Contains DNA for the cell. Nuclear envenlope, chromatin,
nucleolus. Sends mRNA and it is synthesized according to DNA
instructions. Goes with information into cytoplasm and attaches to a
ribosome, transferring the data.
3. Describe the structure and function of a eukaryotic ribosome.
The sites where cell proteins are assembled. (mRNA ribosome - DNA)
4. List the components of the endomembrane system, describe their
structures and functions and summarize the relationships among
them.
Nuclear envelope - encloses nucleus; separates from
cytoplasm. Double membrane.
ER - Smooth (lipids, carbs., system detox.), Rough (making
secretory proteins, grows in place by budding proteins and
phospholipids.)
Golgi apparatus - products of ER modified, stored, released to
destinations.
Lysosomes - digests micromolecules (intracellular).
Vacuoles - Central (store organic compounds; repository of
organic ions, enrich color in pigments; protect plant.)
Plasma membrane - a selective barrier that allows sufficient
passage of oxygen, nutrients, and waste - in and out.
5. Describe the vacuole and list types of vacuoles.
(Refer to last question.)
6. Explain the role of peroxisomes in eukaryotic cells.
Contain enzymes that transfer hydrogen from various
substrates to oxygen; makes hydrogen peroxide. Some break down
fatty acids, liver - detox. alcohol, etc.; in fat-storing tissues of plants fatty acids to sugar.
7. Identify the three functional compartments of a chloroplast.
Thylakoids - membranous system.
Grana- thylakoids stacked like poker chips.
Stroma - fluid outside the thylakoids.
8. Describe probable functions of the cytoskeleton.
Give mechanical support to cell; help maintain its shape.
Enables cell to change shape. Functions in cell motility - movement
of cell and what’s inside of it.
9. Describe the structure, monomers and functions of microtubules,
microfilaments and intermediate filaments.
Tubules - made from tubulins x and B; shape and support cell;
track on which organelles move.
Filaments - made of actin; part of contractile apparatus of the
cell, work with myosin to contract cells.
Inter-keratins - more permanent fixtures of the cell; more
support to shape.
10. Explain how the ultrastructure of cilia and flagella relates to their
function.
Cilia - occur in large numbers’ moves like boat oars;
microtubules - nine doublets in a ring, two in center.
Flagella - longer than cilia, but fewer. Cycle of movements
causes beatings.
11. Describe the structure of intercellular junctions found in plant and
animal cells, and relate their structure to function.
Plasmodesmata in cell wall - allows strands of cytoplasm to
pass though to another and connect with living cells. Unifies plant
cell.
Animal:
1) tight junctions - form continuous belts around the cell.
Membranes of other cells, fused here. Seal prevents extracellular
fluid leaks,
2) desmosomes - function like rivets; fastening cells to epithelial
sheets.
3) gap junctions - provide cytoplasmic channels between adjacent
cells. Special membranes surround each pore, wide enough for salts,
sugars, amino acids.
Chapter 8: Membrane Structure and Function
OBJECTIVES
After reading this chapter and attending lecture, the student should
be able to:
1. Describe the function of the plasma membrane.
It controls the passage of substances into and out of the cell. It
is selectively permeable which means that it allows certain molecules
to cross it more easily than others.
2. Describe the fluid properties of the cell membrane and explain how
membrane fluidity is influenced by membrane composition.
A membrane remains fluid until the temperature cools so much
that it solidifies. It remains fluid to a lower temperature only if there
are phospholipids (many) with unsaturated hydrocarbon tails. They
do not pack as closely together as saturated hydrocarbons.
3. Explain how hydrophobic interactions determine membrane
structure and function.
A membrane is selectively permeable. It allows for the passage
of hydrophobic molecules and small hydrophilic molecules, but does
not allow for the passage of large hydrophilic molecules unless the
movement is facilitated.
4. Describe how proteins are spatially arranged in the cell membrane
and how they contribute to membrane function.
Integral proteins penetrate far enough into the membrane for
their hydrophobic regions to be surrounded by the hydrocarbon tails
of lipids. Some reach only part way across the membrane, while
others span the entire thing. Peripheral proteins are not embedded in
the lipid bilayer. They are attached to the surface of the membrane
(inside) and are exposed to parts of the integral protein.
5. Describe factors that affect selective permeability of membranes.
While hydrophobic molecules can pass easily through the
plasma membrane, those that are hydrophilic cannot do so.
However, specific molecules that need to get into the cell, pass
through transport proteins and therefore avoid passage through the
hydrophobic layer of the plasma membrane.
6. Define diffusion; explain what causes it and why it is a
spontaneous process.
Diffusion is a natural passing of molecules from an area of
higher concentration to an area of lower concentration. It is one
result of thermal energy or, the energy of motion. It is spontaneous
because it decreases free energy.
7. Explain what regulates the rate of passive transport.
The rates of passive transport in diffusion are affected by the
selectively permeable plasma membrane.
8. Define osmosis and predict the direction of water movement based
upon differences in solute concentration.
Osmosis is the passive transport of water across a cell
membrane. If a cell is in a hypertonic solution, water molecules will
diffuse across the membrane and into that solution because in the
hypertonic solution water molecules are bound to the solutes and not
able to move as freely.
9. Describe how living cells with and without walls regulate water
balance.
The problem of water regulation in cells without walls is solved
by keep cells in an isotonic solution. That way, there is no net
movement of water across the cell membrane. In cells with walls, the
water balance is kept because only so much water is allowed into a
cell before it exerts a back pressure to keep more from entering it.
10. Describe one model for facilitated diffusion.
The transport proteins alternate between two different
conformations, moving a solute across the membrane as the shape
of the protein changes. The protein can transport the solute in either
direction, with the net movement being down the concentration
gradient of the solute.
11. Explain how active transport differs from diffusion.
In diffusion, molecules naturally drift into and out of the cell. In
active transport, the energy of ATP is needed to force molecules to go
against their concentration gradient.
12. Explain how large molecules are transported across the cell
membrane.
They are transported across through exocytosis. The
membrane-bounded vesicle comes in contact with the membrane and
fuses, thus releasing the molecules.
13. Give an example of receptor-mediated endocytosis.
It allows the cell to acquire bulk quantities of specific
substances, even though those substances may not be very
concentrated in the extracellular fluid. Human cells use this process
to take in cholesterol for use in the synthesis of membranes and as a
precursor for the synthesis of other steroids.
Chapter 11: The Reproduction of Cells
OBJECTIVES
After reading this chapter and attending lecture, the student should
be able to:
1. Overview the major events of cell division that enable the genome
of one cell to be passed on to two daughter cells.
Cell division involves the distribution of identical genetic
material - DNA - to two daughter cells. In eukaryotes, the compact,
coiled structure of DNA molecules form chomosomes. A cell
preparing for duplication first duplicates all its genes and puts them
equally at opposite ends of the cell.
2. Describe how chromosome number changes throughout the
human life cycle.
When a human life is conceived, each parents’ 23
chromosomes join to give the life 46. Then, meiosis again reduces
that number down to 23 until new fertilization occurs.
3. List the phases of the cell cycle and describe the sequence of
events that occurs during each phase.
Interphase - divided into three: the G1 phase (a cell grows), S
phase (where the chromosomes replicate), and G2 phase (nucleus
well- defined. Chromosomes already duplicated, but
indistinguishable because they are still in the form of loosely packed
chromatin fibers. Two centrosomes outside the nucleus and in
animal cells, each has a pair of centrioles.)
4. List the phases of mitosis and describe the events characteristic of
each phase.
Prophase - nucleus and nucleolus disappear. Chromatin fibers
become tightly coiled. Each duplicated chromosome appears as two
sister chromatids, joined at the centromere. The spindle fibers begin
to form and chromosomes are propelled away from each other by
bundles of microtubules that come between them.
Prometaphase - nuclear envelope fragments. The microtubules
of the spindle are now free to interact with the chromosomes. These
form a row, extending the length of the cell equator. Each of the
attached chromatids has a kinetochore at the centromere region.
Metaphase - the centromeres of the chromosomes are all
aligned with one another along the spindle, and form the metaphase
plate. The identical ends of each chromatid are attached to
kinetochore microtubules that are located at opposite ends of the
parent cell.
Anaphase - The paired centromeres separate and free the two
sister chromatids. Each is now a full chromosome. They begin to
move toward their kinetochores at opposite ends of the cell. By the
end, each poles of the cell has an equivalent and complete set of
chromosomes.
Telophase and Cytokinesis - the nonkinetochore microtubules
that are part of the spindle fibers, begins to elongate. Two new
nuclear envelopes are formed from the fragments of the parent cell’s
envelope and the nucleoli reappears and chromosomes become less
tightly coiled. Now mitosis is complete and cytokiesis (division of
cytoplasm) is under way.
5. Recognize the phases of mitosis from diagrams or micrographs.
Prophase
Telophase
Metaphase
Anaphase
6. Describe what characteristic changes occur in the spindle
apparatus during each phase of mitosis.
Prophase - in the cytoplasm, the spindle begins to form.
Prometaphase - they can now enter the nucleus and interact
with the chromosomes.
Metaphase - becomes comprised of chromosome lined along
the equator, with the respective kinetochores of the chromatids facing
opposite kinetochore microtubules.
Anaphase - provide a track for the new chromosomes to
separate and travel to opposite poles.
Telephase and Cytokinesis - the nonkinetochore microtubules
elongate across the cell and the two daughter cells begin to form at
opposite poles where the chromosomes have gathered.
7. Compare cytokinesis in animals and plants.
Animal - occurs through a process called cleavage. The cell
becomes pinched in the middle, just as microfilaments inside the
plasma membrane (actin) begin to form a ring. Eventually this
causes the cell to pinch in two and separate into two daughter cells.
Plant - a cell plate is formed down the middle of the original
plant cell. These two separate membranes remain connected (no
cleavage), but each develop their own separate plasma membrane.
8. Describe the process of binary fission in bacteria and how this
process may have evolved to mitosis in eukaryotes.
The words literally mean, “to divide in half.” The bacteria’s
genes are carried on a singular chromosome made of a DNA
molecule and other proteins. The chromosome replicates and the
bacterium enlarges to twice its size. Then, the plasma membrane
pinches inward and the parent cell divides, leaving two new bacteria,
each with a complete genome. Mitosis in eukaryotes is similar, but
more advanced in that there are many more thousands of gene that
need replication.
9. Explain how abnormal cell division of cancerous cells differs from
normal cell division.
Cancer cells are immune to the control mechanisms of the
body. They divide excessively and invade other tissues. It is
possible for them to kill the whole organism. As they multiply they
form tumors. Benign tumors are those where cells stay in one place
and cancerous tumors are those where the cells have spread to other
places besides their origin.