Chapter 2 Notes
All eukaryotic cells have these functions in common:
(1) the DNA is contained within a membranebound nucleus
(2) a cell membrane comprised of a phospholipid bilayer (double layer) and embedded proteins separates the cell’s
contents from its surroundings.
(3) filling the cell interior is the jellylike cytoplasm, which consists of everything outside nucleus but within cell
membrane (includes the organelles, cytosol, and molecules/ions dissolved or suspended in the cytosol); cytosol:
the fluid itself
Although most animal cells have similar structures, there is great diversity in the form, size, and specialized features
of animal cells (same with plants).
Nucleus Nucleus contains DNA, which Nucleoplasmthick fluid filling the nucleus
stores and replicated the genetic Nuclear matrixnetwork of protein fibres providing internal
info of the cell. structure and support
Nucleolusa nonmembrane bound structure in the nucleus,
Each molecule of DNA in the which contains RNA, proteins, and chromatin.
nucleus combines with an equal Nuclear envelopea double membrane consisting of 2
mass of protein to form a phospholipid bilayers, which separates the nucleus from the
chromosome. Chromosomes are rest of the cell (surrounds the nucleolus)
visible only in dividing cells; in non
The nuclear envelope is studded with thousands of nuclear
dividing cells, a complex mixture ofpore complexesgroups of proteins that form opening in
DNA and proteins is called the nuclear envelope (small particles such as water and ions
chromatin (unfolded state of travel easily through these openings, but the passage of
chromosomes) macromoleculesRNAis controlled by the nuclear pores. (pg.
Endoplasmic The ER is a complex system of The nuclear envelope is connected to and part of a complex of
channels and sacs composed of membranebound sacs call ER.
Reticulum membranes enclosing lumen Ribosomesstructures composed of RNA and proteins, and
(space in between 2 bilayers); it is
responsible for synthesis of proteins
made up of rough ER and smooth
ER The smooth ER synthesis lipids and lipidcontaining molecules
such as the phospholipids that make up membranes.
In liver, smooth ER helps detoxify drugs and alcohol; in
ovaries/testes, smooth ER produces testosterone and
• Consists of the nuclear envelope, ER, Golgi apparatus, and vesicles.
• This system acts as the transportation and productprocessing section of the cell.
• Endomembrane system divides the cell in particular categories so that particular functions are restricted to
• The organelles that make up the Endomembrane system are connected to one another either directly or by
transport vesicles. Pg. 61
1 Chapter 2 Notes
The Endomembrane system modifies and transports proteins
1. On the surface of the rough ER, polypeptides are produced by bound ribosomes and extruded into the
lumen, rather than being released into the cytosol.
2. These polypeptides travel through the lumen to the smooth ER, where they are stored and processed. When
proteins are ready for transport, pieces of smooth ER pinch off to form vesicles (sacs used for transport
and storage) containing the protein.
3. Vesicles from the smooth ER travel across the cell to the cis face of the Golgi apparatus, which is a stack
of curved cell membrane sacs. There, the vesicles merge with the membrane of the Golgi apparatus and
release their contents into the interior. In the Golgi apparatus, some proteins are stored and others are
modified further (i.e. some proteins have carbohydrate chains added to them in the Golgi apparatus or in the
4. When the modified proteins are ready for transport, pieces of the Golgi apparatus pinch off from the trans
face to form vesicles. These vesicles transport the proteins to the cell membrane, or to other destinations
within the cell.
The Golgi apparatus has other functions including:
• Sorting, packaging, and distributing lipids and proteins
• Manufacturing macromolecules, particularly carbohydrates (i.e. Golgi apparatus in many plant cells
synthesizes pectins, which are noncellulose structural proteins found in cell walls)
• In animals, the Golgi apparatus produces lysosomes, which are membrane enclosed sacs containing
digestive enzymes. Lysosomes contain more than 40 enzymes that catalyze hydrolysis reactions, breaking
down macromolecules into smaller molecules that can be reused by the cell. Lysosomes break down parts
of the cell that are old or no longer needed as well as break down bacteria and other foreign particles that
have been ingested by the cell. Even if a lysosome breaks apart, spilling its enzymes into the cell, the
enzymes are unlikely to break down the parts of the living cell.
• Like lysosomes, Peroxisomes are membraneenclosed sacs containing enzymes.
• Unlike the enzymes in lysosomes, which catalyze hydrolysis reactions, the enzymes in peroxisomes are
oxidative enzymes that break down excess fatty acids and hydrogen peroxide, and participate in the
synthesis of bile acids and cholesterol.
• Because toxic substances accumulate in the liver, liver cells contain many peroxisomes (i.e. peroxisomes in
liver cells oxidize and break down alcohol molecules.
• Many of the reactions that take place in peroxisomes produce toxic hydrogen peroxide (2 2 ), so all
peroxisomes contain an enzyme know as catalase that breaks down hydrogen peroxide into water and
Vesicles and Vacuoles:
2 Chapter 2 Notes
• The term “vesicle” is used to describe membranebound sacs used for the transport and storage of
substances in the cell. Vesicles form by pinching off from cell membranes and organelle membranes. They
can fuse with cell membranes and organelle membranes to release their contents. Animal cells contain
many small vesicles.
• Plant cells contain a single large central vesicle, called a vacuole, which stores water, ions, sugars, amino
acids, and macromolecules. It contains enzymes that break down macromolecules and cell wastes. The
quantity of water in the central vacuole determines the turgor pressure (internal pressure) of the plant cell
▯ causes plant cell to be rigid (evident in the flexible stems of plants); Without enough water, a vacuole will
shrink and pull away from the cell wall. Thus, unwatered plants wilt as the turgor pressure in their cells
Chloroplasts and Mitochondria:
• Chloroplasts organelles in the cells of photosynthetic organisms in which light energy from the sun is
captured and stored in the form of energyrich organic molecules such as glucose.
• Activities and chemical reactions in the cell require a steady supply of energy. In eukaryotic cells,
mitochondria break down highenergy organic molecules to convert stored energy into usable energy
• Both mitochondria and chloroplasts contain some of their own DNA, which encodes some, but not all, of their
Cell Wall and the Cytoskeleton:
• Cell wall in plants provides protection and support; Cellulose and other substances such as pectins comprise
plant cell walls, while chitin comprises fungal cell walls.
• All cells contain an internal network of protein fibres called the cytoskeleton. The fibres of the cytoskeleton
extend throughout the cytoplasm, providing structure and anchoring the cell membrane and organelles in
place. Vesicles and other organelles move along these fibres, which act like tracks that lead from one part of
the cell to another. Pg. 66 Functions of protein fibres in cytoskeleton
Cell Wall and the Cytoskeleton:
• Cilia and flagella are appendages that develop on the outside of some eukaryotic cells. If there are two or
less appendages, they are called flagella. If many shorted appendages are present, they are called cilia.
Flagella are like tails, and their whiplike movement propels cells.
• In unicellular protists, the wavelike motion of cilia enables the organisms to move. In multicellular organisms
(humans), cells that line upper respiratory tract have cilia that sweep debris trapped within mucus back up
• All living cells exist in an aqueous medium. The contents of cells (organelles) are physically separated from
this aqueous environment by the cell membrane, which functions as a selective, dynamic cellular boundary.
If this remarkable and remarkably thin membrane does not function properly, cellular processes fail, and cells
3 Chapter 2 Notes
• Regulates the passage of molecules and ions into and out of the cell.
• Phospholipids are a component of cell membranes and that they are arrange around the cell in two layers (a
bilayer); The presence of lipids cannot account for all the properties of the cell membrane…there remains
another important component:
• There are proteins inserted into the phospholipid bilayer with their nonpolar
segments in contact with the nonpolar interior of the bilayer and their polar portions
protruding from the membrane surface. In this fluid mosaic model, an assortment of
proteins and other molecules floats in or on the fluid phospholipid bilayer. Pg. 69
Carbohydrates, lipids, and proteins are all involved in the cell membrane; anything big or hydrophilic will not be able
to pass phospholipids bilayer (serves as a cellular barrier)
Permeability to polar molecules? Membrane becomes semipermeable via protein
channels; specific channels allow specific material across cell membrane (each protein channel
needs to be different because of the different items they are letting through). Therefore the cell membrane
contains more than lipids: it has transmembrane proteins embedded into the phospholipid bilayer. Protein
channels must be hydrophobic and nonpolar in order to be embedded in that membrane; the polar parts of
the protein will be exposed to the outer parts of the cell.
Within membrane: nonpolar amino acids are hydrophobic and they anchor protein
On outer surfaces of membrane in fluid are polar amino acids that are hydrophilic and
they extend into extracellular fluid & into cytosol
Signal transduction: transmitting a signal from outside the cell to the cell nucleus, like
receiving a hormone, which triggers a receptor on the inside of the cell that then signals to the
nucleus that a protein must be made (pass chemical message from outside to inside).
4 Chapter 2 Notes
Membrane carbohydrates (yellow):
play a key role in cellcell recognition ▯ability of a cell to distinguish one cell from
another (i.e. antigens);Cellcell recognition will recognize and attack it if it doesn’t belong
important in organ & tissue development
basis for rejection of foreign cells by immune system
Fluid Mosaic Model:
• According to the fluid mosaic model, each layer (leaflet) of a membrane bilayer is composed of various
macromolecules. Phospholipids act as the “scaffolding” in which proteins and other macromolecules are
• Because membrane lipids are held together by weak intermolecular forces rather than by strong covalent
bonds, the molecules in a membrane can move about freely. In fact, phospholipids within the same layer in a
membrane exchange places millions of times in a single second, leading to a continual rearrangement of the
membrane surfaces. If a puncture or tear occurs in a membrane, molecules will quickly rearrange
themselves to seal the rupture.
The Fluidity of a Phospholipid Belayer
If a bilayer is too fluid, it permits too many molecules to diffuse in and out of the cell. If it is not fluid enough,
a bilayer prevents too many molecules from crossing. The main factors that affect fluidity include:
1. Temperature – With increasing temperature, the bilayer becomes increasingly fluid until it is unable
to act as a barrier. At decreasing temperatures, the bilayer eventually solidifies into a gellike state.
2. Presence of double bonds in the fatty acid “tails” – Double bonds form “kinks” in a fat