Chapter 2 – THE CELL AND ITS COMPONENTS (Taken from

advertisement
Chapter 2 – THE CELL AND ITS COMPONENTS
(Taken from Biology 12, MHR)
2.1 – STRUCTURES AND FUNCTIONS OF EUKARYOTIC CELLS

Animals, plants, fungi, and protists are composed of eukaryotic cells, which have DNA, a
cell membrane, and cytoplasm.

Cytoplasm consists of organelles, the cytosol, and molecules and ions dissolved or
suspended in the cytosol.

See handout for diagrams of Animal Cell and Plant Cell.
Nucleus (Control Center)
 The nucleus controls the cell’s activities and contains DNA, which carries the genetic
information and instructions for making proteins.
 DNA combines with proteins to form thread-like chromatin. During cell division, the
chromatin condenses to form chromosomes.
 The nucleolus is a small, dense region inside the nucleus where proteins and ribosomal
RNA join to form the subunits of ribosomes.
 The nucleus is surrounded by the nuclear envelope, a double membrane consisting of
two phospholipid bilayers, which separates the nucleus from the rest of the cell.
 Nuclear pore complexes in the nuclear envelope consist of thousands of proteins that
form openings.
 The nuclear pore complexes allow water and small ions to move in and out of the
nucleus, but selectively control the passage of larger molecules such as RNA.
 See Figure 2.4, pg 60
Endoplasmic Reticulum
 The nuclear envelope is continuous with a complex of membrane-bound tubules and sacs
known as endoplasmic reticulum (ER).
 There are two types of ER: rough endoplasmic reticulum and smooth endoplasmic
reticulum.
 Rough ER is studded with ribosomes on its surface and is involved with protein
synthesis.
 Proteins that are part of membranes or intended for export from the cell are assembled
by rough ER ribosomes.
 Proteins that function in the cytosol are made by free-floating ribosomes in the
cytoplasm.
 The smooth ER has no ribosomes on its surface and is involved with the synthesis of
steroids and lipids.
 The smooth ER also forms transport vesicles, which transport proteins to the Golgi body.
 See Figure 2.5, pg 61
Golgi Apparatus (Golgi Body)
 Golgi apparatus (Golgi body) is a stack of curved membrane sacs that packages,
processes, sorts, and distributes proteins, lipids, and other substances within the cell.
 It acts like a “post office” for the cell.
 Golgi apparatus also manufactures macromolecules, particularly carbohydrates.
 In plant cells, the Golgi apparatus synthesizes pectin which is a structural polysaccharide
in cell walls.
 In animal cells, the Golgi apparatus produces lysosomes, which are membrane-bound
vesicles containing digestive enzymes.
 These enzyme help to break down macromolecules (carbohydrates, lipids, proteins) into
smaller molecules. They also break down old organelles, bacteria, and foreign
substances.
Endomembrane System
 The endomembrane system consists of a series of cellular structures that are
interconnected: the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus,
and different types of vesicles.
 The organelles of this system all work together in the synthesis, modification, and
transportation of proteins and lipids.
 See Figure 2.6, pg 61
Peroxisomes
 Peroxisomes are membrane-bound sacs containing oxidative enzymes that catalyze
redox reactions.
 These enzymes break down excess fatty acids and hydrogen peroxide, and participate in
the synthesis of bile acids and cholesterol.
 All peroxisomes contain the enzyme catalase which breaks down hydrogen peroxide
into water and oxygen gas.
Vesicles
 A vesicle is a membrane-bound sac used for transport and storage of substances in the
cell.
 Vesicles form by pinching off from the cell membranes and organelle membranes.
 Animal cells contain many small vesicles.
Vacuoles
 Plant cells contain a single large central vesicle called a vacuole.
 The vacuole stores water, ions, sugars, amino acids, and macromolecules. It also
contains enzymes that break down macromolecules and cell wastes.
Chloroplasts (Plant cells)
 Chloroplasts are organelles with a double membrane that are filled with a fluid called
stroma and grana, which are stacks of chloroplyll-containing thylakoids.
 Chlorophyll, a photosynthetic pigment located inside the membranes of the thylokoids,
absorbs light energy from the Sun as part of the reaction that converts carbon dioxide
and water into energy-rich molecules such as glucose.
 See Figure 2.9, pg 64
Mitochondria
 Both plant and animal cells have mitochondria that carry out cellular respiration.
 Mitochondria break down high-energy organic molecules (glucose) to convert stored
energy into usable energy.
 Mitochondria are composed of a fluid-filled matrix and folds of inner membrane called
cristae.
 See Figure 2.10, pg 65
Cell Wall and Cytoskeleton
 A cell wall is a rigid layer surrounding plant, algae, fungal, bacterial and some archaea
cells.
 It is composed of proteins and / or carbohydrates and it provides structural support and
protection for the cell.
 Cytoskeleton is a network of protein fibres that extends throughout the cytosol,
providing structure, shape, support, and motility
 See Table 2.1, pg 66
Cell Membrane
 The activities of the living cell depend on the ability of its membrane to:

transport raw materials into the cell

transport manufactured products and wastes out of the cell

prevent the entry of unwanted matter into the cell

prevent the escape of the matter needed to perform the cellular functions
 The cell membrane acts as a barrier and regulates the movement of molecules and
ions into and out of the cell.
 In the modern fluid mosaic model, the basic framework of a cell membrane is a
phospholipid bilayer into which proteins are inserted.
 These proteins may be bound on the surface to other proteins or to lipids, including
glycoproteins and glycolipids.
 Glycoproteins and glycolipids are proteins and lipids covalently bonded to
carbohydrates.
 Integral proteins are embedded in the membrane.
 Peripheral proteins are located on the outer surface of the lipid bilayer.
 See Figure 2.12, pg 69
Function of Proteins in a Phospholipid Bilayer
 Functions of membrane proteins include:

Stabilizing the membrane

Transport of substances across the cell membrane

Signal reception and signal transduction

Cell-to-cell recognition (carbohydrate chain)

Reaction catalysis (enzymes in membrane carry out chemical reactions)
 Proteins embedded in membrane serve different functions:
1.
Channel Proteins - form small openings for molecules to diffuse through
2.
Carrier Proteins- binding site on protein surface "grabs" certain molecules and
pulls them into the cell
3.
Receptor Proteins - molecular triggers that set off cell responses (such as release
of hormones or opening of channel proteins)
4.
Cell Recognition Proteins - ID tags, to identify cells to the body's immune system
5.
Enzymatic Proteins - carry out metabolic reactions
 HOMEWORK:
pg 71 #1 - 13
2.2 – THE TRANSPORT OF SUBSTANCES ACROSS A CELL MEMBRANE
 The cell membrane is able to control the movement of substances into and out of the cell
because it is semi-permeable.
 This means that the cell membrane allows certain substances to pass through while
preventing other substances to pass through.
Concentration Gradient
 Concentration gradient is a difference in concentration between one side of a membrane
and the other.
PASSIVE TRANSPORT
 Passive transport is the movement of ions or molecules across a cell membrane from a
region of higher concentration to a region of lower concentration, without the input of
energy.
 There are three forms of passive transport: diffusion, osmosis, and facilitated diffusion.
 In passive transport, the molecules (ions) are moving along the concentration gradient
(from high to low) therefore, no energy is required.
Diffusion
 Diffusion is the net movement of ions or molecules from an area of higher
concentration to an area of lower concentration.
 Brownian motion of molecules and ions in the cytoplasm and extracellular fluid is
responsible for diffusion.
 Diffusion will continue until there is an equilibrium (equal concentration of substances
on either side of the cell membrane).
 Oxygen and carbon dioxide easily cross the cell membrane by diffusion because it works
well for small molecules over short distances.
 See Figure 2.13, pg 72 and Figure 2.14, pg 73
 Diffusion will continue until there is an equilibrium (equal concentration of substances on
either side of the cell membrane).
 Oxygen and carbon dioxide easily cross the cell membrane by diffusion because it works
well for small molecules over short distances.
 It is important for a cell to have a large surface area compared to its volume so that
more materials can diffuse in and out.
Factors Affecting Rate of Diffusion
 Molecule size  rate of diffusion decreases with molecule size
 Molecule polarity  non-polar molecules diffuse faster than polar molecules of the
same size
 Molecule or ion charge  charged molecules and ions cannot diffuse across a cell
membrane
 Temperature  increasing temperature increases rate of diffusion (molecules have
more energy and speed)
 Pressure  increasing pressure increases rate of diffusion
Osmosis
 Osmosis is the movement of water from an area of higher concentration to an area of
lower concentration, across a semi-permeable membrane.
 The cell membrane is impermeable to solutes. This means that only water is able to
pass through the membrane.
 So, if the solute concentrations are different on either side of the membrane, then water
will move either in or out of cell.
 It is the concentration of solutes in a solution that determines its osmotic pressure.
 iso = “equal”
 hypo = “less than”
 hyper = “more than”
Isotonic Conditions
 water concentration inside the cell equals the water concentration outside of the cell
 equal amounts water move in and out of the cell
 size of the cell remains the same
Hypotonic Conditions
 water concentration outside the cell is greater than inside the cell
 water moves into the cell
 size of cell increases
 Lysis may occur (cell is destroyed because it bursts)
Hypertonic Conditions
 water concentration inside the cell is greater than outside the cell
 water moves out of the cell
 size of cell decreases (shrivels)
 Plasmolysis may occur (too much water leaves the cell)
 See Figure 2.15, pg 73
Facilitated Diffusion
 Facilitated diffusion is the transport of ions or molecules across a membrane by
means of a membrane protein along the concentration gradient for that ion or molecule.
 There are two types of membrane proteins: channel proteins and carrier proteins.
Channel Proteins
 form highly specific channels
 permit the passage of ions or polar molecules
 some channels remain open all the time
 other have gates that open or close in response to a variety of signals (hormones,
electric charge, pressure, or light).
Carrier Proteins
 bind to specific molecules, transport them across the membrane, and release them on
the other side
 change shape while transporting molecules
 allow the passage of larger molecules (glucose, amino acids)
 has a slower diffusion rate than channel proteins
 See Figure 2.16, pg 75
ACTIVE TRANSPORT
 Active transport is the transport of a solute across a membrane against its gradient
(from lower concentration to higher concentration).
 requires energy  usually from ATP
 ATP (adenosine triphosphate) is the main source of energy in the cell.
Primary Active Transport
 uses ATP directly to move molecules or ions across a membrane
 An example is the sodium-potassium pump.
 With the sodium-potassium pump, sodium is moved out of cell and potassium is moved
into the cell (both against their concentration gradient) therefore ATP is needed.
 See Figure 2.18, pg 76
Secondary Active Transport
 uses an electrochemical gradient as a source of energy to transport molecules or ions
across a cell membrane
 Electrochemical gradient is a combination of concentration gradient and electrical
potential across a membrane.
 The electrochemical gradient created by primary active transport via an ion pump is used
by a different protein to transport other molecules across a cell membrane.
 This method of transport is found in bacteria and plant cells.
 An example is the hydrogen-sucrose pump.
 See Figure 2.19, pg 77
MEMBRANE-ASSISTED TRANSPORT
 Membrane-assisted transport is a transport method used to move materials that are too
large to cross the cell membrane through a channel or carrier protein.
 It requires energy.
 There are two forms of membrane-assisted transport: endocytosis and exocytosis.
Endocytosis
 when the cell membrane folds inward, engulfing a small amount of matter from the
extracellular fluid bringing it into the cell and forming a vesicle
 There are three types of endocytosis: phagocytosis, pinocytosis, and receptor-assisted
endocytosis.
 See Figure 2.20, pg 78
Phagocytosis (“Cell-Eating”)
 A cell engulfs a large particle (bacteria, bits of organic matter) along with some of the
liquid surrounding it.
 occurs only in specialized cells (single-celled amoeba, bacteria-eating cells of our immune
system – macrophages) and only when they encounter something “suitable for engulfing.
Pinocytosis (“Cell-Drinking”)
 A cell engulfs a liquid and the small particles dissolved or suspended in it.
 Occurs in most eukaryotic cells most of the time.
Receptor-Mediated Endocytosis
 Receptor proteins in the cell membrane attach to specific molecules outside the cell.
 The cell membrane folds inward to form a vesicle that is coated with clathrin, a protein
that forms a cage around a vesicle.
Exocytosis
 Exocytosis is a transport method in which a vacuole fuses with the cell membrane and
releases its contents outside the cell into the extracellular environment.
 Exocytosis is important in cells that specialize in the secretion of various cell products
such as hormones, neurotransmitters, and digestive enzymes.
 Example: specialized cells in the human pancreas secrete the hormone insulin by means
of exocytosis.
 See Figure 2.21, pg 79
 See Table 2.2, pg 79 for a Summary of Mechanisms for Transport of Substances Across a
Cell Membrane.
HOMEWORK:
 pg 81 #1 – 13
 Chapter 2 Review (pg 89 #1-26, 28, 29, 31, 38-41, 45, 47-49, 52-54, 57, 59,
60
Download
Random flashcards
Radioactivity

30 Cards

Nomads

17 Cards

Marketing

46 Cards

Create flashcards