Download VII. Exocytosis and Endocytosis

Hierarchy of Biological Organization
atoms  simple molecules  macromolecules 
membranes  organelles (nonliving/living) 
tissues  organs  organ systems  animals
cells 
HOMEWORK FOR CHAPTERS 4-8.
All review questions and self-quizzes in Chapters
4,5 & 6. Review questions 1&2 in Chapter 7.
Nothing in Chapter 8.
CHAPTER 5
A CLOSER LOOK AT CELL MEMBRANES
_
I. It Isn=t Easy Being Single
The plasma membrane - a surface of lipids, proteins,
and some carbohydrate groups - regulates exchange
of materials between cytoplasm and surroundings.
Within the cytoplasm, exchanges are made across
internal membranes of the organelles.
II. Membrane Structure and Function
A. The Lipid Bilayer - The Fluid Mosaic Model of
Membrane Structure
1. The Afluid@ portion of the cell membrane is made
of phospholipids.
1
a. A phospholipid molecule is composed of a
hydrophilic (Awater-lover@) head and two
hydrophobic (Awater hater@) tails.
2. Proteins embedded in the cell membrane
3. Other macromolecules
a. Glycolipids have sugar monomers attached
at the head end.
b. Cholesterol is abundant in animal
membranes; phytosterols occur in plants.
III. Functions of Membrane Proteins
A. Transport proteins allow water-soluble substances to
move through their interior, which opens on both
sides of the bilayer.
1. A channel protein, whether it be perpetually
open or gated, serves as a pore through which
ions, water, and soluble substances can move.
2. A carrier protein binds specific substances and
changes shape to shunt the materials across;
some work passively, while others require
energy for Apumping.@
B. Receptor proteins have binding sites for hormones
(and like substances) that can trigger changes in cell
action, as in growth processes.
C. Recognition proteins identify the cell as a certain
type, help guide cells into becoming issues, and
function in cell-to-cell recognition and coordination.
2
D. Adhesion proteins are glycoproteins that help cells
stay connected to one another in a tissue.
IV. Diffusion
A. Concentration Gradients and Diffusion
1. Concentration refers to the number of molecules
(or ions) of a substance in a given volume
of fluid.
2. Molecules constantly collide and tend to move
down a concentration gradient (high to low).
3. The net movement of like molecules down a
concentration gradient is called diffusion.
B. Factors Influencing the Rate and Direction of Diffusion
1. The rate of diffusion depends on concentration
differences, temperature (higher = faster), and
molecular size (smaller = faster).
2. When gradients no longer exist, there is no net
movement (dynamic equilibrium).
3. In addition, diffusion may also be modified by
electrical gradients (a difference in charge) and
pressure gradients.
V. Osmosis
Osmosis is the passive movement of water
across a differentially permeable membrane in
response to solute concentration gradients,
pressure gradients, or both.
3
VI. Tonicity
1. Tonicity denotes the relative concentration of
solutes in two fluids - extracellular fluid and
cytoplasmic fluid, for example.
2. Three conditions are possible:
a. An isotonic fluid has the same concentration
of solutes as the fluid in the cell; immersion
in it causes no net movement of water.
b. A hypotonic fluid has a lower concentration of
solutes than the fluid in the cell; cells
immersed in it may swell. Called turgor
pressure in plants (in RBCsShemolysis).
c. A hypertonic fluid has a greater concentration
of solutes than the fluid in the cell;
(RBCs shrivelScrenation).
3. Cells either are dependent on relatively constant
(isotonic) environments or are adapted to
hypotonic and hypertonic ones.
AHome is where the heart is and water is where
the salt is.@
VII. Routes Across Cell Membranes
A. Small, electrically neutral molecules (for example,
oxygen, carbon dioxide, and water) cross the
lipid bilayer by simple diffusion.
4
B. Larger molecules (such as glucose) and charged
ions (such as Na+, Ca+, HCOB3) must be moved by
membrane transport proteins.
1. In passive transport (no energy is required),
material passes through proteins without an
energy boost. When a carrier protein functions
in passive transport, which is "facilitated
diffusion", molecules are moved to the side of
the membrane where they are less concentrated.
2. In active transport, proteins become
activated to move a solute against its
concentration gradient (requires energy in the
form of ATP).
C. Active Transport
1. To move ions and large molecules across a
membrane against a concentration gradient,
special proteins are induced to change shape
(in a series), but only with an energy boost
from ATP.
2. An example of active transport is the sodiumpotassium pump of the neuron membrane, and
the calcium pump of most cells.
_
VII. Exocytosis and Endocytosis
A. In exocytosis, a cytoplasmic vesicle moves
substances from cytoplasm to plasma membrane
during secretion.
5
B. Endocytosis encloses particles in small portions
of plasma membrane to form vesicles that then
move into the cytoplasm.
1. Amoebas are phagocytic (Acell eater@), as
are white blood cells (WBCs) ; lysosomes
fuse with the endocytic vesicles to digest the
contents.
2. Droplets of liquid are also taken in
pinocytosis (Acell drinking@).
3. In receptor-mediated endocytosis, specific
molecules are brought into the cell by
specialized regions of the plasma
membranes that form coated pits which sink
into the cytoplasm.
Chapter 4
Cells Structure and Function
I. Early observations revealed an unseen world:
1. Galileo made first microscope.
2. Robert Hooke saw small compartments in cork,
which he named cells.
3. Van Leeuwenhoek observed several types of
living cells, including sperm.
4. Schleiden and Schwann proposed the idea
that all living things composed of cells.
6
5. Virchow concluded that all cells come from
existing cells
6. Ignaz Semmelweis (1840) described that washing
hands prevent childbirth fever
7. Robert Koch (1870) said that dieases were
caused by pathogenic bacteria (anthrax).
II. The Cell Theory
A. The cell is the smallest biological entity that still
retains the characteristics of life.
B. The basic principles of the cell theory are:
1. All organisms are composed of one or more
cells.
2. The cell is the basic unit of life.
3. New cells arise only from cells that already
existed.
III. The Nature of Cells
A. Basic Aspects of Cell Structure and Function
1. A plasma membrane separates each cell from
the environment, but permits the flow of molecules.
2. A DNA-containing region localizes the DNA,
which can be copied and read.
3. The cytoplasm contains membrane systems,
organelles, the cytoskeleton, and a semifluid
substance.
B. Structure and Functions of Cell Membranes
7
1. The lipid bilayer of plasma membranes forms a
boundary between inside and outside of the cell,
subdivides the cytoplasm into compartments,
and regulates the entry/exit of substances.
2. Proteins positioned in the plasma membrane
serve as channels or receptors.
C. Surface-to-Volume Constraints on the Size and
Shape of Cells
1. Most cells are too small to be seen without a
microscope.
MICROSCOPES-GATEWAY to the CELL (Page 54)
Concepts:light microscope, transmission
(TEM), scanning (SEM), and micrograph
(photogragh of microscope image)
IV. Prokaryotic Cells - Bacteria
A. The term prokaryotic ("before the nucleus") indicates
existence of bacteria before evolution of cells with a
nucleus; bacterial DNA is clustered in a distinct
region of the cytoplasm (nucleoid).
B. Bacteria are some of the smallest and simplest cells.
1. Bacterial flagella project from the membrane
and permit rapid movement.
2. A somewhat rigid cell wall supports the cell and
surrounds the plasma membrane, which
regulates transport into and out of the cell.
8
3. Ribosomes, protein assembly sites, are
dispersed throughout the cytoplasm.
V. Eukaryotic Cells
Functions of Organelles (Alittle organs@):
1. All eukaryotic (Atrue nucleus@) cells contain
organelles.
2. Organelles form compartmentalized portions of
the cytoplasm.
3. Organelles separate reactions with respect to
time (allowing proper sequencing) and space
(allowing incompatible reactions to occur in
close proximity).
VI. The Nucleus
A. The nucleus isolates DNA, which contains the
code for protein assembly, from the sites
(ribosomes in cytoplasm) where proteins will be
assembled.
B. The nucleus has the following components:
1. The nucleolus is a region where subunits of
ribosomes are prefabricated before shipment
out of the nucleus.
2. The nuclear envelope consists of two lipid
bilayers with pore complexes and a
ribosome-studded outer surface.
3. Chromosomes are composed of DNA and
associated proteins (some serve as enzymes,
others as support); DNA is duplicated and
9
condensed before cell division occurs; chromatin
refers to the total collection of DNA and proteins.
VII. Cytomembrane System
A. Within the cytoplasm, newly formed polypeptide
chains may be in solution or may enter the
cytomembrane system.
B. Endoplasmic Reticulum
1. The endoplasmic reticulum is a collection of
interconnected tubes and flattened sacs that
begins at the nucleus and winds its way through
the cytoplasm.
2. Two kinds of ER may be found in a cell:
a. Rough ER consists of stacked, flattened
sacs with many ribosomes attached. Here,
the proteins are placed as they are
synthesized.
b. Smooth ER has no ribosomes; it is the area
from which vesicles carrying proteins and
lipids are budded; it also inactivates harmful
chemicals.
C. Golgi Bodies - Apostoffice@
1. A Golgi body consists of flattened
sacs resembling a stack of flattened
pancakes. Secretory vesicles are formed as
portions of the outer membrane break away.
2. Here proteins and lipids undergo final
processing, sorting, and packaging.
D. Lysosomes - Agarbage disposal of cell@
10
1. These are vesicles that bud from Golgi bodies.
2. They carry powerful enzymes that can digest the
contents of other vesicles, worn-out cell parts, or
bacteria and foreign particles.
E. Peroxisomes
1. These small vesicles contain enzymes that use
oxygen to degrade fatty acids and amino acids.
2. The harmful byproduct, hydrogen peroxide, is
converted to water.
3. Glyoxisomes are abundant in certain seeds such
as peanuts where enzymes in the vesicles
convert fats and oils to sugars necessary for
rapid growth.
VIII. Mitochondria
A. Mitochondria are the primary organelles for
transferring the energy in carbohydrates to ATP
under oxygen-plentiful conditions.
B. Each mitochondrion has an outer membrane and
an inner folded membrane (cristae).
C. Aerobic Respiration occurs in the mitochondria.
1. Yields 36-38 ATP.
2. The aerobic route is summarized:
C6H12O6 + 6O2  6CO2 + 6H2O
3. Three series of reactions are required for
aerobic respiration:
a. Glycolysis is the breakdown of glucose
11
to pyruvate; small amounts of ATP are
generated.
b. Krebs cycle degrades pyruvate to
carbon dioxide, water, ATP, H+ ions, and
electrons.
c. Electron transport chain processes the
H+ ions and electrons to generate ATP.
D. Anaerobic Routes
1. Anaerobic pathways-->LOW oxygen
E. Two different fermentation pathways
1. Yield of only two ATPs
2. Lactate is formed when muscle cells
can=t get enough O2 for Krebs cycle.
3. Ethanol is produced by yeast.
C6H12O6  C2H3OH + CO2 + H2O
IX. Specialized Plant Organelles
A. Chloroplasts and Other Plastids
1. Chloroplasts are critical to PHOTOSYNTHESIS
a. Chloroplasts and mitochondria may have
originated from ancient bacteria engulfed by
predatory cell (endosymbiotic theory).
2. Chromoplasts store red and brown pigments that
give color to petals, fruits, and roots.
3. Colorless amyloplasts store starch granules.
B. Photosynthesis has two main reactions:
12
1. The light-dependent reactions convert light
energy to chemical energy (ATP).
2. The light-independent reactions assemble
sugars.
3. Overall, for glucose formation sunlight
12H2O + 6CO2 --> 6O2 + C6H12O6 + 6H2O
B. Two stages of photosynthesis:
1. Light-dependent reactions occur in the
thylakoid membrane system.
a. The thylakoids are folded into grana
(stacks of disks) and channels.
b. The interior thyaloid spaces are filled
with H+ needed to make ATP.
2. Sugar formation occurs in the stroma (semifluid)
area that surrounds the grana.
C. Central Vacuole
1. In a mature plant, the central vacuole may
occupy 50 to 90 percent of the cell interior.
a. Central vacuoles store amino acids, sugars,
ions, and wastes.
b. The vacuole enlarges during growth and
greatly increases the cell's outer surface
area.
2. The enlarged cell, with more surface area, has an
enhanced ability to absorb nutrients.
13
X. The Cytoskeleton
A. Scaffolds for Cell Shape and Internal Organization
1. The main components are microtubules, and
microfilaments.
2. Some portions are transient, such as the
"spindle" microtubules used in chromosome
movement during cell division; others are
permanent, such as filaments operational in
muscle contraction.
B. The Structural Basis of Cell Movements
1. Through controlled assembly and disassembly
of their subunits, microtubules, and
microfilaments grow or shrink in length, and
the structures attached to them are thereby
pushed or dragged through the cytoplasm.
2. Microfilaments or microtubules actively slide
past one another to bring about contraction (as
in muscle) and amoeboid motion.
3. Microtubules or microfilaments shunt
organelles from one location to another as in
cytoplasmic streaming.
C. Microtubule Organizing Centers
1. Microtubule organizing centers (MTOCs) are
small masses of proteins in the cytoplasm.
2. An MTOC near the nucleus of animal cells
includes a pair of centrioles that govern the
plane of cell division.
14
3. Centrioles also serve as patterns for the
assembly of basal bodies, which in turn organize
flagella and cilia microtubules.
D. The Internal Structure of Flagella and Cilia
1. Flagella are quite long, not usually numerous,
and found on one-celled protistans and animal
sperm cells.
2. Cilia are shorter and more numerous and can
provide locomotion for free-living cells or may
move surrounding water and particles if the
ciliated cell is anchored.
XI. Cell Surface Specializations
A. Cell Walls and Cell Junctions in Plants
1. Most are carbohydrate frameworks for
mechanical support in bacteria, protistans, fungi,
and plants; cell walls are not found in animals.
2. In growing plant parts, bundles of cellulose
strands form a primary cell wall that is pliable
enough to allow enlargement under pressure.
3. Later, more layers are deposited to form the
secondary wall.
4. Cutin, suberin, and waxes are embedded in
many plant cell walls for protection and to
reduce water loss.
5. Numerous channels (plasmodesmata) cross
adjacent walls and connect the cytoplasm of
neighboring cells.
B. Intercellular Material in Animals
15
1. Its components include collagen, other fibrous
proteins, glycoproteins, and polysaccharides that
form the "ground substance" through which
molecules diffuse from cell to cell.
2. In mature bone and other tissues,
intercellular material accounts for much of the
body's weight.
C. Cell Junctions in Animals
1. Tight junctions occur between cells of epithelial
tissues in which cytoskeletal strands of one cell
fuse with strands of neighboring cells.
2. Desmosomes are adhering junctions are like
Aspot welds@ at the plasma membranes of two
adjacent cells that need to be held together
during stretching.
3. Gap junctions are small, open channels that
directly link the cytoplasms of adjacent cells.
Chapter 6
GROUND RULES OF METABOLISM
I. Energy and Life
A. Two important definitions:
1. Energy is the capacity to make things
happen, to do work.
2. Metabolism refers to all the reactions in a
cell.
16
B. How Much Energy Is Available?
1. First law of thermodynamics states that the
total amount of energy in the universe is
constant; it cannot be created nor
destroyed; it can only change form.
2. Energy cannot be produced by a cell; it can
only be changed from one form to another.
C. The One-Way Flow of Energy
1. Second law of thermodynamics states that
the energy flow is not 100% efficient.
2. Heat is often the by-product of energy
conversions.
3. As systems lose energy they become more
disorganized; the measure of this disorder
is called entropy.
4. Life maintains a high degree of
organization only because it is being
resupplied with energy from the sun.
II. Energy and the Direction of Metabolic Reactions
A. Energy Losses and Energy Gains
1. Exergonic (Aenergy exits@) reactions
release energy such that the products have
less energy than the reactants had.
2. Endergonic (Aenergy in@) reactions require
energy in put resulting in products with more
energy than the reactants had.
B. Reversible Reactions
17
1. Chemical reactions can proceed from
reactants to products or reverse.
2. Parts of a
chemical reaction:
Reactants
Products
2H2O2  2H2O +
O2
3. Chemical
reactions will balance.
III. Metabolic Pathways
A. Metabolic pathways form series of reactions.
In biosynthetic pathways, small molecules are
assembled into large molecules. In degradative pathways,
large molecules are broken down to form products of lower
energy.
Released energy can be used for cellular work.
IV. Alternative Energy Sources in the Human Body
A. Carbohydrate Breakdown in Perspective
1. Excess carbohydrate intake is stored.
2. Free glucose is used until it runs low, then
glycogen reserves are tapped.
B. Energy from Fats
18
1. Excess fats
(including those made from
carbohydrates) are
stored away in cells of
adipose tissue.
2. Because fatty
acids have many more carbon
and
hydrogen atoms, they yield greater
amounts of ATP.
C. Energy from Proteins Amino group is released as
ammonia in urine. The amino acid remnant is fed
into the Krebs cycle.
_
PYRAMID OF ENERGY
B. Participants in metabolic pathways:
1. Substrates are substances that enter
reactions (= reactants = precursor).
2. Intermediates are the compounds formed
between the start and the end of a pathway.
3. Enzymes are proteins that catalyze (speed
up) reactions.
4. Cofactors are small molecules and metal
ions that help enzymes by carrying atoms
or electrons.
19
5. Energy carriers are mainly ATP.
6. End products are the substances present
at the conclusion of a pathway.
Glucose  Glucose/G. oxidase  CO2 + H2O + ATP
IV. Enzymes
A. Characteristics of Enzymes
1. Enzymes speed up reactions.
2. Enzymes can be reused.
3. Enzymes are very selective.
B. Enzyme-Substrate Interactions
1. The active site is a crevice where the
substrate binds to the enzyme.
a. In Koshland=s induced-fit model,
structural changes during binding allow
a more precise fit (hand holding a
pencil).
b. Reactants must reach a Atransition@
state in order for a reaction to proceed.
Enzymes increase the rate of a reaction by lowering the
activation energy (the amount of energy needed to bring
colliding molecules to the transition state) through extensive
bonding of substrate at the active site.
20
C. Effects of Temperature and pH on Enzyme Activity
1. High temperatures decrease reaction rate by
disrupting the bonds that maintain 3-D
(denaturation occurs).
2. Most enzymes function best at a pH 7;
higher or lower values disrupt enzymes.
D. Control of Enzyme Activity
1. Some controls regulate the number of
enzymes available by speeding
up/slowing down their synthesis.
2. Inhibitors can bind with an enzyme or
compete for the active site.
3. Allosteric enzymes have (in addition to
active sites) regulatory sites where control
substances can bind to alter enzyme
activity.
V. Enzyme Helpers
A. Cofactors are nonprotein groups that bind to
many enzymes and make them more reactive.
B. Coenzymes are large organic molecules such
as NAD+, FAD, and NADP+.
C. Inorganic metal ions such as Fe- also serve
as cofactors when assisting membrane
cytochrome proteins in their electron transfers
in chloroplasts and mitochondria.
21