Download Chapter 6 A Tour of the Cell

Chapter 6 A Tour of the Cell
I. The Cell Theory:
A. All living organisms are made of one or more cells.
B. The cell is the basic unit of structure and function of living things.
C. All cells come from pre-existing cells.
II. Tools for Studying Cells
- Improvements in technology used to study cells have led to a better understanding of cells.
A. Microscopy
- Scientists use microscopes to visualize cells too small to see with the naked eye.
- Light microscopes pass visible light through a specimen and magnify cellular
structures with lenses.
- Different types of microscopes can be used to visualize different sized cellular structures
and use different methods for enhancing visualization of cellular structures.
- Electron microscopes focus a beam of electrons through a specimen (TEM) or onto
its surface (SEM).
- The scanning electron microscope (SEM) provides for detailed study of the surface
of a specimen.
- The transmission electron microscope (TEM) provides for detailed study of the
internal ultrastructure of cells.
B. Isolating Organelles by Cell Fractionation
- Cell fractionation takes cells apart and separates the major organelles from one
another based on their density.
- The centrifuge is used to fractionate cells into their component parts.
III. Comparing Prokaryotic and Eukaryotic Cells
- Two types of cells make up every organism: prokaryotic and eukaryotic.
A. All cells have several basic features in common
- bounded by a plasma membrane
- contain a semifluid substance called the cytosol
- contain chromosomes
- have ribosomes
B. Prokaryotic cells
- do not contain a nucleus
- have their DNA located in a region called the nucleoid
C. Eukaryotic cells
- contain a true nucleus, bound by a membranous nuclear envelope
- usually quite a bit bigger than prokaryotic cells
- have extensive and elaborately arranged internal membranes which form organelles
- Plant and animal cells have most of the same organelles.
D. Size Limits of Cells
- The logistics of carrying out cellular metabolism sets limits on the size of cells.
- A smaller cell has a higher surface to volume ratio, which facilitates the exchange of
materials into and out of the cell.
- The plasma membrane functions as a selective barrier allowing sufficient passage of
nutrients and waste.
IV. Nucleus and Ribosomes
- involved in the genetic control of the cell
A. The Nucleus: Genetic Library of the Cell
- Contains most of the genes in the eukaryotic cell.
- The nuclear envelope, a lipid bilayer, encloses the nucleus, separating its contents
from the cytoplasm.
- Chromosomes: structures in nucleus that contain the DNA
- Nucleoli: structures in the nucleus that are involved in the production of ribosomes
B. Ribosomes: Protein Factories in the Cell
- particles made of ribosomal RNA and protein
- carry out protein synthesis
- free ribosomes located in the cytosol
- bound ribosomes attached to endoplasmic reticulum or nuclear envelope
V. Endomembrane System
- involved in synthesis and transport of proteins and lipids, and detoxification of poisons
- includes nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles,
and plasma membrane
A. The Endoplasmic Reticulum (ER): Biosynthetic Factory
- accounts for more than half the total membrane in many eukaryotic cells
- is continuous with the nuclear envelope
- consists of the ER lumen (cavities) and cisternae (sacs)
- two distinct regions of ER: Smooth ER, which lacks ribosomes and Rough ER, which
contains ribosomes
1. Functions of Smooth ER
- synthesizes lipids (such as steroids such sex hormones)
- metabolizes carbohydrates
- detoxifies poison (in liver cells)
- stores calcium ions (in muscle cells)
2. Functions of Rough ER
- has ribosomes attached
- produces proteins (esp. secretory) and membranes, which are distributed by
transport vesicles
B. The Golgi Apparatus: Shipping and Receiving Center
- center of manufacturing, storing, sorting, and shipping of cell proteins (esp. secretory
proteins and hydrolytic enzymes)
- receives many of the transport vesicles produced in the rough ER
- consists of flattened membranous sacs called cisternae
- functions of Golgi include:
- modification of the products of the rough ER
- manufacture of certain macromolecules
C. Lysosomes: Digestive Compartments
- membranous sac of hydrolytic enzymes
- digest all kinds of macromolecules
- carry out intracellular digestion by phagocytosis
- recycle the cell’s own organic molecules by autophagy
D. Vacuoles: Diverse Maintenance Compartments
- A plant or fungal cell may have one or several vacuoles.
- Food vacuoles are formed by phagocytosis
- Contractile vacuoles pump excess water out of protist cells
- Central vacuoles, found in plant cells, hold reserves of important organic compounds
and water.
VI. Mitochondria and Chloroplasts
- change energy from one form to another
- Mitochondria are the sites of cellular respiration.
- Chloroplasts found only in plants, are the sites of photosynthesis.
- Both contain their own DNA and ribosomes.
A. Mitochondria: Cellular Respiration
- found in nearly all eukaryotic cells
- enclosed by two membranes: a smooth outer membrane and an inner membrane folded
into cristae
B. Chloroplasts: Photosynthesis
- a specialized member of a family of closely related plant organelles called plastids
- contains chlorophyll
- found in leaves and other green organs of plants and in algae
- Chloroplast structure includes thylakoids, membranous sacs, and stroma, the internal
fluid.
- Other plastids include chromoplasts (store colored pigments) and amyloplasts (store
starch, amylase).
C. Peroxisomes: Oxidation
- produce hydrogen peroxide and convert it to water
- breakdown fatty acids
VII. Cytoskeleton
- a network of fibers extending throughout the cytoplasm that organizes structures and
activities in the cell
- composed of 3 types of molecular structures: microtubules, microfilaments, and
intermediate filaments
A. Roles of the Cytoskeleton: Support, Motility, and Regulation
- gives mechanical support to the cell
- provides anchorage for organelles and some enzymes
- involved in cell motility, which utilizes motor proteins
B. Components of the Cytoskeleton
- three main types of fibers that make up the cytoskeleton
1. Microtubules
- shape and support the cell
- guide movement of organelles
- help separate the chromosome copies in dividing cells
a. Centrosomes and Centrioles
- The centrosome is considered to be a “microtubule-organizing center” and contains
a pair of centrioles (composed of 9 triplets of microtubules).
- Produce a type of microtubule that functions as compression resistant ‘girders’.
b. Cilia and Flagella
- are locomotor appendages of some cells
- share a common ultrastructure
- contain specialized arrangements of microtubules
- Dynein is a motor protein responsible for the bending movement of cilia and flagella.
2. Microfilaments (Actin Filaments)
- twisted, double chain of actin (a protein) molecules
- tension-bearing structures
- found in all eukaryotic cells
- Microfilaments that function in cellular motility contain the protein myosin in addition
to actin.
- Amoeboid movement involves the contraction of actin and myosin filaments.
- Cytoplasmic streaming is another form of locomotion created by microfilaments.
3. Intermediate Filaments
- permanent, tension-bearing structures made of various protein such as keratin
- support cell shape
- fix organelles in place
VIII. Extracellular Components and Intracellular Connections
- help coordinate cellular activities
A. Cell Walls of Plants
- a rigid, protective, extracellular structure of plant, fungal, and bacterial cells
- Plant cell walls are made of cellulose fibers embedded in other polysaccharides and
protein.
- may have multiple layers (middle lamella, and primary and secondary walls)
B. The Extracellular Matrix (ECM) of Animal Cells
- Animal cells, which lack cell walls, are covered by an elaborate matrix, the ECM.
- made up of glycoproteins, such as collagen, and other macromolecules
- functions include support, adhesion, movement, and regulation
C. Intercellular Junctions
- allow neighboring cells to adhere, interact, and communicate
1. Plants: Plasmodesmata
- channels that perforate plant cell walls
- allow water and small molecules to freely pass from cell to cell
2. Animals: Tight Junctions, Desmosomes, and Gap Junctions
a. Tight junctions
- form continuous seals around cells that prevent leakage between cells
b. Desmosomes
- act as rivets fastening cells together into strong sheets
c. Gap junctions
- provide cytoplasmic channels through which ions, sugars, amino acids, etc. can
pass
- allows intercellular communication