Biology
CHAPTER 1: The Cell
Cell Theory
➢ The cell theory has four basic tenets:
○ All living things are composed of cells.
○ The cell is the basic functional unit of life.
○ Cells arise only from preexisting cells.
○ Cells carry genetic information in the form of DNA. This genetic material is passed on
from parent to daughter cell.
➢ Viruses are not considered living things because they are acellular, cannot reproduce without the
assistance of a host cell, and may use RNA as their genetic material.
Eukaryotic Cells
○ Eukaryotes have membrane-bound organelles, a nucleus, and may form multicellular
organisms.
○ The cell membrane and membranes of organelles contain phospholipids, which organize
to form hydrophilic interior and exterior surfaces with a hydrophobic core.
○ The cytosol suspends the organelles and allows diffusion of molecules throughout the
cell.
○ The eukaryotic organelles each serve specific functions:
■ The nucleus contains DNA organized into chromosomes. It is surrounded by the
nuclear membrane or envelope, a double membrane that contains nuclear pores
for two-way exchange of materials between the nucleus and cytosol. DNA is
organized into coding regions called genes.
■ The nucleolus is a subsection of the nucleus in which ribosomal RNA (rRNA) is
synthesized.
■ Mitochondria contain an outer and inner membrane. The outer membrane forms a
barrier with the cytosol; the inner membrane is folded into cristae and contains
enzymes for the electron transport chain. Between the membranes is the
intermembrane space; inside the inner mitochondrial membrane is the
mitochondrial matrix. Mitochondria can divide independently of the nucleus via
binary fission and can trigger apoptosis by releasing mitochondrial enzymes into
the cytoplasm.
■ Lysosomes contain hydrolytic enzymes that can break down substances ingested
by endocytosis and cellular waste products. When these enzymes are released,
autolysis of the cell can occur. The endoplasmic reticulum (ER) is a series of
interconnected membranes and is continuous with the nuclear envelope. The
rough ER (RER) is studded with ribosomes, which permit translation of proteins
destined for secretion. The smooth ER (SER) is used for lipid synthesis and
detoxification.
■ The Golgi apparatus consists of stacked membrane-bound sacs in which cellular
products can be modified, packaged, and directed to specific cellular locations.
■ Peroxisomes contain hydrogen peroxide and can break down very long chain fatty
acids via β-oxidation. They also participate in phospholipid synthesis and the
pentose phosphate pathway.
○ The cytoskeleton provides stability and rigidity to the overall structure of the cell, while
also providing transport pathways for molecules within the cell.
■ Microfilaments are composed of actin. They provide structural protection for the
cell and can cause muscle contraction through interactions with myosin. They also
help form the cleavage furrow during cytokinesis in mitosis.
■ Microtubules are composed of tubulin. They create pathways for motor proteins
like kinesin and dynein to carry vesicles. They also contribute to the structure of
, cilia and flagella, where they are organized into nine pairs of microtubules in a ring
with two microtubules at the center (9 + 2 structure). Centrioles are found in
centrosomes and are involved in microtubule organization in the mitotic spindle.
■ Intermediate filaments are involved in cell–cell adhesion and maintenance of the
integrity of the cytoskeleton; they help anchor organelles. Common examples
include keratin and desmin.
○ Epithelial tissues cover the body and line its cavities, protecting against pathogen invasion
and desiccation. Some epithelial cells absorb or secrete substances, or participate in
sensation.
■ In most organs, epithelial cells form the parenchyma, or the functional parts of the
organ.
■ Epithelial cells may be polarized, with one side facing a lumen or the outside
world, and the other side facing blood vessels and structural cells.
■ Epithelia can be classified by the number of layers: simple epithelia have one
layer, stratified epithelia have many layers, and pseudostratified epithelia appear
to have multiple layers due to differences in cell heights, but actually have only
one layer.
■ Epithelia can be classified by the shapes of the cells: cuboidal cells are
cube-shaped, columnar cells are long and narrow, and squamous cells are flat and
scalelike.
○ Connective tissues support the body and provide a framework for epithelial cells.
■ In most organs, connective tissues form the stroma or support structure by
secreting materials to form an extracellular matrix. Bone, cartilage, tendons,
ligaments, adipose tissue, and blood are all connective tissues.
Classification and Structure of Prokaryotic Cells
➢ Prokaryotes do not contain membrane-bound organelles; they contain their genetic material in a
single circular molecule of DNA located in the nucleoid region.
➢ There are three overarching domains of life; prokaryotes account for two of these:
○ Archaea are often extremophiles, living in harsh environments (high temperature, high
salinity, no light) and often use chemical sources of energy (chemosynthesis) rather than
light (photosynthesis). They have similarities to both eukaryotes (start translation with
methionine, similar RNA polymerases, histones) and bacteria (single circular
chromosome, divide by binary fission or budding).
○ Bacteria have many similar structures to eukaryotes, and have complex relationships with
humans, including mutualistic symbiosis and pathogenesis.
○ Eukarya is the only non-prokaryotic domain.
➢ Bacteria can be classified by shape:
○ Spherical bacteria are called cocci.
○ Rod-shaped bacteria are called bacilli.
○ Spiral-shaped bacteria are called spirilli.
➢ Bacteria can be classified based on metabolic processes:
○ Obligate aerobes require oxygen for metabolism.
○ Obligate anaerobes cannot survive in oxygen-containing environments and can only carry
out anaerobic metabolism. Facultative anaerobes can survive in environments with or
without oxygen and will toggle between metabolic processes based on the environment.
○ Aerotolerant anaerobes cannot use oxygen for metabolism, but can survive in an
oxygen-containing environment.
➢ The cell wall and cell membrane of bacteria form the envelope. Together, they control the
movement of solutes into and out of the cell.
CHAPTER 1: The Cell
Cell Theory
➢ The cell theory has four basic tenets:
○ All living things are composed of cells.
○ The cell is the basic functional unit of life.
○ Cells arise only from preexisting cells.
○ Cells carry genetic information in the form of DNA. This genetic material is passed on
from parent to daughter cell.
➢ Viruses are not considered living things because they are acellular, cannot reproduce without the
assistance of a host cell, and may use RNA as their genetic material.
Eukaryotic Cells
○ Eukaryotes have membrane-bound organelles, a nucleus, and may form multicellular
organisms.
○ The cell membrane and membranes of organelles contain phospholipids, which organize
to form hydrophilic interior and exterior surfaces with a hydrophobic core.
○ The cytosol suspends the organelles and allows diffusion of molecules throughout the
cell.
○ The eukaryotic organelles each serve specific functions:
■ The nucleus contains DNA organized into chromosomes. It is surrounded by the
nuclear membrane or envelope, a double membrane that contains nuclear pores
for two-way exchange of materials between the nucleus and cytosol. DNA is
organized into coding regions called genes.
■ The nucleolus is a subsection of the nucleus in which ribosomal RNA (rRNA) is
synthesized.
■ Mitochondria contain an outer and inner membrane. The outer membrane forms a
barrier with the cytosol; the inner membrane is folded into cristae and contains
enzymes for the electron transport chain. Between the membranes is the
intermembrane space; inside the inner mitochondrial membrane is the
mitochondrial matrix. Mitochondria can divide independently of the nucleus via
binary fission and can trigger apoptosis by releasing mitochondrial enzymes into
the cytoplasm.
■ Lysosomes contain hydrolytic enzymes that can break down substances ingested
by endocytosis and cellular waste products. When these enzymes are released,
autolysis of the cell can occur. The endoplasmic reticulum (ER) is a series of
interconnected membranes and is continuous with the nuclear envelope. The
rough ER (RER) is studded with ribosomes, which permit translation of proteins
destined for secretion. The smooth ER (SER) is used for lipid synthesis and
detoxification.
■ The Golgi apparatus consists of stacked membrane-bound sacs in which cellular
products can be modified, packaged, and directed to specific cellular locations.
■ Peroxisomes contain hydrogen peroxide and can break down very long chain fatty
acids via β-oxidation. They also participate in phospholipid synthesis and the
pentose phosphate pathway.
○ The cytoskeleton provides stability and rigidity to the overall structure of the cell, while
also providing transport pathways for molecules within the cell.
■ Microfilaments are composed of actin. They provide structural protection for the
cell and can cause muscle contraction through interactions with myosin. They also
help form the cleavage furrow during cytokinesis in mitosis.
■ Microtubules are composed of tubulin. They create pathways for motor proteins
like kinesin and dynein to carry vesicles. They also contribute to the structure of
, cilia and flagella, where they are organized into nine pairs of microtubules in a ring
with two microtubules at the center (9 + 2 structure). Centrioles are found in
centrosomes and are involved in microtubule organization in the mitotic spindle.
■ Intermediate filaments are involved in cell–cell adhesion and maintenance of the
integrity of the cytoskeleton; they help anchor organelles. Common examples
include keratin and desmin.
○ Epithelial tissues cover the body and line its cavities, protecting against pathogen invasion
and desiccation. Some epithelial cells absorb or secrete substances, or participate in
sensation.
■ In most organs, epithelial cells form the parenchyma, or the functional parts of the
organ.
■ Epithelial cells may be polarized, with one side facing a lumen or the outside
world, and the other side facing blood vessels and structural cells.
■ Epithelia can be classified by the number of layers: simple epithelia have one
layer, stratified epithelia have many layers, and pseudostratified epithelia appear
to have multiple layers due to differences in cell heights, but actually have only
one layer.
■ Epithelia can be classified by the shapes of the cells: cuboidal cells are
cube-shaped, columnar cells are long and narrow, and squamous cells are flat and
scalelike.
○ Connective tissues support the body and provide a framework for epithelial cells.
■ In most organs, connective tissues form the stroma or support structure by
secreting materials to form an extracellular matrix. Bone, cartilage, tendons,
ligaments, adipose tissue, and blood are all connective tissues.
Classification and Structure of Prokaryotic Cells
➢ Prokaryotes do not contain membrane-bound organelles; they contain their genetic material in a
single circular molecule of DNA located in the nucleoid region.
➢ There are three overarching domains of life; prokaryotes account for two of these:
○ Archaea are often extremophiles, living in harsh environments (high temperature, high
salinity, no light) and often use chemical sources of energy (chemosynthesis) rather than
light (photosynthesis). They have similarities to both eukaryotes (start translation with
methionine, similar RNA polymerases, histones) and bacteria (single circular
chromosome, divide by binary fission or budding).
○ Bacteria have many similar structures to eukaryotes, and have complex relationships with
humans, including mutualistic symbiosis and pathogenesis.
○ Eukarya is the only non-prokaryotic domain.
➢ Bacteria can be classified by shape:
○ Spherical bacteria are called cocci.
○ Rod-shaped bacteria are called bacilli.
○ Spiral-shaped bacteria are called spirilli.
➢ Bacteria can be classified based on metabolic processes:
○ Obligate aerobes require oxygen for metabolism.
○ Obligate anaerobes cannot survive in oxygen-containing environments and can only carry
out anaerobic metabolism. Facultative anaerobes can survive in environments with or
without oxygen and will toggle between metabolic processes based on the environment.
○ Aerotolerant anaerobes cannot use oxygen for metabolism, but can survive in an
oxygen-containing environment.
➢ The cell wall and cell membrane of bacteria form the envelope. Together, they control the
movement of solutes into and out of the cell.
