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1. Plasma membrane
- forms the cell’s outer boundary
- separates the cell’s internal environment
from the outside environment
- is a selective barrier
- plays a role in cellular communication
2. Cytoplasm
- all the cellular contents between the plasma
membrane and the nucleus
- cytosol - the fluid portion, mostly water
- organelles - subcellular structures having
characteristic shapes and specific functions

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3. Nucleus
- large organelle that contains DNA
- contains chromosomes, each of which
consists of a single molecule of DNA and
associated proteins
- a chromosome contains thousands of
hereditary units called genes
 Flexible yet sturdy barrier
 The fluid mosaic model - the arrangement of
molecules within the membrane resembles a
sea of lipids containing many types of
proteins
 The lipids act as a barrier to certain
substances
 The proteins act as “gatekeepers” to certain
molecules and ions

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 Consists of a lipid bilayer - made up of
phospholipids, cholesterol and glycolipids
 Integral proteins - extend into or through the
lipid bilayer
 Transmembrane proteins - most integral
proteins, span the entire lipid bilayer
 Peripheral proteins - attached to the inner or
outer surface of the membrane, do not
extend through it
 Glycoproteins - membrane proteins with a
carbohydrate group attached that protrudes
into the extracellular fluid
 Glycocalyx - the “sugary coating”
surrounding the membrane made up of the
carbohydrate portions of the glycolipids and
glycoproteins

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 Some integral proteins are ion channels
 Transporters - selectively move substances
through the membrane
 Receptors - for cellular recognition; a ligand
is a molecule that binds with a receptor
 Enzymes - catalyze chemical reactions
 Others act as cell-identity markers
 The cell is either permeable or impermeable
to certain substances
 The lipid bilayer is permeable to oxygen,
carbon dioxide, water and steroids, but
impermeable to glucose
 Transmembrane proteins act as channels and
transporters to assist the entrance of certain
substances, for example, glucose and ions

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 Passive processes - substances move across
cell membranes without the input of any
energy; use the kinetic energy of individual
molecules or ions
 Active processes - a cell uses energy,
primarily from the breakdown ofATP, to
move a substance across the membrane, i.e.,
against a concentration gradient
 Steepness of
 concentration
gradient
 Temperature
 Mass of diffusing
substance
 Surface area
 Diffusion distance

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 Net movement of water through a
selectively permeable membrane from an
area of high concentration of water (lower
concentration of solutes) to one of lower
concentration of water
 Water can pass through plasma membrane
in 2 ways:
1. through lipid bilayer by simple diffusion
2. through aquaporins, integral membrane
proteins

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Osmosis
Solutes are transported across plasma membranes with the use of energy, from an area of
lower concentration to an area of higher ConcentrationSodium-potassium pump
1
3 Na+
K+
gradient
Na+
gradient
Na+/K+ ATPase
Extracellular fluid
Cytosol
1
3 Na+ expelled
3 Na+
ADP
P
K+
gradient
Na+
gradient
Na+/K+ ATPase
Extracellular fluid
Cytosol
ATP
21
3 Na+ expelled
3 Na+
ADP
P
P
K+
gradient
Na+
gradient
Na+/K+ ATPase
Extracellular fluid
Cytosol
2K+
ATP
2 31
3 Na+ expelled
3 Na+
ADP
P
P
2 K+
imported
K+
gradient
Na+
gradient
Na+/K+ ATPase
Extracellular fluid
Cytosol
2K+
ATP
2 3 4
Active Transport

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 Vesicle - a small spherical sac formed by budding off from
a membrane
 Endocytosis - materials move into a cell in a vesicle
formed from the plasma membrane
three types: receptor-mediated endocytosis
phagocytosis
bulk-phase endocytosis (pinocytosis)
 Exocytosis - vesiclesfuse with the plasma membrane,
releasing their contents into the extracellular fluid
 Transcytosis - a combination of endocytosis and
exocytosis
Receptor
Mediated
Endocytosis
Neutrophil
Phagocytosis

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1. Cytosol - intracellular fluid, surrounds
the organelles
- the site of many chemical reactions
- energy is usually released by these
reactions
- reactions provide the building blocks
for cell maintenance, structure, function
and growth
2. Organelles
Specialized structures within the cell
The cytoskeleton - network of protein
filaments throughout the cytosol
-provides structural support for the cell
-three types according to increasing
size: microfilaments, intermediate
filaments, and microtubules

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Microtubules
 Centrosome - located near the nucleus,
consists of two centrioles and pericentriolar
material
 Cilia - short, hair-like projections from the cell
surface, move fluids along a cell surface
 Flagella - longer than cilia, move an entire
cell; only example is the sperm cell’s tail

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 Ribosomes - sites of protein
synthesis
 Endoplasmic reticulum - network of
membranes in the shape of flattened
sacs or tubules
- Rough ER - connected to the nuclear
envelope, a series of flattened sacs,
surface is studded with ribosomes,
produces various proteins
-Smooth ER - a network of
membrane tubules, does not have
ribosomes, synthesizes fatty acids
and steroids, detoxifies certain drugs

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 Golgi complex - consists of 3-20 flattened,
membranous sacs called cisternae
- modify, sort, and package proteins for
transport to different destinations
- proteins are transported by various
vesicles
Lysosomes - vesicles that form from the Golgi
complex, contain powerful digestive enzymes

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 Peroxisomes - smaller than lysosomes,
detoxify several toxic substances such as
alcohol, abundant in the liver
 Proteasomes - continuously destroy
unneeded, damaged, or faulty proteins,
found in the cytosol and the nucleus

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Mitochondria - the “powerhouses” of the cell
 Generate ATP
 More prevalent in physiologicallyactive cells: muscles,liver and
kidneys
 Inner and outer mitochondrial membranes
 Cristae - the series of folds of the inner membrane
 Matrix - the large central fluid-filledcavity
 Self-replicate during times of increased cellular demand or before
cell division
 Spherical or oval shaped structure
 Usually most prominent feature of a cell
 Nuclear envelope - a double membrane that separates
the nucleus from the cytoplasm
 Nuclear pores - numerous openings in the nuclear
envelope,control movement of substances between
nucleus and cytoplasm
 Nucleolus - spherical body that produces ribosomes
 Genes - are the cell’s hereditary units, control activities
and structure of the cell
 Chromosomes - long molecules of DNA combined with
protein molecules

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Transcription
Translation

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 The cell cycle is a sequence of events in which
a body cell duplicates its contents and divides
in two
 Human somatic cells contain 23 pairs of
chromosomes (total = 46)
 The two chromosomes that make up each
pair are called homologous chromosomes
(homologs)
 Somatic cells contain two sets of
chromosomes and are called diploid cells
 Interphase - the cell is not dividing
- the cell replicates its DNA
- consists of three phases, G1, S, and G2,
replication of DNA occurs in the S phase
Mitotic phase - consists of a nuclear division
(mitosis) and a cytoplasmic division
(cytokinesis) to form two identical cells

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 Prophase - the chromatin fibers change into
chromosomes
 Metaphase - microtubules align the centromeres of the
chromatid pairs at the metaphase plate
 Anaphase - the chromatid pairs split at the centromere
and move to opposite poles of the cell; the chromatids
are now called chromosomes
 Telophase - two identical nuclei are formed around the
identical sets of chromosomes now in their chromatin
form

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 Division of a cell’s cytoplasm to form two
identical cells
 Usually begins in late anaphase
 The plasma membrane constricts at its
middle forming a cleavage furrow
 The cell eventually splits into two daughter
cells
 Interphase begins when cytokinesis is
complete
1
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
all at 700xLM
1
LateEarly
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Chromosome
(two chromatids
joined at
centromere
(a) INTERPHASE
(b) PROPHASE
Centrioles
Centrosome:
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
2
all at 700xLM
Centromere
1
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Metaphase plate
(a) INTERPHASE
Centrioles
Centrosome:
(c) METAPHASE
2
3
LateEarly (b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
all at 700xLM
Chromosome
(two chromatids
joined at
centromere
Centromere
1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
Chromosome
(a) INTERPHASE
Centrioles
Centrosome:
(c) METAPHASE
2
3
4
Cleavage
furrow
LateEarly (b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
all at 700xLM
Chromosome
(two chromatids
joined at
centromere
Centromere
1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
Cleavage furrow
(e) TELOPHASE
(c) METAPHASE
2
3
4
5
Cleavage
furrow
LateEarly (b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
Chromosome
all at 700xLM
Chromosome
(two chromatids
joined at
centromere
Centromere
1
Early
Late
(d) ANAPHASE
Pericentriolar material
Nucleolus
Nuclear envelope
Chromatin
Plasma membrane
Cytosol
(a) INTERPHASE
Centrioles
Centrosome:
(f) IDENTICAL CELLS IN INTERPHASE
Cleavage furrow
(e) TELOPHASE
(c) METAPHASE
Cleavage
furrow
2
3
4
5
6
LateEarly (b) PROPHASE
Fragments of
nuclear envelope
Mitotic spindle
(microtubules)
Kinetochore
Metaphase plate
Chromosome
all at 700xLM
Centromere
Chromosome
(two chromatids
joined at
centromere
Mitosis
Mitosis
 During sexual reproduction each new organism is the
result of the union of two gametes (fertilization), one
from each parent
 Meiosis - reproductive cell division that occurs in the
gonads (ovaries and testes) that produces gametes with
half the number of chromosomes
 Haploid cells - gametes contain a single set of 23
chromosomes
 Fertilization restores the diploid number of
chromosomes (46)

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 Meiosis occurs in two successive stages:
meiosis I and meiosis II
 Each of these two stages has 4 phases:
prophase, metaphase, anaphase, and
telophase
 Summary - Meiosis I begins with a diploid cell
and ends with two cells having the haploid
number of chromosomes; in Meiosis II, each of
the two haploid cells divides, the net result is
four haploid gametes that are genetically
different from the original diploid starting cell
Meiosis

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 The average adult has
nearly 100 trillion cells
 There are about 200
different types of cells
 Cells come in a variety of
shapes and sizes
 Cellular diversity permits
organization of cells into
more complex tissues
and organs