CELLS
Eukaryotes
Cell Theory
Eukaryotic cells
Cells were discovered in 1665 by Robert Hooke.
-possess a membrane-bound nucleus
Early studies of cells were conducted by
-are more complex than prokaryotic cells
- Mathias Schleiden (1838)
- Theodor Schwann (1839)
Schleiden and Schwann proposed the Cell Theory.
-compartmentalize many cellular functions
within organelles and the endomembrane system
-possess a cytoskeleton for support and to
maintain cellular structure
Anatomy of the Cell
1. All organisms are composed of cells.

Cells are not all the same
2. Cells are the smallest living things.

All cells share general structures
3. Cells arise only from pre-existing cells.

Cells are organized into three main regions
All cells today represent a continuous line of descent
from the first living cells.
Prokaryotic vs Eukaryotic Cells

Plasma membrane

Cytoplasm

Nucleus
Plasma Membrane
Prokaryotes
Prokaryotic cells lack a membrane-bound nucleus.
-genetic material is present in the nucleoid
Two types of prokaryotes:
-archaea
-bacteria
The fluid-mosaic model is the currently accepted
concept
describing plasma membrane structure.

Barrier for cell contents

Double phospholipid layer


Hydrophilic heads

Hydrophobic tails

Protein

Cholesterol

Glycoproteins
Microvilli
-Finger-like projections that increase surface area for
absorption

Inclusions

Non-functioning units
Cytoplasmic Organelles
Other materials in plasma membrane
Plasma Membrane Specializations


Membrane junctions

Tight junctions (seals)

Desmosomes (strength)

Hemidesmosomes (base)

Gap junctions (communication)

Ribosomes

composed of ribosomal RNA and
proteins

Sites of protein synthesis

Found at two locations

Free in the cytoplasm

Attached to rough endoplasmic
reticulum
Endomembrane system
-a series of membranes throughout the
cytoplasm
-divides cell into compartments where different
cellular functions occur
1. endoplasmic reticulum
2. Golgi apparatus
3. vesicles (lysosomes)
Rough endoplasmic reticulum (RER)
Cytoplasm

Material outside the nucleus and inside the
plasma membrane

Cytosol


Fluid that suspends other
elements
Organelles

Metabolic machinery of the cell
-membranes that create a network of channels
throughout the cytoplasm
-attachment of ribosomes to the membrane
gives a rough appearance
-synthesis of proteins to be secreted, sent to
lysosomes or plasma membrane
Smooth endoplasmic reticulum (SER)

Mitochondria
-relatively few ribosomes attached

“Powerhouses” of the cell
-functions:

self-replicating due to mtDNA
-synthesis of membrane lipids and
phospholipids

Carry out reactions where oxygen is
used to break down food
-calcium storage

contain oxidative metabolism enzymes
for transferring the energy within
macromolecules to ATP
-detoxification of foreign substances
Golgi apparatus
•
flattened stacks of interconnected membranes
•
storage, modification, and packaging of
polypeptide and protein products
•
synthesis of cell wall components
•
cis- “forming face”
•
trans “maturing face”

Cytoskeleton

Network of protein structures that
extend throughout the cytoplasm

Provides the cell with an internal
framework

Locomotion and translocation of
macromolecules and organelles within
the cell
Cytoskeleton
Three different types
-Microfilaments
Lysosomes
•
•

membrane bound vesicles containing digestive
enzymes to break down macromolecules
destroy cells or foreign matter that the cell has
engulfed by phagocytosis
System for assembling,
isolating, and secreting
polypeptides and proteins
for export in a eukaryotic
cell, for lysosomes, or for
incorporation into plasma
membrane.
Actin-myosin (contraction)
-Intermediate filaments

Fibrous(mechanical support)
-Microtubules

Tubulin(architecture, organization, transport)

Cytoskeleton
o
Network of protein structures that
extend throughout the cytoplasm
o
Provides the cell with an internal
framework
o
Locomotion and translocation of
macromolecules and organelles within
the cell
Microfilament- cell contraction

Barrier of nucleus

Consists of a double phospholipid membrane

Contain nuclear pores that allow for exchange
of material with the rest of the cell
Microtubules- intracellular architecture, organization,
and transport
Intermediate filaments- provides mechanical support
for the plasma membrane

Centrosome

Centrioles
-Rod-shaped bodies made of microtubules
-Direct formation of mitotic spindle during cell division
Nucleoli

Nucleus contains one or more nucleoli

Sites of ribosome production

Each centrosome contains a pair of centrioles and each
centriole is composed of nine triplets of microtubules
Ribosomes then migrate to the
cytoplasm through nuclear pores
Chromatin
arranged as a cylinder.

Composed of DNA and protein
The Nucleus

Scattered throughout the nucleus

Chromatin condenses to form chromosomes
when the cell divides

Control center of the cell


Contains genetic material (DNA)
Three regions
Cellular Projections

Nuclear membrane

Not found in all cells

Nucleolus

Used for movement

Chromatin

Cilia moves materials across the cell
surface

Flagellum propels the cell
Cellular Physiology: Membrane Transport

Membrane Transport – movement of substance
into and out of the cell

Transport is by two basic methods

Types of diffusion

Passive transport- No energy is required



Diffusion, Osmosis,
Facilitated/Mediated Transport

Active transport- Energy is required

Simple diffusion- unassisted process

lipid-soluble materials

gases

alcohol

urea
Osmosis – simple diffusion of water

Endocytosis, Exocytosis
Highly polar water easily
crosses the plasma membrane
Solutions and Transport

Solution – homogeneous mixture of two or
more components

Solvent – dissolving medium

Solutes – components in smaller
quantities within a solution

Intracellular fluid – nucleoplasm and cytosol

Interstitial fluid – fluid on the exterior of the cell
Selective Permeability

The plasma membrane allows some materials
to pass while excluding others

This permeability includes movement into and
out of the cell
Passive Transport Processes

Diffusion

Particles tend to distribute themselves
evenly within a solution

Movement is
from high
concentration
to low
concentration,
or down a
concentration
gradient


Water and solutes are forced through a
membrane by fluid, or hydrostatic pressure
A pressure gradient must exist
-Solute-containing fluid is pushed from a high
pressure area to a lower pressure area
For example, marine bony fishes
maintain a solute concentration in
their blood about one-third of that
in seawater; they are
hypoosmotic to seawater.
If a fish swims into a river mouth
and then up a freshwater stream,
as salmon do, it would pass through a region
where its blood solutes were equal in
concentration to those in its environment
(isosmotic), Then enter freshwater, where its
blood solutes were hyperosmotic to
those in its environment. It must have
physiological mechanisms
to avoid net loss of water in the sea and gain of
water in the river
Diffusion through the Plasma Membrane
(blood sugar) into body cells that oxidize it as a principal
Diffusion Through Channels
energy source for the synthesis of ATP.
•
Water and dissolved ions, since they are
charged, cannot diffuse through the
phospholipid component of the plasma
membrane.
•
Signalling mechanisms in NS and muscles
•
Instead, they pass through specialized pores or
channels created by transmembrane proteins.
•
Aquaporin- water channel
•
Absorption of water in DS and
kidneys
Active Transport Processes

Gated Channels-signal to open or close them
1. Chemically-gated ion channels
Transport substances that are unable to pass by
diffusion

They may be too large

They may not be able to dissolve in the
fat core of the membrane

They may have to move against a
concentration gradient
2. Voltage-gated ion channels

Chemically- gated ion channel -signalling molecule
binds to a specific binding site on the transmembrane
protein
Voltage gated ion channel- when the ionic charge across
a plasma membrane changes

Two common forms of active transport

Solute pumping

Bulk transport
Solute pumping

Carrier-mediated transport
Nutrients such as sugars and materials for growth such
as amino acids must enter a cell, and wastes of
metabolism must leave.
Transporters/ carriers -special transmembrane proteins
*facilitated diffusion
Transporters are usually quite specific, recognizing and
transporting only a limited group of chemical
substances or perhaps even a single substance
Facilitated diffusion- movement only in a downhill
direction (in the direction of a concentration gradient)
and requires no metabolic energy to drive the transport
system.
In many animals facilitated diffusion aids in transport of
glucose
Amino acids, some sugars and ions are
transported by solute pumps


Na-K ion pump
ATP energizes protein carriers, and in
most cases, moves substances against
concentration gradients

Bulk transport


Exocytosis

Moves materials out of the cell

Material is carried in a
membranous vesicle

Vesicle migrates to plasma
membrane

Vesicle combines with plasma
membrane

Material is emptied to the
outside
Bulk transport

Endocytosis


Extracellular substances are
engulfed by being enclosed in a
membranous vesicle
Types of endocytosis

Phagocytosis – cell eating

Pinocytosis – cell drinking
Centromere-where sister chromatids are attached
Kinetochore- points of attachment of microtubules
(spindle fibers) during cell division
STRUCTURE OF CHROMOSOME
Cell Life Cycle
Stages of Mitosis
Events of Cell Cycle


Prophase
 First part of cell
division
 Centromeres
migrate to the
poles where
the centrioles
are
 Nuclear
membrane
disintegrates
Interphase (G1,S,G2)



Cell grows

Cell carries on metabolic
processes

No cell division occurs
Cell division (Mitosis)

Cell replicates itself

Function is to produce more
cells for growth and repair
processes
Metaphase
 Spindle from
centromeres are
attached to
chromosomes that
are aligned in the
center of the cell

Anaphase
 Daughter
chromosomes are
pulled toward the
poles
 The cell begins to
elongate

Telophase
 Daughter nuclei begin
forming
 A cleavage furrow
(for cell division)
begins to form
 Followed by
cytokinesis (splitting of
the cytoplasm)
Cytokinesis

Division of the cytoplasm

Begins when mitosis is near
completion

Results in the formation of two
daughter cells
Mitosis
•
One part of the cell cycle
•
Growth, cell replacement, tissue repair
•
Unique to eukaryotes
•
Happens in somatic cells only
•
Nuclear & cellular division that maintains
chromosome #
•

Diploid (2n)
Meiosis
Meiosis I: Synapsis & Crossing over
•
Occurs only in sex (gamete) cells
•
1st step in formation of gametes
•
Gametes fuse with opposite sex gametes to
form new individual
•
Humans are diploid (2n) with 46 chromosomes
•
(23 + 23 homologous chromosomes)
•
When chromosomes condense during prophase,
homologous chromosomes stick very closely
together & form a tetrad.
•
•
Meiosis halves chromosome number so
daughter cells (gametes) are haploid (n) with 23
chromosomes
Have only 1 set of
chromosomes
Synapsis- The side by side pairing of homologous
maternal and paternal chromosomes at the start of
meiosis
= haploid (n)
•
•
Each gamete has 1
allele for each gene
In humans = eggs or
sperm
Crossing- over- The interchange of sections between
pairing homologous chromosomes during the
prophase of meiosis
Chiasma (plural chiasmata)- An intersection or crossing
of two tracts in the form of the letter X
During meiosis, one cell goes through 2 divisions to end
with formation of 4 cells, all with haploid (n) nuclei.
Meiosis I: Independent Assortment
•
•
•
Metaphase alignment
Random alignment
Duplicated chromosomes randomly tether to
spindle poles
• i.e. no set rules for where maternal &
paternal chromosomes should be positioned
Meiosis I: Independent Assortment
Which half of homologous chromosome pair
ends up at which pole is totally random
23
2 (8,388,608) possible combos of maternal
& paternal chromosomes!
Meiosis: Interphase
•
•
•
Same as in mitosis:
Cell grows & duplicates cytoplasmic components
DNA is replicated
Meiosis: Things to remember
1. DNA replication:
a. Occurs only during interphase
before Meiosis I
2. Meiosis I
a. Prophase: crossing-over
b. Metaphase: line up in 2 rows
c. Anaphase: separation of
homologous chromosomes
d. Interkinesis: short period of rest
prior to meiosis II
3. Meiosis II
a. Similar to mitosis but no interphase
precedes it
b. Division results in haploid cells
c. Female gametes: completion of
meiosis takes place only when cell
is fertilized.
Source of Genetic
Variability
a. Random
fertilization
b. Crossing over
in prophase I
c. Independent
Assortment in
metaphase I
Mitosis vs Meiosis