Chapter 6:
A Tour of the
Cell
Essential Knowledge
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2.a.2 – Organisms capture and store free energy for use
in biological processes (6.2).
2.b.3 – Eukaryotic cells maintain internal membranes
that partition the cell into specialized regions (6.2-6.5).
4.a.2 – The structure and function of subcellular
components, and their interactions, provide essential
cellular processes (6.2-6.5).
4.b.2 – Cooperative interactions within organisms
promote efficiency in the use of energy and matter
(6.4).
Light Microscope - LM
Uses visible light to illuminate the object
 Relatively inexpensive type of microscope
 Can examine live or dead objects
 Light passes through specimen and then
through various lenses
 Lenses refract/bend light to magnify

Light Microscope
Occular Lens
Objective Lens
Stage with specimen
Light Source
Limitations - LM

Miss many cell structures that are beyond
the magnification of the light microscope
◦ Ex: lysosomes, centrioles

Need other ways to make the
observations
Electron Microscopes
Use beams of electrons instead of light
 Invented in 1939, but not used much until
after WWII
 Advantages:

◦ Much higher magnifications
◦ Magnifications of 50,000X or higher are
possible.
◦ Can get down to atomic level in some cases
Disadvantages of EM
Need a vacuum
 Specimen must stop the electrons
 High cost of equipment
 Specimen preparation

Other Types of Microscopes

Transmission Electron Microscope TEM
◦ Sends electrons through thinly sliced and stained
specimens
◦ Gives high magnification of interior views. Many
cells structures are now visible

Scanning Electron Microscopes – SEM
◦ Excellent views of surfaces
◦ Produces 3-D views
◦ Live specimens possible
Limitations to EM
 TEM:
◦ Specimen dead; specimen prep is difficult
 SEM:
◦ Lower magnifications than the TEM; only see
surface of specimen
TEM - interior
SEM - surface
Cell Biology or Cytology
Cyto = cell - ology = study of
 Should use observations from several
types of microscopes to make a total
picture of how a cell is put together
 Directly related to biochemistry

Tools for Cytology
Cell Fractionation
 Chromatography
 Electrophoresis

Cell Fractionation
Disrupt cells
 Separate parts (organelles and
membrane) by centrifugation at different
speeds

◦ Separates by size and density of the various
structures

Result - pure samples of cell structures
for study
Cell Fractionation
Chromatography
Technique for separating mixtures of
chemicals
 Separates chemicals by size or degree of
attraction to the materials in the medium
 Ex - paper, gas, column, thin-layer

Electrophoresis
Separates mixtures of chemicals by their
movement in an electrical field
 Used for proteins and DNA

Cell History

See alternate Ppt
History of Cells
Robert Hooke - Observed cells in cork
 Coined the term "cells” in 1665

◦ Came from “jail cells” and/or monastery cells

Cells:
◦ Al life is made of cells!!!
◦ Cells are the simplest form of life
History of Cells
1833 - Robert Brown, discovered the
nucleus
 1838 - M.J. Schleiden, all plants are
made of cells
 1839 - T. Schwann, all animals are made
of cells.
 1840 - J.E. Purkinje, coined the term
“protoplasm”
 Late 1800s – Rudolf Virchow (“Omnis
cellula e cellula” - All cells are from
other cells)

Cell Theory: 3 Parts
1.
2.
3.
All living matter is composed of one or
more cells.
The cell is the structural and functional
unit of life.
Cells come only from existing cells.
Two Types of Cells
1) Prokaryotic - lack a nucleus and other
membrane-bound structures.
 2) Eukaryotic - have a nucleus and other
membrane-bound structures.

Examples
Nucleus
Organelles
Prok
Bacteria, blue-green
algae, Archaebacteria
No
Some (ribosomes,
cell mem,
cytoplasm)
Euk
Animal, plants, fungi
Yes
Most (depends on
whether
plant/animal)
DNA
Complexity
# of cells
Prok
Circular, singlestranded, in
cytoplasm
Less
One/Uni,
smaller in size
Euk
Helical, doublestranded, in
nucleus
More
Several/Multi,
larger in size
Eukaryotic
Prokaryotic
Cell diversity
Most cells are between 5-50 micrometers
 Mycoplasmas - bacteria that are .1 to 1.0 mm.
(1/10 the size of regular bacteria)
 # of cells: uni- and multicellular

Why Are Cells So Small?
Cell volume to surface area ratios favor
small size
 Nucleus to cytoplasm consideration
(control)
 Metabolic requirements

Surface area v.Volume
Vol and SA are proportionate (if one
increases, the other increases)
 Vol increases more than surface area (as
cell grows)

◦ Smaller objects have a greater ratio of sa to
vol

Structure/Function:
◦ Villi in intestinal cells – inc sa so cells can
absorb more materials from food
Basic Cell Organization
Membrane*
 Nucleus
 Cytoplasm*
 Organelles
 DNA/RNA*

*EVERY cell has these 3 parts
Animal
Cell
Plant
Cell
Cell Membrane
Separates the cell from the environment
 Boundary layer for regulating the
movement of materials in/out of a cell
 Often called plasma membrane
 Bilayer of phospholipids
 Allows oxygen, nutrients, wastes to pass
through a series of processes:

 Diffusion
 Osmosis
 Active transport
Cytoplasm
Cell substance between the cell membrane
and the nucleus
 The “fluid” part of a cell.
 Neutral pH (serves as a natural buffer)
 Exists in two forms:

◦ gel - thick
◦ sol - fluid
Organelles
Term means "small organ”
 Formed body in a cell with a specialized
function
 Important in organizational structure of
cells
 More prominent/numerous in eukaryotic
cells
 Ex: Mitochondria, Endoplasmic reticulum,
lysosomes

Nucleus
Most obvious organelle
 Usually spherical, but can be lobed or irregular
in shape
 Contains genetic info
 Found ONLY in euk cells
 Function/s:

◦ Control center for the cell
◦ Contains the genetic instructions
◦ Controls protein synthesis by making mRNA and
rRNA (from DNA)
Structure of Nucleus
Nuclear membrane
 Nuclear pores
 Nucleolus
 Chromatin

Nuclear Membrane
Otherwise known as Nuclear Envelope
 Double membrane (lipid bilayer) separated
by a 20-40 nm space
 Inner membrane supported by a protein
matrix (nuclear lamina) which gives the
shape to the nucleus
 Separates nuclear contents from cytoplasm
 Dissolves during cell division

Nuclear Pores
Regular “holes” through both membranes
 100 nm in diameter
 Protein complex gives shape

◦ Lines every nuclear pore

Allows materials, such as
macromolecules, in/out of nucleus
Nucleolus
Dark staining area in the nucleus
 0 - 4 per nucleus
 Storage area for ribosomes
 rRNA made here (from DNA)
 No membrane encloses it??? (Research
about nucleolus continues!!!)

Chromatin
Chrom: colored
- tin: threads
 DNA and protein in a “loose” format
 Will form the chromosomes during
Interphase of cell division (Chromosomes
more condensed)
 Each eukary cell has
specific #

Ribosomes
 Structure: 2
subunits made of protein and
rRNA
 No membrane
 Function: protein synthesis
◦ The more occurrences of protein synthesis,
the more ribosomes
◦ Ex: Pancreatic cells have over 1.2 million
ribosomes
Ribosome structure

2 Subunits:
◦ 1) Large
 45 proteins, 3 rRNA molecules
◦ 2) Small
 23 proteins, 1 rRNA molecule

2 Locations:
◦ 1) Free in the cytoplasm - make proteins for
use in cytosol
◦ 2) Membrane bound - make proteins that are
exported from the cell (Attached to rough
ER)
Endomembrane System
Series of membranes connected by direct
physical continuity or by transfer of
membrane segments called vesicles
 Includes: ER, Golgi, vesicles
 Function: protein synthesis, transport of
proteins, move lipids, detoxify proteins
 Works closely with: nucleus, lysosomes,
ribosomes, plasma membrane

Endomembrane System
Endoplasmic Reticulum



Often referred to as ER
Makes up to 1/2 of the total membrane in
cells
Often continuous with the nuclear
membrane/pores
◦ All cisternae (inner portion) are connected
 Structure:
◦ Folded sheets or tubes of membranes
◦ Very “fluid” in structure with the
membranes constantly changing size and
shape.
2 Types of ER

1) Smooth ER: no ribosomes
◦ Used for lipid synthesis, carbohydrate storage,
detoxification of poisons
◦ Ex: store calcium ions, sex hormones contain LOADS
of these (lipid synthesis)

2) Rough ER: with ribosomes
◦ Makes secretory protein and lipid parts of cell
membrane
◦ Ex: liver cells (add water to detoxify proteins to
secrete), insulin (secretory protein)
◦ Most proteins are called glycoproteins (contain
protein and carb parts)
Golgi Apparatus or
Dictyosomes
Structure: parallel array of flattened
cisternae (looks like a stack of Pita bread)
 3 to 20 per cell
 Likely an outgrowth of the ER system
 Think of the UPS man

2 Faces of Golgi

1) Cis face - side toward the nucleus
Receiving side
◦ Located near ER

2) Trans face - side away from the nucleus.
Shipping side
◦ Gives rise to vesicles

Both contain varying polarity
Function of Golgi
Processing - modification of ER products
 Distribution - packaging of ER products for
transport
 Sorting and Shipping
 UPS man/organelle!!!
 Found in large #s in secretory cells
 Ever-changing organelle

Transport Vesicles
Secretory proteins in transit from one
organelle to another
 Two kinds:

◦ 1) From ER to Golgi
◦ 2) From Golgi to ?
 Otherwise known as Golgi vesicles
Golgi Vesicles
 Small
sacs of membranes that bud off the
Golgi Body
 Transportation vehicle for the modified
ER products
◦ May become polypeptide chains or amino
acids
 Contain
identifiers to help determine
where destination is
Lysosome



Single membrane – made by rough ER
Made from the Trans face of the Golgi
apparatus
Functions:
◦ Breakdown and degradation of cellular materials
 Carry out intracellular digestion
◦ Digest cell’s own materials
 Called autophagy
 Digest old, non-repairable items
◦ Contains hydrolytic enzymes to breakdown fats,
proteins, polysaccs, and nucleic acids
Lysosome Function, cont.
Important in cell death (apoptosis)
 Missing enzymes may cause various
genetic enzyme diseases

◦ Examples:
 Tay-Sachs, Pompe’s Disease
 Tay-Sachs: Can’t break down lipid in brain
(accumulates and causes nervous system disorders)
Vacuoles
Structure - single membrane, usually larger than
the Golgi vesicles
 Function - depends on the organism (most
control hydrolysis and store materials)
 Types - Food, contractile, central
 Function:

◦ Water regulation - hydrolysis
◦ Storage of ions
◦ Storage of hydrophilic pigments (e.g. red and blues in
flower petals)
 Helps attract pollinators
Protist vacuoles
Contractile vacuoles - pump out excess
water.
 Food vacuoles - store newly ingested
food until the lysosomes can digest it

Plant vacuoles
Large single vacuole in mature (making up
to 90% of the cell's volume)
 Tonoplast - vacuole membrane

◦ Regulatory (Semi-permeable)

Function:
◦ Used to enlarge cells and create turgor
pressure
 Absorb water
◦ Store enzymes (various types)
◦ Store toxins
◦ Coloration (may contain pigment)
Microbody
 Contain
specialized enzymes for specific
reactions
 Peroxisomes: use up H peroxide
◦ Some break down fatty acids, detoxify
poisons
 Glyoxysomes: lipid
digestion
◦ Found in plant seeds (used for energy
storage)
Enzymes in a
crystal
Energy Transforming
Organelles

1) Mitochondria
◦ Found in ALL cells (plant, animal, etc)

2) Chloroplasts
◦ Found only in plant, plant-like cells

Considered to be energy transforming
organelles
◦ Mitochondria – food  ATP
◦ Chloroplast – sun/water/CO2  food
Mitochondria

2 membranes:
◦ Inner and outer (each is phospholipid bilayer)
◦ The inner membrane has more surface area
than the outer membrane.
Matrix: inner space
 Intermembrane space: area between the
membranes

Mitochondria
Have ribosomes
 Have their own DNA
 Can reproduce themselves
 May have been independent cells
 Found in nearly ALL eukaryotic cells
 Function:

◦ Site for cell respiration - the release of energy
from food.
◦ Major location of ATP generation
◦ “Powerhouse” of the cell
Inner Membrane of Mito
Folded into cristae
 Amount of folding depends on the level of
cell activity
 Contains many enzymes

◦ Serve as catalysts for cellular respiration

ATP generated here
Chloroplasts
Function: performs photosynthesis
 Structure

◦ Two outer membranes
◦ Complex internal membrane
◦ Fluid-like stroma is around the internal
membranes

3 components/parts:
◦ 1) Stroma
◦ 2) Thylakoid OR Grana
◦ 3) Intermembrane space
Chloroplasts
Contain ribosomes
 Contain DNA
 Can reproduce themselves
 Often contain starch
 May have been independent cells at one
time

Inner/Thylakoid
Membranes of Chloroplast
Arranged into flattened sacs called
thylakoids
 Some regions stacked into layers called
grana
 Contain the green pigment chlorophyll

Cytoskeleton
Network of rods and filaments in the
cytoplasm
 Components:

◦ 1) Microtubules
◦ 2) Microfilaments
◦ 3) Intermediate Filaments
Cytoskeleton Functions
Cell structure and shape
 Cell movement
 Movement of organelles
 Cell division - helps build cell walls and
move the chromosomes apart
 VERY important to animal cells

◦ Why? Because animal cells lack the extra
support of cell wall
Microtubules
Structure - small hollow tubes made of
repeating units of a protein dimer
 Size - 25 nm diameter with a 15 nm
lumen; can be 200 nm to 25 mm in length
 Thickest of three components
 Contains protein called tubulin

Microtubules
Regulate cell shape
 Coordinate direction of cellulose fibers
in cell wall formation
 Tracks for motor molecules

◦ Ex: Guide vesicles from Golgi
Form cilia and flagella
 Internal cellular movement
 Make up centrioles, basal bodies and
spindle fibers

Cilia and Flagella

Cilia - short, but numerous
◦ Hair-like

Flagella - long, but few
◦ Tail-like

Functions –
◦ Flight/Movement/Locomotion, reproductive
processes, filter water


Structure - arrangement of microtubules,
covered by the cell membrane
Dynein - motor protein that connects the
tubules
Dynein Protein
A contractile/motor protein
 Uses ATP
 Creates a twisting motion between the
microtubules causing the structure to
bend or move
 Made of several polypeptide chains

◦ Quaternary structured protein
Centrioles
Usually one pair per cell, located close to
the nucleus
 Found in animal cells
 9 sets of triplet microtubules
 Help in cell division

Microfilaments
5 to 7 nm in diameter
 Structure - two intertwined strands of
actin protein
 Solid rods of
linear filaments

Functions of Microfilaments
Muscle contraction
 Cytoplasmic streaming
 Pseudopodia (ex: amoeba)
 Cleavage furrow formation (ex: cell
division)
 Maintenance and changes in cell shape

Intermediate Filaments
Fibrous proteins that are super coiled
into thicker cables and filaments
8 - 12 nm in diameter
 Made from several different types of
protein
 Functions:

◦ Maintenance of cell shape
◦ Hold organelles in place
Cell Wall
Nonliving jacket that surrounds some
cells
 Function as the cell's exoskeleton for
support and protection
 Found in:

◦
◦
◦
◦
Plants
Prokaryotes
Fungi
Some Protists
Plant: Primary Cell Wall
Thin and flexible
 Cellulose fibers placed at right angles to
expansion
 Placement of fibers guided by
microtubules

Plant: Secondary Cell
Wall
Thick and rigid
 Added between the cell membrane and
the primary cell wall in laminated layers
 May cover only part of the cell; giving
spirals
 Makes up "wood”

Cell wall: Middle Lamella
Thin layer rich in pectin found between
adjacent plant cells
 Glues cells together


The Inner Life of the Cell - Harvard
University
Intercellular Junctions

Plants - Plasmodesmata
◦ Channels between cells through adjacent cell
walls
◦ Allows communication between cells
◦ Also allows viruses to travel rapidly between
cells
Intercellular Junctions

Animals:
◦ Tight junctions
◦ Desmosomes
◦ Gap junctions
Tight Junctions
Very tight fusion of the membranes of
adjacent cells
 Seals off areas between the cells
 Prevents movement of materials around
cells

Desmosomes
Bundles of filaments which anchor
junctions between cells
 Does not close off the area between
adjacent cells
 Coordination of movement between
groups of cells

Gap Junctions
Open channels between cells, similar to
plasmodesmata
 Allows “communication” between cells

Summary
Recognize the types and uses of
microscopes in the study of cells.
 Recognize the limitations on cell size.
 Recognize why cells must have internal
compartmentalization.
 Identify the structures and functions of cell
organelles.
 Identify the structures and functions of the
cytoskeleton.
 Recognize the surface features and intercellular connections of plant and animal cells.
