Cell Structure
Chapter 3
3.1 Looking at Cells
 1600’s the microscope
was invented
 Robert Hooke 1665
looked at cork and saw
little boxes he called
“cells”
 Anton Van
Leeuwenhoek later
looked at pond water
and saw tiny animals
he called “animalcules”
Measuring Cell Structures
 Based on metric system
giga-
mega-
kilo- hecto- deka- BASE deci- centi- milli-
Giga = G
Mega = M
Micro = µ
Nano = n
micro-
nano-
Characteristics of Microscopes
 Light Microscope – light
passes through 1 or more
lenses
 Electron Microscope –
image made by beams of
electrons
 Micrograph – image from a
microscope
– Labeled with what kind of
microscope and
magnification value
 Magnification – how many
times larger it appears
 Resolution – measure of
clarity
Electron Micrograph Ebola Virus
160,000 x magnification
Types of Microscopes
 Compound Light
Microscope
40 x
– 2 lenses with light bulb
shining through slide
– Objective lens in close
to slide
– Ocular lens is near eye
– 40x x 10x = 400x
magnification
400 x
– Third lens hurts
resolution
– Most powerful = 2,000x
– See something 0.5 µm
in diameter
 Electron Microscope
– Up to 200,000x
– Beam and specimen
must be in vacuum so
e- don’t bounce off gas
(no living things)
– Transmission Electron
Microscope
 Stained with metal ions
 Very thin slices of
specimen
 Internal structures
 Black and white but
computers add color
– Scanning Electron
Microscope
 Specimen coated with
thin layer of metal
 3-D cell surface
 Artificial color
 Scanning
Tunneling
Microscope
– Needlelike probe
measures
differences in
voltage caused
by e- that tunnel
from surface of
object
– 3-D image
– Used on living
things
3.2 Cell Features
 Cell Theory
– All living things are made of cells
– Cells are the basic units of structure and
function in organisms
– All cells arise from existing cells
Cell Size
 Smaller is more efficient
 Everything must cross cells surface
 Surface area to volume ratio
– Too low - substances cannot enter and leave in large
enough numbers
– Small cells have a high ratio
Common Features of Cells
 Cell Membrane
– Outer boundary
enclosing cell that
separates interior
– Controls flow in and out
 Cytoplasm
– Cell interior
 Cytoskeleton
– System of microscopic
fibers
– Act as support
structures
 Ribosomes
– Where proteins are
made
 DNA
– All cells have it
– Protein instructions
– Regulate cellular
activities
– Allows for reproduction
Prokaryotes
 Smallest, simplest, singlecelled organism
 No nucleus (and other
parts missing)
 Cannot carry out many
special functions due to
missing parts
 Around at least 3.5 billion
years ago (bya)
 Nearly 2 bya were only
organisms on earth
 Very small from 1 – 15 µm
 Bacteria
– Subset that causes infection
and food spoiling
Characteristics
 Large range of
environments
 Many grow and
divide rapidly
 Some don’t need
oxygen, others
can’t have it
 Some make own
food
 Everything inside cell
membrane is in cytoplasm
 Enzymes and ribosomes free
to move around
 Singular, circular DNA located
in center
 Cell Wall – surround
membrane
– Provides structure and
support
 No cytoskeleton so cell wall
gives shape
– Cell wall made of
polysaccharides connected
by short amino acid chains
– Some cell walls surrounded
by capsule =
polysaccharides (allows
them to cling to many things)
 Flagella – long, threadlike structures that provide
movement
Eukaryotic Cells
 Internal compartments
 Evolved about 2.5 bya
 Have an internal
compartment for DNA =
nucleus
 Have structures that
carry out specific
activities = organelles
 Cytoplasm = everything
inside membrane but
outside nucleus
 Membranes connect
organelles and provide
channels
– Form envelopes called
vesicles that move
proteins between
organelles
 Flagella
 Cilia
– short, hair-like
structures
– Used for cell
movement or
movement of materials
over cell
 Cytoskeleton
– Protein fibers
– Holds cell together,
keeps it from
collapsing
 Cytosol – fluid
surrounding
organelles, internal
membranes and
cytoskeleton
The Cytoskeleton
 Interior framework of animal cell
 Protein fibers anchored to inside
of plasma membrane
 3 kinds of fibers
– Actin Fibers
 Long, slender
microfilaments
 Made of the protein actin
 Determine shape of
animal cells
– Microtubules
 Hollow tubes
 Made of protein tubulin
 Highway for transport
from nucleus to parts of
cell
– Intermediate fibers
 Thick ropes of protein
 Frame for ribosomes and
enzymes keeping them
in certain locations
The Cell Membrane
 Fluid, like a soap bubble
 Lipids form a barrier
allowing only certain things
through - selective
permeability
 Phospholipid = 2 fatty
acids and a phosphate
group
– Polar head – phosphate
group; attracted to H20
– 2 nonpolar fatty acid tails;
repelled by H20
 Phospholipids are in a
double layer so called the
lipid bilayer
 Allows lipids and nonpolar
substances to pass
through
Membrane Proteins
 Proteins are made of
amino acids
– Some are polar and some
are nonpolar
– Some move around
 Marker proteins attached
to carbohydrate tell what
kind of cell it is (liver,
heart)
 Receptor proteins bind
specific substances (signal
molecules)
 Enzymes in cell membrane
important in biochemical
reactions
 Transport Proteins help
move things in and out
3.3 Cell Organelles
 Nucleus
– Controls most cell functions
– Surrounded by nuclear envelope
 Double membrane (two lipid
bilayers)
 Nuclear pores = small
channels allow passage
through
– Nucleolus – ribosomes partially
assembled here
– Most DNA stored here
 Wound around proteins but in
elongated thin strands
 When about to divide they
become more compact into
chromosomes and form dense
rod shaped structures
 Number of chromosomes
depends on species
– Humans = 46
– Peas = 14
Ribosomes and Endoplasmic
Reticulum
 Ribososmes
– Where proteins are made
– Made of dozens of different proteins and RNA
– May be free in cytosol but proteins made there stay in
cell
Production of Proteins
 Endoplasmic Reticulum is a
system of internal
membranes that move
proteins and other structures
through the cell
 It is a lipid bilayer with
embedded proteins
 Rough ER
– Attached ribosomes
– Proteins made enter ER
– Pinched off and form
vesicles
– Keep separate
 Smooth ER
– No ribosomes
– Make lipids
– Break down toxic
substances
Packaging and Distribution of
Proteins


Vesicles go from ER to
Golgi Apparatus
Golgi Apparatus
–
–
–

Flattened membranebound sacs
Enzymes inside modify
proteins
Modified proteins
repackaged by GA and bud
off
Lysosomes – vesicle that
contains digestive
enzymes
 Steps of Protein
packaging and
distribution
1)Ribosomes on Rough
ER make proteins
and they are
packaged
2)Go from ER to GA
3)In the GA proteins
are modified and
repackaged
4)Many vesicles move
to cell membrane and
release cargo
5)Other vesicles remain
in cell and go a job
Mitochondria
 Harvests energy from
organic compounds to
make ATP which is
used as energy by cell
 Most ATP is made here
 Cells that use ATP
have lots of
mitochondria
 2 membranes
– Outer = smooth
– Inner = folded; large
surface area
 Forms 2 compartments
Mitochondrial DNA
 DNA and ribosomes
make their own
proteins though most
come from cytosol
 Mitochondrial DNA
(mDNA) is
independent from
nuclear DNA, similar to
circular DNA of
prokaryotic cell
– Believe prokaryotes
were ancestors to
mitochondria
Structure of Plant Cells
 Cell Wall
– Surrounds cell
membrane
– Made of proteins and
carbohydrates
(cellulose)
– Helps support and
maintain shape
– Protection
– Connects to other cells
 Chloroplasts
– Use light to make carbohydrates from CO2 and H20
– Along with mitochondria supplies much of energy
needed to power cell
– 2 membranes
– Contain their own DNA (ancient prokaryotes)
 Central Vacuole
– Stores water
– May contain ions,
nutrients, or wastes
– When full, cell is rigid