The Microscopic World of Cells
● Organisms
are either:
Single-celled, such as most prokaryotes and protists
or
Multicelled, such as plants, animals, and most fungi
The Microscopic World of Cells
How do we study cells?
Light microscopes can be used to explore the
structures and functions of cells.
The Microscopic World of Cells
10 m
Human height
1m
Length of some
nerve and
muscle cells
10 cm
Chicken egg
1 cm
Frog eggs
1 mm
Plant and
animal cells
10 mm
1 mm
100 nm
Nucleus
Most bacteria
Mitochondrion
Smallest bacteria
Viruses
Ribosomes
10 nm
Electron microscope
100 mm
Light microscope
Microscope
Unaided eye
● Electron
Proteins
Lipids
1 nm
0.1 nm
Small molecules
Atoms
Figure 4.3
The Microscopic World of Cells
TYPES OF MICROGRAPHS
Light micrograph of a protist, Paramecium
Scanning electron micrograph of Paramecium
Colorized TEM
Transmission Electron Micrograph (TEM)
(for viewing internal structures)
Colorized SEM
Scanning Electron Micrograph (SEM)
(for viewing surface features)
LM
Light Micrograph (LM)
(for viewing living cells)
Transmission electron micrograph of Paramecium
The Two Major Categories of Cells
● The
● All
countless cells on earth fall into two categories:
Prokaryotic cells — Bacteria and Archaea
Eukaryotic cells — Eukarya
protists, plants, fungi, and animals
cells have several basic features.
1. They are all bound by a thin plasma membrane.
2. All cells have DNA.
3. All cells have ribosomes.
Cytoplasm-the entire contents of a cell
Prokaryotic Cells
● Prokaryotes
Are smaller than eukaryotic cells
Lack internal structures surrounded by membranes
Lack a nucleus
Have a rigid cell wall
Plasma membrane
(encloses cytoplasm)
Cell wall (provides
Rigidity)
Capsule (sticky
coating)
Prokaryotic flagellum
(for propulsion)
Ribosomes
(synthesize proteins)
Colorized TEM
Nucleoid (contains DNA)
Pili (attachment structures)
Eukaryotic Cells
● Eukaryotic
cells are fundamentally similar.
*Generalized plant cell
*Generalized animal cell
Membrane Structure
● The
plasma membrane separates the living cell from its
nonliving surroundings.
Outside of cell
Hydrophilic
head
Hydrophobic
tail
Hydrophilic
region of
protein
Outside of cell
Hydrophilic
head
Phospholipid
bilayer
Hydrophobic
tail
Phospholipid
Cytoplasm (inside of cell)
(a) Phospholipid bilayer of
membrane
Hydrophobic
regions of
protein
Proteins
Cytoplasm (inside of cell)
(b) Fluid mosaic model of
membrane
Membrane Structure
● Phospholipid
structure
Phospholipids are amphipathic molecules
Membrane Structure
● The
plasma membrane separates the living cell from its
nonliving surroundings.
Outside of cell
Hydrophilic
head
Hydrophobic
tail
Hydrophilic
region of
protein
Outside of cell
Hydrophilic
head
Phospholipid
bilayer
Hydrophobic
tail
Phospholipid
Cytoplasm (inside of cell)
(a) Phospholipid bilayer of
membrane
Hydrophobic
regions of
protein
Proteins
Cytoplasm (inside of cell)
(b) Fluid mosaic model of
membrane
Membrane Structure
● Some
functions of membrane proteins
Cytoplasm
Fibers of
extracellular
matrix
c Enzymatic activity
b Cell signaling
a Attachment to
cytoskeleton and
extracellular
matrix
e Intercellular
joining
d Transport
Cytoskeleton
● Cell
Cytoplasm
surface – Extracellular Matrix
f Cell-cell
recognition
Nucleus
nucleus is an organelle that houses the genetic
Nuclear
material of the cell.
Chromatin envelope Nucleolus Pore
Chromatin
Nucleolus
TEM
Nuclear
envelope
TEM
● The
Nuclear Pore
Surface of nuclear
envelope
Nuclear pores
Chromatin
DNA molecule
Proteins
Chromatin
Chromosome
fiber
Figure 4.9
Ribosomes
● Ribosomes
build all the cell’s proteins (protein synthesis)
Composed of proteins and
Ribosomal RNA
Free: proteins for cytosol
Membrane-bound:
proteins for
cell membranes and export
How DNA Directs Protein Synthesis
● DNA
controls the cell
by transferring its coded
information into RNA
– The information in
the RNA is used to
make proteins
DNA
1 Synthesis of
mRNA in the
nucleus
mRNA
Nucleus
Cytoplasm
2 Movement of
mRNA into
cytoplasm via
nuclear pore
3 Synthesis of
protein in the
cytoplasm
mRNA
Ribosome
Protein
The Endomembrane System
● Many
of the
membranous organelles
in the cell belong to the
endomembrane system
The Endoplasmic Reticulum
– Produces an
enormous variety
of molecules
– Is composed of
smooth and rough
ER
Nuclear
envelope
Ribosomes
Rough ER
Smooth ER
The Endoplasmic Reticulum
After the rough ER synthesizes a molecule it packages
the molecule into transport vesicles
4
Transport vesicle
buds off
Ribosome
3
Secretory
protein inside
transport
vesicle
Protein
1
Polypeptide
2
Rough ER
The Golgi Apparatus
– Works in partnership with the ER
– Refines, stores, and distributes the products of cells
Transport
vesicle
from ER
“Receiving” side of
Golgi apparatus
Golgi apparatus
New vesicle forming
Transport vesicle
from the Golgi
“Shipping” side of
Golgi apparatus
Plasma membrane
Lysosomes
• A lysosome is a membrane-enclosed sac
– It contains digestive enzymes
– The enzymes break down macromolecules
– They break down damaged organelles
Lysosome
Digestion
Damaged
organelle
(b) Lysosome breaking down damaged organelle
Vacuoles
Vacuoles are membranous sacs
Traffic of Large Molecules
–Exocytosis is the secretion of large molecules within
vesicles.
Outside of cell
Plasma
membrane
Cytoplasm
Traffic of Large Molecules
–Endocytosis takes material into a cell within vesicles that
bud inward from the plasma membrane.
Transport of large molecules
Exocytosis
Endocytosis
Types of endocytosis
found in animal cells:
*Phagocytosis
*Pinocytosis
*Receptor-mediated
endocytosis
Protein Sorting and Vesicle Transport
The Endomembrane System
Rough ER
Transport
vesicle from ER
Golgi
apparatus
Secretory
vesicle from Golgi
Secretory
protein
Vacuole
Plasma membrane
Lysosome