1. 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 1

2. The Microscopic World of Cells
How do we study cells?
Light microscopes can be used to explore the structures and functions of cells. 2

3. The Microscopic World of Cells
● Electron Microscope
10 m
Human height
1 m
Length of some
nerve and
muscle cells
10 cm
Chicken egg
Unaided eye
1 cm
Frog eggs
1 mm
100 mm
Plant and
animal cells
Light microscope
10 mm
Nucleus
Most bacteria
Mitochondrion
1 mm
Smallest bacteria
100 nm
Electron microscope
Viruses
Ribosomes
10 nm
Proteins
Lipids
1 nm
Small molecules
Atoms
0.1 nm
Figure 4.3

4. The Microscopic World of Cells
Light Micrograph (LM)
(for viewing living cells)
Light micrograph of a protist, Paramecium LM
Colorized SEM
Scanning Electron Micrograph (SEM)
(for viewing surface features)
Scanning electron micrograph of Paramecium
TYPES OF MICROGRAPHS
Transmission Electron Micrograph (TEM)
(for viewing internal structures)
Transmission electron micrograph of Paramecium
Colorized TEM

5. The Two Major Categories of Cells
● The countless cells on earth fall into two categories:
Prokaryotic cells — Bacteria and Archaea
Eukaryotic cells — Eukarya
protists, plants, fungi, and animals
● All 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

6. Prokaryotic Cells Are smaller than eukaryotic 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)
Nucleoid (contains DNA)
Pili (attachment structures)
Colorized TEM

7. Eukaryotic Cells *Generalized plant cell *Generalized animal cell
● Eukaryotic cells are fundamentally similar.
*Generalized plant cell
*Generalized animal cell

8. Cytoplasm (inside of cell)
Membrane Structure
● The plasma membrane separates the living cell from its nonliving surroundings.
(a) Phospholipid bilayer of
membrane
(b) Fluid mosaic model of
Outside of cell
Hydrophilic
head
Hydrophobic
tail
region of
protein
regions of
Phospholipid
bilayer
Proteins
Cytoplasm (inside of cell)

9. Membrane Structure Phospholipids are amphipathic molecules
● Phospholipid structure
Phospholipids are amphipathic molecules

10. Cytoplasm (inside of cell)
Membrane Structure
● The plasma membrane separates the living cell from its nonliving surroundings.
(a) Phospholipid bilayer of
membrane
(b) Fluid mosaic model of
Outside of cell
Hydrophilic
head
Hydrophobic
tail
region of
protein
regions of
Phospholipid
bilayer
Proteins
Cytoplasm (inside of cell)

11. Membrane Structure ● Some functions of membrane proteins
Fibers of
extracellular
matrix
Cytoskeleton
Cytoplasm
Attachment to
cytoskeleton and a b
Cell signaling c d
Enzymatic activity
Transport e
Intercellular
joining f
Cell-cell
recognition
● Cell surface – Extracellular Matrix

12. Nucleus Chromatin Nuclear envelope Nucleolus Nuclear Pore
● The nucleus is an organelle that houses the genetic material of the cell.
Chromatin
Nucleolus
Pore
Nuclear
envelope
Surface of nuclear
Nuclear pores
TEM
Chromatin
Nuclear envelope
Nucleolus
Nuclear Pore

13. Chromatin
DNA molecule
Chromosome
Proteins
Chromatin
fiber
Figure 4.9

14. Ribosomes Composed of proteins and Ribosomal RNA
● 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

15. How DNA Directs Protein Synthesis
● DNA controls the cell by transferring its coded information into RNA
DNA 1
Synthesis of
mRNA in the
nucleus
mRNA
The information in the RNA is used to make proteins
Nucleus
Cytoplasm 2
Movement of
mRNA into
cytoplasm via
nuclear pore
mRNA
Ribosome 3
Synthesis of
protein in the
cytoplasm
Protein

16. The Endomembrane System
● Many of the membranous organelles in the cell belong to the endomembrane system

17. The Endomembrane System
Rough ER
Transport
vesicle from ER
Golgi
apparatus
Secretory
vesicle from Golgi
Secretory
protein
Vacuole
Lysosome
Plasma membrane

18. The Endoplasmic Reticulum
Produces an enormous variety of molecules
Is composed of smooth and rough ER
Nuclear
envelope
Ribosomes
Rough ER
Smooth ER

19. The Endoplasmic Reticulum
After the rough ER synthesizes a molecule it packages the molecule into transport vesicles 4
Transport vesicle
buds off
Secretory
protein inside
transport
vesicle
Ribosome 3
Protein 1
Rough ER 2
Polypeptide