Most antibiotics kill bacteria while minimally harming the human host by binding to structures found only on bacterial cells.
Some antibiotics bind to the bacterial ribosome, leaving human ribosomes unaffected.
Other antibiotics target enzymes found only in the bacterial cells.
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
Microscopes as Windows on the World of Cells
Light microscopes can be used to explore the structures and functions of cells.
When scientists examine a specimen on a microscope slide
Light passes through the specimen
Lenses enlarge, or magnify, the image
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 Figure 4.1
Light Micrograph (LM) (for viewing living cells) Light micrograph of a protist, Paramecium LM Figure 4.1a
Colorized SEM Scanning Electron Micrograph (SEM) (for viewing surface features) Scanning electron micrograph of Paramecium Figure 4.1b
Transmission Electron Micrograph (TEM) (for viewing internal structures) Transmission electron micrograph of Paramecium Colorized TEM Figure 4.1c
Magnification is an increase in the specimen’s apparent size.
Resolving power is the ability of an optical instrument to show two objects as separate.
Cells were first described in 1665 by Robert Hooke.
The accumulation of scientific evidence led to the cell theory .
All living things are composed of cells.
All cells come from other cells.
The electron microscope (EM) uses a beam of electrons, which results in better resolving power than the light microscope.
Two kinds of electron microscopes reveal different parts of cells.
Scanning electron microscopes examine cell surfaces.
Transmission electron microscopes (TEM) are useful for internal details of cells.
The electron microscope can
Magnify up to 100,000 times
Distinguish between objects 0.2 nanometers apart
10 m 1 m 10 cm 1 cm 1 mm 100 mm 10 mm Human height Chicken egg Frog eggs Length of some nerve and muscle cells Unaided eye Light microscope Plant and animal cells Most bacteria Nucleus Mitochondrion 1 mm 100 nm 10 nm 1 nm 0.1 nm Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms Electron microscope Figure 4.3
The Two Major Categories of Cells
The countless cells on earth fall into two categories:
Prokaryotic cells — Bacteria and Archaea
Eukaryotic cells — plants, fungi, and animals
All cells have several basic features.
They are all bound by a thin plasma membrane .
All cells have DNA and ribosomes , tiny structures that build proteins.
Prokaryotic and eukaryotic cells have important differences.
Prokaryotic cells are older than eukaryotic cells.
Prokaryotes appeared about 3.5 billion years ago.
Eukaryotes appeared about 2.1 billion years ago.
Are smaller than eukaryotic cells
Lack internal structures surrounded by membranes
Lack a nucleus
Have a rigid cell wall
Only eukaryotic cells have organelles , membrane-bound structures that perform specific functions.
The most important organelle is the nucleus , which houses most of a eukaryotic cell’s DNA.
The lipids belong to a special category called phospholipids .
Phospholipids form a two-layered membrane, the phospholipid bilayer .
Animation: Tight Junctions Animation: Gap Junctions Animation: Desmosomes
(a) Phospholipid bilayer of membrane (b) Fluid mosaic model of membrane Outside of cell Outside of cell Hydrophilic head Hydrophobic tail Hydrophilic region of protein Hydrophilic head Hydrophobic tail Hydrophobic regions of protein Phospholipid bilayer Phospholipid Proteins Cytoplasm (inside of cell) Cytoplasm (inside of cell) Figure 4.6
(a) Phospholipid bilayer of membrane Outside of cell Hydrophilic head Hydrophobic tail Phospholipid Cytoplasm (inside of cell) Figure 4.6a
(b) Fluid mosaic model of membrane Outside of cell Hydrophilic region of protein Hydrophilic head Hydrophobic tail Hydrophobic regions of protein Phospholipid bilayer Proteins Cytoplasm (inside of cell) Figure 4.6b
Most membranes have specific proteins embedded in the phospholipid bilayer.
These proteins help regulate traffic across the membrane and perform other functions.
The plasma membrane is a fluid mosaic:
Fluid because molecules can move freely past one another
A mosaic because of the diversity of proteins in the membrane
The Process of Science: What Makes a Superbug?
Observation : Bacteria use a protein called PSM to disable human immune cells by forming holes in the plasma membrane.
Question : Does PSM play a role in MRSA infections?
Hypothesis : MRSA bacteria lacking the ability to produce PSM would be less deadly than normal MRSA strains.
Experiment : Researchers infected
Seven mice with normal MRSA
Eight mice with MRSA that does not produce PSM
All seven mice infected with normal MRSA died.
Five of the eight mice infected with MRSA that does not produce PSM survived.
MRSA strains appear to use the membrane-destroying PSM protein, but
Factors other than PSM protein contributed to the death of mice
The endoplasmic reticulum (ER) is one of the main manufacturing facilities in a cell.
Produces an enormous variety of molecules
Is composed of smooth and rough ER
Nuclear envelope Smooth ER Rough ER Ribosomes Ribosomes TEM Figure 4.13
Nuclear envelope Smooth ER Rough ER Ribosomes Figure 4.13a
Ribosomes TEM Rough ER Smooth ER Figure 4.13b
The “rough” in the rough ER is due to ribosomes that stud the outside of the ER membrane.
These ribosomes produce membrane proteins and secretory proteins.
After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles .
Proteins are often modified in the ER. Secretory proteins depart in transport vesicles. Vesicles bud off from the ER. A ribosome links amino acids into a polypeptide. Ribosome Transport vesicle Polypeptide Protein Rough ER Figure 4.14
The smooth ER
Lacks surface ribosomes
Produces lipids, including steroids
Helps liver cells detoxify circulating drugs
The Golgi Apparatus
The Golgi apparatus
Works in partnership with the ER
Receives, refines, stores, and distributes chemical products of the cell
“ Receiving” side of Golgi apparatus New vesicle forming Transport vesicle from rough ER “ Receiving” side of Golgi apparatus New vesicle forming Transport vesicle from the Golgi Plasma membrane “ Shipping” side of Golgi apparatus Colorized SEM Figure 4.15
Transport vesicle from rough ER “ Receiving” side of Golgi apparatus New vesicle forming Transport vesicle from the Golgi Plasma membrane “ Shipping” side of Golgi apparatus Figure 4.15a
“ Receiving” side of Golgi apparatus New vesicle forming Colorized SEM Figure 4.15b
A lysosome is a sac of digestive enzymes found in animal cells.
Enzymes in a lysosome can break down large molecules such as
Lysosomes have several types of digestive functions.
Many cells engulf nutrients in tiny cytoplasmic sacs called food vacuoles .
These food vacuoles fuse with lysosomes, exposing food to enzymes to digest the food.
Small molecules from digestion leave the lysosome and nourish the cell.
Animation: Lysosome Formation
Plasma membrane Digestive enzymes Lysosome Digestion Food vacuole Lysosome Digestion (a) Lysosome digesting food (b) Lysosome breaking down the molecules of damaged organelles Vesicle containing damaged organelle Vesicle containing two damaged organelles Organelle fragment Organelle fragment TEM Figure 4.16
Vacuole filling with water Vacuole contracting (a) Contractile vacuole in Paramecium (b) Central vacuole in a plant cell Central vacuole Colorized TEM LM LM Figure 4.17
Figure 4.17a Vacuole filling with water Vacuole contracting (a) Contractile vacuole in Paramecium TEM TEM
(b) Central vacuole in a plant cell Central vacuole Colorized TEM Figure 4.17b
To review, the endomembrane system interconnects the
Blast Animation : Vesicle Transport Along Microtubules Video: Chlamydomonas
Golgi apparatus Transport vesicle Plasma membrane Secretory protein New vesicle forming Transport vesicle from the Golgi Vacuoles store some cell products. Lysosomes carrying digestive enzymes can fuse with other vesicles. Transport vesicles carry enzymes and other proteins from the rough ER to the Golgi for processing. Some products are secreted from the cell. Golgi apparatus Rough ER Vacuole Lysosome Transport vesicle TEM Figure 4.18
Golgi apparatus Transport vesicle Plasma membrane Secretory protein Vacuoles store some cell products. Lysosomes carrying digestive enzymes can fuse with other vesicles. Transport vesicles carry enzymes and other proteins from the rough ER to the Golgi for processing. Some products are secreted from the cell. Rough ER Vacuole Lysosome Transport vesicle Figure 4.18a
New vesicle forming Transport vesicle from the Golgi Golgi apparatus TEM Figure 4.18b
CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION
Cells require a constant energy supply to perform the work of life.
Prokaryotic Cells Eukaryotic Cells • Smaller • Simpler • Most do not have organelles • Found in bacteria and archaea • Larger • More complex • Have organelles • Found in protists, plants, fungi, animals CATEGORIES OF CELLS Figure 4.UN12
Outside of cell Cytoplasm (inside of cell) Protein Phospholipid Hydrophilic Hydrophilic Hydrophobic Figure 4.UN13
Light energy Chloroplast Mitochondrion Chemical energy (food) ATP PHOTOSYNTHESIS CELLULAR RESPIRATION Figure 4.UN14