1. Chapter 3: Cells

2. A. Cells are the units of life
All organisms consist of cells
Cells are the smallest unit of life that can function independently
1660 – Robert Hooke first person to see outlines of cells (in cork)
1673 – Antony van Leeuwenhoek improved lenses and drew observations
1830’s – Robert Brown identified the nucleus

3. Cell theory (est. ~ 1839) 2 Main tenets (ideas) 3rd Main tenet
All organisms are made of one or more cells
The Cell is the fundamental unit of life
Ideas developed by Schleiden and Schwann
3rd Main tenet
All cells come from preexisting cells
Contradicts the idea of spontaneous generation
This idea was added in 1855 by Virchow

4. Microscopes are used to study cells
Light microscopes
Compound light microscope - glass lenses focus visible light, 0.2 µm resolution
Confocal microscope – enhanced resolution using white or laser light

5. Electron microscopes – greater magnification and better resolution but specimen must be dead
Transmission Electron Microscope (TEM) – uses beam of electrons focused by magnetic field
Scanning Electron Microscope (SEM) – scans beam of electrons over metal coated specimen
Scanning probe microscope – probe moves over surface giving exquisite detail

6. Features common to all cells
Genetic information, DNA
Proteins carry out cell’s work
RNA participates in producing proteins
Ribosomes manufacture proteins
Cytoplasm
Cell membrane
Complex cells also have organelles – compartments for specialized functions

7. Surface area to volume All cells are small Require large surface area
Surface area limitation on size of cell
May be avoided through
Flattened shape
Fingerlike extensions
Specialized organelles to improve efficiency (explains animal and plant cells being larger than bacterial cells)
Vacuoles in plant cells, etc.

9. B. Cell membrane (separating the cell from the external environment and So much more!)
Composition of the cell membrane:
Made of lipids and proteins
Phospholipid
Glycerol and a phosphate group form head, 2 fatty acids form the tails
Head is hydrophilic, tails are hydrophobic
Together, phospholipids spontaneously form phospholipid bilayer, like a defense move for the tails!
Fluid mosaic – proteins and phospholipids free to move laterally within the bilayer

11. Proteins in the cell membrane:
Transport proteins • Adhesion proteins
Enzymes • Receptor proteins
Recognition proteins

12. Functions of the Cell Membrane:
Signal transduction
A cell receives an external “message” and converts it into an internal signal
Receptor proteins bind to stimulus molecule, first messenger
Triggers chemical reaction whose product is second messenger
Second messenger provokes cell’s response – activating particular genes or enzymes

13. C. Different cell types
Prokaryote – simplest and most ancient forms of life whose cells lack organelles
Eukaryotes – cells contain organelles
3 domains of life
Bacteria – prokaryote
Archaea – prokaryote
Eukarya – eukaryote

14. C. Different cell types Domain Bacteria Domain Archaea
Lack membrane bound nuclei
1 circular DNA molecule found in nucleoid
Rigid cell wall in most – provides protection and shape
Some have capsule and flagella
Domain Archaea
Resemble bacteria superficially only
Phospholipids, cell walls, and flagella unique
Some are “extremophiles”
Burning Question: What IS the smallest certifiable living organism? See p. 59!

15. C. Different cell types Domain Eukarya Huge diversity
Larger than prokaryotes
Internal membranes create internal compartments called organelles that are specialized for specific tasks in the cell
Endosymbiosis theory – maybe ancient organism engulfed another organism and rather than eating it, it stayed as a partner (supported by mitochondria and chloroplasts)
2 Major groups of eukaryotic cells based on structure and functions: animal & plant cells

17. D. Eukaryotic organelles
Organelles carry out coordinated interactions to meet the needs of an organism: Ex: Milk

18. D. Eukaryotic organelles
Nucleus
Contains DNA – information specifying “recipe” for every protein a cell can make
Nuclear pores are holes in the nuclear envelope surrounding the nucleus, lets RNA and other substances through
Nucleolus - dark core in middle of nucleus; assembles ribosomes
Cytoplasm
Watery-jelloish soup
of dissolved substances,
organelles and cytoskeleton

19. D. Eukaryotic organelles
Ribsomes
Site of protein synthesis
Found lose in cytoplasm or attached to ER
Endoplasmic Reticulum
Originates at nuclear membrane and winds throughout the cell
2 types:
Rough ER – studded with ribosomes making proteins destined for secretion (like milk)
Proteins folded and modified
Smooth ER – synthesizes lipids, detoxifies drugs and poisons
Lipids and proteins made by ER exit in vesicles

20. D. Eukaryotic organelles
Golgi apparatus
Processing center for vesicle contents
Proteins complete intricate folding and become functional
Some proteins will become membrane surface proteins
Others packaged for secretion from the cell

21. D. Eukaryotic organelles
Lysosomes
Contain enzymes that lyse substrates
Specific pH inside lysosome prevents enzymes from damaging cell
Vacuoles
Found in plants
Enzymes degrade and recycle materials
Important in growth and maintaining rigidity
Peroxisomes
Dispose of toxic substances
Some reactions produce hydrogen peroxide (H2O2)
Enzyme produces harmless water molecules

23. D. Eukaryotic organelles
Chloroplasts
Found in plant cells
Site of photosynthesis
Uses energy from sunlight to produce glucose
Occurs specifically in thylakoids
Endosymbiosis theory support – has its own DNA

24. D. Eukaryotic organelles
Mitochondria
Cellular respiration extracts energy from food
Cristae – internal folds; contain enzymes for cellular respiration
Also contains its own DNA
Always inherited from mother
in humans

25. D. Eukaryotic organelles
Cytoskeleton
3 major components distinguished by protein type, diameter, and aggregation
Microtubules
Microfilaments
Intermediate filaments

26. D. Eukaryotic organelles
Microtubule
Made of Tubulin protein
Forms very small hollow tubes
Can change length of tube by adding or removing tubulin molecules
“Trackway” within cell for many cellular movements
Cilia – short, many
Flagella – long, few

27. D. Eukaryotic organelles
Microfilaments
Actin
Long, very thin rods
Machinery to move
Intermediate filaments
(10 nm) diameter is intermediate
Made of different proteins in different specialized cell types
Internal scaffold for cell

28. E. Cells adhere and communicate
Cell walls
Surround cell membrane of nearly all bacteria, archaea, fungi, algae, and plants
Not just a barrier
Built of different components
Plasmodesmata connect adjacent cells
(like little bridges between cells)

29. Animal cell junctions Animal cells lack cell walls
Secrete complex extracellular matrix
Intercellular junctions
Tight junctions form impermeable barriers
Anchoring or adhering junctions connect cells by linking intermediate filaments
Gap junctions link cytoplasm of adjacent cells