Cell Biology
Chapters 21 and 22
I.
Introduction
II.
General Features
III.
Major Organelles
A.
Nucleus
B.
Ribosome
C.
Mitochondria
D.
Chloroplast
IV.
Special Functions
A.
Cell respiration (see text for discussion)
B.
Photosynthesis (see text for discussion)
C.
Membranes
1.
Structure
2.
Function a.
Selective Permeability b.
Osmosis c.
Cell-to-Cell communication
D.
Cell division – Mitosis (see text for discussion)
E.
Meiosis (see text for discussion)
Take Home Messages
1. The cell is to biology what the atom is to chemistry and what the ecosystem is to ecology (hierarchy theory)
2.
Cell size is restricted to an upper limit of 0.00001 m (1 x 10 -5 m) due to the limitations of diffusion in transporting nutrients and elements from the cell’s interior to the environment outside the cell.
3.
Compartmentalization is a key and unique attribute of all cells and is analogous to the compartmentalization of a campus dorm. The key compartments are called organelles and include ribosomes , mitochondria , chloroplasts , endoplasmic reticulum , and Golgi Bodies .
4.
The principles of carbon polymer chemistry and biology underpin the four key classes of compounds that comprise the biochemistry of living systems – nucleic acids , amino acids , carbohydrates and lipids .
5.
The following sequence underpins much of the molecular biology of any cell in any organism:
DNA m-RNA Polypeptide Protein Packaging
(Nucleus)
Transcription
(Nucleus/Ribosome) (Ribosome)
Translation
(Golgi)
6.
Membranes are structurally unique ( lipid bilayer ) and functionally very important in understanding the biology of a cell because they control selective permeability , osmosis , and cell-to-cell communication .
7.
Membranes are a perfect example of an emergent property (in this case in a living system) analogous to the other examples discussed this semester but in the disciplines of chemistry and ecology.

LECTURE NOTES
I.
Introduction
Cell is to biology what the atom is to chemistry and physics… expand on that statement
Cell Theory :
A.
All organisms are composed of cells
B.
Cells are the smallest unit of organization that exhibits all of the major themes that are unique to living systems (e.g., open, emergent properties, diversity and similarity, hierarchy…see themes of life lecture notes)
C.
Cells reproduce so that all cells come from pre-existing cells
II. General Features
A.
Structure
Plasma membrane (cell membrane)
Nucleus
Cytoplasm
B.
Size is correlated with function
Cells are restricted in size to an upper limit of 0.00001 m (10 -5 meters).
This upper limit has a functional basis in that as the volume of a cell increases
(gets bigger and bigger), the distance that molecules have to travel from the cell membrane to the interior of the cell gets proportionately longer. This distance is a critical limiting factor because molecules at the cellular level move via diffusion, which is extremely effective at moving molecules over
 m distances but is essentially of no value at longer distances (it is a good thing that your movement is not limited by diffusion!). Thus, the limiting factor to cell size is distance for diffusion of molecules….anything over 0.00001 m is very not functional.
C.
Cells are compartmentalized
All cells have a very elaborate and organized internal structure, and in reality the cell is like a dorm on campus. There are a series of corridors ( endoplasmic reticulum ) and rooms ( organelles ), and each room has a unique environment and the chemistry of that room differs from the chemistry of other rooms.
Membranes are responsible for this compartmentation and the rooms are organelles (e.g., ribosome, chloroplast, mitochondrion, Golgi body, nucleus, vacuole, etc.)
D. Principles of Polymer Chemistry and Biology
1.
Principle of hierarchy theory and emergent properties

2.
Small molecules joined together to form large molecules (tremendously large molecules)…1,000’s of connected carbon atoms
Term: macromolecule (unique term to biochemistry)
3.
Sequence of units in polymer is genetically determined by DNA
4.
Polymer Principles a.
Any long chain of repeating units is called a polymer (chemistry chapter)…key point is repeating units (train car analogy) b.
In biology, this phenomenon is most common for four classes of compounds that are extremely important in the biochemistry of cells i.
Carbohydrates (sugars) ii.
Proteins (amino acids) iii.
Nucleic acids (nucleotides) iv.
Lipids (fatty acids) c.
In biology, the long linkages among carbon atoms are made via covalent bonds (weak bonds that allow for variety of transformations, including release of energy and ability to be spilt easily e.g., nerve impulse of a ringing of the bell) d.
How do you know it is important
Siblings are simple variations in the “box cars” within macromolecules; other example…colors of flowers, colors of eyes
Principles of Polymers Biochemistry in Living Systems
Polymer/Macromole Unit Covalent Structure/ Function cule Function
Bonding Inherited
Comments
Carbohydrates
Proteins
Nucleic Acids
Lipids
Saccharide
Amino Acid
Nucleotide
Fatty Acid
+ Glycerol yes yes yes yes yes yes yes yes
Storage
Structure
Energy
ATP
Enzyme
Structure/Defense
Inheritance
(Information)
Protein Synthesis
Energy
Membranes
Polypeptides
Translation
DNA
(Double stranded)
RNA
Replication
Transcription
Phospholipds
Proteins
Membrane
Functions

III.
Major Organelles
A.
Nucleus
1.
Key features a. contains most of the genome b.
most conspicuous organelle under the light microscope c.
membrane bound with pores
2. Structure a.
DNA organized into chromosomes b.
Each species has a given and specific number of chromosomes that exist as pairs
3.
Functions a.
Storage/harbor of DNA b.
Duplication of DNA is replication c.
Production of mRNA (transcription) that subsequently is transported to the cytoplasm where it serves as template for synthesis of proteins within the ribosomes
B.
Ribosome
1.
Key features a.
Site where proteins are synthesized b.
Most cells have a myriad of ribosomes since all cells produce proteins
(without ribosomes, no protein synthesis)
2. Function – protein synthesis (see text for more discussion) a. mRNA is produced in nucleus, using DNA as a template d.
mRNA is a single strand of nucleotides (remember that DNA is a double strand in the form of double helix) that has a specific sequence of nucleotides as dictated by DNA (process of producing the mRNA is called transcription ) and is only the length necessary to code for one protein (remember that DNA contains all of the genome whereas the mRNA is only that specific sequence of nucleotides that codes for one protein)
G U C A G U G C C mRNA e.
The assembly of the amino acids in the ribosome is directed by another type of RNA (transfer RNA or tRNA ) which reads the mRNA and inserts/attaches the “correct” amino acid…this process is called translation and it is done with fidelity f.
The result is a string of amino acids that forms a polypeptide and when the entire sequence of polypeptides is finished, the polypeptide selfassembles into a functional protein

g.
All of this process is controlled by the sequence of nucleotidesds in the
DNA h.
This biochemical process is the same for all organisms, is genetically determined and is called the “ genetic code
” (see text)
C.
Mitochondria (see text for more discussion)
1.
Sites of cellular respiration (all cells -plant and animal) posses mitochondria, which are energy conversion organelles
2.
Glycolysis and fermentation that generate ATP (adenosine triphosphate), extracting the energy from carbohydrates, lipids and proteins
3.
1,000’s per cell; in one second, leg muscles uses 10 Million ATP
D.
Chloroplast (see text for more discussion)
1.
In a manner similar to mitochondria, chloroplasts are energy conversion organelles…exception is that chloroplasts are only found in plants
2.
100’s to 1,000’s per cell
3.
Structure is very compartmentalized to capture light energy, strip off electrons and chemically transfer the electron to a sugar molecule for storage
IV.
Special Functions of Cells
A.
Cell respiration
See text for discussion of respiration
B. Photosynthesis
See text for discussion of respiration
C. Membranes
1.
Structure
Basic phospholipid structure as presented ( lipid bilayer )
New wrinkle: protein chunks that float in the lipid bilayer, extending through the lipid bilayer and having part of the protein extending to the exterior and interior of the cell (analogous to ice berg that floats on surface of water)
protein
Lipid Bilayer
2.
Protein serves a variety of functions including (i) transport channel for molecules that can not move through lipid bilayer, (ii) enzyme sites
(remember that enzymes are proteins and some membrane-bound proteins function as enzymes on the cell surface and the bilayer is just the “platform”

upon which the enzyme operates), and (ii) cell-to-cell communication (see later)
3.
Functions of membranes
Membranes are a perfect example of the principle of emergent properties in hierarchical systems (theme of living systems)…the impressive structure and functions of membranes could never be predicted based on knowing that you are simply combining phospholipids and proteins…(expand on this point using example of hydrogen and oxygen) a. Selective Permeability
Simple observation….array of ions that exists inside and outside of a cell are very different so obviously cell regulates the transport of ions across the cell membrane; this process is very selective (some are excluded entirely while others pass through easily)
Because the “permeability” is selective, this function of membranes is called “selective permeability” b. Osmosis
Most cells are 70-90% water and water is an essential medium for most of the cell’s biochemistry
Water is transported across cell membranes in a very specific process called osmosis and it is simply based on the process of diffusion (water diffuses from a region of higher concentration to one of lower concentration)…this is highly regulated though so the volume of water is optimum for cell (too much water would burst the cell membrane) c. Cell-to-Cell Communication
Principle: cells are not isolated units but rather communicate with one another not unlike your communication with your peers…(example of “open system”, one of the themes of living systems)
What are the essential components of cell-to-cell communication
Signal : signals are chemical in nature and are usually proteins (e.g., hormones, neurotransmitters)
Signals are received on the surface of cells by the proteins that are bobbing around like icebergs…this process is called cellular reception and it operates like a “lock and key” so that certain cell proteins can only be receptive to specific signals that “fit” into that protein (diagram this)

Example of why some of the students in class are allergic to molds or pollen…surface proteins have a
“lock” for those protein signals produced by molds or pollen and others in the class doe not have these specific proteins on their cell membranes
Cellular Response : the above signal turns on or turns off a gene that codes for a protein that affects the cell’s biochemistry (for those with allergies, this is manifest as a stuffy/runny nose; same goes for poison ivy…those that are extremely allergic have a specific protein on the cell surface that “fits” the poison ivy “poison” that once bound results in inflammation and itching…others are not responsive simply because their DNA does not code for that surface protein to act as a receptor) d.
Cell Division – Mitosis
See text for discussion e.
Meiosis
See text for discussion of the process that results in the formation of gametes