Cell Theory Flashcards
What does it take to make a cell?
- Information
- Chemistry
- Compartments
The Cell Theory
Schleiden and Schwann postulated in 1839 two of the three tenets of the Cell Theory:
1. All living organisms are composed of one or more cells.
2. The cell is the most basic unit of life.
In 1855, Rudolf Virchow added the third tenet to Cell Theory:
3. All cells arise only from pre-existing cells.
Basic Properties of Cells
- Highly COMPLEX and ORGANIZED.
- Activity controlled by a GENETIC program.
- Can REPRODUCE—make copies of themselves.
- Assimilate and utilize ENERGY.
- Carry out many CHEMICAL reactions (enzymes).
- Engage in MECHANICAL activities
- Respond to STIMULI
- Capable of SELF-REGULATION
- They EVOLVE
Prokaryotes
The only form of life on Earth for millions of years until more complicated eukaryotic cells came into being through the process of evolution.
Typical Features of a Prokaryotic Cell
- Single-cell organism
- Size: 1-10μm
- No nucleus or organelles
- Ribosomes are present but small•Reproduce asexually
- Genetic material found in nucleoid (means nucleus-like)—this is not a true chromosome but rater DNA arranged in a circular fashion (plasmid)
Eukaryotes
Protozoa (single-celled eukaryotes), fungi, plants, and animals. Found in multicellular organisms, but can be unicellular as well (protozoa)
Typical Features of a Eukaryotic Cell
- Size: typically 10-100μm
- Nucleus and organelles
- Ribosomes are large
- Genetic material found in a nuclear compartment and arranged as chromosomes
Animal vs. Plant Eukaryotic Cells
Plant Cells: -cell walls -vacuoles -chloroplasts -plasmodesmata Animal Cells: -lysosomes -microvilli
Viruses
Viruses are not cells. Viruses are macromolecular package that can function and reproduce only within living cells. Outside of cells, viruses exist as an inanimate particle called VIRION.
Virion
A VIRION is made of:
•Small amount DNA (DNA virus) or RNA (RNA virus) that encodes a few hundreds of genes.
•A protein capsule called CAPSID.
Families and Subtypes of Viruses
Different classification systems exists. A popular system is the Baltimore classification, which categorizes viruses based on type of genome (RNA/DNA) and their method of replication.
HIV is an example of retrovirus, which is part of the RNA family and can insert a copy of its genome into the DNA of a host cell.
Hepatitis B is a member of the hepadnavirus family (DNA type). Affects human liver and cause serious infections.
Ebola virus is part of the filoviruses family—encode their genome in the form of single-stranded negative-sense RNA.
Adenoviruses are a group of viruses that can cause respiratory illnesses (e.g. bronchitis or pneumonia) or conjunctivitis (an infection in the eye).
A bacteriophage is a virus that infects and replicates within bacteria and archaea.
Structure of Bacteriophage
- Capsid head
- Nucleic acid (DNA) in head
- Collar
- Sheath
- Base plate
- Spikes
- Tail fibre
Host Range
Narrow = human cold/flu virus affects epithelial cells of the respiratory system Wide = rabies affects humans, dogs, foxes, bats, raccoons, etc.
Types of Viral Infection
Once inside a cell, the virus hijacks cellular machinery to synthesize nucleic acids (DNA/RNA) and proteins. These parts are then assembled to make new virus particles to infect other cells.
LYTIC = Production of virus particles ruptures (and kills) cell (e.g. influenza).
NON-LYTIC/INTEGRATIVE/LYSOGENIC = Viral DNA is inserted in the host genome = PROVIRUS. Cell can survive, often with impaired function (e.g HIV)
Functions of Biological Membranes
1) Define cell boundary
2) Define enclose compartments
3) Control movement of material into and out of the cell
4) Allow response to external stimuli
5) Enable interactions between cells
6) Provide scaffold for biochemical activities
