Cell and Molecular Biology

Cell and Molecular Biology
Reviewer

CELL BIOLOGY

  • Study of cell structure and function as well as the general properties shared by all cells.

  • Revolves around the concept that the cell is the basic unit of life.

  • The field started in the 1830s through the works of Matthias Schleiden and Theodore Schwann.

History of Cell Biology

1595: Zacharias Janssen - 1st Compound  Microscope

1655: Robert Hooke - “cellula”

1674: Anton van Leeuwenhoek - animalcules and bacteria

1833: Robert Brown - nucleus

1838: Theodore Schwann and Matthias Schleiden

1858: Rudolf Virchow - omnis cellula e cellula

1857: Rudolf Albert von Kolliker - described a powerhouse of the cell.

1879: Walther Flemming - chromosome behavior during mitosis

1883: Chromosome Theory of Heredity

1890: Richard Altman - Bioblast

1898: Camilo Golgi - Golgi apparatus
Carl Benda - Renamed bioblast to mitochondria

1939: Siemens - 1st commercial transmission electron microscope (TEM)

1965: Cambridge - 1st commercial scanning electron microscope (SEM)

1981: Transgenic mice and fruit flies
Mouse embryonic SCL established

1998: Mice cloned from somatic cells

1999: Hamilton and Baulcombe - siRNA

CELL BIOLOGY

George Palade

  • Father of Modern Cell Biology

  • First to use electron microscopy in the study of cells

  • Discovered ribosome and the action of secretory proteins

  • 1974 Nobel Prize in Physiology and Medicine (along with Albert Claude and Christian de Duve)

MOLECULAR BIOLOGY

  • Study of biology at a molecular level

  • “Bottom-up” approach

  • Overlaps with genetics and biochemistry

  • Deals primarily with the processes of the central dogma and how the biomolecules involved in these processes are regulated.

  • Started in between the 1930s - 1940s; shot up in the 1950s - 1960s.

History of Molecular Biology

1928: Frederick Griffith - Transforming Principle

1929: Phoebus Levene - identified the sugar, four nitrogenous bases and phosphate chain in a DNA

1938: Warren Weaver coined the name Molecular Biology

1940: George Beadle and Edward Tatum - defined relationship between genes and proteins

1944: Oswald Avery, Colin MacLeod, and Maclyn McCarty - DNA is the transforming principle

1952: Alfred Hershey and Martha Chase - the genetic material is made up of DNA
Rosalind Franklin - X-ray diffraction of DNA

1953: James Watson and Francis Crick - double helical structure of DNA

1957: Francis Crick - Central Dogma

1958: Matthew Meselson and Franklin Stahl - semi-conservative DNA replication

1961: Francois Jacob and Jacques Monod - mRNA

1961: Genetic Code
Francis Crick, Sydney Brenner, Lesley Barnett, and R.J. Watts-Tobin - triplet codon
Marshall Nirenberg and Heinrich Matthaei - cracked 54 codes out of the 64 codons.

Study of Cell Biology

What is Cell Biology?

  • Reductionist’s approach: cut a living entity down to the smallest possible unit that is still alive and study that unit’s property.

  • Cells are the smallest unit of all living organisms.

  • Further breaking leads to non living elements.

  • Life originates with the formation of cells.


Introduction to Cell Biology

  • Living and nonliving; classification of living system; Evolution

  • Unit of life: The Cell Theory, Basic Properties of Cell; prokaryotes and eukaryotes

  • Morphologic and structural features of cells; relationship of pro- and eukaryotes in evolutionary terms.

  • Viruses - their origin, mode of propagation, prions

What is the difference between living and non-living matter?

All life contains products made of the element carbon. Elemental composition includes: 60% H, 25% O, 12% C, 5% N, some P, S, and traces of Na, K, Ca, Fe, Cl, Mg, Mn, etc. 

Do non living substances grow?

Of course, crystals grow, but not in the same sense as living matter. Cells are the units of living systems but their constituents are all non-living.

First attempt to study biology is taxonomical classification into kingdoms:

Monerans: bacterium or prokaryotes (origin: 3.5 billion years ago).

Protistans: single-celled eukaryotes, but larger than bacteria

Fungi: Multicellular eukaryotes

Plants: Multicellular photosynthetic eukaryotes

Animals: Multicellular eukaryotes


Charles Darwin’s Theory of Natural Selection

  • Random variability in a population of individuals varying in forms, function, and behavior (DIVERSITY).

  • Some forms are heritable traits (UNITY) helping to adapt and survive, the basis of unity in diversity.

  • Natural selection means survival of the fittest; best adapted retaining TRAITS that permit survival and reproductive success.

  • Populations constantly evolve as some traits are acquired or lost (MUTATION) in response to environmental changes that support propagation.


The Cell Theory of Schwann, Schleiden, and Virchow

  1. All living organisms are composed of cells (one or more).

  2. The cells constitute the living unit of all organisms.

  3. All cells arise from pre-existing cells (now we say, mitosis, meiosis).


UNITY IN DIVERSITY

All cells:
Share fundamental properties conserved through evolution.

DNA is the genetic material (surrounded by membranes in eukaryotes but not in prokaryotes)

Generate energy and utilize nonliving matter from the environment.

Proliferate, divide, and show motility.

Unicellular vs. Multicellular Organisms

Human body has over 200 different cells doing specialized functions: epithelial cells, cells of the connective tissues, blood, muscle, and nervous system. All produced as a result of differentiation.

Plants have fewer cells: Ground tissues containing Parenchyma, collenchyma, and sclerenchyma cells, dermal cells, and vascular cells.

Protozoans and monerans are unicellular.


Fundamentally Different Cell Classes

Prokaryotes (before nucleus): two types: Archaeans & Eubacteria. 3.5 billion years. Largest bacteria are cyanobacteria and the smallest is mycoplasma.

Eukaryotes (true nucleus): From Eukaryotes (1.8 billion years) to multicellularity. Ex. plants, animals, fungus. Of course, RBC in a eukaryotic system does not have a nucleus or organelles either.


Types of Prokaryotic Cells: Two Domains

  • A. Domain Archaea (oldest), ex: Methanogens, Halophiles, Acidophiles, and Thermophiles.

  • B. Domain Bacteria: smallest known cells - mycoplasma; eubacteria (true bacteria) and cyanobacteria (blue-green algae).

  • Both are single-cells (1-2 μm) with a single chromosome containing DNA and polyamines. They reproduce asexually by binary fission.


Types of Eukaryotes

  • A. Unicellular Eukaryotes (larger than prokaryotes - about 10X)

  • B. Multicellular Eukaryotes

    • Characteristics: differentiation into specialized cells different from mother cells.

    • Numbers and arrangements of organelles in relation to function

    • Common features

  • Distinct nucleus, organelles, motility, division



Bacteria vs. Mitochondria and Chloroplasts

  1. Similar size as bacteria

  2. Reproduction by division into two like bacteria

  3. Own DNA that encodes some of their components in the same manner

  4. Divide each time the organelle divides

  5. Use their organelles’ inner structure and ribosome to transcribe and translate.

  6. Have similar ribosome and rRNA as in bacteria

Both organelles have a distinct genetic system separate from the nuclear genome of the cells.


Functional Features of Cells

  1. Acquire and utilize energy (photosynthesis or its product e.g. glucose)

  2. Utilize energy for maintenance (metabolism) & reproduction.

  3. Reproduce: binary fission, conjugation, mitosis, meiosis.

  4. Respond to stimuli (positively/negatively: receptor)

  5. Able to move (locomotion), transport, adhere to form multicellular units, influence neighbors

  6. Self-regulating


Viruses and Prions: Living or Non-living?

  • Viruses are nonliving pathogens that become live in hosts (obligate parasites)

  • A virion is a virus outside the host cell

  • Genetic material in viruses: DNA or RNA. Capsid proteins surround genetic material.

  • Infect either by lytic or intergratic mechanisms.

  • Most likely, viruses evolved after the hosts are fragments of host chromosomes.

  • Viroids are pathogens having only small naked RNA.

  • Prions are abnormal chaperone proteins that cause neurological disorders.


Food for thought

  • Cells are the living units of life, but not their components - true or false?

  • We can isolate and study the properties of cellular components in vitro. They seem to function as predicted from cells’ behavior. Why are they not considered living?


Methodologies for studying cell biology

  • Morphology: tools & techniques - microscopy-light, phase-contrast, fluorescence, video, confocal, EM: transmission and scanning.

  • Biochemical: homogenization & centrifugation, radioisotope tracer techniques, immunoassays, enzyme assay, SDS-PAGE, autoradiography, etc.

  • Molecular: DNA, RNA, Plasmids, PCR