Basic cell and Molecular Biology
The Origin of Life
Characteristics of life
1. Organization – Living organisms consist of cells, the basic unit of life (unicell or multicell)
2. Metabolism – Conversion of non-living materials to organic compounds, the building blocks of
cells. This produces energy for conversion to complex compounds and cell functions (such as cell
movement)
3. Growth – Increase of materials and organelles, a prerequisite for cell division.
4. Cell division – Increase of the number of cells.
5. Reproduction – Production of new individuals. Asexual from one parent, or sexual from at least
two parents. Cell division and reproduction inevitably leads to evolution.
6. Adaptation - Adjustment of organism to environment. It is a fundamental evolutionary process,
and the result of genetic background, organization of the organism and external conditions.
7. Reaction on external signals – Can be very different, from contraction when touched, movement
away from predators, or orientation of leaf to sunlight.
Why is life in our Solar System?
▪ Because we have the optimal conditions
➢ The Earth is old enough to sustain
➢ The Earth is far enough from the centre of the milky way
➢ Temperature is optimal for complex molecules
➢ The Earth is at a perfect distance away from the sun
▪ If the star (sun) is bigger in an universal, the distance has also to be bigger
➢ The size of the planet Earth is good (it only keeps heavy gasses in the atmosphere)
▪ If a planet is too small, the gravitation is too small → NO ATMOSPHERE so no
gasses will sustain (for example the moon)
▪ If a planet is too big, it will keep all gasses in atmosphere
So… Life depends on:
- How far away from the centre of the universe
- How old is the planet
- How far away from a star (for instance the sun)
- How big is the planet
! A habitable planet is a planet that fulfil all the conditions that are required for life, but it doesn’t
mean that there is life.
Biology is full of low probabilities that occur in a very large population
➢ A mutation that leads to bacteria resistance is very low, but the population of bacteria is very
large, so a mutation occurs often.
➢ Very low chance to get cancer, but a
human body contains 1015 cells, so that
makes the chance bigger.
The same goes for the question if there is any
other life in the universe →
,HOW LIFE STARTED
Conditions were…
▪ Very hot and acid
▪ Hydrothermal springs with FeS (catalyst) that can
take and donate elektrons
• This causes chemistry: so the first nucleotides and
organic components were bound
• RNA and peptides also act like chemistry
• DNA is made… in the holes membranes started to
be made and after a long time, the first living cells
are produced
… 0.5 billion years after the first cell had been made, there
was still no oxygen.
- In cyanobacteria (green bacteria) photosynthesis started!
• They have pigment that divide a photon and water into protons, elektrons and as a
byproduct oxygen.
• H2O + e- + photon→ 2H+ + 2O2
• The protons are used for the ATP synthesis
• The photosynthesis of plants evolutes from the photosynthesis of cyanobacteria
So now… there is an atmosphere with oxygen → mitochondria appeared → eukaryote cells
So first, step 1: mitochondria:
I. They evolved from prokaryote cells by endosymbiose (the same happened to plastids in
plants)
! that is why mitochondria and plastids have their own DNA, they originated from
prokaryote cells.
II. Eukaryote cells evolved, with mitochondria in the plasm!
But… it took a really long time to go from unicellular to multicellular.. why?
➢ Instead of going apart after cell division, cells stay together
➢ You need structure in multicellular cells, otherwise the cells in the middle won’t get
blood and they starve (because only the cells on the outside get food resources)
- Filamentous shape
- Hollow shape
So… you need a lot of movement of cells in order to let every cell survive.
➢ Individual cells aggregate
▪ They will grow as an individual, but when the environment isn’t good anymore, they
will come together.
EXAMPLE: social amoeba: they form a spore on a worm, when this worm gets eaten
by a bird, the spore comes in the stomach (very nutrient) and there the individual
cells can eat.
Advantages of unicellular (small size)
▪ Large surface for better uptake nutrients
▪ Very fast growth
▪ Small in the sea → they sink very slowly → stay at the surface where there is light and life
Especially for cyanobacteria in favour, so they can have photosynthesis at the surface
▪ Less attractive to predators
Advantages of multicellular (big size)
▪ Large mobility (you move fast from predators)
▪ ‘graze’ a larger volume of surface
▪ Store more nutrients
, ▪ Differentiation into different cell types for specialization (brain, blood etc)
▪ Number of genes is much bigger → more differentiation
0.5 billion years ago… CAMBRIAN EXPLOSION
➢ Lots of species we know nowadays, started to live from then. So lots of new genes,
complexity
- Unicellular organisms possesses a high degree of complexity for one cell
- Only, the target for eukaryotes is higher, since they have organelles.
! the more complex the genes are, the more complex the organism is. So it is not that we
have so much MORE genes than for example fruit flies, our genes are more COMPLEX.
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Introduction to Cell Biology
Common to all cells:
• storage of information in DNA
• replication, transcription, translation (DNA → RNA → protein) →
• each protein encoded by specific gene
• proteins are catalysts
Different among cells:
• source of energy in plants and animals (all energy on earth comes
(in)directly from the sun)
• number of genes (500 to 31,000).
THREE KINGDOMS OF LIFE
▪ Bacteria
▪ Eukaryotes
▪ Archaea (Archaea is more similar to eukaryotes than bacteria is, because eukaryotes are
originated from archaea!)
! Plastids originated from prokaryotes, eukaryotes from archaea
Organel: all the things surrounded by membranes (a ribosome doesn’t have a membrane, so
that is not an organel)
Prokaryotes are further not interested for cell biology, since it doesn’t contain organelles
EUKARYOTES
Components of the eukaryotic cell:
• Genetic information in the nucleus
• Cell wall (only in plants and fungi)
• Cell membrane
• Cytoplasm (cell content) – Cytosol
– Organelles
SOME ORGANELLES ELABORATED….
▪ Ribosomes: they translate mRNA to proteins.
Mostly attached to the ER
▪ ER: transport for proteins in the cell and the
place where ribosomes synthesis proteins
▪ Golgi apparatus: sorting system, there they decide whether a protein goes in the cell
▪ Mitochondria: energy organelles from the cell! The only organelles originated from a
bacteria, all others are from archaea → especially a difference in membrane
▪ Lysosomes: break down all the waste from a cell
, ▪ Peroxisome are capable of making H2O2 by binding oxygen to water. This is necessary for the
synthesis of phospholipids, or breaking down alcohol in the liver. These enzymes are mainly
in plants or in the kidney.
At a cellular level all organisms are similar; so for several studies you can use model organisms
▪ For study on organelles people often use yeast; these are simple eukaryotic cells, small
genome, strong genetics and cheap to grow.
Strong genetics means that that the effect of mutation and deletion of nearly all genes
have been investigated.
▪ For study on metabolism, transcription translation, people often use: E. Coli Bacterium;
these are simple bacteria with a small genome, cheap to grow and protein purification
▪ For study on multicellular development, people often use worms. Complete network of
neurons is known (Pavlov reaction can be tested on this organisms), even as the exact
lineage of fertilized eggs.
▪ For study on cell movement, people use a protozoa; is an informal term for single-celled
eukaryotes
▪ For study on plant examination
▪ For study on early egg development, people often use frogs. They have big eggs, outside
the mother and cell division without growth.
▪ For study on genetics, people often use fruit flies. They are cheap, lot is known about
their genes and biochemistry and it is ethically not a big issue.
▪ For study on vertebrate development (gewervelde ontwikkeling), people often use the
zebrafish, since this organism is translucent (there is no skin, so you can see all the
organs)
▪ For study on disease and behaviour, people often use mice. They are relatively cheap,
similar to human. People also use human cells for their studies, away from the body.
They often use human cells since their data sets are large.
! Research to cell cycles is often done with single cells.
Biotechnology is the production of larger amounts of specific products, done in bacteria,
yeast or animal cells, but is very inconvenient in, for example, a worm.
Mammalian- = zoogdier-
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Microscopy
Three different kinds of microscopy:
Light microscopy
• Specimen (het monster) is stained with dyes (kleurstoffen) such that different cells in a tissue
or different organelles in a cell will selectively absorb light with different wavelength
• Important to see contrasts
Stains used in classical histology:
➢ Haematoxylin: binds to DNA and makes this nuclei purple
➢ Eosin: makes cytosol red
Drawbacks of a light microscopy:
➢ All specimen are dead, otherwise you won’t see much contrast when it is alive… so they
invented the Phase Contrast Microscope: Phase shifts due to density in specimen, so they
can use living cells
Fluorescence microscopy
• A photon (light particle) has energy; photons with more energy have shorter wavelength.
