Transcript Basic Cell Biology

Bioinformatics Module
Supplementary Lecture 1
Cell biology
Introduction to lecture 1
• Introduction to cellular and multicellular
biology:
– Our current understanding of “Life (living
organisms)”
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Formation of “life”
Overview of a cell: e.g. nucleus/chromosomes
Two major cell classifications
Major cellular stages: cell division: normal cells and
reproductive cells , change in type and death
• Development process in mulit-cellualar organisms
Formation of Life
• Origins of life:
– Formation of first organic molecules; e.g. DNA
(deoxyribonucleic acid).
– Formation of first unicellular organisms; bacteria,
amoeba…
– Formation of multi-cellular organisms. (animals,
plants…)
– Evolution of organisms to ensure both their
adaptable and stability to the environment (Look up
the different environments in which life is know to
exist)
The Prokaryotic Cell
• Viruses:
– contain only DNA surrounded by a protein coat
– require a cell (host) to reproduce
• Prokaryotes (bacteria ):
– contain no defined “nucleus” : the “chromosomal” nuclear
material floating is within the cytoplasm,
– There is also circular DNA referred to as a plasmid.
– These cells are smaller and less complex that the
eukaryotic cell (refer to animal cell).
– Much more numerous and existed before eukaryotic cells.
– Due to smaller size… their generation time is much faster
Cell classifications
• Archaea
– A unicellular organism similar in appearance (morphology) to bacteria.
– A mix between prokaryotic and eukaryotic cells
– Have no nucleus but similar “transcription/translation” to eukaryotic
cells
– Can survive in unusual harsh conditions: e.g. hot springs, salt lakes.
• Eukaryotic cells:
– Can be unicellular (ameobia) or multicellular (homo sapiens: “wise
man”)
– Have a nucleus containing nuclear material: DNA
– Unlike prokaryotic and archaea, whose DNA is circular, the DNA is
linear.
– Exist in the form of a compacted DNA strands called chromosomes.
– Includes fungi , plants and animals…
Prokaryotic cell
The Eukaryotic cell
Components (basic fnts)
• Nucleus:
– Nucleus contains nuclear material (“genes”) stores as
long strands of DNA molecules in the form of
chromosomes.
– The nuclear material (nucleus) is surrounded by a
semi-permeable membrane (shield)
– In the homo sapiens ( human) nucleus there are 23
pairs of chromosomes including sex determinant
chromosomes: the X and the Y chromosome. One of
the pairs is from the father and the other from the
mother.
• The nucleolus contains the RNA (where
transcription occurs)
The Chromosomes of a Human genome:
The image shows the 23 pairs (including X / Y). This is the chromosome set of
a male. A female would have 2 Xs and no Y ; ref [1] chapter 1
Other important Cell components
• Ribosome: They protein producing factories of cells.
They can exits either free in the cytoplasm or
attached to the nuclear membrane.
• Cell Membrane/nuclear membrane semipermeable and protects cell from “harsh” external
environment but does allow certain “chemicals” like
glucose, and proteins to pass into cell.
• Mitochondria:
– the energy producing organelle for the cell.
– They also contain there own set of DNA and are inherited
“exclusively” from the female. So can be used to track the female
linage of a species; e.g. all females descend from
“mitochondrial” eve. [the y chromosome tracts the male linage].
– Have a higher mutation rate and so are good to help determine
evolutionary trees
Cell states
• In Multi-cellular organisms a cell can exist in a number of
“states”; where each state has a different purpose.
– Meiosis converts cell into a reproductive cell: produces to
daughter cells which contains half the amount of DNA
– Mitosis which duplicates the cell with the same amount of DNA
– Differentiation: converts a cell into a different cell type (e.g. of
cell types are: neuron, liver cell, skin cell….)
– Quiescence: a quite “rest” state
– Cell death (suicide) or programmed cell death
• A combination of the states transform the conceived cell (a
single cell (sperm combined with egg) into a fully formed
organism.
The Cells states: Mitosis and Meiosis
Cross-over
Mitosis normal (somatic) cell division produces 2 identical daughter cells.
Meiosis cell division to produce sexual reproductive cells: it produce 4 cells which
contain have half the amount of DNA chromosomes. Moreover parts of the
chromosome pairs “cross over” increasing genetic variability.
Meiosis v Mitosis
• Mitosis normal (somatic) cell division
produces 2 identical daughter cells.
• Meiosis cell division to produce sexual
reproductive cells: it produce 4 cells which
contain have half the amount of DNA
chromosomes. Moreover parts of the
chromosome pairs “cross over” increasing
genetic variability.
Other Cell states
• Cellular differentiation:
– similar to cell division but rather than producing two identical diploid
somatic cells it produces 2 different types of diploid somatic cells :
– It is the basis of multi-cellular organism development. [without such a
process we would just be a clump of the “same” cell type
– Is the reason that stem cells can be used to “produce” different types
of organs
• Quiescent state:
– where the cell is performing its expected activity : e.g. detoxification
by liver cells; transmission of neural signals by neurons (often referred
to as the Go state in mitosis) [fig2.5 p23[1])
• Cell death [programmed] (apoptosis):
– after several mitotic cycles or through significant damage a gene
product causes apoptosis and a mutant form is associated with cancer
(p. 26 [1])
Steps in Organism development
• Sexual fertilization: is the fusion of the 2
gametes to form the zygote:
• Cellular differentiation: Essential the
progenitor or Stem cell, via signalling
molecules…, divide into different cell types
and from there into different tissue types.
• Quiescence / mitosis when fully differentiated
cell.
• Meiosis occurs at puberty
• Cell death via cell damage/numerous mitosis
Cell types
• A human has about 300 distinct cell types.
• A cell types essentially is its genetic profile: the
set of genes that are “on” and that are “off”
• A different profile means a different cell type.
• A precursor cell type (stem cell) can changes its
genetic profile [normally by interaction with
external elements]. While a mature cell type only
changes its profile when it becomes malignant or
carcinogenic.
• The “earlier” the precursor (e.g. stem cell) the
more cell types it can form.
References
• [1]: klug, W.S. et al “essential of genetics” 7th
or 7th ed. Pearson education