Bioinformatics Module

Supplementary Lecture 1 Cell biology

Introduction to lecture 1

• Introduction to cellular and multicellular biology:– Our current understanding of “Life (living

organisms)”• 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 semi-permeable 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

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.

Cross-over

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