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…
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  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) 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 )
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 : klug, W.S. et al “essential of genetics” 7 th or 7 th ed. Pearson education