The Cell: A Very Short Introduction – Terence Allen and Graham Cowling

Thoughts: Decent! Lots of relevant information, presented well. No complaints!

The chapter summaries below were made from memory upon finishing each chapter. They may contain misrememberings or other inaccuracies!

Allen, Terence and Graham Cowling. 2011. The Cell: A Very Short Introduction. Oxford UP.

Chapter 1: The nature of cells

• For a call to be a cell, it must
  • Be separated from its environment, as by a cell membrane
  • Exchange material and energy with the outside world, to be able to grow and divide
  • Be able to reproduce, making copies of itself
• A major division in cells is between prokaryotes and eukaryotes. “Karyote” means “nut”, “eu-“ means “true”, and “pro-“ means “before”; this naming reflects the more complex organization of cellular components into organelles in eukaryotes, whereas in prokaryotes, cell contents all float around together within the cell membrane, mixing freely
• Some key organelles in eukaryotes:
  • Cell membrane, always a lipid bilayer
  • Nucleus, which separates dna from the rest of the cell
  • Ribosomes, which read rna sequences and produce proteins
  • Endoplasmic reticulum, many-folded extensions of the outer layer of the nuclear membrane. Rough ER has ribosomes embedded in its membrane, while smooth ER doesn’t, and is implicated in digesting lipids
    • RER may assemble proteins into larger complexes, but it may actually be the Golgi apparatus that does this
  • mitochondria, which metabolize sugars and produce ATP, used by other organelles as an energy source
  • Chloroplasts, which photosynthesize, using sunlight to turn water and carbon dioxide into sugars plus oxygen gas

Chapter 2: The structure of cells

• Organelles are separated from each other by membranes, each membrane is a lipid bilayer. There exist a variety of transmembrane proteins that help control the flow of substances across membranes. Membranes allow certain chemical reactions to be kept separate, so they do not interfere with each other.
• Mitochondria and chloroplasts have double membranes, as well as their own DNA, reflecting their history as free-living organisms in the past. All other organelles, with single membranes, are known as vaccines or vesicles (the distinction between the two terms is not really discussed)
• RER is associated with the creation and assembly of proteins. SER is associated with the creation and metabolism of lipids
• Golgi bodies transport proteins to where they are needed in the cell, and may also have a quality-control role
• Cell structure and shape can change quite quickly, and is controlled by three structures - microtubules, intermediate filaments, and microfilaments - which comprise the cytoskeleton
  • Microtubules form a relatively rigid structure, and also sometimes aid in transportation of proteins etc. from place to place within the cell.
  • the two types of filaments are more associated with tension and contraction
  • The tubules and filaments work together in tensegrity to give structure to the cell - the authors draw an analogy with the mast and rigging of a sailboat
  • It is likely that microtubule-like structures also exist in the nucleus to control its shape
• Cytoplasm is everything within the cell’s outer membrane that’s not the nucleus. The fluid with dissolved substances that surrounds the organelles is called cytosol

Chapter 3: The nucleus

• A layer of proteins called the nuclear lamina coats the inner membrane of the nucleus. It seems to have a structural function, as well as helping with certain chemical processes
• The nucleus has many pores, protein complexes that control the movement of substances between the nucleus and the cytoplasm
• Eukaryotes have a lot of DNA; in order to fit into the nucleus, the DNA strand is grouped (into chromosomes) and folded and wound in various ways to keep it compact while still keeping it accessible for transcription

Chapter 4: The life of cells

• mitosis, the process of cell division, involves the replication of DNA, the transport if necessary organelles to opposite ends of the cell, and the pinching off of the cell membrane until two daughter cells are created. Episodes of mitosis are separated by interphase, during which RNA is used to create new proteins in preparation for subsequent rounds of mitosis
• The details of which bits of DNA are transcribed to RNA and this expressed in proteins is not fully understood
• Meiosis involves one round of DNA replication but two rounds of cell division, leaving each daughter cell with half as much DNA (i.e., the cells are haploid)
• There’s some discussion of how cells move around bodies and/or their environment
• Programmed cell death in multicellular organisms seems to be controlled in part by the mitochondria, and in many cases causes the cell to break apart into useful components that can be taken up by neighbouring cells

Chapter 5: What cells can do

• A bunch of different differentiated cell types in animals are discussed, including
  • Skin cells
  • Cells on the surface of the small intestine
  • Red blood cells
  • various cells of the immune system
  • Cells involved in sensing light, gravity
  • Nerve cells
• The processes of cell differentiation are briefly touched upon, with mention of the mapping of all the cells of C. elegans
• Some discussion of how genetic mutations occur

Chapter 6: Stem cells

• Whereas the cells that perform specific functions in tissues are differentiated, stem cells can turn into many different cell types
• Embryonic stem cells can turn into all different cell types in the body. Thus, they are said to be totipotent
• Some stem cells can turn into a wide, but more limited, range of cell types. These stem cells are called pluripotent. Stem cells that can turn into only a few closely related cell types are called oligopotent, whereas stem cells that can divide but can only differentiate into a single type of cell are called unipotent
• All plant stem cells are totipotent; this is why many plants can be propagated by cuttings
• It would be bad for an organism if any of their stem cells were to multiply in an uncontrolled way; stem cells thus are usually kept in niches, little pockets of cells dedicated to ensuring the right environment surrounds these stem cells such that they multiply in a controlled manner.
• genetic mutations in stem cells can lead to cancer; there are cellular mechanisms to notice when a cell has had a mutation; these mechanisms lead either to cell senescence (cessation of division) or apoptosis in the mutant cell

Chapter 7: Cellular therapy

• Cellular therapies include blood transfusions and stem cell transplants. One application of stem cell transplants is when a patient’s immune system has been destroyed by chemotherapy
• There has been lots of quackery surrounding cellular therapies in the past, leading to scepticism among the general public
• It is hoped that cellular therapies can be devised to regrow or fortify specific organs, e.g., improving cardiac function by an injection of cells that can turn into cardiac muscle

Chapter 8: The future of cell research

• Many of the pathways forward will involve stepping back from reductionist approaches in favour of “systems biology”
• Some directions for future research mentioned: creating synthetic life, investigating the mechanisms of aging, …