The Royal Society London

Cork cell walls

Lecture 3 The Prokaryotic Cells and Origin of Eukaryotic Cells: Hereditary Features and Replication

Robert Hooke: (1635-1703)

First described cells

The Royal Society, officially founded 11/28/1660, when a group of 12 met at Gresham College after a lecture by Christopher Wren, then the Gresham Professor of Astronomy, and decided to found 'a Colledge for the Promoting of PhysicoMathematicall Experimentall Learning'. This group included Wren himself, Robert Boyle, John Wilkins, Sir Robert Moray, and William, Viscount Brouncker.

http://royalsociety.org/about-us/history/

Cells and the Principle of Biogenesis Recall from last lecture: the work of Redi, Spallanzani and Pasteur debunking the idea of spontaneous generation.

Cell Theory By 1838, Matthias Schleiden (Germany) and the Theodor Schwann (Belgium) over dinner, described the similarities of cell structure of plants and animals, respectively.

Nullius In Verba

How, then, do we explain the occurrence of living things? Among other accomplishments:

www.ucmp.berkeley.edu/history/hooke.html http://www.octavo.com/collection/hkemic.html

Hooke invented the universal joint; the iris diaphragm; an early prototype of the respirator; invented the anchor escapement and the balance spring, which made more accurate clocks possible; served as Chief Surveyor and helped rebuild London after the Great Fire of 1666; worked out the correct theory of combustion; assisted Robert Boyle in working out the physics of gases; worked out the physics of elastic materials; invented or improved meteorological instruments such as the barometer, anemometer, and hygrometer; and so on.

The Cell Theory Implies:

Principle of Biogenesis Ludwig Karl Virchow (1821-1902), in 1855 stated: “Omnis cellula e cellula” = “All cells from cells” Which means that living things arise only from living things.

How did that happen?

Common Characteristics Of Cells • Cells must obtain and process energy

• Cells are the fundamental unit of life (the basic unit of organization). • All organisms are composed of cells. •  All cells come from preexisting cells.

• Cells convert genetic information encoded in DNA into protein Plus one new point: • Cells choreograph numerous biochemical processes both in time and space within the cell: some reactions are incompatible with others.

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Generalized Prokaryotic Cell Prokaryotes have no nucleus or intracellular organelles

Eukaryotic Cell: Yeast, Freeze Fracture Image

Prokaryotes have circular DNA

Prokaryotes have been around at least 3.5 BY Refer to Sadava et al., 2011, Fig. 5.4, p. 82.

Eukaryote: Animal Cell Anatomy Important: Membrane folding and invaginations increase the surface area-to-volume ratio

Eukaryotes have been around 1.6-2.1 BY maybe longer?

Nucleus and intracelluar organelles.

Eukaryote: Plant Cell Anatomy Red boxes = differences between plant and animal cells Note: No centrioles!

Double nuclear envelope: Refer to Sadava et al., 2011, Fig. 5.8, p. 88.

Refer to Sadava et al., 2011, Fig. 5.7, p. 86-7.

Mitochondrion: “Powerhouse of the Cell”

Aerobic metabolism: contains the enzymes of the citric acid cycle, respiratory chain, and oxidative phosphorylation.

FEI Image Gallery

Because mitochondria have circular DNA like bacteria, an endosymbiotic origin is hypothesized.

Refer to Sadava et al., 2011, Fig. 5.7, p. 86-7.

Chloroplasts contain circular DNA and therefore, an endosymbiotic prokaryote origin.

Chloroplasts are derived from endosymbiotic bacteria contains its own circular DNA are found in some protists, plants (and now, some animals!)

Mitochondria replicate (multiply) independently from the division of the cell

are surrounded by a double membrane

Refer to Sadava et al., 2011, Fig. 5.12, p. 92.

Refer to Sadava et al., 2011, Fig. 5.13, p. 93.

contain photopigments in circular sacs called thalakoids

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A Typical Textbook Explanation of the Endosymbiotic Origin of Organelles

Origin of an Organelle’s Double Membrane: Plastids and Mitochondria This process is called: Endosymbiosis ..a bacterium that will eventually become either a mitochondrion or chloroplast

Membrane infolding increases surface area

Mader, 2001 See Sadava et al., 2011, Fig. 27.3, p. 565 for a variant of this diagram. See Sadava et al., 2011, Fig. 5.26, p. 102

See Sadava et al., 2011, Section 27.1, p. 560-66 for this story.

Informational Molecules Some kinds of molecules can contain information by the arrangements of their subunits.

What kind of molecules store and transmit hereditary information from one generation to the next?

It was thought that those molecules must be complex enough to contain the vast amounts of information.

How did we learn about them?

This idea initially lead researchers to examine proteins as the chemical basis for hereditary information. Beck et al., 1991

You should know the following regarding DNA and it’s discovery:

Watson and Crick (1953) - DNA Nobel Prize, awarded in 1962 with Wilkins and without Franklin

1.  The failed hypothesis that proteins were the hereditary material. 2.  Griffith’s experiment using two strains of Streptococcus pneumoniae 3.  Avery, MacLeod and McCarty (1944) - DNA was Griffith’s “transforming” factor 4.  The Hershey-Chase experiment (1952) - DNA was confirmed as the molecule of hereditary 5.  Erwin Chargaff et al. (1950) - the A=T and C=G ratios 6.  Franklin and Wilkins conducted crystallography and X-ray diffraction studies on DNA - (early 1950’s) 7.  Watson and Crick’s (1953) - DNA and it’s replication explained

F. Crick 1916-2004

J. Watson, 1928 -

M. Wilkins, 1916-2004

See Sadava et al., 2011, Ch. 13, Fig. 13.8, p. 274.

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Other Important Folks Hiding in the Background

How Did They Crack the Genetic Code? George Gamow, Russian physicist, established the “RNA Tie Club” in 1954 as a joint effort to crack the code. There were 20 members, one for each amino acid, and four honorary members, one for each nucleotide.

Odile Crick, an artist, created the original sketch of the double helix of DNA.

Franklin’s X-ray photography provided the critical evidence of the molecule’s famed double helix. Her death from ovarian cancer at 37 precluded her sharing the Nobel Prize.

Marshall Warren Nirenberg (1927–2010)

But breakthrough was by: Marshall Nirenberg (a non-member of the club) (with J. Heinrich Matthaei, a post-doc, at the N.I.H.) was the first to make RNA with only U nucleotides that coded for phenylalanine; then showed that CCC = proline

The Universal Genetic Code: The Chemical Language of All Living Things

Nirenberg presented this work in August 1961 at the International Congress of Biochemistry in Moscow. Coming from an “unknown,” Nirenberg received little attention but Francis Crick, co-discoverer of the structure of DNA and a leading figure in molecular biology, organized a repeat performance in a larger hall. P. Leder Science 327, 972 (2010) (2010) Published by AAAS

Refer to Sadava et al., 2011, Fig. 14.6, p. 299.

- and Shared the Nobel Prize, 1968 Robert W. Holley, Cornell University (transfer RNA) (d. 2/11/93) Har Gobind Khorana, Univ. of Wisconsin (protein synthesis) (d. 12/9/2011) Marshall W. Nirenberg, USA National Institutes of Health (triplet code with J.H. Matthaei) (d. 1/15/2010)

..what happened to J. H. Matthaei’s share of the prize???

Prokaryotic Cell Division: Fission

Refer to Sadava et al, 2011, Fig. 11.2, p. 212.

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Circular Bacterial Chromosome

Eukaryote: Cell Division Two division processes: nuclear and organelles

These long looping fibers of DNA from a cell of the bacterium Escherichia coli are all part of one continuous circular chromosome.

genus name = Escherichia; species name = coli

Purves et al, 2001

Hey - Wait a Minute - What About The Endosymbiotic Organelles? Division? Both of these organelles have double membranes - so how does fission work?

http://en.wikipedia.org/wiki/ Mitochondrion

http://en.wikipedia.org/wiki/ Chloroplast

Endoplasmic reticulum-dependent mitochondrial fission.

ER-dependent mitochondrial fission. In this model, the major mitochondrial fission protein Drp1 is recruited from cytosolic or mitochondrial spots to ER-mitochondria contacts sites (containing the Drp1-receptor Mff). At sites of interorganellar contact, Drp1 stabilizaton and/or oligomerization into helices might be facilitated by ER tubule– dependent mitochondrial constriction.

A. S. Rambold, J. Lippincott-Schwartz, Science 334:186-187 (14 Oct. 2011)

In plant cells: chloroplasts divide

Refer to Sadava et al., 2011, Fig. 5.7, p. 86-7.

Circular Mitochondrial DNA Mitochondria, the “metabolic powerhouse” of the cell, contain circular DNA because as discussed earlier, arose through the endosymbiosis of a prokaryotic organism. Recall that prokaryotes have circular DNA. Mitochondria divide independently from the mitotic nuclear division and cytokinesis. Beck et al., 1991

How Chloroplasts Divide Double membrane chloroplasts are derived from the endosymbiosis of a ancient cyanobacterium - thus they divide by fission. The process of division by a ring of proteins (plastid dividing ring) , which is a bundle of PDR1-mediated polyglucan filaments. Yoshida et al., Chloroplasts Divide by Contraction of a Bundle of Nanofilaments Consisting of Polyglucan. Science Vol. 329. no. 5994, pp. 949 - 953 (20 August 2010). DOI: 10.1126/science.1190791

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Eukaryotic Cell Division: A Ballet of the Chromosomes

Dividing Chloroplasts Identification and expression analysis of glycosyltransferase protein PDR1 in C. merolae cells.

Eukaryotes, rather than having a circular chromosome, have their DNA with proteins (chromatin) packaged in two or more units called chromosomes.

A-E: Views using different types of microscopy

Chromosome refers to “stainable nuclear body,” hence the reference to “color” = “chromo.”

Yoshida et al.. Science, Vol. 329. no. 5994, pp. 949 - 953 (20 August 2010)

Mitosis: Creating Identical Cells Remember, mitosis creates an identical copy of a cell or single-celled organism during division. Replication in prokaryotic and eukaryotic cells is very different.

The Result of Cell Division is… … the production of two identical cells where there was one before. To do this, the hereditary material must be duplicated, then packaged into an easily handled form, and then distributed precisely into the two daughter cells. Cells (organisms) are not immortal!

3 Functions of Cell Division

Illustrated is a replicated, and condensed chromosome at a stage called metaphase

Campbell et al., 1999

Major Features of Reproduction DEVELOPMENT Division of embryonic cells for growth and differentiation

Reproduction is the closest thing to a definition of life. Two fundamental principles of reproduction: 1. organisms are not immortal, so reproduction is the essence of continued life 2. principle of heredity, which requires the precise transmission of genetic information

REPRODUCTION Many organisms reproduce by cell division, where a cell divides into two cells forming two individuals.

MAINTENANCE Replacing old, worn-out cells

There are many variations on the timing and process of reproduction, which we will see later.

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Development: The Human Starts As a Zygote (A Fertilized Egg): The average human grows and develops by cell division and cell differentiation into an adult with about 100 trillion (1014) cells. •  To maintain structure and function, the body undertakes about a trillion (1012) cell divisions per day. That is, ten million divisions (107) per second! •  In bone marrow, we produce about 2.3 million (2.3 x 106) new red blood cells per second!

Cells that do not Centrioles also divide are duplicate usually arrested during S phase in the G1 phase

The timing shown is typical of a human cell growing in culture.

Cytokinesis, cell division is distinct from nuclear division and occurs at the end of the M phase

Nuclear division occurs during mitosis Refer to Sadava et al, 2011, Fig. 11.3, p. 213.

Mitosis - Karyokinesis

Refer to Sadava et al, 2011, Fig.11.11, p. 218-9.

Animal and Plant Cytokinesis

The Cell Cycle

Note that mitosis takes about an hour, so only a fraction (1/24th) of cells would be dividing when observing an asynchronous culture.

Mitosis - Karyokinesis and Cytokinesis

Mitosis Timelines (Typical Vertebrate Cell)

Pines, Jonathon and Conly L. Rieder. 2001. Re-staging mitosis: a contemporary view of mitotic progression. Nature Cell Biology Vol 3:E3-E6. http://www.nature.com/ncb/journal/v3/n1/fig_tab/ncb0101_e3_F2.html

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Evolution of Mitosis

Meiosis: Reduction Division

c) Unicellular algae - diatoms Fungi a) Binary fission - bacteria

b) Unicellular algae dinoflagellates

d) Most eukaryotes

Note the chromosome assortment which creates diversity – four kinds of gametes.

This happens in two divisions

Two green chromosomes are from one parent, two blue from the other.

The chromosomes are reduced from the diploid state (2 of each chromosome, one from each parent) to the haploid state (one of each chromosome originating from either parent).

Campbell et al., 1999

Raven and Johnson, 1999

Overview of Meiosis I

-----------------------------------------------------------II

4 nuclei

Meiosis I

Note that Prophase I is shown in five separate steps. This is a significant stage where very important processes are occurring. Note also, that no replication of DNA occurs between the first and second division.

See Sadava et al., 2011, Fig. 11.17, p. 224-5.

Beck et al., 1991

Synapsis: A Most Important Event Synaptonemal Complex during Prophase I

Raven and Johnson, 1999

Five Stages of Meiotic Prophase I First

Condensation

Leptotene (leptos = fine )

Second

Pairing

Zygotene (zygon = yolk,“Y”)

Third

Recombination

Pachytene (pachus = thick )

Fourth

Coiling

Diplotene (diplos = double )

Fifth

Recondensation

Diakinesis (dia =across kinesis = movement )

Solomon et al, 1999

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Sequence of Events in Prophase I

Crossing Over

Raven and Johnson, 1999

Meiosis II Cell Cycles and DNA Copies Per Cell

Beck et al., 1991

See Sadava et al., 2011, Fig. 11.17, p. 224-5.

Comparison Between Mitosis and Meiosis

Number of copies of each chromosome: Diploid is 2C – two copies of each chromosome, one from each parent.

Gametes are haploid, with only one copy of each chromosome. Beck et al., 1991

Timing of Meiosis in Various Life Cycles Gametic Life Cycle = Animals: Adult animals are diploid. Sporic Life Cycle = Plants: Plants show an alternation of generations with both diploid and haploid forms. Zygotic Life Cycle = Fungi: Only the zygote is diploid and undergoes meiosis to form haploid spores.

Beck et al., 1991

Beck et al., 1991

See Sadava et al., 2011, Fig. 11.15, p. 222.

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Animal Life Cycles: Gametic

Plant Life Cycles: Sporic Gametophyte generation: n, haploid, shown in yellow

Beck et al., 1991 Beck et al., 1991

Sporophyte generation: 2n, diploid, shown in blue Campbell et al, 1999

Asexual Reproduction

Fungi Life Cycles: Zygotic Hydra

Beck et al., 1991

Filaments, called hyphae (mycelium), fuse to form a special type of filament called a dikaryon = two nuclei, but they are not joined. Later the nuclei fuse to form a zygote.

Bacteria, E. coli

Raven and Johnson, 1999

Sexual Reproduction

Wouldn’t it be easier to just reproduce asexually? No annoying mates! All of your genes would be passed on! Why not!

Sexual Reproduction

•  Sexual reproduction (sex) is the joining (fertilization or syngamy) of two haploid cells, called germ cells or gametes; one from each parent.

•  Because half of an individual’s genetic information is lost in gamete production, there must be advantages of sexual reproduction.

•  Gametes are distinguished from ordinary body cells (called somatic cells that are diploid, or 2n) because they contain one rather than two of each chromosome (haploid, or n).

•  If asexual reproduction is so simple and efficient, why is it not the universal method of reproduction?

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Why Are There So Many Sexual Species?

Disadvantages Of Sexual Reproduction

ADVANTAGES from the fusion of sperm and egg. • In meiosis there is a reshuffling of genetic material through recombination. The fusion of a set of chromosomes from each of two parents is a very important evolutionary factor. • Sexual reproduction increases genetic variability three ways: 1.  Independent assortment in meiosis 2.  Syngamy of male and female gamete 3.  Crossing-over in prophase I of meiosis

•  Genetic recombination: a major consequence of sexual reproduction is that it breaks up adapted gene complexes. •  Because of meiosis, half of an individual’s genetic information is lost in gamete production. •  Sex has costs: Why produce male offspring which may require care and nurturing, when all they provide is sperm? Why look for mates?

Sexual Reproduction And Evolution Paradoxically, the evolutionary process is both revolutionary and conservative •  Revolutionary in that the pace of evolutionary change is quickened by the process of sexual reproduction, and •  Conservative in that this change may not be favored by selection and is eliminated.

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