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Lecture 3 The Prokaryotic Cells and Origin of

Eukaryotic Cells: Hereditary Features and Replication

Cork cell walls

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 Physico-Mathematicall Experimentall Learning'.

This group included Wren himself, Robert Boyle, John Wilkins, Sir Robert Moray, and William, Viscount Brouncker.

The Royal Society - London

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

Robert Hooke: (1635-1703)

www.ucmp.berkeley.edu/history/hooke.html

Among other accomplishments:

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. http://www.octavo.com/collection/hkemic.html

First described cells

Nullius In Verba

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.

How, then, do we explain the occurrence of living things?

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?

The Cell Theory Implies:

• Cells are the fundamental unit of life (the basic unit of organization).

• All organisms are composed of cells.

•  All cells come from preexisting cells.

Common Characteristics Of Cells • Cells must obtain and process energy

• 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 circular DNA

Prokaryotes have no nucleus or intracellular organelles

Refer to Sadava et al., 2011, Fig. 5.4, p. 82.

Prokaryotes have been around at least 3.5 BY

Eukaryotic Cell: Yeast, Freeze Fracture Image

Nucleus and intracelluar organelles. FEI Image Gallery

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

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

Eukaryotes have been around 1.6-2.1 BY - maybe longer?

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

Eukaryote: Plant Cell Anatomy Red boxes = differences between plant and animal cells

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

Note: No centrioles!

Mitochondrion: “Powerhouse of the Cell” Because mitochondria have circular DNA like bacteria, an endosymbiotic origin is hypothesized.

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

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

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

Chloroplasts are derived from endosymbiotic bacteria

contains its own circular DNA

are found in some protists, plants (and now, some animals!)

are surrounded by a double membrane

contain photo-pigments in circular sacs called thalakoids

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

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

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A Typical Textbook Explanation of the Endosymbiotic Origin of Organelles

Mader, 2001

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

Membrane infolding increases surface area

Origin of an Organelle’s Double Membrane: Plastids and Mitochondria

This process is called: Endosymbiosis

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

..a bacterium that will eventually become either a mitochondrion or chloroplast

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

How did we learn about them?

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

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

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:

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

Watson and Crick (1953) - DNA

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

F. Crick 1916-2004

M. Wilkins, 1916-2004 J. Watson,

1928 -

Nobel Prize, awarded in 1962 with Wilkins and without Franklin

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Other Important Folks Hiding in the Background

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.

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.

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

Published by AAAS P. Leder Science 327, 972 (2010) (2010)

Marshall Warren Nirenberg (1927–2010) Nirenberg presented this work in August 1961 at the International Congress of Bio-chemistry 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.

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

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

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

Purves et al, 2001 genus name = Escherichia; species name = coli

Eukaryote: Cell Division

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

Two division processes: nuclear and organelles

In plant cells: chloroplasts divide

Hey - Wait a Minute - What About The Endosymbiotic Organelles? Division?

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

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

Both of these organelles have double membranes - so how does fission work?

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

Endoplasmic reticulum-dependent mitochondrial fission.

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

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.

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

A-E: Views using different types of microscopy

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

Eukaryotic Cell Division:

A Ballet of the Chromosomes

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

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

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!

Campbell et al., 1999

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

3 Functions of Cell Division

REPRODUCTION Many organisms reproduce by cell division, where a cell

divides into two cells forming two individuals.

DEVELOPMENT Division of embryonic cells for

growth and differentiation

MAINTENANCE Replacing old, worn-out cells

Major Features of Reproduction 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

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!

The Cell Cycle

Refer to Sadava et al, 2011, Fig. 11.3, p. 213.

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

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

Nuclear division occurs during mitosis

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

Cells that do not divide are usually arrested in the G1 phase

Centrioles also duplicate during S phase

Mitosis - Karyokinesis Refer to Sadava et al, 2011, Fig.11.11, p. 218-9. Mitosis - Karyokinesis and Cytokinesis

Animal and Plant 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

a) Binary fission - bacteria

b) Unicellular algae - dinoflagellates

c) Unicellular algae - diatoms Fungi

d) Most eukaryotes Campbell et al., 1999

Meiosis: Reduction Division

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).

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

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

This happens in two divisions

Raven and Johnson, 1999

Overview of Meiosis 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.

4 nuclei

------------------------------------------------------------

I

II

Beck et al., 1991

Meiosis I

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

Synapsis: A Most Important Event Synaptonemal Complex during Prophase I

Raven and Johnson, 1999 Solomon et al, 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 )

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Sequence of Events in Prophase I

Raven and Johnson, 1999

Crossing Over

Meiosis II

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

Cell Cycles and DNA Copies Per Cell

Beck et al., 1991

Beck et al., 1991

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.

Comparison Between Mitosis and Meiosis

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

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

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Animal Life Cycles: Gametic

Beck et al., 1991

Campbell et al, 1999

Plant Life Cycles: Sporic

Beck et al., 1991

Sporophyte generation: 2n, diploid, shown in blue

Gametophyte generation: n, haploid, shown in yellow

Fungi Life Cycles: Zygotic

Beck et al., 1991

Raven and Johnson, 1999

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.

Asexual Reproduction

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

Hydra

Bacteria, E. coli

Sexual Reproduction •  Sexual reproduction (sex) is the joining

(fertilization or syngamy) of two haploid cells, called germ cells or gametes; one from each parent.

•  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).

Sexual Reproduction

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

•  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? 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

Disadvantages Of Sexual Reproduction

•  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.