Cell and MicrobiologyLecture 1

Aim – to look at what makes a ‘cell’Learning outcomesAfter attending lectures, participating in discussions, using

the handouts provided and reading general textbooks, you will have an understanding of:

• Cell theory • Basic requirements of a cell• The common features of cells• Endosymbiotic theory• The formation of internal membranes

MOLECULES MACROMOLECULES

CELLULAR COMPONENTS

CELLS

PROKARYOTES EUKARYOTES

BACTERIA ARCHAEA SINGLE-CELLED

ATOMS

MULTICELLULARPROTISTA

Eg Amoeba Complexity

Robert Hooke 1665

A little history of the discovery and definition of cells

Cork ‘cellulae’

Microscope - ~ 1670s

Antoine van Leeuwenhoek 1632 - 1723

http://www.nature.com/nature/journal/v521/n7553/full/521423a.html

CELL THEORYSchleiden and Schwann (1839)• All living things are made of cells• Cells are the basic building blocks of

life• All cells arise from pre-existing cells

ThenLouis Pasteur (1859)Proved that spontaneous generation could not occur

A CELL

A self-replicating object- something that can make accurate copies of itself

The lowest level of structure capable of performing all the activities of life.

Prokaryotic cell

Nucleic acid (nucleoid)

Cytoplasm

Ribosomes

Cytoplasmic membrane

Cell wall (peptidoglycan)

Cell Sizes

Bacteria (average) 1-10 µm

Eukaryotes (average) 10 – 100 µm

Marine Algae (Acetabularia) 5 cm long

Volume to cell surface ratio – a problem with increasing size

Surface area = 6 x2

Volume = x3

x

If x = 1 µmSurface area = 6 µm2

Volume = 1 µm3

SA/V = 6

If x = 2 µmSurface area = 24 µm2

Volume = 8 µm3

SA/V = 3

If x = 3 µmSurface area = 54 µm2

Volume = 27 µm3

SA/V = 2

0 1 2 3 4 5 6 7 8 9 100.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Length of side of cube

Surf

ace

Are

a/Vo

lum

e

As the size increases the surface area/volume decreases – what is the consequence to the cell?

What can we see?

0.1nm

1cm

10nm

0.1mm

1μm

atoms

proteins

smallest bacteria

most bacteria

most plant &animal cells

frog egg

Electronmicroscope

mitochondria

ribosomes

nucleus

Lightmicroscope

% of total cell weight

Number of types of each molecule

Water 70 1Inorganic ions 1 20Sugars and precursors 1 250Amino acids and precursors 0.4 100

Nucleotides and precursors 0.4 100Fatty acids and precursors 1 50Other small molecules 0.2 ~300Macromolecules (proteins, nucleic acids and polysaccharides

26 ~3000

Approximate chemical composition of a bacterial cell

Timescale of Life

• >3.5 billion years ago

• Prokaryotes

Campbell & Reece, 2005

• Loss of cell wall• Evolution of cytoskeleton• Evolution of mitotic spindle and centromeres• Acquisition of internal membranes• Acquisition of a nuclear envelope• Acquisition of organelles• Acquisition of digestive vesicles

Evolution of eukaryotic cells

Endosymbiotic theory-the evolution of mitochondria/chloroplasts

Mitochondrion

Evidence for endosymbiosis

• Mitochondrion has a double membrane• Mitochondria contain a DNA molecule• Mitochondrial ribosomes have a similar structure to

prokaryotic ribosomes (70S; different to eukaryotes)• Mitochondria divide by binary fission• DNA sequence similar to proteobacteria• Chloroplasts ≡ cyanobacteria• See Lynn Margulis article

Evolution of internal membranes

Endoplasmic reticulum

An early cell

The plasma/cytoplasmic membrane might invaginate

Endoplasmic reticulum

Nuclear membrane

Eventually forming

Endoplasmic reticulum

Ribosome

Intermediate filaments

Nucleoplasm Chromatin (DNA + protein)

Nucleolus

Nuclear pore

Nuclear lamina (protein)

Inner nuclear membrane

Outer nuclear membrane

The nucleus

Introns and the origin of nucleus–cytosol compartmentalizationWilliam Martin and Eugene V. KooninNature 440, 41-45(2 March 2006)

Two different prokaryotic cells may have become united

Now cells have nuclear membrane and mitochondria

Self Study• Clarify keywords / concepts discussed in lecture using any basic biology textbook, eg

Bolsover et al.

• Web sites:– Online biology primer: link from StudyNet– Basic tutorial + test: prokaryotes, eukaryotes, viruses

http://www.biology.arizona.edu/cell_bio/tutorials/pev/main.html– Cells Alive: http://www.cellsalive.com/

• University of California Museum of Paleontology & the National Center for Science Education. From soup to cells – the origin of life http://evolution.berkeley.edu/evolibrary/article/0_0_0/origsoflife_01

• StudyNet resources and activities