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Lecture 2:
Tree of Life and Evolution
How is All Life Connected?
What Does It Mean to Say That Something Is Alive?
• All living organisms share five fundamental characteristics
– Energy
• All organisms acquire and use energy.
– Cells
• All organisms are made up of membrane-bound cells.
– Information
• All organisms process hereditary information encoded in genes as well as information
from the environment.
– Replication
• All organisms are capable of reproduction.
– Evolution
• Populations of organisms are continually evolving.
All Living Things are Composed of Cells
• Cells come from other cells.
• Genome within a cell – carries the information
to make more cells
• All parts of the cell (including genome) are
replicated during cell division
• Cells need to acquire and utilize energy to grow,
divide, communicate
Unity of Cells
• A cell is a highly organized
compartment bounded by a
plasma membrane that contains
concentrated chemicals in an
aqueous solution.
• The amazing diversity of life are
all made from cells that have a
fundamentally similar chemistry
and operate according to the
same basic principles.
Diversity of Cells
• However, cells are not all alike, in
fact they can be widely different.
• Cells come in a variety of shapes
and sizes and vary no less widely
in their functions.
SIMILAR BUT DIFFERENT……..
Grouping Cells
• According to morphology, there are two broad groupings of
life:
1. Prokaryotes, which lack a membrane-bound nucleus
2. Eukaryotes, which have such a nucleus
• According to phylogeny, there are three domains:
1. Bacteria
prokaryotic
2. Archaea
3. Eukarya – eukaryotic
Microscopy was used to determine the morphology of cells - establishing that there
were two major types of cells:
• Prokaryotic (prokaryotes) – lack a membrane enclosed nucleus.
• Eukaryotic (eukaryotes) – have a membrane enclosed nucleus.
Grouping of organisms
according to their
relationship to each other
(phylogeny) showed that
there are actually three
divisions:
• Bacteria
• Archaea
• Eukaryote
Grouping Cells
• According to morphology, there are two broad groupings of
life:
1. Prokaryotes, which lack a membrane-bound nucleus
2. Eukaryotes, which have such a nucleus
• According to phylogeny, there are three domains:
1. Bacteria
2. Archaea
3. Eukarya – eukaryotic
prokaryotic
Prokaryotes Are the Most Diverse of Cells
• Contain essentially no organelles
or nucleus.
• Typically spherical, rod-like, or
corkscrew shaped and small.
• Often have a protective cell wall
surrounding the plasma
membrane.
• Most live as single celled
organisms but some can join
together to form clumps and
clusters.
Prokaryotic Cells – Structural Overview
•
•
•
•
All prokaryotes lack a membrane-bound nucleus.
Recent advances in microscopy reveal complexity in prokaryotic structure.
Archaeal cell structure is relatively poorly understood.
Bacterial cells vary greatly in size and shape, but most bacteria contain
several structural similarities:
–
–
–
–
Plasma membrane
A single chromosome
Ribosomes, which synthesize proteins
Stiff cell wall
• Prokaryotic chromosomes are
found in a localized area of the
cell called the nucleoid.
• Represents 20% of the cell’s
volume
• Genetic material is not
separated by a membrane
• They also carry genetic
information in plasmids which
are extra chromosomal pieces
of DNA.
• Often, these plasmids contain
genes that confer antibiotic
resistance to the organism.
Prokaryotic Cells – Internal Structure
• In addition to the nucleoid chromosome and plasmids, other structures are contained
within the cytoplasm:
– All prokaryotic cells contain ribosomes, consisting of RNA molecules and protein, for protein
synthesis.
– Some prokaryotes have membrane-enclosed compartments that qualify as organelles (“little
organs”).
– An organelle is a membrane-bound compartment inside the cell that contains enzymes or
structures specialized for a particular function.
• Most prokaryotes have a cell wall.
– Bacterial and archaeal cell walls are a tough, fibrous layer that surrounds the plasma membrane.
Eukaryotes and Prokaryotes Compared
• Four key differences between eukaryotic and prokaryotic cells
have been identified:
Eukaryotic Cells
• Are generally bigger and more
elaborate than bacteria and archae.
• Some live as single celled organisms
like yeast, but all more complex
multicellular organisms including
plants, animals and fungi are made of
eukaryotic cells.
• Possession of a nucleus also goes with
possession of a variety of other
organelles that perform specialized
functions.
Eukaryotic Cells
• The relatively large size of the eukaryotic cell makes it difficult
for molecules to diffuse across the entire cell.
– This problem is partially solved by breaking up the large cell volume
into several smaller membrane-bound organelles.
Note size
comparison
Eukaryotic Cells
Processing of genetic information
Protein export
ribosome
Energy production
Protein synthesis
Protein turn-over (degradation)
Genome and Genomic Changes
CENTRAL DOGMA
Genome and Genomic Changes
Genome = DNA sequence of entire organism.
-
Changes in the DNA Sequence (mutations) occur due to:
•
•
Replication errors
DNA damage and repair
-
changes in the genome will be passed on to progeny
-
Some changes in the genome (mutations) result in changes in
cell shape, structure, function
-
Beneficial traits are retained and detrimental traits discarded
Thus heredity, the inheritance of differences, is an intrinsic
property of life.
Genomic Changes over Billions of Years =
Evolution = New Species Emerge
Competition between living species for resources
More competitive species prevails
Genomic changes can help or hurt survival chances (FITNESS)
Changes that are suitable for survival are retained by selection
and passed along to next generation
• If this happens over long periods of time, then enough changes
accumulate to generate new species (a new species cannot
generte viable offspring with other species).
•
•
•
•
ALL SPECIES HAVE A COMMON ANCESTOR
Node –
How is comparison done/phylogenetic tree built?
PHYLOGENETIC TREE
ALL SPECIES HAVE A COMMON ANCESTOR
1.
2.
3.
4.
GGATTCGATCCCCGTC
GGTTTCGATCCCCGTC
GCTTTAAATCCCGCCG
GATATTAATGGCGAGT
Bacteria
3 1 2
Archaea
PHYLOGENETIC TREE
4
Eukarya
How did Eukaryotic cells arise from
Prokaryotic cells?
Eukaryotic cells
Nucleus
1 µm
Prokaryotic cells
0.1 µm
ALL SPECIES HAVE A COMMON ANCESTOR
Figure 1-29 Essential Cell Biology (© Garland Science 2010)
Mitochondria (cellular organelle) was a prokaryote
Figure 1-19 Essential Cell Biology (© Garland Science 2010)
Chloroplast (cellular organelle) was a prokaryote
Figure 1-21 Essential Cell Biology (© Garland Science 2010)
Summary
Key Points:
• Cell theory – all cells come from other cells.
• Cell structure – common features of all cells.
• Prokaryotic versus eukaryotic cells – differences.
• Function of key organelles (nucleus, endoplasmic reticulum, ribosomes, lysosome).
• Natural selection.
• Origin of diversity.
• Selection for fitness.
• How to determine evolutionary tree from DNA sequence data.
Can you:
• Draw and label a prokaryotic and a eukaryotic cell.
• Explain one possible theory for the origin of eukaryotic cells, and how you might test that theory.
• Describe how new species evolve.
• Determine an evolutionary tree from sequence data.