Download Why is evolution considered the greatest unifying theory in biology

Why is evolution considered the greatest unifying theory in biology?
How can Unity of Biological Processes and Cell Theory be explained in Evolution
What were the objections to Darwin’s theory of Evolution and how has science resolved many of
these questions?
Where did the first cells come from? How do you explain the Cambrian explosion and the sudden
appearance of complex cells and organisms? (Precambrian fossils. Stromatolites of
cyanobacteria). How did Eukaryotes evolve from Prokaryotes (Precambrian fossils.
Stromatolites of cyanobacteria).
Origins of life: Panspermia (infection of spores from another planet/star), Special creation, Evolution
First generalization of biology- evolution through natural selection
Evolution: All living organisms arose in the course of history from earlier, more primitive forms
all organisms are related or share a common ancestor.
2 steps: variability (unique characteristics) and natural selection (over-population,
competition)
Second generalization of biology- all organisms share certain biochemical reactions
All organisms have genetic material that contains development instructions
Organisms have the machinery to carry out instructions: proteins
Third generalisation of biology- all organisms consist of cells. Cell Theory
1. All living matter is composed of cells
2. The chemical reactions of life take place in cells
3. All cells arise from other cells
4. Cells contain hereditary information and this information is passed from parent cell to
daughter cells
What structural features characterise the prokaryotes and where are they found?
No nucleus, single circular stranded DNA, no internal compartmentalisation, capsule, pili, simple
rotary motor flagellum made of flagellin
Why are prokaryotes considered highly evolved?
What features of the Archea place them in their own super kingdom?
Why are the cyanbacteria so significant to the evolution of life on earth?
Because of photosynthetic cyanobacteria oxygen was produced and the ozone layer was formed
allowing the growth of life
Prokaryotes have spontaneous mutations which occur at high frequencies and explain their
biochemical diversity. They are highly adaptable and so are present in an enormous range of
environments. Eukaryotes take generations to evolve, bacteria do it much faster. Therefore
prokaryotes are more diverse than eukaryotes. They are morphologically simple but
biochemically complex.
Prokaryotic simple cell division, binary fission. DNA is attached to plasma membrane in a specific
way. Genome is replicated, segregated by growth of cell membrane, cytokinesis with ftsZ
protein with identical daughter cells. 20 minutes taken, much faster than complex eukaryotic
division.
Two super kingdoms in prokaryotes: discovery arose from genome research which showed significant
differences biochemically though similar morphologically
the bacteria
the archea (found in extreme environments, more closely associate with eukarya)
Archea’s central processes transcription and translation are more similar to those of eukaryotes.
They lack a peptidoglycan wall. Generate methane but bacteria don’t. No nitrification. Now found to be everywhere, used to be thought only extreme conditions.
As of 2012 no archaean pathogens, but lots of bacterial diseases
Bacteria cause disease, they mutate quickly to form resistance to antibiotics (can spontaneously
mutate to survive in any condition).
Can help prevent diseases (vaccines made from dead, weakened, fragments)
Bioremediation (saprotrophic bacteria break down waste) e.g sewage treatment plant
Used in foods (fermentation produces CO2 and alcohol)
Nitrogen fixing: convert nitrous gas into usable organic molecules, symbiotic relationship
with root nodules who provide environment for bacteria, bacteria provide fertilizer
Cyanobacteria are major primary producers, contain chlorophyll A (green) plus phycocyanin (blue)
and phycoerythrin (red) as accessory pigments. Pigments which trap light at different
wavelengths and pass it on to chlorophyll a
How do prokaryotes differ from Eukaryotes?
Understand the basic structure of the nucleus, mitochondrion and chloroplasts
What is the evidence that mitochondria and chloroplasts evolved from the processes of primary
endosymbiosis?
How does secondary endosymbiosis explain the origin of protistan pirates?
3 differences between animal/plants: cell wall structure, chloroplast, large central vacuole.
Nucleus: Surrounded by nuclear envelope double membrane, presence of nuclear pores (control entry
and exit of substances to the nucleus) , nucleolus is a subregion which contains ribosome
genes.
DNA strands covered with histones = chromosomes. Wrapped to compact.
1 nucleosome – DNA, central histone, spacer histone.
Mitochondria: power plant of the cell. Two membranes, outer and convoluted inner (called cristae),
matrix
Chloroplasts: two membranes, outer and inner that forms complex networks called thylakoids.
photosynthetic pigments located in thylakoids.
Endosymbiosis: Symbiosis in which one of the symbiotic organisms lives inside the other. Complex
organisms derived from relict symbionts.
Mitochondria- derived from purple bacteria
Chloroplasts- derived from cyanobacteria.
Primary endosymbiosis- primitive eukaryote taking up a cyanobacteria.
Bacteria eaten through phagocytosis but for some reason not broken down.
Gene transfer occurs from bacteria to host nucleus and outer membrane around bacteria
disappears. Outer membrane breaks down as vacuole not needed to eat as cyanobacteria
not food anymore
(3 genomes 1 for mitochondria, 1 for chloroplast, 1 for cell).
The original bacteria/prokaryotes had 2 outer cell membranes
Secondary endosymbiosis- chloroplast is derived from a symbiotic eukaryotic cell rather than a
prokaryote.
3 genome eukaryote eaten by other protistan pirate with its own mitochondria (2 genomes).
Now has 4 genomes (2 nuclei, cholorplast, mitochondria) the 2nd mitochondria disappears.
Gene transfer occurs from the eaten nucleus and chloroplast and 3 genomes now..
Evidence for endosymbiosis:
1. Appear morphologically similar to bacteria
2. Have an outer membrane similar to a cell membrane, inner membrane invaginates to form
cristae
3. Are semi autonomous, retaining their own genome
4. Retain own machinery for protein synthesis. (ribosomes)
5. Metabolism is like existing prokaryotes
6. Some chloroplasts still have peptidoglycan between inner and outer membranes
7. Chloroplasts and mitochondria divide using ftsZ protein which is used in binary fission
What cellular components comprise the endomembrane system and how do they interact with one
another?
The endomembrane system is made up of membrane bound compartments within a cell. These
include the endoplasmic reticulum, the Golgi apparatus, lysosomes, endosomes and some
vacuoles. It does not include mitochondria and chloroplasts. The endoplasmic reticulum
synthesises proteins and lipids. These can be transported to the Golgi apparatus through
vesicles where they are packaged and modified. The trans face then releases secretory
vesicles which find their specific target with their v-SNARE vesicle marker proteins to
combine with t-SNARE target market proteins.
What are the functions of intracellular membranes?
Provide a surface for biochemical reactions.
Establish a number of compartments to prevent mixing
Provide for transport of materials within the cell from the cell to its exterior, or from the cell
to an adjacent cell
How are glycoproteins synthesized within cells and secreted to the cell surface?
Glycoproteins are first synthesised in the endoplasmic reticulum, they enter the cis face of the Golgi
stack through small transport vesicles that bud off the ER membrane and fuse with the
membrane of the cis cisterna. As they pass through the stack the glycoproteins are modified
in many ways. Sugars of the N-link glycoproteins may be trimmed and others added. The
glycoproteins mature as they progress. Once they reach the trans side they are packaged
into secretory vesicles.
Understand the structure and function of the cytoskeleton
The cytoskeleton is made up of intermediate filaments, microtubules and actin microfilaments.
Microtubules are made up of protein tubulin and actin filaments are made up of actin.
The function of the cytoskeleton is to provide scaffolding or as structural elements within
the cytoplasm. They maintain cell shape and are involved in certain cell movements. (i.e
muscle movement, cytoplasmic streaming)
What features of microtubules and actin filaments are similar and how do they differ from one
another?
Both form stiff structures that do not branch or contract
Both are polar and highly dynamic structures
Cell movements are generated by motor molecules associated with actin and microtubules
Microfilaments are small 7-8 nm and are made up of actin
Microtubules are larger with 25nm and are made up of tubulin
Microtubules are more rigid than microfilaments and can provide greater mechanical
support
Why are plant cell walls important?
Plant cell walls inhibit cell movement and have a major influence on many aspects of plant
growth and development. Because cellulose microfibrils have a high tensile strength and do
not stretch, cells expand in a direction perpendicular to the axis of the cellulose microfibrils.
Plant cell walls are penetrated by special plasma-membrane-lined channels called plasmodesmata,
that directly link the plasma membranes and cytosols of adjacent cells and provide a means
of direct communication and transport between cells.
Animal cells have gap or communicating junctions which allow ions to pass freely between adjacent
cells. They are highly regular protein channels composed of six protein subunits that span
the plasma membrane and link to a similar unit in the adjacent cell.
The endomembrane system, a system of compartments that generally includes all of the membranebound components of the cell excluding the mitochondria and chloroplasts.
Functions of intracellular membranes: Provide a surface for biochemical reactions
Establish compartments to prevent mixing
Provide transport of materials within the cell.
Membranes always enclose a space (either as a cisterna or a vesicle). They are never openended or form T-junctions. Their consistency is like oil in water.
ENDOPLASMIC RETICULUM: consists of membrane cisternae throughout the cytoplasm to create
internal compartments and channels. Is a dynamic structure.
If ribosomes attached than rough ER if not then smooth ER (doesn’t synthesise proteins)
ER provides surface for synthesis of proteins, lipids and carbohydrates
GOLGI APPARATUS: consists of flattened stacks of membrane/cisternae called Golgi stacks. Golgi
stacks are functional extensions of the ER and polar. Doesn’t have attached ribosomes
Forming face (cis) and Mature face (trans). Functions in the collection, packaging and
distribution of molecules synthesised elsewhere in the cell.
Almost all the polysaccharide in cells is manufactured within the Golgi. Glycoproteins are
matured in the Golgi apparatus as well.
LYSOSOMES: membrane bound organelles with digestive enzymes. Break down food, foreign bodies,
dead/damaged organelles. They self digest, hydrolytic enzymes eat through the membrane
of lysosomes and then “self destruct” the cell. CYTOSKELETON: Composed of protein not membrane. Components act as a form of scaffolding or as
structural elements within the cytoplasm of cells, help maintain cell shape. Also involved in
some cell movements.
INTERMEDIATE FILAMENTS: structural components- form then die e.g hair/nails.8-10 nm
MICROTUBLES: made of tubulin protein subunits 25nm
ACTIN FILAMENT: made of actin filaments. 7-8nm
both form stiff structures that do not contract or branch. Polar and highly dynamic.
Polymerise and depolymerise to satisfy the cell’s needs.
Cell movements are generated by ‘motor molecules’ which are associated with actin filaments and microtubules. Cytoskeleton is like a train track, needs a motor for movement
MICROTUBLES: tubulin protein forms cylinders. Microtubules have polarity. The + end assembles
faster and the –end is usually capped. Polymerises and depolymerises from + end to control
growth.
ACTIN FILAMENTS: interact with myosin motors, responsible for muscle contractions and cytoplasmic
streaming (ATP causes cytoplasm to be dragged around). Proteins bind actin to each other
and to membranes. Actin molecules form microfilaments that have polarity.
MICROTUBLES ASSOCIATED PROTEINS: motor molecules have vesicles attached on one end and
attached to cytoskeleton on the other. Moves along the microtubules. Flagellum’s bend because of relative sliding between microtubules called doublets.
Understand how cell division in Prokaryotes works
Their single circular molecule of DNA is attached to the plasma membrane at a specific point.
Between divisions the double stranded DNA molecule is replicated by a system of enzymes
that produces an identical copy.
When the growing cell reaches a certain size and replication is complete, the new DNA
molecule is attached to a different point to the membrane.
The two DNA molecules separate by growth of the plasma membrane and cell wall between
their attachment points.
FtsZ protein, a bacterial cytoskeleton, forms a type of sphincter which predicts where binary
fission occurs
Unlike eukaryotic DNA the DNA molecule of prokaryotes does not condense during cell
division
Why is the presence of the ftsZ protein considered evidence for primary endosymbiosis
FtsZ protein is a rudimentary bacterial cytoskeleton. It forms a type of sphincter during binary fission
where it predicts where binary fission will occur and aids in cytokinesis.
FtsZ protein is a homologue of the eukaryotic cytoskeletal protein tubulin (used in flagella,
mitosis).
FtsZ protein is involved in the division of chloroplasts and mitochondria, which are
endosymbiotic bacteria. It is in the exact same position as in prokaryotes
Understand the cell cycle in eukaryotic cells and the mechanism of mitosis
G1 phase: longest part of the cell cycle. The ‘start’, the decision to progress from G1 to S commits the cell to progress through remainder of cell cycle is made. Checkpoint 1
S phase: the period during which DNA is replicated. At the end of S phase the nucleus is
larger and has twice as much DNA. Each homologous chromosome is replicated to have a
sister chromatid
G2 phase: Cell size increases and final preparations for mitosis occur. Prepares for mitosis,
checks the replication of DNA. Checkpoint 2
M phase: the chromosomes become visible and divide to form two new nuclei. Metaphase
checkpoint 3 sees that chromosomes aligned properly. (mitosis/cytokinesis)
Prophase: Chromatin condense into chromosomes composed of sister chromatids within the
nucleus. The microtubules in an animal cell emanate from the centrosome (replicated during
interphase). The centrosomes move to opposite poles and produce increasing numbers of
fibres forming arrays called asters. Nucleolus disappears
Prometaphase: Starts when the nuclear envelope disassembles and microtubules push into
the nuclear region. The chromosomes being to move to midway between poles when
microtubules grow and attach to their kinetochores. Each sister chromatid attaches to one
spindle fibre
Metaphase: Kinetochores are aligned in one plane midway between the poles. Sister
chromatids have been attached to microtubules from opposite poles.
Anaphase: Sister chromatids become detached as the proteins that ‘glue’ them degrade. Anaphase A, initial movement of chromosomes to opposite poles. Anaphase B poles move
further apart, elongating the spindle.
Telophase: The sets of chromosomes at each pole decondense into chromatin and a new
nuclear envelope forms around them. Nucleoli reform.
Why is meiosis called a ‘reduction division’ and what role does it play in sex?
Meiosis is called ‘reduction division’ because it reduces the chromosome number in the reproductive
cells to half that of the parent cell. In meiosis 1 the homologous chromosomes align with
each other and then separate from each other reducing the number of homologous
chromosomes from 2n to n. In fertilization the chromosomes from two reproductive cells
fuse to form a zygote. Meiosis ensures that each gamete contains a haploid number of
chromosomes so that the zygote will have the correct diploid number of chromosomes. The
meiotic divisions also generate four haploid cells whose genetic complement consists of new
combinations of parental genes.
What three unique features characterize meiosis
Meiosis has one round of DNA replication followed by two separate cell divisions, the first splitting
homologous chromosomes and the second splitting sister chromatids.
During prophase 1 of meiosis homologous chromosomes pair up in synapsis and crossing over
between chromatids of homologous chromosomes may occur, allowing the formation of
new combinations of genetic information at the chiasma.
In meiosis 1, metaphase 1, kinetochores in sister chromatids act as a single unit (in mitosis sister
chromatids always end up in opposite poles). The homologous chromosomes attach to
different poles. The chiasma help to hold sister chromatids together. Random orientation
also occurs where the chromosomes line up in no particular orientation (they could go to
either pole)
After meiosis 1 each cell contains only one of the two homologous chromosomes, each made up of
two sister chromatids
Synapsis: homologues pair up
Homologous recombination: crossing over
Reduction division: each gamete contains half the number of chromosomes.
How does cytokinesis differ between plants and animal cells?
Animals: Animals do not have rigid cell walls and cytokinesis occurs by the cell pinching in half to
form two daughter cells.
Actin and myosin filaments form a contractile ring. This constricts the cell and eventually
divides it. Meanwhile the continuous fibres remaining in the spindle are compressed into a
single rod whose dense central region, the midbody, is derived from the region of overlap of
the interacting polar fibres. The nuclear envelop reforms as the kinetochore fibres shorten
and disappear.
Plants: Higher plant cells are enclosed in a rigid wall and do not undergo cleavage as animal cells do.
Instead as they go through anaphase, fibres remaining between the chromosomes thicken
and accumulate forming the fibrous phragmoplast which grows out grows out laterally until
it reaches the sides of the cell. Inside the phragmoplast cell membrane vesicles appear and
slide along the fibres, collecting halfway between the two new forming nuclei. They then
fuse together to form a new sheet of cytoplasmic membrane. This is the cell plate, which is
flimsy at first but soon thickens and separates the two new cells.
The four major macromolecules are comprised mainly of C, H, O and N
Organic molecules are composed principally of the atoms of 6 elements: H, C, O, N, P, S
Understand the unique properties of water, and why all biological molecules have a relationship
with water
Hydrogen bonding between water molecules is responsible for many of the unusual and important
physical attributes of water.
Water has a high specific heat (the amount of heat required to raise the temperature of 1g of a
substance by 10c). Large amounts of energy are required to overcome the many hydrogen
bonds. This means that water can absorb considerable amounts of heat with little change in
temperature. The heat generated by chemical reactions within cells plus heat absorbed from
external environments could damage the cell if not the for the heat buffer that is water.
Water has a high heat of vaporisation (the energy absorbed per g as it changes from a liquid to gas).
Water evaporating from a surface such as skin or leaf will draw heat from the surface
thereby cooling it. This allows overheated organisms to lose heat to the environment
Density of solid water is less than liquid water. Below 4 degrees water molecules are increasingly
bonded to others by hydrogen bonds. At the freezing point every hydrogen atom is engaged
in both covalent and hydrogen bonding to adjacent oxygen atoms, holding the water
molecules rigidly in an open structure in which they are less densely packed than in liquid
water.
In oceans, lakes and streams when the temperature drops below 4celcius the frozen ice rises
to the top and forms a protective barrier to the cold which allows aquatic organisms to
survive.
Hydrogen bonds in water cause cohesion and adhesion. Hydrogen bonds cause water molecules to
tend to stick together called cohesion and to tend to stick to other molecules called
adhesion. (only polar surfaces are wetted, non polar surfaces are water repellent).
The cohesive forces between water molecules are stronger than with water molecules to air,