Transcript Review for Exam 2

Review for Exam 2
Friday 30th March
Evolution
• Charles Darwin (1809 – 1882) - “on the origin of species
by means of natural selection.”
• Had two main hypotheses.
– Branching descent – living species come from a species that lived
in earlier times. This explains common inheritance.
– Natural selection – explains that parents with genotypes that favor
survival and reproduction leave more offspring than other parents.
Therefore, these genetic traits become dominant in a given
population.
• Both of these hypotheses have been tested thousands of
times without being falsified.
Biological Evolution
• First true cells were prokaryotic.
– Eukaryotic cells evolved later, followed by the
other kingdoms.
• Biological evolution is a change in life forms
that has taken place in the past and will take
place in the future.
–Adaptation is a characteristic that makes an
organism able to survive and reproduce in
an environment.
Natural Selection
•
•
•
•
•
Variation in population
Variation inheritable
Some individuals survive and reproduce better
than others
Survival and reproduction are tied to variation in
traits among individuals (non-random)
Therefore, these genetic traits become dominant
in a given population.
Industrial Melanism
• Powerful demonstration of
natural selection.
• Darker colored peppered
moths were discovered in
areas of the UK with high
levels of pollution.
– Known as melanic moths
• First found in 1890s at the
height of the industrial
revolution.
Remember genetic mutation?
• Either a single nucleotide
substitution or an addition or
a deletion in the genetic
material controlling moth skin
color occurred
– Altered the open reading frame
– May be caused by the pollution
itself
• The result was an ever
increasing population of black
peppered moths in certain
areas.
Central Dogma of Molecular
Biology
• DNA holds the code
• DNA makes RNA
• RNA makes Protein
• If pollution altered the
genetic material of peppered
moths, then the protein
product (skin color) would
be altered!
Evidence for Branching Descent
• Homologies: The construction of
family trees in based on shared
similarities and gene sequences.
• Darwin noted the similarities of
forearms in mammals.
• Darwin wondered on why mammals
have the same bones in the same
relative positions.
• All had a ratio of bones from five
(fingers) to two (lower “arm” –radius
and ulna) to one (upper “arm” humerus).
Evidence for Branching Descent
• Convergence – Similarities that
result from common ancestry should
also be similar at a smaller level of
detail.
– Should grow from the same source tissue
• Convergence is an evolutionary
phenomenon in which similar
adaptations evolve independently in
lineages not closely related.
• Bat wings are similar in structure to
whale flippers, the human arm and the
front legs of all mammals.
Post - Darwin
• Steven Jay Gould :
• Punctuated Equilibrium – Species remain static for long
periods of time and then changes abruptly.
• The new species begins as a small isolated population on the
geographic periphery of the original species.
•
The small size of the isolated population allows it to undergo rapid
change
– Therefore producing a new species
• Once new species becomes successful, overcomes original species
and the original species becomes extinct.
Why is it so difficult to design an
AIDS vaccine?
• Natural selection
– Mutation
– Variation
– Selection pressures
• Transmission from other hosts
Application of principles of natural selection
creationism
• Bible-based creationists
– Use a biblical account of creation
– Reject any scientific account that conflicts with scripture
• Intelligent-design creationists
– Work within the framework of science to find evidence of
design in nature
– State that biological systems are so complex that only an
intelligent (and benevolent) designer could have made them.
• Theistic evolutionists
– Believe that God created the universe and all life
– Evolution is in fact Gods creative process and part of the plan.
Human Variation
• Genetics is the study of biological traits. These
traits are coded for in genes, which are parts of
chromosomes.
• An Allele is a variant of a gene. These can be
dominant or recessive, and these are the basis of
inherited traits, both structural and behavioral.
• Chromosomes exist as homologous pairs.
Human Variation
• Somatic Cells - Non-sex Cells. Contain a full
compliment of chromosomes. Characteristic to
their species. Referred to as the diploid number of
chromosomes.
• Gametes - Sex Cells. Cell which carry genetic
information for sexual reproduction. Contain one
half the compliment of chromosomes characteristic
to their species. Referred to as the haploid number
of chromosomes.
Human Variation
• Arms and legs are longer
and thinner in warm areas of
the planet – shorter and
thicker in cold regions.
• Conserves heat in cold
regions by reducing surface
area
• Skin pigmentation is darker
the nearer the equator to
protect the skin from UV.
Polygenic Inheritance
• The additive effects of two or more genes on a single
phenotype
Polygenic
inheritance
Single trait
(e.g., skin color)
Multiple genes
Visual Summary 9.5
Polygenic Inheritance
• Three genes inherited separately
• The dark-skin allele for each gene
(A, B, and C) contributes one “unit”
of darkness to the phenotype and is
incompletely dominant to the other
alleles (a, b, and c).
aabbcc
(very light)
AaBbCc
Eggs
AABBCC
(very dark)
AaBbCc
Sperm
• An AABBCC person would have
very dark skin
• An aabbcc person would have very
light skin
Figure 9.22
Why does
this
happen?
Figure 7.4
Both type A and type B blood
have specific carbohydrates
which are on the surface of the
blood cells.
AB blood has both carbohydrates
on the surface of the blood cells
o blood has no carbohydrates
Carbohydrates are:
N-Acetylglucosamine, galactose
and fucose
Also known as antigens
Why does
this
happen?
Figure 7.4
Controlled by three alleles
Allele A – dominant
has info for making antigen A
Allele B – dominant
has info for making antigen B
Allele o – recessive
produces neither antigen
AA & Ao gives rise to A type blood
BB & Bo give rises to B type blood
AB is co-dominant - AB type blood
oo is recessive – o type blood
•
The genetics of the Rh
factor
Another blood grouping system independent of ABo
– the Rh-factor
– Again, three genes (alleles): located very close together
on the same chromosome.
• First C & c, second D & d, third E & e
• Unlike the ABo system there is no co-dominance, c,
d, and e are recessive to C, D, and E.
• ccddee is known as Rh-negative. All others Rhpositive.
Malaria – an agent of natural
Selection
• Sickle Cell Anemia
• Controlled by intermediate phenotypes at a ratio of
1:2:1
• Red blood cells are not concave
• Normal Hemoglobin (HbA). Sickle cell (Hbs)
• HbA-HbA-normal
Hbs-Hbs – sickle cell
• HbA-Hbs- have the trait
• Therefore, incomplete dominance.
Malaria – an agent of natural
Selection
- Remember mutations? Any change in the
nucleotide sequence of DNA
Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Normal hemoglobin
Glu
Sickle-cell hemoglobin
Val
Figure 10.21
Figure 7.10
A small change in a gene
can have many phenotypic
consequences.
• Testis--paired gonads
within scrotum, sperm and
steroids produced here.
• Epididymis--tightly coiled
duct where sperm
maturation occurs.
• Vas Deferens--delivers
sperm through abdomen to
ejaculatory duct.
• Urethra--duct through
penis where sperm and
urine exit
• Semen--seminal fluid,
contains sperm, fluid
and ATP producing
nutrients (sugars).
• Prostate Gland--adds
fluid to semen.
• Seminal Vesicles-contribute nutrients to
semen.
• Bulbourethral gland-contributes mucoid
Hormonal control of
testes
• Hypothalamus- secretes gonadotropinreleasing hormone (GnRH).
– Stimulates the anterior pituitary to release
•
•
•
•
Follicle-stimulating hormone (FSH)
Promotes sperm production & release of Inhibin
Luteinizing hormone (LH)***
***Sometimes called interstitial cell-stimulating
hormone (ICSH). This stimulates the production of
testosterone.
• All these hormones are involved in negative
feedback that maintains the fairly constant
production of sperm and testosterone.
Female Reproductive System
• Ovaries--produce eggs and
steroid hormones.
• Oviducts--conduct the egg
to the uterus--fertilization
occurs here.
• Uterus--Womb, where we
are developed.
• Cervix--Opening to Uterus.
Female Reproductive System
• Clitoris--Female analog
of the penis. This is also
contains erectile and
sensory tissue.
• Vagina--site of sperm
deposition, birth canal,
exit for menstrual flow.
• Vulva--External folds of
skin that protect the
vagina.
Hormonal Control of Ovaries
• Hypothalamus- secretes gonadotropin-releasing
hormone (GnRH).
– Stimulates the anterior pituitary to release
• Luteinizing hormone (LH)
• Follicle-stimulating hormone (FSH)
• FSH Stimulates the follicle to produce estrogen.
• LH Stimulates the corpus leuteum to produce
progesterone.
• Estrogen and Progesterone maintain uterus and
help regulate the hypothalamus. negative feedback
!!!!!!!!
Ovarian cycle
Ss
s
Days 1-13- FSH secretion
Day 14 –
OVULATION
LH SPIKE
Days 15-28 – LH increases
corpus luteum forms
Progesterone high
Uterine Cycle
s
Days 1-5- Menstruation
Day 6-13 – Endometrium rebuilds
Days 15-28 –Endometrium thickens
mucoid glands develop
and secrete
Fertilization
• Egg-– Corona Radiata: Cells
from follicle that
nourished egg in ovary.
– Zona Pellucida: layer
that covers plasma
membrane--will form
fertilization envelope
– Plasma Membrane: cell
membrane around egg.
– Egg Nucleus: contains
DNA
Fertilization
• Sperm-– Head: Contains sperm
nucleus and acrosome.
– Acrosome: Contains
enzymes.
– Mid Piece: Contains
Mitochondria
– Tail: Flagella made
from Microtubules
How the atmosphere formed
Figure 19.2
Stanly Miller’s Experiment -1952.
Amino acids, simple sugars, and
most of the building blocks for
DNA and RNA were produced.
An energy source is required for
the formation of these molecules.
These expts, repeated thousands
of times have produced so many
biologically important products
that the conclusion is not in doubt
All molecules important to life
where made in the primitive atmosphere
Structure of the atmosphere
• Hint:
• Learn about the
layers of the
atmosphere!
CO2 andFigure
Global
Warming
19.9
•The greenhouse effect:
• The process in which the absorption
of infrared radiation by an atmosphere
warms a planet.
•Without these greenhouse gases, the
Earth's surface would be up to 30° C
cooler.
•CO2 is used in photosynthesis to
make carbohydrates.
CO2 levels rise at night and fall during
the day naturally.
Due to the photosynthetic activity of
plants
•CO2 is released during respiration
or when organic compounds are
burned.
CO2 andFigure
Global
Warming
19.9
•An increase of CO2 decreases the
amount of heat which can escape
through the atmosphere.
•Thus the temperature of the Earth
increases.
•This has many effects.
•Warmer Ocean layers.
•Atmospheric shifts.
•Warmer surface temperatures
•2005 was hottest year on
record.
The Chloroplast
• Membranes contain chlophyll
and it’s associated proteins
– Site of photosynthesis
• Have inner & outer membranes
• 3rd membrane system
– Thylakoids
• Stack of Thylakoids = Granum
• Surrounded by Stroma
– Works like mitochondria
• During photosynthesis, ATP
from stroma provide the energy
for the production of sugar
molecules
The chemical reaction of
photosynthesis is driven by light
• The initial reaction of
photosynthesis is:
– CO2 +H2O
(CH2O) + O2
– Under optimal conditions (red
light at 680 nm), the
photochemical yield is almost
100 %
– However, the efficiency of
converting light energy to
chemical energy is about 27 %
• Very high for an energy
conversion system
Summary of light reactions
• Plants have two reaction centers:
– PS-II
• Absorbs Red light – 680mn
• makes strong reductant (& weak oxidant)
• oxidizes 2 H2O molecules to 4 electrons, 4 protons & 1 O2
molecule
• Mostly found in Granum
– PS-I
•
•
•
•
Absorbs Far-Red light – 700nm
strong oxidant (& weak reductant)
PS-I reduces NADP to NADPH
Mostly found in Stroma
The Carbon
reactions
• The NADPH and ATP move
into the liquid environment of
the Stroma.
• The NADPH provides H and
the ATP provides energy to
make glucose from CO2.
• The Calvin cycle thus fixes
atmospheric CO2 into plant
organic material.
Photorespiration
• Occurs when the CO2 levels inside a leaf become
low
– This happens on hot dry days when a plant is forced to
close its stomata to prevent excess water loss
• If the plant continues to attempt to fix CO2 when its
stomata are closed
– CO2 will get used up and the O2 ratio in the leaf will
increase relative to CO2 concentrations
• When the CO2 levels inside the leaf drop to around
50 ppm,
– Rubisco starts to combine O2 with Ribulose-1,5bisphosphate instead of CO2
The C4 carbon Cycle
• This is a biochemical pathway
that prevents photorespiration
• C4 leaves have TWO chloroplast
containing cells
– Mesophyll cells
– Bundle sheath (deep in the leaf so
atmospheric oxygen cannot diffuse easily to
them)
• C3 plants only have Mesophyll cells
• Operation of the C4 cycle requires the
coordinated effort of both cell types
– No mesophyll cells is more than
three cells away from a bundle
sheath cells
• Many plasmodesmata for
communication
How the rest of plant works
• Roots – absorb water from the soil
as well as many mineral nutrients
• Xylem – transports water from the
roots to the rest of the plant
• Phloem – transports sugars made in
the leaves via photosynthesis to the
pest of the plant
• Leaves – Site of gas exchange CO2
brought in and O2 out. Have
structures called Stomata which also
control water loss.
Plant cell in hypotonic solution
• Flaccid cell in 0.1M sucrose solution.
• Water moves from sucrose solution to cell – swells up –becomes
turgid
• This is a Hypotonic solution - has less solute than the cell. So
higher water conc.
• Pressure increases on the cell wall as cell expands to equilibrium
Plant cell in Isotonic solution
• Water is the same inside the
cell and outside
• An Isotonic solution has the
same solute than the cell. So no
osmotic flow
• Turgor pressure and osmotic
pressure are the same
Plant cell in hypertonic solution
• Turgid cell in 0.3M sucrose
solution
• Water movers from cell to
sucrose solution
• A Hypertonic solution has
more solute than the cell. So
lower water conc
• Turgor pressure reduced and
protoplast pulls away from
the cell wall
Water transport
• Transpiration
• Evaporation of water into the
atmosphere from the leaves and stems
of plants.
• It occurs chiefly at the leaves while
their stomata are open for the passage
of CO2 and O2 during photosynthesis.
• Transpiration is not simply a hazard of
plant life. It is the "engine" that pulls
water up from the roots to:
– supply photosynthesis (1%-2% of the
total)
– bring minerals from the roots for
biosynthesis within leaf
– cool the leaf.
Increasing
crop
yields
Figure 11.13
• To feed the increasing population we
have to increase crop yields.
• Fertilizers - are compounds to
promote growth; usually applied
either via the soil, for uptake by
plant roots, or by uptake through
leaves. Can be organic or inorganic
• Have caused many problems!!
• Algal blooms pollute lakes near
areas of agriculture
Chemical
pest
control
Figure 11.17
• Each year, 30% of crops are lost to insects and other crop pests.
• The insects leave larva, which damage the plants further.
• Fungi damage or kill a further 25% of crop plants each year.
• Any substance that kills organisms that we consider undesirable are
known as a pesticide.
• An ideal pesticide would:–
–
–
–
Kill only the target species
Have no effect on the non-target species
Avoid the development of resistance
Breakdown to harmless compounds after a short time
Good Luck on Friday!