Download produced in photosynthesis

The basic thing to remember about cellular respiration and
photosynthesis is that they are reverse reactions. In other
words, the products of photosynthesis are the reactants in
cellular respiration. You can easily see that in the following:
6CO2 + 6H2O + Energy
C6H12O6 + 6O2
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
Photosynthesis is the process that occurs within the
chloroplasts (palisade mesophyll mostly), that uses the input of
the sun’s energy to produce glucose, and oxygen.
Cellular respiration is the process that occurs within the
cytoplasm and mitochondria, that uses oxygen and glucose to
produce ATP, and the other byproducts, water and carbon
dioxide.
Aerobic respiration requires oxygen. Aerobic respiration
occurs in three phases:
• Gylcolysis
• Krebs Cycle (aka Citric acid cycle)
• Oxidative Phosphorylation (electron transport chain)
Anaerobic respiration does not require the presence of oxygen. It is also
known as fermentation, and it allows glycolysis to continue when the lack of
an electron acceptor shuts down oxidative phosphorylation.
In eukaryotes, glycolysis
takes place in the cytoplasm,
while the Krebs Cycle takes
place in the mitochondria, and
oxidative phosphorylation
(etc) proceeds in the inner
membrane of the
mitochondria, known as
cristae.
Glycolysis and the Krebs cycle strip electrons from glucose
and use them to reduce NAD+ and FAD. The resulting electron
carriers – NADH, and FADH2 – then donate electrons to an
electron transport chain, which gradually steps the electrons
down in potential energy until they are finally accepted by
oxygen, the final electron acceptor. This results in the
formation of water in aerobic organisms.
How Much ATP From Respiration?
Pathway
Substrate Level
Phosphorylation
Oxidative
Phosphorylation
Total
ATP
Glycolysis
2 ATP
2 NADH = 6 ATP
6
2 NADH = 6 ATP
6
CoA
Krebs Cycle
2 ATP
6 NADH = 18 ATP
2 FADH2 = 4 ATP
24
Total
4 ATP
32 ATP
36
Photosynthesis is the conversion of light energy to chemical energy, stored
in the bonds of carbohydrates. The sugars generated by photosynthesis
drives cellular respiration. Photosynthesis provides the energy that
sustains most life on Earth.
Photosynthesis consists of two distinct sets of reactions.
• The light dependent reactions occur in internal
membranes of the chloroplast that are organized into
structures called thylakoids in stacks known as grana.
• The light independent reactions, known as the Calvin
cycle, take place in a fluid portion of the chloroplast called
the stroma.
ATP and the electron carrier NADPH are produced.
ATP and NADPH are used to reduce CO2 to carbohydrate. Energy is
transformed from sunlight into chemical energy in the form of electrons with
high potential energy. Excited electrons either are used to produce NADPH
or are donated to an electron transport chain, which results in the production
of ATP.
Some plants adapted to hot, arid regions have a different photosynthetic mechanism
called CAM photosynthesis.
CAM (Crassulacean Acid Metabolism) photosynthesis is found in cacti and succulents,
including the crassula family.
During the hot daylight hours
their stomata are tightly closed;
however they still carry on vital
photosynthesis as carbon dioxide
gas is converted into simple
sugars. How do they do it?
During the cooler hours of
darkness their stomata are open
and CO2 enters the leaf cells
where it combines with PEP
(phosphoenolpyruvate) to form
4-carbon organic acids (malic
and isocitric acids).
The 4-carbon acids are stored in the vacuoles of photosynthetic cells in the leaf.
During the daylight hours the 4-carbon acids break down releasing CO2 for the
dark reactions (Calvin cycle) of photosynthesis inside the stroma of chloroplasts.
The CO2 is converted into glucose through the Calvin-Benson cycle with the
help of ATP and NADPH, which were synthesized during the light reactions
of daylight in the grana of chloroplasts.
The adaptive advantage of
CAM photosynthesis is that
plants in arid regions can keep
their stomata closed during
the daytime, thereby reducing
water loss from the leaves
through transpiration;
however, they can still carry
on photosynthesis with a
reserve supply of CO2 that was
trapped during the hours of
darkness when the stomata
were open.
The tropical strangler Clusia rosea exhibits CAM photosynthesis. This
unusual tree starts out as an epiphyte on other trees and then completely
envelops and shades out its host.
C4 plants are so named because they form a four-carbon compound as the first
product of the dark reactions of photosynthesis. Several thousand species in at
least 19 families use the C4 pathway.
Agriculturally important C4 plants are sugarcane, corn, and members of the grass
family.
• In C4 plants, such as sugarcane,
these two steps are separated
spatially; the two steps take place in
two cell types. (Mesophyll, and bundle
sheath cells)
• In CAM plants, such as pineapple,
the two steps are separated
temporally (time); carbon fixation
occurs at night, and the Calvin cycle
functions during the day.
Both C4 and CAM are two evolutionary solutions to the problem of
maintaining photosynthesis with stomata partially or completely closed on
hot, dry days. However, it should be noted, that in all plants, the Calvin
cycle is used to make sugar from carbon dioxide.
Typical, or C3 photosynthesis is carried out by most plants growing in
areas with sufficient water. In this type of photosynthesis, an
enzyme called RuBP carboxylase grabs CO2 in one of the first steps of
photosynthesis. This works fine as long as there is plenty of carbon
dioxide and relatively little oxygen.
If there is too much oxygen, RuBP carboxylase will grab that instead
of the CO2, and a process called photorespiration will
occur. Photorespiration does not help build up any sugars, so if
photorespiration occurs, growth stops.
Normally, oxygen (produced in photosynthesis) exits the plant through
the stomata; however, if there isn't enough water available (as would
happen under bright, hot, sunny conditions), excess oxygen may build
up and trigger photorespiration, because the stomata close to conserve
water.
If water is present, however, this process is very efficient because
both the light reactions and Calvin Cycle can occur simultaneously in
the same cell, and almost all of the cells in the leaf will be producing
sugars.
C4 photosynthesis differs from C3 in 2 key ways. First, instead of
RuBP carboxylase, a different enzyme, PEP carboxylase, is used to
grab CO2. The PEP carboxylase is less likely to bind to oxygen, thus
photorespiration is less likely to occur, a decided advantage under hot,
dry conditions where water may be scarce and the stomata remain
closed for long periods, trapping oxygen in the plant.
This process is relatively inefficient, but if
water is in short supply the inefficient C4
route is still better than the C3 route with
photorespiration. Also, since there are
fewer cells involved in making sugars, fewer
sugars can be made.
Thus desert plants can survive the dry
conditions, but at the cost of rapid
growth. Desert plants are often very slow
to grow, and this is one of the reasons they
invest so much energy in defensive structures
(spines) and chemicals
C3 is best under moist conditions, C4 under warm, sunny, dry
conditions, CAM under desert conditions
Photosynthesis
Cellular Respiration
Food synthesized
Food broken down
Energy from sun stored in
glucose
Energy of glucose released
Carbon dioxide taken up
Carbon dioxide given off
Produces sugars from PGAL
Produces CO2 and H2O
Oxygen given off
Oxygen taken in
Requires light
Does not require light
Occurs only in presence of
chlorophyll
Occurs in all living cells
Prokaryotes divide through binary fission. In a
nutshell, binary fission is a simplistic form of
mitosis. There are two processes through which
eukaryotic cells can divide: • Mitosis
• Meiosis
Mitosis is responsible for:
• growth of tissue
• repair of tissue
• cell replacements in
multicellular eukaryotes
Cell Death
Includes:
Interphase, and
Mitosis.
A great deal goes on during
interphase, and while we
used to call this the
“resting” phase, the cell is
hardly at rest. After
interphase, an even more
active part of the cell cycles
progresses. It is known as
Mitosis. Mitosis has four
stages:
• Chromosomes are
visible threads.
• Centrioles begin moving to
opposite ends of the cell and
fibers extend from the
centromeres.
• Some fibers cross the cell to form
the mitotic spindle.
• Nuclear envelope breaks down
•Microtubules from spindle at
each pole push apart.
• Microtubules attach to one
of two sister chromatids of
each chromosome pair
All chromosomes have
become aligned at the
spindle equator
At this stage of mitosis, the
chromosomes are most
tightly condensed.
The sister chromatids of each chromosome pair separate
from each other and move to opposite spindle poles.
Once these sister
chromatids are separated,
we recognize them as
chromosomes
In
Plants
• In animal cells,
a cleavage
furrow forms
• In plant cells, a
cell plate forms
because of the
cell wall
As soon as the two clusters of
chromosomes get to the poles of the
cells, telophase gets under way.
Once the nuclear membranes are
synthesized, and the chromosomes
are separated from the cytoplasm,
mitosis is complete.
In
animals
•Meiosis results in the
formation of haploid (n) cells.
–In Humans, these are the Ova (egg) and
sperm.
–Ova are produced in the ovaries in females
–Sperm are produced in the testes of males.
Meiosis I
Meiosis II
Most important phases in
meiosis:
Chiasma
Crossing over occurs and
form chiasma. An actual
blending of parental
chromosomes occurs during
this phase. It accounts for
great genetic diversity
among filial generations.
Chiasmata separate. Chromosomes,
each with two chromatids, move to
separate poles. Many genetic
chromosomal abnormalities occur
during this stage due to improper
separation.
Meiosis II proceeds directly after Telophase I, and is similar
to mitosis. It is the stage at which the reduction in the
number of chromosomes occurs.
The structure of DNA was
Double-ringed purines:
worked out by James Watson
and Francis Crick in 1953. They
were awarded the Nobel Prize
in 1962 for this work.
Single-ringed pyrimidines:
What type
of bond
joins the
nitrogenous
bases
together?
Deoxyribose
Ribose
Which one is deoxyribose, and
why?
Semiconservative Model:
Watson and Crick showed: the two strands of
the parental molecule separate, and each functions
as a template for synthesis of a new complementary
strand.
• The replication fork
opens with the help of the
enzyme helicase.
• DNA polymerase adds nucleotides at
the free 3’ end, forming new DNA
strands in the 5’ to 3’ direction only in a
continuous fashion, while checking for
errors.
• On the other strand, assembly is
discontinuous because the exposed –OH
group is the only place where nucleotides
can be joined together.
• DNA ligase then helps to wind the new
strands together into a double helix.
Occurs inside the nucleus when DNA is copied by
mRNA. Remember Uracil replaces Thymine in
RNA.
Transcription is
initiated at a
“promoter, and
ended at a
terminator, and it
only occurs on the
DNA strand situated
in the 3’-5’
direction.
A promoter and
terminator are
specific sequences in
the DNA that code
for the “beginning”
and the “end”.
Only the segment that codes for a specific protein needed by the cell (a
gene), will unwind and create the mRNA transcript.
There are coding and non-coding sections
found within DNA. They are exons, and
introns.
These non-coding sections are also
copied by the complementary premRNA, but must be “clipped” from
the molecule before it can leave the
nucleus for translation.
The free transcript is not completed
yet. Before it can leave the nucleus
it must be modified. First the
introns must be lysed out, and then a
protein cap and a polyA tail must be
added.
Finally we have a
mature mRNA
molecule, fully
functional, and
able to leave the
nucleus.
The mRNA moves through the cytoplasm to the ribosomal subunit (rRNA).
Once there, the triplet code (codons) message is read by the tRNA, as
anticodons are brought to the ribosome where polypeptides are assembled.
This is called “translation”.
So…translation occurs at the
ribosome, while transcription
occurs in the nucleus.
The DNA’s original
message is now carried on
the mRNA (messenger
RNA), and is read in threeletter sequences known as
codons.
The tRNA (transfer RNA) interprets those codon “words”, and carries in
appropriate amino acids corresponding to the codon. While it does this, it
is assembling a protein (polypeptide chain of amino acids.) The three letter
sequence on the tRNA is the “anti-codon”
Each codon of
mRNA codes
for a
different
amino acid
which is
associated
with a
specific
tRNA’s
anticodon.
Know how to
determine
possible
sequences
using the
codon chart!
Enzymes are globular proteins that act as catalysis (activators or
accelerators) for metabolic reactions.
Enzyme Characteristics:
• The substrate is the substance or substances upon which the enzyme acts. For
example, amylase catalyzes the breakdown of the substrate amylose (starch)
• Enzymes are substrate specific. The enzyme amylase, for example, catalyzes the
reaction that breaks the α-glycosidic linkage in starch but cannot break the β-glycosidic
linkage in cellulose.
• The induced-fit model describes how enzymes work. Within the enzyme, there is an
active site with which the reactants readily interact because of the shape, polarity, or
other characteristics. The interaction of the substrate and the enzyme causes the
enzyme to change shape. Once the reaction takes place, the product is released.
• An enzyme is unchanged as a result of a reaction. It can perform its enzymatic
function repeatedly.
• The efficiency of an enzyme is affected by temperature and pH. Optimal temperature
for most human enzymes is 98.6°. Above 104°, these enzymes begin to lose their ability to
catalyze reactions as they become denatured. The enzyme pepsinogen becomes active
only at very low pH, as it works on digestion of proteins in the stomach.
• The standard suffix for enzymes is “ase”, so it is easy to identify enzymes that use this
ending (although some do not).
• Competitive inhibition is where a substance
mimics the substrate, inhibiting an enzyme by
occupying the active site. The mimic
displaces the substrate and prevents the
enzyme from catalyzing the substrate.
• Noncompetitive
inhibitor binds to an enzyme at locations
other than an active site. The inhibitor changes the shape
of the enzyme which disables its enzymatic activity.
The Hardy-Weinberg principle is a tool we can use to calculate the
frequency of particular alleles in a population.
The Hardy-Weinberg model enables us to compare a population's actual
genetic structure over time with the genetic structure we would expect if
the population were in Hardy-Weinberg equilibrium (or not evolving)
If the parent generation had 92% B and 8% b and their offspring collectively
had 90% B and 10% b, it would be evident that evolution had occurred between
the generations. There are five basic assumptions that must be occurring in a
population in order to be in Hardy-Weinberg equilibrium. They are:
1. the population is infinitely large, and that
Hardy Weinberg
genetic drift is not an issue within the population.
2. there is no gene flow, or migration in or out of
the population
3. mutation is not occurring
4. all mating is totally random
5. natural selection is not occurring
shows us that
microevolution is
inevitable because
the chance that all
these assumptions can
occur is impossible!
p+q=1
p² + 2pq + q² = 1
p is defined as the frequency of the dominant allele
q is the frequency of the recessive allele for a trait controlled
by a pair of alleles (A and a)
In this equation, p² is the predicted frequency of homozygous
dominant (AA) organisms in a population, 2pq is the predicted
frequency of heterozygous (Aa) organisms, and q² is the
predicted frequency of homozygous recessive (aa) ones!
1. You have sampled a population in which you know that
the percentage of the homozygous recessive genotype
(aa) is 36%. Using that 36%, calculate the following:
A. The frequency of the "aa" genotype. Given: .36
B. The frequency of the "a" allele. .6
C. The frequency of the "A" allele. .4
D. The frequencies of the genotypes "AA" and "Aa." .16; .48
A species is usually defined as a group of individuals capable of
interbreeding. Speciation, the formation of new species,
occurs by the following processes, as illustrated below:
Allopatric speciation begins when a
population is divided by a
geographic barrier so that
interbreeding between the two is
prevented. Once reproductively
isolated by the barrier, gene
frequencies in the two populations
can diverge due to natural
selection, mutation, or genetic
drift.
If the gene pools sufficiently diverge, then interbreeding
between the populations will not occur if the barrier is
removed. As a result, new species have formed.
Sympatric speciation is the formation of new species without
the presence of a geographic barrier. This may happen in
several different ways:
Balanced Polymorphism among
subpopulations may lead to
speciation. Suppose a population
of insects possess a polymorphism
(many genes code) for color. Each
color provides a camouflage to a
different substrate.
And if not camouflaged, the insect is eaten. Under these
circumstances, only insects with the same color can associate
and mate. Similarly colored insects are reproductively
isolated from other subpopulations, and their gene pools
diverge as in allopatric speciation.
Polyploidy is another form of
sympatric speciation. When a
population is in possession of more
than the normal two sets of
chromosomes found in diploid (2n)
cells. Polyploidy often occurs in
plants (and occasionally animals)
where triploid (3n), tetraploid (4n),
and higher ploidy chromosome
numbers are found.
Polyploidy occurs as a result of nondisjunction of all
chromosomes during meiosis, producing two viable diploid
gametes and two sterile gametes with no chromosomes. A
tetraploid zygote can be established when a diploid sperm
fertilizes a diploid egg. Since normal meiosis in the tetraploid
individual will continue to produce diploid gametes,
reproductive isolation with other individuals in the population
(and thus speciation) occurs immediately in a single generation.
Adaptive radiation is the
relatively rapid evolution of
many species from a single
ancestor. It occurs when the
ancestral species colonizes an
area where diverse geographic
or ecological conditions are
available for colonization.
Variants of the ancestral
species diverge as populations
specialize for each set of
conditions.
• the marsupials of Australia began with the colonization and
subsequent adaptive radiation of a single ancestral species.
• the fourteen species of Darwin’s finches on the Galapagos
Islands evolved from a single ancestral South American
mainland species.