what is “oxidative phosphorylation”? first, some basic definitions. when you take hydrogen ions...
TRANSCRIPT
What is “oxidative phosphorylation”? First, some basic definitions. When you take hydrogen ions or electrons away from a molecule, you “oxidize” that molecule. When you give hydrogen ions or electrons to a molecule, you “reduce” that molecule. When you give phosphate molecules to a molecule, you “phosphorylate” that molecule. So, oxidative phosphorylation (very simply) means the process that couples the removal of hydrogen ions from one molecule and giving phosphate molecules to another molecule. How does this apply to mitochondria?
#1
As the Kreb’s cycle runs, hydrogen ions (or electrons) are donated to the two carrier molecules in 4 of the steps. They are picked up by either NAD or FAD and these carrier molecules become NADH and FADH (because they now are carrying a hydrogen ion). They carry the hydrogen ions to the inner mitochondrial membrane (cristae). This is where the electron transport complexes are embedded in the membrane. The following cartoon shows what happens next. The NADH and FADH essentially serve as a ferry in the lateral plane of the membrane diffusing from one complex to the next. At each complex site is a hydrogen (or proton) pump which transfers hydrogen from one side of the membrane to the other. This creates a gradient across the inner membrane with a higher concentration of Hydrogen ions in the intercristae space (this is the space between the inner and outer membranes).
In biochemistry and molecular biology, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates.[1]
Figure 3:Three structures of proteins are illustrated (A) primary structure, its amino acid sequence; (B) secondary structure, polypeptide coiling or folding; (C) tertiary structure, the overall shape of the polypeptide.
Hypertonicity
A hypertonic solution contains a greater concentration of impermeable solutes than the solution on the other side of the membrane.[1] When a cell’s cytoplasm is bathed in a hypertonic solution the water will be drawn into the solution and out of the cell by osmosis. If water molecules continue to diffuse out of the cell, it will cause the cell to shrink. HypotonicityA hypotonic solution contains a lesser concentration of impermeable solutes than the solution on the other side of the membrane.[1] When a cell’s cytoplasm is bathed in a hypotonic solution the water will be drawn out of the solution and into the cell by osmosis. If water molecules continue to diffuse into the cell, it will cause the cell to swell.IsotonicityIsotonic solutions contain equal concentrations of impermeable solutes on both sides of the membrane.
The taxonomic classification of the Red Panda has been controversial since it was discovered. French zoologist Frédéric Cuvier initially described the Red Panda in 1825,
and classified it as a close relative of the Raccoon (Procyonidae), even though he gave it the genus name Ailurus "cat" based on superficial
similarities with domestic cats. The specific epithet is the Latin adjective fulgens "shining".[20] At various times it has been placed in Procyonidae, Ursidae, with Ailuropoda in Ailuridae,
and in its own family, Ailuridae. This uncertainty comes from difficulty determining whether certain characteristics of Ailurus are phylogenetically conservative or
are derived and convergent with species of similar ecological habits.[21]Evidence based on the fossil record, serology, karyology, behavior, anatomy,
and reproduction reflect closer affinities with Procyonidae than Ursidae. However, ecological and foraging specializations and distinct geographical distribution
in relation to modern Procyonids support classification in a separate family (Ailuridae).[21][22][23]
Recent molecular-systematic DNA research also places the Red Panda into its own
family Ailuridae, which is in turn part of the broad superfamily Musteloidea that also includes the Mephitidae (skunks), Procyonidae (raccoons),
and Mustelidae (weasels) families.[3][23][24]It is not a bear, nor closely related to the
giant panda, nor a raccoon, nor a lineage of uncertain affinities. Rather it is a basal lineage of musteloid,
with a long history of independence from its closest relatives (skunks, raccoons, and otters/weasels/badgers).
—Flynn et al. , Whence the Red Panda,[3] p197
A pulmonary vein is a large blood vessel of the human circulatory system that carries blood from the lungs to the left atrium of the heart. There are two pulmonary veins, two from each lung. They carry oxygenated blood, which is unusual since almost all other veins carry deoxygenated blood.
Triglycerides are formed from a single molecule of glycerol, combined with three fatty acids on each of the OH groups, and make up most of fats digested by humans.
Triglycerides, as major components of very low density lipoprotein (VLDL) and chylomicrons, play an important role in metabolism as energy sources and transporters of dietary fat. They contain more than twice as much energy (9 kcal/g) as carbohydrates and proteins. In the intestine, triglycerides are split into monoacylglycerol and free fatty acids in a process called lipolysis, with the secretion of lipases and bile, which are subsequently moved to absorptive enterocytes, cells lining the intestines.
• The salivary glands in mammals are exocrine glands, glands with ducts, that produce saliva. They also secrete amylase, an enzyme that breaks down starch into maltose. In other organisms such as insects, salivary glands are often used to produce biologically important proteins like silk or glues, and fly salivary glands contain polytene chromosomes that have been useful in genetic research.
• Decomposition of Organic Matter in Soil - Fungi alongwith other microbes, chiefly bacteria (including actinomycetes) play vital role in the decomposition of organic matter in soil, thus releasing the nutrients locked up in the dead organic matter of plant, animal and microbial matter and bringing about the recycling of nutrients in nature.In soil, microbes oxidise organic carbon to CO2 and liberate bound materials.
Genetic Infectious
Down Syndrome (extra chromosome)
Malaria (blood/
mosquitoes)
Tay-Sachs (fatal genetic lipid storage disorder )
Influenza (flu)
Ricketts (spotted fever)
#11
#12
AB Ab aB ab
AB AABB AABb AaBB AaBb
Ab AABb AAbb AaBb Aabb
aB AaBB AaBb aaBB aaBb
ab AaBb Aabb aaBb aabb
• #13 There were many important naturalists in the 18th century.
– Linnaeus: classification system from kingdom to species– Buffon: species shared ancestors rather than arising
separately– E. Darwin: more-complex forms developed from less-
complex forms– Lamarck: environmental change leads to use or disuse
of a structure
#14
• Angiosperms, the flowering plants, represent the most advanced condition among terrestrial plants. While their sexual organs -flowers- are unquestionably their crowning achievement, their origin remains a topic of considerable debate. There is general agreement that the precursor to the ancestoral flower was a modified whorl of leaves, and that extant flowers with multiple parts of indefinate number probably represent the ancestoral condition. For an interesting discussion on the origin of flowering plants, the reader is referred to Peter Crane, et.al. (1995) (See references). The angiosperm life cycle possesses the following advances over conifers:
• Reproductive structures are flowers rather than cones. • Ovules embedded in female sporophylls rather than lying bare on
the surface • Gametophyte still further reduced • Double fertilization to produce a diploidtriploid endosperm nutritive
material • Seeds enclosed in fruits that develop from the ovary or related
structures
• The sporophyte is the dominant phase for seed plants.
–sporophyte phase is diploid –begins with fertilized egg –spores produced through
meiosis
• The gamete-producing plant is the mature gametophyte.
• The spore-producing plant is the mature sporophyte.
– gametophyte phase is haploid– begins with spore – gametes produced through
mitosis
15 Learning is adaptive.
• Animals that can learn can better adapt to new situations.
• In associative learning, a specific action is associated with its consequences.
• Trial and error• Conditioning is one type of associative learning
– Classical conditioning: previously neutral stimulus associated with behavior triggered by different stimulus
– Operant conditioning: behavior increased or decreased by positive or negative reinforcement
Innate behaviors are triggered by specific internal and external
stimuli. (instinct)• An instinct is a complex inborn behavior.
• Instinctive behaviors shareseveral characteristics.– innate, or performed
correctly the first time– relatively inflexible
Many behaviors have both innate and learned components.
• Learning takes many forms.• Habituation occurs
when an animallearns to ignore arepeated stimulus.
• Imprinting is a rapidand irreversiblelearning process.– critical period– Konrad Lorenz
and graylag geese
• In imitation, animals learn by observing the behaviors of others.– young male
songbirds learn songs by listening to adult males
– snow monkeys and potato-washing behavior
• Unlike learning by trial-and-error, insight learning is solving problems not based on actual experience (like trial and error steps) but on trials occurring mentally. Often the solution is learned suddenly, such as when a person is in a problem for a period of time and suddenly learns the way to solve it.
• This was observed in the experiments of Wolfgang Kohler in 1900s involving chimpanzees. Kohler found that chimpanzees could use insight learning instead of trial-and error to solve problems. In one example, a banana was placed high out of reach that the chimpanzees found a way to reach it. They stack boxes on top of each other to reach it and used sticks to knock the banana down.
16
• In biochemistry, • allosteric regulation is the regulation of
an enzyme or other protein by binding an effector molecule at the protein's allosteric site (that is, a site other than the protein's active site). Effectors that enhance the protein's activity are referred to as allosteric activators, whereas those that decrease the protein's activity are called allosteric inhibitors.
17• Lysosomes are spherical organelles that contain enzymes (acid
hydrolases). They break up food so it is easier to digest. They are found in animal cells, while in yeast and plants the same roles are performed by lytic vacuoles.
• The size of lysosomes varies from 0.1–1.2 μm.[2] At pH 4.8, the interior of the lysosomes is acidic compared to the slightly alkaline cytosol (pH 7.2). The lysosome maintains this pH differential by pumping protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. The lysosomal membrane protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. The cell is additionally protected from any lysosomal acid hydrolases that leak into the cytosol as these enzymes are pH-sensitive and function less well in the alkaline environment of the cytosol.
• Hydrolysis is a chemical reaction during which molecules of water (H2O) are split into hydrogen cations (H+) (conventionally referred to as protons) and hydroxide anions (OH−) in the process of a chemical mechanism.[
18
19 • An adaptive radiation is a rapid evolutionary radiation characterized by an increase in the morphological and ecological diversity of a single, rapidly diversifying lineage. Phenotypes adapt in response to the environment, with new and useful traits arising.[1] This is an evolutionary process driven by natural selection.
• • Four of the 14 finch species found on the
Galápagos Archipelago, are thought to have evolved by an adaptive radiation that diversified their beak shapes to adapt them to different food sources.
20
• Cephalization is an evolutionary trend, whereby nervous tissue, over many generations, becomes concentrated toward one end of an organism. This process eventually produces a head region with sensory organs.[1]
• Cephalization is intrinsically connected with a change in symmetry.
21• The solubility of oxygen in water is temperature-dependent, and about twice as much (14.6 mg·L−1) dissolves at 0 °C than at 20 °C. To illustrate, recall bubbles forming in a pot of water right before it begins to boil; these bubbles are oxygen that was dissolved at room temperature, but is being ejected as the temperature rises. Oxygen can slip into the crevasses or “holes” that exist in the loose hydrogen-bonded network of water molecules without forcing them apart. A very physical perspective on solubility of oxygen in water is that when the water is colder, the water molecules move less, and the oxygen remains trapped in the aqueous solution.
22
• Proteins are made on the ribosomes which are located on the rough ER.
• Then they move to the Golgi apparatus/ complex that packages them and ships them out
• They go to a vesicle and then plasma membrane
23
• A laboratory centrifuge is a piece of laboratory equipment, driven by a motor, which spins liquid samples at high speed. There are various types of centrifuges, depending on the size and the sample capacity.
• Like all other centrifuges, laboratory centrifuges work by the sedimentation principle, where the centripetal acceleration is used to separate substances of greater and lesser density.
24
• Dicotyledonous plants (dicots) are the second major group of plants within the Angiospermae division (flowering plants with seeds protected in vessels). The other major group is the monocots.
• In contrast to monocots, dicots have an embryo with two cotyledons, which give rise to two seed leaves. The mature leaves have veins in a net-like pattern, and the flowers have four or five parts.
Features Monocotyledon
Dicotyledon
Leaf structure
Parallel veins
Network veins
Roots Fibrous roots
Tap roots
Stem Soft Hard
No. of cotyledons
1 2
25
• In biology, anaerobic respiration is a way for an organism to produce usable energy without the involvement of oxygen; it is respiration without oxygen.[1] Respiration is a redox reaction that processes energy in a form usable by an organism, chiefly the process of producing ATP,[2] the "universal energy currency of life".[3] It employs an electron transport chain, with inorganic molecules other than oxygen used as a final electron acceptor. Anaerobic respiration should therefore not be confused with fermentation, as in ethanol fermentation and lactic acid fermentation.
26 AIDS/HIV
• The virus, entering through which ever route, acts primarily on the following cells:[70]
• Lymphoreticular system: – CD4+ T-Helper cells – Macrophages – Monocytes – B-lymphocytes
• Certain endothelial cells • Central nervous system:
– Microglia of the nervous system – Astrocytes – Oligodendrocytes – Neurones – indirectly by the action of cytokines and the gp-120
27
• Chemo: chemical• Auto: self• Tropic: feeding
• Deep sea vents have no light. Chemoautotrophs generally only use inorganic energy sources. Most are bacteria or archaea that live in hostile environments such as deep sea vents and are the primary producers in such ecosystems. Evolutionary scientists believe that the first organisms to inhabit Earth were chemoautotrophs that produced oxygen as a by-product and later evolved into both aerobic, animal-like organisms and photosynthetic, plant-like organisms.
28
• Plants have a mitochondria and a chloroplast
29• Egg• Frogs and Toads tend to lay many many eggs because there are many
hazards between fertalization and full grown frogness! Those eggs that die tend to turn white or opaque. The lucky ones that actually manage to hatch still start out on a journey of many perils.Life starts right as the central yolk splits in two. It then divides into four, then eight, etc.- until it looks a bit like a rasberry inside a jello cup. Soon, the embryo starts to look more and more like a tadpole, getting longer and moving about in it's egg.Usually, about 6-21 days (average!) after being fertilized, the egg will hatch. Most eggs are found in calm or static waters, to prevent getting too rumbled about in infancy!Some frogs, like the Coast foam-nest treefrog, actually mate in treebranches overlooking static bonds and streams. Their egg masses form large cocoon-like foamy masses. The foam sometimes cakes dry in the sun, protecting the inside moisture. When the rain comes along, after developement of 7 to 9 days, the foam drips down, dropping tiny tadpoles into the river or pond below.
30
• The light-dependent reactions produce ATP.
– hydrogen ions flow through a channel in the thylakoid membrane
– ATP synthase attached to the channel makes ATP
• • A molecule of glucose is formed as it stores some of the energy captured from sunlight.
– carbon dioxide molecules enter the Calvin cycle– energy is added and carbon molecules are rearranged– a high-energy three-carbon molecule leaves the cycle
• Light-independent reactions occur in the stroma and use CO2 molecules.
The second stage of photosynthesis uses energy from
the first stage to make sugars.
Glycolysis is needed for cellular respiration.
• The products of glycolysis enter cellular respiration when oxygen is available.– two ATP molecules are used to split glucose– four ATP molecules are produced
– two molecules of NADH produced
– two molecules of pyruvate produced
• The Krebs cycle produces energy-carrying molecules.
31
• Atoms: smallest piece of matter
• Molecules: two or more atoms
• Cells: smallest living unit
• Organism: living thing made of one or more cells
• ecosystem: An environment made of both biotic and abiotic factors.
32 Analogous structures
• Two structures in biology are said to be analogous if they perform the same or similar function by a similar mechanism but evolved separately.
• Similar structures may have evolved through different pathways, a process known as convergent evolution, or may be homologous.
The wings of pterosaurs (1), bats (2) and birds (3) are analogous: they serve the same function and are similar in structure, but each evolved independently.
Homologous structures
• homology refers to any similarity between characteristics of organisms that is due to their shared ancestry.
Divergent evolution
• Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species adapting to different environments, leading to natural selection defining the success of specific mutations.
Adaptive radiation
• An adaptive radiation is a rapid evolutionary radiation characterized by an increase in the morphological and ecological diversity of a single, rapidly diversifying lineage.
• Four of the 14 finch species found on the Galápagos Archipelago, are thought to have evolved by an adaptive radiation that diversified their beak shapes to adapt them to different food sources.
Punctuated Equilibrium• Punctuated equilibrium is a theory in
evolutionary biology which proposes that most sexually reproducing species will experience little evolutionary change for most of their geological history (in an extended state called stasis). When evolution occurs, it is localized in rare, rapid events of branching speciation (called cladogenesis). Cladogenesis is simply the process by which species split into two distinct species, rather than one species gradually transforming into another.
33• The formal system of naming species
is called binominal nomenclature (especially in zoological circles), binary nomenclature (especially in botanical circles), or the binomial classification system[citation needed]. The essence of it is that each species name is in (modern scientific) Latin and has two parts, so that it is popularly known as the Latin name of the species, although this terminology is avoided by biologists and philologists, who prefer the term scientific name. He adopted the binominal nomenclature scheme, using only the genus name and the specific name or epithet which together form the species name.
• For example, humans belong to genus Homo and their specific name is sapiens. Humans as a species are thus classified as Homo sapiens.
Kingdom World
Phylum USA
Class CA
Order Panorama
City
Family Van Nuys Blvd
Genus 8015
Species A306
– Stabilizing selection favors the intermediate phenotype.
• Natural selection can take one of three paths.
#35
• Natural selection can take one of three paths. – Disruptive selection favors both
extreme phenotypes.
Gas exchange occurs in the alveoli of the lungs. • Oxygen and carbon dioxide are carried by the blood
to and from the alveoli.– oxygen diffuses from alveoli into capillary
– oxygen binds to hemoglobin in red blood cells
– carbon dioxide difuses from capillary into alveoli
ALVEOLI GAS EXCHANGES
capillaries
alveolus
capillary
co2
o2
Co2 diffusesinto alveolus.
O2 diffusesinto blood.
39
KEY CONCEPT The endocrine system produces
hormones that affect growth, development, and homeostasis.
#41
• Hormones are chemical signals that influence cell’s activities.
– produced by glands– travel through the circulatory system– affects cells with matching receptors
target cell
hormone
receptornot a target cell
bloodstream
• There are steroid hormones and nonsteroid hormones.
– Steroid hormones enter the cell. – Nonsteroid hormones do not enter the cell.
Steroid hormone diffuses through the cell membrane
Steroid hormone binds to a receptor within the cell.
The hormone and receptor enter the nucleus and bind to DNA
Steroid hormone causes DNA to make proteins.
Nonsteroid hormone binds to receptor on the cell membrane.
Receptor stimulates a second messenger with in the cell.
Second messenger starts a series of chemical reactions in the cytoplasm.
Second messenger reactions activate enzymes.
Steroid hormone
receptor
nucleus
DNA
proteins
Non-steroid hormone
receptor
second messenger
Chemical reactions
activated enzymes
Endocrine glands secrete hormones that act throughout the
body. • There are many glands located throughout the body.
– Hormones travel through the bloodstream to cells with matching receptors.
HYPOTHALAMUS
PITUITARY
THYROID
THYMUS
ADRENAL GLANDSPANCREASFEMALE GONADS :OVARIES
MALE GONADS : TESTES
The hypothalamus interacts with the nervous and endocrine
systems. – a structure of both the nervous and
endocrine systems– produces releasing hormones,
sent to pituitary gland
• The pituitary gland is found below the hypothalamus in the brain.– controls growth and water
levels in blood – produces releasing hormones
sent throughout the body
• The hypothalamus is a gland found in the brain.
• Releasing hormones stimulate other glands to produce hormones.
– allow glands to communicate with one another
– are used in temperature regulation
#44• The human body wants blood
glucose (blood sugar) maintained in a very narrow range. Insulin and glucagon are the hormones which make this happen. Both insulin and glucagon are secreted from the pancreas, and thus are referred to as pancreatic endocrine hormones. The picture on the left shows the intimate relationship both insulin and glucagon have to each other. Note that the pancreas serves as the central player in this scheme. It is the production of insulin and glucagon by the pancreas which ultimately determines if a patient has diabetes, hypoglycemia, or some other sugar problem.
• Insulin is normally secreted by the beta cells (a type of islet cells) of the pancreas. The stimulus for insulin secretion is a HIGH blood glucose...it's as simple as that!
45 Offspring =successr-selection (unstable environments)• In unstable or unpredictable environments, r-selection predominates as the ability to
reproduce quickly is crucial. There is little advantage in adaptations that permit successful competition with other organisms, because the environment is likely to change again. Traits that are thought to be characteristic of r-selection include: high fecundity, small body size, early maturity onset, short generation time, and the ability to disperse offspring widely. Organisms whose life history is subject to r-selection are often referred to as r-strategists or r-selected. Organisms with r-selected traits range from bacteria and diatoms, through insects and weeds, to various semelparous cephalopods and mammals, especially small rodents.
K-selection (stable environments)• In stable or predictable environments, K-selection predominates as the ability to
compete successfully for limited resources is crucial and populations of K-selected organisms typically are very constant and close to the maximum that the environment can bear (unlike r-selected populations, where population sizes can change much more rapidly). Traits that are thought to be characteristic of K-selection include: large body size, long life expectancy, and the production of fewer offspring that require extensive parental care until they mature. Organisms whose life history is subject to K-selection are often referred to as K-strategists or K-selected. Organisms with K-selected traits include large organisms such as elephants, trees, humans and whales, but also smaller, long-lived organisms such as Arctic Terns.
The excretory system eliminates nonsolid wastes from the body.
• Nonsolid wastes are eliminated through lungs, skin, and kidneys.
• Lungs exhale carbon dioxide and water vapor.
• Sweat glands in skin release excess water and salts.
• Kidneys filter and clean the blood to produce urine.
skin
lungs
kidneys
ureters
urinary bladderurethra
47
• Kidneys have three basic functions in maintaining homeostasis.– remove waste from blood– help to maintain electrolyte, pH, and fluid balances – release key hormones
• Nephrons clean the blood in a three-step process.• The first step is filtration of the blood.
FILTRATION
Water,electrolytes,aminoacids,glucose,urea, and other small molecules diffuse out of the blood,creating the filtrate.
1
Glomerulus
Bowman’s capsule
48
• Plasmodesmata (singular: plasmodesma) are microscopic channels which traverse the cell walls of plant cells and some algal cells enabling transport and communication between them.
49
• Chemiosmosis is the diffusion of ions across a selectively-permeable membrane. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration.
• ATP synthase is the enzyme that makes ATP by chemiosmosis. It allows protons to pass through the membrane using the kinetic energy to phosphorylate ADP making ATP. The generation of ATP by chemiosmosis occurs in chloroplasts and mitochondria as well as in some bacteria.
50
• Wildfires are critical to maintaining the integrity of forest and grassland ecosystems. Forest and grass fires, usually started by lightning, act as an ecologically renewing force by creating necessary conditions for plant germination and continued healthy growth to occur. The primary goal of fire management is to simulate the revitalizing aspects of natural fire cycles. Fire management also attempts to prevent large catastrophic wildfires from occurring by removing accumulated debris from forests. Seen throughout the American West every summer, these extremely intense fires are caused primarily by decades of fire suppression, which has allowed heavy fuels-accumlated debris-to build up. Ironically, by attempting to prevent natural fires, humans have only increased their prevalence.
• True plants evolved through natural selection.
51
Life cycle phases look different among various plant groups.
• Nonvascular plants have a dominant gametophyte phase. – moss gametophytes look like green carpet – moss sporophytes shoot up as stalklike structures
sporophyte (2n)sporophyte (2n)
gametophyte (1n)gametophyte (1n)
capsule
spores (1n)
sporophyte (2n)sporophyte (2n)
sori
• The sporophyte is the dominant phase for seedless vascular plants. – Fern spores form in sacs, sori, on underside of mature
sporophytes (fronds).
• The sporophyte is the dominant phase for seed plants.
Hardy-Weinberg equilibrium describes populations that are
not evolving. • Genotype frequencies stay the same if five
conditions are met.– very large population: no genetic drift – no emigration or immigration: no gene flow – no mutations: no new alleles added to gene pool– random mating:
no sexual selection– no natural selection:
all traits aid equallyin survival
52
– Stomata open and close when guard cells change shape.
– When stomata are open, water evaporates and gas exchanges.
– Stomata close at night and when plant loses too much water.
guard cells stoma
• Guard cells surround each stoma.
53
• Geographic barriers can cause isolation.– called geographic isolation– physical barriers divide population
• Temporal barriers can cause isolation.– called temporal isolation– timing of reproductive periods prevents mating
54
• Mesophyll is between the leaf’s dermal tissue layers.
cuticle
upperepidermis
palisademesophyll
spongymesophyll
lowerepidermis
55
• Photorespiration and C4 Plants• All plants carry on photosynthesis by • adding carbon dioxide (CO2) to a phosphorylated 5-
carbon sugar called ribulose bisphosphate. • This reaction is catalyzed by the enzyme ribulose
bisphosphate carboxylase oxygenase (RUBISCO). • The resulting 6-carbon compound breaks down into two
molecules of 3-phosphoglyceric acid (PGA). • These 3-carbon molecules serve as the starting material
for the synthesis of glucose and other food molecules. • The process is called the Calvin cycle and the pathway
is called the C3 pathway.
• C4 Plants : the Calvin cylcle is confined to a bundle of sheathe cells. • Over 8000 species of angiosperms, scattered among 18 different families, have developed
adaptations which minimize the losses to photorespiration. • They all use a supplementary method of CO2 uptake which forms a 4-carbon molecule instead of
the two 3-carbon molecules of the Calvin cycle. Hence these plants are called C4 plants. (Plants that have only the Calvin cycle are thus C3 plants.)
• Some C4 plants — called CAM plants — separate their C3 and C4 cycles by time. CAM plants are discussed below.
• Other C4 plants have structural changes in their leaf anatomy so that – their C4 and C3 pathways are separated in different parts of the leaf with – RUBISCO sequestered where the CO2 level is high; the O2 level low.
• These adaptations are described now. • The details of the C4 cycle• • After entering through stomata, CO2 diffuses into a mesophyll cell.
– Being close to the leaf surface, these cells are exposed to high levels of O2, but – have no RUBISCO so cannot start photorespiration (nor the dark reactions of the Calvin cycle).
• Instead the CO2 is inserted into a 3-carbon compound (C3) called phosphoenolpyruvic acid (PEP) forming
• the 4-carbon compound oxaloacetic acid (C4). • Oxaloacetic acid is converted into malic acid or aspartic acid (both have 4 carbons), which is • transported (by plasmodesmata) into a bundle sheath cell. Bundle sheath cells
– are deep in the leaf so atmospheric oxygen cannot diffuse easily to them; – often have thylakoids with reduced photosystem II complexes (the one that produces O2). – Both of these features keep oxygen levels low.
• Here the 4-carbon compound is broken down into – carbon dioxide, which enters the Calvin cycle to form sugars and starch. – pyruvic acid (C3), which is transported back to a mesophyll cell where it is converted back into PEP.
• 56 An action potential is a moving electrical impulse.
– It is generated by a stimulus.– Na+ enters, and cell becomes
positively charged.– K+ leaves, and area of positive
charge moves.
area of detail