Bio 10: The Fundamentals of Biology Fall 2005 - 1082

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Bio 10 The Fundamentals of BiologyFall 2005 -
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Chapter 5 Cell Division
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Cell Increase and Decrease

• Cell division increases the number of somatic
  (body) cells, and consists of
• Mitosis (division of nucleus)
• Cytokinesis (division of cytoplasm)
• Apoptosis (cell death) decreases the number of
  cells.
• Both cell increase and apoptosis occur during
  normal development and growth.

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The Cell Cycle

• The cell cycle is an orderly sequence of events
  that occurs from the time when a cell is first
  formed until it divides into two new cells.
• Most of the cell cycle is spent in interphase.
• Following interphase, the mitotic stage of cell
  division occurs.

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The stages of interphase

• G1 stage cell growth, cell doubles its
  organelles, accumulates materials for DNA
  synthesis
• S stage DNA synthesis occurs, and DNA
  replication results in duplicated chromosomes
• G2 stage cell synthesizes proteins needed for
  cell division

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The cell cycle
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The Mitotic Stage

• Following interphase is the M stage, including
  mitosis and cytokinesis.
• During mitosis, sister chromatids of each
  chromosome separate, and become the nuclei of the
  two daughter cells.
• The cell cycle ends when cytokinesis, the
  cleaving of the cytoplasm, is complete.

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Control of the cell cycle

• The cell cycle is controlled at three
  checkpoints
• During G1 prior to the S stage
• During G2 prior to the M stage
• During the M stage prior to the end of mitosis
• DNA damage can also stop the cell cycle at the G1
  checkpoint.

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Apoptosis

• Apoptosis is programmed cell death.
• Apoptosis occurs because of two sets of enzymes
  called capsases.
• The first set, the initiators receive a signal
  to activate the second set, the executioners.
• The second set of capsases activate enzymes that
  tear apart the cell and its DNA.

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Maintaining the Chromosome Number

• When a eukaryotic cell is not dividing, the DNA
  and associated proteins is a tangled mass of thin
  threads called chromatin.
• At the time of cell division, the chromatin
  condenses to form highly compacted structures
  called chromosomes.
• Each species has a characteristic number of
  chromosomes.

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Overview of Mitosis

• The diploid number of chromosomes is found in the
  somatic (non-sex) cells.
• The diploid (2n) number of chromosomes contains
  two chromosomes of each kind.
• The haploid (n) number of chromosomes contains
  one chromosome of each kind.

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• In the life cycle of many animals, only sperm and
  eggs have the haploid number of chromosomes.
• The nuclei of somatic cells undergo mitosis, a
  nuclear division in which the number of
  chromosomes stays constant.
• Before nuclear division occurs, DNA replication
  takes place, duplicating the chromosomes.

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• A duplicated chromosome is made of two sister
  chromatids held together in a region called the
  centromere.
• Sister chromatids are genetically identical.
• At the end of mitosis, each chromosome consists
  of a single chromatid.
• During mitosis, the centromeres divide and then
  the sister chromatids separate, becoming daughter
  chromosomes.

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Mitosis overview
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• Following mitosis, a 2n parental cell gives rise
  to two 2n daughter cells, or 2n ? 2n.
• The cells of some organisms (algae, fungi) are
  haploid as adults n ? n.
• Mitosis occurs when tissues grow or when repair
  occurs.
• Following fertilization, the zygote divides
  mitotically, and mitosis continues throughout the
  lifespan of the organism.

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Mitosis in Detail

• During mitosis, the spindle distributes the
  chromosomes to each daughter cell.
• The spindle contains fibers made of microtubules
  that disassemble and assemble.
• Centrosomes, that divide during interphase,
  organize the spindle.
• Centrosomes contain centrioles and asters.
• Mitosis has four phases prophase, metaphase,
  anaphase, and telophase.

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Late Interphase
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Early Prophase
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Late Prophase
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Metaphase
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Anaphase
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Telophase
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How Plant Cells Divide

• Plant cells lack centrioles and asters, but have
  a centrosome and spindle and the same four stages
  of mitosis.
• Meristematic tissue, in shoot and root tips,
  retains the ability to divide throughout life.
• Lateral meristems accounts for the ability of
  trees to grow in girth.

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Cytokinesis in Plant and Animal Cells

• Cytokinesis, or cytoplasmic cleavage, accompanies
  mitosis.
• Cleavage of the cytoplasm begins in anaphase, but
  is not completed until just before the next
  interphase.
• Newly-formed cells receive a share of cytoplasmic
  organelles duplicated during the previous
  interphase.

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Cytokinesis in Plant Cells

• The rigid cell wall surrounding plant cells does
  not permit cytokinesis by furrowing.
• The Golgi apparatus releases vesicles that
  microtubles move to the cell plate forming
  between the two new cells.
• New plant cell walls form and are later
  strengthened by cellulose fibers.

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Cytokinesis in plant cells
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Cytokinesis in Animal Cells

• In animal cells, a cleavage furrow begins at the
  end of anaphase.
• A band of actin and myosin filaments, called the
  contractile ring, slowly forms a constriction
  between the two daughter cells.
• A narrow bridge between the two cells is apparent
  during telophase, then the contractile ring
  completes the division.

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Cytokinesis in animal cells
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Cell Division in Prokaryotes

• The process of asexual reproduction in
  prokaryotes is called binary fission.
• The two daughter cells are identical to the
  original parent cell, each with a single
  chromosome.
• Following DNA replication, the two resulting
  chromosomes separate as the cell elongates.

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Reducing the Chromosome Number

• Meiosis reduces the chromosome number such that
  each daughter cell has only one of each kind of
  chromosome.
• The process of meiosis ensures that the next
  generation will have
• the diploid number of chromosomes
• a combination of traits that differs from that of
  either parent.

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Overview of meiosis
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Overview of Meiosis

• Meiosis requires two nuclear divisions and four
  haploid nuclei result.
• Humans have 23 pairs of homologous chromosomes,
  or 46 chromosomes total.
• Prior to meiosis I, DNA replication occurs.
• During meiosis I, synapsis occurs.

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• Meiosis I separates homologous pairs of
  chromosomes.
• Daughter cells are haploid, but chromosomes are
  still in duplicated condition.
• No replication of DNA occurs between the two
  divisions.

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• Meiosis II separates sister chromatids.
• In many life cycles, haploid daughter cells
  mature into gametes.
• Fertilization restores the diploid number of
  chromosomes during sexual reproduction.

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Independent assortment
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Meiosis in Detail

• The same four phases seen in mitosis prophase,
  metaphase, anaphase, and telophase occur during
  both meiosis I and meiosis II.
• The period of time between meiosis I and meiosis
  II is called interkinesis.
• No replication of DNA occurs during interkinesis
  because the DNA is already duplicated.

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Meiosis I in an animal cell
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Meiosis II
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Sources of Genetic Variation

• As a result of meiosis followed by fertilization,
  there are three sources of genetic recombination
• Independent alignment of paired chromosomes along
  the metaphase I plate
• Crossing-over during prophase I
• Combining of chromosomes of genetically different
  gametes

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Comparison of Meiosis with Mitosis

• In both mitosis and meiosis, DNA replication
  occurs only once during interphase.
• Mitosis requires one division while meiosis
  requires two divisions.
• Two diploid daughter cells result from mitosis
  four haploid daughter cells result from meiosis.

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• Daughter cells from mitosis are genetically
  identical to parental cells daughter cells from
  meiosis are not genetically identical to parental
  cells.
• Mitosis occurs in all somatic cells for growth
  and repair meiosis occurs only in the
  reproductive organs for the production of gametes.

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Comparison of Meiosis I to Mitosis

• Meiosis I
• Prophase I - pairing of homologous chromosomes
• Metaphase I homologous pairs line up at
  metaphase plate
• Anaphase I homologous chromosomes separate
• Telophase I daughter cells are haploid

• Mitosis
• Prophase has no such pairing
• Metaphase chromosomes align at metaphase plate
• Anaphase sister chromatids separate
• Telophase diploid cells

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Comparison of Meiosis II to Mitosis

• The events of meiosis II are like those of
  mitosis except in meiosis II, the nuclei contain
  the haploid number of chromosomes.
• At the end of telophase II of meiosis II, there
  are four haploid daughter cells that are not
  genetically identical.
• At the end of mitosis, there are two diploid
  daughter cells that are identical.

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Meiosis compared to mitosis
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Chapter 6 Metabolism Energy and Enzymes
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Cells and the Flow of Energy

• Energy is the ability to do work.
• Living things need to acquire energy this is a
  characteristic of life.
• Cells use acquired energy to
• Maintain their organization (a lack of, is
  referred to as entropy which is chaos)
• Carry out reactions that allow cells to develop,
  grow, and reproduce

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Forms of Energy

• There are two basic forms of energy.
• Kinetic energy is the energy of motion.
• Potential energy is stored energy.
• Food eaten has potential energy because it can be
  converted into kinetic energy.
• Potential energy in foods is chemical energy.
• Organisms can convert chemical energy into a form
  of kinetic energy called mechanical energy for
  motion.

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Two Laws of Thermodynamics

• The flow of energy in ecosystems occurs in one
  direction energy does not cycle.
• The two laws of thermodynamics explain this
  phenomenon.
• First Law Energy cannot be created or destroyed,
  but it can be changed from one form to another.
• Second Law Energy cannot be changed from one
  form to another without loss of usable energy.

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• The ultimate source of energy for ecosystems is
  the sun, and this energy is passed from plants to
  animals.

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Metabolic Reactions and Energy Transformations

• Metabolism is the sum of all the chemical
  reactions that occur in a cell (a combo of
  anabolism and catabolsim).
• Reactants are substances that participate in a
  reaction products are substances that form as a
  result of a reaction.

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ATP Energy for Cells

• ATP (adenosine triphosphate) is the energy
  currency of cells.
• ATP is constantly regenerated from ADP (adenosine
  diphosphate) after energy is expended by the
  cell.
• Use of ATP by the cell has advantages
• 1) It can be used in many types of reactions.
• 2) When ATP ? ADP P, energy released is
  sufficient for cellular needs and little energy
  is wasted.

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The ATP cycle
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Metabolic Pathways and Enzymes

• Cellular reactions are usually part of a
  metabolic pathway, a series of linked reactions,
  illustrated as follows
• E1 E2 E3 E4 E5
  E6 A ? B ? C ? D ? E ? F ?
  G
• Here, the letters A-F are reactants or
  substrates, B-G are the products in the various
  reactions, and E1-E6 are enzymes.

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• An enzyme is a protein molecule that functions as
  an organic catalyst to speed a chemical reaction.
• An enzyme brings together particular molecules
  and causes them to react.

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Energy of activation (Ea)
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Enzyme-Substrate Complexes

• Every reaction in a cell requires a specific
  enzyme.
• Enzymes are named for their substrates (and
  usually end
• with the letters -ase )
• Substrate Enzyme
• Lipid Lipase
• Urea Urease
• Maltose Maltase
• Ribonucleic acid Ribonuclease

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Enzymatic reactionscan be to either build OR
break down things!
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Enzyme activity and temperature and pH its
that darn homeostasis again!!

• As the temperature rises, enzyme activity
  increases because more collisions occur between
  enzyme and substrate.
• If the temperature is too high, enzyme activity
  levels out and then declines rapidly because the
  enzyme is denatured.
• Each enzyme has an optimal pH at which the rate
  of reaction is highest.

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Rate of an enzymatic reaction as a function of
temperature and pH
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Enzyme Inhibition

• Enzyme inhibition occurs when an active enzyme is
  prevented from combining with its substrate.
• When the product of a metabolic pathway is in
  abundance, it binds competitively with the
  enzymes active site, a simple form of feedback
  inhibition.
• Other metabolic pathways are regulated by the end
  product binding to an allosteric site on the
  enzyme.

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Feedback inhibition
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Enzyme Cofactors

• Presence of enzyme cofactors may be necessary for
  some enzymes to carry out their functions.
• Inorganic metal ions, such as copper, zinc, or
  iron function as cofactors for certain enzymes.
• - which is why it is critical that you consume
• certain metals in your diet..mmmm,
  metal!

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Enzyme Cofactors and Coenzymes

• Organic molecules, termed coenzymes, must be
  present for other enzymes to function.
• Some coenzymes are vitamins now you know why
  you need them in your diet.and why a lack of
  them can result in disease without them your
  enzymes cannot perform their functions in
  catabolism or anabolism of certain substances..
• EX see page 276, Rickets (Vita D), Dermatitis
  (niacin), and
• Scurvy (Vita C ya limey!)..

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Photosynthesis

• The overall reaction for photosynthesis can be
  written
• 6CO2 6H2O energy ? C6H12O6 6O2
• During photosynthesis, hydrogen atoms are
  transferred from water to carbon dioxide, and
  glucose is formed.
• The Energy to form glucose comes from the sun!
  Solar-poweredplants!

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Cellular Respiration

• The overall equation for cellular respiration is
  opposite that of photosynthesis
• C6H12O6 6O2 ? 6CO2 6H2O Energy

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Organelles and the Flow of Energy

• During photosynthesis, chloroplasts capture solar
  energy and use it to convert water and carbon
  dioxide into carbohydrates that provide food for
  other living things.
• Cellular respiration, the breakdown of glucose
  into carbon dioxide and water, occurs in
  mitochondria.
• It is the cycling of molecules between
  chloroplasts and mitochondria that allows a flow
  of energy from the sun through all living things.

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Relationship of chloroplasts to mitochondria
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• Each reaction requires a specific enzyme.
• Substrate concentration, temperature, pH, and
  enzyme concentration affect the rates of
  reactions.
• Most metabolic pathways are regulated by feedback
  inhibition.
• Photosynthesis and cellular respiration involve
  oxidation-reduction reactions and account for the
  flow of energy through all living things.

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Chapter 7Cellular Respiration
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Cellular respiration
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Cellular Respiration takes place in 4 phases Lets
follow ONE molecule of glucose through its
complete metabolism
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Cellular Respiration takes place in 4 phases
1. Glycolysis is the breakdown of glucose into
pyruvate, 2 ATP molecules are made
Step 1
2
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Cellular Respiration takes place in 4 phases
2. In the transition reaction, pyruvate is
broken down
into acetyl CoA, no ATP is made
Step 2
2
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Cellular Respiration takes place in 4 phases 3.
The Citric Acid Cycle also called the Krebs
cycle, and breaksdown Acetyl-CoA
into CO2.2 ATP are made
Step 3
2
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MITOCHONDRIA
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Cellular Respiration takes place in 4 phases 4.
The Electron Transport System uses the ELECTRONS
removed from glucose molecules to
provide engergy to make TONS of
ATP..about 32-34 ATPs!!!
Step 4
2
2
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MITOCHONDRIA
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Cellular Respiration takes place in 4 phases
Therefore, ONE molecule of glucose generates
2232/34 ATP molecules.a total of 36-38!
Step 4
Step 3
Step 2
Step 1
2
2
32
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Where is all this occuring?!?!
Cell
Outside of the Mitochondria!
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ATP is not only produced.but also NADH and FADH!
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ATP is the currency to run machinery within the
cell.. But NADH and FADH2 run the electron
transport system which then makes the ATP!
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NAD and FAD

• Each step of cellular respiration requires a
  separate enzyme.
• Some enzymes use the oxidation-reduction coenzyme
  NAD (nicotinamide adenine dinucleotide).
• FAD (flavin adenine dinucleotide) is sometimes
  used instead of NAD.

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The function of NADH and FADH2 is to carry and
then donate electrons to the electron transport
system..
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The function of NADH and FADH2 is to carry and
then donate electrons to the electron transport
system.. remember electron transport is
occuring across the mitochondrias cristae!
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What happens when breakdown of glucose is
incomplete? FERMENTATION!!!!

• When oxygen is available, pyruvate enters the
  mitochondria, where it undergoes further
  breakdown, through the citric acid and electron
  transport cycles.
• If oxygen is not available, fermentation occurs
  and pyruvate undergoes reduction.
• Fermentation is an anaeorbic process and does not
  require oxygen. (an-aeorobic" means, without
  oxygen)
• In humans, pyruvate is reduced to lactic acid
  during fermentation.

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In humans..
In bacteria or yeast..
The Fermentation Process remember, its
ANAEOROBIC this situation only occurs when
oxygen levels are LOW!
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In humans..
In bacteria or yeast..
Notice, that in low oxygen you only make 2 ATP,
compared to 36! this is why, when you have
an oxygen debt, you get a lactic acid buildup
in your muscles! AND, you pant to try to Bring
more oxygen into your body to complete cellular
respiration
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Efficiency of Fermentation

• Two ATP produced during fermentation are
  equivalent to 14.6 kcal complete oxidation of
  glucose to CO2 and H2O represents a yield of 686
  kcal per molecule of glucose.
• Thus, fermentation is only 2.1 efficient
  compared to cellular respiration.
• (14.6/686) x 100 2.1

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Advantages and Disadvantages of Fermentation

• Fermentation can provide a rapid burst of ATP in
  muscle cells, even when oxygen is in limited
  supply.
• Lactate, however, is toxic to cells.
• Initially, blood carries away lactate as it
  forms eventually lactate builds up, lowering
  cell pH, and causing muscles to fatigue.
• Oxygen debt occurs, and the liver must reconvert
  lactate to pyruvate.

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But we dont just eat carbohydrates..so what
happens with proteins and lipids?
?
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?
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The metabolic pool concept
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Catabolismcatabolic reactions, break it down

• Molecules aside from glucose can enter the
  catabolic reactions of cellular respiration.
• When a fat is used for energy, it breaks down
  into glycerol and three fatty acids glycerol is
  converted to PGAL, and the fatty acids are
  converted to acetyl-CoA, thus both types of
  molecules can enter the citric acid cycle.

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Fat breaks down into glycerol and three fatty
acids glycerol is converted to PGAL, and the
fatty acids are converted to acetyl-CoA, and
both molecules can then enter the citric acid
cycle.
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Catabolismcatabolic reactions, break it down

• The carbon backbones of amino acids can also
  enter the reactions of cellular respiration to
  provide energy.
• The amino acid first undergoes deamination, or
  the removal of the amino group in the liver the
  amino group becomes ammonia (NH3) and is excreted
  as urea.
• Where the carbon portion of the amino acid enters
  the reactions of respiration depends on its
  number of carbons.

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AnabolismAnabolic reactions build things up

• The substrates of the pathways of cellular
  respiration can also be used as starting
  materials for synthetic reactions.
• This is the cells metabolic pool, in which one
  type of molecule can be converted into another.
• In this way, dietary carbohydrates can be
  converted to stored fat, and come substrates of
  the citric acid cycle can be transaminated into
  amino acids.

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Phases of Complete Glucose Breakdown

• The oxidation of glucose by removal of hydrogen
  atoms involves four phases
• Glycolysis the breakdown of glucose to two
  molecules of pyruvate in the cytoplasm with no
  oxygen needed yields 2 ATP
• Transition reaction pyruvate is oxidized to a
  2-carbon acetyl group carried by CoA, and CO2 is
  removed occurs twice per glucose molecule

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• Citric acid cycle a cyclical series of
  oxidation reactions that give off CO2 and produce
  one ATP per cycle occurs twice per glucose
  molecule
• Electron transport system a series of carriers
  that accept electrons removed from glucose and
  pass them from one carrier to the next until the
  final receptor, O2 is reached water is produced
  energy is released and used to synthesize 32 to
  34 ATP
• If oxygen is not available, fermentation occurs
  in the cytoplasm instead of proceeding to
  cellular respiration.

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Citric acid cycle
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Overview of the electron transport system
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