Bio 10: The Fundamentals of Biology Fall 2005 - 1082
Chapter 5: Cell Division
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.
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.
The stages of interphase • G 1 stage – cell growth, cell doubles its organelles, accumulates materials for DNA synthesis • S stage – DNA synthesis occurs, and DNA replication results in duplicated chromosomes • G 2 stage – cell synthesizes proteins needed for cell division
The cell cycle
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.
Control of the cell cycle • The cell cycle is controlled at three checkpoints: 1. During G 1 prior to the S stage 2. During G 2 prior to the M stage 3. During the M stage prior to the end of mitosis • DNA damage can also stop the cell cycle at the G 1 checkpoint.
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.
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.
Overview of Mitosis • The diploid number of chromosomes is found in the somatic (non-sex) cells. • The diploid (2 n) number of chromosomes contains two chromosomes of each kind. • The haploid (n) number of chromosomes contains one chromosome of each kind.
• 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.
• 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.
Mitosis overview
• Following mitosis, a 2 n parental cell gives rise to two 2 n daughter cells, or 2 n → 2 n. • 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.
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, and telophase.
Late Interphase
Early Prophase
Late Prophase
Metaphase
Anaphase
Telophase
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.
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.
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.
Cytokinesis in plant cells
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.
Cytokinesis in animal cells
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.
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: 1) the diploid number of chromosomes 2) a combination of traits that differs from that of either parent.
Overview of meiosis
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.
• 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.
• 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.
Independent assortment
Meiosis in Detail • The same four phases seen in mitosis – prophase, metaphase, 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.
Meiosis I in an animal cell
Meiosis II
Sources of Genetic Variation • As a result of meiosis followed by fertilization, there are three sources of genetic recombination: 1) Independent alignment of paired chromosomes along the metaphase I plate 2) Crossing-over during prophase I 3) Combining of chromosomes of genetically different gametes
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.
• 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.
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
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.
Meiosis compared to mitosis
Chapter 6 Metabolism: Energy and Enzymes
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
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.
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.
• The ultimate source of energy for ecosystems is the sun, and this energy is passed from plants to animals.
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.
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.
The ATP cycle
Metabolic Pathways and Enzymes • Cellular reactions are usually part of a metabolic pathway, a series of linked reactions, illustrated as follows: • E 1 E 2 E 3 E 4 E 5 E 6 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 E 1 -E 6 are enzymes.
• 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.
Energy of activation (Ea)
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 Lipid Urea Maltose Ribonucleic acid Enzyme Lipase Urease Maltase Ribonuclease
Enzymatic reactions: can be to either build OR break down things!
Enzyme activity and temperature and p. H: it’s 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 p. H at which the rate of reaction is highest.
Rate of an enzymatic reaction as a function of temperature and p. H
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 enzyme’s 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.
Feedback inhibition
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!
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!)…. .
Photosynthesis • The overall reaction for photosynthesis can be written: • 6 CO 2 + 6 H 2 O + energy → C 6 H 12 O 6 + 6 O 2 • 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-powered…plants!
Cellular Respiration • The overall equation for cellular respiration is opposite that of photosynthesis: • C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O + Energy
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.
Relationship of chloroplasts to mitochondria
• Each reaction requires a specific enzyme. • Substrate concentration, temperature, p. H, 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.
Chapter 7: Cellular Respiration
Cellular respiration
Cellular Respiration takes place in 4 phases Lets follow ONE molecule of glucose through its complete metabolism
Cellular Respiration takes place in 4 phases 1. Glycolysis is the breakdown of glucose into pyruvate, 2 ATP molecules are made Step 1: 2
Cellular Respiration takes place in 4 phases 2. In the transition reaction, pyruvate is broken down into acetyl Co. A, no ATP is made Step 2: 2
Cellular Respiration takes place in 4 phases 3. The Citric Acid Cycle also called the “Krebs” cycle, and breaksdown Acetyl-Co. A into CO 2…. 2 ATP are made Step 3: 2 2 MITOCHONDRIA
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 MITOCHONDRIA 32
Cellular Respiration takes place in 4 phases Therefore, ONE molecule of glucose generates 2+2+32/34 ATP molecules……. a total of 36 -38! Step 2: Step 1: 2 Step 3: Step 4: 2 32
Where is all this occuring? !? ! Cell Outside of the Mitochondria!
ATP is not only produced…. but also NADH and FADH!
ATP is the currency to run machinery within the cell…. . But NADH and FADH 2 run the electron transport system *which then makes the ATP!*
NAD+ and FAD • Each step of cellular respiration requires a separate enzyme. • Some enzymes use the oxidationreduction coenzyme NAD+ (nicotinamide adenine dinucleotide). • FAD (flavin adenine dinucleotide) is sometimes used instead of NAD+.
The function of NADH and FADH 2 is to carry and then donate electrons to the electron transport system…. .
The function of NADH and FADH 2 is to carry and then donate electrons to the electron transport system…. . *remember electron transport is occuring across the mitochondria’s cristae!*
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.
In humans…. . In bacteria or yeast…. . The Fermentation Process…… remember, it’s ANAEOROBIC this situation only occurs when oxygen levels are LOW!
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
Efficiency of Fermentation • Two ATP produced during fermentation are equivalent to 14. 6 kcal; complete oxidation of glucose to CO 2 and H 2 O 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%
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 p. H, and causing muscles to fatigue. • Oxygen debt occurs, and the liver must reconvert lactate to pyruvate.
But we don’t just eat carbohydrates…. . so what happens with proteins and lipids? ? ? ?
The metabolic pool concept
Catabolism catabolic 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-Co. A, thus both types of molecules can enter the citric acid cycle.
Fat breaks down into glycerol and three fatty acids; glycerol is converted to PGAL, and the fatty acids are converted to acetyl-Co. A, and both molecules can then enter the citric acid cycle.
Catabolism catabolic 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 (NH 3) and is excreted as urea. • Where the carbon portion of the amino acid enters the reactions of respiration depends on its number of carbons.
Anabolism Anabolic 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 cell’s 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.
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 Co. A, and CO 2 is removed; occurs twice per glucose molecule
• Citric acid cycle – a cyclical series of oxidation reactions that give off CO 2 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, O 2 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.
Citric acid cycle
Overview of the electron transport system
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