Chapter 13: Meiosis and Sexual Life Cycles

Q: Is each human sperm and egg haploid?

A: Yes, (n=23) it is haploid as a result of meiosis. Fertilization restores the diploid condition by combining two haploid sets of chromosomes, and the human life cycle is repeated, generation after generation.

Q: So in how many daughter cells does meiosis result?

A: During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing unreplicated chromosomes.

Q: How do sister chromatids stay together through meiosis I but separate from each other in meiosis II and mitosis?

A: Sister chromatids are attached along their lengths by protein complexes called cohesins. In mitosis, this attachment lasts until the end of metaphase, and in meiosis, the cohesions are cleaved at anaphase I and anaphase II, in two steps.

1. Offspring acquires genes from parents by inheriting chromosomes.

2. Fertilization and meiosis alternate in sexual life cycles.

3. Meiosis reduces the number of chromosome sets from diploid to haploid.

4. Genetic variation produced in sexual life cycles contributes to evolution.

5. Either haploid or diploid cells can divide by mitosis, depending on the type of life cycle. Only diploid cells, however, can undergo meiosis because haploid cells have a single set of chromosomes that cannot be further reduced.

This diagram shows Metaphase II of meiosis. In this phase, the chromosomes are positioned on the metaphase plate as in mitosis,and as we can see, because of crossing over in meiosis I, the two sister chromatids of each chromosome are not genetically identical. Also, the kinetochores of sister chromatins are attached to microtubules extending from opposite poles.

Meiosis is a basic and important process in sexually reproducing eukaryotic organisms, because it produces the haploid gametes that join to produce a new individual, and provides a mechanism for genetic variability, which is important for survival of the species.

Overall, meiosis involves one replication of the genetic material in the chromosomes, followed by two divisions of that genetic material. Therefore, the genetic material is reduced by half. The result of meiosis in a diploid cell is four haploid cells.

Chiasma: the x-shaped, microscopically visible region where homologous nonsister chromatids have exchanged genetic material through crossing over during meiosis, the two homologs remaining associated due to sister chromatic cohesion.

Homologous chromosomes: a pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci. One homologous chromosome is inherited from the organism's father, the other from the mother. Also called homologs, or a homologous pair.

Locus: a specific place along the length of a chromosome where a given gene is located.

Spore: in the life of a plant or alga undergoing alternation of generations, a haploid cell produced in the sporophyte by meiosis. A spore can divide by mitosis to develop into a multicellular haploid individual, the gametophyte, without fusing with another cell.

Synapsis: the pairing and physical connection of replicated homologous chromosomes during prophase I of meiosis.

Diploid cell: a cell containing two sets of chromosomes, one set inherited from each parent.

Haploid cell: a cell containing only one set of chromosomes.

Karyotype: a display of the chromosome pairs of a cell arranged by size and shape.

Sex chromosome: a chromosome responsible for determining the sex of an dindividual.

Crossing over: the reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis.

http://www.youtube.com/watch?v=iCL6d0OwKt8

Chapter 12: The Cell Cycle

Q: What are the five stages that mitosis is conventionally broken down into?

A: Prophase, Prometaphase, metaphase, anaphase, and telophase.

Q: What is G1 phase?

A: This part of cell cycle is where the cell spends most of its functional life. This is the time when the cells are performing their assigned tasks, metablizing, synthesizing etc. At some point in the cycle something triggers the cell to being a cell division event.

Q: How are cancer cells different from normal cells?

A: If and when normal cells stop dividing, cancer cells do so at random points in the cycle, rather than at the normal checkpoints. Moreover, cancer cells can go on dividing indefinitely in culture if they are given a continual of nutrients; in essence, they are "immortal."

1. Cell division results in genetically identical daughter cells.

2. The mitotic phase alternates with interphase in the cell cycle.

3. The eukaryotic cell cycle is regulated by a molecular control system.

4. In each generation of humans, meiosis reduces the chromosome number from 46 to 23. Fertilization fuses two gametes together and returns the chromosome number to 46, and mitosis conserves that number in every somatic cell nucleus of the new individual.

5. It is hypothesized that mitosis had its origins in simpler prokaryotic mechanisms of cell reproduction.

Figure 12.5 The Cell Cycle

In a dividing cell, the mitotic (M) phase alternates with interphase, a growth period. The first part of interphase (G1) is followed by the S phase, when the chromosomes replicate; G2 is the last part of interphase. In the M phase, mitosis divides the nucleus and distributes its chromosomes to the daughter nuclei, and cytokinesis divides the cytoplasm, producing two daughter cells. The relative durations of G1, S, and G2 may vary.

The eukaryotic cell cycle is divided into four phases: M(mitosis), G1(the period between mitosis and the initiation of nuclear DNA replication), S(the period of nuclear DNA replication), G2(the period between the completion of nuclear DNA replication andmitosis).

Chromosome: a cellular structure carrying genetic material, found in the nucleus of eukaryotic cells. Each chromosome consists of one very long DNA molecule and associated proteins. (A bacterial chromosome usually consists of a single circular DNA molecule and associated proteins. It is found in the nucleoid region, which is not membrane bounded.)

Somatic Cells:

Gamete: a haploid reproductive cell, such as an egg or sperm. Gametes unite during sexual reproduction to reproduce a diploid zygote.

Chromatin: the complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.

Cytokinesis: the division of the cytoplasm to form two separate daughter cells immediately after mitosis, meiosis I, or meiosis II.

Cleavage: the process of cytokinesis in animal cells, characterized by pinching of the plasma membrane.

Binary fission: a method of asexual reproduction by "division in half." In prokaryotes, binary fission does not involve mitosis; but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process.

Mitotic spindle: an assemblage of microtubles and associated proteins that is involved in the movements of chromosomes during mitosis.

Checkpoint: a control point in the cell where stop and go-ahead signals can regulate the cycle.

Kinetochore: a structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle.

http://www.youtube.com/watch?v=lf9rcqifx34

Chapter 11: Cell Communication

Q: What are the three stages of signaling?

A: Signal reception, signal transduction, and cellular response.

Q: What are the three major types of plasma-membrane receptors?

A: They are G protein-coupled receptors, receptor tyrosine kinases, and ion channel receptors.

Q: Are all signal receptors membrane proteins?

A: No, some are proteins located in the cytoplasm or nucleus of target cells. To reach such a receptor, a chemical messenger must be able to pass through the target cell's plasma membrane. A number of important signaling molecules can do just that, either because they are small enough to pass between the membrane phospholipids or because they are themselves lipids and therefore soluble in the membrane.

1. External signals are converted to responses within the cell.

2. Reception: A signaling molecule binds to a receptor protein, causing it to change shape.

3. Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell.

4. Response: Cell signaling leads to regulation of transcription or cytoplasmic activities.

5. Apoptosis (programmed cell death) integrates multiple cell-signaling pathways.

Figure 11.2 Communication between mating yeast

Cells of the yeast Saccharomyces cerevisiae use chemical signaling to identify cells of opposite mating type and to initiate the mating process. First cells of mating type A release a-factor, which binds to receptors on nearby cells of mating type B. Meanwhile, B cells release b-factor, which binds to specific receptors on A cells. Both these "factors" are small proteins of about 20 amino acid in length. Binding of these factors to the receptors induces changes in the cells that lead to their fusion, or mating. The resulting A/B cell combines in its nucleus all the genes from both A and B cells, (diploid).

As humans communicate with each other, and so do other animals, it is definitely undoubtful that cell as well need to communicate among themselves. As mentioned above, there are several different ways of how the cells communicate.

All communication involving cells can be explained in terms of a force of attraction (called affinity) between molecules. Components that allow detection are called receptors and they often have a cavity shape which allows other molecules to lock into them. The receptor ahs an affinity for a particular message or signal.

Generally, we can think of chemical signals as being stimulatory-or inhibitory- for controlling levels of activity. However, the situation is seldom the simple as there are hundreds of different types of signals and they all work in concerted coordination to carefully regulate what happens in a cell according to a wide range of influencing factors. Cell processes are not so much on or off, but, held in a dynamic state of tension. Many different protein messages or components may determine the state of a cell (for example, the cell responsible for secreting a pituitary hormone - prolactin - has been shown to respond to at least twenty different signals).

Signal transduction pathway: a series of steps linking a mechanical or chemical stimulus to a specific cellular response.

Amplification: the strengthening of stimulus energy during transduction.

Apoptosis: a program of controlled cell suicide, which is brought about by signals that trigger the activation of a cascade of suicide proteins in the cell destined to die.

Gap junction: a type of intercellular junction in animals that allows the passage of materials between cells.

Growth factor: a protein that must be present in the extracellular environment (culture medium or animal body) for the growth and normal development of certain types of cells.

Ligand: a molecule that binds specifically to another molecule, usually a larger one.

Yeast: Single-celled fungus that reproduces asexually by binary fission or by the pinching of small buds off a parent cell; some species exhibit cell fusion between different mating types.

Protein kinase: an enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein.

Local regulator: a secreted molecule that influences cells near where it is secreted.

Glycogen: an extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.

http://www.youtube.com/watch?v=tMMrTRnFdI4&feature=related

Chapter 10: Photosynthesis

Q: What is the chemical equation of photosynthesis?

A: 6 Co2 + 12 H2O + light ----> C6G12O6 + 6 02 + 6 H2O

Q: What are the two stages of photosynthesis?

A: The light reactions and the Calvin cycle (dark reactions)

Q: How does the excitation of chlorophyll by light work?

A: A pigment goes from a ground state to an excited state when a photon boosts one of its electrons to a higher-energy orbital. This excited state is unstable. Electrons from isolated pigments tend to fall back to the ground state, giving off heat and/or light.

1. Photosynthesis converts light energy to the chemical energy of food.

2. The light reactions convert solar energy to the chemical energy of ATP and NADPH.

3. The Calvin cycle uses ATP and NADPH to convert CO2 to sugar.

4. Alternative mechanisms of carbon fixation have evolved in hot, arid climates.

5. Organic compounds produced by photosynthesis provide the energy and building material for ecosystems.

This picture shows the chemiosmosis in Photosynthesis, how the removed concentrated hydrogene ions in the thylakoid space from the stroma as electrons pass from carrier to carrier are moved out into stroma by ATP synthase.

In summary, photosynthesis is a process in which energy is converted to chemical energy and used to produce organic compounds. In plants, photosynthesis occurs within the chloroplasts. Photosynthesis consists of two stages, the light reactions and the dark reactions.

The light reactions take place in the presence of light. The dark reactions do not require direct light, however in most plants, they occur during the day.

Light reactions occur mostly in the thylakoid stacks of the grana. Here, sunlight is converted to chemical energy in the form of ATP (free energy containing molecule) and NADPH (high energy electron carrying molecule). Chlorophyll absorbs light energy and starts a chain of steps that result in the production of ATP, NADPH, and oxygen (through the splitting of water). Oxygen is released through the stomata. Both ATP and NADPH are used in the dark reactions to produce sugar.

Dark reactions occur in the stroma. Carbon dioxide is converted to sugar using ATP and NADPH. This process is known as carbon fixation or the Calvin cycle. Carbon dioxide is combined with a 5-carbon sugar creating a 6-carbon sugar. The 6-carbon sugar is eventually broken-down into two molecules, glucose and fructose. These two molecules make sucrose or sugar.

Autotroph: an organism that obtains organic food molecules without eating other organisms or substances derived from other organisms. Autotrophs use energy from the sun or from the oxidation of inorganic substances to make organic molecules from inorganic ones.

Outer and inner membranes: protective coverings that keep chloroplast structures enclosed.

Stroma: dense fluid within the chlroplast. Site of conversion of carbon dioxide to sugar.

Thylakoid: flattened sac-like membrane structures. Site of conversion of light energy to chemical energy.

Grana: Dense layered stacks of thylakoid sacs. Sites of conversion of light energy to chemical energy.

Chlorophyll: a green pigment within the chloroplast. Absorbs light energy.

Wavelength: the distance between the crests of electromagnetic waves

C3 plant: A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.

C4 plant: A plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle.

CAM plant: A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. In this process, carbon dioxide entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed.

http://www.youtube.com/watch?v=C1_uez5WX1o

Chapter 9: Cellular Respiration: Harvesting Chemical Energy

Q: What is the basic balanced equation for cellular respiration?

A: C6H12O6 + 6 02 -------> 6 O2 + 6 H20 + Energy(ATP + heat)

Q: What are the three metabolic stages of cellular respiration?

A: Glycolysis, the citric acid cycle, and Oxidative

phosphoryation: electron transport and chemiosmosis

Q: What are the two electron carriers?

A: NADH+ and FADH2

1. Catabolic pathways yield energy by oxidizing organic fuels.

2. Glycolysis harvests chemical energy by oxidizing glucose to pyruvate.

3. The citric acid cycle completes the energy-yie

lding oxidation of organic molecules.

4. During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis.

5. Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen.

This diagram shows the whole Cellular Respiration. It also shows when each ATP is produced, and shows that Glycolysis occurs in the cytoplasm. Then, in Mitochondria, the Krebs Cycle and Electron Transport System occur. The total ATP that can be produced from Cellular Respiration would be 36-38.

Cellular respiration allows organisms to use (release) energy stored in the chemical bonds of glucose(C6H12O6). The energy in glucose is used to produce ATP. Cells use ATP to supply their energy needs. Cellular respiration is therefore a process in which the energy in glucose is transferred to ATP. In respiration, glucose is oxidized and thus releases energy. Oxygen is reduced to form water. Then, the carbon atoms of the sugar molecule are released as carbon dioxide (CO2). The complete breakdown of glucose to carbon dioxide and water requires two major steps: 1: glycolysis and 2: aerobic respiration. Glycolysis produces two ATP and thirty-four more ATP are produced by aerobic pathways if oxygen is present. In the absence of oxygen, fermentation reactions produce alcohol or lactic acid but no additional ATP.

Fermentation: a partial degradation of sugars that occurs without the use of oxygen.

Oxidation-reduction (Redox) reactions: transfers of one or more electrons from one reactant to another.

Acetyl CoA: Acetyl coenzyme A; the entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme.

NAD+: Nicotinamide adenine dinucleotide, a coenzyme that can accept an electron and acts as an electron carrier in the electron transport chain.

Oxidative phosphorylation: The production of ATP using energy derived from the redox reactions of an electron transport chain; the third major stage of cellular respiration.

Substrate-level phosphorylation: The formation of ATP by an enzyme directly transferring a phosphate group to ADP from an intermediate substrate in catabolism.

Cytochromes: proteins that are mostly the remaining electron carriers between ubiquinone and oxygen.

ATP(adenosine triphosphate): an adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.

ATP synthase: the enzyme that actually makes ATP from ADP and inorganic phosphate.

Chemiosmosis: the process in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesis of ATP

http://www.youtube.com/watch?v=_hGW6NjCUSs&feature=related