Chapter Nine: Patterns of Inheritance

Questions:

1. What are most human genetic disorders caused by?
2. What are some dominant disorders?
3. What is the chromosome theory of inheritance?

Answers:

1. Most human genetic disorders are recessive.  They range in severity from relatively mild, such as albinism (lack of pigmentation), to life-threatening, such as cystic fibrosis.  Most people who have recessive disorders are born to normal parents who are both heterozygotes.  That is, they are carriers of the recessive allele for the disorder but are phenotypically normal. 
2. One serious dominant disorder is achondroplasia, a form of dwarfism.  In people with this disorder, the head and torso of the body develop normally, but the arms and legs are short.  Another is Huntington's Disease, a degenerative disorder of the nervous system that usually does not appear until 35 to 45 years of age.
3. The chromosome theory of inheritance states that genes occupy specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment during meiosis.  Thus, it is the behavior of chromosomes during meiosis and fertilization that accounts for inheritance patterns.

Important Facts:

1. The rule of addition is the probability that an event can occur in two or more alternative ways is the sum of the separate probabilities of the different ways. 
2. An organism's appearance does not always reveal its genetic composition.  An organism's physical traits are called its physical traits.  It's genetic makeup is its genotype.
3. The law of independent assortment states that each pair of alleles segregates independently of other pairs of alleles during gamete formation.
4. Pleiotropy is the property that most genes influence multiple characters.
5. Polygenic inheritance are the additive effects of two or more genes on a single phenotypic character.

Key Terms:
Hybrids- the offspring of two different varieties.
P Generation- the true-breeding parental plants.
F1 Generation- P generation's hybrid offspring.
F2 Generation- offspring when F1 plants self-fertilize or fertilize each other.
Alleles- the alternative versions of a gene.
Homozygous- when an organism has two identical alleles for a gene, it is homozygous for that gene.
Heterozygous- when an organism has two different alleles for a gene, it is heterozygous for that gene.
Dominant allele- allele that determines the organism's appearance.
Recessive allele- allele that has no noticeable affect on the organism's appearance.
Law of Segregation-  A sperm or egg carries only one allele for each inherited character because allele pairs separate from each other during the production of gametes.

Diagram: This diagram is used to predict an outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach, and is used by biologists to determine the probability of an offspring having a particular genotype. The Punnett square is a summary of every possible combination of one maternal allele with one paternal allele for each gene being studied in the cross.

Relevant Video:
http://www.youtube.com/watch?v=oVl8OH_7QSc&feature=related

Summary: This chapter focuses first on Mendelian genetics and crosses.  It then discusses more human genetics before moving on to genes and chromosomes.  It talks about the chromosomal basis of inheritance.  The chapter then details sex chromosomes and sex-linked genes.

Chapter Eight: The Cellular Basis of Reproduction and Inheritance

Questions:

1. What are the various steps of mitosis and meiosis?
2. What are the two methods of reproduction?
3. What is the difference between cytokinesis in plant and animal cells?

Answers:

1. The steps of mitosis are interphase, prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis.  Meiosis first begins with meiosis I.  During meiosis I, prophase I, metaphase I, anaphase I, and telophase I all occur.  Meiosis II follows meiosis I without chromosome duplication.
2. The two methods of reproduction are asexual reproduction and sexual reproduction.  In asexual reproduction, offspring are identical to the original cell or organism.  The offspring also inherits all  its genes from one parent.  In sexual reproduction, offspring are similar to parents, but show variations in their traits and involve the inheritance of unique sets of genes from two different parents.
3. A ring of microfilaments pinches an animal cell in two, a process called cleavage.  In a plant cell, membranous vesicles form a disk called the cell plate at the midline of the parent cell, cell plate membranes fuse with the plasma membrane, and a cell wall grows in the space.  

Important Facts:

• Somatic cells have pairs of homologous chromosomes, receiving one member of each pair from each parent.  Homologous chromosomes are matched in length, centromere position and gene locations.  
• Cancer cells escape control on the cell cycle.  They divide rapidly, often in the absence of growth factors.  They spread to other tissues through the circulatory system.  The growth is not inhibited by other cells and tumors form.
• The factors that control cell division include: presence of essential nutrients, growth factors, proteins that simulate division, presence of other cells causes density-dependent inhibition, and contact with a solid surface, as most cells show anchorage dependence.
• Separation of homologous chromosomes during meiosis can lead to genetic differences between gametes.  Homologous chromosomes may have different versions of a gene at the same locus.  One version was inherited from the maternal parent, and the other came from the paternal parent.  Since homologues move to opposite poles during anaphase I, gametes receive either the paternal or maternal version of the gene.
• An imbalance in chromosome number results in Down Syndrome, which is characterized by characteristic facial features, susceptibility to disease, shortened life span, mental retardation, and variation in characteristics.

Key Terms:
Fertilization- the union of sperm and egg
Chromatin- DNA and proteins.
Cell Cycle- an ordered sequence of events for cell division.  Consists or interphase and Mitotic phase.
Interphase- duplication of cell contents.
Mitotic phase- division of cell.  Includes mitosis (division of the nucleus) and cytokinesis (division of cytoplasm)
Centrosomes- Structures in the cytoplasm that produce a mitotic spindle required to divide the chromosomes.  They organize micro-tubule arrangement and contain a pair of centrioles in animal cells.
Cell Cycle Control System- A set of molecules, including growth factors, that triggers and coordinates events of the cell cycle.
Diploid Cells- have two homologous sets of chromosomes.
Haploid Cells- have one set of chromosomes.
Nondisjunction- the failure of chromosomes or chromatids to separate during meiosis.


Relevant Diagram:  This diagram shows the whole process of meiosis.  Meiosis is the process of cell division in germ line cells to form gametes. This process furthers sexual reproduction because each gamete has half the number of chromosomes of normal cells, so that when two gametes (one from each parent) combine, the correct number of chromosomes is preserved in the resulting zygote organism. This process is unlike mitosis, where the cells are simply replicated, preserving the number chromosomes.

Relevant Video:
http://www.youtube.com/watch?v=BFWelOJ7fW0

Summary:
This chapter mainly discusses cell division/reproduction.  The chapter begins with mitosis, detailing first the role of chromosomes and then moving on to the different phases of mitosis.  It talks about cell cycle control and then moves on to meiosis and homologous chromosomes.  The many phases of meiosis are discussed in great detail.  The chapter then finishes with genetic variation and chromosome number which directly affects mutation.

Chapter Seven: Photosynthesis: Using Light to Make Food

Questions:

1. What are the similarities and differences between the two photo systems in photosynthesis?
2. Why does a poison that inhibits an enzyme of the Calvin cycle also inhibit the light reactions?
3. How might phytochemicals benefit a cell?

Answers:

1. Both photosystems have primary accepters and both accept light power from electrons.  They both  take place in the thylakoid membrane.  They both use ATP.  Photosystem 2 takes place before Photosystem 1.  They also use different wavelengths.  Photosystem 2 takes in water and releases oxygen and hydrogen.  Photosystem 1 does not do this.    
2. The light reactions require ADP and NADP+, which are not recycled from ATP and NADPH when the Calvin cycle stops.  
3. Phytochemicals can act as antioxidants that protect from reactive forms of oxidative molecules.

Important Facts:

1. Photosynthesis occurs in two metabolic stages.  One stage involves the light reactions.  H+ ions reduce NADP+ to NADPH, which is an electron carrier similar to NADH.  The Calvin cycle is the second stage that occurs in the stroma.  It is a cyclic series of reactions that builds sugar molecules from CO2......NADPH produced by the light reactions provides the electrons for reducing carbon in the Calvin cycle.  ATP from the light reactions provides chemical energy for the Calvin cycle, which is often known as a dark reaction.
2. In photosynthesis, electrons gain energy by being boosted up an energy hill.  Light energy captured by chlorophyll molecules provides the boost for the electrons.  As a result, light energy is converted to chemical energy, which is stored in the chemical bonds of sugar molecules.
3. Cellular respiration uses redox reactions to harvest the chemical energy stored in a glucose molecule.  This is accomplished by oxidizing the sugar and reducing O2 to H2O.  The electrons lose potential as they travel down an energy hill, the electron transport system.  In contrast, the food producing redox reactions of photosynthesis reverse the flow and involve an uphill climb.
4. Chemiosmosis is the mechanism that not only is involved in oxidative phosphorylation in mitochondria but also generates ATP in chloroplasts.  ATP is generated because  the electron transport chain produces a concentration gradient of hydrogen ions across a membrane.  ATP synthase couples the flow of H+ to the phosphorylation of ADP.  The chemiosmotic production of ATP in photosynthesis is called phosphorylation.
5. The energy released by electrons is conserved as it is passed from one molecule to another.  All of the components to accomplish this are organized in thylakoid membranes in clusters called photosystems.  Photosystems are light-harvesting complexes surrounding a reaction center complex.  Energy is passed from molecule to molecule within the photosystem.  The energy finally reaches the reaction center where a primary electron acceptor accepts these electrons and consequently becomes reduced.  This solar- powered transfer of an electron from the reaction center pigment to the primary electron acceptor is the first step of the light reactions.
   

Key Terms: 
Photosynthesis- Process that converts solar energy to chemical energy.  Plants use water and atmospheric carbon dioxide to produce a simple sugar and liberate oxygen.  This sugar is food for humans for and animals.
Autotroph- an organism that makes its own food, thereby sustaining itself without eating other organsims or their molecules.
Cloroplasts- organelles consisting of photosynthetic pigments, enzyme, and other molecules grouped together.
Chlorophyll- a green pigment located within the chloroplasts of plants, algae, and certain prokaryotes.
Electromagnetic Spectrum- the entire spectrum of radiation.
Mesophyll- the middle layer of tissue inside a leaf.
Photoautograph- an organism that obtains energy from sunlight and carbon from CO2 by photosynthesis.
Thylakoid- one of the number of disk-shaped membranous sacs inside a chloroplast.
Stomata- tiny pores in the leaf that allow carbon dioxide to enter and oxygen to exit.
Stroma- the dense fluid within the chloroplast that is contained in two membranes.

Diagram: The light-dependent reactions are the first stage of photosynthesis, the process by which plants capture and store energy from sunlight. In this proces, light energy is converted into chemical energy, in the form of the energy-carrying molecules ATP and NADPH.

Relevant Video: http://www.youtube.com/watch?v=GR2GA7chA_c

Summary: This chapter begins by detailing the stages of photosynthesis.  It then continues to discuss the light reactions and the converting of solar energy to chemical energy.  It mentions photosystems and photophosphorylation.  The chapter then discusses the Calvin cycle and the converting of CO2 to sugars.  It details C3, C4, and CAM plants before discussing solar radiation and the Earth's atmosphere.

Chapter Six: How Cells Harvest Chemical Energy

Questions:

1. What are the three different catagories of cellular poisons that affect cellular respiration?
2. What are the two common types of fermentation? Why are they important?
3. What are obligate anaerobes?

Answers:

1. The first category blocks the electron transport chain.  Examples of these are rotenone, cyanide and carbon monoxide.  The second inhibits ATP synthase (oligomycin).  The third makes the membrane leaky to hydrogen ions (dinitrophenal).
2. The two common types of fermentation are alcohol fermentation and lactic acid fermentation.  Fermentation is important because it allows a cell to continue to produce ATP without the use of oxygen, that is, under anaerobic conditions.
3. Obligate Anaerobes are prokaryotes that live in stagnant ponds or deep in the soil because they require anaerobic conditions and are poisoned by oxygen.

Important Facts:

1. Cellular respiration equation shows the changes in hydrogen atom distribution.  Glucose loses its hydrogen atoms and is converted to CO2.  As this happens, O2 gains two hydrogen atoms, while losing an oxygen atom.  This means that this reaction is a redox reaction.
2. Glycolysis begins respiration by breaking glucose, a six carbon molecule, into two molecules of a three-carbon compound called pyruvate.  This stage occurs in the cytoplasm.  The second stage is the Citric Acid cycle or Krebs cycle.  It breaks down pyruvate into carbon dioxide and supplies the next stage with electrons.  This stage occurs in the mitochondria.  During Oxidative phosphorylation, electrons are shuttled through the electron transport chain.  It also produces ATP with chemiosmosis.  This stage occurs in the membrane of the mitochondria.
3. Catabolic pathways occur when molecules are broken down and their energy is released.  Two types of catabolism are fermentation (the partial degradation of sugars that occurs without the use of oxygen) and cellular respiration.
4. Hydrogen ions flow back down their gradient through a channel in the transmembrane protein known as ATP synthase.  ATP synthase harnesses the proton motive force (the gradient of hydrogen ions) to phosphorylate ADP, forming ATP.  The proton motive force is in place because the inner membrane of the mitochondria is impermeable to hydrogen ions.  Electrons are held behind the inner membrane with their only exit the ATP synthase.
5. In alcohol fermentation, pyruvate is converted to ethanol, releasing CO2 and oxidizing NADH in the process to create more NAD+.

Key Terms:

Cellular Respiration- the aerobic harvesting of energy from sugar molecules by cells.

Oxidative Phosphorylation- Step 3 of cellular respiration.  Involves the electron transport chain and chemiosmosis.  NADH and FADH2 shuttle electrons to the electron transport chain imbedded in the inner mitochondrion membrane.  This is where most of the ATP for a cell is produced.  The energy released by the downhill fall of electrons from NADH and FADH2 to O2 is used to phosphorylate ADP.

ATP Synthases- protein complexes built into the inner membrane that synthesize ATP. 

Dehydrogenase- the enzyme that removes hydrogen from an organic molecule.  Requires a coenzyme, NAD+.

Intermediates- Compounds that form between the initial reactant and the final product.

Glycolysis- the multistep chemical breakdown of a molecule of glucose into two molecules of pyruvate.

Chemiosmosis- The energy coupling mechanism.  The production of ATP using the energy of hydrogen ion gradients across membranes to phosphorylate ADP.

Substrate Level Phosphorylation- This is a form of ATP synthesis that occurs when when an enzyme transfers a phosphate group from a substrate molecule to ADP.

Redox Reaction- The movement of electrons from one molecule to another.  Oxidation reduction reaction.

Lactic Acid Fermentation- A process  by which muscle cells, some other cells, and certain bacteria generate NAD+.  NADH is oxidized to NAD+ as pyruvate is reduced to lactate.  

Diagram: This shows cellular respiration which is the set of the metabolic reactions and processes that take place in organism's cells to convert energy from nutrients into ATP, and then release waste products. The reactions involved in respiration are catabolic reactions that involve the oxidation of one molecule and the reduction of another. Respiration is one of the key ways a cell gains useful energy to fuel cellular reformations.

Relevant Video:
http://www.youtube.com/watch?v=vlZZUtpyCgQ


Summary: In this chapter, redox reactions, and the stages of fermentation and cellular respiration are covered.  The major steps of each of the processes , as well as the results are focused on.  Glycolysis, the Citric acid cycle, and oxidative phosphorylation are discussed in great detail.